Alkaline pre-treatment (NAOH) as a strategy to increase the performance and feasibility of the anaerobic digestion of cattle slurry

Abstract

ABSTRACT Dairy cattle manure with bedding (CB), including manure, urine, water, and shavings, is lignocellulosic biomass and needs to be pre-treated in anaerobic reactors to enhance biomass digestibility. This study analyzed the technical and economic feasibility of physical treatment (milling) and alkaline treatment of CB for biogas production. Pre-treatment included drying, milling, and alkaline hydrolysis at room temperature for 24 h. Maximum biogas production was determined using the biochemical methane potential (BMP) test. Physicochemical analyses were performed to characterise CB before and after pre-treatment and the BMP test. The characteristics of the lignocellulosic material were examined by scanning electron microscopy. The economic feasibility (return on investment) of each treatment (USD per ton of CB) was determined. Treatment with 3% NaOH achieved the highest biogas production (771 mL per kg of volatile solids) and was 104.5% higher than that of milling and 124.7% higher than that of chemical pre-treatment with 4% NaOH. The analysis of economic feasibility showed that the payback period of treatment with 3% NaOH was 1.4 years for scenario 1 (continuous stirred tank reactor - CSTR) and 3 years for scenario 2 (covered lagoon digester). These results demonstrate the feasibility of producing biogas as a renewable energy source via the anaerobic digestion of CB.