Communities stimulated with ethanol to perform direct interspecies electron transfer for syntrophic metabolism of propionate and butyrate

Enhancing anaerobic digestion of poultry blood using activated carbon

The potential of using anaerobic digestion for the treatment of poultry blood has been evaluated in batch assays at the laboratory scale and in a mesophilic semi-continuous reactor. The biodegradability test performed on residual poultry blood was carried out in spite of high inhibitory levels of acid intermediaries. The use of activated carbon as a way to prevent inhibitory conditions demonstrated the feasibility of attaining anaerobic digestion under extreme ammonium and acid conditions. Batch assays with higher carbon content presented higher methane production rates, although the difference in the final cumulative biogas production was not as sharp. The digestion of residual blood was also studied under semi-continuous operation using granular and powdered activated carbon. The average specific methane production was 216 ± 12 mL CH4/g VS. This result was obtained in spite of a strong volatile fatty acid (VFA) accumulation, reaching values around 6 g/L, along with high ammonium concentrations (in the range of 6-8 g/L). The use of powdered activated carbon resulted in a better assimilation of C3-C5 acid forms, indicating that an enhancement in syntrophic metabolism may have taken place. Thermal analysis and scanning electron microscopy (SEM) were applied as analytical tools for measuring the presence of organic material in the final digestate and evidencing modifications on the carbon surface. The addition of activated carbon for the digestion of residual blood highly improved the digestion process. The adsorption capacity of ammonium, the protection this carrier may offer by limiting mass transfer of toxic compounds, and its capacity to act as a conductive material may explain the successful digestion of residual blood as the sole substrate.

Enhanced treatment of Fischer-Tropsch (F-T) wastewater using the up-flow anaerobic sludge blanket coupled with bioelectrochemical system: Effect of electric field

The coupling of bioelectrochemical system (BES) with an up-flow anaerobic sludge blanket (UASB) was established for enhanced Fischer-Tropsch (F-T) wastewater treatment while the UASB (control group) was operated in parallel. The presence of electric field could offer system a more reductive micro-environment that lower the ORP values and maintain the appropriate pH range, resulting in the higher chemical oxygen demand (COD) removal efficiency and methane production for BES-UASB (86.8% and 2.31±0.1L/(L·d)) while those values in control group were 72.1% and 1.77±0.08L/(L·d). In addition, the coupled system could promote sludge granulation to perform a positive effect on maintaining stability of pollutants removal. The high-throughput 16S rRNA gene pyrosequencing in this study further confirmed that the promoting direct interspecies electron transfer (DIET) between Geobacter and Methanosarcina might be established in BES-UASB to improve the syntrophic degradation of propionate and butyrate, finally facilitated completely methane production.

Thermodynamically enhancing propionic acid degradation by using sulfate as an external electron acceptor in a thermophilic anaerobic membrane reactor

In this study, sulfate was employed as an external electron acceptor for enhancing the degradation of propionate in a thermophilic anaerobic membrane reactor (AnMBR). The organic loading rate (OLR) was increased gradually from the initial 3.9 kg-COD/m³d to the inhibiting OLR of 14.6 kg-COD/m³d. Feeding was stopped for 98 days but the process did not recover until 500 mg/L of sulfate was added into the AnMBR. After that, the enhanced propionate degradation was achieved up to an OLR of 15 kg-COD/m³d with a reduced sulfate addition of 300 mg/L. However, the thermodynamic calculation indicated that the syntrophic propionic acid degradation, coupled with methanogenesis, was unfavorable with a △G of +3 kJ/mol under the enhanced conditions. Conversely, the utilization of propionic acid by sulfate reduction bacterial (SRB) would be more favourable by having a much lower △G of -180 kJ/mol. The hydrogen conversion was presumed to go through the methanogenesis pathway according to the thermodynamic results. The mechanism of the propionic and hydrogen metabolism was supported as well by comparing the microbial communities with and without sulfate addition. As a result, the role of the sulfate enhancing propionic degradation can be concluded by combining the process performance, thermodynamic, and microbiology results.

Stimulation of methanogenesis in anaerobic digesters treating leachate from a municipal solid waste incineration plant with carbon cloth

Bio-methanogenic digestion of incineration leachate is hindered by high OLRs, which can lead to build-up of VFAs, drops in pH and ultimately in reactor souring. It was hypothesized that incorporation of carbon cloth into reactors treating leachate would promote DIET and enhance reactor performance. To examine this possibility, carbon cloth was added to laboratory-scale UASB reactors that were fed incineration leachate. As expected, the carbon-cloth amended reactor could operate stably with a 34.2% higher OLR than the control (49.4 vs 36.8kgCOD/(m³d)). Microbial community analysis showed that bacteria capable of extracellular electron transfer and methanogens known to participate in DIET were enriched on the carbon cloth surface, and conductivity of sludge from the carbon cloth amended reactor was almost twofold higher than sludge from the control (9.77 vs 5.47μS/cm), suggesting that microorganisms in the experimental reactor may have been expressing electrically conductive filaments.