Effects Of Nitrogen And Phosphorus Concentrations On Growth And Thermal Effects Of Chlorella Vulgaris

At present,reclaimed water has become one of the important measures to solve the problem of urban water shortages.But most urban water bodies are required to meet Class III water quality standards for surface water,and the quality of reclaimed water is far from this,especially nitrogen and phosphorus pollutants.Combined with the characteristics of slow flow rate and shallow water depth in urban water,the use of reclaimed water as urban replenishment will lead to frequent occurrence of eutrophication and loss of landscape function in urban water bodies.The overgrowth of algae caused by excess nitrogen and phosphorus nutrients is the main reason of the eutrophication.In addition,the current eutrophication evaluation indicators,there are defects,which makes it difficult to control eutrophication.Based on the nitrogen and phosphorus concentrations in the Class III surface water standard for surface water and the reclaimed water quality standard,this study used Chlorella as a research object to explore the effects of nitrogen and phosphorus concentrations on the algal life activities in water bodies,and The preliminary evaluation of the thermodynamic evaluation index was conducted.The main conclusions are as follows:1.Nitrogen and phosphorus concentrations affect the biomass and growing period of algae,and the effects of nitrogen and phosphorus are different under different growth modes.In the case of autotrophic cultivation,the phosphorus concentration is the main influencing factor for the growth of Chlorella,and the nitrogen concentration has little effect on Chlorella;In the case of mixotrophic cultivation,the nitrogen concentration is the main influencing factors for the growth of Chlorella,while the phosphorus concentration has little effect on chlorella.2.The absorption and utilization of nitrogen and phosphorus by Chlorella were influenced by the interaction of culture mode and nitrogen and phosphorus concentrations.In the case of autotrophic cultivation,chlorella absorbs a large amount of phosphorus in the body during the early culture period,and the absorption rate of nitrogen is low.In the later culture period,the absorption rate of nitrogen gradually increases,and the rate of phosphorus absorption is almost zero.The absorption and utilization levels of nitrogen by Chlorella are affected by the concentration of phosphorus.In the case of mixotrophic cultivation,due to the influence of external carbon sources,the absorption and utilization rate of nitrogen in the early culture period of Chlorella vulgaris is faster,while the absorption and utilization rate of phosphorus is slower,and it is the opposite in the later culture period.The absorption and utilization of phosphorus by Chlorella is affected by the nitrogen concentration.3.Algae mainly consists of five elements: C,H,O,N,and P.In the case of autotrophic cultivation,the content of C,H,O,and N is 40%,10%,30%,and 5%,respectively.In the case of mixotrophic cultivation,the contents of C,H,O,and N in the cultured chlorella were 50%,5%,40%,and 2.5%,respectively.The contents of C and N in Chlorella were affected by the concentration of P.4.The results of microcalorimetry and combustion calorific value show that nitrogen and phosphorus concentration affect the thermal effect of Chlorella,and the concentration of nitrogen and phosphorus is positively correlated with the thermal effect of Chlorella.The increase of nitrogen and phosphorus concentration will lead to the increase of algae thermal effect.The effect of nitrogen on the thermal effects of algae is even more pronounced.