| Phosphorus is an important and non-renewable resource with limited reserves in nature.There are abundant phosphorus in the excess sludge which can be used as an alternative phosphorus resource.Effects of ozone and alkaline on the sludge disintegration were studied based on the investigation of sludge characteristics in Shijiazhuang.The migration and transformation of phosphorus in the process of ozonation and alkaline hydrolysis was explored respectively to obtain the optimal method for phosphorus recovery.The ammonium magnesium phosphate precipitation method was used to recover the phosphorus in supernatant after alkaline hydrolysis of the sludge.The purpose of this paper aimed to provide technical support for sludge recycling.The main conclusions are as follows:The investigation data showed that the excess sludge obtained from three typical sewage treatment plants in Shijiazhuang was weakly alkaline and the pH was between7.15 and 8.47.The average moisture content was 99.13%,and the mixed liquor suspended solids?MLSS?was about 15 569 mg·L-1.The average content of total phosphorus was22.15 mg·g-1.The sludge has great potential for phosphorus recovery.The contents of common heavy metal pollutants in excess sludge can meet the standard of landscaping for sludge disposal in municipal sewage treatment plants?GB/T 234862009?.The optimum ozone dosage was 0.15 gO3·gSS-1,and the total phosphorus in liquid phase(TP?L?)in the supernatant was 38.26 mg·L-1.In the process of ozonation(0.020.20gO3·gSS-1),the orthophosphate in liquid phase(PO43--P)was the main form and occupied71.27%89.62%of TP?L?.TP?L?mainly came from the release of apatite phosphorus?AP?in solid phase.The contribution of AP to TP?L?was 118.74%49.81%at ozone dosage0.020.20 gO3·gSS-1.33.61%of total phosphorus?TP?was released into the supernatant and the TP?L?and PO43--P in supernatant were 101.48 mg·L-11 and 88.83 mg·L-1,respectively,under the optimum alkali dosage 0.10 gNaOH·gSS-1.Inorganic phosphorus?IP?contributed about66.53%82.90%of TP?L?at alkali dosage 0.100.20 gNaOH·gSS-1.The optimum reaction conditions for phosphorus recovery by magnesium ammonium phosphate precipitation were as follows:reaction time 25 min,initial solution pH 9.15,n?Mg?:n?P?1.78.The phosphorus and ammonia nitrogen recovery rate was 76.81%.Under the optimum reaction conditions,the main composition of the precipitate is magnesium ammonium phosphate and the purity reached 86.98%.Magnesium ammonium phosphate precipitation method has good practicability for recovering nitrogen and phosphorus from the supernatant of alkaline hydrolysis sludge. |
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