A pilot scale study on high biomass systems: Energy and cost analysis of sludge production

A pilot scale high biomass filtration system (capacity: 100 m3/d) was evaluated in terms of energy consumption and operational costs based on energy and sludge withdrawal. The pilot plant was operated for over two years and results of a particular period, which comprises complete sludge retention time, were presented as the sludge yield (kgMLSS/kgCOD). The energy and operation cost of the system was compared to that of a full-scale conventional biological nutrient removal (BNR) plant where it was constructed as a pilot plant. The total energy consumption in the pilot plant was about 1.03–1.17 kWh/m3 of permeate; 65–70% of this energy was consumed for air scouring. On the other hand, the full-scale plant consumed 0.45 kWh/m3 of treated wastewater on the average. The sludge production per COD removed in the full-scale plant was about 0.65 kgSS/COD and the MLSS concentration in the tanks was kept around 5000 mg/L. The initial (21 days) average sludge yield (MLSS between 2500 and 5000 mg/L) was 0.72 kgMLSS/kgCOD in the pilot tank. However, the major decline in the sludge yield was observed until the sludge concentration reaches 7000 mg/L (after 62 days) and the average yield was about 0.25 kgMLSS/kgCOD when the MLSS concentration was nearly 15,000 mg/L (after 140 days). Operating the full-scale plant as a biomass filtration system, despite the increase in the electricity cost for aeration by 28–41% as a result of membrane scouring air, the total operation cost decreases by 9–15% because of the decrease in the expenses for sludge dewatering, drying and ultimate disposal.