Research On Biosynthesis Microbial Protein Technology And Mechanism Of High Nitrogen Wastewater

As the population grows and living standards improve,the demand for high-protein foods is increasing.The existing protein supply chain based on crop cultivation suffers from low production efficiency,high energy consumption,and saturated supply.Therefore,it is crucial to seek new sources of protein supply.Microbial proteins are high protein products produced using microorganisms.In this paper,we first domesticated and enriched hydrogen oxidizing bacteria,and then investigated the growth characteristics and microbial protein synthesis of hydrogen oxidizing bacteria under different carbon nutrient conditions.After that we investigated the effect of carbon to nitrogen ratio on microbial protein synthesis of hydrogen oxidizing bacteria under mixotrophic conditions.Finally,we investigated the growth characteristics of hydrogen oxidizing bacteria under different organic carbon sources and the potential of using synthetic biogas slurry for microbial protein synthesis.(1)In this study,the inoculum was firstly domesticated and enriched,and finally with hydrogen oxidizing bacteria as the dominant species was obtained.After that,the growth characteristics and microbial protein synthesis of hydrogen oxidizing bacteria under different carbon nutrient conditions were investigated.The results show that the growth of the mixed flora under different carbon nutrient conditions are quite different.The mixed flora mainly carried out chemoautotrophic metabolism under autotrophic conditions,while under heterotrophic and mixotrophic conditions,it can carry out both chemoautotrophic and chemoheterotrophic metabolism.When cultured under mixotrophic conditions,the mixed flora showed the best ammonia nitrogen conversion and microbial protein synthesis.Under mixotrophic conditions,the ammonia nitrogen conversion rate of the mixed flora was 68.8%,the biomass production and microbial protein content were 5.8g/L and 41.8%,respectively.In addition,the biomass products of the flora under the mixotrophic conditions had higher nutritional value when analyzed in terms of amino acid yield,amino acid type and content.Therefore,the mixotrophic condition is the best condition for microbial protein synthesis.After incubation with different carbon nutrient conditions,the community of the original domesticated flora changed significantly.Xanthobacter remained as the main microbial protein synthesizing bacteria under autotrophic conditions,Xanthobacter and Corynebacterium were the main functional genera under heterotrophic conditions,Corynebacterium and Klebsiella were the main functional genera under mixotrophic conditions.(2)The effect of C/N ratio on the growth and microbial protein synthesis of hydrogen oxidizing bacteria under mixotrophic conditions were investigated.The growth and CO2 fixation potential of the mixed flora were significantly higher when the C/N ratio was above 9.The ammonia nitrogen conversion and biomass yield of the mixed flora increased with the increase of C/N ratio.When the C/N ratio was above 9,the ammonia nitrogen conversion rate and the biomass yield of the bacterial flora were above 80%and 4.8gCDW/L,respectively.Afterwards,the increase in C/N ratio has limited improvement in the microbial protein synthesis capacity of the mixed flora.The YMP/N of the mixed flora was maintained at about 3.5 g MP/g N,resulting in a decrease in the relative content of microbial protein in the biomass products and a subsequent decrease in nutritional value.It can be seen from the types and contents of amino acids that the nutrient value of the biomass product was higher when the C/N ratio was less than or equal to 9.Besides,the amino acid yield of the mixed flora is the highest when the C/N ratio was 9,which was 3337.6 mg/L.Therefore,the C/N ratio of 9 under mixotrophic conditions is the best conditions for hydrogen oxidizing bacteria to carry out ammonia nitrogen conversion and microbial protein synthesis.(3)The growth characteristics of hydrogen oxidizing bacteria using acetate,propionate,butyrate,glycerol and glucose as organic carbon sources were explored,and the potential of the mixed flora to synthesize microbial protein using synthetic biogas slurry as a substrate was further judged.Studies have found that hydrogen oxidizing bacteria can use acetate,propionate,butyrate,glycerol,or glucose as the single organic carbon source for ammonia nitrogen conversion and microbial protein synthesis.When acetate,propionate,butyrate,glycerol was used as the single organic carbon source,the ammonia nitrogen conversion ability of bacteria was weak,but the microbial protein synthesis ability was strong.Under that conditions,the ammonia nitrogen conversion rate of the mixed flora was about 50%-60%,and the YMP/N was above 4 g MP/g N.When glucose was used as the single organic carbon source,the ammonia nitrogen conversion capacity of the mixed flora was stronger,and the microbial protein synthesis capacity was weak.The ammonia nitrogen conversion rate was about 90%,but the YMP/N was only 1.9 g MP/g N.In addition,the biomass products of each experimental group contained 17 kinds of amino acids,and the nutritional value of the biomass products was high.Under mixotrophic conditions,hydrogen oxidizing bacteria can grow using synthetic biogas slurry as a substrate,and the bacteria can completely degrade organic acids.The growth and potential for CO2 fixation of the mixed flora were increased with the increase of the C/N ratio.When the C/N ratio was increased from 3 to 6,the biomass yield increased by about 52%.Optimal biomass yield was achieved as the C/N ratio was above 6,which was above 4.4 g CDW/L.However,as the C/N ratio raised from 6 to 9,biomass yield only increased by 10%.There was a limit in biomass yield as the C/N ratio was above 6.The ammonia nitrogen conversion of the mixed flora was positively correlated with the C/N ratio,and the ammonia nitrogen conversion rate was as high as 77%under the C/N ratio of 9.The microbial protein synthesis capacity of the flora decreased with the increase of the C/N ratio.When the C/N ratio was less than or equal to 6,the YMP/N of the mixed flora was 4g MP/g N.As the C/N ratio increases to 9,the YMP/N dropped by 13%.Therefore,the excessively high content of organic acids in synthetic biogas slurry was beneficial to the conversion of ammonia nitrogen,but it was not conducive to the synthesis of microbial protein.From the perspective of ammonia recovery,a C/N ratio of 6 can be considered.Under this condition,the mixed flora has both a strong ammonia nitrogen conversion capacity and a microbial protein synthesis capacity.