Treatment of Domestic Wastewater by Enhanced Primary Decantation and Subsequent Naturally Ventilated Trickling Filtration

To treat household wastewater, a sequence of ‘primary decantation–trickling filter percolation’ was applied in a lab-scale designed treatment system. Poly-electrolyte was used as coagulant to enhance the primary treatment and charcoal was used as carrier material in the trickling filters. Oxygen was supplied to the trickling filters by means of natural ventilation. In the lab-scale system, the enhanced primary stage removed more than 91% of the suspended solids (SS), and 79% of the total chemical oxygen demand (CODt). The subsequent trickling filtration brought a complete nitrification to the wastewaters at a volumetric loading rate (Bv) of 0.7–1.0 g CODt L^-1 d^-1. On average, the concentrations of the CODt and SS in the final effluents were about 55 and 15 mg L^-1 respectively. With respect to phosphate, physico-chemical removal was the dominant process. About 46–62% of total P was removed from the tested wastewaters. The integrated treatment system also achieved a fair degree of hygienisation. The numbers of total coliforms, fecal coliforms and fecal streptococci were decreased by 2–4 log units. The sludge production of the entire treatment system was about 1.7% (v/v) of the treated wastewater. Only primary sludge was produced; secondary sludge produced in the trickling filters was negligible. The cost savings in terms of minimization of sludge production and aeration energy are estimated to be substantial (i.e. some 50%) relative to a conventional activated sludge system.