Application And Mechanism Of Iron Mud To Delay Calcification Of Anaerobic Granular Sludge From High Calcium Wastewater

During the period of 2009-2018,China has become the main producer and consumer of paper products in the world,of which waste paper as the main raw material has been stable at 55%-65%.However,due to the high content of Ca²⁺,Mg²⁺in wastewater,the calcification of anaerobic granular sludge easily occur,the methane production capacity of calcified granular sludge is reduced,and the COD degradation capacity is reduced.The plant needs to replace sludge regularly to maintain the normal operation of the wastewater treatment system,which greatly increases the production cost.Therefore,alleviating the calcification of anaerobic granular sludge and improving its methanogenic activity have become a topic of concern to many researchers.Fe-oxide is considered to improve the methane production capacity of anaerobic granular sludge and has attracted extensive attention of researchers.In the Fenton advanced oxidation section of wastewater treatment,a large number of Fenton iron sludge will be produced,in which iron is mostly oxidized and its content is more than 30%.In order to solve the problem of calcification of anaerobic granular sludge and develop efficient anaerobic treatment technology,this study attempts to add Fenton iron sludge and several iron oxides in anaerobic reaction,through the study of the extracellular polymer of anaerobic granular sludge,and the development of efficient anaerobic treatment technology.The variety and quantity of microorganisms and the change of physical properties of granular sludge were analyzed.The inducement and advantages of Fenton iron sludge in improving the activity of granular sludge were analyzed.The main conclusions are as follows:?1?Iron mud improved the methane production capacity of normal anaerobic granular sludge significantly,and the methane production increased by 22.5%when the additive amount was 15 g L^-1.Among them,Fe?III?stimulated the secretion of microbial extracellular polymer,increased the content of C-type cytochrome,strengthened the reduction of dissimilated iron and microbial interspecific electron transfer,and promoted the growth of microorganisms in anaerobic granular sludge.The microbial species were more abundant and distributed more evenly.Hydrogen-trophic methanogens were dominant in archaeological communities,effectively promoting microbial anaerobic digestion.?2?The methane capacity of FeO,Fe₂O₃ and Fe₃O₄ was significantly improved,and the methane yield of FeO was the highest.FeO and Fe₂O₃stimulated the secretion of microbial extracellular polymers,while Fe₃O₄ had little effect on the secretion of extracellular polymers.The addition of FeO,Fe₂O₃ or Fe₃O₄ did not change the dominant bacteria,but could make the community structure change obviously.Different Fe oxides would enrich different bacteria and show different methanogenic efficiency and different EPS components.In the reactor of Fe₂O₃,the proportion of interacting bacteria increased.The interacting copolymers formed by interacting bacteria and methanogenic archaea participated in and accelerated the species.Intermediate hydrogen transfer may promote methanogenesis efficiency of Archaea methanogenesis.?3?The promoting effect of iron mud on anaerobic digestion of methane production was likely to depend on the content of Fe₂O₃ in Fenton iron mud.However,the microbial community and structure in the experimental group with iron mud and Fe₂O₃ were obviously different because of the complex composition of iron mud.?4?Iron mud had significantly effect the methane production of calcified granular sludge.The methane production of calcified granular sludge increases by 12.7%when the dosage of Fenton iron sludge is 15 g L^-1,the secretion of microbial EPS increases by 92.23%compared with the control group,respectively.The VSS/TSS ratio of calcified granular sludge increased from0.25 to 0.52,which slowed down the process of granular sludge calcification and strengthened the COD degradation ability of calcified granular sludge to make granular sludge more efficient.The activity of sludge was increased.It promotes the intracellular and extracellular electron transfer and interspecific electron transfer of microorganisms,improves the overall performance of granular sludge,enhances its viability under high calcium conditions,is conducive to slowing down the resistance of granular sludge to harsh environment,and to a certain extent slows down the calcification of granular sludge.