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Process Control of Activated Sludge Plants by Microscopic Investigation
Abstract
Foreword 5 1.- Introduction 7 2.- Microscopy 9 2.1 Basic principles 9 2.2 Bright field and phase contrast 11 23 Preparing a slide 11 2.4 Adjusting and using a microscope 12 2.5 Measuring and counting 13 2.6 Staining techniques 13 2.6.1 Gram staining 14 2.6.2 Neisser staining 15 2.7 Sulphur storage test 18 2.8 Other microscopic techniques 19 3.- Microscopic investigation of activated sludge 23 3.1 Sampling and handling samples 23 3.2 Method for the analysis 23 3.3 The microscopic image 24 3.4 Choosing the correct objective 25 3.5 Recording the observations 25 4.- Characteristics of activated sludge flocs 29 4.1 Morphological characteristics 29 4.2 Composition of the floc 34 4.3 Free-living cells, spirochaetes and spirils 38 4.4 Floc types 39 5.- Filamentous micro-organisms 43 5.1 The filament index 43 5.2 Identifying filamentous micro-organisms 47 5.2.1 Identification characteristics 48 5.2.2 The concepts of `predominant' and `secondary' 53 5.2.3 Identification procedure 53 5.3 Description of the various filamentous species 58 5.3.1 Actinomycetes 58 5.3.2 Beggiatoa 59 5.3.3 `Cyanophyceae 60 5.3.4 Flexibacter 62 5.3.5 Haliscomenobacter hydr.ossis 62 5.3.6 Leucothrix 63 53.7 Microthrix parvicella 64 5.3.8 Nostocoida limicola I 66 5.3.9 Nostocoida limicola IIL 66 5.3.10 Fungi 67 5.3.11 Sphaerotilus natans 68 5.3.12 `Streptococcus 68 5.3.13 Thiothrix 69 5.3.14 Type 0041/0675 71 5.3.15 Type 0092 72 5.3.16 Type 0211 73 5.3.17 Type 021N 73 5.3.18 Type 0411 74 5.3.19 Type 0581 76 5.3.20 Type 0803 76 5.3.21 Type 0914 77 5.3.22 Type 0961 78 5.3.23 Type 1701 78 5.3.24 Type 1702 80 5.3.25 Type 1851 81 5.3.26 Type 1852 81 5.3.27 Type 1863 83 6.- Protozoa and metazoa 85 6.1 Protozoa 86 6.1.1 Ciliates 86 6.1.2 Flagellates 94 6.1.3 Amoeba, testate amoeba and heliozoa 97 6.2 Metazoa 99 6.2.1 Rotifers 99 6.2.2 Nematodes 100 6.2.3 Tardigrades 100 6.2.4 Worms 101 6.3.- Indicator function 101 7.- Conclusions of sludge investigation 103 8.- The activated sludge process 105 8.1.-Use and acceleration of natural cyclic .processes 105 8.2.- Formation of activated sludge flocs 106 8.3.- Factors that determine the composition of activated sludge flocs 107 8.3.1 Sludge load and sludge age 108 8.3.2 Composition of the waste water 109 8.3.3 Oxygen 112 8.3.4 Configuration 112 8.3.5 Temperature and pH 115 8.4 Uptake of nutrients by the floc 116 9.- Operationalproblems 119 9.1 High sludge load and/or lack of oxygen 120 9.2 Poisoning of the sludge 122 9.3 Many small flocs; deflocculation 122 9.4 Heavy sludge 123 9.5 The final clarifier does not function well 123 9.6 Treatment performance inadequate; but effluent is clear 124 9.7 Decline in sludge production 124 10.- Bulking sludge 127 10.1 Filament index and sludge volume index 128 10.2 Growth of filamentous micro-organisms 130 10.3 Process conditions and population composition 131 10.3.1 Sludge load > 0.2 kg BOD/kg MLSS.day and domestic influent 132 10.3.2 Characteristic of low sludge loading levels. 132 10.3.3 The effect of biological nutrient removal 135 10.3.4 The competition between filamentous organisms 136 10.4.-Controlling bulking sludge 136 10.4.1 Selection of floc forming bacteria by the application of a high floc load 138 10.4.2 Designing an aerobic selector 140 10.4.3 Combination with nutrient removal 141 10.5.- Zoogloea bulking sludge 143 11.- Scum formation 145 11. l Scum formation in which filamentous species play no decisive role 145 11.2 Stabilized gas bubbles 147 11.3 Effect of the size and composition of the filamentous population on scum formation 149 11.4.- Controlling 152 12.- Closing remarks 153 13.- Literature 155 Appendix 1 CD architecture Appendix 2 Form for recording the characteristics of filamentous micro-organisms Appendix 3 Analysis form
... For instance, a turbid effluent can be caused not only by poor settlement of flocs in the final clarifier owing to a massive growth of filamentous microorganisms, but also by flocs that are too small, the absence of protozoa, or dispersed bacterial growth. Correlations have been identified between AS characteristics and operational conditions, such as carbon-to-nitrogen ratio, biochemical-to-chemical oxygen demand ratio, hydraulic and sludge-loading rates, recirculation ratio, aeration equipment, substrate-uptake rate, oxygen-uptake rate, toxic compound inhibition, and treatment efficiency (Eikelboom, 2000). Operational faults are often caused by incorrect biomass composition (Johnston et al., 2019). ...
... A frequency of at least once per week is necessary to identify and monitor changes in the composition of the sludge if the sludge age is short (days). In WWTPs with much longer sludge ages (weeks), a frequency of once every month is considered sufficient (Eikelboom, 2000;Mesquita et al., 2013). Microscopic image investigation of the AS biological process requires well-equipped specialized laboratories and expert wastewater microbiologists and biochemists to analyze the sewage condition. ...
... A total of 1448 sludge images were acquired. Spherical flocs, open flocs, protozoa, and filaments were chosen as the indicative classes for AS analysis because they provide key information on the state of the system, and due to database size limitations (Eikelboom, 2000) (Table 1). ...
... Microscopic analyses were performed to assess the sludge biotic index (SBI; Table 4) [11,23] and flocks' morphology [24]. For SBI, sludge was analyzed under the microscope at 200and 400-times magnification, in five replications. ...
... When calculating the SBI of the sludge, individual species of ciliates are taken as individual taxa, but flagellates, rotifers, nematodes, tardigrades, gastropods, and oligochaetes are taken without distinguishing into species [11]. Flocks were assessed based on their morphology with a focus on shape, structure, strength, and size [22,23]. Microscopic analyses were performed on an optical system for image analysis, which includes the optical microscope OPTA-TECH with the camera OPTA-TECH and the OptaView software. ...
... The optimal values were exceeded in three out of eleven analyzed samples. Flocks of activated sludge are characterized by shape, structure, strength, and size [23]. The shape of the flock can vary from more or less round to irregular. ...
Container on-site wastewater treatment plants are systems of growing interest in the areas where sewer systems cannot be implemented. In this study, container on-site wastewater treatment plant with low-loaded activated sludge has been examined. The aim of the study was: (i) to assess the efficiency of the plant; and (ii) to evaluate the relationship between the condition of activated sludge and selected parameters of effluent quality. Effluent quality has been characterized by the reliability factor (RF) and technological purity index (TPI). Sludge quality assessment covered measurements of volume (Vo), dry matter (DM), sludge index (SI), and the unit oxygen consumption rate (UOCR). Microscopic analysis has been performed to assess the morphological (flocks) and biotic quality (sludge biotic index, SBI) of activated sludge. The research has been completed by an on-site measurement of dissolved oxygen concentration in an activated sludge chamber with 30 sec. intervals. Results confirmed a significant (p < 0.05) correlation (CC = −0.9277) between biochemical oxygen demand (BOD5) and SBI for the oxygen level in the aeration chamber between 1–2 mg/L. Negative significant correlation (p < 0.05) has also been found between SBI and electrical conductivity (EC) (CC = −0.7478). In the examined case, the optimal EC of the effluent was in the range of 600–800 µS/cm.
... According to some research works [25,26], a high Food/Microorganisms (F/M) ratio or Organic Loading Rate (OLR) induced the generation of SMP and more bound extracellular polymeric substances (EPS), resulting in a decrease of sludge filterability and lower filtration index. On the other hand, low Dissolved Oxygen (DO) increased filaments concentration and especially Type 0041 and M. parvicella [27,28]. Regarding the favorable DO concentration, it has been reported that the limitation or deficiency of DO was often responsible for the proliferation of filamentous bacteria in activated sludge processes [29,30]. ...
... Filamentous Index (FI) was used, according to the Eikelboom method [27,28], to measure the population of filamentous microorganisms in the activated sludge mixed liquor of the MBR units. For the FI measurement, a Light Sheet Microscope (LSM, Observer Z1, Zeiss) was used mainly in 100× magnification, whereas in some cases 50× and 200× magnifications were, also, used to take a better view of the samples. ...
... Going back to the operating conditions, low DO concentrations or DO deficiency increase filamentous population in wastewater treatment processes [27][28][29][30]. In this study, the decrease of DO concentration at 1.2 ± 0.5 mg/L during Stage 2, verified the literature and led to a sharp increase of the filamentous population to FI = 5. ...
A promising solution for membrane fouling reduction in membrane bioreactors (MBRs) could be the adjustment of operating parameters of the MBR, such as hydraulic retention time (HRT), food/microorganisms (F/M) loading and dissolved oxygen (DO) concentration, aiming to modify the sludge morphology to the direction of improvement of the membrane filtration. In this work, these parameters were investigated in a step-aerating pilot MBR that treated municipal wastewater, in order to control the filamentous population. When F/M loading in the first aeration tank (AT1) was ≤0.65 ± 0.2 g COD/g MLSS/d at 20 ± 3 °C, DO = 2.5 ± 0.1 mg/L and HRT = 1.6 h, the filamentous bacteria were controlled effectively at a moderate filament index of 1.5–3. The moderate population of filamentous bacteria improved the membrane performance, leading to low transmembrane pressure (TMP) at values ≤2 kPa for a great period, while at the control MBR the TMP gradually increased reaching 14 kPa. Soluble microbial products (SMP), were also maintained at low concentrations, contributing additionally to the reduction of ΤΜP. Finally, the step-aerating MBR process and the selected imposed operating conditions of HRT, F/M and DO improved the MBR performance in terms of fouling control, facilitating its future wider application.
... Static light scattering (Mastersizer, Malvern, UK) was used to determine the size distribution of aggregates with a diameter larger than 10 µm. Activated sludge and effluent were also observed under a Light Sheet Microscope (LSM, Observer Z1, Zeiss, Oberkochen, Germany) and filamentous index (FI) evaluation was also performed [30,31] in order to measure the population of filamentous microorganisms in the activated sludge mixed liquor. The microscope images were edited using ZEN software version 3.6 (ZEISS Group, Singapore). ...
... The filamentous index (FI) for the activated sludge, according to Figure 13a, ranged 1-2 during the entire operation of all three MBBR-MBR units [30]. On the optical microscope image in Figure 13b, it is shown that quite large aggregates and filamentous microorganisms exit into the filtrate. ...
Moving bed biofilm reactor combined with membrane bioreactor (MBBR-MBR) constitute a highly effective wastewater treatment technology. The aim of this research work was to study the effect of commercial K1 biocarriers (MBBR-MBR K1 unit) and 3D-printed biocarriers fabricated from 13X and Halloysite (MBBR-MBR 13X-H unit), on the efficiency and the fouling rate of an MBBR-MBR unit during wastewater treatment. Various physicochemical parameters and trans-membrane pressure were measured. It was observed that in the MBBR-MBR K1 unit, membrane filtration improved reaching total membrane fouling at 43d, while in the MBBR-MBR 13X-H and in the control MBBR-MBR total fouling took place at about 32d. This is attributed to the large production of soluble microbial products (SMP) in the MBBR-MBR 13X-H, which resulted from a large amount of biofilm created in the 13X-H biocarriers. An optimal biodegradation of the organic load was concluded, and nitrification and denitrification processes were improved at the MBBR-MBR K1 and MBBR-MBR 13X-H units. The dry mass produced on the 13X-H biocarriers ranged at 4980–5711 mg, three orders of magnitude larger than that produced on the K1, which ranged at 2.9–4.6 mg. Finally, it was observed that mostly extracellular polymeric substances were produced in the biofilm of K1 biocarriers while in 13X-H mostly SMP.
... Static light scattering (Mastersizer, Malvern) was used to determine the size distribution of aggregates with a diameter larger than 10 μm in mixed liquor. Activated sludge was also viewed under a Light Sheet Microscope (LSM, Observer Z1, Zeiss, Oberkochen, Germany) and filamentous index (FI) evaluation was also performed [30,31], during which the population of filamentous microorganisms in the activated sludge mixed liquor was measured. The microscope images were edited using ZEN software. ...
... As observed in the standard image of mixed liquor taken from an optical microscope ( Figure 11), there are filamentous microorganisms protruding from the outer surfaces of the sludge flocculates, with the FI values ranging from 1-2 throughout the operation of the units for all three MBBRs [30]. ...
In the present work, a comparative evaluation of an MBBR unit performance was carried out for the following cases: when adding 3D-printed biocarriers fabricated with 13X and bentonite, when using K1 commercial biocarriers and when not adding biocarriers at all. For the evaluation of the MBBR efficiency, various physicochemical parameters were measured, while static light scattering and optical microscopy observations were additionally used. Finally, biofilm extracted from the biocarriers was evaluated. The findings suggest that there is an optimal biodegradation of the organic load in all MBBR units. The nitrification and denitrification process were improved at the 3D MBBR as compared to the control MBBR and MBBR K1. The dry mass of the biofilm in the 3D-printed biocarriers was two orders of magnitude larger than the one in the K1 biocarriers. What is more, in the K1 biocarriers the mass of the biofilm varied in relation to time, due to the fact that it could not be kept inside the holes, something that was not observed to happen with the 3D-printed biocarriers. Finally, it was observed, mostly in the 3D MBBR and less in the K1 MBBR, that the growth of nitrifying bacteria and heterotrophs inside the units increased the biomass production in the form of SMP, which in turn favored the adhesion of biomass on the surface of biocarriers.
... Static light scattering (Mastersizer, Malvern Panalytical Ltd., Malvern, UK) was used to determine the size distribution of aggregates with a diameter larger than 10 µm in mixed liquor. Activated sludge was also viewed under a light sheet microscope (LSM, Observer Z1, Zeiss, Oberkochen, Germany) and filamentous index (FI) evaluation was also performed [32,33], during which the population of filamentous microorganisms in the activated sludge mixed liquor was measured. The microscope images were edited using ZEN software, v3.6. ...
... As observed in the standard image of mixed liquor taken with an optical microscope (Figure 8), there are filamentous microorganisms protruding from the outer surfaces of the sludge flocculates, with the FI values ranging from 1-2 throughout the operation of the units for all three MBBRs [32]. ...
The current study investigated the performance of a moving bed biofilm reactor (MBBR), when adding 3D-printed biocarriers fabricated with 13X and bentonite (MBBR 3D), when using K1 commercial biocarriers (MBBR K1) and when not adding biocarriers at all (control MBBR). For the evaluation of the MBBR efficiency, various physicochemical parameters were measured, while biofilm extracted from the biocarriers was evaluated. The findings suggest that there is an optimal biodegradation of the organic load in all MBBR units. The nitrification and denitrification processes were improved in MBBR 3D as compared to the control MBBR and MBBR K1. The dry mass of the biofilm in the 3D-printed biocarriers was two orders of magnitude larger than in the K1 biocarriers. Moreover, in the K1 biocarriers the mass of the biofilm varied in relation to time, since it could not be protected inside the holes, something that did not happen with the 3D-printed biocarriers. Finally, it was found, mostly in MBBR 3D and less in MBBR K1, that the growth of nitrifying bacteria and heterotrophs inside the units increased the biomass production in the form of soluble microbial products, which in turn favored the adhesion of biomass on the surface of biocarriers.
... Static light scattering (Mastersizer, Malvern) was used to determine the size distribution of aggregates with a diameter larger than 10 μm. Activated sludge and effluent were also observed under a Light Sheet Microscope (LSM, Observer Z1, Zeiss, Oberkochen, Germany) and filamentous index (FI) evaluation was also performed [29,30], in order to measure the population of filamentous microorganisms in the activated sludge mixed liquor. The microscope images were edited using ZEN software. ...
... 16 of 21 Filamentous microorganisms protruding from the sludge flocs are observed in the mixed liquor photograph drawn by an optical microscope (Figure 10 (a)). This shows that the filamentous index (FI) for the specific sludge ranges from 1-2 during the entire operation of all three MBBR-MBR units [29]. On the optical microscope image in Figure 10 (b) it is shown that quite large aggregates and filamentous microorganisms exit into the filtrate. ...
For this research, a comparative evaluation was performed in which the addition of 3D-printed biocarriers fabricated with 13X and Halloysite (13Χ-Η) and commercial Kaldnes K1 biocarriers were evaluated as opposed to the non addition of biocarriers in a semi-pilot scale MBBR-MBR unit. For the evaluation of the MBBR-MBR efficiency, various physicochemical parameters were measured while static light scattering and optical microscopy observations were additionally used. Biofilm extracted from the biocarriers was also evaluated. It was observed that in the MBBR-MBR K1 unit, the membrane filtration improved while in the MBBR-MBR 13X-H unit the membrane fouling rate was the same as in the control MBBR-MBR unit. This is due to the production of large amount of SMP which resulted from the large amount of biofilm created in the 13X-H biocarriers. An optimal biodegradation of the organic load was concluded for all three MBBR-MBR units. The nitrification and denitrification processes were improved at the MBBR-MBR units using 13X-H and K1. The dry mass produced on the 13X-H biocarriers was three orders of magnitude larger than that produced on the K1. Finally, it was observed that mostly EPS was produced in the biofilm of K1 biocarriers while in the biofilm of 13X-H mostly SMP.
... 8 La base para el estudio de las bacterias filamentosas causantes del bulking fue propuesta por Eikelboom y Van Buijsen, 1985, en la publicación "Microscopic sludge investigation manual", 9 donde se documentan las técnicas y procedimientos claves para el estudio de bacterias filamentosas en los lodos activados y los morfotipos filamentosos, algunos denominados alfanuméricamente debido a la dificultad para aislarlos e identificarlos; no obstante gracias a los avances en la biología molecular, actualmente ha sido posible determinar el género, e incluso, la especie de varios morfotipos presentados por estos autores. 10 Los microorganismos filamentosos comúnmente asociados a la aparición de bulking en las PTAR son: Beggiatoa spp., Nocardia spp., Microthrix parvicella, Nostocoida limicola I, II y III, Sphaerotilus natans, Thiothrix I y II, Tipo 021N, Tipo 0041, Tipo 1863, Tipo 0211, Tipo 1851, Haliscomenobacter hydrossis. 7,11,12 No obstante, el conocimiento cinético y fisiológico de las bacterias filamentosas no es profundo debido a las limitaciones técnicas existentes para aislarlas, haciendo que la descripción de su crecimiento sea esencialmente mecanicista 8 y el control del fenómeno de bulking sea parcial y a corto plazo. ...
... Valores de IVL superiores a 150 mL/g e IF mayor a 3 están asociados con la aparición del bulking. 10 Las técnicas de microscopía implementadas para el estudio de las bacterias filamentosas en los lodos activados son las más frecuentes debido a su fácil ejecución y bajo costo, entre ellas se destacan el conteo de filamentos en fresco, la observación de muestras coloreadas con tinción de Gram, Neisser y Sudán; no obstante existen técnicas moleculares que permiten cuantificar y medir los filamentos de forma más exacta como el método de hibridación fluorescente in situ (FISH), 15 el cual genera mayor confianza frente a la subjetividad de las técnicas microscópicas. Otra técnica útil para el estudio de las bacterias filamentosas es la electroforesis en gel por gradiente de degradación (DGGE), la cual permite conocer la diversidad de bacterias en una muestra de lodo, pero su limitación está en la discriminación de filamentos importantes debido a la baja abundancia relativa de los mismos. ...
Introducción Las plantas de tratamiento de aguas residuales (PTAR), que implementan el proceso de lodos activados presentan problemas de bulking filamentoso. Se ha encontrado que los morfotipos más comunes ligados al fenómeno son: Microthrix parvicella, Thiothrix spp., Nostocoida limicola, Sphaerotilus natans, Tipo 0041 y Haliscomenobacter hydrossis. La asociación de los parámetros fisicoquímicos en el sistema con la aparición del bulking es di vergente en todos los estudios. Objetivo Describir los parámetros físicoquímicos que condicionan la proliferación de morfotipos bacterianos en el fenómeno de bulking filamentoso, mediante el análisis comparativo de diversos estudios a nivel mundial. Materiales y Métodos Se hizo una revisión sistemática a partir de artículos de investigación publicados en los últimos 18 años, en las bases de datos Science Direct, Scielo, Web of Knowledge, EBSCO, Wiley, y Springer Link. Resultados Se seleccionaron 15 artículos, éstos se organizaron según el tamaño de planta. Se encontró que los parámetros con mayor incidencia en la proliferación de las bacterias filamentosas son: la baja concentración de OD, la baja relación F/M, baja temperatura y el tipo de agua a tratar. Los parámetros indicadores de la presencia de bulking en la mayoría de estudios son el IVL, el IF y los morfotipos filamentosos. Conclusión No hay consenso en los valores de los parámetros fisicoquímicos de las PTAR asociados a la proliferación de bacterias filamentosas. Sin embargo, su proliferación puede depender de muchos factores como la entrada masiva desustrato fácilmente asimilable, las bajas temperaturas y disponibilidad de oxígeno disuelto por unidad de carga orgánica.
... However, the dynamics of filamentous bacteria were not clear before and after sludge micropowder addition, although it was found that Type 021N took the main responsibility for AGS break-up using filamentous morphology [27,28]. At present, more than 30 different filamentous bacterial strains have been identified [13,29]. As we know, Thiothrix eikelboomii and defluvii species as the gamma-subclass of Proteobacteria belong to Type 021N [13], while Acinetobacter, Anaerolinea, Flavobacterium, Sphaerotilus, and Singulisphaera also contribute to the filamentous groups [9]. ...
... It was reported that the wastewater characteristics (excess nutrient/substrate in feed, feed rate, and C/N ratio) played a key role in the overgrowth of filamentous strains [8,9,12,13,29]. The remarkable feature of high-ammonia nitrogen wastewater was a low C/N ratio. Ammonia removal technologies/processes mainly include microalgae-bacteria, activated sludge, integrated fixed-film activated sludge, moving-bed membrane bio-reactors, adsorption, and membrane separation [30]. ...
This work investigated the roles of sludge micropowder addition in microbial structure and partial nitrification and denitrification (PND) in an extended filamentous aerobic granular sludge-sequencing batch reactor (AGS-SBR) using high-ammonia wastewater. Type 1683 Acinetobacter with a high percentage became the dominant extended filaments, remarkably shifted and remained at a low level, acting as a framework for AGS recovery after micropowder addition. The sludge volume index (SVI5) decreased from 114 to 41.7 mL/g, mixed liquid suspended solids (MLSS) and extracellular polymers (EPS) both increased and balanced at 6836 mg/L and 113.4 mg/g•MLVSS, respectively. COD and NH4+-N were degraded to certain degrees in the end. However, the effluent NO2−-N accumulated to the peak value of 97.6 mg/L on day 100 (aeration stage), then decreased and remained at 45.3 mg/L with development of the stirring and micropowder supplemented in the SBR on day 160 (anoxic stage), while the influent NO2−-N always remained at zero. Interestingly, the influent/effluent NO3−-N both remained at zero throughout the whole experiment. These results demonstrated that PND was successfully obtained in this work. Sludge micropowder addition not only restrained the extended filaments’ overgrowth, but also contributed to PND realization with carbon released. Citrobacter and Thauera played an essential role in the PND process for high-ammonia wastewater treatment. Running condition, wastewater characteristic, and sludge structure played an important role in microbial composition.
... On the other hand, a filamentous bacteria shortage may lead to hardly settleable pinpoint flocs (Eikelboom, 2000;Jenkins et al., 2003). ...
... Filamentous bacteria may be responsible, or take part, in quite different consequences in AS, ranging from filamentous bulking to foaming, among others. Classical methods for the identification of filamentous bacteria have relied on their morphology (Eikelboom, 2000;Jenkins et al., 2003), despite the uncertainty derived from the resemblance between some organisms. As a result, novel identification strategies have been developed relying primarily in the use of immunological or molecular biology techniques combined with the use of fluorescent dyes. ...
... Following proper sample handling and staining methods (Jenkins et al., 2003), observations were made using light microscopy under direct illumination (Zeiss Axioplan EL-Einsatz, White plains, NY, USA). General floc properties (e.g., size, shape, and structure) and filament index were recorded following the protocols by Eikelboom, 2000. The circumscribing diameter was used to define the floc size (Jarvis et al., 2005), and the measurement was performed in Carl Zeiss AxioVision Rel. ...
... For example, the Nostocoida filament type, which may translate to Trichococcus in this study (Nielsen et al., 2009), favors moderate to long SRTs; therefore, if excessive growth occurred, one approaching for controlling its growth is to reduce the SRT (Grady et al. 2011). However, unlike conventional AS processes where bulking and foaming are major operational problems (Eikelboom, 2000, Jenkins et al., 2003, Nittami and Batinovic, 2022, the anoxic suspended growth may face the issue of insufficient filaments and thereby easily sheared flocs. One standard approach applied in BNR systems when insufficient filaments are present is to provide a modest level of aeration in the anoxic zone to encourage the controlled growth of a modest fraction of low-DO filaments (Jenkins et al., 2003). ...
A fully anoxic suspended growth process is an appealing alternative to conventional activated sludge (AS) due to considerable aeration reduction and improved carbon processing efficiency for biological nutrient removal (BNR). With development of the hybrid membrane aerated biofilm reactor (MABR) technology, implementation of a fully anoxic suspended growth community in BNR facilities became practical. To better understand potential limitations with the elimination of aeration, we carried out microscopic examination and 16S rRNA gene‐based microbial community profiling to determine how an anoxic suspended growth would differ from the conventional aerobic process in floc characteristics, microbial diversity, microbial temporal dynamics, and community assembly pattern. Fewer filamentous populations were found in the anoxic mixed liquor, suggesting easily sheared flocs. The anoxic microbial community had distinct composition and structure, but its diversity and temporal dynamics were similar to the conventional aerobic community. A variety of well‐studied functional guilds were also identified in the anoxic community. The anoxic microbial community assembly was more stochastic than the conventional aerobic community, but deterministic assembly was still significant with a large core microbiome adapted to the anoxic condition.
Practitioner Points
Flocs developed under the anoxic conditions had less filamentous backbones, implying reduced flocculation capacity and easily sheared flocs.
Knowledge about the ecophysiology of Thauera, Thiothrix, and Trichococcus can help achieve good properties of the anoxic flocs.
A diverse microbial community sustainably adapted to the fully anoxic condition, containing a variety of filaments, denitrifiers, and PAOs.
The anoxic microbial community displayed a similar degree of diversity and temporal dynamics compared to the aerobic counterpart.
The anoxic community's assembly was more stochastic, so it may be less subject to changes in environmental variables.
... Biological approach can be implemented by manipulating the natural predators of the BFBs which are rotifers (Drzewicki et al., 2007;Eikelboom, 2000;Fiałkowska and Pajdak-Stós, 2008;Jenkins et al., 2003), ciliates (Fyda et al., 2015), and amoebae (Fiałkowska and Pajdak-Stós, 2008). Rotifers are reported to appear in systems with low organic loads and/or higher sludge age (Drzewicki et al., 2007;Eikelboom, 2000;Jenkins et al., 2003). ...
... Biological approach can be implemented by manipulating the natural predators of the BFBs which are rotifers (Drzewicki et al., 2007;Eikelboom, 2000;Fiałkowska and Pajdak-Stós, 2008;Jenkins et al., 2003), ciliates (Fyda et al., 2015), and amoebae (Fiałkowska and Pajdak-Stós, 2008). Rotifers are reported to appear in systems with low organic loads and/or higher sludge age (Drzewicki et al., 2007;Eikelboom, 2000;Jenkins et al., 2003). The characteristics of rotifers are very similar to those of ciliates as both of them are sensitive to toxins present in the system (Jenkins et al., 2003). ...
The formation of bulking and foaming in biological wastewater treatment could cause a series of operational issues with biomass and effluent quality, ultimately affect the treatment performance of the system. The essential parameters influencing the growth of bulking and foaming bacteria are comprehensively summarised in this paper. Existing bulking and foaming control approached are critically reviewed and addressed, as well as their drawbacks and limitations. Despite the abundance of information and implementation, a complete control technique for limiting filamentous sludge bulking and foaming remains insufficient. Magnetic field application is emphasised as a viable control strategy in this regard. The present review study provides new insight of this application by comparing the use of magnetic fields to conventional treatments. Future outlooks on the use of magnetic fields to prevent BFB proliferation were also highlighted.
... Summing up, a well-working activated sludge should be dominated by crawling and stalked ciliates remaining in balance with each other. In addition, a moderate number of metazoa and shell amoebas is also desirable [22,23,24,25,26,27]. ...
... The quantitative analysis was performed by placing a defined volume of activated sludge (50-100 µL) under the microscope and counting the microorganisms. Determination of quantitative indexes for individual groups of microorganisms was performed on the basis of the generally accepted recommendations of Madoni, Eikelboom and other commonly accepted solutions [26,27,28]. The index of filamentous organisms was established by comparing the microscopic image with reference images, in accordance with commonly accepted methods [26]. ...
The operating parameters of membrane biological reactors (MBRs) differ significantly from those of conventional activated sludge (CAS) reactors, especially with regard to solids retention time (SRT) and food-to-mass ratio (F/M). This has an impact on the structure of the activated sludge biocenosis and its susceptibility to seasonal variations. The aim of this research was to find out the structure and variability of the activated sludge biocenosis in a small wastewater treatment plant using MBR reactors situated in southern Poland. The results were compared with the results obtained from a CAS wastewater treatment plant with a similar capacity and showed that the sludge biocenosis in MBRs differs significantly from that in CAS reactors. There was a noticeable difference in the ratio of attached to crawling ciliates in the sludge from MBRs and CAS, and it was also shown that the MBR biocenosis, despite the long SRT, undergoes stronger seasonal changes during the year, with a clear deterioration of the biocenosis structure in the autumn and winter period and a visible improvement in the spring. Despite this, no noticeable impact of changes in the MBR biocenosis structure was found with regards to the technological efficiency of the wastewater treatment process.
... It is known that human eye cannot see objects that have diameters smaller than 0.1 mm, since bacteria have a diameter of 0.001 mm, that on its own has increased the use of microscopic investigations in the wastewater treatment plants to assess the quality of activated sludge (Eikelboom, 2000). The microscopic images provided data that helped in understanding the properties of activated sludge and the number of microorganisms found in the waste water treatment plant. ...
... Schematic diagram showing the procedure on how to view microscopic slides. This was the manner in which the slide was systematically views(Eikelboom, 2000) ...
The overall aim of this study was to investigate the activated sludge by using sludge activity (TTC) screening and microscopic method in determining the differences in the activated sludge of the three different wastewater treatment plants located in Hungary. The study presented the use of two methods to determine the state of activated sludge in the wastewater samples. The first method was to use the Sludge activity (TTC) Screening method I to determine the sludge activity respiration or the activity of the hydrogenase in the activated sludge. Since the investigation was conducted in three wastewater treatment plants, the Sludge activity (TTC) Screening method evaluated different setbacks and advantages that were incurred in the wastewater treatment plants. This method encouraged the use of biological treatment of wastewater since it is the currently most used method in wastewater treatment systems worldwide. The biological wastewater treatment limited the naturally occurring bacteria in a very high concentration in the treatment works. Henceforth the need to understand the composition of activated sludge in the wastewater works remained vital and significant. The results depicted that out of the five samples taken from these three wastewater treatment plants, only two (sample number 7328 and 7332) were above the minimum acceptable sludge activity measurement range. At the same time, the chemical examinations have also shown that the highest enzyme activity system had the lowest cleaning efficiency. However, chemical tests have shown that the highest enzyme activity system has the lowest cleaning efficiency. On the basis of microscopic examination of the activated sludge, Nocardia bacterial species were present in this system in large numbers, which shows the appearance of unfavorable circumstances. This indicated the importance of using all the types of examination methods together to determine how a wastewater treatment systems works.
... High-performance liquid chromatography (HPLC) equipped with a dual pump with micro-vacuum degasser and UV detector (UV) (Prostar 210, Varian, USA) was used to measure CPS concentration at 230 nm wavelength using analytical column (Agilent 5 TC-C18, particle size 5 μm, 250 × 4.5 mm) following the procedure suggested by Liu et al. (2016). A previous study by Kumar et al., 2023a presented methodology for the estimation of interface settling velocity (ISV) (Metcalf and Eddy, 2003), aerobic sludge biomass activity (ASBA) (Negi et al., 2020(Negi et al., , 2022, sludge volume index (SVI) (APHA et al., 2005), filamentous index (FI) (Eikelboom, 2000), microscopic observation, photographic evidence, cell viability test (Jones and Senft, 1985), extracellular polymeric substance (EPS) (Tomar and Chakraborty, 2018), polysaccharides (PS) (Frølund et al., 1996), Protein (PN) (Lowry et al., 1951), enzymatic activities (catalase, dehydrogenase, protease, and urease) (Lv et al., 2008;Yao et al., 2010) and amplified ribosomal DNA restriction analysis (ARDRA) (Gich et al., 2000;Meng et al., 2015). ...
Non-agricultural sources of pesticides in urban areas are responsible for their presence in domestic wastewater. Therefore, pesticides are typically found in sewage treatment plants in developed and developing countries as micro-pollutant. The presence of pesticides in the wastewater can impart stress on the aerobic sludge biomass and disrupt the functioning of the plant. However, there exists a knowledge gap regarding the resilience of aerobic sludge biomass towards stress due to the presence of pesticides in the wastewater. This study investigated the impact of chlorpyrifos (CPS) – a widely used pesticide, on sludge biomass and explored its recovery capability when CPS is discontinued in the influent. Four duplicate reactors were operated with different CPS concentrations ranging from 50 – 200 mg/L. Chemical oxygen demand (COD) removal for reactors has ranged within 18-73% at the steady state of the stressed phase, whereas COD removal for the control reactor was 91%. CPS stress slightly inhibited filamentous biomass growth. Biomass activity and cell viability have decreased significantly, whereas biochemical contents have varied slightly under CPS stress. The activities of the enzymes dehydrogenase and urease were significantly inhibited when compared to catalase and protease. Amplified ribosomal DNA restriction analysis reflected changes in the microbial community. The discontinuation of CPS has allowed aerobic sludge biomass to recover in its organic degradation capability (COD removal of more than 88% at steady-state conditions of recovery phase operation), biomass growth, and cell viability. In addition, enzyme activities have retrieved to their original levels, and 78-93% similarity of microbial community structure has been displayed between CPS-exposed and control reactor biomasses. Overall, the present study has indicated the orderly changes in the quality of aerobic sludge biomass under CPS stress through physico-chemical and biological characteristics. The study also has highlighted the self-recovery of sludge biomass characteristics stressed with different concentrations of CPS.
... Filamentous index (FI), a method of subjective scoring of lamentous bacteria abundance suggested byEikelboom (2000) 28 , was applied to evaluate the abundance of lamentous bacteria present in the samples.Sludge settling velocity (SV%) was measured using the canning method. MLSS uses the drying weighing method. ...
With the cancellation of primary sedimentation tanks, a large number of particles have entered the biochemical treatment units of wastewater treatment plants. Based on the more common problem of filamentous bulking in wastewater treatment plants, the paper investigates the effect of particles on activated sludge filamentous bulking, using polyethylene terephthalate (PET) microparticles as test particles. The results showed that the particles could significantly reduce the number of filamentous bacteria in activated sludge, and had a significant effect on its growth morphology. The role of 0.5 mm and 1.0 mm particles on filamentous bacteria was more obvious than that of 0.1 mm particles, and 0.1 mm particles were easily adsorbed by activated sludge and became biofilm carriers. Its improvement in the settling ability of filamentous expanded activated sludge is more significant than that of particles with 0.5 mm and 1.0 mm. The addition of 0.1 mm PET particles to the Anaerobic-Anoxic-Oxic (AAO) reactor promoted the coalescence of loose bacterial agglomerates under the combined effects of hydraulic shear, impact, friction, and extracellular polymeric substances (EPS) adhesion, which had a positive role on the settling properties of the activated sludge. The test abundance of particles in activated sludge at 4000 particles/L had no significant effect on the removal of COD and total phosphorus, but the removal of ammonia nitrogen decreased by 5–7%, showing some inhibition of nitrification; the sludge volume index (SVI) decreased from 358 mg/L to 198 mg/L, which had a significant control on filamentous bulking.
... This parameter is considered the volume, in milliliters, of 1 G of suspended solids after 30 min of settling. A sludge with good sedimentation has SVI values of less than 150 ml/g, while a value greater than 200 ml/g indicates that the activated sludge system has bulking problems (Eikelboom, 2000;Bitton, 2005). Based on this criterion, it can be deduced that the sample of activated sludge taken from the treatment plant (PC, positive control) has bulking problems (Table 2), which is also accompanied by a high TSS content, greater than what is recommended by local standards (SEMARNAT, 2022). ...
Most wastewater treatment plants use activated sludge-based biological systems for this purpose. The latter must effectively remove organic matter and, at the same time, show good sedimentability. However, sometimes there is an excessive proliferation of certain bacteria, giving rise to filamentary swelling, compromising the excellent sedimentability of the sludge. In this sense, the study’s objective was to evaluate the effect of applying two different technologies, the application of low-frequency ultrasound and UV radiation. Some bench-scale experiments were performed using the bulked sludge from the secondary clarifier of a wastewater treatment facility in an industrial park (CIVAC) in Morelos, Mexico, affected by filamentous organisms. Results showed that for the UV application for two, four, and 6 min, the settleability of the mixed liquor suspended solids was not improved; on the other hand, the cavitation effect caused by the ultrasound application demonstrated effective action against the destruction of filamentous organisms. The 10 min condition showed a significant decrease in the filament integrity of the microorganisms and a significant improvement of sedimentation velocity and sludge volume index (SVI) values and settleability of the sludge, but not enough to satisfy national discharge regulations related to total suspended solids in the treated effluent. Molecular identification indicates the presence of the genera Thauera and Brevundimonas in the sludge.
... All values are the mean of three determinations. The morphological cluster analysis and identification of aerobic and anaerobic microorganisms were performed with an Olympus BX40 microscope (Olympus Corporation, Shinjuku City, Tokyo) with a digital camera and phase contrast, as prescribed by Eikelboom [42]. Both fresh samples and those after Gram staining were observed in a clear field, with 100× magnification [43]. ...
The wastewater treatment plant of Agnita, Romania was designed with a rotational biological contactor system for a population of approximately 9500, but for environmental protection reasons it must comply with regulations concerning nitrogen and phosphorus designed for larger communities. In order to achieve the prescribed limits for these pollutants, we have used a 40% FeCl3 solution, continuously added to the distributor, without changes in flow or equipment. Its use boosts the removal of ammonia nitrogen, and phosphorus, bringing them within the limits and with reasonable cost. To determine the ferric chloride to be used we considered, aside from the pollutant load, the water temperature, and introduced a new parameter: specific removal power that enabled us to optimize the volume of FeCl3. A major contribution to nitrogen removal was achieved by the denitrification bacteria favored by the presence of ferric ions, which also precipitate phosphorus. The results of this study, performed since September 2021, enable us to continue to use this method and enlarge its application to other plants owned by the local operator.
... Some filamentous bacteria are ubiquitously dominant, while others, such as Eikelboom Type 0092 (designated as members of the Chloroflexi phylum) have been documented as dominant in AS WWTPs in some countries across the world, but not others (Table 1). Studies suggest that certain filamentous bacteria may be associated with WWTPs with different design configurations, operational practices, and influent characteristics [32,33]. The regional variations in filamentous bacterial distributions have therefore been ascribed to differences in combinations of influent biochemistries, environmental conditions, and operational factors [34][35][36]. ...
Filamentous bulking and foaming are the most common settling problems experienced in activated sludge (AS) wastewater treatment plants (WWTPs). The quality of the final effluent is poor during episodes of bulking and foaming, which is an environmental, human health and economic burden. Remedial measures are often ineffective, and traditional non-specific methods such as chlorination may also negatively impact important functional bacterial species such as nitrifiers. Modifications to older methods as well as new strategies are required for controlling filamentous bulking. Laboratory testing needs to be followed by testing at scale in WWTPs. This review describes the filamentous bacteria responsible for filamentous bulking, with a focus on their global distribution and known factors which are selective for the growth of specific filaments. Traditional and new non-specific and biological control strategies are reviewed and discussed. Research gaps are identified with the aim of promoting continued efforts to establish effective control strategies for filamentous sludge bulking.
... The morphology of microbe was observed by optical microscope (OLYM-PUSBX51). The method proposed by Ed was used to determine the abundance index of filamentous bacteria FI (Eikelboom 2000), the method proposed by Zhou was used to determine the total phosphorus of activated sludge (Zhou 2005). DO, pH and ORP were measured by WTW Multi 3401 DO tester. ...
In order to explore the effect of influent -P concentration on the relationship of phosphorus remove performance and sludge settleability, three sequencing batch reactors (SBRs) operated as anaerobic/aerobic mode were used to treat wastewater with different -P concentrations (same COD), and the organic loading rate (OLR) was changed through adjusting the anaerobic (aerobic) duration. The sludge settleability, nutrients removal, and microorganism species were investigated. The results showed that when the influent -P were 4.3 mg·L−1 and 8.6 mg·L−1, increasing the OLR through decreasing aerobic duration could significantly improve sludge settleability, while decreasing anaerobic duration could not. It was found that increase the OLR could promote the denitrification compete for carbon sources with phosphorus release process by inhibiting the accumulation of -N, leading to the decrease of phosphorus removal ability. When the influent -P was 17.2 mg·L−1, sufficient nitrification was beneficial to enrich denitrifying phosphorus accumulating bacteria (DPAO), and the activities of Thauera and Flavobacterium (DPAO) were stronger. Therefore, increasing influent -P concentration and reducing aerobic duration could help phosphorus accumulating bacteria (PAO) compete with denitrification for COD and enrich DPAO, thus reducing carbon source consumption.
... The proteobacteria Zoogloea was the third-most abundant genus in the two systems. The characteristic 'finger-like' microcolonies in activated sludge were already recognized during the microscopic examination (Eikelboom 2000). Ordinary heterotrophic organisms such as Bacteroidota; Terrimonas and OLB12 were identified as well. ...
For a successful granulation process in activated sludge systems, the stimulation of slow growing organisms such as glycogen accumulating microorganisms (GAOs) is a key factor. Here we show that the introduction of an anaerobic feast followed by an aerobic famine phase successfully transforms bulking sludge, caused by the abundance of genus Kouleothrix, to a hybrid floccular-granular sludge. Two sequencing batch reactors (SBRs) were operated for 228 days treating the same industrial wastewater derived from the cleaning of trucks transporting liquid food (the cargo consists of approximately 70% chocolate and 30% beer). By respectively applying a fast and slow feeding in two parallel SBRs, different degrees of substrate build-up were achieved in the two reactors during the feast phase. The F/M ratio over the feeding time was 1.41 ± 0.48 and 0.57 ± 0.16 kg COD·(kg VSS*d)−1 for the fast-fed and the slow-fed SBR respectively. Our results demonstrate that substrate build-up during the anaerobic selection step is not necessary to obtain well-settling granular-like sludge.
HIGHLIGHTS
Increasing the substrate gradient in the bulk liquid by applying a faster anaerobic feeding regime did not lead to better granulation.;
By only applying a feast (anaerobic)/ famine (aerobic) regime as selection pressure for granulation, a hybrid of floccular and granular sludge was achieved in the timeframe of 228 days while treating industrial wastewater derived from a tank truck cleaning site.;
... The DSVI was determined by using the lowest dilution at which the volume after 30 min of settling (V 30) was less than 300 ml. It was calculated using the formula (1) (Eikelboom, 2000;Van der Waarde et al., 2002;Jenkins et al., 2003). ...
Benfreha, B.M., Belgharbi, A. A., Mokrani, S., Tir.Touil, M.A., Moussa-Boudjemâa, B. (2022). Microbiological aspects of the aeration tanks of an activated sludge treatment plant in dysfunction: Consequences on its treatment performance. Lebanese Science Journal, 23 (1): 17-32. The present study was conducted in a sewage treatment plant, called "El Kouwaer", located in the department of Mascara, NorthWest of Algeria. Mainly, the objective of this investigation is to evaluate the relevant settling and pollution parameters and to assess the proliferation level of filamentous microbial communities during the dysfunction period to further the effectiveness of the operative treatment. Sludge parameter values were estimated such us Settling Test, Diluted Sludge Volume Index (DSVI), and Total Suspended Solids (TSS) content to set up the sludge classification, the performance analysis of treatment was conducted by computing pollution indicators and removal efficiencies of organic pollution, as well as the Principal Component Analysis (PCA) of dysfunction parameters. The results showed that in aeration tanks 65% of samples represented a maximum Filament Index (FI) of 6. Diluted Sludge Volume Index (DSVI) was greater than 300 mg/L in 23% of samples. A high level of filamentous bacteria biodiversity was also noted during the assessment of the (FI) P a g e | 18 including Microthrix parvicella, Bogiotae , and Sphaerotilus natans. The effluent in the biological unit was characterized by BOD5/COD ratio of 0.17 and COD removal efficiency of 53.32%. Those results demonstrated that the sewage treatment plant is frequently affected by bulking problems. This study had confirmed the importance of continuous monitoring of different process parameters like Wastewater Biodegradability Index, Dissolved Oxygen, filamentous flora, and Dilute Sludge Volume Index (DSVI) to avoid irreversible damage at the level of a wastewater treatment plant.
... In treating traditional contaminants and micro-contaminant degradation, these processes are essential. The presence or absence of protozoa is also an indication of the number of bacteria in the sludge and the extent of treatment (Eikelboom, 2000). Ciliated protozoa are the significant bio-indicator of the activated sludge process. ...
Slaughterhouse plants, especially meat and poultry products (MPPs), generate significant quantities of wastewater during the slaughtering process and the cleaning of machinery. The handling and final disposal of wastewater from the slaughterhouse is a public and environmental health issue due to its pollution potential. The monitoring of three full-scale buffalo meat-based abattoir effluent treatment plants (ETPs) to remove organic matter and nutrients was conducted at three separate sites in India. Rotary and static screens, an equalization tank, a dissolved air flotation (DAF) system, aeration tanks, and clarifiers were the component unit operations/processes of the wastewater treatment systems. All the treatment plants were operating at an average flow rate of 254 m³/d Meem Agro (designed capacity 500 m³/d); 427 m³/d Al Noor (designed capacity 500 m³/d), and 353 m³/d International Agro Foods (IAF) plant (designed capacity 750 m³/d) for the treatment of slaughterhouse wastewater. The Al Noor and Meem Agro’s ETP consisted of a DAF unit working at the surface-loading rates of 5.7 and 1.48 m3/m² h, respectively, applied during the analysis to the DAF system, resulting in 46.5 and 56.8% efficiencies of O&G and SS removal. The ETP of Al Noor and Meem Agro and IAF was loaded at an organic loading rate of 276 kg COD/day, 746 kg COD/day, and 629 kg COD/day, respectively. Performance of ETPs showed that the efficiency of total COD, total BOD, and TSS removal was 97, 98, and 99%; 94, 94, and 93%, and 95, 98, and 99% for Al Noor, Meem Agro, and IAF plants, respectively. The treatment plants’ efficiencies in all three plants for the removal of organic matter surpassed the effluent discharge level (as per Indian standards). Still, it is concluded that the ETPs need to be upgraded by incorporating the advanced wastewater treatment methods for the removal of nutrient concentration from treated effluents.
... Floc size distribution was monitored using automated image analysis with a Malvern Morphologi G3 analyzer. Microscopic examination of the AS samples were performed according to Eikelboom (2000) and filamentous index (FI) was used as a parameter for quantification of filamentous microorganism population in the sludge. ...
With an increasing frequency of extreme weather events wastewater treatment plant operators face a need to increase plant hydraulic capacity while continuing to comply with effluent quality requirements. An economically attractive way to meet this challenge is to significantly improve secondary settling tank performance and therefore assure safe wet weather plant operation. The objective of this study was to evaluate gravimetric selection technology conducted in hydrocyclones as a way for improving activated sludge settling characteristics in continuous flow BNR with a long sludge retention time and assess its ability to form granular sludge. Long term operational data and sludge morphology monitoring data were analysed. A significant drop in sludge volume index (SVI) (to values under 50 ml/g) and increase in return activated sludge solids concentration (to values above 20 g/L) was observed. Hydrocyclone installation consistently, selectively retained denser, larger flocs in the system and after a start-up phase large granules begin to appear. Gravimetric selection did not prevent the seasonal filamentous biomass outgrowth and temperature drop at the beginning of winter resulted in rapid rise of SVI and SST sludge blanket height especially after heavy rain. Technology under study proved to be effective under certain process conditions but it needs further research to consistently maintain low SVI values throughout the whole year. HIGHLIGHTS
Gravimetric selection in hydrocyclones improved seasonally activated sludge settling.;
Shear force in hydrocyclones did not prevent filamentous outgrowth.;
... • The amounts of detritus, filamentous algae and filamentous bacteria, including cyanobacteria, were ranked from 0 to 5 using the samples processed for microscopy detailed above and their relative abundance in the 75-µl of water examined (Eikelboom, 2000). We measured filamentous organisms because they prevent sedimentation and cause sludge bulking (Martins et al., 2004). ...
Nature-based solutions including rooftop-water storage ponds are increasingly adopted in cities as new eco-designs to address climate change issues, such as water scarcity and storm-water runoff. Macrophytes may be valuable additions for treating stored rooftop waters and provisioning other services, including aquaponics, aesthetic and wildlife-conservation values. However, the efficacy of macrophyte treatments has not been tested with influxes of different labile carbon loadings such as those occurring in storms. Moreover, little is known about how macrophytes affect communities of metazoans and microbes, including protozoans, which are key players in the water-treatment process. Here, we experimentally investigated the effectiveness of two widely distributed macrophytes, Ceratophyllum demersum and Egeria densa, for treating drained rooftop water fed with two types of leaf litter, namely Quercus robur (high C lability) and Quercus rubra (low C lability). C. demersum was better than E. densa at reducing water conductivity (by 10 ̶ 40 µS/cm), TDS (by 10 ̶ 18 mg/L), DOC (by 4 ̶ 5 mg/L) and at increasing water transparency (by 4 ̶ 9 %), water O2 levels (by 19 ̶ 27 %) and daylight pH (by 0.9 ̶ 1.3) compared to leaf-litter only microcosms after 30 days. Each treatment developed a different community of algae, protozoa and metazoa. Greater plant mass and epiphytic chlorophyll-a suggested that C. demersum was better at providing supporting habitat than E. densa. The two macrophytes did not differ in detritus accumulation, but E. densa was more prone to develop filamentous bacteria, which cause sludge bulking in water-treatment systems. Our study highlights the superior capacity of C. demersum and the usefulness of whole-ecosystem experiments in choosing the most adequate macrophyte species for nature-based engineered solutions.
... Among them are as follows: dispersed growth of microorganisms when they do not stick together, formation of pinpoint flocs (PP) when only very small, and mechanically fragile flocs are present; and zoogleal bulking caused by excessive amount of extracellular material (EPS) produced by microorganisms (Jenkins et al. 2003;Mesquita et al. 2011). However, the most common problem of liquid-solid separation is activated sludge bulking caused by an overproliferation of filamentous bacteria (Eikelboom 2000;Jenkins et al. 2003). To limit the development of such bacteria, WWTPs operators use various coagulants such as ferrous chloride, ferric chloride, hydrated aluminum sulfate, polyaluminum chloride, or cationic polymers (Jenkins et al. 2003;Mamais et al. 2011). ...
PAX-18 (polyaluminum chloride) is frequently used in WWTPs (wastewater treatment plants) to overcome sludge bulking. An alternative biological method is the usage of Lecane rotifers, which can be endangered by predacious fungi. We investigated the influence of different PAX-18 concentrations on the relationship between Lecane inermis and predacious fungi ( Zoophagus and Lecophagus ) differing in feeding mode. High PAX concentration (6 mg Al ³⁺ L ⁻¹ ) strongly limited the number of the rotifers, which in low concentration (1.2 mg Al ³⁺ L ⁻¹ ), after an initial decline, increased, but significantly slower than in control. Under the simultaneous influence of Lecophagus and PAX, rotifers were driven almost extinct at the high concentration, but survived at the lower concentration and increased in the control. When treated with Zoophagus , only one or two rotifers survived in treatments and control. High concentrations of PAX significantly restricted the growth of fungi, whereas in low concentrations and control conditions, their length increased, with Zoophagus growing much quicker than Lecophagus . Zoophagus was significantly more efficient in trapping rotifers regardless of PAX concentration. The trapping ability of mycelium following extended exposure to PAX was strongly limited at high concentrations, in comparison to control. Conidia of Zoophagus turned out to be considerably more resistant to PAX-18 and starvation than Lecophagus conidia.
... Microscopic analysis of activated sludge samples (mixed liquor) was performed with a Zeiss Jenaval microscope, according to the method recommended by Eikelboom (2000), Gerardi (2008) and Jenkins et al. (2004). The photos were taken with a Euromex VC.3038 HD-Pro camera. ...
As biochemical oxygen demand (BOD) properly illustrates transformation of toxic organic compounds to harmless and biodegradable substances, it is often used to demonstrate the efficiency of wastewater treatment technologies. Nevertheless, H2O2 can form when solutions are subjected to advanced oxidation processes (AOP). H2O2 production is typical in high energy irradiation treatments. Toxic effect of H2O2 on microbes is a well known fact in the field of biology, however, the impact of H2O2 is usually not taken into account when evaluating effectiveness of AOP. To quantify the impact of the forming H2O2 on the outcome of BOD tests, the BOD of glucose-glutamic acid reference solution was determined in the presence of hydrogen peroxide in the 0.1 and 75 mg dm⁻³ concentration range. Results showed that H2O2 distorts the BOD measurement in two ways. Prolonged lag period takes place that ensures adaptation of microbes to toxic environment and promotes production of catalase enzyme that decomposes hydrogen peroxide. On the other hand, appearance of catalase producing bacterial groups leads to reduced BOD values because the oxygen released from the H2O2 results in a negative error as it acts against oxygen depletion. The correlation between H2O2 concentration and the shift in lag period was described, as well as the relationship between the initial H2O2 concentration and the final BOD results. To validate the effects studied, BOD was measured in 0.1 mmol dm⁻³ oxacillin solutions irradiated with gamma rays. It was confirmed that the presence of H2O2 may lead to underestimation of the actual BOD as increase in BOD was observed when hydrogen peroxide was eliminated from the solution before starting the measurement.
... The FI was determined according to the method proposed by Eikelboom [13] (please see also Section S1 in Supplementary Material). A Light Sheet Microscope (LSM, Observer Z1, Zeiss) was used at 50×, 100× and 200× magnification to determine the filament index (FI) of the mixed liquor samples. ...
This is the first study that examines the effect of operating conditions on fouling of Membrane Bio-Reactors (MBRs), which treat municipal wastewater in field conditions, with specific regard to the controlled development of filamentous microorganisms (or filaments). The novelty of the present work is extended to minimize the dissolved oxygen (DO) in recirculated activated sludge for improving the process of denitrification. For this purpose, two pilot-scale MBRs were constructed and operated in parallel: (i) Filament-MBR, where an attempt was made to regulate the growth of filaments by adjustment of DO, the Food-to-Microorganisms (F/M) ratio and temperature, and (ii) Control-MBR, where a gentle stirring tank was employed for the purpose of zeroing the DO in the recycled sludge. Results showed that low temperature (
... Due to the wide fluctuation range of water quality and large temperature difference in urban sewage treatment plants, it is easy to cause the growth of filamentous bacteria. And the excessive reproduction of filamentous bacteria is also one of the main causes of sludge bulking [1,2]. Studies have shown that when the composition of filamentous bacteria in the system reaches 1%-20%, it may cause sludge bulking [3,4]. ...
Three groups of SBR reactors A, B and C with different aeration time were set up to culture the activated sludge which has already bulked. The results showed that the settling performance of activated sludge in reactor A changed a little, but reactors B and C had been significantly improved. High-throughput sequencing results showed that the aeration time had a significant inhibitory effect on the growth of Thothrix, and the longer the aeration time was, the more obvious the inhibition was. When the aeration time is more than 6h, the SBR mode can effectively inhibit filamentous sludge bulking, and the longer the aeration time, the better the effect.
... According to the Table 4, all the studied samples have SVI values higher than the optimum value of 80 (especially in the case of ABS-WWTP), which can partly be attributed to the presence of filamentous organisms. It has previously been proved that the SVI increases when the number of filamentous microorganisms increase in the biological reactor [37,38]. ...
Fungi are eco-friendly agents and significant contributors to the various functions of activated sludge and can be as efficient as bacteria in the removal of organic matters from wastewater; however, how the types of wastewater and operating conditions affect the fungal communities are remained unex-plored compared to bacteria. In this study, a culture-dependent method was used to assess the fungal diversity in three full-scale plants treating petrochemical, acrylonitrile butadiene styrene (ABS) resin manufacturing and municipal waste waters. Moreover, some physiochemical factors and operational parameters were determined. A total of 256 strains belonging to nine genera of Penicillium, Chrysosporium, Aspergillus, Trichoderma, Trichothecium, Cladosporium, Fusarium, Acremonium, and Geo-trichum were isolated. Among them, Geotrichum, Cladosporium, Aspergillus, Penicillium, Chrysosporium and Trichoderma were the most frequent populations isolated from the wastewater treatment plants (WWTPs). The results indicated that the types of wastewater, as well as the operating conditions are the important factors influencing fungal community structure and abundance.
The on-site-treated effluent from an automobile manufacturing company is discharged into the public sewage system for further treatment. However, the upgrade of the treatment plant to reduce the effluent pollutant load led to the discharge limit for phenols being occasionally exceeded. The concern of the water authority prompted a study to investigate whether the toxicity of phenols could affect the performance of the receiving municipal wastewater treatment plant. To this end, mixtures of the industrial effluent and synthetic municipal wastewater were tested in a laboratory-scale activated sludge system. The bioreactor was fed with increasing ratios of the industrial wastewater in the combined influent (from 10 to 50%) over 7 months. No significant differences were observed in the system performance fed only with the synthetic wastewater (during the acclimation stage) or with the industrial wastewater. The bioreactor achieved average removal efficiencies of 70% for phenols even when half of the combined influent was the industrial wastewater. Bearing in mind the question of phenols, an important drawback was the high uncertainty in their determination by the conventional phenol index method due to the matrix effect. To overcome this a spectrophotometric procedure based on the serial dilutions of each pair of influent and effluent samples has been developed. Although strong microbial selection was observed by the changing bioreactor environment, the industrial effluent was found to be fully compatible with further treatment by conventional activated sludge process.
The ecological engineering of granular sludge relies on a continuum from microbiological research to process engineering. Designing granular sludge systems for biological nutrient removal should thrive on the 100 years of activated sludge research and practice. Flocs and granules are made of the same guilds of microorganisms that convert nutrients. Granules are suspended biofilm particles that form by self-aggregation of microbes. Granules (0.5–2 mm scale) differ from flocs (10–100+ µm) in metrics and are prone to substrate diffusion limitations. Niches of microbial populations involved in C–N–P conversions establish at different locations along substrate and redox gradients in the architecture of granules, enabling an almost simultaneous removal of all nutrients. Granulation densifies the biomass and increases its concentration for faster volumetric conversions, and more compact bioreactors. Fundamental processes of bioaggregation need to get uncovered in relation to microbial selection and process performances. Deriving microbial ecology principles is important to understand the composition and functioning of the granular sludge ecosystem, and to manage the microbial resource for an efficient granulation and nutrient removal. Reactor engineering relies on a multi-scale knowledge from process to granules, microorganisms, and their metabolisms. Combining systems microbiology, environmental biotechnology, and mathematical modelling enables concepts and methodologies for engineering.
Phosphorous (P) removal in wastewater treatment is essential to prevent eutrophication in water bodies. Side‐stream enhanced biological phosphorous removal (S2EBPR) is utilized to improve biological P removal by recirculating internal streams within a side‐stream reactor to generate biodegradable carbon (C) for polyphosphate accumulating organisms (PAOs). In this study, a full‐scale S2EBPR system in a water resource recovery facility (WRRF) was evaluated for 5 months. Batch experiments revealed a strong positive correlation ( r = 0.91) between temperature and C consumption rate (3.56–8.18 mg‐COD/g‐VSS/h) in the system, with temperature ranging from 14°C to 18°C. The anaerobic P‐release to COD‐uptake ratio decreased from 0.93 to 0.25 mg‐P/mg‐COD as the temperature increased, suggesting competition between PAOs and other C‐consumers, such as heterotrophic microorganisms, to uptake bioavailable C. Microbial community analysis did not show a strong relationship between abundance and activity of PAO in the tested WRRF. An assessment of the economic feasibility was performed to compare the costs and benefits of a full scale WRRF with and without implementation of the S2EBPR technology. The results showed the higher capital costs required for S2EBPR were estimated to be compensated after 5 and 11 years of operation, respectively, compared to chemical precipitation and conventional EBPR. The results from this study can assist in the decision‐making process for upgrading a conventional EBPR or chemical P removal process to S2EBPR.
Practitioner Points
Implementation of S2EBPR presents adaptable configurations, exhibiting advantages over conventional setups in addressing prevalent challenges associated with phosphorous removal.
A full‐scale S2EBPR WRRF was monitored over 5 months, and activity tests were used to measure the kinetic parameters.
The seasonal changes impact the kinetic parameters of PAOs in the S2EBPR process, with elevated temperatures raising the carbon demand.
PAOs abundance showed no strong correlation with their activity in the full‐scale S2EBPR process in the tested WRRF.
Feasibility assessment shows that the benefits from S2EBPR operation can offset upgrading costs from conventional BPR or chemical precipitation.
The discharge of industrial water requires the removal of its pollutants, where biological wastewater treatment plants (WWTPs) are the most used systems. Biological WWTPs make use of activated sludge (AS), where bacteria are responsible for the removal of pollutants. However, our knowledge of the microbial communities of industrial plants is limited. Understanding the microbial population is essential to provide solutions to industrial problems such as bulking. The aim of this study was to identify at a high taxonomic resolution the bacterial population of 29 industrial WWTPs using 16S rRNA amplicon sequencing. Our results revealed that the main functional groups were dominated by Thauera and Zoogloea within denitrifiers, Dechloromonas in phosphate-accumulating organisms, and Defluviicoccus in glycogen-accumulating organisms. The activated sludge characterization indicated that 59% of the industrial plants suffered from bulking sludge, with DSVI values of up to 448 mL g⁻¹. From the bulking cases, 72% corresponded to filamentous bulking with Thiothrix as the most abundant filament; meanwhile, the other 28% corresponded to viscous bulking sludge in which Zoogloea was the most abundant genus. Furthermore, the bacterial population did not share a core of taxa across all industrial plants. However, 20 genera were present in at least 50% of the plants comprising the general core, including Thauera, Ca. Competibacter, and several undescribed microorganisms. Moreover, statistical analysis revealed that wastewater salinity strongly affected the microbial richness of the industrial plants. The bacterial population across industrial plants differed considerably from each other, resulting in unique microbial communities that are attributed to the specificity of their wastewaters.
Key points
• The general core taxa of industrial plants were mostly made up of undescribed bacterial genera.
• Filamentous bacteria constituted on average 4.1% read abundance of the industrial WWTPs.
• Viscous bulking remains a significant type of bulking within industrial WWTPs.
The performance of sludge and the effectiveness of wastewater treatment in various biological treatment facilities are influenced by the morphological features of activated sludge flocs. Currently, these features are assessed qualitatively through visual inspection, without statistical processing of the data. The article presents the results of quantitative determination of the strength of activated sludge flocs. A computerized method has been created to quantify the morphological characteristics of activated sludge flocs by analyzing sludge micrographs using the ImageJ software. Color and contrast indices were used to quantify the strength of the flocs. Photographs of activated sludge from the work of D. Eikelboom were used as standards for determining strength. In the calculations, we used photographs by D. Eikelboom taken at a magnification of 300 times (100 pixels) and 150 times (50 pixels). A laboratory study of the effect of Mg ions on the properties of activated sludge flocs was carried out when controlling the morphology of the flakes using the developed computerized technique. Examining the impact of Mg ions on activated sludge flocs revealed that higher magnesium concentrations in the sludge liquid result in increased linear dimensions (by 59%), floc area (by 81%) and floc volume (by 275%), but concurrently lead to a decrease in the strength of activated sludge flakes (by 21%). The obtained results in general indicated the positive effect of magnesium ion on the sedimentation properties of sludge in the aerotank-settlement system. A scale for quantitative determination of the strength of activated sludge flocs has been constructed. The developed computerized method enhances the precision and detail of visual evaluations of the technological attributes of activated sludge flocs, enabling the detection of even the smallest changes in the morphological characteristics across different wastewater treatment technologies. Keywords: activated sludge, flocs, concentration of magnesium, strength, technological characteristics.
The morphological characteristics (shape and structure) of activated sludge flocs affect the operational characteristics of sludge and the reliability of wastewater treatment in various biological treatment facilities. Currently, these characteristics are determined visually, they are evaluated only qualitatively, and the data are not processed statistically. A computerized methodology for quantifying the morphological characteristics of activated sludge flocs during the processing of sludge micrographs in the ImageJ software product has been developed. Testing of the methodology in the study of sludge flocs in the adhesions on the membranes of a membrane biological reactor showed that flocs from the surface aerobic zone of the adhesions have a slightly rounder shape, smaller linear dimensions and volume than sludge flocs from the anaerobic zone in the depth of the adhesions. The study of the effect of Mg ions on the properties of activated sludge flocs showed that with an increase in the concentration of magnesium in the sludge liquid, a decrease in the roundness of the flocs, a slight deterioration in the structure is observed, but there is a much more significant increase in linear dimensions (almost 60%) and an extraordinary increase (275%) in the volume of the flocs. The developed computerized methodology makes it possible to significantly detail and refine the results of visual assessments of the technological characteristics of activated sludge flocs and to detect the smallest changes in the morphological characteristics of flocs in different wastewater treatment technologies.
Filamentous Chloroflexota are abundant in activated sludge wastewater treatment plants (WWTPs) worldwide and are occasionally associated with poor solid-liquid separation or foaming, but most of the abundant lineages remain undescribed. Here, we present a comprehensive overview of Chloroflexota abundant in WWTPs worldwide, using high-quality metagenome-assembled genomes (MAGs) and 16S rRNA amplicon data from 740 Danish and global WWTPs. Many novel taxa were described, encompassing 4 families, 13 genera, and 29 novel species. These were widely distributed across most continents, influenced by factors such as climate zone and WWTP process design. Visualization by fluorescence in situ hybridization (FISH) confirmed their high abundances in many WWTPs based on the amplicon data and showed a filamentous morphology for nearly all species. Most formed thin and short trichomes integrated into the floc structure, unlikely to form the typical inter-floc bridging that hinders activated sludge floc settling. Metabolic reconstruction of 53 high-quality MAGs, representing most of the novel genera, offered further insights into their versatile metabolisms and suggested a primary role in carbon removal and involvement in nitrogen cycling. The presence of glycogen reserves, detected by FISH-Raman microspectroscopy, seemed widespread across the phylum, demonstrating that these bacteria likely utilize glycogen as energy storage to survive periods with limited resources. This study gives a broad overview of the Chloroflexota community in global activated sludge WWTPs and improves our understanding of their roles in these engineered ecosystems.
IMPORTANCE
Chloroflexota are often abundant members of the biomass in wastewater treatment plants (WWTPs) worldwide, typically with a filamentous morphology, forming the backbones of the activated sludge floc. However, their overgrowth can often cause operational issues connected to poor settling or foaming, impairing effluent quality and increasing operational costs. Despite their importance, few Chloroflexota genera have been characterized so far. Here, we present a comprehensive overview of Chloroflexota abundant in WWTPs worldwide and an in-depth characterization of their morphology, phylogeny, and ecophysiology, obtaining a broad understanding of their ecological role in activated sludge.
Filamentous Chloroflexota are abundant in activated sludge wastewater treatment plants (WWTPs) worldwide and are occasionally associated with poor solid-liquid separation or foaming, but most of the abundant lineages remain undescribed. Here, we present a comprehensive overview of Chloroflexota abundant in WWTPs worldwide, using high-quality metagenome-assembled genomes (MAGs) and 16S rRNA amplicon data from 740 Danish and global WWTPs. Many novel taxa were described, encompassing 4 families, 13 genera and 29 novel species. These were widely distributed across most continents, influenced by factors such as climate zone and WWTP process design. Visualization by fluorescence in situ hybridization (FISH) confirmed their high abundances in many WWTPs based on the amplicon data and showed a filamentous morphology for nearly all species. Most formed thin and short trichomes integrated into the floc structure, unlikely to form the typical inter-floc bridging that hinders activated sludge floc settling. Metabolic reconstruction of 53 high-quality MAGs, representing most of the novel genera, offered further insights into their versatile metabolisms and suggested a primary role in carbon removal and involvement in nitrogen and sulfur cycling. The presence of glycogen reserves, detected by FISH-Raman microspectroscopy, seemed widespread across the phylum demonstrating that these bacteria likely utilize glycogen as an energy storage to survive periods with limited resources. This study gives a broad overview of the Chloroflexota community in global activated sludge WWTPs and improves our understanding of their roles in these engineered ecosystems.
Importance
Chloroflexota are often abundant members of the biomass in wastewater treatment plants (WWTPs) worldwide, typically with a filamentous morphology, forming the backbones of the activated sludge (AS) floc. However, their overgrowth can often cause operational issues connected to poor settling or foaming, impairing effluent quality and increases operational costs. Despite the importance, few Chloroflexota genera have been characterized so far. Here, we present a comprehensive overview of Chloroflexota abundant in WWTPs worldwide and an in-depth characterization of their morphology, phylogeny, and ecophysiology, obtaining a broad understanding of their ecological role in activated sludge.
Для кількісного контролю технологічних характеристик активного мулу в біологічних очисних спорудах в рамках представленого дослідження розроблено комп’ютеризовану методику, використання якої підвищує надійність та техногенну безпеку експлуатації біоло-гічних очисних споруд. Методика базується на визначенні в кількісних показниках геомет-ричних (площі, об’єму) та морфологічних (форми та структури) характеристик пластівців активного мулу при обробці мікрофотознімків мулу в програмному продукті Imadge J. Фо-тографування мікроскопічних зображень мулу виконували при збільшенні в 100 разів і ма-сштабуванні з допомогою окуляр-мікрометра. Наразі морфологічні характеристики актив-ного мулу визначають тільки візуально, що не дозволяє усереднити дані великої кількості зразків та загалом зумовлює суб’єктивний характер оцінок. Дослідження пластівців мулу в налипаннях на мембранах мембранного біологічного реактора показали, що пластівці з по-верхневої аеробної зони налипань мають дещо круглішу форму, менші лінійні розміри, площу та об’єм, ніж пластівці мулу з анаеробної зони в глибині налипань. Дослідження впливу іонів магнію на властивості пластівців активного мулу показали, що при збільшенні концентрації магнію в муловій рідині спостерігається зменшення округлості пластівців, не-значне погіршенні структури, проте відбувається значно суттєвіше збільшення лінійних ро-змірів (майже на 60 %), площі (на 134 %) і надзвичайне збільшення (на 275 %) об’єму плас-тівців. Ці показники свідчать про покращення технологічних властивостей пластівців та зменшення їх здатності до налипань на мембранах реактора. Розроблена комп’ютеризована методика дозволяє значно деталізувати й уточняти результати візуальних оцінок техноло-гічних характеристик пластівців активного мулу та у великому масиві даних виявляти най-дрібніші зміни морфологічних показників пластівців в різних технологіях очистки стічних вод.
U radu su prikazani rezultati diverziteta vrsta obraštajnih organizama na osnovu analize eksprimentalnih polietilenskih kolektora sa različitim periodom imerzije koji su bili postavljeni na postojećem uzgajalištu školjki u Kamenarima. Cilj istraživanja pored diverziteta, bio je utvrditi i abundancu obraštajnih organizama u zavisnosti od dužine imerzije polietilenskih kolektora. Najveća abundanca obraštaja zabilježena je nakon imerzije od 12 mjeseci, 278 jedinki, dok je najmanje zabilježeno nakon imerzije od 6 mjeseci, 149 jedinki. Od obraštajnih grupa organizama, najzastupljeniji su bili Crustacea (38 %), dok su Gastropode (0.2%) bile najmanje zastupljene. Diverzitet vrsta bio je najveći nakon imerzije od 4 mjeseca, 18 vrsta, a najmanji nakon imerzije od 12 mjeseci, 11 vrsta. Statistički značajna razlika u abundanci obraštaja uočena je između kolektora koji su bili u imerziji 12 mjeseci sa kolektorima nakon imerzije od 4 odnosno 6 mjeseci. Invazivna vrsta sunđera Paraleucila magna bila je zastupljena na kolektorima nakon svakog perioda imerzije.
Tannery effluents with a high organic matter load (indicated by their COD level) have to be treated before they are discharged, so as to minimize their negative impact on the environment. Using field mesocosm systems, this study evaluated the feasibility of treating such effluents through bioaugmentation with activated sludge, followed by phytoremediation with aquatic macrophytes (Lemnoideae subfamily). Regardless of its quality, the activated sludge was able to remove approximately 77% of the COD from effluents with a low initial organic load (up to 1500 mg/L). The macrophytes then enhanced removal (up to 86%), so the final COD values were permissible under the current legislation for effluent discharge. When the initial organic load in the undiluted effluents was higher (around 3000 mg/L), the COD values obtained after consecutive bioaugmentation and phytoremediation were close to the legally allowed limits (583 mg/L), which highlights the potential of phytoremediation as a tertiary treatment. This treatment also brought total coliform counts down to legally acceptable values, without plant biomass decreasing over time. Moreover, the plant biomass remained viable and capable of high COD removal efficiency (around 75%) throughout two additional reuse cycles. These findings indicate that the efficiency of the biological treatments assayed here depends largely on the initial organic load in the tannery effluents. In any case, the sequential application of activated sludge and aquatic macrophytes proved to be a successful alternative for remediation.
Graphical abstract
In this study, the filamentous bulking was demonstrated to improve anammox capability and anammox bacteria (AnAOB) population density under organic stress. The selective heterotrophic bacteria (HB) washout that involved in shear detachment, enmeshment and biomass washout was triggered. The microbial spatial distribution and granular detachment properties revealed that the filamentous bulking transferred the "location advantage" of HB from granules interior to surface, and endowed granular surface low shear tolerance for shear detachment, ultimately resulted in selective HB detachment. The detached filaments-mediated enmeshment provided additional selective pressure for free HB-flocs, eventually achieving the retention time differentiation between AnAOB (34 - 141 days) and HB (3 - 15 days), and a high anammox population density. Controlling dissolved oxygen level was crucial for regulating sludge bulking. Collectively, the filamentous bulking was developed as an effective anti-organic stress strategy to broaden the application of granular anammox process in actual wastewater treatment.
BACKGROUND
The study defined a sustainable management scheme to eliminate the toxic impact of extreme salinity on the ecology and performance of an activated sludge process. The scheme was implemented on a plant treating pickle plant effluents involving significant flow and salinity transients. It was conducted in two phases. Firstly, the plant was operated without attenuating extreme salinity transients, enabling observation of all adverse impacts on the microbial ecology. The second phase was implemented with a new management scheme tempering all salinity gradients revealing the recovery of the microbial ecology into a stable and sustainable state.
RESULTS
Initially, the microbial community could not cope with rapid salinity increase and exhibited significant changes resulting in the predominance of filamentous microorganisms, disruption of the floc structure and almost total loss of eukaryotic microorganisms. Settling problems and deterioration of effluent quality were observed, followed by plasmolysis and repeated total loss of the biomass. The new waste management strategy allowed only transients limited to ±500 μS cm⁻¹ in the influent; in this way, the microbial ecology steadily improved. The effluent chemical oxygen demand could be maintained below 80–90 mg L⁻¹ with no appreciable particulate matter escape.
CONCLUSIONS
Results identified sharp salinity transients as the key factor triggering total destruction of activated sludge. The novel scheme provided conclusive evidence that a stable microbial community could be maintained even when continuously exposed to a salinity level of around 10 000 μS cm⁻¹ in the reactor, provided that variations remained limited to ±500 μS cm⁻¹, ensuring satisfactory effluent quality. © 2022 Society of Chemical Industry (SCI).
The biological wastewater treatment systems are mostly based on the activated sludge method and endangered by exploitation problems connected to sludge bulking and/or foaming. Chloroflexi bacteria often cause bulking episodes and should be investigated in that matter, especially regarding the unusual metabolic activities. The aim of the study was to evaluate if the activity of microbial populations measured by the Biolog system is changing in reaction to diluent and homogenisation. The thesis was it that it differs for activated sludge samples with high and low abundance of Chloroflexi. The systematic review was performed to identify and fill a research gap concerning the best approach to study metabolism of activated sludge of various origins. We tested samples of municipal and industrial sludge with differing abundance of Chloroflexi and showed that activity of distinct types of sludge is influenced incongruously by preparation. The homogenisation unified the composition of activated sludge and influenced the microbial communities responsible for the hydrolysis of complex sugars. The homogenised sludge showed activity for the same substrates as the non-homogenised one, but the carbohydrate uptake was higher for the second one. Dilution with supernatant also influenced the metabolism. Substrate uptake was lower for 60% of the substrate groups for the less diluted sludge. On the other hand, the higher dilution of activated sludge inoculum resulted in a bigger spectrum of the substrates assimilated by bacteria on EcoPlate. Interestingly the type of diluent and time of homogenisation do not significantly affect the results within the same wastewater treatment plant.
Aerobic biological treatment systems are very suitable for removing contaminants of organic matter in the sewage. Accordingly, the continuity of the inlet flow to the treatment plant, in design and exploitation of these processes, is necessary to consider. One of the differences between industrial and low population areas wastewater, such as military garrisons, and the Municipal sewage, is their volumetric fluctuations. These fluctuations may have a negative effect on the activated sludge process; thus the efficiency of using balancing pool in activated sludge systems has been analyzed in this research. Wastewater treatment process is based on biologically activated sludge method and extensive aeration. In this method, the raw wastewater is directed to the pumping station gravitationally. Results illustrated that, the inlet flow rate to the treatment plant, has high fluctuations from 0 to 40 (m3/hour) at different hours of the day due to the low population. Based on the samplings, it has been determined that the efficiency of activated sludge process in removing the parameters of BOD5, COD, TSS and ammonia during one week is averagely 61, 61, 68 and 24%, respectively. According to the sewage standards, this treated sewage is not suitable for injection into water wells or surface water or for reuse in agriculture. Whilst, using the balancing pond and controlling the inlet flow to the aeration pond at a rate of 12 cubic meters per hour, the removal efficiency of BOD5, COD, TSS and ammonia escalates averagely 90, 90, 89/19 and 81.59%, respectively during a week.
Activated sludge bulking caused by filamentous bacteria is still a problem in wastewater treatment plants around the world. Bulking is a microbiological problem, and so its solution on species-specific basis is likely to be reached only after their ecology, physiology and metabolism is better understood. Culture-independent molecular methods have provided much useful information about this group of organisms, and in this review, the methods employed and the information they provide are critically assessed. Their application to understanding bulking caused by the most frequently seen filament in Japan, 'Ca. Kouleothrix', is used here as an example of how these techniques might be used to develop control strategies. Whole genome sequences are now available for some of filamentous bacteria responsible for bulking, and so it is possible to understand why these filaments might thrive in activated sludge plants, and provide clues as to how eventually they might be controlled specifically.
Biological foaming (or biofoaming) is a frequently occurring problem in wastewater treatment plants (WWTPs) and is attributed to the overwhelming growth of filamentous bulking and foaming bacteria (BFB). Biological foaming has been intensively investigated, with BFB like Microthrix and Skermania having been identified from WWTPs and implicated in foaming. Nevertheless, studies are still needed to improve our understanding of the microbial diversity of WWTPs biofoams and how microbial activities contribute to foaming. In this study, sludge foaming at the Qinghe WWTP of China was monitored, and sludge foams were investigated using culture-dependent and culture-independent microbiological methods. The foam microbiomes exhibited high abundances of Skermania , Mycobacterium , Flavobacteriales , and Kaistella . A previously unknown bacterium, Candidatus Kaistella beijingensis, was cultivated from foams, its genome sequenced, and it was phenotypically characterized. Ca . K. beijingensis exhibits hydrophobic cell surfaces, produces extracellular polymeric substances (EPS), and metabolizes lipids. Ca . K. beijingensis abundances were proportional to EPS levels in foams. Several proteins encoded by the Ca . K. beijingensis genome were identified from EPS that was extracted from sludge foams. Ca . K. beijingensis populations accounted for 4–6% of the total bacterial populations in sludge foam samples within the Qinghe WWTP, although their abundances were higher in spring than in other seasons. Co-occurrence analysis indicated that Ca . K. beijingensis was not a core node among the WWTP community network, but its abundances were negatively correlated with those of the well-studied BFB Sker mania piniformis among cross-season Qinghe WWTP communities.
Importance
Biological foaming or scumming is a sludge separation problem that has become the subject of major concern for long-term stable activated sludge operation in decades. Biological foaming was considered induced by foaming bacteria. However, the occurrence and deterioration of foaming in many WWTPs are still not completely understood. Cultivation and characterization of the enriched bacteria in foaming are critical to understand their genetic, physiological, phylogenetic, and ecological traits, as well as to improve the understanding of their relationships with foaming and performance of WWTPs.
Cost-efficient and environmentally friendly treatment of hydraulic fracturing effluents is of great significance for the sustainable development of shale gas exploration. We investigated the synergistic effects of plant-microbial treatment of shale gas fracturing waste fluid. The results showed that illumination wavelength and temperature are direct drivers for microbial treatment effects of CODCr and BOD5, while exhibit little effects on nitrogen compounds, TDS, EC, and SS removals as well as microbial species and composition. Plant-microbial synergism could significantly enhance the removal of pollutants compared with removal efficiency without plant enhancement. Additionally, the relative abundance and structure of microorganisms in the hydraulic fracturing effluents greatly varied with the illumination wavelength and temperature under plant-microbial synergism. 201.24 g water dropwort and 435 mg/L activated sludge with illumination of 450–495 nm (blue) at 25 °C was proved as the best treatment condition for shale gas fracturing waste fluid samples, which showed the highest removal efficiency of pollutants and the lowest algal toxicity in treated hydraulic fracturing effluents. The microbial community composition (36.73% Flavobacteriia, 25.01% Gammaproteobacteria, 18.55% Bacteroidia, 9.3% Alphaproteobacteria, 4.1% Cytophagia, and 2.83% Clostridia) was also significantly different from other treatments. The results provide a potential technical solution for improved treatment of shale gas hydraulic fracturing effluents.
Graphical abstract
Recopilación de ponencias sobre fangos activos ocurridas en las Jornadas de GBS de 2014 en ocasión de la celebración de los 100 años de fangos activos.
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