A cost-effective method for the treatment of reject water from sludge dewatering process using supernatant from sludge lime stabilization

•Sludge lime stabilization supernatant was used as a cheap Ca source for P removal.•High content of calcium and alkalinity in the supernatant favors P precipitation.•Phosphorus removal from reject water achieved 90% by dosing 15% supernatant.•Precipitates transformed from hydroxyapatite to tri-calci...

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Bibliographic Details
Published in:Separation and purification technology 2015-03, Vol.142, p.123-128
Main Authors: Ren, Weichao, Zhou, Zhen, Jiang, Lu-Man, Hu, Dalong, Qiu, Zhan, Wei, Haijuan, Wang, Luochun
Format: Article
Language:English
Subjects:
Calcium
Dewatering
Dosing
Lime
Lime stabilization
Phosphates
Phosphorus
Phosphorus removal
Reject water
Sludge
Stabilization
Wastewater treatment
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Summary:•Sludge lime stabilization supernatant was used as a cheap Ca source for P removal.•High content of calcium and alkalinity in the supernatant favors P precipitation.•Phosphorus removal from reject water achieved 90% by dosing 15% supernatant.•Precipitates transformed from hydroxyapatite to tri-calcium phosphate with rising pH. This paper describes a cost-effective method for phosphorus removal from reject water of sludge dewatering process by using supernatant from sludge lime stabilization (SLS) processes, which are extensively used in China. Supernatant from SLS processes contains high concentration of calcium and high alkalinity hindering COD and ammonium nitrogen removal but favoring phosphate precipitation. Effects of pH and dosing ratio between supernatant and reject water on simultaneous removal of phosphorus and organic substances were evaluated. Both pH and Ca/P ratio increased with increasing dosing ratio of supernatant and reject water. The phosphorus removal achieved 90% when dosing ratio maintained above 15%. COD and humic substances were also effectively removed from reject water by adding SLS supernatant. X-ray diffraction analysis and morphology of harvested precipitates revealed that when pH increased from 7.49 to 9.77, the crystallinity increased, and hydroxyapatite converted to tri-calcium phosphate simultaneously. This method not only saves costs for chemical precipitants, but also favors nutrient removal by increasing alkalinity for nitrification and adding carbon source for denitrification, meanwhile reduces risks of pipeline blockage in wastewater treatment plants.
ISSN:1383-5866
1873-3794
DOI:10.1016/j.seppur.2014.12.037