Contact stabilization process for hospital wastewater treatment: effects of colloidal organic matter

In this study, the treatability of hospital wastewater was investigated using a contact stabilization process on a laboratory scale. A detention time of one hour was selected for sludge settling and separation of treated effluent, and removal efficiency was measured at contact times of 30, 60, and 90 min, and stabilization times of 4.5 and 5.5 h. Based on the different detention times, 6 series of experiments were designed. Results showed that after an initial rapid COD removal in the first 30 min, COD values fluctuate in the time range of 30–90 min. However, in the case where COD values reduce in the second stage, this recovery is negligible; thus, the time of 30 min is considered as the optimal detention time for the contact reactor. Sludge volume index (SVI) values of 119.20 and 109.17 mL/g were obtained for stabilization times of 4.5 and 5.5 h, respectively. Therefore, the longer the stabilization time, the closer the SVI is to 100 mL/g. Moreover, lower settled sludge volume (SSV) value at 5.5 h of stabilization shows better characteristics compared to 4.5 h of stabilization. Furthermore, COD removal efficiency at the optimum contact time is higher when 5.5 h is selected for stabilization.