Bench-scale study of the biodegradation of grease trap sludge with yard trimmings or synthetic food waste via composting

The aim of this study was to evaluate the biodegradation of lipid-rich residues (grease trap sludge) when composted under aerobic conditions, using two different substrates - yard trimmings and synthetic food waste. Addition of lipids seemed to have a very marked effect on the temperature profiles. For the high-rate phase of composting, grease trap sludge was degraded by 39%-51% for the yard trimmings experiments and 10%-27% for the synthetic food waste treatments. For the curing phase, lipids reductions were 9%-26% and 16%-45% for treatments with yard trimmings and synthetic food waste, respectively. For the active phase of composting, the volatile solids biodegradation rate coefficient for the grease trap sludge treatments was 0.009-0.033 d(-1), while the average biodegradation rate coefficient for grease trap sludge alone was 0.058 d(-1). The yard trimmings treatment with grease trap sludge added at 5% dry solids (ds) resulted in enhanced performance, in terms of temperature profile, rate and extent of biodegradation of solids and lipids, and reduction in wet mass and water content, when compared with the composting of yard trimmings alone. For the synthetic food waste treatments, the addition of grease trap sludge (up to 10% ds) seemed to be inhibitory of the composting process.