| In the anaerobic digestion of pig slurry,the anaerobic methanogenesis of the particulate matter was restricted due to its slow dissolution and hydrolysis rate,which became the limiting step of the anaerobic treatment of pig slurry.The two-phase anaerobic digestion reactor was used to treat pig wastewater to enrich the hydrolytic acid-producing bacteria and further enhance the hydrolytic efficiency of granular pig manure.This study explored the effects of adding Fe3O4 and setting the external circulation on the solid dissolution,hydrolysis,acidification and methanogenesis of pig slurry in the hydrolysis and acidification reactors.Also,the sludge activities and degradation rates of different kinds of organic matter were analyzed.Besides,the different strengthening strategies for the hydrolysis and acidification of pig slurry were proposed.Firstly,different amounts of Fe3O4 were added to the anaerobic digestion system to enhance the dissolution and anaerobic hydrolysis efficiency of solid particles in pig slurry.When 5 g·L-1 Fe3O4 was added,the hydrolyzed efficiency of protein substances in pig slurry increased by 112.8%,and the activity of anaerobic production of VFAs from pig slurry increased by 15.5%.With adding Fe3O4,the hydrogenotrophic methanogenic activity of sludge was inhibited.While the aceticlastic methanogenic activity of sludge was improved.At the same time,the secretions of SMP and EPS of anaerobic sludge were increased.Secondly,the effect of external circulation on the treatment of pig slurry by the hydrolytic acidification reactor was studied.The results showed that the hydrolytic efficiency of pig wastewater was enhanced by the refluxed acidizing liquid.Compared with the blank group,the external circulation group increased the yield of VFAs by 33.5%.This also made the effluent of the added external circulation reactor had better methanogenic potential and increased the total methane production by15.1%.With 8.0 g VS·L-1 of the pig slurry,the p H in the external circulation reactor was maintained at 5.76±0.07.Besides,the dissolution efficiency,hydrolysis and acidification activity of pig manure solids increased by 34.4%,80.6%,and 16.6%,respectively.Therefore,adding external circulation in the hydrolysis and acidification reactor could enhance the hydrolysis and acidification efficiency of pig slurry.Thirdly,adding Fe3O4 and setting external circulation were coupled in the hydrolysis and acidification reactor for treating pig slurry.The results showed that coupling Fe3O4 and applied external circulation could improve the hydrolysis efficiency in the reactor by 46.1%,and the proportion of acetic acid in the wastewater was 54.68%.Coupled Fe3O4 addition and external circulation increased the dissolution rate of solid particles in pig manure by 238.8%,and the hydrolysis and acidification activities of sludge increased by 123.0%and 171.3%,respectively.Therefore,for the hydrolytic acidification reactor to treat pig slurry,coupling Fe3O4and external circulation can significantly enhance the hydrolysis efficiency and methanogenic potential. |
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