Anaerobic digestion (AD) has been commercially operated worldwide in full scale as a resource recovery technology underpinning a circular economy. However, problems such as a long start-up time, or system instability, have been reported in response to operational shocks. These issues are usually linked to the dynamics of the functional microbiota in AD. Exploring the microbiota-functionality nexus (MFN) could be pivotal to understand the reasons behind these difficulties, and hence improving AD performance. Here we present a systematic MFN study based on 138 samples taken from 20 well-profiled lab-scale AD reactors operated for up to two years. All the reactors were operated in the same lab within the same period of time using the same methodology to harvest physio-chemical and molecular data, including key monitoring parameters, qPCR, and 16S sequencing results. The results showed a core bacterial microbiota prevailing in all reactor types, including Bacillus, Clostridium, Bacteroides, Eubacterium, Cytophaga, Anaerophaga, and Syntrophomonas, while various methanogens dominated different communities due to different inocula origins, reactor temperatures, or salinity levels. This core bacterial microbiota well correlated with biogas production (Pearson correlation coefficient of 0.481, p < 0.0001). Such strong correlation was even comparable to that between the biogas production and the methanogenic 16S rRNA gene content (Pearson correlation coefficient of 0.481, p < 0.0001). The results indicated that AD performance only modestly correlated with microbial diversity, a key governing factor. AD microbiota was neither functionally redundant nor plastic, and a high variety in communities can exhibit a strong difference in reactor performance. Our study demonstrates the importance of a core bacterial microbiota in AD and supports inspiring considerations for design, bioaugmentation, and operational strategies of AD reactors in the future.

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This study provides a comparison of the sludge characteristics along the height of an upflow anaerobic sludge blanket (UASB) reactor in terms of sludge morphology, activity and stability. The main aim of this study was to identify the best location (i.e. where sludge is of lowest stability and/or highest concentration) in the sludge bed for conveying the sludge from the low temperature UASB reactor to a digester. The sludge profile was investigated by collecting sludge samples along the different heights of the UASB-anaerobic membrane bioreactor treating municipal wastewater. Results showed that total solids and volatile solids concentrations decreased with height, and the highest chemical oxygen demand concentration was observed at the bottom of the reactor. Active biomass remained near inlet of the reactor; whereas, non-active biomass consisted of loose, suspended particles and flocculents moved towards the top. This was confirmed by the high specific COD consumption rate near the inlet and poor specific COD biodegradation in the remaining portions of the bioreactor. Apparently, the assumption of a completely mixed sludge bed behavior for the UASB reactor, being part of an AnMBR system, does not hold for this type of reactor systems even at low temperatures, which makes the location in sludge bed from where the sludge is to be conveyed to the digester of operational importance. Considering the observed sludge bed stratification, the sludge to be recirculated from the UASB reactor to the digester is recommended to be taken from 40 to 50% of the sludge bed height.

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Submerged and external anaerobic dynamic membrane bioreactors (AnDMBRs) have been compared in terms of removal efficiency, filtration characteristics and microbial community structure. High COD removal efficiencies were obtained with both submerged and external AnDMBRs. To obtain an effective dynamic membrane (DM) layer enabling high quality permeate, longer time was required in the external AnDMBR configuration compared to the submerged one. A difference in microbial community structure was identified using pyrosequencing analyses between the submerged and external AnDMBRs. The number of archaeal types decreased in the bulk sludge of the external AnDMBR. External sludge recirculation might have had a negative effect on the archaeal community in the bulk sludge of the external AnDMBR. However, the sludge recirculation in the external AnDMBR configuration led to a filtration at lower total filtration resistance and TMP in comparison to the submerged one at the same gas sparging rate. Results showed that the submerged AnDMBR system can provide a shorter start-up period, slightly better permeate quality in terms of COD concentration, and higher biogas production in comparison to the external one in gas-lift mode.

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BACKGROUND: Membrane technology is used for the treatment of produced water enabling high permeate quality to meet discharge standards or potable and irrigation water quality standards. In this study, the effect of hybrid membrane-activated carbon processes on the performance of nanofiltration (NF) and reverse osmosis (RO) membrane systems treating mixed oil and gas field produced water was investigated. Different pre-treatment alternatives including combinations of microfiltration unit and powdered activated carbon (PAC) or granular activated carbon (GAC) systems were applied prior to nanofiltration and reverse osmosis processes. RESULTS: The activated carbon process increased chemical oxygen demand (COD) and conductivity removal efficiencies due to the organic matter and ion adsorption capacity of activated carbon. PAC addition gave the best removal efficiencies for COD, whereas highest conductivity removals were obtained in studies with GAC addition. CONCLUSION: Differences obtained in the performance of different pre-treatment alternatives based on targeted pollutants and membrane characteristics confirmed synergetic/antagonistic effects between pre- and final membrane treatment.

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A laboratory scale external anaerobic dynamic membrane bioreactor (AnDMBR) treating high strength wastewater (influent COD ≈ 20 g/L) was operated to assess the effect of biogas sparging velocity (GSV) and hydraulic retention time (HRT) on removal efficiency and dynamic membrane (DM) filtration characteristics. An increase in GSV resulted in a decrease in DM filtration resistance. DM or cake layer was identified as the main contributor to the total filtration resistance. The external AnDMBR achieved over 99% COD removal efficiency irrespective of the GSV. The results showed that the DM formation process proceeded until a stable cake layer was reached. Reducing of HRT resulted in an increase in protein/carbohydrate ratio in soluble microbial products (SMP) and an increase in biomass concentration in the bioreactor. Therefore, HRT affected TMP and total filtration resistance in the AnDMBR. A high permeate quality was obtained by an effective DM layer at organic loading rates (OLRs) between 2 and 3.6 kg COD/m³ d. Based on the fluxes observed in this research, the filter cloth costs would be in the range of 0.17 €/m³ of treated wastewater. The investment and operational costs of the AnDMBRs are expected to be substantially lower than that of conventional membrane filtration.

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In the last 40 years, anaerobic sludge bed reactor technology has evolved from localized laboratory-scale trials to worldwide successful implementations in a variety of industries. High-rate sludge bed reactors are characterized by a very small footprint and high applicable volumetric loading rates. Best performances are obtained when the sludge bed consists of highly active and well settleable granular sludge. Sludge granulation provides a rich microbial diversity, high biomass concentration, high solids retention time, good settling characteristics, reduction in both operation costs and reactor volume, and high tolerance to inhibitors and temperature changes. However, sludge granulation cannot be guaranteed on every type of industrial wastewater. Especially in the last two decades, various types of high-rate anaerobic reactor configurations have been developed that are less dependent on the presence of granular sludge, and many of them are currently successfully used for the treatment of various kinds of industrial wastewaters worldwide. This study discusses the evolution of anaerobic sludge bed technology for the treatment of industrial wastewaters in the last four decades, focusing on granular sludge bed systems.@en

Anaerobic membrane bioreactors (AnMBRs) physically ensure biomass retention by the application of a membrane filtration process. With growing application experiences from aerobic membrane bioreactors (MBRs), the combination of membrane and anaerobic processes has received much attention and become more attractive and feasible, due to advantages provided by the combination with regard to developments for energy-efficient wastewater treatment. The major drawbacks of MBR technology are related with membrane costs, especially for the full-scale applications, fouling and low flux. Dynamic membrane (DM) technology may be a promising approach to resolve the drawbacks encountered in MBR processes. One of the most important potential benefits of DMs is that the membrane itself may be no longer necessary, because solids rejection is accomplished by the secondary membrane layer that can be formed and re-formed as a self-forming DM in situ. Different kinds of materials such as mesh, woven or nonwoven fabric instead of microfiltration and ultrafiltration membranes can be used as the support layer for creating DM. In this way, the replacement of the membrane by a low cost filter material is possible. By decreasing membrane cost and generating energy, dynamic AnMBRs (AnDMBRs) would be attractive for waste(water) treatment. The main aim of this study was to investigate the applicability of DM technology for the treatment of concentrated wastewaters in AnMBRs. Moreover, this thesis provides additional information and understanding of DM technology, including assessment of DM formation and filtration characteristics under different conditions. Submerged and external membrane module configurations were used in order to determine the effect of the configuration on removal efficiency and DM filterability. Synthetic concentrated wastewater with an average COD concentration of 20 g/L was used as the substrate. Determination of an optimal support material and investigations about its structure were achieved by testing various types of support materials including monofilament, multifilament and staple yarn types. Besides, different operating conditions were tested at low fluxes under mesophilic conditions to determine the optimal operation conditions enabling the optimal removal efficiency and permeate quality. Moreover, cost estimation in terms of support material acquisition was also presented. The results show that support material properties were critical for the formation of an effective dynamic membrane (cake) layer over the filter surface. The critical fluxes obtained with the staple and monofilament filter cloths were higher than those obtained with multifilament material. The results indicate that staple filter cloth was more suitable for depth 8 filtration, whereas mono-monofilament filter was more suitable for surface (cake) filtration. Thus, mono-monofilament filter was considered more appropriate for DM technology. The results presented in this thesis show that the DM filtration concept can turn one of the most important disadvantages of MBRs, membrane fouling, into an advantage. Polypropylene mono-monofilament filter cloth was used to form a dynamic membrane (cake) layer and to provide filtration by this self-forming layer as an alternative to microfiltration or ultrafiltration membranes. The AnDMBR achieved over 99% organic matter removal and particulate matter retention. Moreover, over 60% soluble COD removal and over 50% VFA removal were obtained by the DM layer. Considering the results of this research, it was shown that a stable operation with AnDMBRs could be possible for a long period. Sludge retention time (SRT) was found an important factor in AnDMBRs that had a significant effect on soluble microbial products (SMP) and extracellular polymeric substances (EPS) production, protein/carbohydrate ratio, particle size of the sludge, DM layer formation and bulk sludge filterability. Bound EPS is mainly composed of cell surface materials, including proteins, polysaccharides, lipids, nucleic acids and humic acids. EPS keeps the sludge flocs together on the membrane surface by surrounding them. EPS had a significant positive effect on particle flocculation and thus, particle size distribution in the bulk sludge. Prolonged SRT resulted in lower EPS concentrations in the bulk sludge compared to short SRTs. A combination of backwashing and biogas sparging enabled the control of DM layer thickness, which is of great importance to obtain a stable operation and high quality permeate. A combined effect of biomass activity and physical retention capacity through the cake layer might be responsible for the removal of organic matter and retention of particulate matter by the DM layer. Pyrosequencing analyses showed that diversity and richness of the microbial communities including bacteria and archaea in the DM layer were high and microbial population composition in the DM layer was different compared to the bulk sludge in the AnDMBR. Following the DM layer morphological analyses results, the DM layer was formed by both organic and inorganic materials, such as sludge particles, SMP, EPS, Ca, N, P, and Mg precipitates. Moreover, a partial gel layer formation under the cake layer was detected. Accumulation of SMP and bound EPS in the DM layer in high amounts led the formation of a dense cake layer and effective retention. Accumulation of organic matters is also related with operating conditions such as SRT. This research also showed that although slightly better permeate quality in terms of COD concentration was obtained by submerged AnDMBR, high COD removal efficiencies were achieved in both submerged and external AnDMBR configurations. Comparison of the effects of membrane configuration on treatment and filterability performance showed that more time was needed in the external AnDMBR in order to form an effective DM layer enabling a stable removal efficiency and low soluble COD concentration in the permeate. Therefore, submerged AnDMBR configuration appears more suitable when a short start-up period is 9 necessary. Higher methane production rate and methane yield were obtained in the submerged configuration compared to the external configuration reflecting the negative effect of sludge recirculation in the external DM configuration. Conversely, sludge recirculation in the external configuration was more effective in decreasing DM thickness, thus transmembrane pressure, than the bottom biogas sparging in the submerged configuration. Considering the tested different gas sparging velocities (GSVs), over 99% organic removal was obtained with the external AnDMBR configuration for high strength wastewater treatment irrespective of the GSV, although total filtration resistance increased with decreasing GSV. Total filtration resistance mainly consisted of the resistance by the DM layer that provided effective and stable treatment. Following the organic loading rate study, the AnDMBR achieved high COD removal efficiency at 3.6 kg COD/m3.d. In conclusion, following the results obtained in this study, DM technology achieved a stable and high quality permeate. Thus, AnDMBRs can be used as a reliable and satisfactory treatment technology for treatment of high strength wastewaters. Low capital costs of support material and energy generation can make AnDMBRs feasible for those situations in which a high flux is not necessary, such as sludge and slurry treatment or highly concentrated industrial wastewater treatment. However, research on AnDMBRs is still very limited. Longterm applicability and reliability of the DM applications need further research, focusing on cake layer control methods to allow satisfactory DM layer formation as well as on the effect of sludge properties on DM filtration characteristics for large-scale applications.@en