Study On The Process Of Inducing Cyanobacteria Bloom To Produce Sugar And Promoting Nitrogen Removal In Eutrophic Water

Excessive nitrogen in water will lead to the outbreak of cyanobacteria.In order to reduce the nitrogen entering the natural water body,engineering process is usually used to strengthen denitrification to achieve the purpose of removal,but organic carbon is the limiting factor of denitrification.Recent studies have shown that after the death and deposition of cyanobacteria,they secrete carbohydrates to the water body and promote the denitrification process.Therefore,starting from the engineering application of cultivating cyanobacteria as denitrification carbon source,this paper explores the feasible methods to improve the content of cyanobacteria carbohydrate.The changes of useful substances in cyanobacteria after nitrogen limited culture are studied and applied as engineering parameters for denitrifying carbon source application.The conclusions are as follows:The light dark cycle of cyanobacteria bloom culture changed from 16L∶8D to24L∶0D,the daily average carbohydrate yield increased from 9.6 mg L-1 to 80.3 mg L^-1,and the peak daily output increased from 18.1 mg L^-1to 117.3 mg L^-1.In order to further improve sugar yield,the methods of adding inorganic carbon source and salt stress were adopted.The results showed that both methods could achieve the goal.The carbohydrate components of cyanobacteria before and after nitrogen limiting culture were analyzed.It was found that the intracellular carbohydrate content of cyanobacteria increased significantly after nitrogen limiting culture,especially glucose,which increased by 4.76 times,during the sugar production culture of cyanobacteria in July,August and September 2019,it was found that although the sugar production effect of cyanobacteria in September is not as good as that of cyanobacteria in July and August,it was still significantly improved compared with that before culture.In order to explore the promoting effect of cyanobacteria as denitrifying carbon source on denitrification under different conditions,the composition of algae powder leaching solution was analyzed.It was found that the organic carbon release efficiency of algae powder after nitrogen limiting culture was much higher than that of uncultured cyanobacteria,in which the organic carbon leaching amount increased from 15.4 mg L^-1to 23.0 mg L^-1,and the total sugar leaching amount increased from8.24 mg L^-1to 40.2 mg L^-1,BOD₅/COD increased from 0.65 to 0.90;The denitrification rate could be adjusted according to the relationship between the proportion of cyanobacteria in carbon source and din removal rate;Finally,from the influence of HRT on cyanobacteria denitrification,the best HRT was 1d.