Alleviating acid inhibition via bentonite supplementation during acidulated swine manure anaerobic digestion: Performance enhancement and microbial mechanism analysis

Swine manure is usually transmitted by the collection-storage-transport mode of the biogas project. However, this particular application pattern results in high volatile fatty acids (VFAs) concentration due to the long transition time in the collection-storage-transport process. In this work, acidulated swine manure anaerobic digestion (AD) with bentonite supplementation was firstly investigated with an expectation of acid alleviation, performance enhancement and microbial mechanism. Results indicated that the methane production rate in the 20 g/L bentonite-added digester was 2.87 fold higher than that of the control digester. Chemical oxygen demand (COD) removal rate was elevated by 140.1% via bentonite supplementation. Besides, the rapid decrease of VFAs and ammonia indicated that bentonite supplementation could offer buffering capacity and alleviate acid inhi-bition. Microbial community analysis revealed that acetoclastic methanogenesis (Methanosaeta and Meth-anosarcina) was the predominant methanogenesis pathway in this AD system. Syntrophic acetate oxidation (SAO) bacteria were discovered in the bentonite-added digester, and they converted acetate into H2/CO2 to support hydrogenotrophic methanogenesis. This study could offer guidance for acidulated swine manure AD in the practical biogas project.

Automated summary

This study investigates the acidulated swine manure anaerobic digestion (AD) with bentonite supplementation. Results show that bentonite addition can alleviate acid inhibition, improve gas production performance, and enhance microbial mechanism. The methane production rate in the bentonite-added digester is 2.87 times higher than that of the control digester, and the chemical oxygen demand (COD) removal rate is increased by 140.1% via bentonite supplementation. Microbial community analysis reveals the dominant methanogenesis pathway and the presence of syntrophic acetate oxidation (SAO) bacteria. This study provides guidance for the practical biogas project.