Influence of temperature on process performance of activated sludge in coking wastewater treatment plant

摘要

Coking wastewater contains toxic compounds such as ammonia, phenolics, cyanides, thiocyanate, andnthiosulfate. In normal situation, these compounds can be 100% decomposed by activated sludge in thenwastewater treatment plant. However, a new factor, high water temperature, caused by the covering of thenbasins, has been found to reduce the removal rate of the pollutants, especially the thiocyanate.nSeveral remediation measures were applied to improve the biological process performance. A series ofnbatch and continuous-flow biodegradation tests have demonstrated that the relatively low temperaturenranging from 20 to 37°C attained perfect removal efficiency (~100%) of SCN- from the coke plant wastewater.nWhen the temperature is increased to 38, 39°C, the SCN- removal rate decreased to 30~50% after 48 hours ofntemperature shift. Moreover, when the temperature is increased to 40 to 45°C, SCN- biodegradation isnsignificantly decayed one day after the temperature shock, and the SCN- removal efficiency dropped graduallynto 0%, with microbial deterioration during day 1 to day 4. Meanwhile, the COD removal has also decreasednfrom 85% down to 45% at 45°C. Both laboratory verifications confirmed that 40°C should be the critical waterntemperature for the SCN- degrading microbe to function well in the activated sludge process.nIn order to stabilize the pollutant removing ability of the procedure, the water temperature of aeration basinnis set to operate under 37°C. Four modifications were practiced on site to decrease the temperature ofnactivated sludge. Only the last alternative measure worked well with the opened hand hole, 50% of total covernarea, to discharge the water vapor and gas emission from the head space of aeration basin. The waterntemperature has dropped from 41 to 36°C in the early summer of June with ambient temperature of 37°C,nsuggesting that partially uncovering the basin does help maintain the water temperature.nFinally, we suggest some measures that can be applied to establish a standard process on site in order tonensure that the aeration basin temperature stays under 37°C and that our biotreatment system can maintainnits function in the future.