Transformation of lipids in activated sludge

Transformation of lipids in activated sludge treatment plants is of interes t for two reasons: lipids contribute 30-40 % of the chemical oxygen demand (COD) in wastewater, and they may stimulate the growth of filamentous micro organisms in nutrient removal activated sludge plants. The transformation o f lipids was investigated under aerobic and anoxic conditions by measuring the oxygen and nitrate uptake rates (OUR and NUR). The maximal OUR and NUR of long-chain fatty acid was found to be at the same level as acetate indic ating that long-chain fatty acid was as easily consumable. However, the ads orption of long-chain fatty acid to surfaces of sludge flocs made it diffic ult to determine initial uptake rates of long-chain fatty acids. It was not possible to describe the hydrolysis rate of triacylglyceride by OUR and NU R to long-chain fatty acids because the hydrolysis rate was very slow. For a better description of the processes involved in transformation of lipids, a conceptual model was suggested. The processes in the suggested model wer e the adsorption/desorption of both triacylglyceride, and long-chain fatty acid onto surfaces of sludge flocs, hydrolysis of triacylglyceride by lipas es and the uptake of long-chain fatty acid by bacteria under various condit ions. The model can be helpful to structure design and evaluation of activa ted sludge experiment with lipids.