Research On Directed Adjustment For Acidification Of Kitchen Waste And PHBV Production

Based on the normalization of garbage classification,the technology of kitchen waste resource utilization has been given more widely attentions.Biochemical treatment technology is a method for kitchen waste disposal,which can bring environmental and economic benefits.Using kitchen waste as raw material produces volatile fatty acids（VFAs）with useful value by anaerobic acidification and further produces Polyhydroxyalkanoate（PHA）with higher value,which is one of the ways of kitchen waste treatment by biotechnology.The optimal parameters of VFAs production by kitchen waste,enhancing the hydrolysis of kitchen waste and propionic acid production by bio-augmentation,and isolating bacteria to produce poly（3-hydroxybutyrate-co-3-hydroxyvalerate）（PHBV）with acidific production of kitchen waste were investigated in this research.This study provided theoretical support for the technology,which the high valued PHA was produced by kitchen waste.Firstly,the effects of four key factors（pretreatment,temperature,p H value and inoculation ratio）on VFAs production from kitchen waste were investigated.It was found that the optimal pretreatment conditions were thermophilic pretreatment at 100℃and alkaline pretreatment with p H value at 8,which could increase the VFAs production by118.73%and 34.95%,respectively.Besides,the best VFAs production arrived at 31.82±1.39 g/L with 35℃and p H of 7;and VFAs production further improved to above 35 g/L by adjusting the ratio of kitchen waste to seeding sludge at 9:1.Secondly,using kitchen waste to produce VFAs was further optimized by Box-Behnken response surface methodology.The quadratic polynomial regression model of VFAs production which included reaction temperature,inoculation ratio,and reaction time was established.The optimum condition for VFAs production is as follows:the reaction temperature at 38℃,the ratio of kitchen waste to seeding sludge at 7:3,and the reaction time at 8 days;the maximum VFAs production（31.85 g/L）was produce under this condition.Adjusting the reaction temperature at 33℃,the ratio of kitchen waste to seeding sludge at4:1,and the fermentation time at 9 days could not only guarantee the higher VFAs production but also reach the best propionic acid production.This also helps to further promote the polymerization of PHBV,which could enhance toughness for products.Besides,the effects of biofortification on the VFAs production and conversion efficiency from kitchen waste acidification were investigated.The results showed that the VFAs production after the coprocessing of cellulase and hemicellulase was higher than that after single enzyme treatment.After the coprocessing of cellulase and hemicellulase,40.03%cellulose and 36.67%hemicellulose were hydrolyzed;besides,the VFAs production increased to 36.31±0.56 g/L,which were increased by 61.61%.As for bio-augmentation of P.acidipropionici,the results showed that the production of total VFAs and propionic acid from acidification of kitchen waste were significantly increased when the P.acidipropionici(OD₆₀₀=1.5)doses set up with 30%inoculum of seeding sludge quality.The total VFAs production arrived at 41.16±1.49 g/L and propionic acid production was increased by79.57%.Based on metagenomics analysis,8 pathways that were related to Propanoate metabolism were enhanced after bio-augmentation of P.acidipropionici,and the conversion from Propanoyl-Co A to propionic acid was stimulated.Finally,two bacterial strain that used the product of acidification to produce PHA with high efficiency were respectively screened out from the activated sludge system and PHA synthetic system.16S r DNA molecular biotechnology was used and showed that these strains belonged to Bacillus xiamenensis and Bacillus cereus,respectively.The ability of PHBV production was arrived at 18.07%and 34.01%by Bacillus xiamenensis SY-2 and Bacillus cereus PY-9,respectively.