Experimental Study On Algae Growth Control And Noval Utilization Pathway For Resource Recovery

Eutrophication of water bodies has always been a problem that plagues natural ecology.Controlling microalgae growth in natural bodies is the focus of academic research,especially the control of nitrogen?N?and phosphorus?P?inputs.On the other hand,controlling the growth of microalgae to make them accumulate bio-oils and bio-proteins is also a hot topic in the world.This study combined these two aspects.Firstly,the effect of N and P concentrations on the growth of microalgae in an artificial environment was studied to confirm the N and P thresholds controlling the reproduction of microalgae.Secondly,in addition to bio-oil and bio-proteins production from algae,the present study tried to use microalgae to synthesize poly-?-hydroxybutyrate?PHB?mainly with inorganic carbon source CO₂.The experimental results showed that the N and P thresholds?TN<0.2 mg/L,TP<0.01mg/L?for microalgae growthwere very low.The microalgae were cultivated even with tap water and mineral water?N&P?at certain temperature,time and illumination.The growth of microalgae was indeed controlled by the remaining N and P levels in the water?microalgae can stagnate or even die?,but the artificial addition of a small amount of N and P would immediately resurrect the microalgae.The results also showed that controlling microalgae growth does not require a two-pronged approach but only N or P can work.PHB is usually synthesized by heterotrophic bacteria with exogenous organic matter and is an energy storage substance in the cell.The physical properties of PHB are similar to petroleum-based plastics,but they are completely biodegradable.Therefore,the use of PHB to produce biodegradable plastics is highly expected.Cyanobacteria,a kind of photoautotrophic microalgae,can directly synthesize PHB using light and CO₂.The present study attempted to enhance the accumulation of PHB by dosage of a small amount of organic carbon source and reach a level comparable to heterotrophic bacteria using organic carbon source exclusively.In the experiment,cyanobacteria was cultured with secondary effluent to accumulate PHB and also with the enhancement by adding 4¹5 mg/L sodium acetate?equivalent to 2.3⁸.7 mg COD/L?.Under suitable environmental conditions,a maximum PHB yield of 24%?dry cell weight;10 mg/L sodium acetate?was obtained.However,considering the operation of the reactor and the survival of cyanobacteria,a higher addition of carbon source did not induce a higher production of PHB.There was an optimal value of dosage?10 mg/L?.In addition,the experiment also tested the suitability of other carbon sources?fructose?and changing environmental conditions to stimulate PHB accumulation,but the results were not satisfactory.It can be seen that there is an optimal environment for PHB production by cyanobacteria.