Research On The Effects Of Ree Ce Addition On The Chlorella Pyrenoidosa For Treatment Of Domestic Sewage

With the rapid development of urbanization,the discharge of domestic sewage in China has risen sharply.Faced with the current situation of water resources,China has been increasing the intensity of sewage treatment in recent years.Traditional wastewater treatment process usually has the problems of high energy consumption,secondary pollution,high investment cost,high N and P content in effluent.The use of microalgae to purify domestic sewage,which combines sewage treatment with microalgae culture,can not only realize the resource utilization of sewage,but also have high economic value and social value.However,the application of microalgal photobioreactor is limited by light conditions,so it is urgent to develop microalgal photobioreactor with low energy consumption,good sewage treatment effect and high microalgal density.In this study,based on the "Hormesis" effect of rare earth elements on microalgae.As the main process,photobioreactor can realize the high-density cultivation of microalgae under low light intensity by adding rare earth element Ce.On the basis of reducing the energy consumption of the reactor,the removal efficiency of N,P and other pollutants in domestic sewage was improved.Firstly,the effects of rare earth elements on the growth of microalgae were studied.Illumination,as one of the most important factors in the growth environment of microalgae,has a strong regulatory effect on the growth of algae.The effects of rare earth elements with different intensity of illumination and different concentration gradient on the growth state of pure algae and sewage treatment were investigated.The results showed that the effect of rare earth element Ce on Chlorella pyrenoidosa was affected by the light intensity.When the light intensity was 50 ?mol/?m2·s?,the promotion effect of low concentration of Ce³⁺ on the growth of Chlorella pyrenoidosa was the most obvious,the concentration range was 0.2-5 mg/L,and the optimal concentration was 1 mg/L.At this concentration,the algal density was 22.39% higher than that of the control group.In the later stage of culture,the promoting effect gradually weakened.The growth promoting effect was the second when the light intensity was 25 ?mol/?m2·s?,but not when the light intensity was 100 ?mol/?m2·s?.However,high concentration of Ce³⁺ has always had an inhibitory effect on the growth of Chlorella pyrenoidosa.At the same time,it was found that the optimal light intensity of domestic sewage treatment was 50 ?mol/?m2·s?,and the optimal dosage of rare earth element Ce was 1mg/L.Secondly,the effect mechanism of rare earth elements on the growth of microalgae was explored.It was found that with the increase of Ce³⁺ concentration,the content of chlorophyll-a,photosynthesis efficiency and protein in algae cells increased first and then decreased when the light intensity was 50 ?mol/?m2·s?.When Ce³⁺ concentration was 1 mg/L,there was a peak value.The total chlorophyll a content increased 38.43%,the chlorophyll a content of per algae cell increased by 13.1%,the Fv/Fm increased by 27.9%,and the protein content increased by 48.5%.It can be seen that,under the experimental conditions,the low concentration of Ce³⁺ can promote the absorption of N,P and other nutrients by Chlorella pyrenoidosa,increase the chlorophyll content,improve the photosynthetic capacity,increase the protein content,and promote the growth of Chlorella pyrenoidosa.At the same time,the activity of antioxidant enzymes was enhanced to ensure the normal growth and physiological activities of algal cells.High concentration of rare earth elements will cause excessive ROS in algae cells,destroy the antioxidant defense system and destroy the structure of algae cells.Finally,a rare earth element Ce+ microalgae photobioreactor was constructed and its operation conditions were optimized.The results showed that when the light intensity was 50 ?mol/?m2·s?and Ce³⁺ concentration was 1 mg/L,the aeration intensity was 0.6 L/min,the effluent quality of the system was the best.The removal rate of TN was 73.33%,the removal rate of ammonia nitrogen was 89.98%,the removal rate of TP was 94.53%,the removal rate of COD was 75.55%.Under the optimal operating conditions,the degradation of pollutants in the reactor accords with the first-order kinetics.