Study On Low-Temperature Drying Of Sewage Sludge And The Condensate Pollution Characteristics

With the constant perfection of the sewage treatment plant, the sludge production sharp increases. Sludge drying technology can effectively reduce the sludge volume and make the sludge stabilized. Even the sludge can be used as energy source after drying. However, the research on sludge drying characteristics and the water quality of the condensate with different sewage sludge treatments has not been reported widely. This paper mainly studies the effects on sludge particle drying characteristics from different sewage and sludge treatments and emphatically analyses the drying temperature influence on the water quality and the change law of organic compounds composition of the drying condensate.Three dewatered sludge with different particle sizes were dried at constant temperature 65℃, 85℃, 105℃and 125℃respectively. The results showed that reducing sludge particle size or increasing the drying temperature had good effect on improving the drying rate of sludge. The drying rates of three sludges were followed by digested sludge, biological aerated filter sludge and excess sludge, respectively. SEM analysis indicated that there were significant differences in the micro-morphologies of three sludges, such as digested sludge with very rough surface and loose structure, excess sludge with smooth surface and dense structure and biological aerated filter sludge with rough surface and less dense structure. Therefore, there was a positive correlation between the surface roughness of sludge and the drying rate.In this paper,the water quality and organic compounds composition of the liquor condensate has been analyzed through the simulation for sludge low-temperature drying under laboratory conditions. The results showed that: when the temperature was higher than 185℃, the COD and NH₄⁺-N concentrations of the liquor condensate was respectively more than 2000mg/L and 1000mg/L, which belongs to the high concentration organic wastewater and could not be discharged without proper treatment to reach the standard. The organic compositions in the liquor condensate were complicated: in low temperature stage （105℃ ¹45℃）, the main components were alcohol and chain alkane, the content of which were 23% and 32% severally; In high temperature stage （205℃）, the mains were olefins and aromatics, the contents were 19.39% and 26.34% respectively. There were no organic pollutants controlled in《Surface Water Environment Quality Standard》and EPA in the condensate. Therefore the toxic of condensate is relatively lower.