Research On Efficiency And Mechanism Of Alkyl Glucosides Promoting Anaerobic Fermentation Of Sludge For Volatile Fatty Acid Production

In recent years,the problem of sludge in China has caused serious environmental pollution and public concern,and the total volume and growth rate of sludge have been increasing year by year.However,80% of sludge is improperly disposed and discarded,caused environmental pollution and huge waste of resources.Therefore,the recent studies on the use of surfactants to promote the production of volatile fatty acids(VFAs)from fermentation of sludge have attracted the attention of researchers.Through the production of VFAs by fermentation,both the reduction of sludge and the production of VFAs with added value were achieved.In this dissertation,the environmentally friendly biosurfactants alkyl glycosides(APG)and secondary sedimentation tank activated sludge were investigated.Six kinds of APGs were added to the sludge fermentation system to further enhance the VFAs production and optimize the reaction conditions,and the effects of different chain lengths of APG on VFAs production were compared.This study was devoted to the screening of a green,non-polluting,high-efficiency surfactant to enhance the effect of sludge fermentation on VFAs production,and to further analyze its mechanism.In this dissertation,the effect of six different APG with different carbon chain lengths and different dosages on the VFAs production of anaerobic fermentation of sludge was studied.It was found that long and short chain APG exhibited different VFAs production patterns with the same dosage.The APG06 experimental group obtained the highest VFAs yield(348.6 mg COD/g VSS),released less ammonia nitrogen and phosphate into the fermentation broth,but still not reach its optimal dosage.The addition of six APGs significantly increased the concentrations of soluble polysaccharides,proteins,and COD in the fermentation broth.As the APG chain length increased,the inhibitory effect on methanogenesis increased.In the second part of this dissertation,the concentration of APG06 with the highest acid production and the longest chain alkyl glycoside APG1214 with similar acid production were selected to conduct subsequent concentration optimization experiments,and comparisons were made from various aspects.The highest VFAs yield of 479.3 mg COD/g VSS was achieved with the addition of APG06 at 0.4 g/g TSS,and the composition ratios of the various VFAs were suitable for use.Compared to APG1214 requires a lower dosage and a shorter fermentation time.The APG1214 experimental group's ammonia nitrogen release amount and rate is higher than the APG06 experimental group during the fermentation process.APG06 provides a higher polysaccharide concentration for the VFAs production by the sludge fermentation,but its ability to dissolve protein is slightly inferior to APG1214,inhibiting the production of methane,but weaker than APG1214.In the third part of this dissertation,the mechanism of long-and short-chain APG promoting VFAs production by anaerobic fermentation was analyzed and compared.By using APG as a fermentation substrate for the experiment,it was found that APG06 has better degradation extent and rate.Through community analysis,it was found that the addition of APG promoted the formation of a community structure that facilitates the accumulation of VFAs in the fermentation system: a large number of hydrolyzed,acidified microflora and a very small amount of methanogenic microflora,and the microflora in the APG06 experimental group was more conducive to VFAs production,while APG1214 is more capable of killing bacteria and methanogenic archaea.