Synthesis Of Single Cell Protein In The Process Of Photosynthetic Bacteria Treating Wastewater

Wastewater is a reusable resource.Traditional wastewater treatment technologies face inevitable challenges such as high energy consumption,low carbon capture efficiency,and greenhouse gas emissions,which have become serious constraints on wastewater treatment efficiency.Photosynthetic bacteria（PSB）can produce biomass and single cell protein（SCP）from wastewater treatment.As a good protein source and feed ingredient,SCP can replace expensive protein raw materials,and has significant economic advantages.In order to improve the yield of PSB synthetic protein,this article took the production of SCP in the PSB wastewater system as the goal,explored the effects of different influencing factors on the growth characteristics of PSB and the synthesis of microbial protein,and optimized the key influencing factors;Based on energy metabolism and SCP synthesis pathways,the effects of key factors on the activity of key enzymes and the expression of key functional genes during SCP synthesis in PSB cells were clarified,and the biological mechanism of key factors regulating the synthesis of SCP by PSB was revealed at the molecular level.Based on the above theoretical research,in order to further improve the efficiency of PSB synthesis and recovery of SCP,the membrane materials of the PSB-Membrane Bioreactor（PSB-MBR）wastewater system were improved,laying a foundation for the application of subsequent research projects.The results show that it is feasible to treat protein wastewater with PSB and simultaneously produce SCP.The optimal nutrient source conditions selected in the experiment are as follows:the optimal carbon source concentration（C element percentage）combination is 0.442%sodium acetate,0.577%sodium bicarbonate,and 0.510%fructose;The optimal combination of nitrogen source concentration（N element percentage）is urea0.600%,ammonium sulfate 0.679%,and sodium glutamate 0.805%;The optimal carbon nitrogen ratio（C/N ratio）is 20.Optimal lighting conditions:incandescent light source;The light intensity range is 2000-4000 lux;The light/dark cycle is 16 h/8 h.The optimal growth condition is p H 7.0;Light anaerobic;Both trace elements Mg²⁺and Zn²⁺can significantly increase the yield of SCP,while Cu²⁺inhibits the growth of PSB and the synthesis of SCP to varying degrees.Based on the experimental optimization of nutrient sources,growth conditions,and lighting conditions,the optimal protein yield of PSB is 0.650 g·L^-1.The results of mechanism analysis indicate that Mg²⁺,Zn²⁺,and Cu²⁺all affect the production of SCP synthesis by regulating the differential expression of key functional genes（glt X and ghd A）in the SCP biosynthesis pathway,and by changing the activity of key enzymes（glutamine synthetase and glutamate synthetase）.Photoperiodic regulation of SCP synthesis mainly relies on the promotion of synthesis of photosynthetic pigments to enhance energy metabolism,thereby improving the material synthesis and metabolism of SCP.On the basis of batch culture and mechanism discussion,in order to further improve the recovery rate of SCP,the PVDF hollow fiber membrane material in the PSB-MBR wastewater system was double modified with nano functional materials and zwitterionic polymers.Sulfobetaine type zwitterionic polymer-nano silver（PSBMA-Ag NPs）and sulfobetaine type zwitterionic polymer-graphene oxide（PSBMA-GO）composite membranes were prepared,respectively.The characterization of membrane materials and the results of filtration performance showed that the porosity and rejection of the two modified composite membranes were significantly improved compared to the original membrane;The results of the flux attenuation when the membrane was contaminated with humic acid and the pure water flux recovery rate after the membrane was contaminated with BSA confirmed that the anti organic pollution performance of the two membranes was significantly improved;CLSM analysis results showed that few living cells were observed on the surface of the modified membrane,while higher concentrations of living cells were observed on the surface of the contaminated original PVDF membrane,further confirming that the modified membrane had improved biological pollution resistance.Combining modified membranes with PSB bioreactors can facilitate the collection of PSB bacteria and effectively reduce membrane pollution,providing new ideas for the production of SCP under stable yield control.