Production Of Volatile Fatty Acids And Alginate Extraction By Sludge Anaerobic Fermentation Based On Thermal Pretreatment

The biggest drawback of activated sludge process is that a large amount of waste activated sludge(WAS)needs later treatment and disposal.At the same time,WAS contains a large number of organic compounds.How to recycle and utilize these organic compounds to achieve the resource recovery of sludge is an urgent problem to be solved at present.Sludge anaerobic fermentation is an effective method to treat sludge and recover resources from sludge,but the value of methane produced by traditional anaerobic fermentation is limited,volatile fatty acid(VFA)as an intermediate has higher commercial value and wider application.In recent years,some pretreatment methods and fermentation strategies have been widely studied to improve the efficiency of sludge anaerobic fermentation,among which alkali,low temperature thermal hydrolysis and surfactant can promote the process of sludge dissolution,hydrolysis and acidification.In this paper,low-thermal combined surfactant sodium dodecyl benzene sulfonate(SDBS)pretreatment of excess sludge,examines the VFA production and fermentation process of change,and break through the change of the microbial community,sludge effect,dissolution of organic compounds and simulate the substrate degradation experiments proved the pretreatment methods,such as promoting mechanism of produce acid fermentation.Thermo-alkaline pretreatment(TAP)is commonly used to pretreatment sludge,and alginate is the main component of sludge extracellular polymer(EPS),and its extraction method is also commonly used TAP.Therefore,this paper also studied the optimal conditions for TAP to extract the remaining alginate from sludge,and investigated the influence of alginate extraction on the process of sludge anaerobic fermentation to produce acid.The main conclusions are as follows:(1)Low-thermal combined with SDBS pretreatment can significantly improve VFA yield.The maximum VFA yield was 320±7.7mg COD/g VS obtained by combined pretreatment(70 ?+ 0.01 g SDBS /g TS)on day 4,which was 1.79,1.71 and 3.98 times of that obtained by low-thermal alone,SDBS alone and control tests,respectively.Combined pretreatment reduced the abundance and diversity of the microbial community,and low heat had a greater impact on the microbial community than SDBS.Combined pretreatment increased the abundance of Firmicutes and promoted the fermentation process.(2)During the low-thermal combined with SDBS pretreatment,more proteins and polysaccharides were released from the solid phase and accumulated in the liquid phase.The effect of 70 ? on EPS was stronger than that of SDBS.When combined pretreatment(70 ?+ 0.01 g SDBS/g TS,60min),the maximum protein and polysaccharide concentrations of dissolved EPS were 1000±35 mg COD/L and 186.2±1.6 mg COD/L,which were more than 10 times higher than the original sludge.The reason may be not only the transformation of inner EPS to outer layer EPS,but also the lysis of microbial cells and the release of intracellular organic matter.Three-dimensional fluorescence spectrum and molecular weight distribution showed that low-thermal combined with SDBS pretreatment produced more biodegradable organics for anaerobic fermentation than single pretreatment.Low-thermal combined with SDBS pretreatment inhibited sludge hydrolysis,acidification and methane production,but the degree of inhibition of methane production was far greater than that of hydrolysis and acidification.(3)The optimum reaction conditions for TAP to extract alginate from the remaining sludge: temperature 90 ?,reaction time 60 min,sodium carbonate concentration 4m M/g VS,p H adjusted to 2.5.After TAP sludge and alginate extraction after(AEA),the sludge VFA yield was similar,428 and 430 mg COD/ g VSadd respectively,indicating that the TAP and alginate extraction had no effect on the yield and composition of the anaerobic fermentation VFA.In the fermentation process,the order of p H and ammonia nitrogen is: TAP sludge >AEA sludge > original sludge,and the order of phosphate is:TAP sludge >AEA sludge ? original sludge.TAP sludge will deteriorate the dehydration performance after fermentation,but AEA sludge will not,indicating that polysaccharide has a greater impact on the dehydration performance of sludge.