Experimental Study On Release Efficiency And Recovery Technology Of Phosphorus In Sludge

Studying the recovery of phosphorus（P）in sludge was of great significance for the realization of sludge waste utilization,the sustainable development of P resources and the prevention and control of water eutrophication.For the purpose of recovering P in sludge,this paper analyzed the proportion of different forms of P in sludge of the sewage treatment plant with three different treatment processes,and focused on the impact of different reaction conditions on the release of P from the sludge;The experimental conditions were optimized by response surface method（RSM）to obtain P-rich supernatant.Phosphorus was recovered in the form of magnesium ammonium phosphate（MAP）,and the recovery efficiency was analyzed.At the same time,the P leaching efficiency of sludge incineration ash was discussed.The main findings were as follows:1.After the sewage was treated,P was discharged in two forms:effluent and sludge,of which the proportion of P discharged in the form of sludge was as high as more than 60%.The total P content of the sludge was high and it was an available P-rich resource.The P in the sludge mainly existed in the form of inorganic P,accounting for 71.7%-89.3%of the total P;non-apatite was the main form of inorganic P,accounting for about 50%.2.During pyrolysis at low temperature,the release rate of total P in the sludge was the highest at 50℃,reaching more than 50%.When acid and alkali were added,the P release effect of the sludge was better than the neutral condition under acidic or alkaline conditions.The sludge had the highest P release rate at pH 4.0,about 40%;under alkaline conditions,the P in the sludge Limestone inorganic P would be released in large quantities.When EDTA was added,the release rate of apatite inorganic P was greater than that of non-apatite inorganic P.3.Adopted RSM to study the influence of pH,reaction temperature and EDTA concentration on the release process of P,and optimized the reaction conditions.With the release rate of P as the response value,established a mathematical model to obtain the optimal experimental conditions.The model had a high degree of fit（R² is 0.9870）,and the effect of various factors on P release was:pH>reaction temperature>EDTA concentration.The optimized reaction conditions were:pH value 4.0,reaction temperature 53℃,and EDTA concentration 14.5 mmol·L^-1.Under this reaction condition,the P release rate reached 62.91%.4.The P in the supernatant of the sludge was recovered by the MAP precipitation method,and the condition range for recovering P was obtained.The precipitation reaction of MAP could be completed quickly within 10 minutes.Considering comprehensively the economics of the experiment,the optimal reaction conditions for P recovery were:pH 9.5,n（Mg）:n（P）1.2,and reaction time 10 min.5.Burned the dried sludge at different temperatures（600,700,800,850 and900℃）and obtained incineration ash;acid and alkali were used for leaching P from the incineration ash to obtain the optimal leaching parameters.The leaching effect of H₂SO₄ was better than that of HCL and HNO₃,and alkali could not effectively leaching P.When the incineration temperature was 900℃,the total P leaching rate of the sludge was the highest,and the content of phosphate in the supernatant was above80%,which was suitable for the recovery of P.When the leaching agent was H₂SO₄,the optimal liquid-solid ratio for leaching P was 60mL·g^-1.