Treatment System of Wastewater from Rural Settlements with Batch-Activated Sludge Process

The treatment system for rural communities with Batch-Activated Sludge Process was improved. The focus was on removal of nitrogen by intermittent aeratyion. Following the experimental results, treated water quality lower than 10 mg/l of BOD and T-N was ensured throughout the year, under the operational conditions of hydraulic retention time in aeration tank longer than 24 h and MLSS higher than 2,500 mg/l. Treated water quality of T-N was less than 5 mg/l within cumulative frequency of 66%. Removal capacity of T-N did not reach its limit under condition less than 0.05 kgN/m³d⁻¹ of influent load. Estimating from the nitrogen removal rate, consumption of alkalinity, characteristics of biomass growth and the amount of nitrogen content in MLSS, 77% of influent nitrogen was denitrified, 18% of that was discharged as treated water and 5% of that was extracted as excess sludge or SS in treated water. Fluctuation patterns of DO and ORP in a cycle by seasonally changed water temperature were effective indices for regulation of operation. A remote monitoring system was helpful to support the management, because it enabled maintenance staff to judge urgency of management from the latest real time data.