A novel free ammonia based pretreatment technology to enhance anaerobic methane production from primary sludge

This study proposed a novel free ammonia (FA, i.e., NH₃) pretreatment technology to enhance anaerobic methane production from primary sludge for the first time. The solubilization of primary sludge was substantially enhanced following 24 h FA pretreatment (250–680 mg NH₃-N/L), by which the release of soluble chemical oxygen demand (SCOD) (i.e., 0.4 mg SCOD/mg VS added; VS: volatile solids) was approximately 10 times as much as that without pretreatment (i.e., 0.03 mg SCOD/mg VS added). Then, biochemical methane potential (BMP) tests demonstrated that FA pretreatment of 250–680 mg NH₃-N/L was capable of enhancing anaerobic methane production while the digestion time was more than 7 days. Model based analysis indicated that the improved anaerobic methane production was due to an increased biochemical methane potential (B₀) of 8–17% (i.e., from 331 to 357–387 L CH₄/kg VS added), with the highest B₀ achieved at 420 mg NH₃-N/L pretreatment. However, FA pretreatment of 250–680 mg NH₃-N/L decreased hydrolysis rate (k) by 24–38% compared with control (i.e., from 0.29 d⁻¹ to 0.18–0.22 d⁻¹), which explained the lower methane production over the first 7 days’ digestion period. Economic analysis and environmental evaluation demonstrated that FA pretreatment technology was environmentally friendly and economically favorable. Biotechnol. Bioeng. 2017;114: 2245–2252.