Production Of Short-chain Carboxylic Acids By Co-digestion Of Swine Manure And Corn Silage

Regarding the issues that the types of products from treatment of agricultural waste are less and the conversion efficiency is low,swine manure and corn silage were used to produce short-chain carboxylic acids?SCCAs?for value-added utilization,the important intermediates of anaerobic digestion?AD?,from the anaerobic co-digestion in this study.Concentration and composition of SCCAs were investigated in the batch digestion of the mixture with different C/N ratio?12.7,15,20,25,30,35,45 and 50.2?.On the basis of the optimal C/N ratio,the semi-continuous co-digestion was used to explore the influence of organic load rate?OLR??2,3,3.5 and 4 g VS/L·d?on the SCCAs concentration,components and fermentation stability.The dominant bacteria groups under different C/N ratio and OLR were also determined.The results in this study provide the basis for improving the the directional SCCAs production and the cultivation of microbial functional bacteria,which optimizes the value-added utilization of agricultural waste.The results are shown as follows:1)The C/N ratio had significant influence on the concentration and composition of SCCAs.The maximum SCCAs concentration of 26214 mg COD/L was achieved at the C/N ratio of 25 on day 18.The highest lactic acid?LA?production,468.5±44.3 mg COD/g VS_added,was produced at a C/N ratio of 35after 12 days of fermentation.When the C/N ratio was 12.7,the highest VFAs production,601.1±42.4 mg COD/g VS_added,was observed on day 12.VFAs were the main components of SCCAs when the C/N ratio was 12.7,15,and 20.However,when the C/N ratio was 30 to 50.2,LA became the main component of SCCAs.VFA composition in the AD was changed with increasing C/N ratio.With the increase of C/N,the complexity of VFAs became low.Acetic acid percentage decreased when the C/N ratio increased from12.7 to 20.However,caproic acid percentage increased and then gradually decreased to finally fall below the detection limit as the C/N ratio continued to increase.Butyric acid was the main component of VFAs under different C/N ratio.The dominant bacterial groups changed from Clostridium to Lactobacillus with the increase of C/N ratio.When the C/N ratio was 25,Clostridium and Captopriciproducens were the dominant bacterial groups,while Latobacillus and Clostridium were the dominant bacterial groups at the C/N ratio of 35.2)The concentration of SCCAs was significantly affected by the OLR.The maximum SCCAs concentration was 19082 mg COD/L at OLR of 3.5 g VS/L·d on day 105.The maximum SCCAs concentration at OLRs of 3.5 and 4 g VS/L·d was higher than that at OLRs of 2 and 3 g VS/L·d,but the digestion stability was lower and the yield fluctuation was higher when the OLR was higher.OLR had a significant influence on the composition of acid products and the hydrolysis and acidification process.When OLR was 2 and 3 g VS/L·d,acetic acid and n-butyric acid were the main components of VFAs,the proportion of caproic acid significantly increased at OLR of 3.5 and 4 g VS/L·d.Furthermore,high OLR contributed to carbon chain extension.With the increase of OLR,the hydrolysis rate decreased and the highest hydrolysis rate was 50.61%.The acidification rate and the yield of SCCAs increased first and then decreased.The highest acidification rate was 50.80%at OLR of 3 g VS/L·d.The maximum yield of SCCAs was 0.45 mg COD/mg VS at OLR of 3.5 g VS/L·d,and the acidification process was the rate-limiting step of the yield of SCCAs.OLRs could significantly affect the composition of microbial communities.The relative abundance of Lactobacillus increased with the increase of OLR.The relative abundance of Bifidobacterium decreased,while the relative abundance of Aeriscardovia with more acid-resistance increased when OLR increased from 3.5 to 4 g VS/L·d.