Specific Methanogenic Activity Research Articles

Study on the feasibility of carbon source recovery by upflow anaerobic sludge blanket in simulated municipal wastewater

The influence of hydraulic retention time (HRT) on the granulation process, methane-producing capacity, microbial community structure, and pollutant removal efficiency of an up-flow anaerobic sludge blanket (UASB) with simulated municipal wastewater at a mesophilic temperature was investigated. The carbon recovery capacity of the anaerobic fermentation of municipal wastewater at mesophilic temperatures is one of the problems to be investigated for the realisation of carbon neutrality in municipal wastewater treatment plants. In this study, the HRT was gradually shortened (24–6 h), and the effluent chemical oxygen demand (COD), ammonia nitrogen, pH, volatile fatty acid concentration, and specific methanogenic activity (SMA) were investigated. The sludge morphology, the particle size distribution of the different HRT, and changes in the microbial community structure were determined by scanning electron microscopy, wet screening, and high-throughput sequencing. The results indicated that even if the COD concentration was only 300–550 mg/L, with a decrease in HRT, the proportion of granular sludge in the UASB still exceeded 78 %, and the COD removal efficiency reached 82.4 %. The SMA of granular sludge increased with an increase in the size of granules and was 0.289 g CH4-COD/(g VSS d) at an HRT of 6 h, but the proportion of dissolved methane in the effluent accounted for 38–45 % of the total methane production and the proportion of Methanothrix in UASB sludge was 82.44 %. In this study, dense granular sludge was obtained by gradually shortening the HRT to start the UASB, and the lower effluent COD reduced the load of subsequent treatment processes, which could be used as a low carbon/nitrogen ratio influent for activated carbon-activated sludge, activated sludge-microalgae, and partial nitrification-anaerobic ammonia oxidation processes.

How anaerobic sludge microbiome respond to different concentrations of nitrite, nitrate, and ammonium ions: a comparative analysis.

High concentrations of ammonium, nitrite, and nitrate always induce inhibition in anaerobic wastewater treatment. Due to the complexity and vulnerability of the microbial community (especially methanogens) in anaerobic sludge, little is understood about its underlying microbial mechanism under such inhibition. In this study, the shifts of microbial communities in anaerobic sludge under increasing levels of nitrite, nitrate, and ammonium ions were compared. Results show that although half maximal inhibitory concentrations (methanogenesis) were different for nitrite, nitrate, and ammonium ions with EC50 values of 12, 30, and 3000mg N/L, respectively, bacteria genera Kosmotoga and Brooklawnia dominated in all of the three high-stress inhibitory systems. Network analysis and redundancy analysis (RDA) of the microbial community showed the treatments with nitrate and nitrite ions decreased the modularity of anaerobic microorganisms. RDA showed that specific methanogenic activity was positively related to coenzyme F420 under nitrite inhibition (rp = 0.833, p < 0.05) and closely correlated with viability under nitrate inhibition. Gram-positive and nonmotile Brooklawnia genus showed a negative correlation with physiological characteristics in the ammonia treatments, suggesting its high resistance to ammonia.

Accelerated performance recovery of anaerobic granular sludge after temperature shock: Rapid construction of protective barriers (EPS) to optimize microbial community composition base on quorum sensing

Poor temperature shock resistance of anaerobic granular sludge (AnGS) is one of its main disadvantages. In this study, enhancing the temperature shock resistance of AnGS by regulating quorum sensing (QS) based on the exogenous addition of N-acyl homoserine lactones (AHLs) was investigated, and the regulatory mechanism of AHLs-mediated QS based on extracellular polymeric substances (EPS) action in AnGS was revealed. The results indicated that adding 10 μM AHLs significantly enhanced the COD removal (increased by 9.3 ± 1.2%) and specific methanogenic activity (increased by 15.2 ± 3.6%) of AnGS after temperature shock, and the recovery time was reduced by 4 days. The sludge breakage and particle size reduction induced by temperature shock were attenuated by AHLs-mediated QS. Meanwhile, exogenous AHLs increased EPS concentration and the number of hydrophobic functional groups in AnGS. The addition of 10 μM AHLs reduced the ratio of Firmicutes to Bacteroidota (decreased by 0.17 ± 0.01), leading to higher microbial community stability. The enrichment of major functional bacteria (Bacteroidota, Desulfobacterota and Firmicutes) and hydrogenotrophic methanogens (Methanothermobacter and Methanobacterium) was promoted by 10 μM AHLs. The increased EPS induced by AHLs provided the protection for microbial community optimization, leading to the rapid recovery of the temperature-shocked AnGS performance. This study provided a new comprehensive insight into the regulatory mechanisms of AHLs-mediated QS in AnGS.

Achieving high electrogenic output from microbial fuel cell by chloroform-biotin pretreatment of wetland soil inoculum

Bioelectricity generation by microbial fuel cell (MFC) is governed by the electrogenic microbes, whereas presence of non-electrogenic microbes, mainly the methanogens hamper its performance. Chloroform is known to suppress methanogens while its effect on electrogenic microbes is not well documented. In this study, a novel biotin-chloroform combination was used for pretreatment of the inoculum to neutralize any negative effect of chloroform and promote the growth of electrogenic bacteria by using biotin, a vitamin. The aim is to enhance power generation by MFC through pretreatment of wetland soil inoculum with acid (MFC-A), chloroform (MFC-Ch), and biotin-chloroform combination [MFC-(Ch+B)], while nontreated inoculum (MFC-NT) served as control. The novel biotin-chloroform pretreatment in MFC-(Ch+B) exhibited a distinctively superior performance, yielding high power density (5.79 W/m3), which was about 81% higher than that of control, MFC-NT (3.2 W/m3), 37% higher than that of MFC-A (4.23 W/m3) and 21% higher than that of MFC-Ch (4.8 W/m3). With pretreatment inoculum, COD removal in MFCs was, however, reduced, which can be attributed to the partial elimination of microbial communities. Coulombic efficiency was much higher in response to pretreated inoculum, particularly in MFC-(Ch+B). Estimation of the specific methanogenic activity in the MFC anodes indicated less methane production on pretreatment of inoculum with acid (0.102 mLCH4/gVSS.d), chloroform (0.096 mLCH4/gVSS.d) and Ch+B (0.095 mLCH4/gVSS.d) treatment compared to that of control (0.226 mLCH4/gVSS.d). This further implies that while chloroform suppresses methanogens, biotin supplement is majorly boosting electrogenic activity rather than affecting methanogenic activity in the MFC anode.

Promoting the Circular Economy on an Island: Anaerobic Co-Digestion of Local Organic Substrates as a Possible Renewable Energy Source

The local waste co-digestion is an interesting option to tackle in reduced and isolated areas like the islands. The islands have limited territory and scarce fuel production. Moreover, organic waste can create serious environmental problems in soil, water and air. Anaerobic co-digestion (AcoD) is a technology fulfilling the concept of waste-to-energy (WtE) based on local resources. The valorisation of organic waste through AcoD on an island would prevent environmental impacts, while being a source of renewable energy. In this study, cow manure (outdoor and indoor), pig slurry, bird manure, kitchen waste, sewage sludge and oily lacteous waste produced on Island Terceira (Portugal) were tested in mesophilic -35 °C- Biochemical Methane Potential (BMP) co-digestion assays. The goals were to analyse the recalcitrant and high potential produced waste and to estimate the energetic supply source on the island. The cow manure and pig slurry were used as inocula and specific methanogenic activities (SMAs) were carried out. The results showed that both substrates have a significant methanogenic activity-SMA 0.11 g-COD/(g-VSS.d) and 0.085 g-COD/(g-VSS.d), respectively. All the studied combinations were feasible in AcoD, showing TS removals in the range of 19-37%; COD removals in the range 67-78% and specific methane yields from 0.14 to 0.22 L/gCOD removed, but some differences were found. The modified Gompertz model fitted the AcoD assays (R2 0.982-0.998). The maximum biogas production rate, Rmax. was highest in the AcoD of Cow+Pig+Oily and in the Cow+Pig+Sludge with 0.017 and 0.014 L/g-VSadded.day, respectively, and the lowest in Cow+Pig+Bird with 0.010 L/g-VSadded. In our AcoD studies, the bird manure limited the performance of the process, since it was recalcitrant to anaerobic degradation. On the other hand, the oily lacteous waste showed a great potential in the anaerobic digestion. The estimated biogas production, from the best-studied condition, could cover the 11.4% of the energy supply of the inhabitants. These preliminary results would prevent the environmental impact of organic waste on the island and promote the use of local waste in a circular economy scenario.

Biodegradation mechanism of perfluorooctane sulfonic acid (PFOS) in domestic sewage: Specific methanogenic activity, molecular biology, and ecotoxicological aspects

Among the perfluorinated compounds (PFCs), perfluorooctane sulfonic acid (PFOS) is one of the most used ones worldwide, specially in the textile industry as a surfactant. In addition, this contaminant is present in several products, such as: fire extinguisher foams, insecticides formulations, electronic devices, and kitchen products. PFOS is an endocrine disruptor, undergoes bioaccumulation, resists to biological degradation, and has been detected in human blood, animals, dusts, sediments, surface waters, and groundwater as well. Therefore, this research aimed at assessing the degradation of PFOS (100 μg L−1) in anaerobic conditions using simulated domestic sewage as co-substrate. After 10 days, at pH 6 and 35 °C, a 24 % PFOS degradation was achieved. In this period of time, inhibition of specific methanogenic activity (SMA) and changes to the microbial consortium (Archaea and Bacteria Domains) were not observed. The biodegradation products (BPs) were identified by high performance liquid chromatography coupled to high resolution mass spectrometry (HPLC-MS). One of them is reported here for the first time: C4F9CHO (2,2,3,3,4,4,5,5,5-nonafluoropentanal). BPs acute and chronic ecotoxicities for three aquatic organisms (fishes, daphnids, and green algae) and lipophilicity (log D, pH 7.4) were estimated using the ECOSAR 1.11 and Chemicalize software, respectively. Taken as a whole, they presented increased lipophilicities and ecotoxicities compared to PFOS. The present study showed, for the first time, that PFOS degradation is possible by a biological process in anaerobic conditions (although low efficiencies were achieved). Three possible degradation mechanisms were proposed.

Assessment of Specific Methanogenic Activity from Cow Dung

The specific methanogenic activity (SMA) is a test to measure the producing potential of an anaerobic bacteria until it’s allowing a relevant organic loading rates to be applied for a selectedsubstrate. Commonly, acetate is used as substrate for the SMA test. Anaerobic bacteria were mostly taken from an anaerobic digester and cow dung was also implemented as a source of an anaerobic bacteria. However, the results of SMA of cow dung was less reported. Therefore, this study is initiated to determine the potential of methane production from the cow dung by using the SMA test. Prior the SMA test, the cow dung was characterized for solids where the results showed that the cow dung is having 12.00 g L-1for total solid and 10.50 g L-1for volatile solid. The SMA test was conducted at mesophilic condition by using an automatic methane potential system test (AMPTS II) and the SMA of the cow dung was found as 0.04 in unit g COD-CH4g-1VS-1d-1. The significance of this research is to determine the anaerobic bacteria potential of cow dung for use in the anaerobic digestion process, which offers numerous advantages for manufacturing, particularly in industrial applications such as methane production (fuel).

Effect of anthraquinone-2,6-disulfonate on anaerobic digestion of fracturing flowback fluid under high salinity stress

The anaerobic digestion has been proved to be effective in treating fracturing flowback fluid. However, the high salinity in fracturing flowback fluid seriously inhibits the anaerobic treatment performance. A new strategy was proposed to improve the anaerobic digestion of fracturing flowback fluid under high salinity stress by adding anthraquinone-2,6-disulfonate (AQDS) in this study. The results showed that the addition of AQDS (45 mg/L) effectively alleviated the inhibition of high salinity (25 g/L) on the anaerobic digestion of fracturing wastewater, COD removal efficiency and cumulative methane yield increased by 17.8 % and 30.2 %, respectively. AQDS could alleviate the damage of anaerobic microorganisms caused by high salinity, the proportion of the damaged cells in anaerobic granular sludge decreased from 68.9 % to 38.3 %. Moreover, AQDS promoted the metabolic activity of anaerobic granular sludge under high salinity stress. The specific methanogenic activity, coenzyme F420 and dehydrogenase of anaerobic granular sludge increased by 30.0 %, 21.1 % and 21.4 %, respectively. Electrochemical analysis results showed that the addition of AQDS improved the electron transport of the anaerobic digestion system, and electron transport system activity increased by 62.4 %. This study provides an attractive strategy to alleviate the inhibition of high salinity on anaerobic digestion performance of fracturing flowback fluid.

Simultaneous methanogenesis and denitrification coupled with nitrifying biofilm for high-strength wastewater treatment: Performance and microbial mechanisms

A combined system consisting of an upflow blanket filter (UBF) and a moving-bed biofilm reactor (MBBR) was developed for the simultaneous removal of organic matters and ammonia from high-strength wastewater. With a constant COD of approximately 2000 mg/L and ammonium nitrogen in a series of concentrations (e.g., 50, 200 and 400 mg/L in stages I to III) of the influent wastewater, the removal efficiencies of COD, ammonium nitrogen and total nitrogen reached 96.10%-98.19%, 100%, and 79.12%-82.15%, respectively. With the increase of influent ammonia nitrogen concentration, the specific methanogenic activity of the UBF granules decreased significantly, while the specific denitrification rates of the UBF granules and specific nitrification rates of the MBBR biofilms increased significantly. Microbial community analysis showed that Methanobacterium and Methanosaeta were the dominant methanogens in the UBF granules, while Candidatus Competibacter, Thauera and Acinetobacter were identified as dominant denitrifiers. In addition, nitrifiers were enriched in MBBR biofilms at 11.33% and 13.87% of the average abundance of Nitrosomonas and Nitrospira, respectively, at stage III (influent ammonium at 400 mg/L, COD/NH4+-N = 5). The ecological network analysis, including full-networks and sub-networks, indicated that the interactions between methanogens and denitrifiers in the UBF granules were strong when the influent ammonium concentration reached 400 mg/L. No intensive interactions were observed among the functional bacteria in the MBBR biofilms over the entire operation. Overall, this study provides a new strategy for the application and construction of efficient biological processes to achieve simultaneous removal of organic matter and nitrogen for high-strength wastewater treatment.

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.

Effects of short-term inhibition of Tetracyclines and Macrolides on specific methanogenic activity and swine biodegradability

Limited studies have examined kinetic models related to the impact of antibiotics on acetoclastic methanogenesis and swine wastewater biodegradability, which can be useful for improvement and correct operation of anaerobic systems. Many researchers have evaluated the inhibition on this main methane-producing pathway by antibiotics individually but in rare cases as a mix. Thus, two tetracyclines: oxytetracycline (OTC) and tetracycline (TCN) and one macrolide: tylosin (TYL) were used separately and in combination OTC+TCN+TYL (MIX) to evaluate their inhibition effects. Short-term inhibition assays are useful to evaluate the antibiotics impact detected on swine wastewater specific methanogenic activity (SMA) and biodegradability (BD) at different concentrations of antibiotics (15, 30 and 45 μ g/mL); OTC and MIX showed the highest inhibition on SMA (78 and 76%, respectively) while the lower one was on methane production at 45 μ g/mL of MIX (61%). The assays with swine wastewater showed that OTC and TCN had the highest inhibition on BD at 45 μ g/mL, 71 and 51%, respectively. As expected, the maximum decrease in methane production (43.0% and 56.0%, respectively) occurred in the assays with the highest OTC and MIX concentrations, while TYL did not impact methane production in all assays. In specific activity, the results showed half-maximal inhibitory OTC concentrations (3.8 and 2.8 μ g/mL) in SMA and BD assays, respectively, while OTC recorded in methane production 4.5 and 54 . 2 μ g /mL in SMA and BD assays, respectively. These results indicate that antibiotics affect specific methanogenic activity and biodegradability more than methane production and inhibition was proposed as uncompetitive. • SMA is 80% inhibited when OTC concentration is up to 45 μ g/mL. • Combined toxicities of antibiotic MIX present a highest negative synergistic effect. • The propose kinetic model describe the inhibition of OTC, TCN and TYL on SMA and BD. • The observed effect of antibiotics was compatible with uncompetitive inhibition.

Electrical voltage application as a novel approach for facilitating methanogenic granulation

Despite having high-rate methanogenic performance, up-flow anaerobic sludge blanket reactor still has challenges regarding long-start up period (3–8 months) for granulation. In this study, “electrical voltage (EV, 0.3 V) application” was attempted for facilitating granulation in the continuous operation with increased organic loading rates (0.5–11.0 kg COD/m3/d). Up to 11.0 kg COD/m3/d, EV-reactor exhibited the stable performance, while the control failed. After 49 days of operation (at 7 kg COD/m3/d), the granules collected from EV-reactor had larger diameter (2.3 vs 1.6 mm), higher settling velocity (2.6 vs 1.9 cm/s), and higher hydrophobicity (52.1 % vs 34.5 %), compared to the control. EV application also increased the specific methanogenic activity for propionate and hydrogen almost by two times. The relative abundance of Pseudomonas sp. (quorum sensing (QS)-related microbe) in EV-reactor was 17 % higher than that in the control. In addition, EV application increased the expression of QS genes significantly by 27 times.

Heterogeneous photocatalysis and an anaerobic biological process for leachate treatment

The research used a coupling heterogeneous photocatalysis (TiO2-UVsolar) and an anaerobic biological process (Specific Methanogenic Activity Test) to study the treatment of leachate from a landfill in Norte de Santander (Colombia). It developed photocatalysis in a Composite Parabolic Collector (CPC), H2O2 as oxidation assistant, and the combination of different TiO2 levels and pH modeled with a factorial design 32. In the biological test, for a maximum load of 4,500 mg. L-1 of Chemical Oxygen Demand (COD) leachate, 2.0 g. L-1 of Volatile Suspended Solids (VSS) inoculum, and a hydraulic retention time of 23 days, there were no significant COD removal percentages, evidencing the recalcitrant character of these leachates. In the Advanced Oxidation Process (AOP) there was mineralization in terms of DOC of 57%, which evidences the capacity of the process to support the pollutant load of the leachate. The combined process (AOP-Biological) allows additional mineralization in terms of DOC of 21% in the biological process, for a total contribution of the coupling of 78%, which shows the capacity of the AOP to convert toxic wastewater into one with characteristics more suitable for its subsequent degradation in anaerobic biological reactors.

Sludge granulation in ASBR: Reactor performance, sludge physiochemical properties evolution and the unique clustered structure of the granular sludge

Anaerobic granular sludge was successfully cultivated in the anaerobic sequencing batch reactor (ASBR) after 45 days of operation. The results showed that the mature granular sludge exhibited better physicochemical characteristics: granule percentage of 62.6 ± 8.8 %, 0.8–1.2 mm in diameter, with smooth edges and regular shapes, and sludge volume index of 20.0 mL/g SS. 16S rRNA-targeted fluorescence in situ hybridisation (FISH) and scanning electron microscope (SEM) examination revealed that the granular sludge had a unique clustered microbial community structure, which would to be an optimal microbial arrangement for syntrophic colonies. The large substrate concentration gradient that derived from the feast-famine alternation regime of the substrate in a running cycle of ASBR was the major cause of the clustered microbial distribution structure. Lots of syntrophic consortia formed by acetogens and methanogens randomly distributed throughout the interior of the granules, furthermore, the cavities existing amongst the syntrophic consortia were convenient for substrate transfer and biogas liberation, thus enhancing the digestion performance of ASBR and preventing granule disintegration caused by gas scour. With sludge granulation, the methane yield of ASBR increased from the initial 0.23 L/g COD to 0.28 L/g COD, meanwhile, the maximum specific methanogenic activities (SMAs) of acetoclastic and hydrogenotrophic methanogens respectively increased from 0.51 gCOD/(gVSS·d) to 0.73 gCOD/(gVSS·d) and from 0.35 gCOD/(gVSS·d) to 0.62 gCOD/(gVSS·d). The exploration of granular sludge formation, sludge characteristic evolution and treatment performance in ASBR reactor has theoretical value for its engineering promotion.

Inoculum production from pig slurry for potential use in agricultural biogas plants

Biogas production may benefit from the use of specialized microbial consortia (inocula) to increase biogas yields in anaerobic digesters. For this study, a specialized inoculum was obtained from raw pig slurry by applying an innovative procedure. The aims of this research were: i) to compare the performance of this inoculum in the anaerobic digestion (AD) of four agricultural feedstocks with that of digestates commonly used for bioaugmentation of agricultural biogas plants; ii) to assess the duration of the methanogenic activity of this inoculum. The nutrient content of the residual liquid from inoculum production for its potential re-use as fertilizer was also assessed. Specific methanogenic activity and specific methane yield of the inoculum from pig slurry were higher (+28% and + 39% on average) than those of the two digestates. The inoculum successfully maintained its AD performance, almost unchanged, for a prolonged storage period (up to one year). The residual clarified liquid from inoculum preparation contains nutrients and mineral salts at very low concentrations. A possible way to recycle it could be fertigation. Inoculum production from pig slurry represents an additional possibility of valorisation of animal waste, from the storage tank to land spreading, in a context of biorefinery.

METHANE PRODUCTION IN THE CO-DIGESTION OF LANDFILL LEACHATE WITH DOMESTIC SEWAGE AND THE METHANOGENIC ACTIVITY OF FULL-SCALE UASB REACTORS

The study aimed to individually assess the specific methanogenic activity of the sludge of 10 UASB reactors from a full-scale domestic sewage treatment plant (STP) and the sludge behavior under conditions of anaerobic co-digestion of leachate with domestic sewage in dilutions (v/v) of 0.1%, 1.0%, 2.5%, 5.0%, 10.0%, 25.0%, 50.0%, 75.0% and 100%. In order to compare the influence of the activity on co-digestion sludge, a parallel test was performed with sludge coming from the treatment of swine wastewater under the same conditions as the test with STP sludge. Specific methanogenic activity results showed the difference between STP sludge conversion capacities at each reactor, as well as preponderant conversion routes, which can have several origins within the mesh of factors that affect the units. Co-digestion analyses pointed out a better adaptation of piggery sludge to higher organic loads, such as the viability of up to 50% of leachate in relation to treated sewage volume, while the STP sludge showed a more delayed response in methane production. The best co-digestion condition was 10% leachate. The study highlights the possibility of increased leachate fractions in the co-digestion with domestic sewage with methane production potential, with incorporation of sludge from agro-industrial wastewater treatment.

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 30days. 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.

Biohydrogen and biomethane production from food waste using a two-stage dynamic membrane bioreactor (DMBR) system

This study examined a two-stage dynamic membrane bioreactor (DMBR) system for biohydrogen and biomethane production from food waste (FW) in mesophilic condition. The two-stage DMBR system enabled high-rate H2 and CH4 production from particulate feedstock by enhanced microorganism retention. Chemical energy in FW was recovered up to 79% as renewable energy. The highest average hydrogen production rate of 7.09 ± 0.42 L/L-d was observed at a hydraulic retention time (HRT) of 8 h in the H2-DMBR, while the highest CH4 average production rate of 0.99 ± 0.02 L/L-d was observed at an HRT of 6 d in the CH4-DMBR. The high specific methanogenic activity of 71.7 mL CH4/g VSS-d was maintained at the short HRT, which also contributed to the high MPR. The genus Clostridium was dominant in the H2-DMBR, while bacterial and archaeal populations in the CH4-DMBR were dominated by the class Clostridia and genera Methanobacterium and Methanosaeta, respectively.

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.