Anaerobic Membrane Reactor Research Articles

Methanogenic degradation of long-chain fatty acids associated with syntrophic microbial dynamics during thermophilic AnMBR treatment of lipid-rich dairy wastes

Anaerobic membrane reactors (AnMBRs) have been applied to effectively treat dairy wastes because they can address the drawbacks of sludge flotation and biomass washout. However, when dairy wastes contain considerable proportion of lipids, any anaerobic systems will likely encounter challenges with long-chain fatty acid (LCFA) inhibition. In this study, a thermophilic AnMBR was operated to treat dairy processing wastewater (DPW) plus ice cream waste (ICW). To evaluate the impact of LCFAs, the lipid-rich ICW was gradually introduced at different levels (0, 5, 10, and 20 %) into the AnMBR, along with a stepwise increase in lipid loading rate (LLR) from 0.22 to 11.24 g lipid/L/d. The results of biomethanation revealed that the AnMBR could be successfully operated when the LLR was maintained at 5.73 g lipid/L/d with a lipid/VS ratio of 50.22 % in the feedstock. However, at ultra-high LLR of 11.24 g lipid/L/d (20 % ICW added), a significant inhibitory effect on methane yields was observed, resulting in a reduction of 56.90 %. Dynamic analysis of the LCFAs profiled that a lower degradation rate was an important factor contributing to LCFA accumulation, and the inhibition concentration of various LCFAs was identified. Based on microbial evolution and co-occurrence network results, potential syntrophic partnerships between LCFA-degrading bacteria and methanogens were proposed. The responsible enzyme genes in the LCFA-degrading, acetoclastic, and hydrogenotrophic methanogenic pathways played crucial roles in LCFA inhibition and degradation. These findings offer practical insights for the efficient methanogenic treatment of lipid-rich wastes.

Synergetic association of hydroxyapatite-mediated biofilm and suspended sludge enhances resilience of partial nitrification/anammox (PN/A) system treating high-strength anaerobic membrane bioreactor (AnMBR) permeate

A single-stage partial nitrification/anammox (PN/A) system with biocarriers was used to treat the permeate from an anaerobic membrane reactor (AnMBR) processing organic fraction of municipal solid wastes. The suitable Ca/P ratio and high pH in the AnMBR permeate facilitated hydroxyapatite (HAP) formation, enhancing the biofilm attachment and the settleability of suspended sludge. This maintained sufficient biomass and a stable microbial structure after flushing to mitigate the free nitrous acid inhibition. Robust anammox bacteria in the biofilm and ammonia-oxidizing bacteria in the suspended sludge ensured that the PN/A system achieved an 87.3 % nitrogen removal efficiency at an influent NH4+-N concentration of 1802 mg/L. This study demonstrates that AnMBR permeate with high Ca, P and NH4+-N content is suitable for single-stage PN/A system with biocarriers due to the high resilience enhanced by HAP, offering a reference for the treatment of high-strength AnMBR permeate.

Bioenergy production from swine wastewater based on a combined process of anaerobic dynamic membrane reactor and microalgae cultivation: Feasibility and performance

Enhanced methane production and sustainable reduction of pollutants from anaerobic digestate are crucial for swine wastewater treatment. In this study, anaerobic dynamic membrane bioreactor (AnDMBR) was introduced to enhance methane production, then microalgae were cultivated on the digestate for nutrients recovery and lipid production. Results showed that pollutants can be effectively removed under various hydraulic retention time (HRT) conditions during long-term operation. Methanogenesis was enhanced with the reduction of HRT from 20 days to 10 days (0.23 L-CH4/g-CODremoved), but inhibited by shortening HRT to 5 days (0.09 L-CH4/g-CODremoved). Ammonia and phosphate in the digestate were effectively removed after microalgae cultivation. In addition, the highest microalgal biomass and lipid productivity (1.7 g/L and 17.5 mg/(L·d), respectively) were obtained using digestate ratio of 20 %, while microalgal growth was seriously restricted at high digestate content (>50 %). This work provides a prospective pathway for pollutants control and energy production from swine wastewater through integrating of AnDMBR technology with microalgae cultivation.

Long-term in-situ starvation and reactivation of co-digestion with food waste and corn straw in a continuous AnDMBR: Performance, sludge characteristics, and microorganism community

To explore the effects of in-situ starvation and reactivation in a continuous anaerobic dynamic membrane reactor (AnDMBR), the anaerobic co-digestion system of food waste and corn straw was firstly start-up and stability operated, and then stopped feeding substrate approximately 70 days. After long-term in-situ starvation, the continuous AnDMBR was reactivated using the same operation conditions and organic loading rate as the continuous AnDMBR used before in-situ starvation. Results shown that the anaerobic co-digestion of corn straw and food waste in the continuous AnDMBR can resume stable operation within 5 days, and the corresponding methane production of 1.38 ± 0.26 L/L/d was completely returned to the methane production before in-situ starvation (1.32 ± 0.10 L/L/d). Through analysis of the specific methanogenic activity and key enzyme activity of the digestate sludge, only the acetic acid degradation activity of methanogenic archaea can be partially recovered, however, the activities of lignocellulose enzyme (lignin peroxidase, laccase, and endoglucanase), hydrolase (α-glucosidase) and acidogenic enzyme (acetate kinas, butyrate kinase, and CoA-transferase) can be fully recovered. Analysis of microorganism community structure using metagenomic sequencing technology showed that starvation decreased the abundance of hydrolytic bacteria (Bacteroidetes and Firmicutes) and increased the abundance of small molecule-utilizing bacteria (Proteobacteria and Chloroflexi) due to lack of substrate during the long-term in-situ starvation stage. Furthermore, the microbial community structure and key functional microorganism still maintained and similar with that of starvation final stage even after long-term continuous reactivation. The reactor performance and sludge enzymes activity in the continuous AnDMBR co-digestion of food waste and corn straw can be well reactivated after long-term in-situ starvation, even though the microbial community structure can not be recovered to the initiating stage.

Bioaugmentation of the green alga to enhance biogas production in an anaerobic hollow-fiber membrane bioreactor

Anaerobic membrane reactors (AnMBRs) offer an alternative wastewater treatment system, presenting both reclamation of value through biogas production, and efficient treatment of recalcitrant contaminants such as antibiotics from wastewater. The effects of bioaugmentation with the green alga Haematococcus pluvialis on anaerobic treatment of pharmaceutical wastewaters, alleviating membrane biofouling, biogas production and impact on the indigenous microbial communities were evaluated using AnMBRs. The outputs of the bioreactor experiments revealed that bioaugmentation strategies with the green alga increased removal of chemical oxygen demand by 12% and delayed membrane fouling by 25% and increased biogas production by 40%. Furthermore, bioaugmentation with the green alga led to a significant change in relative abundance of archaea and the main methanogenesis pathway shifted from Methanothermobacter to Methanosaeta, accompanied by their respective syntrophic bacteria.

Microbial population dynamics and meta-proteomic evaluation for functional insight into an anaerobic membrane bioreactor during startup

Startup of an anaerobic membrane reactor (AnMBR) involves a significant concentration of active and functioning microbial communities participating in the process. Here, we monitored the physical, microbial, and functional performance during the first 90 days of AnMBR operation. The results indicate initiation of anaerobic digestion on days 31–60 (transitional stage) and its stabilization on days 61–90 (stable stage), with an average COD removal efficiency of 93.14 ± 1.41% and biogas production of 0.82 ± 0.15 L/d. Moreover, the microbial population and its associated proteome were studied using 16s rDNA-based PCR-DGGE and SDS-PAGE-LC/MS/MS techniques to acquire a detailed understanding of reactor startup conditions. Later, a conventional library was created through the UniprotKB protein database using the observed community of all organisms identified with 16s rDNA sequencing. The results clearly depicted Gammaproteobacteria as the dominant fermentative during the initial and transitional stages. Firmicutes predominated over Gammaproteobacteria during the stabilization stage. During the transitional stage, methanobacteriales and metheanosarcinales coexisted. In the two-step reaction, a combination of syntrophic acetate oxidation and hydrogenotrophic methanogenesis was observed. During the stabilization stage, diverse metheanosarcinales were detected. The methanogenic pathway seemed to shift to acetoclastic methanogenesis, as indicated by detection of acetyl-coenzyme A synthetase, aminomethyltransferase, and methyl-coenzyme M reductase. Thus, by linking microbial community dynamics with the meta-proteomic functions of AnMBR during startup, a stable reactor performance with up-regulated acetoclastic methanogenesis was observed in 90 days.

Neural network modelling and prediction of an Anaerobic Filter Membrane Bioreactor

Anaerobic membrane bioreactors have become an environmentally friendly solution for wastewater treatment. The lack of sufficiently accurate mathematical procedures to model their behaviour and the fouling process of the membranes, poses a challenge when trying to optimise their energy consumption and maintenance costs. An accurate model of the fouling process of the membranes is critical to make the most of this technology. This is a perfect scenario in which to introduce neural networks (NN) as an alternative to mathematical modelling. However, the duration of the experiments and the difficulties in measuring some relevant variables, make it hard to collect high quality datasets to train the NN. Our goal is to obtain a good prediction of the fouling status of the membranes to enable an adjustment of operation conditions and maintenance procedures ahead in time. To do so we must obtain high quality datasets to train our neural networks. The combination of static and dynamic networks enables us to leverage the best prediction capabilities of each one. This combination requires a preprocessing of the datasets that separates trends from oscillations. The outputs obtained need to be put together to build up the predicted evolution of fouling. Accurate predictions are then extended from 25 to up to 75 filtration cycles. To maintain and even extend accuracy after sudden changes in operating conditions, retraining the NN every 25 cycles is proposed. AI based real time predictions open a new scope for decision making, and optimisation in the field of anaerobic membrane reactors.

Two-Phase improves Bio-hydrogen and Bio-methane production of anaerobic membrane bioreactor from waste activated sludge with digestate recirculation

The conventional recirculated two-phase anaerobic digestion (R-TPAD) equipped with two continuous stirred tank reactors (CSTR) usually shows poor water quality, insufficient bioconversion degree and low methane productivity. In this study, a new R-TPAD with CSTR as acidogenic phase and anaerobic membrane reactor (AnMBR) as methanogenic phase was constructed to digest waste activated sludge (WAS) for renewable energy recovery (H2 and CH4). The effects of recirculation ratio (R) on start-up time, long-term performance, membrane fouling behaviors, microbial community evolution, and energy recovery efficiencies were investigated systematically. Result showed that the R-TPAD possessed high H2 (6.1 mL/g-COD) and CH4 (67.9 mL/g-COD) yields with the corresponding COD removal of up to 96.1% at R0.2. During the whole process, the transmembrane pressure was lower than −3.3 kPa with negligible membrane fouling observed. The 16S rRNA gene analysis revealed that the synergistic role of membrane separation and recirculation system promoted the proliferation of fatty acids-producing and organics-degrading bacteria (i.e. Coprothermobacteraeota, Bacteroidetes, etc.) in acidogenic phase and CH4-producing methanogens (i.e. Methanobacterium, Methanosaeta, etc.) in methanogenic phase, thus accelerating the biodegradation of WAS. This positive stimulation sustained the high diversity and the dynamic balance of key microorganisms in the R-TPAD process. Energy balance analysis further indicated that the R-TPAD with R0.2 could increase net energy output by 77.9% compared to the control TPAD without recirculation. This work provides a fundamental data base for the scientific management of WAS and push forward the real-world application of R-TPAD technology in the real-world scenarios.

A novel system of two-stage partial nitritation/hydroxyapatite (HAP)-anammox treating effluent of anaerobic membrane reactor: Performance, elemental flow and nutrient recovery potentials

As a measure towards achieving carbon neutrality and sustainability in the wastewater treatment industry, an autotrophic PN/HAP-A (airlift reactor/EGSB reactor) system is proposed in this study. The undiluted effluent from an AnMBR digesting municipal organic waste was applied for the practical validation of the system. With continuous feeding mode, the high efficiency, stability and operational simplicity were confirmed. In both reactors, the sludge manifested macro-aggregates and HAP-anammox granules with a satisfactory settling velocity and well-functional microorganisms. The alkalinity/IC consumptions and the buffer capacity were given individually and systematically. The elemental flow and potentials of precipitations indicated the high possibility and viability of phosphorus recovery by the formation of HAP, and in turn, the accumulation of precipitates in the biomass enhanced the settling velocity of the sludge. It is confirmed that the PN/HAP-A system is a promising approach to achieving nitrogen removal and phosphorus recovery from high-strength wastewater.

Looking for lipases and lipolytic organisms in low-temperature anaerobic reactors treating domestic wastewater

Poor lipid degradation limits low-temperature anaerobic treatment of domestic wastewater even when psychrophiles are used. We combined metagenomics and metaproteomics to find lipolytic bacteria and their potential, and actual, cold-adapted extracellular lipases in anaerobic membrane bioreactors treating domestic wastewater at 4 and 15 °C. Of the 40 recovered putative lipolytic metagenome-assembled genomes (MAGs), only three (Chlorobium, Desulfobacter, and Mycolicibacterium) were common and abundant (relative abundance ≥ 1%) in all reactors. Notably, some MAGs that represented aerobic autotrophs contained lipases. Therefore, we hypothesised that the lipases we found are not always associated with exogenous lipid degradation and can have other roles such as polyhydroxyalkanoates (PHA) accumulation/degradation and interference with the outer membranes of other bacteria. Metaproteomics did not provide sufficient proteome coverage for relatively lower abundant proteins such as lipases though the expression of fadL genes, long-chain fatty acid transporters, was confirmed for four genera (Dechloromonas, Azoarcus, Aeromonas and Sulfurimonas), none of which were recovered as putative lipolytic MAGs. Metaproteomics also confirmed the presence of 15 relatively abundant (≥ 1%) genera in all reactors, of which at least 6 can potentially accumulate lipid/polyhydroxyalkanoates. For most putative lipolytic MAGs, there was no statistically significant correlation between the read abundance and reactor conditions such as temperature, phase (biofilm and bulk liquid), and feed type (treated by ultraviolet light or not). Results obtained by metagenomics and metaproteomics did not confirm each other and extracellular lipases and lipolytic bacteria were not easily identifiable in the anaerobic membrane reactors used in this study. Further work is required to identify the true lipid degraders in these systems.

A successful start-up of an anaerobic membrane bioreactor (AnMBR) coupled mainstream partial nitritation-anammox (PN/A) system: A pilot-scale study on in-situ NOB elimination, AnAOB growth kinetics, and mainstream treatment performance

In this pilot-scale study, an innovative mainstream treatment process that couples the anaerobic membrane reactor (AnMBR) with a one-stage PN/A system was proposed for advancing the concept of carbon neutrality in the municipal wastewater treatment plant. This work demonstrates the start-up procedure of a pilot-scale one-stage PN/A system for mainstream treatment. The 255-day start-up of the one-stage PN/A system involved the cultivation of ammonium-oxidizing bacteria (AOB) from the activated sludge, suppression of nitrite-oxidizing bacteria (NOB), investigation of in-situ growth kinetics of anammox bacteria (AnAOB), and the 50-day operation of the pilot-scale AnMBR-PN/A process for natural mainstream treatment. It is verified in the pilot-scale system for the first time that the in-situ free ammonia (FA) and free nitrous acid (FNA) exposure could effectively eliminate the Nitrospira (the NOB genus) while retaining the Nitosonomas (the AOB genus) community in the suspended sludge. NOB community rebounding was not detected even at the mainstream conditions with low nitrogen concentrations (Influent ammonium concentration=38±6 mg-NH4+-N/L) by intermittent aeration to control the system dissolved oxygen (DO) below 0.5 mg/L. The results of the mainstream treatment showed that the average effluent total nitrogen (TN) in the coupled process was generally lower than 10 mg-N/L, which meets the discharge limits of most prefectures in Japan. The investigated results of the in-situ anammox bacteria (AnAOB) growth kinetics suggested that the promoted start-up strategy of taking advantage of the warm months with higher mainstream temperature to achieve the rapid in-situ growth of the AnAOB is applicable in the investigated regions. From the perspective of the removal performance of the TN and organic substance, the AnMBR-PN/A process has great potential as the layouts of the carbon-neutral mainstream wastewater treatment plants.

Performance of AnMBR in Treatment of Post-consumer Food Waste: Effect of Hydraulic Retention Time and Organic Loading Rate on Biogas Production and Membrane Fouling.

Anaerobic digestion of food waste (FW) is typically limited to large reactors due to high hydraulic retention times (HRTs). Technologies such as anaerobic membrane reactors (AnMBRs) can perform anaerobic digestion at lower HRTs while maintaining high chemical oxygen demand (COD) removal efficiencies. This study evaluated the effect of HRT and organic loading rate (OLR) on the stability and performance of a side-stream AnMBR in treating diluted fresh food waste (FW). The reactor was fed with synthetic FW at an influent concentration of 8.24 (± 0.12) g COD/L. The OLR was increased by reducing the HRT from 20 to 1 d. The AnMBR obtained an overall removal efficiency of >97 and >98% of the influent COD and total suspended solids (TSS), respectively, throughout the course of operation. The biological process was able to convert 76% of the influent COD into biogas with 70% methane content, while the cake layer formed on the membrane gave an additional COD removal of 7%. Total ammoniacal nitrogen (TAN) and total nitrogen (TN) concentrations were found to be higher in the bioreactor than in the influent, and average overall removal efficiencies of 17.3 (± 5) and 61.5 (± 3)% of TAN and TN, respectively, were observed with respect to the bioreactor concentrations after 2 weeks. Total phosphorus (TP) had an average removal efficiency of 40.39 (± 5)% with respect to the influent. Membrane fouling was observed when the HRT was decreased from 7 to 5 d and was alleviated through backwashing. This study suggests that the side-stream AnMBR can be used to successfully reduce the typical HRT of wet anaerobic food waste (solids content 7%) digesters from 20 days to 1 day, while maintaining a high COD removal efficiency and biogas production.

Integrating microbial electrolysis cell based on electrochemical carbon dioxide reduction into anaerobic osmosis membrane reactor for biogas upgrading

It has been reported that anaerobic osmosis membrane bioreactors have the potential for energy recovery since dissolved methane was almost rejected by commercial forward osmosis membranes. Notwithstanding, upgraded biogas has to be achieved by removing as much carbon dioxide as possible. In this study, a novel anaerobic osmotic membrane bioreactor-microbial electrolysis cell (AnOMBR-MEC) system was developed for simultaneous biogas upgrading and wastewater treatment. The AnOMBR-MEC elicited an excellent and stable soluble chemical oxygen demand and phosphorus removal. As the experiment progressed, unwanted carbon dioxide produced from biogas was reduced to formate using a SnO2 nanoparticles electrocatalytic cathode in an electrocatalytic-assisted MEC, with the highest faradic efficiency of formate being 85% at 1.2V. Compared to AnOMBR, the methane content increased from 55% to 90% at the end of operation and methane yield experienced a1.6-fold increment in the AnOMBR-MEC. Microbial community analysis revealed that hydrogenotrophic methanogens (e.g. Methanobacterium and Methanobrevibacter) converted the produced H2 and formate to methane at saline conditions. These results have demonstrated an efficient strategy based on the integration of an electrocatalytic-assisted MEC into AnOMBR for upgrading biogas, enhancing methane yield and wastewater treatment.

Insight into using up-flow anaerobic sludge blanket-anammox to remove nitrogen from an anaerobic membrane reactor during mainstream wastewater treatment

A partial nitritation/anammox system treating the effluent of an anaerobic membrane bioreactor was investigated in this study with emphases on the nitrogen conversion and microbial dynamics along the up-flow anaerobic sludge blanket. An average total nitrogen concentration of 12.3 mg/L was achieved in effluent, which resulted in a total nitrogen removal efficiency of 75.9% ± 0.6%, in which the contribution of anammox was over 98%, and mainly occurred at the bottom of the up-flow anaerobic sludge blanket. Furthermore, external nitrite produced from nitrate reduction enhanced the nitrogen removal efficiency. Ca. Brocadia was the dominant anammox bacteria and was enriched at the bottom; Dokdonella and Thermomonas were identified as the denitrifiers for nitrite production and existed in the whole reactor. Findings of this study can be used in a practical model for the future development of integrating anaerobic digestion with partial nitritation/anammox in mainstream wastewater treatment.

A hybrid anaerobic and microalgal membrane reactor for energy and microalgal biomass production from wastewater

In the concept of a circular economy, wastewater is no longer waste but a resource for water, energy and nutrients. In this study, a hybrid system containing an anaerobic membrane bioreactor (AnMBR) and a microalgal membrane reactor (MMR) was developed to harvest energy, nutrients, and microalgal biomass from food and agribusiness industrial wastewater. The AnMBR removed over 97% of chemical oxygen demand (COD) and generated 4.7 ± 0.15 L (n=80) of biogas equivalent to 2.4 kWh kg−1 COD (feed) d−1. Through anaerobic metabolism, the microorganism in AnMBR generated NH4+ and PO43− -rich effluent. Their effluent concentrations were 1.9 and 1.4 times of that in the influent, respectively. NH4+ and PO43−-rich effluent was directly used (i.e. without filtration or sterilization) to culture microalgae Chlorella vulgaris in the MMR. . Microalgal biomass production reached up to 700 mg/L after 6 days of operation and nutrient removal rates of above 75% were achieved. However, biomass production and nutrient removal declined towards the end of experiment. The generated biomass was completely harvested using cationic polyacrylamide at the dose of 36 mg g−1 dry weight. Overall, the AnMBR has great potential to produce energy. Future research is needed to intensify the microalgal growth (e.g. genetic modification of strains, addition of plant hormones) in the MMR for continuous operation of the hybrid system.

Versatile zero valent iron applied in anaerobic membrane reactor for treating municipal wastewater: Performances and mechanisms

Comprehensive insight into the long-term impact of applying zero valent iron (ZVI) in anaerobic membrane reactor (AnMBR) was conducted here. ZVI showed its versatility for enhancing the performances of AnMBR including COD and TP removal, H2S removal and membrane fouling suppression in this study, and the iron ions releasing rate of ZVI had great influence on the enhancing performances. Two iron ions releasing states were used including “with electric field” and “without electric field”. Applying electric field could boost iron ions releasing rate by 12 times here. COD removal rate increased by 3% via coagulation effect with and without electric field. H2S in biogas was decreased from >500 ppm to <60 ppm via the formation of FeS precipitation with and without electric field. Applying ZVI with electric field increased the removal rate of TP by 50% via the formation of Fe3(PO4)2, but applying ZVI without electric field did not change the TP removal due to the insufficient iron ions. Utilizing ZVI without electric field suppressed the membrane fouling rate by 20% via the improvement of mixed liquor filterability, however utilizing ZVI with electric field accelerated the membrane fouling rate by 17 times due to the formation of dense Fe-enriched fouling layer with server inorganic and organic fouling. This study provided a novel approach to improve the performances of AnMBR by utilizing versatile ZVI. Meanwhile, this study enclosed that the iron ions releasing rate of ZVI is vital technical parameter for its application.

Anaerobic membrane reactor: Biomethane from chicken manure and high-quality effluent

Chicken manure was treated in a pilot scale reactor anaerobic membrane bioreactor constituted by a completely mixed reactor combined with an ultrafiltration tube-shaped membrane in a side-stream configuration. The process operated under mesophilic condition and the inhibition of high concentration of ammonia was avoided using an ammonia stripping system. The experimental plan included a preliminary evaluation, where organic loading rates between 1.0 and 7.6 kgVS/m3/day were tested. The organic load higher than 4 kgVS/m3/d caused the accumulation of volatile fatty acids and process instability. Application of the ammonia stripping was also evaluated. The best performances were achieved using a retention time of 21 days, an organic load between 1.4 and 2.0 kgVS/m3/d, and the recirculation of stripped permeate. Reduction of the ammonia permeate content by 90% through stripping and utilization of a mixture of chicken manure/water/permeate in a ratio of 0.22/0.72/0.72 w/w led to a specific biogas production of 0.59 m3biogas/kgVS and methane content of 66–69%. The ammonia thus removed can be recovered by sulphuric acid treatment as ammonium sulphate, which can be used as a fertilizer. The proposed configuration allowed satisfactory biogas production with appropriate methane percentages, recovery of ammonium sulphate, and a high-quality effluent.

Acclimatised rumen culture for raw microalgae conversion into biogas: Linking microbial community structure and operational parameters in anaerobic membrane bioreactors (AnMBR)

Ruminal fluid was inoculated in an Anaerobic Membrane Reactor (AnMBR) to produce biogas from raw Scenedesmus. This work explores the microbial ecology of the system during stable operation at different solids retention times (SRT). The 16S rRNA amplicon analysis revealed that the acclimatised community was mainly composed of Anaerolineaceae, Spirochaetaceae, Lentimicrobiaceae and Cloacimonetes fermentative and hydrolytic members. During the highest biodegradability achieved in the AnMBR (62%) the dominant microorganisms were Fervidobacterium and Methanosaeta. Different microbial community clusters were observed at different SRT conditions. Interestingly, syntrophic bacteria Gelria and Smithella were enhanced after increasing 2-fold the organic loading rate, suggesting their importance in continuous systems producing biogas from raw microalgae.

Cross comparative analysis of liquid phase anaerobic digestion

This work developed and used performance indicators to quantitatively cross-compare over 82 liquid phase anaerobic digestion treatment processes/technologies. Results showed that anaerobic membrane reactors generally performed best in terms of reduction of total chemical oxygen demand, while upflow anaerobic sludge blanket reactors exceled with respect to the volumetric reduction of total chemical oxygen demand. Although packed bed and moving bed reactors showed large variations in reduction of total chemical oxygen demand, they generally produced higher methane yields (i.e. >0.25 m3 methane produced per kg total chemical oxygen demand reduced). While high performance was desired across all performance indicators, it was generally not achieved by any specific reactor type. The performance indicators were also used to directly cross-compare performance of two separate reactors treating identical wastewater streams. Result showed that both systems demonstrated good performance relative to the literature but neither was dominant in head-to-head comparison.

A viable approach for commercial VFAs production from sludge: Liquid fermentation in anaerobic dynamic membrane reactor.

A novel strategy of liquid fermentation using anaerobic dynamic membrane reactor (AnDMBR) was proposed to enhance volatile fatty acids (VFAs) production from sewage sludge. Results indicated that liquid sludge fermentation in AnDMBR had the potential in commercial VFAs production. VFAs productivity and concentration as well as substrate conversion rate could reach as high as 7.8 kg VFA-COD/m3 d, 60 g/L and 0.38 kg VFA-COD/kg VS, respectively. Moreover, dynamic membrane was stably operated for approximately 70 days. During the operational period, membrane flux was increased from 6.25 to 25 L/m2 d and only once online membrane cleaning was implemented. Results of microbial analyses showed bacterial richness and evenness in AnDMBR were increased by membrane separation and organic loading rate (OLR) increase, but reduced by excessive OLR, which should led the variations in the performances of AnDMBR. Furthermore, the necessity of liquid sludge fermentation for VFAs production was further confirmed by economic assessment and the bioavailability analysis of the residual solids in pretreated sludge. The residual solid was proved to be not conducive to enhance VFAs yield. Conversely, the energy consumption for VFAs production could be reduced from over 100 to below 20 kwh/kg VFAs by avoiding the "useless" residual solids entering into fermenters.