| Municipal sewage sludge is rich in nitrogen,phosphorus and nutrients,making it an excellent choice for waste utilization and resource recovery.Different from conventional sludge treatment methods,the addition of potassium ferrate is an ideal sludge conditioning method as it has a strong destructive effect on the sludge flocs and cells and is environmentally friendly.The addition of potassium ferrate to the sludge system can facilitate the release of phosphorus,but the release effect,pathway and mechanism are still unclear.How to use potassium ferrate to economically maximise the release of elemental phosphorus and other nutrients from sludge has also become an urgent challenge.In order to fully and efficiently explore the mechanism of potassium ferrate to promote the release of phosphorus from sludge,three systems of potassium ferrate coupled with sodium sulfite,alkali and potassium ferrate coupled with alkali were constructed in this study.After the sludge was treated with potassium ferrate and sodium sulfite,it was found that total phosphorus and inorganic phosphorus increased significantly to 33.26 mg/L and 20.16 mg/L 40 minutes after the start of the reaction.Proteins,polysaccharides and total organic carbon are released in large quantities into loosely bound extracellular polymers(LBEPS)and soluble EPS(SEPS).3D-EEM revealed a dramatic decrease in dissolved organic matter in TBEPS,while a marked increase in tyrosine-like proteins and soluble microbial by-product substances in LBEPS and SEPS.These phenomena indicate that the potassium ferrate coupled sodium sulfite system has deeply destroyed the sludge flocs and cells,and the innermost nutrients flow into the sludge liquid phase.At the same time,the quenching reaction of free radicals and the experimental phenomenon using methyl phenyl sulfoxide(PMSO)as a probe show that the yield of high-valent iron oxidation of methyl phenyl sulfone(PMSO2)is as high as 26%,which proves that the system can decontaminate sludge and extracellular polymer,the main substance that promotes the release of phosphorus is high-valent iron.In an aim to eliminate the interference of the increase of pH value caused by the selfdecomposition of potassium ferrate in the potassium ferrate system to the research on the release mechanism of phosphorus in the sludge,an alkaline hydrolysis sludge system and an alkali-coupled potassium ferrate system were further designed to trea the sludge.The pH of the sludge system was adjusted to 10.5,and the phosphate concentration in the system reached 28.9 mg/L after the reaction for 10 min,and the total phosphorus concentration in SEPS,LBEPS and TBEPS changed to 15.11,6.4 and-8.18 mg/L.The 3D-EEM showed the strongest fluorescence signal of soluble organic matter in TBEPS.However,in the potassium ferrate system with coupled alkali,the nutrients in TBEPS were obviously lost.Compared with the raw sludge,the nutrients in the TBEPS after the alkaline hydrolysis of the sludge still accounted for the largest proportion,indicating that the alkaline treatment of the sludge alone has less effect on the release of EPS and intracellular phosphorus,and cannot deeply crack the sludge.Potassium acid can realize the in-depth cracking of sludge EPS and the release of intracellular nutrients.The three sludge treatment systems have significantly different behaviour with regard to the release of phosphorus.In this study,the release and changes of phosphorus elements before and after the reaction of three sludge systems of potassium ferrate coupled with sodium sulfite,alkali,and potassium ferrate coupled with alkali were explored.Using methyl phenyl sulfoxide as a probe,the mechanism of sludge disintegration and cell destruction in potassium ferrate system was deeply elucidated,which provided a theoretical reference for the subsequent recovery of phosphorus and nutrients in sludge. |
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