Experimental study on optimization of multiple substrates anaerobic co-digestion

Abstract

Co-digestion is becoming an important method to increase specific biogas production. Co-digestion of cow manure with corn straw was investigated and optimized in this study, and the influence of vegetable residues additive on co-digestion was explored preliminarily. The research was divided into two parts, i.e., the co-digestion of cow manure and corn straw was carried out in part A, and the co-digestion of cow manure, corn straw and vegetable residues was carried out in Part B. The experimental design with duplicates was adopted to examine the improvement of batch digestion in terms of biogas production volume, CH4 content in the biogas, contents variation of cellulose and lignin. All the digesters were run simultaneously under controlled temperature at 37 ± 0.1 °C. The results showed that the corn straw addition significantly increased biogas production, among which the substrate, with 1/7 of TS ratio of corn straw to cow manure, performed the best with a accumulative biogas volume of 350.01 ml/g•VS, increasing by 30.19% compared to the cow manure digestion alone. However, adding 1% (TS) vegetable residues to the mixture of corn straw and caw manure didn’t bring about a significant change in biogas production, the addition of vegetable residues greater than 5% (TS) caused the acidification problem. The results show that it was efficient to improve the biogas productivity by co-digesting corn straw and cow manure, but the acidification problem should be avoided when adding vegetable residues.