Research On The Characteristics Of Activated Sludge At Different Temperature

Treatment processes usually treat wastewater at common or moderatetemperatures, however, many kinds of industrial wastewater are produced at hightemperature. It has been suggested that thermophilic aerobic processess areadvantageous compared to conventional mesophilic alternatives because of thereduced colling cost. Additionally, residual heat will be produced in the industrialproduction process. If the biological treatment process can be used at hightemperature, reaction rate will be quicken up and reactor volume will be reduced. Butat different temperatures, the composition of microorganism population and relevantcharacteristics are different. So the research on characteristics of microorganisms is ofsignificance to biological treatment at high temperatures.For the purpose of making clear the characteristics of activated sludge frommoderate temperature to high temperature, in the range from 25℃ to 70℃ organicpollutant degradation rate, activated sludge concentration, activated sludge settlingcharacteristics and effluent turbidity and kinetics of microorganism growth werestudied.This experiment was conducted from moderate temperature to hightemperature using sequencing batch reactors, synthetic wastewater, and activatedsludge from Tianjin Jizhuangzi wastewater treatment plant. Under three differentCOD inffluent load, activated sludge is cultivated and observed as temperatureincreases.The experiment results show in the temperature range from 25℃ to 35℃ thedegradation capacity of COD, phosphorus and NH4+-N is very strong and stable, andalso degradation rate will decrease as temperature increases. The increase oftemperature has more effect on adsorption of organic pollutant than decomposabilityof COD. 40℃ can be looked on as the dividing line of moderate microorganismsand thermophilic microorganisms. Compared to the range 25-35℃, beyond 45℃ thedegradation capacity of activated sludge on COD is doubled. The drop of degradationrate at high temperature is caused by low microorganism concentration. In addition, astemperature increases, the settleability of activated sludge will decrease and effluentturbidity will rise. Meantime, the color of activated sludge will change from darkbrown to brick red. No protozoan and filamentous fungus were observed in activatedsludge at high temperature.The theoretical analysis reveals that with the increase of temperature sludgeconcetration will be reduced, but the degradation capacity will be strengthened.Meanwhile, it was found that vmax and Kd of thermophilic microorganisms are higherthan those of moderate microorganisms, but coefficient Y of them are similar. Alsowhen equivalent organic substrate is decomposed, the sludge production ofthermophilic microorganisms is less than that of mesophilic microorganisms.