A Comparative Study On Phosphate Release From Sewage Sludge With Different Disintegration Processes

Phosphorus is a nonrenewable and irreplaceable resource.The recycling and utilization of phosphorus has important practical significance,which is widely concerned all over the world. Selecting the optimum conditions plays a crucial role on the effective recovery of available phosphorus in cracked sludge.This work compared the extraction efficiency and mechanism of the six different extractions methods,which includes physical crack treatment(thermal disintegration, freeze-thaw disintegration), physical chemistry crack treatment (ultrasonication disintegration,acid/alkaline disintegration and advanced oxidation disintegration)and.We analysis the variation of sludge supernatant concentrations of total phosphorus and orthophosphate and determine the optimum conditions for each crack methods and optimal conditions of phosphate release rate of sludge.The results show that after thermal cracking process, the total phosphorus and phosphate concentration were positively correlated to pyrolysis temperature and time.The total phosphorus concentration reaches a maximum(69.8mg/L)after the pyrolysis for60minutes under50oC and sludge phosphate release rate reaches36.94%.In Freeze-thaw cracking process, freezing temperature, chilled and frozen time are the main factors which affects the effectiveness of sludge crack, and melting time shows a small crack effect on the impact of sludge.Curing stage plays important impact to improve sludge characteristics.Ultrasonic energy density and ultrasonic time have a significant influence in ultrasonic crack.An intermittental ultrasound sludge crack with pulse ratio of1:1is optimal.Technology combined with different crack greatly reduces crack length and in the same phosphorus release amount, it needs less energy consumption, and it also shows a better crack treatment effect, which concludes that the order of crack effect is ultrasonication+alkaline disintegration>thermal and alkaline disintegration> alkaline. In advanced oxidation crack process,the release of orthophosphate concentrations results in descending order as follows:pH value>S2O82-dosage>Fe2+dosage.The concentration of phosphate in the sludge supernatant raises up to49.4mg/L and the rate of phosphate releaseis57.35%at room temperature (25oC) for10minutes with the reaction conditions as follows:[Fe2+]=1.5mmol/gVSS,[S2O82-]=1.2mmol/g VSS and pH=6.5.Biological phosphorus release plays a great impact on biological analysis disintegration process,but changes little on valid biological phosphorus.The largest amount of biological anaerobic phosphorus release is49.98mg/L with phosphate release rate of66.19%under the anaerobic conditions for6hours under30oC with sodium acetate as carbon source and organical loading rate of0.132gSCOD/gMLSS. It shows that the effect on physical crack is not obvious,but it operates easier and it costs less.Especially,freeze-thaw disintegration can be used in cold regions by natural treatment for high phosphate release rate.The rate of physical chemistry crak treatment is much higher than others,but besides ultrasonication disintegration crcks need add pharmacy,change original sludge state,which causes secondary pollution.In the same degree of crack, ultrasonication disintegration needs more energy consumption.The effect on disintegration process is unstable,treat process lasts long and it is difficult to achieve the requirement of anaerobic environment.To achieve higher effect of phosphorus recovery,the joint use of physical and physical chemistry crack is suitable.It provides a theoretical basis to achieve sludge utilization,and gives technical groundwork on the feasibility of recycling in nitrogen and phosphorus removal stage of sewage treatment plant by magnesium ammonium phosphate precipitation method.