Influence of rain events on the efficiency of a compact wastewater treatment plant: a case study on a university campus aiming water reuse for agriculture

In this study, the efficiency of contaminant removal from a compact wastewater treatment plant (CWTP) in a university campus under different rain conditions was evaluated. Wastewater samples were collected weekly for 1 year and the physicochemical parameters were monitored. Removal efficiency higher than 77%, reaching values above 95% for samples with lower wastewater flow rates, was found for biological oxygen demand (BOD) and total and fecal coliforms. The pH values remained in the range of 6.0–8.0. However, pH values below 6.8 impaired the nitrification rate and, therefore, the removal of total Kjeldahl nitrogen (TKN) and ammonia was lower than the expected, with concentration values above those set by the Brazilian regulation for wastewater discharge. The results show that the flow rate of wastewater at the entrance of the CWTP is directly related to the rain events, thus affecting its efficiency, mainly in the removal of total solids, turbidity, and organic matter. The assessment of the treated wastewater reuse on site for agricultural purposes showed to be a prominent and more sustainable alternative regarding the discharge of wastewater into water bodies.