Biodegradation of high cellulose-lignin content agricultural wastes in bioreactors

Abstract

Bioreactor landfills are a solid waste disposal method that supply rapid solid waste degradation and methane acquirement. Bioreactors in which leachate circulation is carried out are generally operated anaerobically. However, they can also be operated under different operating conditions, depending on the type of solid waste. The biodegradation of wastes with high lignin and cellulose content is very difficult. Especially in anaerobic conditions (moreover, if there is a lack of moisture), such wastes almost never decompose. In this study, the degradation of agricultural solid wastes which are difficult to biodegrade and have high lignin-cellulose content, and the production of methane gas in semi-aerobic bioreactors have been investigated. For this purpose, two laboratory scale stainless steel simulated bioreactors were used. Sunflower stalk, which is difficult to biodegrade, were loaded into the bioreactors in different proportions and mixed with the organic fraction of municipal solid waste (OFSWM). The bioreactors were operated under different operating conditions. The contents of cellulose, hemicellulose, lignin, and initial and final organic matter in the wastes loaded into the bioreactors were examined. Parameters such as pH, COD, BOD, NH4-N in the leachate were analyzed, and the amounts of total and methane gas were measured. Initially, all bioreactors were operated anaerobically. In the decomposition of the sunflower stalk, while 43% of organic matter removal was achieved in anaerobic bioreactor, 60% of organic matter removal was realized in the semi-aerobic/anaerobic bioreactor. Thereupon, other agricultural wastes were subjected to decomposition under semi-aerobic/anaerobic operating conditions. As a result of the study, it can be said that semi-aerobic pretreatment accelerates the breakdown of agricultural wastes with high lignin and cellulose content, decreases the COD values of leachate and increases the amount of methane.