PERFORMANCE OF A CONTACT STABILIZATION PROCESS FOR DOMESTIC WASTEWATER TREATMENT OF CALI, COLOMBIA

The contact stabilization process has been applied in full-scale plants which treat domestic wastewater. The main advantage of this process is the short hydraulic retention time (HRT) in the contact reactor (CR), allowing treatment volumes significantly lower than in conventional activated sludge processes. This paper presents an analysis of the influence of the HRT and sludge recycle rate (r), on the performance of a contact stabilization process to remove organic matter and solids from the domestic wastewater of the city of Cali (Colombia). The research was carried out at Canaveralejo Wastewater Treatment Plant (C-WWTP) facilities. The contact stabilization process was assessed at a pilot-scale unit treating raw wastewater influent to the C-WWTP. The HRT varied between 0.84 to 1.66 h in the contact reactor and 2.56 to 4.65 h in the stabilization reactor (SR). The evaluation of HRT was carried out with different r varying between 40 and 100%. The operational conditions that allowed for us to obtain the best performance in terms of organic load removal (14.05 kgCOD.d(-1)), with removal efficiencies of chemical oxygen demand (COD), biological oxygen demand (BOD5), and total suspended solids (TSS) of 86, 87, and 82 %, respectively, were an HRT of 0.84 h in CR, and 4.11 h in SR, with a sludge recycle rate of 40%. In order to guarantee this performance, average values of sludge retention time (SRT) of 6 d; a volumetric organic load (VOL) of 2.13 kgBOD(5).(m(3).d)(-1); a food microorganism relation (F/M) of 0.89 kgBOD(5).(kgVSS.d)(-1); and a mixed liquor volatile suspended solids (MLVSS) of 1125 mg.L-1 in CR, and 3173 mg.L-1 in SR, must be maintained.