Enhanced Anaerobic Digestion Performance Of Waste Activated Sludge And Degradation Of Fermentative Liquid Based On Functionalized Hydrogel

Anaerobic digestion is an important way to achieve simultaneous reduction of waste activated sludge and resource/energy recovery.However,traditional anaerobic biotechnology has problems such as low hydrolysis efficiency and poor anabolic ability of microorganisms,which seriously limits the application of anaerobic digestion technology.In view of this,the strengthening strategy of using functional hydrogel materials to improve the anaerobic biological treatment efficiency of waste activated sludge,to realize energy recovery and utilization and efficient degradation of fermentative liquid was proposed in this study.Firstly,sodium alginate/Fe（Ⅲ）hydrogel bead combined with persulfate pretreatment technology was developed to rapidly destroy the residual sludge floc structure and increase the content of volatile fatty acids（VFAs）,and to explore the synergic effect and mechanism.Secondly,a methanogenesis system of resazurin/polyaniline（RZ/PANI）conductive hydrogel-sludge anaerobic digestion was constructed,and the strengthening mechanism was elucidated through the material conversion rule and electron transfer process in the system.Finally,aiming at the problem of difficult degradation of fermentative liquid,bismuth iodide/Graphite oxide-polyethylene glycol photothermal hydrogel（Bi OI/GO-PEG）photocatalytic degradation of refractory substances in fermentative liquid provides theoretical basis and technical support for the whole process management of sludge anaerobic biological treatment.The main research contents are as follows:1.The recovery of VFAs by anaerobic fermentation is usually limited by the poor biodegradability of the remaining sludge.A new strategy of activating persulfate（PMS）with iron-supported sodium alginate hydrogel bead（Fe-SA）was proposed to improve the performance of anaerobic fermentation.The experimental results showed that Fe-SA and PMS co-pretreatment significantly increased the production of VFAs.When Fe-SA supplemental level was 4.0 m M/g TSS,the maximum acid production could reach 2013 mg COD/L,which was 93.7%and 8.82 times higher than that of PMS alone and blank control group,respectively.The mechanism study showed that Fe-SA could activate PMS to produce more abundant active free radicals such as SO₄·^-and·OH,which promoted the rapid degradation of refractory compounds.In addition,Fe-SA can enhance the activities of key enzymes（protease,α-glucosidase,phosphate transacetylase and acetate kinase）during hydrolysis and acid production in anaerobic fermentation systems.Microbial analysis showed that the unique three-dimensional pore structure of Fe-SA could provide a good growth environment for microorganisms,significantly improving the abundance of fermentation microorganisms and the expression of functional genes related to acid production.This study confirmed the potential application of Fe-SA hydrogel beads to activate PMS for the production of VFAs,which provides an important reference for the development of anaerobic fermentation enhancement technology based on advanced oxidation processes.2.Previous studies have shown that adding conductive materials to anaerobic systems can promote direct interspecific electron transfer（DIET）of microorganisms and improve methanogenic efficiency,while electron shuttles have also been confirmed to mediate extracellular electron transfer and improve microbial metabolic efficiency.However,the traditional conductive materials and electronic shuttles will be easily lost after use,increasing the processing cost.Therefore,in this study,PANI was used as conductive medium to load natural electron shuttle RZ,and an enhanced sludge anaerobic digestion system based on RZ/PANI conductive hydrogel was constructed.The experimental results showed that the total methane production in the anaerobic system supplemented with RZ/PANI hydrogel increased by 1.42 times compared with the control group.Further mechanism studies showed that RZ/PANI hydrogels could enhance the electron transport system（ETS）as an electron channel and improve the DIET process.At the same time,RZ/PANI hydrogel can improve the activity of acid-producing enzyme（phosphate transacetylase and acetate kinase）,coenzyme F420 and other key enzymes.Microbial analysis showed that the addition of RZ/PANI hydrogel promoted the enrichment of Methanosarcina,Methanosaeta and other related methanogens.This study provides an effective scheme for enhancing sludge methane production by conducting hydrogel coupled electron shuttles,which provides a new idea for directional enhancement of anaerobic digestion.3.The fermentative liquid produced by anaerobic digestion contains a large number of refractory pollutants（such as lignocellulose,humus and antibiotics）,which will pose a threat to the ecological environment and human health if not properly treated.In this thesis,Bi OI/GO-PEG composite photothermal hydrogel was prepared,and oxytetracycin was selected as a typical refractory organic matter in fermentative liquid for photocatalytic degradation experiment.The experimental results showed that Bi OI/GO-PEG had a good catalytic performance for oxytetracycline degradation of 82.4%.Bi OI/GO-PEG can effectively inhibit the combination of photogenerated carrier and hole,and the sunlight absorption capacity is significantly enhanced.The mechanism studies show that·OH and·O₂^-are the main active free radicals in photothermal catalysis.PEG,as a phase change hydrogel material,can release latent heat under intermittent light irradiation,maintain the temperature of the catalytic system,and then improve the photocatalytic activity of Bi OI/GO-PEG,which has potential application value.The results can provide a reference for the application of photothermal hydrogel materials in the field of catalytic degradation of pollutants.