Introducing electrolysis to enhance anaerobic digestion resistance to acidification

Enhancing the anaerobic sludge characteristics and inorganic impurities removal from synthesis wastewater through integration of electrocoagulation process with up-flow anaerobic sludge blanket reactor

The present study investigated effects of coupling electrocoagulation (EC) process with an anaerobic digestion bioreactor, namely up-flow anaerobic sludge blanket (UASB), for the synthetic wastewater treatment. The EC-UASB mode of operation consisted of one anode and two cathodes subjected to an intermittent electrical current (10 min ON/30 min OFF) with current density of 1.5 mA/cm2. In light of this integration, the concentration of mixed liquor suspended solids and mixed liquor volatile suspended solids within anaerobic granular sludge (AGS) increased by 20.0 ± 1.4% and 12.8 ± 0.8%, respectively. The results of sludge volume index, loosely and tightly bound extracellular polymeric substances and their constituents (protein and carbohydrate) revealed that through this integration the quality of AGS has been improved. Furthermore, results of scanning electron microscopy and Fourier-transform infrared spectroscopy showed alteration in the morphology and functional groups of AGS, respectively. Additionally, this combination has demonstrated promising results in terms of performance improvement by increasing the removal efficiency of total dissolved solids by 12.1 ± 0.3% and reducing the ionic pollution in treated wastewater. However, the integration of the EC system within the UASB resulted in energy consumption and operating cost of 1.33 kWh/m3 and 0.099 USD/m3, respectively.

Efficient phosphate and hydrogen recovery from sludge fermentation liquid by sacrificial iron anode in electro-fermentation system

Electro-fermentation (EF) has been extensively studied for recovering hydrogen and phosphorus from waste activated sludge (WAS), while was limited for the further application due to the low hydrogen yield and phosphorus recovery efficiency. This study proposed an efficient strategy for hydrogen and vivianite recovery from the simulated sludge fermentation liquid by sacrificial iron anode in EF. The optimum hydrogen productivity and the utilization efficiency of short chain fatty acids (SCFAs) reached 45.2 mmol/g COD and 77.6% at 5 d in pH 8. Phosphate removal efficiency achieved at 90.8% at 2 d and the high crystallinity and weight percentage of vivianite (84.8%) was obtained. The functional microbes, i.e., anaerobic fermentative bacteria, electrochemical active bacteria, homo-acetogens and iron-reducing bacteria were highly enriched and the inherent interaction between the microbial consortia and environmental variables was thoroughly explored. This work may provide a theoretical basis for energy/resource recovery from WAS in the further implementation.

The influencing mechanism of AD-MEC domesticated sludge to alleviates propionate accumulation and enhances methanogenesis

Anaerobic digestion combined with microbial electrolysis cell (AD-MEC) could maintain stable reactor operation and alleviating the anaerobic digestion (AD) propionate accumulation. In this study, the addition of sludge to AD-MEC was examined as a way to enhance system performance and explore the microbial interaction mechanism after electric field domestication. The results showed that under 1000 and 4000 mg/L propionate, the methane production of the sludge from AD-MEC increased by 34.29 % and 9.70 %, respectively, as compared to the AD sludge. Gompertz fitting analysis showed that sludge after electric field domestication enhancing its continuous methanogenic capacity. Further analysis showed that sludge extracellular electron transfer capacity was enhanced in AD-MEC and that its domesticated granular sludge formed a microbial community function with acid-degrading synergistic methanogenesis. The results of the study may provide theoretical support and optimization strategies for the application of AD-MEC system.

Distinguishing anaerobic digestion from electrochemical anaerobic digestion: Metabolic pathways and the role of the microbial community

In this study, we explored why electrochemical anaerobic digestion (EAD) results in higher methane conversion and lower CO₂ emissions than anaerobic digestion (AD). Single-chamber AD and EAD reactors were used in this experiment, and the temperature was set as the disturbance factor. Current, pH, electrode potential, gas content, and microbial community were used as indicators for our analysis. Flux balance analysis (FBA) and high-pass next-generation sequencing (NGS) were used to explore the relationships between AD and EAD methane-producing metabolic fluxes and microorganisms. The results showed that the average methane fluxes were 22.27 (AD) and 29.65 (EAD). Compared with AD, EAD had improved hydrogen-dependent CO₂ reduction pathway. Trichloromonas was the dominant electricity-producing microorganism on the EAD anode film, which was closely related to the H₂ flux at the cathode. Oscillibacter and Syntrophomonas were the dominant bacteria in the fermentation broth, specific to EAD. The abundance of Oscillibacter was positively correlated with the H₂ flux, and the presence of Oscillibacter enhanced CO₂ reduction by hydrogen. Methanosaeta was the only dominant methanogenic bacterium in AD and EAD, and its abundance was higher in the experimental group with a greater methane flux.

Aerobic electrotrophic denitrification coupled with biologically induced phosphate precipitation for nitrogen and phosphorus removal from high-salinity wastewater: Performance, mechanism, and microbial community

Electrotrophic denitrification (ED) is a promising nitrogen removal technique; however, the potential of ED coupled with biologically induced phosphate precipitation (BIPP) has not been fully explored. In this study, the performances, mechanisms, and microbial communities of the coupled system were investigated. The results showed that excellent nitrogen and phosphorus removal (both exceeding 92 %) was achieved in the salinity range of 20-60 g/L. ED contributed to approximately 83.4 % of nitrogen removal. BIPP removed approximately 63.5 % of the phosphorus. Batch activity tests confirmed that aerobic/anoxic bio-electrochemical and autotrophic/heterotrophic denitrification worked together for nitrate removal. Sulfate reduction had a negative impact on denitrification. Moreover, phosphorus removal was controlled by ED and calcium ions. The alkaline solution environment created by denitrification may greatly promote the formation of hydroxyapatite. Microbial community analyses indicated that the key bacteria involved in aerobic ED was Arcobacter. These findings will aid in the advanced treatment of high-salinity wastewater.

Polyaniline-Derived Nitrogen-Containing Carbon Nanostructures with Different Morphologies as Anode Modifier in Microbial Fuel Cells

Anode modification with carbon nanomaterials is an important strategy for the improvement of microbial fuel cell (MFC) performance. The presence of nitrogen in the carbon network, introduced as active nitrogen functional groups, is considered beneficial for anode modification. In this aim, nitrogen-containing carbon nanostructures (NCNs) with different morphologies were obtained via carbonization of polyaniline and were further investigated as anode modifiers in MFCs. The present study investigates the influence of NCN morphology on the changes in the anodic microbial community and MFC performance. Results show that the nanofibrillar morphology of NCNs is beneficial for the improvement of MFC performance, with a maximum power density of 40.4 mW/m2, 1.25 times higher than the anode modified with carbonized polyaniline with granular morphology and 2.15 times higher than MFC using the carbon cloth-anode. The nanofibrillar morphology, due to the well-defined individual nanofibers separated by microgaps and micropores and a better organization of the carbon network, leads to a larger specific surface area and higher conductivity, which can allow more efficient substrate transport and better bacterial colonization with greater relative abundances of Geobacter and Thermoanaerobacter, justifying the improvement of MFC performance.