Abstract
The effects of different initial pH value, temperature and heating time on sludge dewatering performance were studied by treating sludge with acid-heat combination at low temperature and taking dewatering rate (amount of filtrate per unit time) and dewatering degree (moisture content of mud cake) as indexes to evaluate the sludge dewatering performance. And the mechanism of action was preliminarily discussed by analyzing the concentration of SCOD, protein and polysaccharide in sludge supernatant, Zeta potential and floc morphology of sludge. The results showed that the concentration of organic matter in sludge supernatant increased significantly when the sludge was treated by acid-heat combination, which indicated that the method promoted the fragmentation and dissolution of sludge flocs, and the internal bound water was released more, at the same time, the decrease of Zeta potential and the increase of temperature were beneficial to the flocculation of sludge, which effectively improved the degree and rate of sludge dewatering. The optimal conditioning conditions were determined as follows: pH 3, temperature 90°C and heating time 40 min. Under such condition, the sludge dewatering rate reached 21.30 ml/min and the moisture content of mud cake decreased to 63.20%.
Highlights
The effects of different initial pH value, temperature and heating time on sludge dewatering performance were studied by treating sludge with acid-heat combination at low temperature and taking dewatering rate and dewatering degree as indexes to evaluate the sludge dewatering performance
Xu [15] et al found that after acid-heat treatment of sludge at 170°C, pH 2 and heating time 60 min, the combined water decreased from 11.21 g/gDS to 7.07 g/gDS, and the moisture content of mud cake after centrifugation was as low as 55.65%
Because the dewatering rates at pH values of 6.00 and 6.67 were too low, the filtration time was too long, and the error caused by water self-evaporation was relatively large, so the moisture content of mud cake of these two values was not given in the figure
Summary
When urban sewage treatment plants adopt activated sludge method to treat sewage, a large amount of residual sludge will be generated. Studies have shown that when the sludge heating temperature is lower than the critical value, the dewatering performance decreases [12]. Raynaud et al [13] found that under acidic conditions, sludge flocs would be decomposed, which could reduce the moisture content of filter cake, enhance the stability of flocs and improve the sludge dewatering performance. Xu [15] et al found that after acid-heat treatment of sludge at 170°C, pH 2 and heating time 60 min, the combined water decreased from 11.21 g/gDS (raw mud) to 7.07 g/gDS, and the moisture content of mud cake after centrifugation was as low as 55.65%. This paper mainly studied the effect of acid-heat combined treatment at low temperature (
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