| Food waste is a kind of waste with characteristics of high organic content,large yield and rich in nutrient elements.At present,the method of anaerobic fermentation to produce methane is mainly used to treat food waste.However,due to the characteristics of complex composition and high water content of food waste,the anaerobic fermentation liquid of food waste has a high yield and is hard to deal with,which poses a threat to the environment.Due to the high content of volatile fatty acids in fermentation liquid,Polyhydroxyalkanoates(PHAs)can be synthesized by microorganisms to realize the resource utilization of food waste.PHAs has a similar physical properties to plastic and can be degraded by microorganisms in the environment,making it a good alternative to conventional plastics.Nowadays,the commercial production of PHAs mainly adopts the way of pure bacteria and pure substrate,which cause a high production cost and a limited commercial application.In order to reduce the production cost,synthesis of PHAs by mixed culture has become a hotspot in the biosynthesis of PHAs.However,the PHAs producing mixed culture is mainly in the form of flocculent sludge,which has the problems of long cultivation time and low PHAs yield.Granular sludge has the characteristics of high biomass content,resistance to toxic substances and shock loading,which can overcome these defects well and have a better adaptation to the complex composition of the fermentation liquid of food waste.Therefore,this study using simulated food waste fermentation liquid as substrate to investigate the influence of lactic acid content on the cultivation of granular sludge,optimize the cultivation process of granular sludge and explore the feasibility of the cultivation of granular sludge;using food waste fermentation liquid to cultivated PHAs producing granular sludge,so as to improve the yield of PHAs and reduce the production cost of PHAs,which can provide theoretical and technical support for the realization of low-cost and large-scale production of PHAs.The main research results are as follows:1.Based on the coupled process of anaerobic plug flow feeding and feast famine mode,the influence of different lactic acid contents(0%,20% and 40% of COD)on the enrichment of PHAs-producing mixed culture was investigated.The results showed that the higher the content of lactic acid,the higher the value of mixed liquid suspended solids(MLSS),the smaller the value of sludge volume index(SVI),the higher the biological activity and the better the sludge granulation.In the cultivation process in 40% reactor,the highest MLSS concentration of sludge reached 8.07 g /L,SVI was less than 150 m L/g,biocativity of sludge was up to 0.92,and the maximum sludge particle size was higher than 1.6 mm.At the end of cultivation,the maximum PHAs content of the enriched mixed cultures with 0%,20% and 40% lactic acid content accounted for 36.15%,45.67% and 47.03% of cell dry weight(CDW),respectively.The relative abundance of microbial community at the genus level showed that,the genera with extracellular polymer substance synthesis capacity in the reactor containing 40% lactic acid content had the highest relative abundance(74.89%).The dominant genera were Neomegalonema,Thiothrix,Pseudoxanthomanos and Acidovorax,of which Thiothrix was only found in the reactor of 40% lactic acid content,and might play an important role in the formation of granular sludge.2.Under the condition of 40% lactic acid content,the effects of aerobic dynamic feeding(ADF),aerobic dynamic discharge(ADD)and anaerobic dynamic extend feeding(ADEF)(intermittent addition of carbon sources to extend the feast period on the basis of ADD process)on the cultivation of PHAs producing granular sludge was investigated.Baesd on these results,the cultivation process was optimized again to enhance the granulation effect of sludge.The results showed that,compared with ADF reactor and ADD reactor,the sludge in ADEF reactor had a SVI value around 60 m L/g,and had a better settling capacity.The sludge in ADEF reactor had the highest amount of active biomass,the highest MLSS concentrations in the cultivation process was 7.44 g/L.The granulation of sludge in ADEF reactor was the best,85.87% of the sludge with particle size greater than 0.25 mm,while the percentage of sludge in ADD reactor and ADF reactor with particle size greater than 0.25 mm was 20.55% and13.99%,respectively.After 25 days of cultivation,the maximum PHAs content of sludge in ADEF,ADD and ADF reactor were 60.6% CDW,75.0% CDW and 54.9%CDW,respectively,and the volumetric yield of PHAs was 4.00 g/L,1.59 g/L and 2.63g/L,respectively.The microbial diversity and species number in ADEF reactor were higher than those in ADD and ADF reactor.At the end of cultivation process,Paracoccus was a dominant bacterium genus in all three reactors,but the composition and structure of the microorganisms in these reactors were significantly different due to the effects of the different cultivation methods.Therefore,ADEF stratrgy was optimize by continuous feed,and simulated fermentation liquid was used for the cultivation experiment.The results showed that the optimized anaerobic continuous extend feeding process(ACEF process)could cultivate granular sludge with higher PHAs synthesis capacity,the content of PHAs was up to 71.67% CDW.And the sludge cultivated by ACEF process had larger particle size and higher strength,the average particle size and instability coefficient were 0.47 mm and 0.0974,respectively.On the thirty-fifth day,Plasticicumulans was the dominant genus,and the relative abundance of was higher in ADEF reactor(29.59%).After 55 days of cultivation,the dominant bacteria in ADEF reactor and ACEF reactor were Amaricoccus and uncultured＿f＿Saprospiraceae.3.Fruit and vegetable waste was the substrate used for anaerobic fermentation,and the fermentation liquid obtained was rich in lactic acid.The proportion of lactic acid to fermentation products(organic acids and ethanol)was 59.19% ± 6.46% COD,when the fermentation experiment was running stably.The ACEF process was selected as the operating process,and the fermentation liquid(the content of lactic acid was 23.97 ± 12.67% COD)of fruit and vegetable waste was used for the cultivation of PHAs-producing granular sludge.The granular sludge with a average particle size of 0.35 mm and maximum PHAs content of 78.39% CDW was obtained,which was stronger than that of the granular sludge cultivated with simulated fermentation liquid using the same process.The dominant bacteria in the reactor were Plasticicumulans(64.77%),Flavobacterium(2.81%)and Hydrogenophaga(2.66%).The genus of Plasticicumulans has the ability to produce PHAs,and it can be inferred that this genus may play an important role in the cultivation of granular sludge producing PHAs using fruit and vegetable waste fermentation liquid. |
