Research On The Synthesis Of Polyhydroxy Fatty Acid Esters From Anaerobic Acidification Solutions For Food Waste

Since the introduction of the garbage classification policy,the output of Food waste has increased sharply,and the treatment of food waste has become a key issue for scholars.Due to the large amount of organic matter in food waste,the intermediate products of its anaerobic fermentation,volatile fatty acids（VFAs）,can be used as carbon sources for microbial synthesis of polyhydroxyalkanoate（PHA）.In this paper,in order to improve the yield of VFAs,the effect of ultrasonic-alkali combined pretreatment on the hydrolysis and acidification of food waste was studied,the effect of the addition of exogenous substances on the fermentation of food waste was explored,and the fermentation broth under optimal acid-producing conditions was used as a carbon source for the synthesis of Rhodopseudomonas palustris,and the process conditions for microbial synthesis of PHA were optimized.In this paper,the acid-producing effects of anaerobic fermentation of food waste under different ultrasound-base combined pretreatment conditions were studied.The results showed that with the continuous increase of ultrasound time and the increase of p H,the total amount of VFAs gradually increased,and when the sonic treatment time was 10 minutes and the initial p H was 9.0,the acid-producing effect was the best,and the output of VFAs reached 7830.98 mg/L,and the fermentation system mainly used acetic acid and butyric acid as products.Secondly,exogenous additives were added to the anaerobic fermentation acid production system under the pretreatment conditions of ultrasonic time of10min and initial p H of 9.0.The comparison of magnetite（Fe₃O₄）,anthraquinone-2-sulfonic acid（AQS）and alkyl glycosides（APG06）to enhance the efficiency of sludge fermentation to produce acid.The results show that Fe₃O₄ can promote the anaerobic fermentation of food waste to produce acid.Under the condition of low dosage,the yield of VFAs does not increase significantly.When the Fe₃O₄ dosage was 10 g/L,the highest yield of VFAs was22895.92 mg/L.AQS can also promote the accumulation of VFAs.Similar to the Fe₃O₄ intensified fermentation process,the promotion effect is not obvious when the dosage of AQS is low,and when the dosage of AQS is increased to120 mg/L,the production of VFAs can reach 18125.95 mg/L.APG06 can also promote the process of acid production by anaerobic fermentation of sludge.When the dosage is 9.45 g/L,the output of VFAs is 15927.55 mg/L.The main components of VFAs produced by the three exogenous substances enhanced fermentation are acetic acid and butyric acid,and the sum of the two can reach 80.50%,79.57%,73.74%,which is a typical butyric acid fermentation.The concentrations of dissolved proteins,total sugars and ammonia nitrogen in the acidification system increased significantly after the addition of exogenous substances,and gradually increased with the progress of fermentation and acid production.In addition,the addition of exogenous substances increased the activity of the relevant hydrolase,and promoted the hydrolytic acidification process of organic matter.The microbial population structure of the acid-producing process was analyzed,and the microbial population structure of the acid-producing process of each experimental group was analyzed under the optimal acid-producing conditions,and the results showed that the bacterial dominant bacteria in the FW+IS+Fe₃O₄ and FW+IS+AQS experimental groups were Clostridium＿sensu＿stricto＿1 and Terrisporobacter.The dominant bacteria in the FW+IS+APG06 test group were Entrerococcus and Terrisporobacter.Finally,the liquid phase product obtained after the solid-liquid separation of the anaerobic fermentation product of food waste was used as raw material,and the study of the synthesis of PHA by Rhodopseudomonas palustris using fermentation acid-producing solution was carried out,and the consumption law of each component in VFAs was analyzed.The process optimization was achieved by the regulation of four factors of culture time,substrate concentration,p H and inoculation amount,which improved the synthesis efficiency of PHA by bacteria,and the results showed that the synthesis rate of PHAs was 48.62%under optimal conditions（incubation time 30 d,substrate concentration 2202.21 mg/L,initial p H=8.0,inoculation amount was 15%）.Pseudomonas marsh erythrocytes first use even-numbered carbon VFAs in hydrolysates to propionate poly-3-hydroxybutyrates（PHB）,followed by odd-numbered VFAs,such as propionic acid,which contribute to the synthesis of poly-3-hydroxyvalerates（PHV）.