Effect of carbonate on phosphorus recovery from anaerobic digestion supernatant of sewage sludge
- Received Date: 30/07/2009
- Accepted Date: 11/07/2009
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Key words:
- anaerobic digestion supernatant of sewage sludge /
- carbonate /
- phosphorus recovery /
- calcium phosphates /
- leaching liquor of fly ash
Abstract: The influence of carbonates in the anaerobic digestion supernatant on the precipitation of calcium phosphates was studied with the leaching liquor of fly ash as the calcium source, the effects of carbonates on the precipitation of calcium phosphates and the characteristics of the product were investigated. The experimental results showed that, when the reaction pH value, the reaction Ca/P molar ratio and the reaction time were 10.0, 1.67 and 10 min, respectively, at the concentration of carbonates 2 400 mg/L (as CaCO3), the P recovery rate was 78.53%, and the P content (as P2O5) in the recovered product was 28.93%. By adding hydrochloric acid for adjusting the digestion supernatant to the pH value 4 and below, the P recovery rate approximated to 100%, and the P content (as P2O5) in the recovered product reached 43.08%. The calcium carbonate in the digestion supernatant tended to precipitate under the condition of high concentration of carbonates, and thus reduced the P recovery rate, the P content in the product and the purity of the product. The carbonates were removed effectively by the acidification, as decreased its adverse influence on the P recovery.
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