Effects Of Edta On Recovery Efficiency And Purity Of Struvite From Low Temperature Hot-water Degradation Sludge

Recovering phosphorus from waste sludge of sewage treatment plant can not only reduce eutrophication of water body,but also alleviate the shortage of phosphorus resources:In this study,the residual sludge in secondary clarifier of sewage treatment plant was treated as the object,and the sludge treatment process of "hot water hydrolysis+anaerobic digestion"was carried out.By adding metal complexing agent(EDTA)to the supernatant of hot-water sludge,the effects of EDTA on phosphorus release from low-temperature hot-water sludge were compared and analyzed.and the optimal operating conditions for phosphorus release were determined by response surface methodology.The effects of EDTA addition on the recovery efficiency of bird droppings were studied,and the purity of bird droppings was analyzed by scanning electron microscopy-energy dispersive X-ray spectrometer(SEM-EDS).The effect of phosphorus recovery by EDTA on anaerobic cdigestion of sludge from low temperature hot water hydrolysis was discussed.The main conclusions of this study are as follows:(1)Sludge pyrolysis was carried out at low temperature(T=75,pH=3)by adding EDTA of diferent concentration(Ommol/L?15mmol/L).The total phosphorus(TP)and orthophosphate(pO43-)release from supernatant increased from 249mg/L and 189m/IL to 547mg/L and 450.6 mg/L,respectively.About 84%of phosphorus in sludge could be released into liquid phase.EDTA not only improves the release of phosphorus,but also makes most of the phosphorus released into supernatant in the form of PO43-by destroying the extracellular polymer and cell structure and complexing the release of Ca,Mg,Al,Fe and other metal ions into supernatant to avoid their binding with phosphorus,which is conducive to phosphorus recovery from struvite.(2)With pH,temperature and EDTA concentration as independent variables;phosphorus release rate and economic cost as response values,response surface simulation analysis was carried out to determine the optimal conditions for phosphorus release(T=62?,pH=3.9,EDTA concentration=9.2 mmol/L)and better phosphorus release rate(74.2%)and lower economic cost.(3)Phosphorus in the supernatant of the above-mentioned hot-water sludge was recovered by means of struvite.The optimum recovery conditions were Mg/P=1.2:1,pH=9,T=25 ?.The recovery rate of phosphorus in supernatant was 97.3%,the removal rate of NH4+-N was 24.7%,and the purity of struvite was 61.3%.The results of SEM-EDS analysis showed that n(Mg):n(N):n(P)=1.16:1:1.46,which was close to the molecular formula ratio of magnesium ammonium phosphate(struvite),so the main component of the recovered precipitation product was magnesium ammonium phosphate.(4)After 15 days of anaerobic digestion,the concentration of SCOD in the sludge with EDTA was significantly higher than that of the sludge without EDTA.The average decomposition rate of organic matter in the anaerobic digestion process was 292mg/d,and that of the sludge without EDTA was 239mg/d,indicating that the anaerobic digestion efficiency could be achieved by adding appropriate EDTA.To improve.When EDTA was added to the digestive juice,PO43-release was less than 30mg/L after phosphorus recovery from bird droppings,which could effectively avoid uncontrolled deposition of bird droppings in digestive equipment and pipes.