Abstract
The high water content and huge volume of activated sludge greatly increase the costs for disposal and transportation. Combined use of acid and flocculant can effectively enhance the sludge dewatering performance. In the present work, the influence of dosing order of acid and polydiallyldimethylammonium chloride (PDMDAAC, a typical flocculant) on sludge dewaterability was investigated. Results showed that the PDMDAAC + acid process exhibited a better dewatering capability than the acid + PDMDAAC process under the identical conditions, which indicated that PDMDAAC should be dosed before acid treatment. The water content decreased from 75.4% to 67.8% for the PDMDAAC + citric acid process. The potential mechanisms behind sludge dewatering were explored, and the decomposition of tightly-bound extracellular polymeric substances (TB-EPS), increased particle size and aggregated morphology of the sludge flocs were found to be closely correlated with the enhanced dewatering performance. These results confirmed that the PDMDAAC + acid treatment achieved a better performance in enhancing sludge dewatering, and will help to understand the combined conditioning process of acid and flocculant.
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