Statistical Research On The Mechanism Of Co-fermentation Process Under The Influence Of Surfactants

In order to achieve the aim of treating the domestic sewage containing surfactants,straw and livestock excrement,and simultaneously producingbioenergy,,this study added different surfactants to the anaerobic cofermentation system with cow dung and corn stover as substrates.The biogas yields were measured and fitted by modified Gompertz model.After the optimal concentration was obtained,the biogas properties,process stability,degradation of raw materials,enzyme activity and microbial constructure were analyzed through statistical methods,including one-way analysis of variance(one-way ANOVA)and correlation analysis.The results revealed the mechanism of anaerobic fermentation under the influence of different surfactants,and would support the disposal and reutilization of waste water and residues,as well as the bioenergy production.The mainstatistical and experimental results are as follows:(1)Anionic surfactant(LAS)and cationic surfactant(DDBAC)promoted biogas production at low concentrations and inhibited at high concentrations.The threshold concentration was 10 and 20 mg/L for LAS and DDBAC.The inhibitory effect of DDBAC on biogas yields was weaker than the corresponding concentration of LAS.Different concentrations of TX(0-100 mg/L)measured in the present study promoted biogas production.Furthermore,adding low concentrations of LAS brought forward the biogas yields peak period,and significantly increased the peak daily biogas yields,resulting in the increment of cumulative biogas yields.The fitting results of the Gompertz model showed that the inhibitory effect of LAS and DDBAC on biogas production was more remarkable than TX at the same concentration.The influence of DDBAC on biogas yields and producing rate was greater than LAS and TX,which ultimately resulted in a slightly lower biogas yield.(2)1 mg/L LAS and TX induced higher cumulative biogas yields than 1 mg/L DDBAC,which as 62.76%,36.96%,and 6.85%higher than the control group,respectively.The LAS and TX groups increased the final cumulative biogas yields by prolonging the peak biogas producing period and increasing the daily biogas yields.Adding LAS,TX and DDBAC into fermentative system inhibited the coenzyme F420 activity,thereby reducing the methane content(the correlation coefficients between coenzyme F420 and methane content:LAS 0.755,p<0.05;TX 0.770,p<0.01;DDBAC 0.777,p<0.01,respectively).Meanwhile,the inhibitory effect of LAS and TX on methane production was stronger than DDBAC.Though adding surfactants improved the activity of coenzyme M in DDBAC and LAS groups,it did not increase the methane content.(3)LAS and TX not only promoted the conversion of organic nitrogen into ammonia nitrogen in cow dung,but also increased the abundance of Firmicutes and Bacteroidetes that participated in the hydrolysis and acidification reactions.Futhermore,the positive correlation(0.998,p<0.01)between Bacteroidetes and VFAs in the LAS group was in line with this result.Those acidic and alkaline substances were conducive to better process stability as shown by the more suitable pH conditions than the control group.In addition,the presence of Bacteroidetes in the TX group was conducive to the degredation of lignin(-0.955,p<0.05).According to the results of one-way ANOVA,LAS and TX significantly enhanced the peak daily biogas yields,cellulase activities,VFA concentration and the degradation of lignin(p<0.05).Meanwhile,the effect was more remarkable than the addition of DDBAC.(4)The addition of surfactants did not change the dominant microbial population,which were Phylum Firmicutes,Bacteroidetes.In addition,LAS and TX impacted thevairatoin of microbial species in the fermentation system,which was reflected by the fluctuation of the Observed species throughout the whole fermentation process.However,during the peak biogas production period,the higher Sannon and Simpson indices indicated that the species diversity and evenness of microorganisms in LAS and TX groups were better than those of CK and DDBAC groups.(5)The common dominant fungi in all groups during the fermentation process were Ascomycota and Basidiomycota,followed by the unidentified fungi.The xylanase secreted by Eurotiales in Ascomycota hydrolyzed hemicellulose.The relative abundance of Eurotiales in CK,DDBAC,LAS,and TX gradually increased.However,since the enzyme activity was limited by pH,there was no remarkable difference on the degradation of hemicellulose between different groups.In addition,the positive correlation between Ascomycota and VFAs in the LAS group(0.998,p<0.01)indicated that Ascomycota participated in the degradation of substrates.The negative correlation between the Basidiomycota and lignin in the TX group(-0.956,p<0.05)suggested that the increase of Basidiomycota was conducive to lignin degradation.In the LAS group,the syntrophic relationship between unidentified fungi and methanogens were essential for high methane content at the later stage.TX was helpful to maintain the stability of the fungal community structure in the fermentation system,however reduced the diversity of fungi.The fungal community structure,diversity,evenness and observed species varied greatly in CK,DDBAC,and LAS groups.This study explored the effect of various surfactants with different concentrations on anaerobic fermentation.Thepotential biogas yields were analyzed using the modified Gompertz model.Furthermore,statistical methods including one-way ANOVA and Pearson correlation analysis were used for analyzing the variations and relationships of fermentation indexes such as biogas characteristics,pH,raw material degradation,enzyme activity,and microbial characteristics during the fermentation process.This study revealed the impact mechanism of surfactants on the anaerobic cofermentation process.It provided references for the treatment and disposal of sewage and agricultural waste as well as the development of biomass energy.