Some properties of a sequencing batch reactor for treatment of wastewater containing thiocyanate compounds

Thiocyanate (SCN) compounds in photo-processing wastewater (PPWW) could be treated by an SBR system without any release of thiocyanate to the atmosphere during the aeration step. An SCN loading greater than 84 g m−3 d−1 showed negative effects on the growth of bio-sludge and removal efficiencies of the system. The acclimatization period of the system was increased with an increase in SCN concentration or loading. The COD, BOD5, TKN, and SCN removal efficiencies were 96.0±1.6%, 72±2%, 49±5%, and 82±3%, respectively, under an SCN loading of up to 84 g m−3 d−1. The removal efficiency of the system was repressed by SCN due to the repressed growth rate of nitrification bacteria. However, the removal efficiency could be increased with an increase in HRT or a decrease in SCN loading. Also, increases in HRT or decreases in SCN loading led to increased sludge age or solid retention time (SRT) and decreased the sludge volume index (SVI) value. The SRT and SVI of the system with synthetic wastewater containing 840 mg l−1 SCN under an HRT of 3 days (SCN loading of 280 g m−3 d−1) were 3.9±0.7 days and 65±4 ml g−1, respectively, while they were 11.2±0.8 days and 55±6 ml g−1, respectively under an HRT of 10 days (SCN loading of 84 g m−3 d−1).