Operational mode and powdered activated carbon promoting syntrophic propionate oxidation during anaerobic digestion of complex organic substances.

Operational mode and powdered activated carbon (PAC) are key factors facilitating microbial syntrophy and interspecies electron transfer during anaerobic digestion, consequently benefiting process stability and efficient methanogenesis. In this study, continuous-flow reactor (CFR) and sequencing batch reactor (SBR), with and without the addition of PAC, respectively, were operated to examine their effects on system performance and methanogenic activity. Based on the cycle-test result, the PAC-amended CFR (CFRPAC) recorded both the highest methane yield (690.1 mL/L) and the maximum CH4 production rate (28.8 mL/(L·h)), while SBRs exhibited slow methanogenic rates. However, activity assays indicated that SBRs were beneficial for organics removal in batch experiments fed with peptone. Taxonomic and functional analysis confirmed that CFRs were optimal for proliferating oligotrophs (e.g., Geobacter) and SBRs were more suitable for copiotrophs (e.g., Desulfobulbus). Metagenomic analysis revealed that CFRs had efficient acetate metabolic pathways from propionate and ethanol, whereas SBRs did not, resulting in the buildup of propionate. Furthermore, Methanobacterium and Methanothrix were acclimated to the different operational conditions, while acetoclastic Methanosarcina and hydrogenotrophic Methanolinea were acclimated in SBRs (5.1-13.4%) and CFRs (0.3-1.7%), respectively. This study confirmed the enhancement of microbial syntrophy by the addition of PAC as well as the acclimation of electroactive bacteria (e.g., Geobacter) with complex organic substances.

Incorporating saline microalgae biomass in anaerobic digester treating sewage sludge: Impact on performance and microbial populations.

The aim of this study was to acclimate anaerobic prokaryotes to saline microalgae biomass. Semi-continuous experiments were conducted using two 1.5 L mesophilic reactors for 10 weeks, (hydraulic retention time of 21 days). The first reactor was solely fed with sewage sludge (control), while the second received a mixture of sewage sludge and microalgal biomass (80/20 %w/w) cultivated at 70 g·L-1 salinity. The in-reactor salinity reached after the acclimation phase was 14 g·L-1. Biomethane production was comparable between the control and acclimated reactors (205 ± 29 NmLMethane·gVolatileSolids-1). Salinity tolerance assessment of methanogenic archaea revealed that salinity causing 50% inhibition of methane production increased from 10 to 27 g·L-1 after acclimation. Microbial diversity analyses revealed notable changes in methanogenic archaea populations during co-digestion of saline microalgae biomass, particularly methylotrophic (+27%) and acetotrophic (-26%) methanogens. This study has highlighted the possibility of treating efficiently saline microalgae in co-digestion with sewage sludge in future industrial biogas plants.

Roles of entrapped bubbles in methanogenic granules under oscillating pressure: Respiration and embolization for intra-granular transport.

Anaerobic granular sludge plays a pivotal role in the treatment of concentrated organic wastewater. However, previous studies on intra- granular transport have generally overlooked lung-like respiration that expedites transport in response to fluctuating pressure. This study explored the activities of calcified and normal granules under simulated hydrostatic pressure oscillations. The results revealed a significant enhancement in the bioactivity of calcified granules under oscillating pressure, contrasting with the comparatively lower bioactivity observed in normal granules. The hypothesis posited that the gas pockets in calcified granules facilitated respiration as the functional structure. The presence of tiny bubbles exhibited a propensity for inducing clogging, thereby diminishing the capillary connectivity essential for substrate diffusion. The proposed respiration and embolization concepts decipher the distinct roles of entrapped bubbles in the granular bioactivity across diverse fluid states. This study offers valuable insights into the impact of fluidization on microscopic transport within granule-based bed reactors.

From start-up to maximum loading: An approach for methane production in upflow anaerobic sludge blanket reactor fed with the liquid fraction of fruit and vegetable waste.

This investigation provides a reproducible approach for determining the limits of an upflow anaerobic sludge blanket (UASB) reactor designed for the methanization of the liquid fraction of fruit and vegetable waste (FVWL). Two identical mesophilic UASB reactors were operated for 240 days with a three-day fixed hydraulic retention time and an organic load rate (OLR) increased from 1.8 to 10 gCOD L-1 d-1. Because of the previous estimation of flocculent-inoculum methanogenic activity, it was possible to design a safe OLR for the quick start-up of both UASB reactors. The operational variables obtained from the operation of the UASB reactors did not show statistical differences, ensuring the experiment's reproducibility. As a result, the reactors achieved methane yield close to 0.250 LCH4 gCOD-1 up to the OLR of 7.7 gCOD L-1 d-1. Furthermore, the maximum volumetric methane production rate of 2.0 LCH4 L-1 d-1 was discovered for the OLR ranges between 7.7 and 10 gCOD L-1 d-1. The possible overload at OLR of 10 gCOD L-1 d-1 resulted in a significant reduction of methane production in both UASB reactors. Based on the methanogenic activity of the UASB reactors sludge, a maximum loading capacity of approximately 8 gCOD L-1 d-1 was estimated.

Seasonal characterization of the prokaryotic microbiota of full-scale anaerobic UASB reactors treating domestic sewage in southern Brazil.

Upflow Anaerobic Sludge Blanket (UASB) reactors are alternatives in the anaerobic treatment of sanitary sewage in different parts of the world; however, in temperate environments, they are subject to strong seasonal influence. Understanding the dynamics of the microbial community in these systems is essential to propose operational alternatives, improve projects and increase the quality of treated effluents. In this study, for one year, high-performance sequencing, associated with bioinformatics tools for taxonomic annotation and functional prediction was used to characterize the microbial community present in the sludge of biodigesters on full-scale, treating domestic sewage at ambient temperature. Among the most representative phyla stood out Desulfobacterota (20.21-28.64%), Proteobacteria (7.48-24.90%), Bacteroidota (10.05-18.37%), Caldisericota (9.49-17.20%), and Halobacterota (3.23-6.55%). By performing a Canonical Correspondence Analysis (CCA), Methanolinea was correlated to the efficiency in removing Chemical Oxygen Demand (COD), Bacteroidetes_VadinHA17 to the production of volatile fatty acids (VFAs), and CI75cm.2.12 at temperature. On the other hand, Desulfovibrio, Spirochaetaceae_uncultured, Methanosaeta, Lentimicrobiaceae_unclassified, and ADurb.Bin063-1 were relevant in shaping the microbial community in a co-occurrence network. Diversity analyses showed greater richness and evenness for the colder seasons, possibly, due to the lesser influence of dominant taxa. Among the principal metabolic functions associated with the community, the metabolism of proteins and amino acids stood out (7.74-8.00%), and the genes related to the synthesis of VFAs presented higher relative abundance for the autumn and winter. Despite the differences in diversity and taxonomic composition, no significant changes were observed in the efficiency of the biodigesters.

Spatial distributions of granular activated carbon in up-flow anaerobic sludge blanket reactors influence methane production treating low and high solid-content wastewater.

The impacts of granular activated carbon (GAC) spatial distributions in up-flow anaerobic sludge blanket (UASB) reactors treating different solid-content wastewater were evaluated in the present study. When treating high solid-content wastewater, the highest methane yield was observed for UASB supplemented with self-floating GAC (74.2 ± 3.7 %), which was followed by settled + self-floating GAC reactor (65.1 ± 3.8 %), then settled GAC reactor (58.3 ± 1.4 %). When treating low solid-content wastewater, all UASBs achieved improved methane yield, and settled + self-floating GAC reactor achieved the highest methane yield (83.4 ± 3.3 %). Self-floating GAC amended reactor showed the best performance for treating high solid-content wastewater, while settled + self-floating GAC amended reactor was optimal for treating medium and low solid-content wastewater. The spatial distributions of microbial communities differed in the reactors with settled GAC and floating GAC. This study underlines the importance of considering feedwater characteristics when adopting GAC-based UASB processes.

Exploring key factors in anaerobic syntrophic interactions: Biomass activity, microbial community, and morphology.

The present work evaluated the impacts of microbial communities, biomass activity and sludge morphology on anaerobic syntrophic reactions. Experiments were conducted using mature floc sludge and granular sludge under different food/microbes ratios, and with different sludge types (floc sludge, concentrated floc sludge and granular sludge) and sludge morphology (granules, vortexed granules, and granules with different particle sizes). The results show that the intact granules achieved the most effective syntrophic reaction among all sludge types. The granule structure facilitated the enrichment of syntrophic acetate oxidation bacteria (g_Syner-01 and g_Mesotoga) and methanogens, which corresponds to their superior specific methanogenic activity and high production of communication compounds. Despite the high diffusion and substrate uptake capacities, the disintegrated granules had low H2 consumption rates, which led to poor syntrophic activities. The results underline the importance of sludge spatial structures in promoting excellent syntrophic activities and the development of diverse microbial communities.

The effects of ammonia acclimation on biogas recovery and the microbial population in continuous anaerobic digestion of swine manure.

This study investigated the ammonia toxicity and the acclimation of anaerobic microbiome in continuous anaerobic digestion of swine manure using unacclimated inoculum. When the total ammonia nitrogen concentration (TAN) reached 2.5 g N/L, the methane yield decreased from 254.1 ± 9.6 to 154.6 ± 9.9 mL/g COD. The free ammonia nitrogen concentration of the inhibited condition was 190 mg N/L. The methane yield was eventually recovered as 269.6 ± 3.6 mL/g COD with a further operation. Anaerobic toxicity assay (ATA) showed that mixed liquor from the recovered phase possessed enhanced tolerance to ammonia, not only within the exposed level in continuous operation (<2.5 g NH3/L) but also over the range (>2.5 g NH3/L). Microbial analysis revealed that continuous operation under ammonia stress resulted in the change of both bacterial and archaeal populations. The ammonia adaptation was concurrent with the archaeal population shift from Methanosaeta to Methanosarcina and Methanobacterium. The dominancy of Clostridia in bacterial population was found in the recovered phase. It is highly recommended to use an inoculum acclimated to a target ammonia level which can be pre-checked by ATA and to secure a start-up period for ammonia adaptation in the field application of anaerobic digestion for swine manure.

Need of adjustment of methanogenic activities from solids digester sludge: Modelling dilution effects on micro-organisms biomass concentration.

Anaerobic digestion is a widespread technology used for organic-based solid waste management. Specific methanogenic activity tests are simple and cost-effective tools for sludge characterization and system diagnosis. However, in solid digesters, substrate and organic inert material dilute micro-organisms, enlarging the activity tests and distorting experimental results. To correct this situation, correction factors, defined as the ratio of micro-organisms concentration to total volatile solids content, are considered. Due to the impossibility to have a quick measurement of the mass of micro-organisms in the digester content, correction factors were evaluated based on the simulation of a simple model. To verify the importance of the correction, hydrogenotrophic and acetoclastic methanogenic activities were studied, involving a stage for sludge acclimatization and subsequent processing in a continuous digester. This situation was compared with a wastewater up-flow anaerobic reactor where no dilution effects are presented. A correcting factor of 0.79 was obtained for the acclimatization period, whereas correcting factors of 0.25-0.30 were estimated for the two periods of the digester. Tendencies shown for raw activities differed from those observed after using correcting factors to adjust activity values for periods 1 and 2 of the digester; also, the gap between the up-flow anaerobic reactor (without solids dilution effects) and the digester activities was reduced from sixfold to double, evidencing the relevance of this correction tool. Additionally, correcting factors also enabled a reasonable calculation of the inoculum size during the design of the activity tests.

Bioremediation of Perfluoroalkyl Substances (PFAS) by Anaerobic Digestion: Effect of PFAS on Different Trophic Groups and Methane Production Accelerated by Carbon Materials.

Per- and polyfluoroalkyl substances (PFAS) are recalcitrant pollutants which tend to persist in soils and aquatic environments and their remediation is among the most challenging with respect to organic pollutants. Anaerobic digestion (AD) supplemented with low amounts of carbon materials (CM), acting as electron drivers, has proved to be an efficient process for the removal of organic compounds from wastewater. This work explores the impact of PFAS on different trophic groups in anaerobic communities, and the effect of carbon nanotubes (CNT), activated carbon (AC), and oxidized AC (AC-HNO3), as electron shuttles on the anaerobic bioremoval of these compounds, based on CH4 production. The inhibition of the specific methanogenic activity (SMA) exerted by perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), at a concentration of 0.1 mg L-1, was below 10% for acetoclastic and below 15%, for acetogenic communities. Hydrogenotrophic methanogens were not affected by the presence of PFAS. All CM reduced the negative impact of PFAS on the CH4 production rate, but AC was the best. Moreover, the methanization percentage (MP) of sewage sludge (SS) increased 41% in the presence of PFOS (1.2 g L-1) and AC. In addition, AC fostered an increase of 11% in the MP of SS+PFOS, relative to the condition without AC. AC promoted detoxification of PFOA- and PFOS-treated samples by 51% and 35%, respectively, as assessed by Vibrio fischeri assays, demonstrating the advantage of bringing AD and CM together for PFAS remediation.

Effect of fruits and vegetables in the anaerobic digestion of food waste from university restaurant.

The aim of this study was to evaluate the theoretical potential of methane production of the food waste generated by a university restaurant, as well as to verify the influence of the fruit and vegetable waste in the feeding composition of an anaerobic bioreactor treating this type of waste. Four feeding compositions combining three fractions of the food waste (fruit and vegetable fraction, soy protein and beans fraction, and rice fraction) at different concentrations were tested in anaerobic processes lasting 10 and 30 days. Additionally, a study of the theoretical potential of methane production from each fraction that composes the food waste was carried out, as well as the evaluation of the specific methanogenic activity of the anaerobic sludge. Despite its low theoretical potential of methane production (0.037 LCH4/g), the presence of the fruit and vegetable mixture in three of the feeding compositions led to greater organic matter degradation (above 69%) and CH4 yields (above 0.20 LCH4/gVS) in both periods tested, in comparison with the achieved by the feeding composition lacking this fraction. The results suggest that the presence of the fruit and vegetable mixture contributed with the supplementation of micro- and macroelements to the anaerobic sludge during the digestion of food waste.

Sodium nitrate as a methanogenesis suppressor in earthen separator microbial fuel cell treating rice mill wastewater.

The microbial fuel cell (MFC) is one of the sustainable technologies, which alongside treating wastewater, can generate electricity. However, its performance is limited by factors like methanogenesis where methanogens compete with the anode respiring bacteria for substrate, reducing the power output. Thus, sodium nitrate, which has been previously reported to target the hydrogenotrophic methanogens, was used as a methanogenic suppressor in this study. The performance of MFC with and without sodium nitrate was studied during the treatment of rice mill wastewater. A significantly higher power density and coulombic efficiency (CE) were noted in the MFC with sodium nitrate (MFCT) (271.26 mW/m3) as compared to the control MFC (MFCC) (107.95 mW/m3). Polarization studies showed lower internal resistance for the MFCT (330 Ω) as compared to MFCC (390 Ω). Linear sweep voltammetry and cyclic voltammetry indicated a higher electron discharge on the anode surface due to enhancement of electrogenic activity. Considerable reduction (76.8%) in specific methanogenic activity was also observed in anaerobic sewage sludge mixed with sodium nitrate compared to the activity of anaerobic sewage sludge without any treatment. Due to the inhibition of methanogens, a lower chemical oxygen demand (COD) and phenol removal efficiency were observed in MFCT as compared to MFCC. The COD balance study showed an increase in substrate conversion to electricity despite the increase in nitrate concentration. Therefore, selective inhibition of methanogenesis had been achieved with the addition of sodium nitrate, thus enhancing the power generation by MFCs.

Response of anaerobic granular sludge to long-term loading of roxarsone: From macro- to micro-scale perspective.

Extensive use of organoarsenic feed additives such as roxarsone has caused organoarsenicals to occur in livestock wastewater and further within anaerobic wastewater treatment systems. Currently, information on the long-term impacts of roxarsone on anaerobic granular sludge (AGS) activity and the underlying mechanisms is very limited. In this study, the response of AGS to long-term loading of roxarsone was investigated using a laboratory up-flow anaerobic sludge blanket reactor spiked with 5.0 mg L-1 of roxarsone. Under the effect of roxarsone, methane production decreased by ∼40% due to the complete inhibition on acetoclastic methanogenic activity on day 260, before being restored eventually. Over 30% of the influent arsenic was accumulated in the AGS and the capability of AGS to prevent intracellular As(III) accumulation increased with time. The AGS size was reduced by ∼30% to 1.20‒1.26 mm. Based on morphology and confocal laser scanning microscopy analysis, roxarsone exposure stimulated the excretion of extracellular polymeric substances and the surface spalling of AGS. High-throughput sequencing analysis further indicated roxarsone initially altered the acidogenic pathway and severely inhibited the acetoclastic methanogen Methanothrix. Acetogenic bacteria and Methanothrix were finally enriched and became the main contributor for a full restoration of the initial methane production. These findings provide a deeper understanding on the effect of organoarsenicals on AGS, which is highly beneficial for the effective anaerobic treatment of organoarsenic-bearing wastewater.

Exogenous N-acyl-homoserine lactones accelerate resuscitation of starved anaerobic granular sludge after long-term stagnation.

So as to accelerate the resuscitation of starved anaerobic granular sludge after long-term stagnation, an innovative method was tried derived from the regulation of N-acyl-homoserine lactones (AHLs)-mediated quorum sensing (QS). The mixture of four AHLs was added to the starved anaerobic granular sludge system in this research. The results confirmed that the exogenous AHLs shortened the recovery time of the granular sludge, and improved the treatment performance and methanogenic capacity of the recovered anaerobic sludge to the level before stagnation. At the same time, exogenous AHLs enhanced the synthesis of extracellular polymeric substances (EPS) during the resuscitation period of starved anaerobic granular sludge. The outcomes of microbial composition detection showed that the change of bacterial and methanogenic bacteria communities towards accelerated performance recovery was significantly correlated with exogenous AHLs. This exploration provided a new technical idea for speeding up the recovery of starved anaerobic granular sludge.

Applying EEM- PARAFAC Analysis With Quantitative Real-Time PCR to Monitor Methanogenic Activity of High-Solid Anaerobic Digestion of Rice Straw.

The methanogenic activity is an important indicator to assess the efficiency of high-solid anaerobic digestion. However, it is not yet elucidated clearly how to detect the parameter rapidly and reliably in the rice straw feeding reactor. Co-inoculated with ruminal digesta and anaerobic sludge, the digestion performance was studied at three different organic loading rates (OLRs). The excitation emission matrix-parallel factor analysis (EEM-PARAFAC) was used to detect dynamic changes in the characteristic of fluorescence components. Our results revealed that CH4 productivity reached 280.90 mL/g volatile solid (VS) with a 54.39% CH4 content under the OLR of 2.26 g/(L⋅d), which amount to 80.29% of its theoretical value. At the OLR of 2.47 g/(L⋅d), the average accumulated NH4 + concentration was 1082.63 mg/L, which resulted in the hydrogenotrophic Methanobacteriales decreasing from 1.70 × 109 to 1.04 × 106 copies/g in the solid residues, whereas the acetotrophic Methanosarcinales increased from 7.89 × 106 to 9.44 × 106 copies/g. The dynamics of the methanogenic community consequently influenced the bioconversion efficiency of rice straw, and CH4 productivity was reduced to 256.54 mL/g VS. The three fluorescent components, at the excitation/emission wavelength of 420 nm/470 nm, 340 nm/430 nm, and 280 nm/340 nm, were decomposed by PARAFAC model in the digestate. Fluorescence intensities of coenzyme F420 and NADH reflected the dynamic changes of CH4-producing activity and anaerobic digestion efficiency, respectively. The coenzyme F420, unique to hydrogenotrophic methanogens, was correlated with methane yield, suggesting they played a dominant role in the anaerobic reactor. This study demonstrates that the EEM-PARAFAC combined with Q-PCR can be used to characterize methanogenic activity variation during the high-solid anaerobic digestion of rice straw with 15% total solid (TS).

Evidence of thermophilic waste decomposition at a landfill exhibiting elevated temperature regions.

There have been several reports of landfills exhibiting temperatures as high as 80 to 100 °C. This observation has motivated researchers to understand the causes of the elevated temperatures and to develop predictive models of landfill temperature. The objective of this research was to characterize the methanogenic activity of microbial communities that were derived from landfill samples excavated from a section of a landfill exhibiting gas well temperatures above 55 °C. Specific objectives were to: (1) determine the upper temperature limit for methane production; (2) evaluate the kinetics of methane generation when landfill-derived microcosms are incubated above and below their excavation temperature and derive a temperature inhibition function; and (3) evaluate microbial community shifts in response to temperature perturbations. Landfill microcosms were derived from 57 excavated landfill samples and incubated within ±2.5 °C of their excavation temperature between 42.5 °C and 87.5 °C. Results showed an optimum temperature for methane generation of ~57 °C and a 95% reduction in methane yield at ~72 °C. When select cultures were perturbed between 5 °C below and 15 °C above their in-situ temperature, both the rate and maximum methane production decreased as incubation temperature increased. Microbial community characterization using 16S rRNA amplicon sequencing suggests that thermophilic methanogenic activity can be attributed to methanogens of the genus Methanothermobacter. This study demonstrated that from a microbiological standpoint, landfills may maintain active methanogenic processes while experiencing temperatures in the thermophilic regime (<72 °C).

Ciprofloxacin, diclofenac, ibuprofen and 17α-ethinylestradiol differentially affect the activity of acetogens and methanogens in anaerobic communities.

Pharmaceutical compounds end up in wastewater treatment plants but little is known on their effect towards the different microbial groups in anaerobic communities. In this work, the effect of the antibiotic Ciprofloxacin (CIP), the non-steroidal anti-inflammatory drugs Diclofenac (DCF) and Ibuprofen (IBP), and the hormone 17α-ethinylestradiol (EE2), on the activity of acetogens and methanogens in anaerobic communities, was investigated. Microbial communities were more affected by CIP, followed by EE2, DCF and IBP, but the response of the different microbial groups was dissimilar. For concentrations of 0.01 to 0.1 mg/L, the specific methanogenic activity was not affected. Acetogenic bacteria were sensitive to CIP concentrations above 1 mg/L, while DCF and EE2 toxicity was only detected for concentrations higher than 10 mg/L, and IBP had no effect in all concentrations tested. Acetoclastic methanogens showed higher sensitivity to the presence of these micropollutants, being affect by all the tested pharmaceutical compounds although at different degrees. Hydrogenotrophic methanogens were not affected by any concentration, indicating their lower sensitivity to these compounds when compared to acetoclasts and acetogens.

Hydrogenotrophic activity: A tool to evaluate the kinetics of methanogens.

Anaerobic-digestion-based technology is key to achieving sustainable water management and resource recovery. It is essential to understand the material flux and kinetics involved in methanogenesis to optimize the organic matter removal and methane production. In this sense, specific methanogenic activity is a cost-effective tool to characterize the biological activity of anaerobic biosludge, to monitor the performance of reactors, and study the kinetics of acetate and H2 conversion to methane. Established protocols are applied for the acetoclastic activity test. However, hydrogenotrophic activity assay remains less widespread and is not standardized. In this work, the assay design for hydrogenotrophic activity is discussed and full calculation is presented, based on the kinetics for the H2/CO2 conversion to methane. An equation to calculate the inoculum size is proposed, suitable for a wide variety of types of biosludge: from a wastewater treatment plant to solid digesters, from a high-rate reactor to lagoons. The applied zero-order model fitted adequately to data for pilot-scale and full-scale anaerobic reactors: the p-values from the ANOVA F-test were below 1E-03; standard deviations for triplicate experiments were between 3 and 12%, coherent with the values found in the literature. Microbial growth during the test was negligible, below 1.2% of the biomass dosed in the vial. As a complement, acetoclastic activity was determined for each sample. The use of both acetoclastic and hydrogenotrophic activity is relevant for the study of the methanogenesis and gives a better characterization of the performance of the biosludge in anaerobic reactors rather than only using the specific acetoclastic methanogenic activity.

Improved Performance of Microbial Fuel Cell by In Situ Methanogenesis Suppression While Treating Fish Market Wastewater.

The fish market wastewater, which is rich in ammonium concentration, was investigated to explore its ability of in situ suppression of methanogenesis in the anodic chamber of microbial fuel cell (MFC) while treating it and to ensure non-reoccurrence of methanogenic consortia in the anodic chamber during its long-term operations. A lower specific methanogenic activity (0.097g chemical oxygen demand (COD)CH4/g volatile suspended solids (VSS). day) with a higher power density (3.81 ± 0.19 W/m3) was exhibited by the MFC operated with raw fish market wastewater as compared to the MFC fed with synthetic wastewater (0.219g CODCH4/g VSS. day and 1.75 ± 0.09 W/m3, respectively). The enhanced electrochemical activity of anodic biofilm of MFC fed with raw fish market wastewater than the MFC fed with synthetic wastewater further advocated the enhanced electrogenic activity and suppression of methanogenesis, because of the presence of higher ammonium content in the feed. This, in response, reduced the internal resistance (55 Ω), enhanced the coulombic efficiency (21.9 ± 0.3%) and normalized the energy recovery (0.27 kWh/m3) from the MFC fed with fish market wastewater than the MFC fed with synthetic wastewater (92 Ω, 15.7 ± 0.3% and 0.13 kWh/m3, respectively). Thus, while treating the fish market wastewater in the anodic chamber of MFC, any costly and repetitive treatment procedures for anodic microorganisms are not required for suppression of methanogens to ensure higher activity of electrogenic bacteria for higher electricity harvesting.

Cation exchange membrane behaviour of extracellular polymeric substances (EPS) in salt adapted granular sludge.

This paper aims to elucidate the role of extracellular polymeric substances (EPS) in regulating anion and cation concentrations and toxicity towards microorganisms in anaerobic granular sludges adapted to low (0.22 M of Na+) and high salinity (0.87 M of Na+). The ion exchange properties of EPS were studied with a novel approach, where EPS were entangled with an inert binder (PVDF-HFP) to form a membrane and characterized in an electrodialysis cell. With a mixture of NaCl and KCl salts the EPS membrane was shown to act as a cation exchange membrane (CEM) with a current efficiency of ∼80%, meaning that EPS do not behave as ideal CEM. Surprisingly, the membrane had selectivity for transport of K+ compared to Na+ with a separation factor ( [Formula: see text] ) of 1.3. These properties were compared to a layer prepared from a model compound of EPS (alginate) and a commercial CEM. The alginate layer had a similar current efficiency (∼80%.), but even higher [Formula: see text] of 1.9, while the commercial CEM did not show selectivity towards K+ or Na+, but exhibited the highest current efficiency of 92%. The selectivity of EPS and alginate towards K+ transport has interesting potential applications for ion separation from water streams and should be further investigated. The anion repelling and cation binding properties of EPS in hydrated and dehydrated granules were further confirmed with microscopy (SEM-EDX, epifluorescence) and ion chromatography (ICP-OES, IC) techniques. Results of specific methanogenic activity (SMA) tests conducted with 0.22 and 0.87 M Na+ adapted granular sludges and with various monovalent salts suggested that ions which are preferentially transported by EPS are also more toxic towards methanogenic cells.