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Abstract

Oil refineries generate wastewater pollutants such as sulfide and nitrate from gasoline sweetening and other concomitant processes, respectively. However, the concentration of biodegradable organic substrate in the industrial wastewater is insufficient for the complete denitrification process. Thus, this study investigated sulfide-based denitrification treatment for real sulfide-rich industrial wastewater, with a low C/N molar ratio, produced in the oil refinery. The performance of two continuous laboratory packed-bed reactors (PBRs) packed with different biomass carriers was evaluated. PBRs were denoted as R1 (polyester type carriers) and R2n (polyester type carriers coated with nanofibers) and operated at 24 °C with the fixed S/N molar ratio at 0.28, respectively. The maximum sulfide and nitrate-nitrogen applied loading rate was 0.17 kg/(m³⋅d) and 0.25 kg/(m³⋅d), respectively. Results showed nitrate removal efficiency was 94.8 % and 95.3 % in R1 and R2n, respectively. Sulfide was almost completely removed in both PBRs, achieving the sulfide removal efficiency of 99 % throughout the entire experiment. The R2n achieved a higher specific volumetric denitrification rate then R1 since nanofiber carriers enhanced bacterial attachment. This study indicated great potential for further application in petrochemical wastewater treatment.

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... The intermediate product S 0 is used widely in various industries [11,12]; however, its thermodynamics is precarious, though it could not remain and be collected from within the bioreactor easily. The autotrophic denitrification, especially at low molar S/N ratios (less than one), leads the oxidation process toward the complete conversion of sulfide to sulfate [13,14]. Moreover, the energies read by Eqs. ...
... Although nitrate is an electron acceptor, it cannot complete the reaction in the direction of sulfate production because of its weakness compared to dissolved oxygen [19]. Furthermore, the stoichiometry of nitrate reduction is in a form that does not allow the oxidation surplus to the way of sulfate formation [14]. In this regard, considering nitrate removal and pH effect, good attempts were made to determine the S/N ratio for the most effective autotrophic denitrification [20][21][22][23]. ...
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This study focused on the challenges of the maximum and fastest production of sulfate-free elemental sulfur through simultaneous reduction of sulfide by autotrophic denitrifying microbes. A microbial oil consortium was used to supply biomass which developed and synthetized by Research Institute of Petroleum Industry of Iran (RIPI). Having main feeds of concentrated nitrate and sulfide, this reaction was anaerobically conducted under batch conditions (8 h) and 3 different molar S/N ratios (1.75, 2.00, and 2.25). The results convinced us to look for a fourth S/N ratio (the optimal point) that our data did not show. Molar S/N ratio 1.9 was the point that the highest amount of elemental sulfur was achieved and sulfide removal rate reached the highest and fastest value (197 mg/L, 3 h) with no sulfate production. Bio-kinetics studies showed that a substrate limitation and a chemical/physical product inhibition mechanism controlled the reaction conditions. Three bio-kinetic mechanisms were investigated to predict the parameters of bio-kinetic models. Inhibition-free substrate limitation, substrate inhibition, and product inhibitions parameters were calculated and studied by MATLAB software version 17b.
... This process has the advantages of not needing any organic matter for nitrogen removal and having a low sludge yield (Nguyen et al., 2022). Thus, it has been widely used in the nitrogen removal treatment of surface water and groundwater (Andreides et al., 2021;Li et al., 2020;Liang et al., 2022). The SADN system with S 0 and S 2 O 3 2− as electron donors will not only produce a large amount of acid, and need a large amount of alkali to maintain the pH value, but also produce a large amount of SO 4 2− , which requires a large amount of calcium ions to be added for advanced treatment (Sahinkaya & Dursun, 2012;Sahinkaya et al., 2011). ...
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Double short-cut sulfur autotrophic denitrification (DSSADN) coupled with Anammox is of great significance in the low-carbon treatment of nitrogen-containing wastewater. In order to achieve high salinity autotrophic nitrogen removal, the effects of different salinities on the accumulation characteristics of NO2⁻-N and S⁰ and microorganisms in DSSADN process were studied. The results showed that the effect of salinity on the DSSADN process could be categorized into the stimulation, stable, and inhibition. When the salinity gradually increased to 2.5%, the highest NO2⁻-N production rate (NiPR) and S⁰ production rate (S⁰PR) of DSSADN were 0.54kg/(m³·d) and 1.1kg/(m³·d) respectively. NiPR and S⁰PR gradually decreased as the salinity increased to more than 3%. However, salinity had a relatively low impact on nitrite accumulation efficiency and S⁰ accumulation efficiency, which were 80% and 81.5%, respectively, when the salinity reached 5%. Salinity has a great influence on the structure and abundance of microbial communities in the system.
... Free hydrogen in petrochemical effluent reduces the pH of the water, prevents microbial growth, decreases water's capacity to purify itself, corrodes structures like ships and buildings, and makes water harder. It will also impact groundwater and drinking water quality if petrochemical wastewater seepage occurs into the soil (Andreides et al., 2021;Priyadarshini et al., 2021;Shiri et al., 2015;Verma et al., 2022). ...
Preprint
Remediation by algae is a very effective strategy for avoiding the use of costly, environmentally harmful chemicals in wastewater treatment. Recently, industries based on biomass, especially the bioenergy sector, are getting increasing attention due to their environmental acceptability. However, their practical application is still limited due to the growing cost of raw materials such as algal biomass, harvesting, and processing limitations. Potential use of algal biomass includes nutrient recovery, heavy metals removal, COD, BOD, coliforms, and other disease-causing pathogens reduction and production of bioenergy and valuable products. However, the production of algal biomass using the variable composition of different wastewater streams as a source of growing medium and the application of treated water for subsequent use in agriculture for irrigation has remained a challenging task. The present review highlights and discusses the potential role of algae in removing beneficial nutrients from different wastewater streams with complex chemical compositions as a biorefinery concept and subsequent use of produced algal biomass for bioenergy and bioactive compounds. Moreover, challenges in producing algal biomass using various wastewater streams and ways to alleviate the stress caused by the toxic and high concentrations of nutrients in the wastewater stream have been discussed in detail. The technology will be economically feasible and publicly accepted by reducing the cost of algal biomass production and reducing the loaded or attached concentration of micropollutants and pathogenic microorganisms. Algal strain improvement, consortium development, biofilm formation, building an advanced cultivation reactor system, biorefinery concept development, and life-cycle assessment are all possible options for attaining a sustainable solution for sustainable biofuel production. Furthermore, producing valuable compounds, including pharmaceutical, nutraceutical, and pigment contents generated from algal biomass during biofuel production, could also help reduce the cost of wastewater management by microalgae.
... Hence, future research targeting the post-processing of the sulfide-rich effluent, as well as the processing of the sulfide-rich biogas is required. Available approaches include using sulfide as an electron donor in autotrophic denitrification systems (Andreides et al., 2021) or the recovery of elemental sulfur in microaerophilic reactors (Camiloti et al., 2016;de Sousa et al., 2017). Regardless of these complementary studies, implementing AnSTBR-based treatment plants will always provide a solid basis for developing reliable pollution prevention solutions. ...
Article
The competition between sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) depends on several factors, such as the COD/SO4²⁻ ratio, sensitivity to inhibitors and even the length of the operating period in reactors. Among the inhibitors, salinity, a characteristic common to diverse types of industrial effluents, can act as an important factor. This work aimed to evaluate the long-term participation of sulfidogenesis and methanogenesis in the sulfate-rich wastewater process (COD/SO4²⁻ = 1.6) in an anaerobic structured-bed reactor (AnSTBR) using sludge not adapted to salinity. The AnSTBR was operated for 580 d under mesophilic temperature (30 °C). Salinity levels were gradually increased from 1.7 to 50 g-NaCl L⁻¹. Up to 35 g-NaCl L⁻¹, MA and SRB equally participated in COD conversion, with a slight predominance of the latter (53 ± 11%). A decrease in COD removal efficiency associated with acetate accumulation was further observed when applying 50 g-NaCl L⁻¹. The sulfidogenic pathway corresponded to 62 ± 17% in this case, indicating the inhibition of MA. Overall, sulfidogenic activity was less sensitive (25%-inhibition) to high salinity levels compared to methanogenesis (100%-inhibition considering the methane yield). The wide spectrum of SRB populations at different salinity levels, namely, the prevalence of Desulfovibrio sp. up to 35 g-NaCl L⁻¹ and the additional participation of the genera Desulfobacca, Desulfatirhabdium, and Desulfotomaculum at 50 g-NaCl⁻¹ explain such patterns. Conversely, the persistence of Methanosaeta genus was not sufficient to sustain methane production. Hence, exploiting SRB populations is imperative to anaerobically remediating saline wastewaters.
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In the field of wastewater treatment, nitrate nitrogen (NO3⁻-N) is one of the significant contaminants of concern. Sulfur autotrophic denitrification technology, which uses a variety of sulfur-based electron donors to reduce NO3⁻-N to nitrogen (N2) through sulfur autotrophic denitrification bacteria, has emerged as a novel nitrogen removal technology to replace heterotrophic denitrification in the field of wastewater treatment due to its low cost, environmental friendliness, and high nitrogen removal efficiency. This paper reviews the advance of reduced sulfur compounds (such as elemental sulfur, sulfide, and thiosulfate) and iron sulfides (such as ferrous sulfide, pyrrhotite, and pyrite) electron donors for treating NO3⁻-N in wastewater by sulfur autotrophic denitrification technology, including the dominant bacteria types and the sulfur autotrophic denitrification process based on various electron donors are introduced in detail, and their operating costs, nitrogen removal performance and impacts on the ecological environment are analyzed and compared. Moreover, the engineering applications of sulfur-based electron donor autotrophic denitrification technology were comprehensively summarized. According to the literature review, the focus of future industry research were discussed from several aspects as well, which would provide ideas for the application and optimization of the sulfur autotrophic denitrification process for deep and efficient removal of NO3⁻-N in wastewater. Graphical abstract
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The development of industrial parks has become an important global trend contributing significantly to economic and industrial growth. However, this growth comes at a cost, as the treatment of multisource industrial wastewater generated in these parks can be difficult owing to its complex composition. Microorganisms play a critical role in pollutant removal during industrial park wastewater treatment. Therefore, our study focused on the microbial communities in five full-scale industrial park wastewater treatment plants (WWTPs) with similar treatment processes and capacities. The results showed that denitrifying bacteria were dominant in almost every process section of all the plants, with heterotrophic denitrification being the main pathway. Moreover, autotrophic sulfur denitrification and methane oxidation denitrification may contribute to total nitrogen (TN) removal. In plants where the influent had low levels of COD and TN, dominant bacteria included oligotrophic microorganisms like Prosthecobacter (2.88 % ~ 10.02 %) and hgcI_clade (2.05 % ~ 9.49 %). Heavy metal metabolizing microorganisms, such as Norank_f__PHOS-HE36 (3.96 % ~ 5.36 %) and Sediminibacterium (1.86 % ~ 5.34 %), were prevalent in oxidation ditch and secondary settling tanks in certain plants. Functional Annotation of Prokaryotic Taxa (FAPROTAX) revealed that microbial communities in the regulation and hydrolysis tanks exhibited higher potential activity in the nitrogen (N) and sulfur (S) cycles than those in the oxidation ditch. Sulfate/sulfite reduction was common in most plants, whereas the potential occurrence of sulfide compounds and thiosulfate oxidation tended to be higher in plants with a relatively high sulfate concentration and low COD content in their influent. Our study provides a new understanding of the microbial community in full-scale industrial park WWTPs and highlights the critical role of microorganisms in the treatment of industrial wastewater.
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Elemental sulfur-driven autotrophic denitrification (SADN) is a cost-effective approach for treating secondary effluent from wastewater treatment plants (WWTPs). Additional organics are generally supplemented to promote total nitrogen (TN) removal, reduce nitrite accumulation and sulfate production, and balance the pH decrease induced by SADN. However, understanding of the impacts of organic supplementation on microbial communities, nitrogen metabolism, denitrifier activity, and SADN rates in sulfur-based denitrification reactors is still limited. Here, a sulfur-based denitrification reactor was continuously operated for 272 days during which six different C/N ratios were tested successively (2.7, 1.5, 0.7, 0.5, 0.25, and 0). Organic supplementation improved TN removal and decreased NO2- accumulation, but reduced the relative abundance of denitrifiers and the contribution of autotrophic nitrate-reducing bacteria (aNRB) to TN removal during the long-term operation of reactor. Predictive functional profiling showed that nitrogen metabolism potential increased with decreasing C/N ratios. SADN was the predominant removal process when the C/N ratio was ≤0.7 (achieving 60% contribution when C/N = 0.7). Although organic supplementation weakened the dominant role of aNRB in denitrification, batch tests for the first time demonstrated that it could accelerate the SADN rate, attributed to the improvement of sulfur bioavailability, likely via the formation of polysulfide. A possible nitrogen removal pathway with multiple electron donors (i.e., sulfur, organics, sulfide, and polysulfide) in a sulfur-based denitrification reactor with organic supplementation was therefore proposed. However, supplementation with a high level of organics could increase the operational cost and effluent concentrations of sulfide and organics as well as enrich heterotrophic denitrifiers. Moreover, microbial community had substantial changes at C/N ratios of >0.5. Accordingly, an optimal C/N ratio of 0.25-0.5 was suggested, which could simultaneously minimize the additional operating cost associated with organic supplementation and maximize TN removal and SADN rates.
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Sulfide-oxidizing autotrophic denitrification (SOAD) implemented in a moving-bed biofilm reactor (MBBR) is a promising alternative to conventional heterotrophic denitrification in mainstream biological nitrogen removal. The sulfide-oxidation intermediate - elemental sulfur - is crucial for the kinetic and microbial properties of the sulfur-oxidizing bacterial communities, but its role is yet to be studied in depth. Hence, to investigate the performance and microbial communities of the aforementioned new biosystem, we operated for a long term a laboratory-scale (700 d) SOAD MBBR to treat synthetic saline domestic sewage, with an increase of the surface loading rate from 8 to 50 mg N/(m2·h) achieved by shortening the hydraulic retention time from 12 h to 2 h. The specific reaction rates of the reactor were eventually increased up to 0.37 kg N/(m3·d) and 0.73 kg S/(m3·d) for nitrate reduction and sulfide oxidation with no significant sulfur elemental accumulation. Two sulfur-oxidizing bacterial (SOB) clades, Sox-independent SOB (SOBI) and Sox-dependent SOB (SOBII), were responsible for indirect two-step sulfur oxidation (S2-→S0→SO42-) and direct one-step sulfur oxidation (S2-→SO42-), respectively. The SOBII biomass-specific electron transfer capacity could be around 2.5 times greater than that of SOBI (38 mmol e-/(gSOBII·d) versus 15 mmol e-/(gSOBI·d)), possibly resulting in the selection of SOBII over SOBI under stress conditions (such as a shorter HRT). Further studies on the methods and mechanism of selecting of SOBII over SOBI in biofilm reactors are recommended. Overall, the findings shed light on the design and operation of MBBR-based SOAD processes for mainstream biological denitrification.
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We propose a sulfate reduction, denitrification/anammox and partial nitrification process to treat organic wastewater. Nitrogen removal in the anoxic reactor in this process was examined using an anaerobic-anoxic biofilter reactor. When nitrate medium was added to the anoxic reactor simulating the return flow from a nitrification reactor, mainly heterotrophic and sulfur denitrification occurred. However, anammox as well as denitrification occurred in the anoxic reactor when nitrite was fed into the reactor simulating partially nitrified water. The proportion of nitrite removal by the anammox reaction reached over 30%. By 16S rRNA gene sequencing analysis, the coexistence of heterotrophic and sulfur denitrification bacteria was confirmed in the anoxic reactor, although the heterotrophic denitrification and sulfur oxidation bacterial communities were different in each reactor. Candidatus Brocadia was detected in the nitrite-fed reactor, meaning that anammox bacteria coexist with denitrification bacteria even in high-sulfide conditions.
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This study aims to explore an alternative way to accelerate the start-up of sulfide-oxidizing autotrophic denitrification (SOAD) in moving-bed biofilm reactors (MBBRs). Two approaches were tested: i) cultivating sulfide-based autotrophic denitrifiers with sulfide and nitrate (MBBR1); and ii) cultivating facultative denitrifiers by switching the feed from organic carbon/nitrate to sulfide/nitrate (MBBR2). The mechanisms behind these two approaches are discussed. The results showed that both MBBRs could achieve stable nitrate removal (≥90%) after 20 days, while the SOAD microbial communities cultivated in MBBR2 performed better than those cultivated in MBBR1 in terms of the sulfur oxidation activity (0.47 ± 0.03 vs. 0.21 ± 0.07 kg SO4²⁻-Sgenerated/(m³·d)), biomass activity and immobilization (540 mg attached volatile solids (AVS)/L vs. 390 mg AVS/L, respectively). Moreover, the proportion of sulfur-oxidizing bacteria (SOB) enriched was higher in MBBR2 (35.0% Paracoccus) than in MBBR1 (9.7% Sulfurimonas and 5.2% Thauera), further legitimizing the hybridized approach for significant SOB enrichment. The findings of this study provide important clues for accelerating and optimizing the development of the MBBR-based SOAD bioprocess.
Article
The integrated sulfur- and Fe⁰-based autotrophic denitrification process in an anoxic fluidized-bed membrane bioreactor (AnFB-MBR) was developed for the nitrate-contaminated water treatment in order to control sulfate generation and avoid alkalinity supplement. The nitrate removal rate of the AnFB-MBR reached 1.22 g NO3⁻-N L⁻¹d⁻¹ with NO3⁻–N ranging 40–200 mg L⁻¹ at hydraulic retention times of 1.0–5.0 h. The denitrification in the integrated system was simultaneously carried out by sulfur- and Fe⁰-oxidizing autotrophic denitrifiers. The effluent sulfate generation was decreased by 29.3–70.3% and 31.2–50.9% due to the functional role of Fe⁰-based denitrification in the integrated system. Alkalinity produced by Fe⁰-oxidizing autotrophic denitrification could compensate for the alkalinity consumption by sulfur-based autotrophic denitrification. The sulfur- and Fe⁰-oxidizing autotrophic denitrifying bacterial consortium was composed mainly of bacteria from Thiobacillus, Sulfurimonas, and Geothrix genera. The integrated modes leads to a harmonious co-existence of sulfur- and Fe⁰-oxidizing denitrifying microbes, which may make a difference to the functional performance of the bioreactor. Overall, the integrated sulfur- and Fe⁰-based autotrophic denitrification could overcome the shortcomings of excess sulfate generation and external alkalinity supplementation compared to the sole sulfur-based autotrophic denitrification, indicating further potential for the technology in practice.
Article
Removal of H2S from gas streams using NO3--containing synthetic wastewater was investigated in an anoxic biotrickling filter (BTF) at feed N/S ratios of 1.2-1.7 mol mol-1 with an initial nominal empty bed residence time of 3.5 min and a hydraulic retention time of 115 min. During 108 days of operation under autotrophic conditions, the BTF showed a maximum elimination capacity (EC) of 19.2 g S m-3 h-1 and H2S removal efficiency (RE) above 99%. Excess biofilm growth reduced the HRT from 115 to 19 min and decreased the desulfurization efficiency of the BTF. When the BTF was operated under mixotrophic conditions by adding organic carbon (43.2 g acetate m-3 h-1) to the synthetic wastewater, the H2S EC decreased from 16.4 to 13.1 g S m-3 h-1, while the NO3- EC increased from 9.9 to 11.1 g NO3--N m-3 h-1, respectively. Thiobacillus sp. (98-100% similarity) was the only sulfur-oxidizing nitrate-reducing bacterium detected in the BTF biofilm, while the increased abundance of heterotrophic denitrifiers, i.e. Brevundimonas sp. and Rhodocyclales, increased the consumed N/S ratio during BTF operation. Residence time distribution tests showed that biomass accumulation during BTF operation reduced gas and liquid retention times by 17.1% and 83.5%, respectively
Article
The characteristics of reaction between S0 and NO2--N or NO3--N in the sulfur autotrophic denitrification (SADN) process were studied using S0 as an electron donor and NO2--N and NO3--N as electron acceptors. The effect of changes in pH and temperature on the processes of NO2--N and NO3--N reduction were also studied to identify the optimum control parameters for strengthening the preference of S0 on NO3--N; thus, achieving the efficient accumulation of NO2--N. The results showed that the affinity of S0 for NO3--N was considerably higher than that for NO2--N. The optimum pH values for the reductions of NO2--N and NO3--N were 7.0 and 8.5, respectively, and both optimum temperatures were 35 °C. By controlling different pH, the NO3--N conversion efficiency reached 90%, at which time the accumulation of NO2--N was more than 95%. Microbial community analysis showed that Thiobacillus, Sulfurimonas, and Thioahalobacter were the main genera in the S0-SADN process.
Article
Anoxic thiosulfate (S2O3²⁻) oxidation using autotrophic denitrification by a mixed culture of nitrate reducing, sulfur oxidizing bacteria (NR-SOB) was studied in a fluidized bed reactor (FBR). The long-term performance of the FBR was evaluated for 306 days at three nitrogen-to-sulfur (N/S) molar ratios (0.5, 0.3 and 0.1) and a hydraulic retention time (HRT) of 5 h. S2O3²⁻ removal efficiencies >99% were obtained at a N/S ratio of 0.5 and a S2O3²⁻ and nitrate (NO3⁻) loading rate of 820 (±84) mg S-S2O3²⁻ L⁻¹ d⁻¹ and 173 (±10) mg N-NO3⁻ L⁻¹ d⁻¹, respectively. The S2O3²⁻ removal efficiency decreased to 76% and 26% at N/S ratios of 0.3 and 0.1, respectively, and recovered to 80% within 3 days after increasing the N/S ratio from 0.1 back to 0.5. The highest observed half-saturation (Ks) and inhibition (KI) constants of the biofilm-grown NR-SOB obtained from batch cultivations were 172 and 800 mg S-S2O3²⁻ L⁻¹, respectively. Thiobacilus denitrificans was the dominant microorganism in the FBR. Artificial neural network modeling successfully predicted S2O3²⁻ and NO3⁻ removal efficiencies and SO4²⁻ production in the FBR. Additionally, results from the sensitivity analysis showed that the effluent pH was the most influential parameter affecting the S2O3²⁻ removal efficiency.
Article
Sulfur reduction is a promising alternative to sulfate reduction as it can generate sulfide at a low cost for the precipitation of heavy metals or autotrophic denitrification in wastewater treatment. However, the extremely low water solubility of elemental sulfur limits its bioavailability and results in a low sulfur-reduction rate. Polysulfide, which is naturally generated through reactions between sulfur and sulfide, can enhance the bioavailability of sulfur and thus contribute to high-rate sulfur reduction. Based on this principle, a laboratory-scale sulfur-reducing bioreactor was designed in this study for wastewater treatment. After 164 days of operation, the sulfide production rate (SPR) in the bioreactor reached 126 mg S/L-h, which is significantly higher than those of other sulfate-reducing systems. Moreover, dissolved zero-valent sulfur (referred to as polysulfide) was detected in the sulfur-reducing reactor when the organics were completely depleted, indicating that polysulfide can form naturally and be readily reduced to sulfide in the bioreactor. We found that the produced sulfide promoted the formation of more polysulfide, which enabled a self-accelerating chain reaction of sulfur reduction via polysulfide. This stimulation effect was further validated by the seven-hour batch tests. In the batch test without sulfide addition initially, a continuous increase in the hourly SPR was observed with increasing sulfide concentration. Furthermore, in the batch tests with the addition of 50 to 200 mg S/L sulfide at the beginning, the average SPR in the first three hours increased with elevating initial sulfide concentration due to more polysulfide formation and reduction. However, high sulfide concentration (> 250 mg S/L) hindered the continuous increase in SPR. Additionally, when polysulfide formation was prevented through the addition of Fe2+, the SPR dropped by 97.6% compared to that in the presence of polysulfide. This validates the key role of polysulfide in the high-rate sulfur reduction process. Overall, the findings suggest that high-rate sulfur reduction can be achieved for autotrophic denitrification or heavy-metal removal in wastewater treatment.
Article
A moving bed biofilm reactor (MBBR) was used with an immobilized Pseudomonas sp. SZF15 strain in a Yu long filter (a novel bioactive carrier), which has the ability to remove nitrate and Fe (II) simultaneously. Optimum operating conditions were achieved with a nitrate removal ratio of 95.62% and an Fe (II) oxidation ratio of 88.09%. Meanwhile, high-throughput sequencing results confirmed that the immobilized Pseudomonas sp. SZF15 was not lost during the operation. This study lays the foundation for practical application of future groundwater treatment biotechnologies.
Article
Chemolithotrophic denitrification is an inexpensive and advantageous process for nitrate removal and represents a promising alternative to classical denitrification with organics. Chemolithotrophic denitrifiers are microorganisms able to reduce nitrate and nitrite using inorganic compounds as source of energy. Ferrous iron, sulfur-reduced compounds (e.g. hydrogen sulfide, elemental sulfur and thiosulfate), hydrogen gas, pyrite and arsenite have been used as inorganic electron donors resulting in diverse outcomes. In the last 40 years, a large number of engineered systems have been used to maintain chemolithotrophic denitrification and improve rate and efficiency of the process. Among them, biofilm reactors proved to be robust and high-performing technologies. Packed bed reactors are particularly suitable for the removal of low nitrate concentrations, since high retention times are required to complete denitrification. Fluidized bed and membrane biofilm reactors result in the highest denitrification rates (>20 kg N-NO3−/m3 d) when hydrogen gas and sulfur reduced compounds are used as electron donors. Hydrogen gas pressure and current intensity rule the performance of membrane biofilm and biofilm electrode reactors, respectively. Biofouling is the most common and detrimental issue in biofilm reactors. Bed fluidization and hydrogen supply limitation are convenient and effective solutions to mitigate biofouling.
Article
In order to achieve the biological removal of nitrate of groundwater, the denitrification properties of an environmental strain of Thiobacillus denitrificans were studied at a pilot scale. This strain was previously described and showed good denitrification abilities at low temperatures. Its mean nitrate removal velocity was twice as great at 10°C, than at 20°C. A pilot plant in fixed bed conditions, filled with a pouzzolane / Neutralg® mixture was used for this purpose. The feed solution was tap water to which only nitrate and thiosulphate were added; the temperature was 10°C. An optimum volumetric nitrate loading rate of 1.5 kg N-NO3-. m-3 d-1 was determined for which 100 % denitrification yield was reached. The maximum volumetric nitrate loading rate of the plant was evaluated. The influence of the operating conditions such as residence time and nitrate concentrations were investigated as well as the efficiency of the plant by studying molar ratios between the removed and released products.
Article
Anoxic H2S oxidation under denitrifying conditions produced sulphur and sulphate in almost equal proportions by an isolated Thiobacillus denitrificans. Under nitrate reducing conditions the rate of sulphide oxidation was approximately 0.9g sulphide/g biomass h. Nitrate was reduced to nitrite and accumulated during sulphide oxidation. Above 100mg nitrite/l, the sulphide oxidation rate declined and at 500mg/l it was totally arrested. The optimum pH for the anoxic sulphide oxidation was around 7.5. Concentrations of sulphate 1500mg/l and acetate 400mg/l had no effect on anoxic sulphide oxidation.
Article
A strain of Thiobacillus denitrificans was isolated after enrichment under anaerobic conditions by the continuous culture technique using thiosulfate as energy source and nitrate as electron acceptor and nitrogen source. The isolate was an active denitrifyer, the optimal conditions being 30°C and pH 7.5–8.0. Denitrification was inhibited by sulfate (the reaction product) above 5 g SO 4=/l, whereas high concentrations of the substrates nitrate and thiosulfate were less harmful; nitrite affected denitrification above 0.2 g NO 2−/l. During the time course of denitrification in a batch culture growth and substrate consumption slowed down already after only half the substrate was utilized due to product inhibition. The following parameters were determined in continuous culture under nitrate limitation: μmax=0.11 h−1, K S=0.2 mg NO 3−/l, maximum denitrification rate=0.78 g NO 3−/g cells·h, YNO3=0.129Y_{{\text{NO}}_{\text{3}} } = {\text{0}}{\text{.129}}g cells/g NO 3−, YS2O3=0.085Y_{{\text{S}}_{\text{2}} {\text{O}}_{\text{3}} } = {\text{0}}{\text{.085}}g cells/g S2O 3=. Nitrite did not accumulate during steady state denitrification; the denitrification gas was almost pure N2. The concentrations of N2O and NO were below 1 ppm.
Article
Biooxidation of sulphide under denitrifying conditions is a key process in control of souring in oil reservoirs and in treatment of gas and liquids contaminated with sulphide and nitrate. In this work, biooxidation of sulphide was studied using a representative culture originated from an oil reservoir. Effects of sulphide concentration, sulphide to nitrate molar ratio, and loading rates of sulphide and nitrate on their removal rates and composition of the end products were investigated. In the batch system sulphide removal rate passed through a maximum as sulphide concentration was increased from 2.1 to 16.3 mM, with the highest rate (2.06 mM h−1) observed with 10.7 mM sulphide. Nitrate removal was coupled to sulphide oxidation and the highest removal rate was 1.05 mM h−1. In the continuous bioreactors fed with 10 and 5, 15 and 7.5, and 20 and 10 mM sulphide and nitrate, cell wash-out occurred as dilution rate was increased above 0.15, 0.13 and 0.08 h−1, respectively. Prior to cell wash-out linear increases in sulphide and nitrate removal rates were observed as loading rate was increased. The highest sulphide and nitrate removal rates of 2.0 and 0.92 mM h−1 were obtained in the bioreactor fed with 15 mM sulphide and 7.5 mM nitrate at loading rates of 2.1 and 0.93 mM h−1, respectively. Short residence times and high sulphide to nitrate ratios promoted the formation of sulphur, a desired end product for ex situ treatment of contaminated streams. Combination of long residence times and low sulphide to nitrate ratios, which favours formation of sulphate, is the suitable strategy for in situ removal of H2S from oil reservoirs.
Article
The denitrifying sulfide removal (DSR) process with bio-granules comprising both heterotrophic and autotrophic denitrifiers can simultaneously convert nitrate, sulfide and acetate into di-nitrogen gas, elementary sulfur and carbon dioxide, respectively, at high loading rates. This study determines the reaction rate of sulfide oxidized into sulfur, as well as the reduction of nitrate to nitrite, would be enhanced under a micro-aerobic condition. The presence of limited oxygen mitigated the inhibition effects of sulfide on denitrifier activities, and enhanced the performance of DSR granules. The advantages and disadvantages of applying the micro-aerobic condition to the DSR process are discussed.
Article
In this paper we describe an alternative flow-chart for full treatment of wastewaters rich in organic substrates, ammonia (or organic nitrogen), and sulfate, such as those generated in fish cannery industries. Biogas generated during anaerobic pretreatment of these wastewaters is rich in hydrogen sulfide that needs to be removed to enable application of the biogas. Nitrogen elimination is traditionally achieved by subsequent nitrification and denitrification of the effluent of the anaerobic reactor. Alternatively, the hydrogen sulfide in the biogas can be applied as an electron donor in an autotrophic post-denitrification step. In order to study whether sufficient hydrogen sulfide containing biogas for denitrification was produced in the anaerobic reactor, the biogas composition as a function of the anaerobic reactor-pH was estimated based on a typical wastewater composition and chemical equilibrium equations. It is demonstrated that typical sulfate and nitrogen concentrations in fish cannery wastewater are highly appropriate for application of autotrophic post-denitrification. A literature review furthermore suggested that the kinetic parameters for autotrophic denitrification by Thiobacillus denitrificans represent no bottleneck for its application. Initial experimental studies in fixed-film reactors were conducted with sodium sulfide and nitrate as an electron donor-acceptor couple. The results revealed that only moderate volumetric treatment capacities (< 1 g-NO3- N l(-1) day(-1)) could be achieved. Mass balances suggested that incomplete sulfide oxidation to elemental sulfur occurred, limiting biomass retention and the treatment capacity of the reactor. Future research should clarify the questions concerning product formation from sulfide oxidation.
Article
Biotechnology can be used to assess the well being of ecosystems, transform pollutants into benign substances, generate biodegradable materials from renewable sources, and develop environmentally safe manufacturing and disposal processes. Simultaneous elimination of sulfide and nitrite from synthetic wastewaters was investigated using a bioreactor. A laboratory scale anoxic sulfide-oxidizing (ASO) reactor was operated for 135 days to evaluate the potential for volumetric loading rates, effect of hydraulic retention time (HRT) and substrate concentration on the process performance. The maximal sulfide and nitrite removal rates were achieved to be 13.82 and 16.311 kg/(m3 day), respectively, at 0.10 day HRT. The process can endure high sulfide concentrations, as the sulfide removal percentage always remained higher than 88.97% with influent concentration up to 1920 mg/L. Incomplete sulfide oxidation took place due to lower consumed nitrite to sulfide ratios of 0.93. It also tolerated high nitrite concentration up to 2265.25mg/L. The potential achieved by decreasing HRT at fixed substrate concentration is higher than that by increasing substrate concentration at fixed HRT. The process can bear short HRT of 0.10 day but careful operation is needed. Nitrite conversion was more sensitive to HRT than sulfide conversion when HRT was decreased from 1.50 to 0.08 day. Stoichiometric analyses and results of batch experiments show that major part of sulfide (89-90%) was reduced by nitrite while some autooxidation (10-11%) was resulted from presence of small quantities of dissolved oxygen in the influent wastewater. There was ammonia amassing in considerably high amounts in the bioreactor when the influent nitrite concentration reached above 2265.25mg/L. High ammonia concentrations (200-550 mg/L) in the bioreactor contributed towards the overall inhibition of the process. Present biotechnology exhibits practical value with a high potential for simultaneous removal of nitrite and sulfide from concentrated wastewaters at shorter HRT.
Article
An autotrophic denitrification process using reduced sulfur compounds (thiosulfate and sulfide) as electron donor in an activated sludge system is proposed as an efficient and cost effective alternative to conventional heterotrophic denitrification for inorganic (or with low C/N ratio) wastewaters and for simultaneous removal of sulfide or thiosulfate and nitrate. A suspended culture of sulfur-utilizing denitrifying bacteria was fast and efficiently established by bio-augmentation of activated sludge with Thiobacillus denitrificans. The stoichiometry of the process and the key factors, i.e. N/S ratio, that enable combined sulfide and nitrogen removal, were determined. An optimum N/S ratio of 1 (100% nitrate removal without nitrite formation and low thiosulfate concentrations in the effluent) has been obtained during reactor operation with thiosulfate at a nitrate loading rate (NLR) of 17.18 mmol N L(-1) d(-1). Complete nitrate and sulfide removal was achieved during reactor operation with sulfide at a NLR of 7.96 mmol N L(-1) d(-1) and at N/S ratio between 0.8 and 0.9, with oxidation of sulfide to sulfate. Complete nitrate removal while working at nitrate limiting conditions could be achieved by sulfide oxidation with low amounts of oxygen present in the influent, which kept the sulfide concentration below inhibitory levels.
Article
Present investigation deals with the effect of sulfide to nitrate (S/N) molar ratio on the simultaneous anaerobic sulfide and nitrate removal on capacity, stability and selectivity of the process. The volumetric sulfide-sulfur and nitrate-nitrogen removal rates at molar S/N ratio of 5:2 were 4.86 kg(m(3)d)(-1) and 0.99 kg(m(3)d)(-1), respectively, which were higher than those at S/N molar ratios of 5:5 and 5:8. Moreover, the fluctuations in the effluent at S/N ratio of 5:2 were less than those at the other two tested ratios. During the operation, the ratio of converted sulfide to converted nitrate tended to approach 5:2. The selectivity for elemental sulfur and dinitrogen was improved when the S/N molar ratio was set at 5:2 rather than 5:5 or 5:8. The process became unstable if the influent sulfide surpassed its critical concentration. The electron balance between reactants was also analyzed for different S/N molar ratios.