Simultaneous Release Of Polymorphic Phosphorus From Sludge By Anaerobic Fermentation Combined With Sulfate Reduction

Phosphorus is one of the essential nutrients for living organisms and a non-renewable mineral resource.In the municipal waste stream,phosphorus is enriched into the excess sludge through a centralized sewage treatment system.Therefore,the phosphorus circulation channel of the municipal waste stream system of phosphorus can be reconstructed by recovering phosphorus from the sludge.Phosphorus in sludge contains various forms such as organic phosphorus?OP?,poly-phosphorus?Poly-P?,and inorganic phosphorus?IP?.The content of the sludge mainly depends on the phosphorus removal process in the sewage treatment process.In recent years,with the improvement of sewage treatment standards,it is difficult to achieve the discharge of sewage only through biological phosphorus removal.Therefore,iron coagulant is widely used in wastewater treatment systems,and iron-bound phosphorus?Fe-P?is in sludge,and it also has a considerable weight in waste activated sludge?WAS?.However,due to the extremely low solubility of Fe-P,it is difficult to recover from sludge,and the release of Fe-P is considered to be a bottleneck in achieving phosphorus recovery in sludge systems.Therefore,anaerobic fermentation combined with sulfate reduction?AF-SR?system was proposed in this study.Through the fermentation process,the accumulation of polyphosphorus?Poly-P?in the process of biological phosphorus could be released,and the simultaneous release of Fe-P could be achieved by sulfate reduction process to generate S^2-,which was more easily Fe²⁺/Fe³⁺combined with Fe²⁺/Fe³⁺compared with P.The residual sludge AF-SR system was constructed by externally adding sulfate,and the release efficiency of phosphorus in the control group and the experimental group was analyzed.The feasibility of AF-SR promoted phosphorus release and the suitable environmental conditions of the system were also investigated.At the same time,through the actual sewage coagulation process,iron-enhanced coagulated sludge was prepared,and the coagulated sludge was used as a substrate to re-examine the phosphorus release effect in the AF-SR system,and the actual residual sludge AF-SR process phosphorus.The release rates were compared to explore the potential optimization process for wastewater and sludge phosphorus recovery systems.The main research contents and conclusions were as follows:?1?By adding sulfate to the AF-SR system,the release of Poly-P and Fe-P in the excess sludge under different S/Fe and the migration and transformation of P in solid and liquid phases were studied.The results showed that it was difficult to be released in the original excess sludge without added sulfate.In the experimental group with S/Fe element ratio of 2.0,PO₄^3--P was completely released within 10 days,while PO₄^3--P concentration was 238.9 mg/L,accounting for 40.8%of the total P content of the sludge.?2?Through the simulation calculation of Visual MINTEQ 3.0,the factors affecting the release rate of PO₄^3--P in AF-SR system and the mechanism of phosphorus release in AF-SR system were analyzed.The results show that the reduction rate of SO42--S determines the release rate of PO₄^3--P.The optimal release ratio of S^2-/Fe²⁺in the AF-SR system was 1.0,and the optimum pH was in the range of 7.0-8.0.Phosphorus in the system mainly existed in the form of inorganic phosphorus,and 60.9-61.9%of phosphorus in the AF-SR system could be released.?3?Through the batch fermentation experiment of coagulation sludge based on AF-SR system,the effect of Fe-enhanced wastewater coagulation and phosphorus removal process on the overall phosphorus recovery efficiency was studied.The results showed that the phosphorus in the coagulated sludge could be completely released within 3-5 days.The concentration of phosphorus in the supernatant could reach 272.6mg/L,accounting for 58.9%of the total phosphorus content.The fermentation rate and the phosphorus release rate of the condensate sludge were significantly improved and the effect of the pre-iron enhanced wastewater coagulation and phosphorus removal process on the overall phosphorus recovery efficiency was verified.?4?By comparing the release efficiency of phosphorus in sludge treated by different methods,combined with the initial cost analysis of pharmaceuticals,the economics and application potential of AF-SR system were explored.The results indicated that the AF-SR system,which relied on sulfate addition,was relatively inexpensive and easy to handle.At the same time,this study put forward the concept of sewage and sludge treatment and disposal process based on AF-SR system,in order to realize the efficient recycling of P,N and the recycling of Fe,S and C elements.