Conductive Polypyrrole Enhances Methane Production From Anaerobic Wastewater Treatment

Organic wastewater contains a large amount of organic matters,and the degradation and transformation of the organics to methane?CH₄?by the anaerobic biological has been considered as an effective way to recover the source from the wastewater.However,a hydraulic retention time?HRT?is required for this anaerobic biodegradation and conversion processes.Therefore,the conductive polypyrrole?PPy?was synthesized in this study and used as the conductive medium to enhance the direct interspecies electron transfer?DIET?in the anaerobic system,improving the CH₄production from the anaerobic wastewater treatment.The conductive PPy was prepared by chemical oxidation method,the PPy conductivity was adjusted in the range from 0.164 to 0.643 S/cm by adjusting the PPy polymerization conditions.The results showed that more metahen was generated from the ananrobic system by adding the PPy with a higher conductivity.In addition,PPy materials have good bio-friendliness and stability in anaerobic biological systems.The synthesized PPy was added to the anaerobic sludge to enhance the CH₄production.In this study,the effect of the PPy dosage,the concentration of organic matters in the wastewater and the type of substrates on the improvement of CH₄production have been investigated.When the influent COD is 2000 mg/L,the optimal dosage of PPy optimized is 400 mg/L.Under this condition,4.6 m L/h was generated from the anaerobic system,which is 50%higher than that from the control group.Also,the CH₄production can be improved by more than 30%,when the COD is in the range from 2000 to 8000 mg/L.Moreover,the CH₄production can be ncreased by 35%,45%and 60%by the anaerobic systems with the acetic acid,propionic acid and butyric acid as the substates.The improvement of degradation of the VFAs mitigates the acidification of the ananerobic wastewater treatment system.The PPy was further used as the conductive medium and added in the upflow anaerobic sludge bed?UASB?reactor.The methane production can be improved by 33%with adding400 mg/L of PPy,compared with the control group without adding PPy.Moreover,the PPy amended UASB presented a stable performance in the 81-day operation.In order to improve the transfer efficiency of extracellular electrons in the anaerobic system at the interface of PPy,the graphene oxides?GO?was used to modify the condutive PPy.The results showed that the GO-modified PPy had a beeter performance on CH₄production than PPy alone.The activity of enzymes involved in the methanogensis process was increased by adding the conductive PPy/GO.Moreover,the Syntophomonadaceac bacteria and Methanosaeta archaea with DIET ability were enriched in the ananerobic sludge by the conductive PPy/GO.These were disclosed as the main mechainsms involved in the improved methane production from the anaerobic system by the condutive PPy.