Study On Influence Factors And Mechanisms Of Short Chain Fatty Acids Production And Phosphorus Release During Waste Activated Sludge Anaerobic Fermentation Process

Waste activated sludge(WAS),as the main by-products of wastewater treatment plants,is characterized by high yields,organic matters storages and nutrients enrichments,which exhibits great potential for resource recovery and utilization.This study took cascade recycling of WAS resource as the starting point,and the WAS was considered as the source of carbon and phosphorus.In view of low efficiencies of carbon organics matters conversion and phosphorus release during WAS anaerobic fermentation process,this study focused to explore the influence factors and mechanism laws on rapid carbon organic matters conversion and phosphorus release.Considering the low efficiency and rate of short chain fatty acids(SCFAs)from WAS anaerobic fermentation process,the SCFAs promotion performance under initial alkaline condition was studied,and two novel methods,including potassium ferrate(PF)and combination of alkaline and PF,were proposed.Results showed that the optimal time for enhanced hydrolysis and acidification of WAS was 30 min when the sludge was treated at initial pH=10.0.The maximal SCFAs,240 mg COD/g VSS,was achieve on 3th day,which was 2.88 times higher than that of control.The PF treatment could significantly improve the accumulation of SCFAs,mainly acetic acid.The optimal addition dosage was 56 mg Fe(VI)/g TSS,and the corresponding SCFAs accumulation was 343 mg/g VSS,which was 5.72 times more than that of control.It is noted that PF stimulated by alkaline could further enhance SCFAs production from sludge anaerobic fermentation.Different from PF treatment alone,for the combination method,the optimal PF dosage was 28 mg Fe(VI)/g TSS and the pH was 10.0,the SCFAs production increased by 22%,and the sludge retention time was shortened from 5 to 4 days.Considering the current market price of PF was much higher than that of alkaline,reducing the PF dosage to 28 mg Fe(VI)/g TSS and simulating by adjusting initial pH=10.0 to enhance SCFAs production,has greatly potential economic benefits.Considering the quaternary ammonium compounds,i.e.,benzalkonium chlorides(BACs)widely presented in WAS,the effects and mechanisms of chain length and content of BACs on SCFAs production from sludge anaerobic fermentation was investigated,also,the corresponding succession of microbial community and core functional microbes was revealed.Results showed that the BACs accumulation in WAS enhanced the accumulation performance of SCFAs from sludge anaerobic fermentation,and short alkyl chain and high content was more significant for enhancement of sludge hydrolysis and acidification,conversely,the methane production was greatly inhibited.Meanwhile,the existence of BACs significantly altered the distribution characteristics of functional microbial community.The highest relative abundance of functional acid-producing bacteria in control group was Proteiniclasticum with value of 12.8%,and the corresponding methanogens was Methanosaeta with value of 55.1%.When BACs were existed,the highest relative abundance of bacteria was Candidatus_Microthrix with value of 26.6%,while Methanosarcina was the predominant methanogens,which reached 61.2%.For the long-term operation system,the low concentration(2 mg/gTSS)of BACs had no obvious influence on SCFAs production from sludge anaerobic fermentation process.At medium BACs concentration(15 mg/gTSS),the accumulation of SCFAs increased,which was 1.86 times higher than that of control.And the SCFAs production further increased to 2.15 times more than that of control when the content of BACs was further increased(i.e.,50 mg/gTSS).When BACs content was not higher than medium concentrations,the main species of acid-producing microorganisms were basically the same.Compared to the other three experiments,when BACs were at high concentration,the functional acid-producing microorganisms were obviously changed,the relative abundance of Clostridia reduced to 15.2%,whereas the relative abundance of Actinobacteria increased to 31.8%.Especially,the Synergistia was enriched at high concentration of BACs with the relative abundance of 10.5%.The migration and transformation rule and mechanism of different phosphorus species were revealed by investigating the effects of pretreatment methods and BACs on phosphorus release during anaerobic fermentation process.Results showed that different from carbon organic matters release rule,the pretreatment methods and BACs showed different phosphorus release rule.The contents of phosphorus in supernatant and loosely bound EPSs(LB-EPSs)showed an increase trend,whereas it showed a reduction trend in tightly bound EPSs(TB-EPSs)and intracellular and other parts,the maximal release rates were 20.30% and 34.88%,respectively.The main species of supernatant and LB-EPSs was phosphate radical,and the content of organic phosphorus in TB-EPSs was relatively high.By analyzing the phosphorus species in WAS,it was found that the phosphorus mainly existed in solid phase,in which,the biologically effective phosphorus,i.e.,nonapatite inorganic and organic phosphorus accounted for more than 80% of the total solid phosphorus.The non-apatite inorganic phosphorus was more likely to be released under alkaline conditions,and the maximum release efficiency was 89.84%,in contrast,the apatite inorganic phosphorus was more likely to be released under acid condition,the release efficiency could be reached to 93.69%.In brief,the dominant phosphorus species is the key factor to determine the release efficiency of phosphorus.