Performance enhancement of integrating microbial electrolysis cell on two-stage anaerobic digestion of food waste: Electro-methanogenic stage versus electro-two stages

Anaerobic Volatile Fatty Acid Production Performance and Microbial Community Characteristics from Solid Fraction of Alkali-Thermal Treated Waste-Activated Sludge: Focusing on the Effects of Different pH Conditions

The waste-activated sludge (WAS) is rich in organic matter and various nutrients. Alkali-thermal hydrolysis of WAS can be employed to produce a liquid fertilizer with high plant-promoting nutrient content. However, the solid fraction (abbreviated as SF) generated from this process requires further treatment. Although there have been studies on the recovery of plant nutrients from WAS via alkali-thermal hydrolysis, researches on the safe treatment of the SF are limited. This study aims to explore the potential and the microbiological mechanisms on anaerobic volatile fatty acid (VFA) production from the SF under different pH conditions (i.e., 6, 7, 8, 9, and 10). The results showed that the VFA yield was highest at pH 6, reaching 4095.84 mg COD/L (i.e., 0.16 g-COD/g-volatile solids), followed by pH 10, 8, 7, and 9, with acetate being the main component (> 56%). Microbial community analysis revealed that members in phyla Firmicutes and Bacteroidota constituted the main acid-producing microbial community during the anaerobic fermentation of SF. Furthermore, different pH conditions influenced the yield and composition of VFAs by altering the structure and functions of microbial community. This research provides a new direction for the fully resourceful utilization of sludge by producing both liquid fertilizer and VFAs from WAS.

Cellulosic ethanol stillage for methane production by integrating single-chamber anaerobic digestion and microbial electrolysis cell system

Anaerobic digestion provides a solution to the inefficient use of carbon resources caused by improper disposal of corn stover-based ethanol stillage (CES). In this regard, we developed a single-chamber anaerobic digestion integrated microbial electrolysis cells system (AD-MEC) to convert CES into biogas while simultaneously upgrading biogas in-situ by employing voltages ranging from 0 to 2.5 V. Our results demonstrated that applying 1.0 V increased the CH4 yield by 55 % and upgraded the CH4 content in-situ to 82 %. This voltage also promoted the well-formed biofilm on the electrodes, resulting in a 20-fold increase in current. However, inhibition was observed at high voltages (1.5-2.5 V), suppressing syntrophic organic acid-oxidizing bacteria (SOB). The dissociation between SOB and methanogens led to accumulation of propionic and butyric acid, which, in turn, inhibited methanogens. The degradation of CES was accelerated by unclassified_o_norank_c_Desulfuromonadia on the anode, likely leading to an increase in mixotrophic methanogenesis due to the synergistic interaction among Aminobacterium, Sedimentibacter, and Methanosarcina. Furthermore, the enrichment of electroactive bacteria (EB) such as Enterococcus and Desulfomicrobium likely facilitates direct interspecies electron transfer to Methanobacterium, thereby promoting the conversion of CO2 to CH4 through hydrogenotrophic methanogenesis. Rather than initially stimulating the EB in the bulk solution to accelerate the start-up process of AD, our study revealed that applying mild voltage up to 1.0 V tended to mitigate the negative impact on the original microorganisms, as it gradually enriched EB on the electrode, thereby enhancing biogas production.

Study on membrane fouling mechanisms and mitigation strategies in a pilot-scale anaerobic membrane bioreactor (P-AnMBR) treating digestate

Anaerobic Membrane Bioreactor (AnMBR) are employed for solid-liquid separation in wastewater treatment, enhancing process efficiency of digestion systems treating digestate. However, membrane fouling remains a primary challenge. This study operated a pilot-scale AnMBR (P-AnMBR) to treat high-concentration organic digestate, investigating system performance and fouling mechanisms. P-AnMBR operation reduced acid-producing bacteria and increased methane-producing bacteria on the membrane, preventing acid accumulation and ensuring stable operation. The P-AnMBR effectively removed COD and VFA, achieving removal rates of 82.3 % and 92.0 %, respectively. Higher retention of organic nitrogen and lower retention of ammonia nitrogen were observed. The membrane fouling consisted of organic substances (20.3 %), predominantly polysaccharides, and inorganic substances (79.7 %), primarily Mg ions (10.1 %) and Ca ions (4.5 %). To reduce the increased transmembrane pressure (TMP) caused by fouling (a 10.6-fold increase in filtration resistance), backwash frequency experiment was conducted. It revealed a 30-min backwash frequency minimized membrane flux decline, facilitating recovery to higher flux levels. The water produced amounted to 70.3 m³ over 52 days. The research provided theoretical guidance and practical support for engineering applications, offering practical insights for scaling up P-AnMBR.

Microbial community changes and metabolic pathways analysis during waste activated sludge and meat processing waste anaerobic co-digestion

Waste activated sludge (WAS) and meat processing waste (MPW) were acted as co-substrates in anaerobic co-digestion (AcD), and biochemical methane potential (BMP) test was carried out to investigate the methane production performances. Microbial community structure and metabolic pathways analyses were conducted by 16S rRNA high-throughput sequencing and functional prediction analysis. BMP test results indicated that AcD of 70% WAS+30% MPW and 50% WAS+50% MPW (VS/VS) could significantly improve methane yield to 371.05 mL/g VS and 599.61 mL/g VS, respectively, compared with WAS acting as sole substrate (191.87 mL/g VS). The results of microbial community analysis showed that Syntrophomonas and Petrimonas became the dominant bacteria genera, and Methanomassiliicoccus and Methanobacterium became the dominant archaea genera after MPW addition. 16S functional prediction analysis results indicated that genes expression of key enzymes involved in syntrophic acetate oxidation (SAO), hydrogenotrophic and methylotrophic methanogenesis were up-regulated, and acetoclastic methanogenesis was inhibited after MPW addition. Based on these analyses, it could be inferred that SAO combined with hydrogenotrophic and methylotrophic methanogenesis was the dominant pathway for organics degradation and methane production during AcD. These findings provided systematic insights into the microbial community changes and metabolic pathways during AcD of WAS and MPW.

Enhanced hydrolysis and methane yield of temperature-phased dewatered sludge anaerobic digestion by microbial electrolysis cell

Temperature-phased anaerobic digestion (TPAD) and microbial electrolysis cell (MEC) are both able to improve hydrolysis and methane yield during anaerobic digestion (AD) of dewatered sludge. However, the effect of TPAD and MEC integration at different temperatures and different phases is unclear. This study investigated the effect of the integration of intermittent energization MEC in different phases of TPAD on the digestion of dewatered sludge. Thermophilic and MEC hydrolysis could release higher total ammonia nitrogen of 186.0% and 10.3% than control, mesophilic methanogenesis phase integrated with MEC relieved the ammonia inhibition and accelerated the acid utilization leading to the relief of acid accumulation. The ultimate methane yield of the TPAD integrated with MEC was increased by 118.9%, in which the relative abundance of Methanothermobacteria and Methanosarcina was increased. Therefore, intermittent energization MEC integrated TPAD synchronously improved the hydrolysis and methane yield.

Paradigm shift in Nutrient-Energy-Water centered sustainable wastewater treatment system through synergy of bioelectrochemical system and anaerobic digestion

With advancements in research and the necessity of improving the performance of bioelectrochemical system (BES), coupling anaerobic digestion (AD) with BES is crucial for energy gain from wastewater and bioremediation. Hybridization of BES-AD concept opens new avenues for pollutant degradation, carbon capture and nutrient-resource recovery from wastewater. The strength of merging BES-AD lies in synergy, and this approach was employed to differentiate fads from strategies with the potential for full-scale implementation and making it an energy-positive system. The integration of BES and AD system increases the overall performance and complexity of combined system and the cost of operation. From a technical standpoint, the primary determinants of BES-AD feasibility for field applications are the scalability and economic viability. High potential market for such integrated system attract industrial partners for more industrial trials and investment before commercialization. However, BES-AD with high energy efficacy and negative economics demands performance boost.

Comprehending the impact of berberine on anaerobic digestion of waste activated sludge

Berberine is a natural isoquinoline alkaloid performing wide-spectrum antimicrobial and antiviral effects like antibiotics. Its production generates berberine containing wastewater, and berberine adsorbed on waste activated sludge (WAS) will unavoidably enter the anaerobic digestion (AD) system while its impact on the AD process is unknown. Our research found that berberine of 20 mg/L (BBR20) slightly enhanced the methane yield (4.2 ± 0.6%) under mesophilic condition (35.0 ± 1.0 °C). However, 100 and 500 mg/L (BBR100 and BBR500) depressed methane production by 17.3 ± 4.3% and 83.2 ± 0.4%; meanwhile more soluble chemical oxygen demand (SCOD) including volatile fatty acid (VFA), protein, and polysaccharide were left in the fermentation broth, which led to an increase in sludge reduction. 88.3 ± 0.09%-99.1 ± 0.04% of berberine was distributed in the sludge phase and could be efficiently removed even under a high berberine level of 500 mg/L during the AD process. Exposure to different berberine concentrations promoted sludge dissolution and triggered more sludge extracellular polymeric substances (EPS) being dissolved. Lower berberine concentration (20 mg/L) enhanced acidification and methanogenesis steps, resulting in a final methane generation increase. While hydrolysis, acidification and methanogenesis processes were all inhibited by 100 and 500 mg/L berberine. Microbial analysis revealed that the main acid-producing bacteria genera were changed as Bacteroidetes vadinHA17 dominated in control, BBR20 and BBR100 groups, was replaced by Petrimonas in BBR500. Additionally, Methanosaeta, as a strict acetoclastic methanogen, was suppressed under exposure to 100 and 500 mg/L berberine. Accordingly, the declined abundance of archaea genera consuming acetic acid caused more VFA accumulation and less methane production in BBR100 and BBR500 groups.