Effect And Mechanism Of Alkaline Plant Ash On Inhibiting Harmful Gas Generation In Sewage Sewer

The main type of sewage pipeline in China is gravity pipeline.In some areas,the ventilation is not smooth,and anaerobic microorganisms generate hydrogen sulfide,methane and other toxic and harmful gases,resulting in prominent problems of sewage pipe network odor,corrosion,carbon emission and so on,which seriously restricts the efficiency of sewage pipe network and the high-quality development of cities and towns.Adding alkaline agents can effectively inhibit the generation and interface migration of toxic and harmful gases in sewage network,but it is not economical to add a large number of alkaline agents,which restricts the application of this technology.Alkaline plant ash comes from a wide range of sources,and its aqueous solution is highly alkaline,which can be used to control the generation of toxic and harmful gases in sewage pipes instead of alkaline agents.However,the effect of alkali plant ash on the control efficiency and water quality of hydrogen sulfide and methane is still unclear.In this study,a simulated pipeline reactor built in the laboratory was used to carry out experimental research,focusing on the control efficiency of harmful gases,the analysis of microbial community changes and mechanisms,and the analysis of water quality changes and their effects,so as to provide data support for the application of alkaline plant ash to inhibit toxic and harmful gases in sewage network.Firstly,a variety of technical means were used to analyze the alkalinity,composition,phase composition,morphology and other physicochemical indexes of straw crop ash.The control effect of ash impact on toxic and harmful gases was investigated by single-time experiment.The results showed that the alkalinity of the saturated ash solution was about 1809.67 mg CaCO₃/L,and the calcium and potassium compounds in the components were the main sources of alkalinity.Under the condition of single impact,the concentration of harmful gas decreases rapidly,but the concentration of harmful gas can recover to the level before impact 3 days after impact,indicating that the plant ash has significant control effect on harmful gas,but the single impact time is limited.The results showed that the ash had better control effect of harmful gas under the same impact pH.Secondly,the long-term impact experiment was carried out after changing the application mode of plant ash.The H₂S（g）concentration in sewage pipes replaced daily and every six days is less than 1.8ppm,the CH₄ concentration was reduced by 62.96%and 53.41%,and the dissolved sulfide concentration was reduced by 87.29%and 78.65%,respectively.The data showed that the ash impact inhibited the growth and propagation of sulfate-reducing bacteria（SRB）dominated by Vibrio desulphurosa and sulfur-oxidizing bacteria（SOB）dominated by Mycobacterium,indicating that alkaline ash made the bacteria involved in sulfur cycle lose the appropriate growth environment,and the growth and reproduction ability was inhibited.In addition,the control effect of changing plant ash every day can be achieved by repeatedly changing plant ash intermittently.Again,after the long-term impact of alkaline plant ash,the surface of biofilm was changed,the structure and composition were damaged and changed,and the extracellular polymer was lost in large quantities.Protein and polysaccharide content decreased by42.29%.TB-EPS is the polymer layer closest to the cell,which is significantly related to the flocculation of biomass and settlement of microbial aggregates.The average total amount of ash was 7.21 mg/g VS during daily replacement,which decreased by 37.03%compared with the stable stage.The total amount of ash during intermittent replacement decreased in a step pattern.The results of three-dimensional fluorescence spectrum show that tryptophan is the most important fluorescent substance in biofilm EPS,and the fluorescence intensity becomes weak after impact.Fourier infrared spectroscopy shows the transformation of proteins.Changes in the quantity and properties of proteins and polysaccharides can directly indicate changes in the growth of biofilms,and bacteria and other microorganisms coated with extracellular polymers will be damaged after the bacterial micelles break.Finally,the long-term impact of alkaline plant ash can change the composition of microbial community and the environment of sewage pipes.The microbial mortality rate was more than 21%after ash impact.The biodiversity of bacteria and archaea decreased,and the influence on bacteria was greater than archaea.Bacteria related to the production of harmful gases,such as Clostridia and BRH-c20a,were significantly inhibited,reducing the accumulation of hydrogen sulfide gas from the source.The ash impact made the dominant species of archaea change and the total proportion decreased.The pH value of the sewage will increase from 7 to about 10,and the ORP value of the sewage in daily change group and every six days change group will increase by about 65 mV and 43 mV respectively.The absolute value of zeta potential of sewage in daily change group increases by 5.70 mV on average,and that of sewage in every six days change group increases by 2.19 before a new impact,thus increasing electrostatic repulsion and reducing flocculation ability.After the ash impact,the concentration of ammonia nitrogen and total phosphorus decreased,and the C/N ratio increased in different degrees.