Effect Of Waste Scrap Iron On Sludge Anaerobic Digestion And In Situ H₂S Control

In recent years,the production of excess sludge has been huge and most of them have not been treated and disposed effectively.The anaerobic digestion technology can realize sludge reduction and utilization,but conventional sludge anaerobic digestion technology presents a low energy conversion and a low methane production,and the biogas contains relatively high content of hydrogen sulfide?H₂S?,which needs to be purified before further used.Theses restrict the promotion and popularization of anaerobic digestion technology for excess sludge treatment.Waste scrap iron?WSI?is a kind of cheap industrial waste.Based on the reduction properties of zero-valent iron,WSI can strengthen the anaerobic digestion of sludge and accords with the concept of waste comprehensive utilization.This study mainly focused on the application of WSI to enhance sludge anaerobic digestion for methanogenesis and in-situ control of H₂S,to maximize the sludge utilization.Slaughterhouse sludge was used as the substrate for this research,and the following conclusions were obtained:?1?The effect of addition of WSI and zero-valent iron powder?ZVI?on methane production during sludge anaerobic digestion was investigated.Both WSI and ZVI enhanced the production of acetic acid and butyric acid,limited the accumulation of propionic acid,therefore the methane production increased.However,the effect of WSI addition on improvement of anaerobic digestion was better than that of ZVI.The acetic acid concentration with an addition of 0.4 g/g VSS WSI dosage was 13.10%higher than that with the addition of ZVI,and the methane production was 7.41%higher.With a dosage of 0.70 g WSI/g VSS,205.02 mL/g VSS cumulative methane production was achieved,increasing by 21.34%compared with the control,the digestion time reduced by 8 days,and the VSS degradation increased by 25.97%.?2?The effect of WSI dosage on the control of H2S durng sludge anaerobic digestion was investigated.The cumulative H₂S accumulation with 0.70 g/g VSS WSI dosage reduced by 62%compared with the control.However,with the further increase of the WSI dosage,the control of H₂S was insignificant.The WSI addition can significantly reduce the concentration of dissolved sulfides in the sludge digester and avoid inhibition of excessive sulfides in anaerobic microbial community.?3?The WSI addition improved the richness of microbial communities and promoted the degradation of complex organic matters by related microbial communities of,such as Firmicutes,Bacteroidetes,Thermotogae etc.The WSI addition also increased the relative abundance of hydrogenotrophic methanogens such as Methanobacterium,Methanobrevibacter and Methanoregula.