Effects Of Membrane Separation And CaO₂/SAM-SS On The VFAs Production Of Sludge Anaerobic Fermentation

Sludge anaerobic fermentation is an effective way to achieve sludge reduction and resource utilization.It can convert organic matters in sludge into volatile fatty acids(VFAs),which can be a platform to synthesize products with higher economic value.Enhancement of the product VFAs and separation of VFAs from the mixture are the major factors limiting the application of VFAs.For the enhancement of VFAs production in sludge anaerobic fermentation,this paper studied(1)the effects of a submerged MF membrane separation on the production of VFAs in sludge anaerobic fermentation;and(2)the effects of additives calcium peroxide and calcium peroxide loaded modified steel slag on VFAs production in sludge anaerobic fermentation.A submerged microfiltration membrane module was installed into a sludge anaerobic fermentation reactor for enhancement of VFAs production and the extraction of VFAs.The results showed that the application of microfiltration membrane separation can effectively recover more than 90%of VFAs.The organic matters in the sludge were also effectively retained,and the retention rate of the polysaccharide reached 73%.After the membrane separation was applied,the concentration of VFAs in the reactor gradually increased and stabilized at 1837 mg/L level which was 53%higher than the control.Regarding the composition of the VFAs,acetic acid was the dominant species.Based on enzyme activity and microbial community structure analysis,the main reason for the increase in VFAs was that,the microfiltration membrane effectively retained soluble organic substances such as polysaccharides,which can improve the activity of the polysaccharide-utilizing bacteria,and increase the activity of a-glucosidase.The enhanced bacterial activity further promoted the degradation of polysaccharide,and then the concentration of polysaccharide in the reactor gradually decreased,which was converted into VFAs by acid-producing bacteria.The species Christensenella minuta,which can degrade polysaccharides to produce VFAs,proved to be enriched after the application of microfiltration membrane,increasing from 6.89%to 14.06%,becoming the dominant species.The effects of calcium peroxide on the production of VFAs in sludge anaerobic fermentation were studied.The results showed that CaO2 could promote the hydrolysis and acidification of sludge.The best dosage to promote the production of VFAs during the sludge anaerobic fermentation was 0.3 g CaO2/g VS,which could get a VFAs concentration 10.83 times of the control.In order to further promote the production of VFAs,CaO2/SAM-SS particle was prepared using a co-precipitation method.The successful loading of calcium peroxide was proved by SEM,EDS,FTIR and XPS techniques.Effects of SAM-SS,CaO2 and CaO2/SAM-SS on the sludge anaerobic fermentation were carried out.The results showed that CaO2/SAM-SS was also effective in promoting the hydrolysis and acidification of sludge,which can increase the production of VFAs to 1296 mg/L.Furthermore,due to the delayed release of calcium peroxide from the porous surface of SAM-SS,CaO2/SAM-SS experimental group could get long-lasting and more stable levels of VFAs.Microbial community structure analysis showed that,the abundance of the Class Bacteroidia and Clostridia increased rapidly from 6.6%,4.5%of the Control to 37.3%,13.8%(CaO2 test)and 25.6%,17.1%(CaO2/SAM-SS test),respectively.The Class a-,β-,γ-Proteobacteria maintained high abundance in the four groups of experiments,while the Classε-Proteobacteria tends to appeared under alkaline conditions.These bacteria can grow in the alkaline environment and are associated with the degradation of proteins and polysaccharides which was one of the reason for promoting the production of VFAs...