2023 Volume 46 Issue 1 Pages 21-33
We compared the water quality level in "the ISO guidelines for treated wastewater irrigation" with that of wastewater treated by the intermittent-aeration activated-sludge process widely adopted in rural sewerage treatment plants, and we examined the operation management necessary to achieve the required water quality level in each category. The study revealed that the BOD and SS concentrations of treated wastewater were likely to meet the water quality levels of category A in the ISO guidelines under the condition that the DO in the aeration tank is managed to be 1–2 mg L-1 at the end of the aeration period. The water quality after the intermittent-aeration activated-sludge process was higher than that after the anaerobic filter-aerobic submerged biofilter process with a flow equalization tank in rural sewerage treatment plants. Since the response of the DO concentration in the aeration tanks varied greatly depending on the diffuser system used, the importance of the management of the degree of aeration in accordance with the diffuser system was clarified. The number of coliform groups in the treated wastewater was likely to meet the quality levels of categories B and A in the case where residual chlorine is more than 0.15 mg L-1. From the perspective of using treated wastewater in irrigation, the monitoring of the residual chlorine concentration is important.
