Synergistic Interactions And Enhancement During The Co-digestion Process Of Agricultural Straw With Municipal Sludge

Agricultural straw and municipal sludge are two types of organic solid wastes produced during the process of agricultural production and urban living activities.Improper disposal of straw and sludge will cause pollution to the environment.The anaerobic co-digestion technology is an environment-friendly method to realize the recycling and reduction of straw and sludge at a low cost.During the co-digestion process,the interaction between the components of straw and the interaction between sludge and the components of straw would affect the methane production performance,and the related research was scarce.In this study,artificial biomass containing cellulose,hemicellulose,and lignin were designed through the Simplex lattice design method.Several types of natural straw were selected and the experimental studies on mono-digestion of straw and the co-digestion of straw with sludge were conducted（with or without p H regulation）.The interaction mechanism of the co-digestion process was deeply explored,as well as the strengthening mechanism of additives on the co-digestion process was investigated.The main research contents and conclusions are as follows:Firstly,the experiments were conducted under the condition without p H regulation.As for the mono-digestion of artificial straw（without adding sludge）,the methane production potential of cellulose was the highest among the three components,reaching 434.98±9.97 ml/g VS.The hydrolysis rate of hemicellulose was the fastest,leading to the excessive acidification of the digestion system.Lignin was undegradable under anaerobic conditions.The interaction between cellulose and hemicellulose significantly enhanced the cumulative methane production,and the interaction between cellulose and lignin inhibited the methane production potential and lag phase time of the digestion of cellulose.As for the co-digestion process,the interaction between sludge and cellulose,sludge and hemicellulose produced the synergistic effect to promote methane production,and the cumulative methane production was increased by 33.33%and 259.32%,respectively.The co-digestion of sludge could optimize the structure of VFAs.The co-digestion system selectively enriched Methanobrevibacter and Methanosarcina,promoting the metabolic pathway of hydrogenotrophic and acetoclastic methanogenesis.With the p H regulation,the degree of acidification of cellulose was alleviated,decreasing the methane production performance of cellulose.However,p H regulation restored the methane production performance of mono-digestion of hemicellulose,and the cumulative methane production from hemicellulose reached 355.07±4.23 m L/g VS.In the lignin-cellulose digestion system,the relative abundance of Methanosarcina was decreased by 28.76%as compared with the cellulose mono-digestion system,indicating that the lignin had significant inhibition on the metabolic pathway of acetoclastic methanogenesis of cellulose.As for the co-digestion,the synergistic interaction between sludge-cellulose,and sludge-hemicellulose could increase the cumulative methane production by 16.76%and 33.01%,respectively.The participation of sludge improved the diversity of the bacterial community and accelerated the hydrolysis and acidification processes,thus shortening the lag phase time of cellulose and hemicellulose by 5.50d～11.24d and5.03d～9.71d.However,during the co-digestion of sludge with lignin,lignin mainly inhibited the growth and metabolism of Bacteroidota and decreased the hydrolysis rate and acidification rate of sludge.Compared with the mono-digestion of sludge,the lag phase time of co-digestion of lignin with sludge was delayed by 4.18d～15.30d.Effects of different types of additives（biochar,magnetic biochar,and Fe₃O₄）on methane production from the co-digestion of corn straw and sewage sludge were investigated.The addition of 5g/kg and 10g/kg Fe₃O₄could improve the cumulative methane production by 60.47%and57.17%,respectively.After the first batch experiment,the magnetic additives were recycled by the magnet and reused in the next batch experiment.It was found that the recycled of 5g/kg and 10g/kg Fe₃O₄additives further enhanced the co-digestion performance,and the cumulative methane production was increased by 66.17%and 79.81%,respectively.In the semi-continuous co-digestion system,by adding 10g/kg Fe₃O₄additive and continuous magnetic recovery and recycling,the methane yield could be increased by 45.75%.Through the above research,the interaction among components of straw and the interaction among sludge and components of straw during the anaerobic digestion process was analyzed,the mathematical prediction models for estimating the cumulative methane production of the co-digestion were established,and the strategy of recycling utilization of Fe₃O₄as additives during the co-digestion of straw with sludge was proposed,which provided a feasible technical way for realizing the efficient and stable operation of co-digestion of sludge and straw and the resource utilization of this two types of solid waste.