Biodegradation and environmental impact of lipid-rich wastes under aerobic composting conditions

The aim of this research was to evaluate the 'compostability' of organic wastes rich in lipids, such as canola oil and grease trap sludge, when added to yard trimmings or food wastes. This study was divided in three parts: composting process performance, environmental impact, and compost quality. In addition, a composting simulation model was developed in this study. Aerobic biodegradation of yard trimmings and food waste loaded with lipidic compounds, up to 35% dry solids (ds) for the canola oil tests, and up to 10% ds for grease trap sludge, produced satisfactory results in terms of temperature profile, lipids and volatile solids reduction, wet mass consumption, and moisture content removal. For the high rate phase of composting, treatments with either canola oil or grease trap sludge added resulted in biodegradation rate values for volatile solids (kvs) of 0.009- 0.039 day"1. In contrast, yard trimmings alone had a kv sof 0.033 day"1 and food waste alone had a kv sof 0.023 day-1. For treatments with yard trimmings as main substrate, the addition of 5% ds grease trap sludge had similar air emission as yard trimmings alone. The addition of 10% ds grease trap sludge to yard trimmings resulted in more nitrous oxide and carbon dioxide, less ammonia, and similar odor emissions, when compared with the emissions of yard trimmings alone. As for the phytotoxic potential, treatments with 10% ds grease trap sludge added (to food waste or yard trimmings) resulted in germination indexes similar to the treatment with distilled water alone, but their values were significantly smaller than the values for the treatments with 5% ds or no lipid added. A 'macrokinetic' model was developed using a dynamic modeling approach (mass and energy balances with kinetic parameters) for the simulation of the composting process. The model allowed for the inclusion of lipid wastes as an energy amendment, while including provisions for temperature control through aeration. These produced satisfactory results in terms of thermal parameters simulation. As a practical recommendation, yard trimmings composting with grease trap sludge added at 5% ds would result in enhanced thermal performance, improved rate and extent of biodegradation of solids and lipids, and greater overall reduction in wet mass and water content, when compared with the composting of yard trimmings alone.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat