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Factors influencing the re-release of anaerobic phosphorus in SBR sludge treatment

A Sequencing Batch Reactor (SBR) and a T oxidation ditch were used as a model to calculate the amount of phosphorus returned from the mud line to the water line,and laboratory-scale and pilot-scale SBR reactors were applied to study the effects of carbon sources,nitrate concentration and primary sludge proportion on anaerobic phosphorus re-release. The results indicated that the amount of phosphorus returned from the mud line to the water line accounted for 10%~16% of phosphorus removed from daily treatment. It was found that different carbon sources could lead to different P-release rates and a rapid P-release rate could be obtained with low-grade volatile fatty acid (VFA),such as acetate,acting as carbon source. Phosphorus re-release was significantly inhibited by nitrate,but the P-release rate became rapid after 4 h when the nitrate concentration was less than 0.2 mg·L-1. The phosphorus re-release was advanced by 4 h by adding primary sludge. As the proportion of primary sludge increases,the P-release rate will grow,but the total amount will remain unchanged. The results could provide reference data for control of phosphorus re-release in sludge treatment at SBR sewage plants.