Research On Phosphorus Recovery Technology Of Municipal Sludge Based On EDTA Coupled With Low-Temperature Pyrolysis

With the increase of municipal wastewater discharge,the amount of residual sludge generated during the wastewater treatment process is also increasing.After biological treatment,most of the phosphorus in wastewater is transferred to the residual sludge.Phosphorus is a non-renewable resource and an indispensable resource in modern industry and agriculture,and the phosphorus resources in China are very poor.How to recover phosphorus from sludge and realize the recycling of phosphorus resources?It has been a hot spot for industry research.In this paper,municipal sludge was treated with EDTA coupled with low-temperature pyrolysis process,and then the phosphorus released from sludge was recycled using guanoite crystallization method.The recovered products were characterized by XRD,FTIR and SEM,and the migration and transformation patterns of different forms of phosphorus and the mechanism of phosphorus release during the sludge treatment process were analyzed by SMT method.（1）In this paper,we firstly used EDTA coupled with low-temperature pyrolysis process to treat sludge,and studied the effects of four factors,namely,EDTA dosage,p H,temperature and reaction time,on the phosphorus release effect of sludge and the optimal reaction conditions.The four-factor four-level orthogonal experiments were further carried out,and the results were analyzed in the order of p H>EDTA dosage>temperature>reaction time.The results of ANOVA showed that p H and EDTA dosage had a significant effect on PO₄^3-and TP release,temperature had a significant effect on PO₄^3-and TP release,while reaction time only had a significant effect on TP release.In the controlled experiment of EDTA-coupled anaerobic treatment of sludge,the optimal working conditions for phosphorus release were determined as,EDTA 0.5 g and anaerobic time of 2.5 days.Comparing the phosphorus release effect of EDTA-coupled low-temperature pyrolysis with EDTA-coupled anaerobic sludge,it was found that the proportion of orthophosphate released from the sludge treated by low-temperature pyrolysis was higher and the reaction time was shorter.（2）In this paper,the phosphorus released from EDTA-coupled low-temperature pyrolysis treatment was recycled using guano stone crystallization method.The effects of Mg/P,N/P,p H,reaction time and other factors on the phosphorus recovery effect were investigated.According to the results of single-factor experiments,three main factors,Mg/P,N/P and p H,were selected and the experiments were optimized by response surface method to explore the optimal reaction conditions.The order of the factors affecting the phosphorus recovery was obtained by ANOVA:p H>Mg/P>N/P.The 3D projection and contour plots of the response surface reflected that there were significant interactions between Mg/P and N/P,Mg/P and p H,and N/P and p H.The optimization experiments were validated and the phosphorus recovery was obtained as 87.89%,which was close to the predicted value.Finally,the recovered products were characterized using XRD,FTIR,and SEM-EDS,which indicated that there was a relatively pure guanoite generation in the products.（3）In this paper,the transformation of phosphorus morphology in sludge during the treatment process was analyzed by SMT method.The semi-quantitative detection of the experimental raw sludge using XRF and the TP results measured by SMT method were basically consistent,indicating that the SMT method is suitable for the analysis of phosphorus morphology of sludge in this experiment.The analysis of the experimental raw sludge,EDTA-coupled low-temperature pyrolysis reaction substrate and EDTA-coupled anaerobic reaction substrate respectively revealed that the phosphorus released by EDTA-coupled low-temperature pyrolysis was mainly from the IP in the sludge,and more deeply from the NAIP,which is known as biologically effective phosphorus,while the anaerobic phosphorus release was mainly from the organic phosphorus in the sludge.The phosphorus content and morphological changes during the treatment of sludge by Fenton were investigated,and the strong oxidation could convert organic phosphorus and other active bound phosphorus into inorganic phosphorus,and finally it was concluded that the best conversion to NAIP was achieved at p H 4.5,Fenton ratio of 4 and H₂O₂ dosage of 1.5 ml,and NAIP belonged to BAP and could be used as a slow-release fertilizer.