Study On Sewage Sludge Dewatering By Sludge From Water Treatment Plant

The increase of population raises water demand and discharge,thus increasing water treatment load to water supply plants and sewage plants.As a by-product of water treatment,the discharge of sludge also increases rapidly,which brings inconvenience to the disposal of sludge.The sludge of water supply plant is composed of a large amount of inorganic and a small amount of organic.The inorganic component mainly comes from the residue of flocculants such as iron and aluminum.It can be used to regulate excess sludge so as to realize the dehydration of the excess sludge and the recycling of the water supply sludge.In this paper,Iron sludge of water supply plant was modified and extracted which were used as skeleton particles and flocculant materials respectively to recuperate the excess sludge to dewater,and the effect and mechanism of the dewatering were also studied.This paper leads to results as below.Under the conditions of 300℃calcined temperature and 3 hours calcined,the Iron Sludge-Modified（ISM）as a skeleton particles had the best dewatering effect.When the initial sludge p H was 3 and the ISM dosage was 30%DS,the SRF and CST were reduced to 0.8×10⁹ s²/kg and 10.6 s,which had a decreased of 48.2%and42.7%respectively.When ISM was combined with Fe Cl₃,30%DS ISM was added first and then 60 mg/g Fe Cl₃ was added after that,it could reduce W_c to 68.5%.Compared with the raw sludge,the supernatant polysaccharide and protein were reduced by 22.2%and 28.1%respectively.Turbidity and SCOD reduced by 80.9%and 65.8%.When the ISM was used separately,the compression coefficient of the sludge cake was reduced from 1.39 to 0.95,and when it was combined with ferric chloride,the compression coefficient was further reduced to 0.75.The hydrochloric acid was used to extract the iron in the ISM.The optimum conditions for acid extraction were:the ISM calcined temperature was 500℃,the extraction temperature was 70℃,and the extraction time was 1 h.The iron concentration in the acid extraction could reach 10.64 g/L.When the dosage of acid extract was 8 mg Fe/g,the SRF and CST were reduced to 0.9×10⁹ s²/kg and 17.4 s respectively,which were 58.1%and 27.8%lower than that of the raw sludge.When combined acid extract with ISM,under the conditions of 8mg Fe/g acid extract and 30%DS ISM,the SRF and CST could reduce to 0.83×10⁹ s²/kg and19.3 s respectively,and Y_N reached 46.07 kg/（m²h）.Compared with the raw sludge,the supernatant polysaccharide and protein were reduced by 30.9%and 38.5%respectively.Turbidity and SCOD were reduced by 86.9%and 73.2%.When the acid extract was used separately,the compression coefficient of the sludge cake was reduced from 1.39 to 1.07,and the compression coefficient could be further reduced to 0.69 when it combined with the ISM.According to the relationship between the fractal dimension and dewatering indexes,it could be concluded that the fractal dimension had a correlation with dewatering performance,settlement performance and supernatant turbidity.The change of floc fractal dimension could be used to monitor the sludge dewatering effect and effluent water quality.