Article

Biofilm development, activity and the modification of carrier material surface properties in moving-bed biofilm reactors (MBBRs) for wastewater treatment

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  • Veolia Water Technologies AB - AnoxKaldnes
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Abstract

In the last decades, moving-bed biofilm reactors (MBBRs) have found a niche in the treatment of municipal and industrial wastewaters due to advantages of compactness, simplicity, stability and increased reaction rates. Recently, the material surface properties of MBBR carriers and their modification have been investigated, as reviewed herein, in order to enhance the control of microbial attachment and biofilm development, and MBBR performance by faster reactor startups or increased specific activity per surface area. Biofilm formation is a complex process influenced by the solid substratum surface properties and microbial composition and characteristics. MBBR carriers can be made to facilitate biofilm formation by modifying their physico-chemical surface characteristics using blended polymers, mixed materials, coatings and incorporating different chemical functional groups. The chemical modification of the substratum polymeric surface for biofilm treatment reactors has comprised plasma oxidation treatment, radiolysis in a gas phase, liquid-phase oxidative treatment and polymer grafting. This review focusses on carrier material surface properties, the modification of such properties and carrier material choices relevant to biofilm development and functionality of MBBRs, in order to identify opportunities and challenges in future biofilm carrier development.

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... To date, different studies have discussed the basic mechanisms of organics and nutrient removals through biodegradation and nitrification-denitrification in the MBBR process [3,41]. The detailed documentation on system design and the role of influencing parameters affecting the performance of MBBR have been reported in some studies [42,43]. However, only a limited number of researchers have reviewed the modifications of the MBBR process [4,21]. ...
... The movement of the carriers outside the reactor is prevented using a sieve. The biocarriers in the MBBR process should have the following characteristics [43]: (a) sufficient protected surface area per unit volume of the carrier, (b) sufficient contact with the bulk liquid to allow the efficient mass transfer among bulk liquid and biofilm, (c) slightly lesser density than water, (d) sufficient size to prevent the passage through a sieve, (e) enough strength to resist the turbulence, and f) cost-effective. Various types of commercially available carriers like polymeric reticulated foam-based cuboid carriers or plastic carriers of different shapes and sizes are used in the MBBR process. ...
... These carriers are majorly made of high-density polyethylene (HDPE), recycled HDPE, and high-density polypropylene (HDPP) [111]. These types of carriers are highly durable (not easily degraded until they are exposed to intense ultraviolet irradiation) and need not be replaced throughout the life of the MBBR process [43]. The growth of biofilm on these carriers can vary from 5 to 30 mg TSS/m 2 . ...
Article
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The increase in the generation of wastewater along with the presence of different recalcitrant pollutants has stressed the existing conventional biological treatment systems beyond capacity. Given the necessity of advanced biological treatment processes, moving bed biofilm reactor (MBBR) is preferred for treating high organic and nutrient load and recalcitrant contaminants with enhanced removal efficiency, less footprint, reduced operational difficulties, and increased technical feasibility for large-scale as well as package-based-unit implementation. The present review attempts comprehensive documentation on the application of the MBBR process, its advantages and disadvantages, and comparative analysis with other advanced biological processes. The influencing design and operational parameters, such as hydraulic retention time, filling ratio of carriers and wastewater in the reactor, aeration, biofilm thickness, etc., have significant effects on the performance of MBBR. Furthermore, some modifications/up-gradation of the MBBR are analyzed targeting the enhanced nitrification and denitrification, organic matter removal, reduction of cost during the operational phase, etc. Among them, modification of biocarriers, aeration techniques, hybridization of MBBR with other biological and physicochemical processes exhibited promising performance concerning the removal of organics and nutrients. The present review also highlighted the areas of further research on the MBBR based-systems, their sustainability aspects, and subsequent field-scale applications.
... Compared with the CAS process, this technology has better tolerability to load variation and toxic shock, higher activated biomass concentration, less sludge recirculation and almost no sludge bulk issue [9][10][11][12][13]. For MBBR technology, the surface properties of suspending carriers are critical factors for biofilm formation, including the surface energy, hydrophobicity, hydrophilicity, surface charge, osmolality, roughness and morphology [14,15]. Consequently, various suspending carriers are applied in MBBR, such as polyurethane foam (PUF), plastics (e.g., polyvinyl chloride, polyvinyl alcohol, polypropylene, polyethylene, etc.), waste tires, nonwoven, ceramic and their modified materials [10,11,14,16]. ...
... The surface characteristics of suspending carriers are critical factors for the biofilm formation. It affects the rate of the initial biofilm formation, strength of formed biofilm, and functional characteristics of the biofilm [14,15,55]. In particular, the surface morphology of biofilm carriers has been a significant research issue because rough and porous surfaces can increase the contact area with activated sludge and protect biofilms against shear forces of water flow [56,57]. ...
Article
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This paper aims to improve the biological nitrogen removal performance by using magnetic polystyrene composite microparticles (PS@Fe3O4). Three types of PS@Fe3O4 with different surface morphologies were prepared by in-situ emulsion polymerization. Then, the optimum was creatively used as a biofilm carrier to form magnetic activated sludge (MAS) in lab-scale reactors. Compared to the conventional activated sludge, the utilization of PS@Fe3O4 accelerated the sludge settling velocity to 0.76 m/h. In addition, the ammonium nitrogen removal, total nitrogen removal and simultaneous nitrification and denitrification improved by 7.08%, 24.27% and 19.53%, respectively. The dissolved oxygen concentration and pH were observed to reveal the effect of PS@Fe3O4 on the nitrogen removal process. Based on microbial community analysis, there were more nitrifying and denitrifying bacteria in the MAS. Therefore, the novel developed PS@Fe3O4 can be a promising utilization material as a biofilm carrier for biological wastewater treatment.
... These techniques include film-coating, pre-seeded biofilm and physical-chemical changes of the surface (Morgan-Sagastume, 2018). For example, film coatings of carriers using molecules similar to extracellular polymeric substance (EPS), such as D-glucoronic acid and dextran, have been successful in enhancing attachment of nitrifiers and Bacillus subtilis (Duanis-Assaf et al., 2018;Morgan-Sagastume, 2018). Pre-seeding carriers with biofilm has also demonstrated the potential as a precursor for accelerating attachment of specific microorganisms. ...
... These results suggest that silica coating and denitrifying pre-seeded biofilm carriers can reduce the start-up period for anammox attached growth systems by achieving elevated ammonia removal kinetics earlier than virgin carriers and dextran-functionalized carriers. It is likely that the roughness of the silica coated carriers increased the protected surface area for anammox bacteria (Morgan-Sagastume, 2018). Similarly, the denitrifying pre-seeded biofilm carriers provided an ideal attachment surface for anammox bacteria. ...
Article
This study investigates and compares the ammonia removal kinetics, attachment, biofilm development and anammox bacteria enrichment on various surface modified carriers throughout the 163 days of start-up of an MBBR system: virgin, dextran-functionalized carriers, silica-functionalized and pre-seeded denitrifying carriers. Silica-functionalized carriers along with pre-seeded denitrifying carriers induced significant higher kinetics, faster biofilm growth and greater anammox bacteria enrichment during the 64 days of operation compared to non-modified virgin and dextran-functionalized carriers. The elevated anammox bacteria counts along with the elevated kinetics of all carriers measured at day 106 indicated that the completed biofilm growth and biofilm maturation are achieved prior to or at day 106 of start-up. The NH4⁺-N removal rate for virgin, dextran-functionalized, silica-functionalized and pre-seeded denitrifying carriers were achieved 0.684 ± 0.019, 0.608 ± 0.016, 0.634 ± 0.017 and 0.665 ± 0.018 g NH4⁺-N/m²/d, respectively, at day 106. The results demonstrate that the silica-functionalized and pre-seeded denitrifying carriers offer advantages during the early stage of start-up while the dextran-functionalized carriers did not reduce the start-up period for anammox biofilm.
... Microorganisms grow on the surface area of the bio-carrier, making the bio-media process effective; the biofilm surface area is a key design parameter [19]. A wide range of support materials, some of them organic or synthetic, for example, wood, gravel, rock, and synthetic materials: ceramic, nylon, and polyethylene [23,24], have advantages, as lower density can influence air flows and hydraulic speeds and can have an impact on the mass and oxygen transfer [25]. As well as resistance, there is less volume requirement, no recycling or backwashing, and no mechanical intervention in the case of load fluctuations. ...
Article
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In this study, a lab-scale fixed-film bio-media process was developed and operated to evaluate nitrogen removal from domestic sewage treatment plants. For nitrogen removal, the fixed-film bio-media process was applied in series with anaerobic, anoxic, and aerobic units in three separate reactors that were operated continuously at the same loading rates and hydraulic retention time. A biofilm separation bioreactor was developed for on-site domestic wastewater treatment and the bioreactor employed synthetic fiber modules so that the biomass could be completely attached to the media. In this paper, the performance of the fixed-film bio-media process with an average flow rate was evaluated before and after stabilization of the treatment system for nitrogen removal. The results show that the fixed-film bio-media process was successful for improved nitrogen removal from secondary and tertiary treated wastewater, with a 77% decrease in the total nitrogen discharge. Rapid nitrification could be achieved, and denitrification was performed in the anoxic filter with external carbon supplements during tertiary treated sewage wastewater. However, aeration was supplied after the stabilization process to achieve the nitrification and denitrification reaction for nitrogen removal. However, stable aeration supply could enhance nitrification at moderate temperature with benefits from complete retention of nitrifying bacteria within the system due to bio-media separation.
... Instead, natural packing materials like brick rubbles [20], sheep bone chips [12], gravel [21], laterite pebbles [22], and seashells [23] have been used. However, compared to natural packing materials, plastic carrier materials are more appropriate in industrial wastewater treatment processes as they are chemically inert, cheap, non-degradable, have a light weight, and provide a high surface-to-volume ratio [24]. ...
Article
A fixed bed biofilm reactor (FBBR) was developed and its performance in decolorizing synthetic dye mixture and textile industry effluents was evaluated in both batch and continuous modes. It was observed that yeast extract was important as the carbon source in the FBBR feed for color removal. However, the requirement for yeast extract in FBBR is very small compared to that in suspended cell cultures. Structural changes in dyes due to biological treatment were assessed from ultraviolet‐visible spectral and high‐performance liquid chromatography (HPLC) analyses. Gas chromatography‐mass spectrophotometry (GC‐MS) investigations confirmed the metabolites formed were non‐toxic and benign.
... Buoyant carrier media as biofilm growth supports have been employed in various types of attached biofilm processes. Biofilm carriers are support media providing a protected surface area to promote the growth of heterotrophic and autotrophic bacteria in the biological wastewater treatment process (Morgan-Sagastume, 2018;Sajjad et al., 2020). Increasingly, biofilm reactors are being used as cost effective wastewater treatments with many advantages (e.g., high concentration of active biomass and resistance to toxic shock loads). ...
Article
Since the 1980s, many studies have reported the importance of biofilm carrier roughness on microbial attachment. Roughness can enhance the wettability (hydrophobicity or hydrophilicity) of biofilm carriers. Roughness and wettability can lead to firmly attached biofilms with proper thickness communities and can protect them from being detached. However, roughness and wettability have not been adequately defined and discussed with regard to biofilm activity. Also, there is a contradiction among literature reports on how wettability affects bacterial adhesion. This systematic review presents a discussion of these properties as they affect biofilm formation and stability. In addition, it critically reviews past developments that occurred to advance carrier properties. It was found that an effective biomass immobilization requires rough surfaces having edges, and peaks and valleys. These carrier surfaces need to be substantially less or more hydrophobic/hydrophilic than the suspended biomass. The difference in wettability is the driving force to determine the degree of interaction with bacteria. Rough and wetted surfaces ensure the initial adhesion of bacterial communities and provide robust protection from detachment. If roughness was inadequate and the carrier wettability range was close to that of the biomass, it would significantly destabilize the overall biofilm system performance and deteriorate biofilm attachment.
... Although, following studies of Hadjiev et al. (2007), Paul et al. (2007), Dias et al. (2018), and Morgan-Sagastume (2018) evidently disagreed with Ødegaard et al. (2000) and Rodgers and Zhan (2003) by demonstrating that the shape of biofilm carrier essentially determines the hydrodynamic conditions, protects biofilms from abrasion, and further influences the mass transfer of dissolved oxygen and nutrients (Dias et al., 2018b;Hadjiev et al., 2007;Paul et al., 2007;Morgan-Sagastume, 2018). Alvarado-Lassman et al. (2008) reported that the carrier shape is a major factor responsible for the differences in colonization (Alvarado-Lassman et al., 2008). ...
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Shapes and pores of biofilm carriers play a major role in deciding fluidization efficiency, biomass immobilization and removal efficiency. However, little is known about their impact on the efficiency of bioremediation. This review study sheds light on the function of carrier geometry (i.e., pores and shapes) on the bioremediation productivity, where the wrong selection of such carrier geometry may prevent attached microbes at the core from accessing nutrients. It was found that the ideal porous biofilm carrier undoubtedly has to be spherically shaped, with ridges on its surfaces, and characterized by larger than 1 mm of irregular pore size openings. The irregular pore openings provide various environments to culture various cells, develop uneven biofilm, and retain different sizes of cells and biomass. The findings challenge current literature knowledge and commercial strategies that have chosen the surface area as the critical factor.
... These results suggest that the enrichment of MMCs with PHA-storing capacity supports the development of dynamic microbial communities, which may respond to the incoming wastewater characteristics and process operating conditions, but which may manifest a similarly performing PHA-storage phenotype. The potential for microbial diversity and abundance in PHA-storing microorganisms is clear [34], but this diversity does not necessarily influence the performance in amount and quality of the polymer produced [3]. ...
Article
Production of a mixed microbial culture (MMC) biomass for polyhydroxyalkanoate (PHA) production was integrated into the wastewater treatment (WWT) of a potato-starch factory. A pilot-scale on-site evaluation was conducted over ten months, with inherent water quality variations including organic composition, temperature, and pH. The wastewater was rich in acetate and the organic matter content fluctuated from 50 to 90 % with respect to volatile fatty acids (VFAs). The PHA accumulation potential (PAP) of the surplus biomass, nevertheless, remained from 0.40 to 0.70 gPHA/gVSS. Biomass PAP characteristics were benchmarked at both pilot and laboratory scales using different feedstocks and accumulation methods. The resultant co-polymer type could be readily shifted by changes in feedstock VFA content. Selected polymer batches were recovered at pilot scale as commercial-quality prototype materials for development of PHA-based wood-fibre composites. WWT performance with 98 % organic contaminant removal remained consistent throughout. The good settleability of the pilot-scale biomass was in contrast to the poorly settleable biomass from the factory’s full-scale activated sludge. Metered nitrogen and phosphorus addition ensured stable WWT without major nitrification levels. Successful robust outcomes of both feast-famine selection principles and WWT can be translated and integrated into the full-scale WWT by a proposed adaptation to existing infrastructure. Analogous aerobic feast enrichment is proposed to be achievable with continuous or intermittent flow through a process selector/zone. This pilot-scale experience under actual field conditions of industrial WWT provides further evidence for the technical viability to produce biomass for PHA production while maintaining standards in effluent water quality.
... Furthermore, our results also showed that the MD-PU filler had a higher TN removal effect than the PU filler at HRTs of 12 h, 6 h, and 3 h. Overall, the MBBR containing modified MD-PU filler in this study had almost as good a pollutant removal efficiency, but it needed shorter HRTs in comparison with previous studies [1,7,26,33], which ensured that the same amount of wastewater could be treated in a shorter period of time. According to the concentration changes in ammonia, nitrite, and nitrate during the batch experimental period, our results reconfirmed that nitrification and denitrification could occur simultaneously in one MBBR because biofilms could create external aerobic and internal anaerobic environments [46]. ...
Article
The application of moving bed biofilm reactors is a prospective water remediation technology, but its treatment efficiency needs to be further improved. In this study, moving bed biofilm reactors were applied for ex situ remediation of polluted rivers, and medical stones were newly used for modification of polyurethane sponge filler. The porosity, water-holding capacity and apparent density of the modified filler were 8.24%, 32.74% and 5.2 times higher than non-modified filler, respectively, which is more favourable to microbial attachment and growth. The developed moving bed biofilm reactors had a good removal effect on the chemical oxygen demand, ammonia, and total nitrogen of polluted urban-river water with hydraulic retention times of 12 h, 6 h, and even 3 h. The chemical oxygen demand, ammonia, and total nitrogen removal rates of moving bed biofilm reactors containing modified filler were 88.06%, 93.67% and 67.10%, respectively, which are 4.86%, 8.89% and 9.01% higher than moving bed biofilm reactors with non-modified filler, respectively, at the shortest hydraulic retention time, 3 h. In summary, this study provides a new kind of filler for moving bed biofilm reactors in ex situ remediation of polluted urban rivers, targeting rapid removal of chemical oxygen demand, ammonia, and total nitrogen.
... The MBBR process using biocarriers allows both attached and suspended bacterial growth in the biological reaction vessel (bioreactor). The core component of the MBBR system is the biocarrier, where the bacteria adhere to create a biofilm structure (Morgan-Sagastume, 2018). Therefore, the properties of biocarriers play a vital role in influencing MBBR performance, as they directly affect the growth and propagation of bacteria in biofilm formation (Zhang et al., 2013). ...
Article
Preferable biocarrier is vital for start-up and operation of moving bed biofilm reactor (MBBR). Effects of three separate biocarriers - PPC, PU, and PP on MBBRs were systematically investigated including nutrients removal performances, biomass attachment, microbial community, and relevant functional genes. Results showed that three biocarriers achieved similar removal efficiencies for chemical oxygen demand (COD) and total phosphorus (TP), though much higher biomasses were found attached onto PPC and PU carriers. PPC and PU performed better than PP for ammonia nitrogen (NH4⁺-N) removal. However, PPC exhibited the greatest and most reliable denitrifying efficiency, mainly due to simultaneous nitrification and denitrification during better micro-anoxic-environment created within PPC carriers than the two others. Further studies by 16S rRNA gene and metagenomic sequencing analysis uncovered the bacterial diversity and structures, and relevant functional genes for nitrogen-transformation and pathways of nitrogen metabolisms, which laid the biological basis for the best performances via biocarrier PPC. This study inspired a feasible approach for municipal wastewater treatment through PPC filled MBBR.
... The MBBR system overcomes the limitation of uncontrolled biomass by generating a shear force controlling biofilm growth through a continuous motion of the biofilm attached carriers (di Biase et al., 2019). In addition, the compact design, easy operation, and no requirement of sludge recycling make it efficient for the treatment of highly polluted wastewater (Morgan-Sagastume, 2018). The present review summarizes MBBR technology for wastewater treatment, highlighting the importance of bacterial biofilm and EPS and modifications of biofilm carrier surface. ...
Article
Among the several biofilm-based bioreactors, moving bed biofilm reactors (MBBR) have been extensively used for wastewater treatment due to low operational costs, technical feasibility, and stability. Biofilm forming strains, e.g., Stenotrophomonas maltophila DQ01, achieved 94.21% simultaneous nitrification and denitrification (SND) and 94.43% removal of total nitrogen (TN) at a cycle time of 7 h, and a biofilm consortium consisting of Chryseobacterium sp. and Rhodobacter sp. achieved 86.8% removal of total organic carbon (TOC) at hydraulic retention time (HRT) of 24 h using lab-scale MBBR. Modifications in the surface properties of the biocarrier materials achieved 99.5 ± 1.1% chemical oxygen demand (COD) and 93.6 ± 2.3% NH4⁺-N removal, significantly higher than the conventional commercial carrier. This review article summarizes the application of MBBR technology for wastewater treatment. The importance of bacterial biofilm and extracellular polymeric substances (EPS), anammox-n-DAMO coupled processes, and carrier surface modifications in MBBR technology have also been discussed.
... This can make it possible that simultaneous nitrification-denitrification can occur in the continuously aerated bioreactor independent of the solid retention time of suspended biomass 17 . There are a wide range of support materials, some of them may be organic or synthetic, for example: wood, gravel, rock and synthetic materials: ceramic, nylon, polyethylene and polyurethane 18 Polyethylene and polyurethane are the most commonly used due to their surface area (200-1200 m 2 /m 3 ) and the number of pores promote the adherence of bacterias 19 . Some advantages of these supports media have lower densities than water which can influence air flows, hydraulic speeds and impact on the mass and oxygen transfer 20 as well as resistant, less volume requirement, no recycling or backwashing and no mechanical intervention in case of load fluctuations. ...
Article
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Swine wastewater treatment is a complex challenge, due to the high organic matter (OM) and nitrogen (N) concentrations which require an efficient process. This study focused on evaluating two different support media for OM and N removal from an Upflow Anaerobic Sludge Blanket (UASB) reactor fed with swine wastewater. Maximum specific nitrification (MSNA) and denitrification (MSDA) activity test for both biofilm and suspended biomass were carried out using as supports: polyurethane foam (R1) and polyethylene rings (R2). The results showed that R2 system was more efficiently than R1, reaching OM removal of 77 ± 8% and N of 98 ± 4%, attributed to higher specific denitrifying activity recorded (5.3 ± 0.34 g NO3-N/g TVS∙h). Furthermore, 40 ± 5% of the initial N in the wastewater could have been transformed into molecular nitrogen through SND, of which only 10 ± 1% was volatilized. In this sense, MSDA tests indicated that suspended biomass was responsible for at least 70% of N removal and only 20% can be attributed to biofilm. SND could be confirmed with the analysis of microbial diversity, due to the presence of the genus Pseudomonas dominated the prokaryotic community of the system in 54.4%.
... Biofilms provide a micro-environment for microorganisms to effectively resist adverse external influences [27•]. From the internal environment to the external environment, microorganisms attaching to carriers form a unique anaerobic-anoxic-aerobic structure, which makes microbial species more complex and diverse, thus increasing the stability of the system [28,29]. As a result, it is very necessary to choose an optimal filler for wastewater treatment and biomass harvesting. ...
Article
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Purpose of Review The utilization of attached microalgae and bacteria to degrade wastewater has become a more promising treatment process to replace traditional methods. That is because the algae-bacteria biofilm can not only remove nutrients from the water but also achieve the effect of carbon fixation. Besides, the attached microalgae are easy to harvest and can be used for the processing of high value-added products. This paper reviews the knowledge of microalgae biofilm combined with bacteria to treat wastewater and provides insights into the bioremediation of the ecosystem by algae and bacteria. Recent Findings Due to the photosynthesis of algae and the oxidative decomposition of bacteria, the symbiotic system of algae biofilm and bacteria from wastewater has significant advantages in harvesting and degradation. To further improve wastewater utilization efficiency and carbon fixation, it is necessary to understand the algae-bacteria symbiotic system of mechanism and influencing factors of nitrogen and phosphorus removal and carbon fixation. The photobioreactor for microalgae cultivation is gradually developed and optimized, laying a solid foundation for actual production and application. Summary The algae-bacteria symbiotic system is more effective compared to individual microalgae treatment since the algae-bacteria biofilm has better removal efficiency and adsorption capacity as well as easy to harvest. This article introduces the mechanism and influencing factors of the algae-bacteria symbiotic system to remove nutrients and organic pollutants from water in detail. Furthermore, the research progress of photobioreactors is summarized as well. Finally, the application prospect of microalgae biofilm in wastewater treatment was prospected.
... Several research efforts have been directed at exploring variations on the design of the biocarrier, with the goal of improving the performance in MBBRs through the amount of bacterial biofilm retained [15]. These variations include shapes, sizes, and materials that can be varied to affect biocarrier performance [16][17][18][19]. ...
Article
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... Additionally, the enhanced adsorption capacity and hence higher concentration of organic matter at the carrier surface serves as a food source for the microorganisms and impacts microbial attraction. Apart from these, the highly porous structure of the CBMC carrier provides a better protected environment for cell growth [24][25][26]. ...
Article
This study reveals that the type of carrier material affects the stoichiometry of the anaerobic conversion and the metabolism in cultures enriched with polyphosphate-accumulating organisms (PAOs) and helps increase the biological phosphorus removal performance. PAO-enriched biofilms were cultivated in two identical lab-scale sequencing batch reactors containing different carrier types: a typical moving bed bioreactor carrier (MBBR) and a novel carbon-based moving carrier type (CBMC) coated by activated carbon particles. The experiments were conducted at various influent PO4³⁻ concentrations (14, 17, 20 mg-PO4³⁻-P/L) and two aeration periods (220 and 460 min) under similar operating conditions. The results showed that due to the particular characteristics of the highly porous CBMC carriers, biomass adhesion increased by approximately 15% compared to the MBBR carriers. It was also found that the CBMC carrier biofilm relied more on intracellularly stored polyphosphate than glycogen (which could be used by glycogen accumulating organisms (GAO)) as a source of energy for anaerobic uptake of organic substrates, which resulted in a greater dominance of PAO metabolism within the biofilm, especially at lower P concentrations. Conversely, a microbial community with mixed PAO-GAO metabolism was observed within the MBBR carrier biofilm, which changed to PAO dominated metabolism with increasing P concentration. Therefore, a higher specific PO4³⁻ uptake rate was obtained for the CBMC reactor (0.072-0.082 P-mol/C-mol.h), indicating a significant enhancement in the range of 13.1-19.6% compared to the MBBR reactor, depending on the influent P concentration. In addition, better resistance of the CBMC biofilm to prolonged aeration corroborated that although the highly porous structure of the CBMC carriers was effective in achieving a higher P-removal efficiency by 13.5%, the carrier material still played the major role in PAO metabolism dominance.
... This approach has been shown to result in faster bacterial attachment to the carrier surfaces. Moreover, some studies have shown that the coating of carriers to increase the roughness enhanced the attachment of the biofilm [64]. ...
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Biological treatments are integral processes in wastewater treatment plants (WWTPs). They can be carried out using sludge or biofilm processes. Although the sludge process is effective for biological wastewater systems, it has some drawbacks that make it undesirable. Hence, biofilm processes have gained popularity, since they address the drawbacks of sludge treatments, such as the high rates of sludge production. Although biofilms have been reported to be essential for wastewater, few studies have reviewed the different ways in which the biofilm properties can be explored, especially for the benefit of wastewater treatment. Thus, this review explores the properties of biofilms that can be exploited to enhance biological wastewater systems. In this review, it is revealed that various biofilm properties, such as the extracellular polymeric substances (EPS), quorum sensing (Qs), and acylated homoserine lactones (AHLs), can be enhanced as a sustainable and cost-effective strategy to enhance the biofilm. Moreover, the exploitation of other biofilm properties such as the SOS, which is only reported in the medical field, with no literature reporting it in the context of wastewater treatment, is also recommended to improve the biofilm technology for wastewater treatment processes. Additionally, this review further elaborates on ways that these properties can be exploited to advance biofilm wastewater treatment systems. A special emphasis is placed on exploiting these properties in simultaneous nitrification and denitrification and biological phosphorus removal processes, which have been reported to be the most sensitive processes in biological wastewater treatment.
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Aim of the study The work aims to assess the possibility of the application of selected types of biological beds to support the revitalization processes of strongly degraded water reservoirs. Material and methods The authors reviewed the literature on biological methods used in the treatment processes of various types of wastewater. Certain types of beds have been selected that show tolerance to temperature changes and significant changes in organic pollutant loads. The self-purification potential of water and the role of natural methods in the revitalization of water reservoirs were characterized. The characteristics of biological methods based on MBBR moving and fixed beds are presented. Results and conclusion The possibility of application of selected types of MBBR moving and fixed beds in supporting the treatment of highly contaminated surface waters were assessed. Biotechnological methods based on liquid and solid biopreparations normally used in water revitalization were discussed. It has been shown that when biotechnological methods are not able to operate efficiently, it is very beneficial to start additional biological processes to improve the efficiency of the revitalization process.
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In recent years, government investments in implementing restrictive public policies on the treatment and discharge of effluents from the aquaculture industry have increased. Hence, efficient and cleaner methods for aquaculture production are needed. Recirculating aquaculture systems (RAS) offers water conservation by recycling the treated aquaculture water for reuse. RAS wastewater treatment using a moving bed bioreactors (MBBRs) process has been considered well suited for maintaining good water quality, thereby making fish farming more sustainable. Currently, improvements were achieved in tackling the influence of salinity, organic matter, disinfectant, and bioreactor start-up process on the MBBR performance efficiency. This review highlights an updated overview of recent development made using MBBR to treat the residual water from RAS. Precisely, nitrification and simultaneous nitrification-denitrification (SND), and other hybrid processes for nitrogen removal were elucidated. Finally, future challenges and prospects of MBBRs in RAS facilities that need to be considered were also proposed.
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Harnessing the potential of biocatalytic conversion of renewable biomass into value-added products is still hampered by unfavorable process economics. This has promoted the use of biofilms as an alternative to overcome the limitations of traditional planktonic systems. In this paper, the benefits and challenges of biofilm fermentations are reviewed with a focus on the production of low-value bulk chemicals and fuels from waste biomass. Our study demonstrates that biofilm fermentations can potentially improve productivities and product yields by increasing biomass retention and allowing for continuous operation at high dilution rates. Furthermore, we show that biofilms can tolerate hazardous environments, which improve the conversion of crude biomass under substrate and product inhibitory conditions. Additionally, we present examples for the improved conversion of pure and crude substrates into bulk chemicals by mixed microbial biofilms, which can benefit from microenvironments in biofilms for synergistic multi-species reactions, and improved resistance to contaminants. Finally, we suggest the use of mathematical models as useful tools to supplement experimental insights related to the effects of physico-chemical and biological phenomena on the process. Major challenges for biofilm fermentations arise from inconsistent fermentation performance, slow reactor start-up, biofilm carrier costs and carrier clogging, insufficient biofilm monitoring and process control, challenges in reactor sterilization and scale-up, and issues in recovering dilute products. The key to a successful commercialization of the technology is likely going to be an interdisciplinary approach. Crucial research areas might include genetic engineering combined with the development of specialized biofilm reactors, biofilm carrier development, in-situ biofilm monitoring, model-based process control, mixed microbial biofilm technology, development of suitable biofilm reactor scale-up criteria, and in-situ product recovery.
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Moving-bed biofilm reactor (MBBR) or integrated floating-film activated sludge (IFFAS) process has been proved to be one of the ideal candidates for anammox application. However, the slow development of anammox bacteria (AnAOB) biofilm and unstable bioactivity always limit their wide application. This study developed a type of novel zero-valent iron (ZVI)-based modified carrier for strengthening AnAOB attachment and enhancing anammox performance. Surface properties analysis indicated the iron-based modified carrier revealed electropositive, less hydrophobic, and higher surface free energy compared with conventional high density polyethylene (HDPE) carrier. These surface parameters were positively correlated with total biomass attachment, anammox biofilm development, EPS secretion and heme-c production. IFFAS process filled with iron-based modified carriers could keep relatively stable and high anammox activity at different influent TN loadings (varied from 0.6 to 1.4 kg/(m³∙d)) and showed potential to keep and recover AnAOB bioactivity after six-months-freeze. Microbial analysis confirmed that anammox genus, Candidatus Kuenenia, had a significant niche preference on iron-based modified carrier than conventional HDPE carrier. As a result, the population of Candidatus Kuenenia in IFFAS process filled with modified carriers that contained 2 wt% or 3 wt% ZVI was 1.34 × 10⁶–1.55 × 10⁶ copies/ mg DNA, increased by 20.7–39.6% comparing with that in the control reactor (1.11 × 10⁶ copies/ mg DNA). This study demonstrated AnAOB could be enriched and maintained in situ with high abundance and bioactivity on the iron-based modified carriers, which would be significant for anammox process wide application in full-scale.
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In this study, two typical carrier types, microporous and macroporous carriers, were collected from a full-scale partial nitritation/anammox reactor for analysis and comparison of the biofilm structure characteristics, performance and removal nitrogen pathway. For microporous carriers, a thicker biofilm (>5 mm) was obtained with higher biomass and abundance of anammox bacteria as well as a higher nitrogen removal efficiency due to the integration of denitrifying and anammox bacteria. In addition, higher microbial community stability can be expected under varying environmental conditions. In comparison, macroporous carrier biofilm exhibited a lower thickness (0.4-2.3 mm) and lower microbial richness, with a strong network correlation among genera. Analysis showed that the mainly positive correlation between anammox bacteria and ammonium oxidizing bacteria, enhancing coupling partial nitritation and anammox. These findings help further our understanding of the mechanisms of anammox biofilm nitrogen removal and provide a baseline for optimization of the design of carrier structures.
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Last two decades have brought commendable respect for biofilm processes in wastewater treatment. Preeminent components from both the biofilter processes and activated sludge are utilized in evolving the moving bed process which eliminates major pollutants, organic matter and nutrients from municipal as well as industrial wastewater. The present review work is an endeavor to focus on the moving bed biofilm process for wastewater treatment applied in different aspects. An overview of MBBR development along with the factors affecting the operational performance of the system is discussed. It also analyses and investigates the state of the art of MBBR process for organic matter and nutrient removal. The review further assesses the MBBR technology as a hybrid system with current findings. Furthermore, the scope for future research prospects and challenges of the moving bed process has been discussed.
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Two types of continuous stirred tank moving bed biofilm reactors (ST-MBBR) and plug flow MBBR (PF-MBBR) were compared for nitrification. PF-MBBR showed strong shock resistance to temperature, and ammonium oxidation ratio (AOR) was 9.63% higher than that in the ST-MBBR, although the average biomass and biofilm thickness of ST-MBBR were 7.32 - 18.59%, 9.44 - 14.06% higher than those in the PF-MBBR. Meanwhile, a lower nitrite accumulation ratio (NAR) was observed (54.88%) in the PF-MBBR than the ST-MBBR (78.92%) due to different operation modes, and the divergence was demonstrated by the microbial quantitative analysis. Nitrification kinetics revealed that the temperature coefficient (θ) in the ST-MBBR (1.068) was much higher than that in the PF-MBBR (1.006 - 1.015), proving the contrasting nitrification performances caused by temperature shock. According to the Monod equation, the half-saturation coefficient (KN) in the ST-MBBR was 0.19 mg/L while it varied around 0.12 - 0.24 mg/L in the PF-MBBR, revealing various NH4⁺ affinity owing to different biofilm thickness and microbial composition. Finally, MBBR optimization related to operation mode, temperature, and free ammonium (FA) inhibition for nitrite accumulation was discussed.
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A moving bed biofilm reactor (MBBR) is a kind of commonly used biological sewage treatment process. A carrier, the core of MBBR, could directly affect the treatment efficiency of MBBR. In this experiment, a hybrid carrier composed of an MBBR carrier and fluidized bed porous carrier was innovatively utilized to treat low-concentration simulated domestic sewage through an MBBR reactor to investigate the effects of different hydraulic retention times (HRT) and different carrier dose ratios on the reactor performance. The results indicated that when the volume ratio of the carrier dosage was 5% : 20% when the reactor HRT was 5 h, the removal rates of ammonia nitrogen, total nitrogen (TN) and chemical oxygen demand (CODCr) were optimal, which were 96.5%, 60.9% and 91.5%, respectively. The ammonia nitrogen, total nitrogen and CODCr concentrations of the effluent were 1.04 mg L-1, 12.20 mg L-1 and 29.02 mg L-1, respectively. Furthermore, the total biomass concentration in the hybrid carrier biofilm reactor (HCBR) was 3790.35 mg L-1, which also reached the highest value. As the experiment progressed, the concentrations of protein, polysaccharide and soluble microbial products (SMP) were reduced to 7.68 mg L-1, 11.10 mg L-1 and 18.08 mg L-1, respectively. This was basically consistent with the results of the three-dimensional fluorescence spectrum. The results showed that the combined-carrier biofilm reactor could reduce the volumetric filling rate, improving the removal capability of organic matter and the denitrification efficiency. This study provided technical support for the composite carrier biofilm wastewater treatment technology, and also had a good prospect of application. This journal is
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Nitrogen removal from wastewater under low carbon/nitrogen (C/N) ratio and low dissolved oxygen (DO) level via simultaneous nitrification and denitrification (SND) can reduce energy consumption and exogenous carbon source, however, the stressful conditions would impair nitrogen removal performance. In this study, integrated floating fixed-film activated sludge (IFFAS) filled with novel surface-modified carriers was adopted and exogenous N-acyl-homoserine lactones (AHLs) were introduced to enhance SND. Results showed that efficient SND performance was achieved at low C/N ratio of 4 and DO concentration of 0.8 mg/L. AHLs could raise polysaccharide contents of extracellular polymeric substances (EPS) remarkably, which strengthened bacterial adhesion and provided structural and functional benefits to resource capture, digestive capacity and intercellular interactions. Bacterial community analysis indicated AHLs could enhance the abundance of mixtrophic denitrifying genera that participated in quorum sensing on carriers, such as anoxic denitrifiers (Flavobacterium, relative abundance 12.7 %), aerobic denitrifiers (Zooglaea, relative abundance 16.9 %) and autotrophic denitrifiers (Silanimonas, relative abundance 5.2 %). The efficient SND was mainly attributed to the structural/compositional-improved biofilm and coexistence of enriched mixtrophic nitrogen-removal microorganisms caused by AHLs. This study inspired a feasible strategy towards synchronous enhancement of biofilm structure and SND performance at low C/N ratio and low DO level through exogenous AHLs.
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The effects of aeration regimes (intermittent and continuous aeration) on nitritation performance and biofilm EPS composition were evaluated in moving bed biofilm reactors (MBBRs), and a hypothesis that the aeration regimes affect EPS composition by affecting the microbial activity and sludge discharge content was proposed. The effluent NO2⁻/NH4⁺ ratio corresponded to that of an anammox reaction (1.07 ± 0.20) for the MBBR with continuous aeration (MBBRcon.), while that in the MBBR with intermittent aeration (20 min on/15 min off) (MBBRint.) was relatively lower (0.75 ± 0.19). Furthermore, the activity of ammonia-oxidizing bacteria in MBBRcon. was 0.4–7.9 mg-N·L⁻¹·h⁻¹ more than that in MBBRint., which was consistent with the lower proportion of dead cells in MBBRcon. compared with MBBRint. (9.4% vs. 31.8%). The higher microbial activity in MBBRcon. led to more sludge discharge than MBBRint., which was reflected in the higher biofilm detachment rate in MBBRcon. compared with MBBRint. (0.15 ± 0.02 vs. 0.11 ± 0.02 g m⁻²·d⁻¹). The ratio of humic substances to polysaccharides in the EPS was high (0.96 ± 0.08) in the detachment biomass, while the ratios in the nitritation biofilm on carriers from MBBRcon. and MBBRint. were 0.52 ± 0.13 and 0.72 ± 0.16, respectively. We hypothesized that biofilm matrix with high ratios of humic substances to polysaccharides are structurally unstable and prone to fall off. In addition, the higher proportion of dead cells in MBBRint. made the proportion of humic substances in EPS high. Meanwhile, less sludge discharge in MBBRint. than MBBRcon. caused more humic substances to accumulate in the biofilm. These was responsible for the higher ratio of humic substances to polysaccharides in MBBRint. compared with MBBRcon. The findings elucidate the connection between aeration regimes and biofilm EPS composition, and guide the choice of aeration regimes in the design of biofilm reactors for partial nitritation.
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This study investigated biofilm establishment, biofilm structure, and microbial community composition of biofilms in three laboratory-scale moving bed biofilm reactors. These reactors were filled with three types of plastic carriers with varied depths of living space for microbial growth. The reactors were operated under the same influent and operational conditions. Along with the operation, the results showed that carriers with grids of 50 μm in height delayed the biofilm development and formed the thinnest biofilm and a carpet-like structure with the lowest α-diversity. In comparison, another two carriers with grids of 200 and 400 μm in height formed thick biofilms and large colonies with more voids and channels. Quantified properties of biofilm thickness, biomass, heterogeneity, portion of the biofilm exposed to the nutrient, and maximum diffusion distance were examined, and the results demonstrated that they almost (except for heterogeneity) strongly correlated to the α-diversity of microbial community. These illustrate that depth of living space, as an important parameter for carrier, could drive the formation of biofilm structure and community composition. It improves understanding of influencing factors on biofilm establishment, structure and its microbial community, and would be helpful for the design of biofilm processes.
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Biofilm, the aggregates of microbial layers that are attached on the surface of biofilter carriers, plays a central role in the removal and conversion of nutrients in recirculating aquaculture systems (RAS). The bacterial activity in biofilm involves autotrophic and heterotrophic processes. These biological processes are crucial for the water quality in RAS but are difficult to monitor. In this study, we demonstrate a new method based on intermittent respirometry to selectively estimate bacterial activity in biofilm following a spike in substrate concentration. The method was tested with three different biofilter carriers (extruded polypropylene, injection molded polypropylene and polymeric foam) from moving bed biofilm reactors in a common freshwater RAS. Oxygen consumption rates of biofilm-associated bacteria were measured in closed metabolic chambers under standard conditions. The protocol included sequential flushes of either pure tap water, or tap water spiked with nitrite, ammonium or acetate. The results showed consistent carrier-specific metabolic activities of endogenous respiration, nitrite-oxidizing bacteria (NOB), ammonia-oxidizing bacteria (AOB) and heterotrophic bacteria (HB) in biofilm. The highest activities normalized to volumetric oxygen consumption rates, were found in polymeric foam with values of 677 ± 125, 764 ± 156 and 166 ± 36 g O2·m⁻³·d⁻¹ for NOB, AOB and HB, respectively. The biofilter performance evaluation based on respirometric data showed satisfactory accordance with the values from substrate degradation batch kinetic tests for all three tested carriers, confirming the feasibility and robustness of the method as a means to assessing biofilter performance. Our study provides an on-site tool in biofilter performance tests and leads to a better understanding of dynamic and relationship between biofiltration and water quality.
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Two kinds of biocarriers were adopted and a combined process of “AMC (Anaerobic microorganism carrier)-UASB and PBG (Porous bio-gel)-MBBR” was operated at the pilot scale for the treatment of real textile wastewater. The influence mechanism of the two carriers on the start-up, pollutant removal and sludge reduction were investigated within 118 days of operation. The dominant functional bacteria in anaerobic and aerobic systems were identified by high-throughput sequencing, and the possible ways and related mechanisms of nutrient removal and sludge reduction were analyzed based on the data. 37.0 ± 7.5 % and 53 ± 12.7 % of COD removal efficiencies were achieved in anaerobic system and aerobic system, respectively. Ammonia nitrogen concentration decreased from 20 to 45 to 3.49 ± 0.54 mg/L after treatment. An anaerobe was found to be closely related to color removal, which existed in both anaerobic and aerobic systems, achieving 84.0 % of color removal. With the operation of the system, the sludge yield decreased gradually. The sludge yields of anaerobic and aerobic systems were calculated individually and compared with similar studies. Aging biofilms were characterized to explore the factors associated with biofilm renewal.
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Ammonia nitrogen in water negatively impacts aquatic life. Nitrifying bacteria are slow-growing and sensitive microorganisms, and technology using biofilm is an attractive option for their support. This study aims to demonstrate an optimal structure for microfilament carriers for growth of nitrifying bacteria in the tertiary stage of wastewater treatment (post-nitrification). Eleven samples of three polymer types (polyester, polypropylene, polyamide) that display different numbers of fibrils, fibril diameters, and structures were chosen for testing. Biofilm growth was monitored weekly using total protein concentrations and optical and fluorescence microscopy aided by image analysis. Final samples were characterized using molecular biological analysis (quantitative polymerase chain reaction and next-generation sequencing). Contents of ammonia-oxidizing bacteria (AOB) were significantly (four- to five-fold) lower than those of nitrite-oxidizing bacteria (NOB) in all tested samples. The relative abundance of NOB dominant strain, Nitrospira, reached >20%, whereas the abundance of Nitrosomonas, the only AOB representative, ranged between 3% and 6%. Polyester material was identified as optimal for support of nitrifying bacteria. This material displays maximum numbers of multifilament fibrils, and diameters of fibril and interspaces were minimal. These parameters play a crucial role for immobilization of nitrifying bacteria.
Chapter
Over the years anammox has emerged as a promising technique to replace the conventional biological nitrogen removal and has been a research hotspot in the field of wastewater treatment. Anammox is an energy-autarchic process that possesses advantages like cost effectiveness, no organic carbon requirement, less sludge production and lesser footprints. Nevertheless, substantial difficulties still persist, making the mainstream industrial applications of anammox confined and less observed around the world. Slow growth, long start-up time, reactor configuration, operational strategy are the key regulators that limits the potential of anammox. Reactor configuration is a powerful tool that plays a significant role in the application of anammox. Different bioreactor configurations including sequencing batch reactor, moving bed biofilm reactor, upflow anaerobic sludge blanket, membrane bioreactor, etc., have been tried and tested for harnessing the full potential of anammox. The innovations and advances made in form of hybrid reactor systems such as integrated fixed-biofilm activated sludge reactor and processes such as denitrifying ammonium oxidation has significantly aided in extending the mainstream applications of anammox worldwide. Strategies have been devised to retrofit or integrate these anammox-based systems in the existing wastewater treatment plants in order to make the existing nitrogen removal process more commercially viable and environmentally sustainable.
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The relatively poor settling characteristics of particles produced in moving bed biofilm reactor (MBBR) outline the importance of developing a fundamental understanding of the characterization and settleability of MBBR-produced solids. The influence of carrier geometric properties and different levels of biofilm thickness on biofilm characteristics, solids production, particle size distribution (PSD), and particle settling velocity distribution (PSVD) is evaluated in this study. The analytical ViCAs method is applied to the MBBR effluent to assess the distribution of particle settling velocities. This method is combined with microscopy imaging to relate particle size distribution to settling velocity. Three conventionally loaded MBBR systems are studied at a similar loading rate of 6.0 g/m²•day and with different carrier types. The AnoxK™ K5 carrier, a commonly used carrier, is compared to so-called thickness-restraint carriers, AnoxK™ Z-carriers that are newly designed carriers to limit the biofilm thickness. Moreover, two levels of biofilm thickness, 200 μm and 400 μm, are studied using AnoxK™ Z-200 and Z-400 carriers. Statistical analysis confirms that K5 carriers demonstrated a significantly different biofilm mass, thickness, and density, in addition to distinct trends in PSD and PSVD in comparison with Z-carriers. However, in comparison of thickness-restraint carriers, Z-200 carrier results did not vary significantly compared to the Z-400 carrier. The K5 carriers showed the lowest production of suspended solids (0.7 ± 0.3 g-TSS/day), thickest biofilm (281.1 ± 8.7 μm) and lowest biofilm density (65.0 ± 1.5 kg/m³). The K5 effluent solids also showed enhanced settling behaviour, consisting of larger particles with faster settling velocities.
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The effect of limiting biofilm volume using carriers with maximum thickness control on the performance and microbial community composition was investigated in anaerobic moving-bed biofilm reactors (AnMBBRs). Three parallel, continuous AnMBBRs (4 L) were operated (288 d, 24/36°C) to treat the soluble fraction of a wastewater from a food-manufacturing facility. Two different biofilm carriers controlling maximum biofilm thickness at 200 and 1000 μm (AnoxK™Z-200 and Z-1000) were used in the three reactors, targeting the same projected surface area for biofilm growth (410m²/reactor): R200(Z-200), R1000(Z-1000) and RMix(both Z-200 and Z-1000). The composition of the bacterial and methanogenic communities was analysed using 16 S rRNA gene amplicon sequencing. Under relatively constant organic loads (3.6-4.2gSCOD/Ld, 34-39gSCOD/m²d, hydraulic retention time=7.7-8 h), R200 presented lower soluble chemical oxygen demand (SCOD) removals (51-60%) than the other reactors (R100 = 91-93%, RMix = 86-91%), likely due to a limited amount of active protected biofilm volume. Lower SCOD removals were associated with higher concentrations of volatile fatty acids in the effluent (R200=400-800mgCOD/L; R1000 and RMix<200mgCOD/L) and lower methane production (R200=0.66; R1000=0.72; RMix=0.73 gCH4-COD/gSCODremoved). The Z-200 carriers contained a different fermentative/acidogenic bacterial community abundant in representatives of the families Christensenellaceae, Anaerovoracaceae and Synergistaceae, and led to less amount of biofilm biomass growth, albeit more active than that of carriers allowing for thicker biofilms (Z-1000). In contrast, methanogenic populations were less sensitive to biofilm thickness restraint by these carriers. This study shows for the first time that limiting biofilm volume in MBBR carriers can impact the performance and bacterial community in AnMBBR biofilms.
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The anaerobic ammonium oxidation (ANAMMOX) process was proposed as the most promising nitrogen removal process. Biofilm carriers were demonstrated to effectively enhance the anaerobic ammonium oxidating bacteria (AnAOB) retention. This paper reviews the effect of carrier properties on the AnAOB biofilm development according to the biofilm development process and the application state-of-art of three major kinds of conventional carriers, organic-based, inorganic-based carriers, and gel carriers, from the view of system performance and functional microorganisms. The carrier modification methods and purpose are thoroughly summarized and classified into three categories corresponding to various carrier defects. Four important aspects of the desirable carrier for the mainstream ANAMMOX process were proposed, including providing spatial configuration, enhancing the biomass retention, reinforcing the activity, and improving the growth environment, which needs to combine the advantages of organic and inorganic materials. Eventually, the future application directions of novel carriers for the ANAMMOX-based process were also highlighted.
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This study aimed at understanding how growth conditions influence the biofilm structural properties and the competition between microbial aggregates (biofilms, streamers, suspended biomass). The biological aggregates were developed during more than one month with constant C/N ratio (25 gCOD/gN) but under contrasted conditions in terms of shear stress, hydraulic retention time (HRT), apparent surface organic loading rate (SOLR) (fourteen conditions). At high HRT (absence of streamers) an increase of shear stress led to a decrease of the average biofilm thickness whereas it increased with the apparent SOLR. In addition, biofilm density increased with shear stress and with the apparent SOLR at high shear stress. The presence of streamers was observed only at low HRT (< 3 h). This presence has been attributed to the residual concentration in the bulk and to the hydrodynamic conditions of growth. Turbulent conditions and low substrate concentration considerably favor the development of streamers which benefit from a higher external mass transfer compared to biofilms due to their flapping movement. In some conditions, the mass of streamers in the reactor were close to the biofilm one’s, highlighting the necessity to consider such morphotypes in further studies since they can have a significant impact on the global microbial activity.
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Aims: For upgrading and reconstructing a municipal wastewater treatment plant, a biofilm-microflocculation filter system was designed and established towards synergistic improvement of denitrification and phosphorus removal from the secondary effluent. Methods and results: The establishment of the biofilm-microflocculation filter system underwent several processes, including sludge inoculation, biofilm formation and polyaluminum chloride (PAC) addition as flocculating agent. Microbial community analysis indicated that the dominant denitrification bacteria of the biofilm filter were in the phylum Proteobacteria and the genera Hydrogenophaga and Dechloromonas. On the basis of the initiation of filter system under optimal parameters such as C/N ratio of 5.3, HRT of 1.06 h and PAC of 5 mg·L-1 , approximately 75% COD, 80% TN and 75% TP could be effectively removed to satisfy discharge standards. Comparing the variations of microbial community structure at the genus level during the operating period of the filter system, it was found that the relative abundance of denitrification bacteria merely shifted from 53.14% to 48.76%, demonstrating that the effect of PAC addition on the main microorganisms is marginal. Conclusions: From the above results, it can be verified that the established biofilm-microflocculation filter system has practical and reliable performance for simultaneous biological denitrification and phosphorus removal. Significance and impact of study: This study provides a reference method for improving the advanced treatment of wastewater plant secondary effluent.
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A three-stage plug flow moving bed biofilm reactor (PF - MBBR, consisting of three identical chambers of N1, N2 and N3) was proposed for nitrifier enrichment using synthetic wastewater. During the stable operation, the average NH4⁺-N effluent was 0.67 mg/L and NH4⁺-N removal was as high as 97.19% with the nitrite accumulation ratio (NAR) of 54.23%, although the biofilm thickness and biomass both presented downward trends from N1 (296 μm, 2280 mg/L), N2 (248 μm, 1850 mg/L) to N3 (198 μm, 1545 mg/L). Particularly, the comparative results of three stages revealed that N2 showed the optimum NH4⁺-N removal (77.27%) and NAR (75.21%) in the continuous-flow, while NAR of N3 unexpectedly maintained a high level of 65.83% in the batch test, suggesting that ammonia oxidizing bacteria (AOB) accounted for absolute advantage over nitrite oxidizing bacteria (NOB). High-throughput sequencing initially verified different distribution of bacterial community structure, where N2 was far away from N1 and N3 with the lowest community richness and community diversity (operational taxonomic units (OTUs): 454(N2)<527(N3)<621(N1)). Proteobacteria (77.60%–83.09%), Bacteroidetes (1.66%–3.66%), Acidobacteria (2.28%–4.67%), and Planctomycetes (1.19%–6.63%) were the major phyla. At the genus level, AOB (mainly Nitrosomonas) accounted for 5.08% (N1), 20.74% (N2) and 14.24% (N3) while NOB (mainly Nitrospira) increased from 0.14% (N1), 7.06% (N2) to 4.91% (N3) with the total percentages of 5.22%, 27.80% and 19.15%. Finally, the application feasibility of MBBR optimization linked with nitrite (NO2⁻-N) accumulation for deep-level nutrient removal was discussed.
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Retrofitting conventional denitrification filters into partial denitrification‐anammox (PdNA) or anammox (AnAOB)‐based filters will reduce the needs for external carbon addition. The success of AnAOB‐based filters depends on anammox growth and retention within such filters. Studies have overlooked the importance of media selection and its impact on AnAOB capacity, head loss progression dynamics, and shear conditions applied onto the AnAOB biofilm. The objective of this study was to evaluate viable media types (10 types) that can enhance AnAOB rates for efficient nitrogen removal in filters. Given the higher backwash requirement and lower AnAOB capacity of the conventionally used sand, expanded clay (3‐5 mm) was recommended for AnAOB‐based filters in this study. Owing to its surface characteristics, expanded clay had higher AnAOB activity (304 vs 104 g NH4+‐N‐N/m2/d) and higher AnAOB retention (43% more) than sand. Increasing the iron content of expanded clay to 37% resulted in an increase in zeta potential, which led to 56% more anammox capacity compared to expanded clay with 7% iron content. This work provides insight into the importance of media types in the growth and retention of AnAOB in filters and this knowledge could be used as basis in the development of PdNA filters.
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Media-supported biofilm is a powerful strategy for growth and enrichment of slow-growing microorganisms. In this study, a single-stage nitritation-anammox process treating low-strength wastewater was successfully started to investigate the biofilm development on porous polyurethane hydrogel carrier. Suspended biomass migration into the carrier and being entrapment by its internal interconnected micropores dominated the fast initial colonization stage. Both surface-attached growth and embedded growth of microbes occurred during the following accumulation stage. Fluorescence in situ hybridization analysis of mature biofilm indicated that ammonium-oxidizing bacteria located at the outer layers featured a surface-attached growth, while anammox microcolonies housed in the inner layers proliferated as an embedded-like growth. In this way, the growth rate of anammox bacteria (predominated by Candidatus Kuenenia) could be 0.079 d⁻¹. The anammox potential of the biofilm reactor reached 1.65±0.3 kg/m³/d within two months. This study provides novel insights into nitritation-anammox biofilm formation on the porous polyurethane hydrogel carrier.
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The application of mainstream anammox process is hampered by its overlong start-up and instability under disturbance. A lab-scale mainstream anammox moving bed biofilm reactor (MBBR) was successfully started in 120 days with stepwise decrement in influent nitrogen concentration from sidestream to mainstream condition. The initial colonization by Candidatus Jettenia and filamentous fermenter Anaerolineaceae were potentially mediated by hydrophobic interaction and type IV pilus. Ca. Kuenenia with higher substrate affinity outcompeted Ca. Jettenia, and the predominant fermenters shifted to fermentative Ignavibacteriaceae in the mature biofilm. A novel mainstream anammox biofilm development (MABD) model was constructed to describe biofilm growth, population dynamics, and nitrogen removal performance. The simulation results suggested that higher inocula biomass (460-690 mgVSS·L-1), relative abundance of low-affinity AnAOB in the inocula (e.g., Ca. Jettenia, 1.3-2%), and the early-stage solids retention time (45-68 days) were desired to form thicker biofilm and improve effluent quality during 120-day mainstream anammox MBBR start-up. The mechanistic insights into biofilm formation and predictive power of the newly developed MABD model are of importance to the design and operation of mainstream anammox processes towards more biofilm biomass and higher nitrogen removal efficiency.
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In order to enhance the performance and sustainability of wastewater treatment technologies, researchers are showing keen interest in the development of novel materials which can overcome the drawbacks associated with conventional materials. In this context, 3D printing gained significant attention due to its capability of fabricating complex geometrics using different material compositions. The present review focuses on recent advancements of 3D printing applications in various physicochemical and biological wastewater treatment techniques. In physicochemical treatment methods, substantial research has been aimed at fabricating feed spacers and other membrane parts, photocatalytic feed spacers, catalysts, scaffolds, monoliths, and capsules. Several advantages, such as membrane fouling mitigation, enhanced degradation efficiency, and recovery and reusability potential, have been associated with the aforementioned 3D printed materials. While in biofilm-based biological treatment methods, the use of 3D printed bio-carriers has led to enhanced mass transfer efficiency and microbial activities. Moreover, the application of these bio-carriers has shown better removal efficiency of chemical oxygen demand (∼90%), total nitrogen (∼73%), ammonia nitrogen (95%), and total phosphorous (∼100%). Although the removal efficiencies were comparable with conventional carriers, 3D printed carriers led to ∼40% reduction in hydraulic retention time, which could significantly save capital and operational expenditures. This review also emphasizes the challenges and sustainability aspects of 3D printing technology and outlines future recommendations which could be vital for further research in this field.
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Rapid developments are habitually connected with substantial wastewater production (sources- municipal, textile, landfill, digester reject, saline industry, tannery, greywater, petroleum, pharmaceuticals, coal gasification, etc.), which contains different pollutants like nitrogen, phosphorous, carbon, heavy metals, emerging pollutants (pharmaceuticals, personal care products, endocrine disruptive compounds) and others. In this critical situation and rising water demand, biological techniques are the need of the hour for wastewater treatment and reuse, thereby protecting the environment. This paper highlights the most used bioreactors like Biofilter, Vermifiltration, MFC, MBBR, UASB, and MBR and their unique features. Additionally, details like intermediates, microbiology, operational conditions, mechanisms, implications, advantages, recent advancements, shortcomings, and removal efficiency of target pollutants (carbon, nitrogen, phosphorous- CNP; emerging contaminants- pharmaceuticals, personal care products, endocrine disruptive compounds) were discussed. The traditional and advanced versions of those bioreactors were also emphasized. Moreover, the review highlights different case studies related to the reuse scope of treated water that must be addressed for upcoming expansions and large-scale application of biological techniques in water reuse and the further development of hybrid systems. MFC is a well-known treatment technology for removing pollutants from wastewater when undertaken on a small scale; however, attempts should be made to make it successful on a larger scale. In Vermifiltration, further attempts must to be conducted to develop and design of robust systems as earthworms are sensitive to temperature and moisture.
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In a moving bed-biofilm reactor (MBBR), the fluidization efficiency, immobilization of microbial cells, and treatment efficiency are directly influenced by the shape and pores of biofilm carriers. Moreover, the efficacy of bioremediation mainly depends on their interaction interface with microbes and substrate. This review aims to comprehend the role of different carrier properties such as material shapes, pores, and surface area on bioremediation productivity. A porous biofilm carrier with surface ridges containing spherical pores sizes >1 mm can be ideal for maximum efficacy. It provides diverse environments for cell cultures, develops uneven biofilms, and retains various cell sizes and biomass. Moreover, the thickness of biofilm and controlled scaling shows a significant impact on MBBR performance. Therefore, the effect of these parameters in MBBR is discussed detailed in this review, through which existing literature and technical strategies that focus on the surface area as the primary factor can be critically assessed.
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The efficiency of anaerobic digestion could be increased by promoting microbial retention through biofilm development. The inclusion of certain types of biofilm carriers has differentiated existing AD biofilm reactors through their respective mode of biofilm growth. Bacteria and archaea engaged in methanogenesis during anaerobic processes potentially build biofilms by adhering or attaching to biofilm carriers. Meta-analyzed results depicted varying degrees of biogas enhancement within AD biofilm reactors. Furthermore, different carrier materials highly induced the dynamicity of the dominant microbial population in each system. It is suggested that the promotion of surface contact and improvement of interspecies electron transport have greatly impacted the treatment results. Modern spectroscopy techniques have been and will continue to give essential information regarding biofilm’s composition and structural organization which can be useful in elucidating the added function of this special layer of microbial cells.
Article
This research aims to improve simultaneous nitrification-denitrification and phosphorus removal (SNDPR) using novel carriers and to demonstrate the effect of carrier characteristics on nutrient removal in a biofilm reactor. For this purpose, biofilms enriched with both polyphosphate-accumulating organisms (PAOs) and nitrifiers were cultivated in two parallel sequencing batch reactors containing conventional moving bed bioreactor carriers (MBBR) and a novel type of carriers (carbon-based moving carriers (CBMC)). The new carriers were produced based on recycled waste materials via a chemical-thermal process and their specific surface area were 10.4 times higher than typical MBBR carriers of similar dimensions. The results showed that the use of CBMC carriers increased bacterial adhesion by about 18.5% and also affected the microbial population inside the biofilms, leading to an increase in PAOs abundancy and thus an increase in biological phosphorus removal up to 12.5%. Additionally, it was corroborated that the volume of the anoxic zones with dynamic behavior is strictly influenced by the carrier structure and biofilm thickness due to a limitation in oxygen penetration. Accordingly, the formation of broader anoxic zones and shrinkage of these zones to a lesser extent resulted in the continuation of anoxic reactions for longer periods using the novel carriers. Thereby, an increase in nitrogen removal by about 15% was obtained mainly by denitrifying PAOs. The results also exhibited that a higher simultaneous nitrification-denitrification (SND) efficiency can be achieved by selecting an appropriate aeration program influencing the dynamic changes of anoxic zones. Overall, a biofilm system using the new carriers, with phosphorus and nitrogen removal efficiencies of 97.5% and 92.3%, was presented as an efficient, compact, and simple operation SNDPR process.
Article
The microbial degradation of pesticides by pure or mixed microbial cultures has been thoroughly explored, however, they are still difficult to apply in real environmental remediation. Here, we constructed a synthetic microbial consortium system (SMCs) through the immobilization technology by non-living or living materials to improve the acetochlor degradation efficiency. Rhodococcus sp. T3–1, Delftia sp. T3–6 and Sphingobium sp. MEA3–1 were isolated for the SMCs construction. The free-floating consortium with the composition ratio of 1:2:2 (Rhodococcus sp. T3–1, Delftia sp. T3–6 and Sphingobium sp. MEA3–1) demonstrated 94.8% degradation of acetochlor, and the accumulation of intermediate metabolite 2-methyl-6-ethylaniline was decreased by 3 times. The immobilized consortium using composite materials showed synergistic effects on the acetochlor degradation with maximum degradation efficiency of 97.81%. In addition, a novel immobilization method with the biofilm of Myxococcus xanthus DK1622 as living materials was proposed. The maximum 96.62% degradation was obtained in non-trophic media. Furthermore, the immobilized SMCs showed significantly enhanced environmental robustness, reusability and stability. The results indicate the promising application of the immobilization methods using composite and living materials in pollutant-contaminated environments.
Article
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Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms-such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials-all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.
Article
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Increasing volumes of wastewaters combined with limited space availability and progressively tightening standards and quality control, promote the development of new intensive biotechnologies for water treatment. Fixed biomass processes offer several advantages compared with conventional biological treatments, respectively, higher volumetric load, increased process stability and compactness of the reactors. The purpose of this paper is to present an overview of the principal characteristics of advanced aerobic biofilm processes (performance, reactor configurations, scale-up, energy consumption, field of application, etc.), completed by a synthesis of their advantages and disadvantages. Emphasis is placed on the factors and techniques ensuring effective control of biofilm thickness and better mass transfer. For better understanding of biofilm processes, a new bioreactor classification is proposed as a function of the state of the biomass, the state of the medium and the hydrodynamic conditions. The control of the biofilm thickness is recognized as one of the most important parameters influencing process performance and efficiency. It is concluded that three-phase bioreactors ensure enhanced biological reaction rates through an effective biofilm control. However, further studies are needed to develop new economically attractive full scale mobile bed bioreactors.
Article
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The moving bed biofilm reactors (MBBRs) were used to remove the residual NO3 −-N of wastewater treatment plant (WWTP) effluent, and the MBBR carriers for denitrification were compared. The results showed that high denitrification efficiency can be achieved with polyethylene, polypropylene, polyurethane foam, and haydite carriers under following conditions: 7.2 to 8.0 pH, 24 to 26 °C temperature, 12 h hydraulic retention time (HRT), and 25.5 mg L−1 external methanol dosage, while the WWTP effluent total nitrogen (TN) was between 2.6 and 15.4 mg L−1 and NO3 −-N was between 0.2 and 12.6 mg L−1. The MBBR filled with polyethylene carriers had higher TN and NO3 −-N removal rate (44.9 ± 19.1 and 83.4 ± 13.0 %, respectively) than those with other carriers. The minimum effluent TN and NO3 −-N of polyethylene MBBR were 1.6 and 0.1 mg L−1, respectively, and the maximum denitrification rate reached 23.0 g m−2 day−1. When chemical oxygen demand (COD)/TN ratio dropped from 6 to 4, the NO3 −- N and TN removal efficiency decreased significantly in all reactors except for that filled with polyethylene, which indicated that the polyethylene MBBR can resist influent fluctuation much better. The three-dimensional excitation–emission matrix analysis showed that all the influent and effluent of MBBRs contain soluble microbial products (SMPs)-like organics and biochemical oxygen demand (BOD), which can be removed better by MBBRs filled with haydite and polyethylene carriers. The nitrous oxide reductase (nosZ)-based terminal restriction fragment length polymorphism (T-RFLP) analysis suggested that the dominant bacteria in polyethylene MBBR are the key denitrificans.
Article
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In this study a novel methodology is proposed to estimate the adhesion strength of biofilm developed in an attached-growth reactor. The time variation of adhesion strength was quantified in the course of formation or a biofilm consisting or denitrifiers. The model biofilm was formed on the surfaces of polyvinyl-chloride plates placed in a rectangular open-channel reactor. The result indicates that the adhesion strength was not uniformly distributed throughout biofilm but had a tendency to increase with biofilm depth and with the progression of biofilm formation. For example on the 32nd day from start-up the adhesion strength near the substratum interface attained a level in the order of 102 dyne.cm-2, whereas that in the vicinity of biofilm outer surface was only in the order of 100 dyne.cm-2. As well the biofilm dry density did not remain constant throughout biofilm having a tendency similar to that of the adhesion strength. A strong correlation was observed between the dry density and the extracellular biopolymer content per unit biofilm volume. It was suggested that the adhesion strength was significantly affected by the dry density.
Article
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A renovated suspended carrier biofilm reactor was investigated for its capability of carbon oxidation and nitrification. The carrier used was polyvinyl chloride cylinder with 2.5 mm diameter and 2.5–3.0 mm height. The carrier filling ratio, which is defined as the volume ratio of carrier to the whole reactor, is a key characteristic parameter for the new reactor. The operational experiments under different carrier filling ratio ranging from 10 to 75% were conducted. Meanwhile, the pollutant removal rate and behaviour of the microorganisms, such as biomass and specific oxygen utilization rate (SOUR) activity, were monitored and analyzed. The results showed that when the influent chemical oxygen demand (COD) and ammonia was about 200 and 20 mg/l, hydraulic retention time of 1.0 h, the optimum carrier concentration was about 50%with the average COD and ammonia removal rate about 70 and 30%, respectively.
Article
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The nitrifying performance of the biofilm formed onto polymeric supports (high density polystyrene, polyethylene, polypropylene, polyvinylchloride and polymethyl-methacrylate) was correlated with the hydrophobicity and surface charge of both bacteria and support media. Polypropylene , the most hydrophobic material, had the best properties for biofilm formation. The adhesion of nitrifying bacteria was mainly governed by hydrophobic interactions though electrostatic interactions were a determinant when the supports had identical hydrophobicity.
Article
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The modification of polymers has received much attention recently. Among the methods of modification of polymers, grafting is one of the promising methods. In principle, graft co-polymerization is an attractive method to impart a variety of functional groups to a polymer. Graft co-polymerization initiated by chemical treatment, photo-irradiation, high-energy radiation technique, etc. is documented in this review. Several prime controlling factors on grafting are discussed. In the past several years, there has been increased emphasis on applications of grafted polymers. The modified polymers through grafting have a bright future and their development is practically boundless. In this review, we have tried to cover two important applications employing grafting technique, viz. membrane separation science and conducting polymers.
Article
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The moving bed biofilm reactor (MBBR) can operate as a 2- (anoxic) or 3-(aerobic) phase system with buoyant free-moving plastic biofilm carriers. These systems can be used for municipal and industrial wastewater treatment, aquaculture, potable water denitrification, and, in roughing, secondary, tertiary, and sidestream applications. The system includes a submerged biofilm reactor and liquid-solids separation unit. The MBBR process benefits include the following: (1) capacity to meet treatment objectives similar to activated sludge systems with respect to carbon-oxidation and nitrogen removal, but requires a smaller tank volume than a clarifier-coupled activated sludge system; (2) biomass retention is clarifier-independent and solids loading to the liquid-solids separation unit is reduced significantly when compared with activated sludge systems; (3) the MBBR is a continuous-flow process that does not require a special operational cycle for biofilm thickness, L(F), control (e.g., biologically active filter backwashing); and (4) liquid-solids separation can be achieved with a variety of processes, including conventional and compact high-rate processes. Information related to system design is fragmented and poorly documented. This paper seeks to address this issue by summarizing state-of-the art MBBR design procedures and providing the reader with an overview of some commercially available systems and their components.
Article
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Two different types of carriers differing fundamentally in size, shape and structure were evaluated in parallel testing for nitrification potential using the moving-bed biofilm reactor (MBBR) technology. One of the carriers used was a cylindrical high-density polyethylene ring shaped carrier (AnoxKaldnes, K1 carrier) and the other was a spherical polyvinyl alcohol (PVA) gel bead shaped carrier (Kuraray, PVA-gel carrier). For each MBBR process, using artificial wastewater under autotrophic conditions, high maximal nitrification rates at 20 degrees C were obtained. For the K1 carrier up to 27 mgNH(4)-N/L.h (at 37% filling fraction) was found, corresponding to 49 mgNH(4)-N/L.h at the recommended maximum filling fraction of 67%. This corresponds to a nitrification area rate of 3.5 gNH(4)-N/m(2).d for the K1 carrier at 20 degrees C. For the PVA-gel carrier up to 32 mgNH(4)-N/L.h (at 9.6% filling fraction) was found, corresponding to 50.0 mg NH(4)-N/L.h at the recommended maximum filling fraction of 15%. At the recommended filling fractions, the two carriers therefore required about the same reactor volume to reach the maximum observed nitrification rate. This presumption allowed us to estimate the effective specific surface area for the PVA gel carrier up to 2,500 m(2)/m(3) versus 1,000 m(2)/m(3) when only the outer surface is considered.
Book
This book presents recent developments in advanced biological treatment technologies that are attracting increasing attention or that have a high potential for large-scale application in the near future. It also explores the fundamental principles as well as the applicability of the engineered bioreactors in detail. It describes two of the emerging technologies: membrane bioreactors (MBR) and moving bed biofilm reactors (MBBR), both of which are finding increasing application worldwide thanks to their compactness and high efficiency. It also includes a chapter dedicated to aerobic granular sludge (AGS) technology, and discusses the main features and applications of this promising process, which can simultaneously remove organic matter, nitrogen and phosphorus and is considered a breakthrough in biological wastewater treatment. Given the importance of removing nitrogen compounds from wastewater, the latest advances in this area, including new processes for nitrogen removal (e.g. Anammox), are also reviewed. Developments in molecular biology techniques over the last twenty years provide insights into the complex microbial diversity found in biological treatment systems. The final chapter discusses these techniques in detail and presents the state-of-the-art in this field and the opportunities these techniques offer to improve process performance.
Article
The formation of stable and highly active anammox biofilm is a lengthy process leading to long start-up times of deammonifying reactors of several months or more. This study aims to provide a quick and simple solution to the problem of long start-up periods for biofilm reactors by pre-treating the surface of carrier material, thereby increasing attachment rates of anammox cells and creating a significant improvement in the adhesion of cells to the carrier material. Two different techniques were investigated. The first one focused on growing a layer of heterotrophic biofilm on the surface of the plastic carriers prior to inoculation with anammox biomass. Specific anammox activity increased by almost 400% as compared to seed values and was equal to 250 mg NH4-N/gVSS/d. In the second technique, carrier material was coated with high porosity thin film of granular activated carbon to provide higher surface area. The anammox activity increased by approximately 50%. In comparison, control reactor with no media pretreatment did not develop any biofilm and no anammox activity was detected. Rapid attachment of the anammox biomass was achieved in a reactor with media that had a pre-developed layer of a biofilm. This biofilm acted as a scaffold with EPS matrix that allowed for a very quick attachment of anammox bacteria. In a way, this approach is analogous to a primer or an undercoat that is put on materials before painting to ensure better adhesion of paint to the surface, hence the suggested name - bioprimer.
Article
BACKGROUND The integrated free‐floating biofilm and activated sludge (IFFAS) process is an ideal candidate for simultaneous nitrification and denitrification (SND). However, traditional carriers have their inherent drawbacks, such as the weak hydrophilicity and negative charges on the surface. In this study, novel carriers with favorable hydrophilicity and electrophilicity were prepared and implemented in an IFFAS‐based SND reactor. RESULTS Compared with traditional carriers, the water contact angle of the novel carriers dropped to 60.2° and positive charges on the surface (+11.7 mV, pH 7.0) were acquired. Through accurate control of dissolved oxygen (DO), it took only 30 days to start SND, with a total nitrogen (TN) removal efficiency of 80.2%. In contrast, the start‐up period was 42 days with weaker TN removal capacity in a control reactor filled with traditional carriers. Novel carriers provided a favorable niche for more types of bacteria to survive, of which Nitrosomonadales and Nitrospirale were identified as nitrifiers while anoxic denitrifiers, aerobic denitrifiers and anammox bacteria also co‐existed in the system, contributing to TN removal. CONCLUSION Novel carriers with favorable hydrophilicity and electrophilicity were successfully prepared through a relatively facile approach, and a novel carriers‐based SND process enabled a shorter start‐up period, higher biomass and better TN removal efficiency. © 2017 Society of Chemical Industry
Article
In the biofilm wastewater treatment process, the start-up period of biofilm process is affected by the biofilm formation on the surface of carriers. Controlling surface charge property of carriers could accelerate the biofilm formation. The surface of conventional biofilm carriers, such as polyethylene (PE), polypropylene (PP) and high-density polyethylene (HDPE) is negatively charged, as is the surface of bacterial cells of activated sludge, which could lead to electrostatic repulsion between the biofilm carriers and the bacteria. Herein, the conventional high-density polyethylene (HDPE) carriers were modified by two kinds of positively charged polymers with different charge strength, which were noted as polyquaternium-10 (PQAS-10) and cationicpolyacrylamides (CPAM), respectively, to accelerate the startup of biofilm-based wastewater treatment process. The results showed that the positive Zeta potential was measured on the surface of modified carriers, whereas the surface Zeta potential of unmodified carriers was negative. It indicated that the modified carriers carried positive charge. Furthermore, the positive charge on the modified PQAS-10 carriers was higher than that on the modified CPAM carriers. The reactor with modified PQAS-10 carriers achieved shorter reactor start-up time and higher attached biomass compared to that with unmodified carriers and modified CPAM carriers. As a result, the removal efficiencies of COD, NH4⁺-N and TN in the reactor with the modified carriers were higher than that with the unmodified carriers. These findings demonstrated that the success of electrophilic modification on the surface of carriers was expected to accelerate the startup of biofilm-based reactors and improve the reactor performance in the practical application.
Article
Suppression of nitrite oxidizing bacteria (NOB) is of vital importance to achieve successful, energy efficient, mainstream anammox processes for wastewater treatment. In this study, biofilm carriers from a fully nitrifying MBBR system, fed with mainstream wastewater, were temporarily exposed to reject water from sludge dewatering, to evaluate this as a possible strategy to inhibit NOB and achieve nitrite production under realistic conditions. Two different carrier types were compared, in which biofilm thickness was maintained at approximately 400 and 50 μm, respectively, and reject treatment was tested at different exposure time and loading rates. Reject exposure almost always resulted in an increased nitrite production in the thinner biofilm, and overall, nitrifiers growing in the thin biofilm were more sensitive than those grown in the thicker biofilm. The effect from reject exposure remained in the systems for four days after returning to mainstream operation, with nitrite production gradually increasing for three days. Increased concentrations of free ammonia correlated with reject exposure and may be the cause of inhibition, although other factors cannot be excluded.
Article
In biofilm systems for wastewater treatment (e.g., moving bed biofilms reactors—MBBRs) biofilm thickness is typically not under direct control. Nevertheless, biofilm thickness is likely to have a profound effect on the microbial diversity and activity, as a result of diffusion limitation and thus substrate penetration in the biofilm. In this study, we investigated the impact of biofilm thickness on nitrification and on the removal of more than 20 organic micropollutants in laboratory-scale nitrifying MBBRs. We used novel carriers (Z-carriers - AnoxKaldnesTM) that allowed controlling biofilm thickness to 50, 200, 300, 400, and 500 µm. The impact of biofilm thickness on microbial community was assessed via 16S rRNA gene amplicon sequencing and ammonia monooxygenase (amoA) abundance quantification through quantitative PCR (qPCR). Results from batch experiments and microbial analysis showed that: (i) the thickest biofilm (500 µm) presented the highest biotransformation rate constants (kbio, L gTSS-1 d-1) for 14 out of 22 micropollutants; (ii) biofilm thickness positively associated with biodiversity, which was suggested as the main factor for the observed enhancement of kbio; (iii) the thinnest biofilm (50 µm) exhibited the highest nitrification rate (gN d-1 gTSS-1), amoA gene abundance and kbio values for some of the most recalcitrant micropollutants (i.e., diclofenac and targeted sulfonamides). Although thin biofilms favored nitrification activity and the removal of some micropollutants, treatment systems based on thicker biofilms should be considered to enhance the elimination of a broad spectrum of micropollutants.
Increased contamination of the environment with toxic pollutants has paved the way for efficient strategies which can be implemented for environmental restoration. The major problem with conventional methods used for cleaning of pollutants is inefficiency and high economic costs. Bioremediation is a growing technology having advanced potential of cleaning pollutants. Biofilm formed by various microorganisms potentially provide a suitable microenvironment for efficient bioremediation processes. High cell density and stress resistance properties of the biofilm environment provide opportunities for efficient metabolism of number of hydrophobic and toxic compounds. Bacterial biofilm formation is often regulated by quorum sensing (QS) which is a population density based cell-cell communication process via signalling molecules. Numerous signalling molecules such as acyl homoserine lactones, peptides, autoinducer-2 (AI-2), diffusion signalling factors and α-hydroxyketones have been studied in bacteria. Genetic alteration of QS machinery can be useful to modulate vital characters valuable for environmental applications such as biofilm formation, biosurfactant production, exopolysaccharide synthesis, horizontal gene transfer, catabolic gene expression, motility and chemotaxis. These qualities are imperative for bacteria during degradation or detoxification of any pollutant. QS signals can be used for the fabrication of engineered biofilms with enhanced degradation kinetics. This review discusses the connection between QS and biofilm formation by bacteria in relation to bioremediation technology.
Article
Deammonification (partial nitritation-anammox) is a proven process for the treatment of high-nitrogen waste streams, but long startup time is a known drawback of this technology. In a deammonification moving bed biofilm reactor (MBBR), startup time could potentially be decreased by increasing the attachment rate of anammox bacteria (AMX) on virgin plastic media. Previous studies have shown that bacterial adhesion rates can be increased by surface modification or by the development of a preliminary biofilm. This is the first study on increasing AMX attachment rates in a deammonification MBBR using these methods. Experimental media consisted of three different wet-chemical surface treatments, and also media transferred from a full-scale mainstream fully nitrifying integrated fixed-film activated sludge (IFAS) reactor. Following startup of a full-scale deammonification reactor, the experimental media were placed in the full-scale reactor and removed for activity rate measurements and biomass testing after 1 and 2 months. The media transferred from the IFAS process exhibited a rapid increase in AMX activity rates (1.1 g/m(2)/day NH4(+) removal and 1.4 g/m(2)/day NO2(-) removal) as compared to the control (0.2 g/m(2)/day NH4(+) removal and 0.1 g/m(2)/day NO2(-) removal) after 1 month. Two out of three of the surface modifications resulted in significantly higher AMX activity than the control at 1 and 2 months. No nitrite oxidizing bacteria activity was detected in either the surface modified media or IFAS media batch tests. The results indicate that startup time of a deammonification MBBR could potentially be decreased through surface modification of the plastic media or through the transfer of media from a mature IFAS process.
Article
In this study, two moving-bed biofilm reactors (MBBR1 and MBBR2) filled with different carrier media (Kaldnes K1 and Mutag Biochip, respectively) were subjected to increasing organic loading rates for 700 days. Regardless of the carrier used, both systems could withstand high organic loads up to 3.2 kgCOD/(m3.d), condition under which complete ammonium removal was achieved. However, the type of media influenced the quantity and distribution of attached biomass in the support, which in turn affected the activity of specific microbial functional groups in the biofilm. As the chemical oxygen demand (COD) input was gradually increased, the biofilm got thicker and the surface detachment rates were enhanced. Consequently, the amount of suspended solids has increased considerably to levels commonly found in hybrid bioreactors. Activity batch tests have shown that the contribution of the bulk phase biomass to the overall nitrification was very significant, being more relevant as the biofilm sloughing events became more intense. At constant organic loading rate, the hydraulic retention time (HRT) had a noticeable impact on the nitrification process, as it directly influenced the fraction of ammonium oxidized either by the attached or suspended biomass. Total nitrogen removal amounted up to 86 and 73% in MBBR1 and MBBR2, respectively.
Article
The central theme of the book is the flow of information from experimental approaches in biofilm research to simulation and modeling of complex wastewater systems. Probably the greatest challenge in wastewater research lies in using the methods and the results obtained in one scientific discipline to design intelligent experiments in other disciplines, and eventually to improve the knowledge base the practitioner needs to run wastewater treatment plants. The purpose of Biofilms in Wastewater Treatment is to provide engineers with the knowledge needed to apply the new insights gained by researchers. The authors provide an authoritative insight into the function of biofilms on a technical and on a lab-scale, cover some of the exciting new basic microbiological and wastewater engineering research involving molecular biology techniques and microscopy, and discuss recent attempts to predict the development of biofilms. This book is divided into 3 sections: Modeling and Simulation; Architecture, Population Structure and Function; and From Fundamentals to Practical Application, which all start with a scientific question. Individual chapters attempt to answer the question and present different angles of looking at problems. In addition there is an extensive glossary to familiarize the non-expert with unfamiliar terminology used by microbiologists and computational scientists. ISBN: 9781843390077 (Print) ISBN: 9781780402741 (eBook)
Article
Biofilms are communities of sessile microorganisms that grow and produce extrapolymeric substances on an abiotic or biotic surface. Although biofilms are often associated with negative impacts, the role of beneficial biofilms is wide and include applications in bioremediation, wastewater treatment and microbial fuel cells. Microbial adhesion to a surface, which is highly dependent on the physicochemical properties of the cells and surfaces, is an essential step in biofilm formation. Surface modification therefore represents an important way to modulate microbial attachment and ultimately biofilm formation by microorganisms. In this review different surface modification processes such as organosilane surface modification, plasma treatment, and chemical modification of carbon nanotubes, electro-oxidation and covalent-immobilization with neutral red and methylene blue molecules are outlined. The effectiveness of these modifications and their industrial applications are also discussed. There is inadequate literature on surface modification as a process to enhance beneficial biofilm formation. These methods need to be safe, economically viable, scalable and environmental friendly and their potential to fulfil these criteria for many applications has yet to be determined.
Article
Imaging and modeling are two major approaches in biofilm research to understand the physical and biochemical processes involved in biofilm development. However, they are often used separately. In this study we combined these two approaches to investigate substrate mass transfer and mass flux. Cross-sectional biofilm images were acquired by means of optical coherence tomography (OCT) for biofilms grown on carriers. A 2D biofilm model was developed incorporating OCT images as well as a simplified biofilm geometry serving as structural templates. The model incorporated fluid flow, substrate transfer and biochemical conversion of substrates and simulated the hydrodynamics surrounding the biofilm structure as well as the substrate distribution. The method allowed detailed analysis of the hydrodynamics and mass transfer characteristics at the micro-scale. Biofilm activity with respect to substrate fluxes was compared among different combinations of flow, substrate availability and biomass density. The combined approach revealed that higher substrate fluxes at heterogeneous biofilm surface under two conditions: pure diffusion and when high flow velocity along the biofilms surface renders the whole liquid-biofilm interface to be highly active. In-between the two conditions the substrate fluxes across the surface of smooth biofilm geometry were higher than that of the heterogeneous biofilms. This article is protected by copyright. All rights reserved.
Article
This study focused on characterizing the structure of biofilms developed on carriers used in lab-scale moving bed biofilm reactors. Both light microscopy (2D) and optical coherence tomography (OCT) were employed to track the biofilm development on carriers of different geometry and under different aeration rates. Biofilm structure was further characterized with respect to average biofilm thickness, biofilm growth velocity, biomass volume, compartment filling degree, surface area, etc. The results showed that carriers with a smaller compartment size stimulated a quick establishment of biofilms. Low aeration rates favored fast development of biofilms. Comparison between the results derived from 2D and 3D images revealed comparable results with respect to average biofilm thickness and compartment filling degree before the carrier compartments were fully willed with biomass. However, 3D imaging with OCT was capable of visualizing and quantifying the heterogeneous structure of biofilms, which cannot be achieved using 2D imaging.
Article
This study evaluates the effect of biofilm thickness on the nitrifying activity in moving bed biofilm reactors (MBBRs) in a controlled environment. In-depth understanding of biofilm properties in MBBRs and their effect on the overall treatment efficiency compose the key to optimizing process stability and efficiency. However, evaluating biofilm properties in continuously operated MBBRs can be extremely challenging. This study uses a carrier design which enables comparison of four different biofilm thicknesses, in otherwise equally operated lab-scale MBBRs. The results show that, within the studied range (200-500 µm) and specific operation conditions, biofilm thickness alone had no significant effect on the overall ammonium removal. The nitrate production, however, decreased with a decreasing biofilm thickness, and the ratio between nitrite and ammonia oxidizing activity decreased both with increasing load and decreasing oxygen concentration for all thicknesses. The suggestion that nitratation is disfavored in thin biofilms is an interesting contribution to current research being performed on NOB inhibition for deammonification applications. By indicating that different groups of bacteria respond differently to biofilm thickness, this study accentuates the importance of further evaluation of these complex systems.
Article
Increasingly stricter ammonia and nitrogen release regulations with respect to wastewater effluents are creating a need for tertiary treatment systems. The moving bed biofilm reactor (MBBR) is being considered as an upgrade option for an increasing number of wastewater treatment facilities due to its small footprint and ease of operation. Despite the MBBRs creation as a system to remove nitrogen, recent research on MBBR systems showing that the system's performance is directly related to carrier surface area and is irrespective of carrier shape and type has been performed exclusively on chemical oxygen demand (COD) removal systems. Furthermore, the influence of carrier type on the solids produced by MBBR systems has also been exclusively studied for COD removal systems. This work investigates the effects of three specific carrier types on ammonia removal rates, biofilm morphology, along with solids production and settleability of tertiary nitrifying MBBR systems. The study concludes that carrier type has no significant effect on tertiary nitrifying MBBR system performance under steady, moderate loading conditions. The research does however highlight the propensity of greater surface area to volume carriers to become clogged under high loading conditions and that the high surface area carriers investigated in this study required longer adjustment periods to changes in loading after becoming clogged.
Article
The moving bed biofilm process is based on plastic carriers on which biomass attaches and grows. The original Kaldnes carrier was made of high- density polyethylene (density 0.95 gcm-1) that could be used in filling fractions (volume of carriers in empty reactor) up to 70% that gives a specific area of 350 m2m-3. Lately there has been an interest in the use of larger carrier elements, especially when using the process for upgrading of activated sludge plants. This paper analyses the influence of the carrier size and shape on performance, especially related to highly loaded plants working on municipal wastewater. The results demonstrate that moving bed biofilm reactors should be designed based on surface area loading rate (g COD/m2d) and that shape and size of the carrier do not seem to be significant as long as the effective surface area is the same. The results indicate that very high organic loads can be used in order to remove soluble COD but that the settleability of the sludge is negatively influenced at high loading rates.
Article
LINPOR®-systems are modified activated sludge plants, where the aeration tanks contain a certain quantity of highly porous plastic foam particles, which serve as a carrier material for active biomass. Thus a substantial performance improvement is achieved as compared to conventional activated sludge systems without having to renounce the well proven elements of the activated sludge technology. The LINPOR®-CN process for the simultaneous elimination of organic and nitrogen pollutants is particularly suitable for upgrading existing plants, because it can be made to fit into existing tanks with no or only little change of the once installed facilities.
Article
A new device was designed to compare the biomass retention capacity of different microcarriers. Microcarriers were placed in as many as 28 independent, parallel minibioreactors under selected and identical flow conditions. Sepiolite, pozzolana, clay, and foam glass (Poraver™)were examined for biomass retention capacity, characterized in tenns of attached volatile solids and specific methanogenic activity, and examined with scanning electron microscopy. Sepiolite had the greatest biomass retention capacity and better internal porous volume for biomass immobilization. The specific methanogenic activity of the immobilized biomass in different materials was found to be inversely correlated to the amount of attached biomass. A maximum difference of 19% overall activity of the colonized material was observed between foam glass and pozzolana. Compared with the suspended biomass, a clear enhancement of syntrophic activity (up to 110%)and reduction of acetoclastic activity (up to 73%) was observed in the biofilm. This system of examination provides information useful for preselecting microcarriers for biomass colonization.
Article
This study aimed to investigate biofilm properties evolution coupled with different ages during the start-up period in a moving bed biofilm reactor system. Physicochemical characteristics including adhesion force, extracellular polymeric substances (EPS), morphology as well as volatile solid and microbial community were studied. Results showed that the formation and development of biofilms exhibited four stages, including (I) initial attachment and young biofilm formation, (II) biofilms accumulation, (III) biofilm sloughing and updating, and (IV) biofilm maturation. During the whole start-up period, adhesion force was positively and significantly correlated with the contents of EPS, especially the content of polysaccharide. In addition, increased adhesion force and EPS were beneficial for biofilm retention. Gram-negative bacteria mainly including Sphaerotilus, Zoogloea and Haliscomenobacter were predominant in the initial stage. Actinobacteria was beneficial to resist sloughing. Furthermore, filamentous bacteria were dominant in maturation biofilm. Copyright © 2015 Elsevier Ltd. All rights reserved.
Article
In this study hydrophilic cationic modified polyurethane foam (MPUF) carriers were developed to achieve faster water immersion and increased affinity for biofilm attachment in a moving bed biofilm reactor compared with generally used polyurethane foam (PUF) carriers. Biofilm was more susceptible to attachment to MPUF carrier than to PUF carrier. At the steady state of reactor operation, the amount of biofilm attached to MPUF carriers was 1.3 times more than that to PUF carriers. Phylogenetic analysis using 454-pyrosequencing revealed that biofilms attached to MPUF carrier displayed more complex community diversity, with higher Ace, Chao1 and Shannon indices and a lower Simpson index.
Article
The objective of this work is to investigate the effects of surface area loading rates (SALRs) and hydraulic retention times (HRTs) in moving bed bioreactor (MBBR) systems on the morphology and thickness of the attached biofilm along with subsequent effects on particle size distribution and the settling characteristics of the biologically produced solids. The morphology of biofilm attached to the MBBR carriers changed from a porous biofilm to a biofilm with a more filamentous structure throughout the study at various operating conditions without observable correlation with SALR and HRT. Although, biofilm morphology did not demonstrate an effect on the biologically produced solids observed in this study, the thinnest biofilms resulted in the highest concentration of solids in the effluent. Furthermore, the particle size distribution analysis demonstrated that both higher SALRs and longer HRTs resulted in a shift towards larger-sized particles. Increases in SALR and HRT, independent of each other, also showed increases in effluent solid concentration and lower settleability of the solids.
Article
The cell retention capacities of three porous microcarriers with diversified pore characteristics and Ottawa silica sand were studied in methanogenic fluidized bed reactors with acetic acid as the sole substrate. Batch kinetic experiments on substrate utilization at different initial bulk-liquid substrate concentrations were also performed.The experimental data reveal that, under similar startup conditions, porous microcarriers are capable of reducing the startup times by more than 50% as compared to sand. Furthermore, under pseudo-steady-state conditions at an organic loading of 6 g total organic carbon (TOC)/1-day, porous microcarriers are capable of retaining three times more immobilized cells as compared to sand. More than 90% of total reactor cell mass is immobilized on porous microcarriers as opposed to 80% on sand. As a result, porous microcarriers are conducive for better proliferation of slow-growing methanogenic bacterial consortia. The experimental data clearly indicate that surface area, total pore volume and mean pore diameter should be used concomitantly to obtain better insight into the cell retention capacity of a given porous microcarrier.Batch kinetic data on substrate utilization reveal that mass transfer limitations are absent in methanogenic fluidized bed reactors at bulk-liquid TOC concentrations > 10 mg/l. The observed maximum substrate utilization rates, which are independent of initial bulk-liquid TOC concentrations ranging from 200 to 1000 mg/l, are low for porous microcarriers as compared to sand (0.5 vs 2.25 day−). These data confirm the results of the microscopic examinations performed which indicate that porous microcarriers attract Methanothrix type bacterial consortia whereas Ottawa silica sand attracts a mixture of Methanothrix and Methanosarcina.
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The adhesion of Alcaligenes denitrificans to several polymeric materials was investigated. As the nature of the surfaces of the micro-organisms and the substrate materials is an important factor in the adhesion process, characteristics such as the electrokinetic potential and hydrophobicity were also determined and correlated with the capacity of bacterial cells to adhere to solid surfaces. The substrates used were high-density polyethylene (HDPE), polypropylene (PP), poly(vinyl chloride) (PVC), and poly(methyl methacrylate) (PMMA). The electrokinetic potential of the cells and the substrates was determined by measurements of electrophoretic mobility and the hydrophobicity was determined by contact angle measurements. All the substrates studied as well as the bacterial strain have a negative zeta potential, which means that adhesion is not mediated by electrostatic interactions. As far as hydrophobicity is concerned, PP is the most hydrophobic material, PMMA is the least hydrophobic, whereas HDPE and PVC present an intermediate behavior. As bacteria cells are hydrophilic, adhesion is favored to PP; therefore, this substrate material seems to be the one that promotes a stronger adhesion and the development of the most stable biofilm for use as a biomass carrier in denitrifying inverse fluidized bed reactors. This was confirmed by the results of adhesion tests. In this way, adhesion seems to be dominated by hydrophobic interactions.
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Submerged biofilm systems, such as integrated fixed-film activated sludge (IFAS) and moving bed bioreactors (MBBRs), are increasingly being used for domestic wastewater treatment, often to improve nitrification. Little is known about whether and how biofilm attachment surface chemical properties affect treatment performance, although surface chemistry is known to affect attachment in other systems, and work with pure strains has suggested that attachment of nitrifying bacteria may be enhanced on high surface energy surfaces. The objective of this research was to systematically evaluate the effects of surface chemistry on biofilm quantity and rates of nitrification and estrogen removal. Biofilms were grown on four plastic attachment surfaces with a range of hydrophobicity and surface energy values (nylon, melamine, high-density-polyethylene [HDPE], and acetal polymeric plastic) by immersing them in a full scale nitrifying activated sludge wastewater treatment system, followed by batch test experiments. The attachment surface water contact angles ranged from 53° to 98° and surface energies ranged from 48.9 to 20.9 mJ/m(2). Attachment surface hydrophilicity and surface energy were positively correlated with total biomass attachment, with more than twice as much biomass on the highest surface energy, most hydrophilic surface (nylon) than on the lowest surface energy, least hydrophilic surface (acetal plastic). Absolute and specific nitrification rates were also correlated with hydrophilicity and surface energy (varying by factors of 5 and 2, respectively), as were absolute and specific removal first order rate constants of the hormones estrone (E1), β-estradiol (E2) and 17α-ethynylestradiol (EE2). These results suggested that attachment surface chemistry may be a useful design parameter for improving biofilm performance for removal of ammonia and endocrine disrupting hormones from wastewater. Further research is required to verify these results at longer time scales and with typical media geometries.