Wastewater characteristics in partially sealed cesspit: case study from Beit Dajan, Palestine

Abstract

Raw domestic wastewater from an individual home was characterised and the water quality was followed after disposal to a partially sealed cesspit over the whole filling period of 4 months. The results revealed that raw wastewater was of medium strength according to the US EPA classification, and was more concentrated than Palestinian municipal sewage. Septage is the water accumulating in the pit, but above the accumulated bottom sludge. The septage was more concentrated than the raw sewage. The specific household water consumption, wastewater generated, septage collected by vacuum truck and septage water infiltration were respectively (59 L/c.d; 100%), (52 L/c.d; 87%), (11 L/c.d; 19%) and (40 L/c.d; 68%). The specific removal of pollutants in the cesspits were: BOD5 (78 g/c/d), COD (62 g/c/d), N total (52 g/c/d), PO4-P (66 g/c/d) and TSS (69 g/c/d). The specific pollution loads of emptied septage were BOD5 (5.6 g/c/d), COD (19.3 g/c/d), N total (4.8 g/c/d), PO4-P (0.17 g/c/d) and TSS (25.5 g/c/d). The concentrations of heavy metals (Cu, Pb, Mn, Fe and Zn) in septage water were not in compliance with heavy metals concentration limits of the Palestinian regulations for wadi disposal and effluent reuse in agriculture. As a consequence, septage disposal in wadis and agricultural fields is not safe. However, according to municipal regulations, the heavy metals concentrations allow septage to be disposed in the Al-Bireh wastewater treatment plant septage receiving unit, to be further treated in the aerobic system. Regarding nitrogen that is removed in the cesspit, the vast majority will most likely exfiltrate out of the cesspit into the surrounding soil, and might potentially reach the groundwater. Therefore, cesspits should be replaced by proper wastewater treatment systems.