Research On The Feasibility And Mechanism Of Strengthening Methane Production Technology To Alleviate Sludge Calcification In Waste Paper High Calcium Wastewater

With the enhancement of national environmental awareness and the continuous tightening of environmental standards,the transformation and upgrading of the paper industry are imminent.Waste papermaking has become an important part of China's papermaking industry due to its potential to achieve cleaner production.However,to reduce costs and improve paper quality in the papermaking process,a large amount of calcium carbonate filler will be added,resulting in a large number of calcium ions in the wastewater.When anaerobic digestion of high-calcium wastewater,calcification of granular sludge will occur,resulting in reduced biological activity of the sludge,weakened processing capacity of the reactor,and in severe cases,the entire treatment system will collapse.Therefore,the calcification of granular sludge has become a persistent disease of anaerobic digestion of waste papermaking wastewater,which needs to be solved urgently.Through analysis,it can be found that high calcium ion is equivalent to an inhibitory factor during anaerobic digestion,and its core inhibition is to weaken the methanogenic effect of sludge.Conversely,if certain methods or technical means can be used to strengthen the sludge methanogenesis stage,enrich and accelerate the growth and metabolism of methanogens,it is possible to reduce the inhibitory effect of high calcium ions and delay calcification.Based on the clarification of how calcium ions are exerted and the optimization of enhanced methanogenic technology,this study introduces enhanced methanogenic technology into calcified sludge systems.The feasibility of the method was verified by analyzing the methane production,physical and chemical properties,biological activity,microbial community structure,and methanogenesis pathways of calcified sludge,and tried to find a more efficient and simple method to alleviate sludge calcification.The specific conclusions are as follows:In the first part,we explore the interaction between high calcium ion and extracellular polymer substances?EPS?.The results show that high calcium ions can change the composition,concentration,and functional group structure of extracellular polymers.More importantly,in the high-calcium reactor,the EPS concentration was positively correlated with the COD degradation rate,and the correlation coefficients R²were 0.90,0.89,and 0.91,respectively.However,the relationship between EPS concentration and COD degradation rate in the control group was not obvious?R²=0.63?.Therefore,it is speculated that Ca²⁺may affect the digestion performance of granular sludge by changing the composition,concentration,and functional group structure of EPS.In the second part,the effect of acetylene black?ACET?and EPS on the performance of sludge methane production were explored,the strengthening mechanism was clarified,and the methane production strengthening method was optimized.The results show that:?1?ACET can significantly increase the methane production of granular sludge by a maximum of 44.36%.In addition,ACET can induce the enrichment of functional microorganisms?norank?f?Synergistaceae,norank?f?Anaerolineaceae,unclassified?f?Clostridiaceae?3?,and enhance the hydrolytic acidification capacity of sludge and the methanogenic capacity of acetic acid nutrients.This result was verified by 16S function prediction.Therefore,the significant increase in anaerobic digestion efficiency is attributed to the fact that ACET can construct and accelerate direct interspecies electron transfer?DIET?between unclassified?f?Clostridiaceae?3,norank?f?Anaerolineaceae,and Methanosaetaeta.?2?EPS as a conductive carrier can also increase methane production and the content of C-Cyts?c-Cyts?,with maximum increases of 36.5%and 15.24%,respectively.In addition,EPS can optimize the microbial community structure and induce functional microbial enrichment.Correlation analysis of the flora revealed that 8.86%of the important OTUs may be the microbial basis for the enhanced methanogenic capacity of granular sludge in the EPS reactor.Similarly,the 16S function prediction also indicates that EPS can increase the functional abundance of microorganisms and enhance the hydrogen trophic methanogenesis pathway of sludge.Therefore,it can be inferred that the strengthening mechanism of EPS is to induce the enrichment of functional microorganisms,increase the extracellular active medium?c-Cyts?,establish and accelerate the DIET methanogenesis process,and thus enhance the efficiency of sludge methanogenesis.The third part is to introduce EPS and ACET into the calcified sludge system to explore the feasibility of strengthening methane production technology to alleviate sludge calcification.The results show that EPS and ACET can significantly increase the methane production of calcified sludge compared with the control group,increasing by 16.8%and 10.2%,respectively.In addition,EPS and ACET can also increase the organic components of calcified sludge,enhance the INT-ETS activity and conductivity of calcified sludge,and improve the physical and chemical properties of calcified sludge.More importantly,the VSS/TSS and INT-ETS activities of calcified sludge in the control reactor were significantly lower than the initial digestion?seed sludge?.This shows that EPS and ACET can improve the performance of calcified sludge and delay sludge calcification.Further analysis found that the mechanism of action of ACET and EPS is to improve the performance of calcified sludge and delay sludge calcification by inducing the enrichment of functional microorganisms and establishing and accelerating the DIET between the collaborating bacteria and methanogens.