Treatment of wastewater from a school in a decentralized filtration system by percolation over organic packing media

Based on results obtained in the laboratory a WWTP composed of a septic tank and an aerated percolating filter packed with organic media was built for a school. The system can treat 18 m³ d⁻¹ and was operated with a hydraulic loading rate of 0.078 (m³ m⁻² d⁻¹). For 360 days different operational conditions including start-up; stabilization; operation with aeration and non aeration; effect of rainy season, breaks from activities due to holidays and restart; were monitored and described in the article. Once stabilized, the system was able to remove, without the need for mechanical aeration, 97% of BOD₅, 71% of COD, 93% of TKN, 11% of PO₄⁻-P, 95% of TSS, 96% of VSS, in addition to having a removal efficiency of 4 log units of Faecal Coliforms (FC) and 100% helminthes eggs (HE). With this quality, the treated wastewater can be chlorinated and reused to irrigate green areas and/or in toilets. Although sanitary wastewater has a high concentration of Total-N (250 mg L⁻¹) and a C/N ratio of less than 1, the system removed 65% of Total-N. Finally it was observed that after non activity periods, there was neither system failure nor the need to re-stabilize the system.