Signal Molecule AHLs Enhances The Activity Of Anaerobic Granular Sludge To Delay Calcification

With the tightening of national environmental protection policies and the continuous improvement of national environmental protection awareness,the pulp and paper industry is required to carry out continuous clean and intensive upgrading.Due to the advantages of resource saving,simple process and less investment in production equipment,waste papermaking has become an important part of the paper industry in China.However,due to the addition of a large amount of calcium carbonate and other fillers in the papermaking process,there are a large amount of Ca²⁺and Mg²⁺in the waste water of paper-making,which will make the anaerobic granular sludge(An GS)calcify and seriously affect the anaerobic treatment efficiency.Therefore,the problem of An GS calcification has become a big problem in the paper industry,which needs to be solved urgently.When An GS are used to treat wastewater,bacteria can conduct information transmission and communication through AHLs(acyl homoserine lactones)signal molecules,and produce quorum sensing(QS),which affects the physiological and biochemical characteristics of the whole bacteria.Therefore,this paper will add signal molecule AHLs to the anaerobic system to enhance the activity of An GS to delay calcification by guiding the quorum sensing of bacteria.Moreover,the performance of AHLs on sludge,secretion of EPS(Extracellular Polymeric Substance),changes in microbial diversity and porosity of granular sludge were analyzed to verify its feasibility and analyze its mechanism of action.The specific conclusions are as follows:(1)Under the influence of high concentration of Ca²⁺,uncalcified An GS has the ability to secrete more AHLs to regulate its own adaptive environment,while alcified granular sludge,due to the low microbial activity,is difficult to produce enough signal molecules to regulate the quorum sensing of the granular sludge microbial community,in response to new environmental changes.(2)Signal molecules C4-HSL,C6-HSL,C8-HSL and 3O-C6-HSL can improve the SMA(Specifific Methanogenic Activity),COD removal efficiency,and organic components of uncalcified An GS,and promote the secretion of EPS.Among them,3O-C6-HSL had the best enhancement effect compared with SMA,reaching 30.83%at the maximum.All the four signal molecules can enhance the SMA of uncalcified An GS by enhancing the methane metabolic pathway of sludge and improving the gene abundance of methane-producing enzymes.(3)Signal molecules C4-HSL and C8-HSL significantly inhibited the COD removal efficiency of calcified An GS,while C4-HSL enhanced the SMA,while C8-HSL significantly inhibited the SMA.The addition of C6-HSL had no significant effect on COD removal efficiency,but it significantly improved the SMA of sludge.The addition of 3O-C6-HSL can obviously improve COD removal efficiency and promote SMA.C6-HSL and 3O-C6-HSL can improve VSS/TSS of calcified sludge and promote the secretion of EPS.AHLs can change the community structure of bacteria and archaea in calcified sludge,enhance the methane metabolism pathway and quorum sensing pathway in calcified sludge,and promote the secretion of methanogenic enzymes.The addition of C6-HSL,C8-HSL,and 3O-C6-HSL increased methanosaeta population,thus increasing the aceticlastic pathway in sludge.(4)1?M of 3O-C6-HSL can improve the activity of calcified An GS by increasing the porosity,increasing the proportion of macropores,reducing the deposition area,increasing the biomass and optimizing the structure of bacteria.The higher dosage(10?M)of 3O-C6-HSL increased the organic content of An GS and blocks the mass transfer channel,affecting the activity of An GS.With the increase of the amount of 3O-C6-HSL,the organic components of sludge showed a trend of gradual increase,and the methane-producing pathway that induced calcified An GS was more toward eosinophilic acid pathway.