Abstract
To investigate the influence of lipid concentration (of total solids, w/w) on anaerobic treatment of food waste under thermophilic condition, a siphon-driven self-agitated anaerobic reactor was operated for 220 days. The average lipid concentration was changed from 12.8% to 59.3% (w/w) step by step. The gas production rate increased from 1.97 to 2.31 L/L/d with lipid concentration increased from 12.8% to 19.7% (w/w), whereas decreased sharply to 0.78 L/L/d when the concentration further increased to 59.3% (w/w). The COD recovery from output at different lipid concentration was analyzed in this study. With the concentration increased from 12.8% to 59.3% (w/w), the percentage of COD recovered as methane gas decreased from 80.9% to 35.4%, while the percentage of COD remained in the effluent was also decreased significantly from 15.5% to 2.60%. The lipid concentration under 40% (w/w) was recommended in the co-digestion of food waste and grease trap waste.
Highlights
High-strength lipid wastes FOG normally could not be directly released to the collection system in many metropolitan areas
After day 53, during the co-digestion of grease trap waste (GTW) and food waste (FW), the influent lipid concentration was increased to 16.1 g/L (59.3% w/ w of total solids (TS)), step by step
This concentration is much lower than the reported effluent lipid concentrations (1.1 to 4.5 g/L) in the codigestion of GTW and FW using a mesophilic semi-continuous anaerobic digester [27]
Summary
High-strength lipid wastes FOG (fat, oil, and grease) normally could not be directly released to the collection system in many metropolitan areas. This is mainly because lipid wastes can accumulate in drainage pipes, and forming hardened deposits through a chemical reaction or a physical aggregation process [1]. These deposits lead to a reduction in conveyance capacity and to sanitary sewer overflow that cost municipalities millions of dollars each year in cleaning, repairing, and maintenance fees [2]. A growing number of researchers have investigated the codigestion of lipid-rich waste with other organic wastes [12,13,14]
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