Regulation Strategy And Mechanism Of Potassium Ferrate Promoting Acid Production By Anaerobic Fermentation Of Waste Activated Sludge

As the main by-product of sewage treatment plant,the output of waste activated sludge（WAS）was increasing.The main component of sludge were organic matters,which would lead to serious environmental pollution.On the other hand,sludge was the carriers of available resources.Anaerobic fermentation can recover sludge resources in the form of methane,hydrogen,short-chain fatty acids（SCFAs）,etc.But the problem of low yield hindered the popularization and application of anaerobic fermentation technology.Based on the above background,in view of the disintegration was the key limiting step of sludge anaerobic fermentation,this paper studied the regulation strategies based on potassium ferrate（K₂Fe O₄,PF）to promote the disruption of WAS and improve SCFAs production by anaerobic fermentation,and analyzed the reaction mechanisms,so as to establish a highly efficient technology to improve the SCFAs production and to provide theoretical and technical basis for resource recovery of sludge.Firstly,a treatment strategy combining PF and low temperature heat treatment was proposed to reduce the consumption of PF and utilize the heat energy of municipal sewage in situ,so as to promote the SCFAs production efficiency of sludge fermentation.The results showed that PF treatment followed by thermal treatment（PF-T）could effectively promote sludge fermentation to produce SCFAs.The SCFAs accumulation corresponding to the combination of low concentration PF and thermal treatment was the largest,which was 230 mg COD/g VSS,the 1.36 times of that sole PF pretreatment.The corresponding soluble polysaccharides and proteins were 1.93 and 1.31 times of those in sole PF treatment.PF could promote the release of organics from cells,and thermal treatment was beneficial to the release of organic matter in EPSs,while the combination of PF and thermal treatment promoted the release of organics in cells and EPSs simultaneously.In addition,compared with the sole PF treatment,the combined treatment with the low concentration PF and thermal treatment improved the hydrolysis performance of sludge by 69.7%,and had a better inhibition effect on methane production.Overall consideration,taking acid production as evaluation,low concentration PF combined with thermal treatment was the best regulation strategy to enhance the SCFAs production.Secondly,this paper evaluated the effects of PF at different concentrations combined with ammonia stripping on promoting SCFAs production and nitrogen recovery potential from sludge,and revealed the mechanism of PF combined with ammonia stripping on anaerobic fermentation.The results showed that low concentration PF combined with direct ammonia stripping could further promote the accumulation of SCFAs,and the maximum accumulation of SCFAs increased by 9.40%.The total production of acetic acid and propionic acid increased by 6.63%when the maximum accumulation of SCFAs was reached,and the inhibition rate of methane production increased from 50.9%to75.6%.Mechanism analysis showed that low concentration PF combined with direct ammonia stripping promoted the disruption and solubilization of sludge.Compared with sole PF treatment,the concentration of free ammonia increased,which was a byproduct of hydrolysis.The results also showed that PF combined stripping process affected the activity of methanogens and could further inhibit methane production.The combined treatment of high concentration PF and ammonia stripping was beneficial to nitrogen recovery.After direct stripping treatment,the recovery of nitrogen was about 49 mg/L,calculated by NH₄⁺-N).Finally,considering the high cracking degree of sludge under alkaline condition and more ammonia nitrogen in the form of free ammonia,the technology of the combination of PF and alkali-regulated ammonia stripping（PF-p H-strip）was proposed to investigate the SCFAs production efficiency.The results showed that PF-p H-strip could further promote SCFAs accumulation at low concentration,and acetic acid production increased by 8.69%when the SCFAs accumulation was the highest.Contrast to the PF combined with alkali-regulated group without stripping（PF-p H）,the concentration of ammonia nitrogen and free ammonia decreased by 28.0%and 31.1%respectively,which not only alleviated the adverse effects of strong alkaline environment on anaerobic acid-producing bacteria,and realized the recovery of ammonia nitrogen.At high concentration,PF-p H-strip could further improved nitrogen recovery potential to 116 mg/L,calculated by NH₄⁺-N,which realized the high efficiency of nitrogen recovery.Consequently,PF-p H-strip treatment at low concentration was the most ideal regulation method to improve SCFAs yield in stripping groups,while the high concentration PF greatly improved the nitrogen recovery potential.In conclusion,the pretreatment technology based on PF proposed in this paper could realize simultaneous recovery of carbon and nitrogen sources,and provided theoretical basis and technical support for efficient resource recovery from sludge.