Synthesis Of Valuable Organic Material From Food Processing Wastewater By Purple Non-Sulfur Bacteria And The Influencing Factors

Photosynthetic bacteria（PSB）wastewater treatment technology not only remove the organic pollutants in wastewater,but also it recycle some high valuable material including single-cell protein,carotenoids,5-aminolevulinic acid（ALA）,which has been received wide attention and extensive research.However,when using PSB to treat food wastewater,it’s a general phenomenon that pollutants removal,bacterial biomass and high valuable material yield,such as carotenoids,ALA are not high,which hinders the promotion and apply of PSB technology in wastewater treatment.In this paper,based on comparing and optimizing purple non-sulfur bacteria（PNSB）growth and secondary metabolite,biosynthesis systems of carotenoids and ALA were established in which food wastewater was as nutrient medium by using Rhodopseudomonas palustris（Rp.palustris）and Rhodobacter sphaeriodes（Rb.sphaeriodes）.Batch culture and continuous flow culture methods were used to study the key influencing factors and optimize the control parameters.Based on the energy metabolism and material synthesis pathway,biological mechanism of the key factors regulating PNSB treating wastewater from molecular level was explored.In the four experimented strains,Rp.palustris had the strongest ability of producing carotenoids,and Rb.sphaeriodes was fit for producing ALA.The best matrix of cultivating Rp.palustris and Rb.sphaeriodes were volatile fatty acid wastewater and soybean protein wastewater,respectively.The growth dynamic of these two strains fitted to Logistic model,carotenoids or ALA biosynthesis dynamic fitted to Luedeking Piret model.Mg²⁺,light intensity and light cycle,p H and appropriately additional biostimulation all had an appreciable impact on carotenoids biosynthesis.Under the conditions that the concentration of Mg²⁺ was 15 mmol/L,5000 lux,the ratio of light and dark was 4:2,pH 8.0 and the content of biostimulation was 40 μL/L,the bacterial biomass and carotenoids yield of Rp.palustris were 3.90 g/L and 4.83 mg/g-DCW using volatile fatty acid wastewater as substrate.As the functional gene analysis indicated,Mg²⁺ increased carotenoids yield by regulating the crt gene expression.However,additional biostimulation had a good influence on carotenoids yield by inhibiting the peroxidase activity.Too high light intensity would inhibit PNSB growth,proper dark stimulation enhanced the carotenoids yield.The increase of p H in a certain range controlled the biosynthesis of oxidation reduction potential（ORP）of system at a lower level,promoting the synthesis of carotenoids.As the research that ALA synthesis by Rb.sphaeriodes indicated,Fe²⁺,synthetic substrates（glucose,succinate and glycine）and additional biostimulation were key influencing factors for ALA biosynthesis.Under the condition s that the concentration of Fe²⁺ was 400 μmol/L,3000 lux,the content of biostimulation was 40 μL/L,and the succinate,glycine and glucose concentrations were 8.56,5.06 and 7.82 mmol/L,the bacterial biomass and ALA yield of Rp.palustris were 4.02 g/L and 15.86 mg/g-DCW using soybean protein wastewater as substrate.The regulatory mechanism of Fe²⁺ had relationship with the key enzyme activity,ATP yield and functional gene expression.Based on batch culturing and mechanism discussion,continuous flow biological treatment systems for treating food processing wastewater by Rp.palustris and Rb.sphaeriodes were established,such as volatile fatty acid wastewater and soybean protein wastewater.They were also used to produce carotenoids and ALA,respectively.The result showed that,for the continuous flow of biological treatment s ystem by Rp.palustris,under the conditions that the HRT was 48 h,the organic load rate（OLR）was 2.51g/L/d,Mg²⁺ concentration was 15 mmol/L,5000 lux,the ratio of light and dark was 4:2,p H 7.0 and the content of biostimulation was 40 μL/L,the average removal rate of COD was 85.7%,the biomass production rate and carotenoids production rate were 1.36 g DCW/L/d and 5.32 mg/L/d.The carotenoids content of biomass reached 3.92 mg/g DCW.In the system for treating soybean protein wastewater by Rb.sphaeriodes,under the conditions that the HRT was 60 h,the OLR was 2.48 g/L/d,Fe²⁺ concentration was 400 μmol/L,3000 lux,and the content of biostimulation was 40 μL/L,the average removal rate of COD was 89.5%,the biom ass production rate and ALA production rate of bacteria were 1.06 g DCW/L/d and 7.86 mg/L/d,The ALA content of biomass was 7.40 mg/g DCW.