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Effect of Hydraulic Retention Time on Pollutant Removal Performance of Biological Contact Oxidation Process Treating Hospital Wastewater

A study on hospital wastewater treatment was carried out using biological contact oxidation process. The effect of hydraulic retention time (HRT) on BOD5, CODCr and SS removal was investigated. The results showed that the removal rate of BOD5, and CODCr was ascending with the increase of HRT using the contrast test of five different HRTs. When the HRT was more than 4h, the effluent BOD5, CODCr could meet the discharge standard (GB18466-2005). In considering of raising the biodegradability of effluent, 4h was recommended in this study. However, the whole trend of SS variation of system was not obvious with the increase of HRT, and the effluent SS could not meet the discharge standard (20mg/L). Thus, the additional processing steps to remove SS would be necessary.