Effect Of Different Operating Parameters On Digestates Environmental Risk And Performance During Anaerobic Co-digestion Of Chicken Manure And Corn Stover

Anaerobic digestion has gained popularity as a bio-stabilization technology for extracting energy and treating ubiquitous agricultural wastes such as chicken manure(CM)and corn stover(CS).However,applications of anaerobic digestion for the management of CM and CS is usually limited by high water consuming and gradually serious hazardous metals pollution or antibiotics residues.This study investigated the possibility of overcome these limitations from anaerobic co-digestion of CM and CS based on the optimized initial substrate concentration,digestion temperature,and mixture ratio To examine this possibility,the effect of operating parameters on methane yield,process stability,and ecological risk of digestates during anaerobic co-digestion was investigated.Results showed that the highest cumulative methane yield of 223.7 ± 16.0 mL/g VSadded was obtained at CS:CM ratio of 1:1 at mesophilic hemi-solid state anaerobic digestion(HSS-AD).The highest volumetric methane productivity of 20.3±1.4 L/Lreactor was obtained at CS:CM ratio of 3:1 in mesophilic SS-AD,which was 1.5-fold higher compared with the maximum value in HSS-AD.The stability of the mesophilic HSS-AD processes was significantly better than that of another AD process,which was less prone to the accumulation of inhibitors,such as ammonia and volatile fatty acids.The potential ecological risk of heavy metals(Mn,Zn,Cu,Ni,As,Cd,Pb,Cr)and the concentration of tetracyclines were quantitatively evaluated.Results showed that Digestion processes increased the direct toxicity of heavy metals,except for Pb and Cr.Cd,Cu,and Zn were the main responsible for the potential ecological risk of digestate.Despite the potential ecological risk index increased slightly,digestates were all classified as the low levels.Tetracycline,oxytetracycline,and chlortetracycline reduced averagely by 76.7%,87.6%and 75.5%during anaerobic co-digestion,respectively.Furthermore,in the HSS-AD processes,the reduction rate of tetracycline and chlortetracycline was significantly(p<0.05)higher than that of solid-state anaerobic digestion.The highest volumetric methane productivity and digestate with lower potential ecological risk were obtained at CS:CM ratio of 3:1 in mesophilic solid state anaerobic digestion,indicating that this is optimal condition for co-digestion of CM and CS.