Effect Of Substrate Ratio On Lactic Acid Production By Co-fermentation Of Swine Manure

China is the largest country in pork production.How to utilize the increasing resources of swine manure(SM),control environmental pollution and protect the health of human and animals has been widely concerned.Anaerobic fermentation technology could convert SM into biomethane and other energy,but there were still problems such as difficult process control and low added-value.At present,relevant researches have preliminarily confirmed that co-anaerobic fermentation(co-AF)has the potential to improve the energy conversion of SM.However,the current research of this technology mainly focuses on the methane of terminal product.There were few studies on the conversion mechanism of lactic acid(LA)which was the high added value products and the interaction of different fermentation process parameters in the co-AF process.Therefore,organic wastes with high carbohydrate content,i.e.,distiller’s vinasse(DV),apple waste(AW)and potato waste(PW),were used as the co-substrate for the co-AF with SM to produce LA through different material ratios,and then the appropriate treatment was determined.Meanwhile,the three factors(co-substrate ratio of different wastes,fermentation temperature,and fermentation concentration)and microbial community were studied.The main objectives of this study were to(a)evaluate the feasibility of co-AF of SM with other organic wastes to simultaneously enhance LA production,(b)reveal the variation rule of LA production from SM in the co-AF process,(c)provide the theoretical basis and technical support for the practical application of LA production from SM mixed fermentation.The main conclusions of this research were as follows:(1)It has a significant impact on LA production during the co-AF of SM with different organic wastes,and the highest LA concentration was achieved when the volatile solids(VS)of SM to AW of 25:75.The experiments were conducted during the co-AF of SM with AW or PW at the ratio of 100:0,10:90,25:75,0:100 and SM with DV at the ratio of 100:0,50:50,0:100,respectively.Results showed that the addition of AW or PW significantly increased the production of LA.The maximum concentrations of LA were 27.61 and 8.91 g COD/L in the ratio of SM to AW or PW was 25:75,which were around 3.53-and 1.14-folds of that of the mono-fermentation of SM,respectively.But the co-AF of SM with DV did not improve the LA production.Meanwhile,the significance test showed that the co-AF of SM with AW showed significantly higher LA production than that of SM with PW and SM with DV(P<0.05).Pearson correlation analysis showed that there was a significant positive correlation between reducing sugar content and LA concentration.(2)The quadratic regression model of LA concentration with co-substrate ratio of AW,fermentation temperature and fermentation concentration were developed,and the optimal parameters of LA production were obtained by co-AF.The LA concentration was optimized by response surface methodology(RSM)and Box-Behnken design(BBD)during the co-AF of SM with AW.The results showed that interactive effect was found between the three factors(co-substrate ratio of AW,fermentation temperature and fermentation concentration),and has an important influence on the LA production during the co-AF of SM with AW.The predicted value of LA concentration was 29.59 g/L when the 60.4% cosubstrate ratio of AW,34.7 ℃,and 5.0 % VS through the quadratic regression model.At the optimum conditions,the concentration of LA was 31.18 g/L,and the relative error between it and the predicted value was small.(3)The analysis of microbial community revealed that it had a significant effect on the abundance of microbial community by the addition of AW.Lactobacillus and Clostridium＿sensu＿strito＿1 were dominant bacteria when the maximum LA concentration was obtained during the co-AF of SM with AW,which was beneficial to the degradation of macromolecular organic matter,and resulting in a remarkably LA accumulation.In conclusion,AW as the co-substrate can significantly improve the LA production.In this study,the quadratic regression model and optimization parameters provide theoretical and data basis for the LA production during the co-AF of SM with AW.