Investigation On The Anaerobic Co-Digestion Of Cow Dung And Corn Stalks Pretreated By Acid

In this study, the straw of silage maize was pretreated by3kinds of acids, known as sulfuric acid, acetic acid and phosphoric acid. After pretreatments, the straw was mixed with the cow dung and proceeded to the anaerobic fermentation under high temperature conditions. This experiment investigated the responses of maize straw to acid pretreatment, studied the biogas yield and character of anaerobic fermentation and analyzed the degradation of the substrate to obtain the impact of acid pretreatment on the anaerobic fermentation with mixed maize straw and cow dung.The results showed that:(1) The percent of VS, lipid, cellulose, hemicellulose and ligin content in the straw were increased by acid pretreatment, while the percent of protein, starch and soluble sugar were decreased. Acetic acid had less influence on protein content comparing with sulfuric acid and phoshoric acid. Sulfuric acid decreased the content of starch and hemicellulose more than other two acids, but increased the content of lipid and ligin. The effect of acetic acid pretreatment on the initial pH was more gently than the other two acids.(2) The highest accumulative biogas yield was50.72mL/g TS,71.70mL/g TS and75.26mL/g TS for sulfuric acid, acetic acid and phosphoric acid, when the acid concentrations were0%,4%and6%, respectively. For sulfuric acid (0%), acetic acid (4%) and phosphoric acid (4%) pretreament, the highest methane content was obtianed of54.9%,63.6%and63.2%respectively when the anaerobic digestion was proceeded for9,16and7days.(3) During the fermentation, the content of carbon dioxides which was advance decreased before the methane, and changed in the same way with the content of methane, while the content of hydrogen content was contrary changed. The peak yields of methane were delayed by sulfuric acid and acetic acid pretreatments and were brought forward by phosphoric acid pretreatments. The content of methane under acetic acid and phosphoric acid pretreatments were higher than that in the control test.(4) The fermentation system was faintly acid. Along with the fermentation, the total solid (TS) and VS of the system were variously dicreased according to different acid varieties and concentrations.(5) Lipid, cellulose, hemicellulose and ligin were the main compositions that were digested during the fermentation, while the protein, starch and soluble sugar were not. Acid pretreatment increased the utilization of lipid. Acetic acid and phosphoric acid pretreatments were helpful for the degradation of hemicellulose, while sulfuric acid pretreatments were helpful for the degradation of ligin. Low concentrations of sulfuric acid and high concentrations of phosphoric acid were helpful for the utilization of strach and cellulose.The anaerobic fermentation with mixed acid pretreated maize straw and cow dung is an important question in improving the efficency of bioenergy production. This study is conducted at molecular level to investigate the biogas production with acid pretreated straw, and explored the fermentation process influenced by acid pretreatments. The results are instructive for the engineering practice of bioenergy exploition in the village.