Study On The Removal Of Nitrous Nitrogen In Wastewater And Flue Gas By Continuously Pre-harvesting Spirulina Platensis

Wastewater and flue gas treatment by microalgae was a promising biological treatment technology,However,the high concentration of nitrite in wastewater and nitric oxide in flue gas could inhibit the growth of microalgae and even lead to the death of microalgae.Therefore,the process of microalgae removing nitrate nitrogen from wastewater and flue gas was limited.In the middle and late stage of intermittent microalgae culture,a large amount of biomass accumulation led to shading effect among microalgae,which made it difficult for microalgae to obtain sufficient light and reduced the growth rate.In this paper,a spirulina platensis(S.platensis)strain with high concentration of nitrite and NO tolerance was cultured.Nitrous nitrogen in waste water and flue gas was directly used as nitrogen source,and the productivity of S.platensis and the removal efficiency of nitrous nitrogen in waste water and flue gas were improved by continuously pre-harvesting cultivation mode.The specific research results was as follows:(1)For optimizing the light distribution in the photobioreactor(PBR)during the middle and late period of microalgae culture,the continuously pre-harvesting cultivation mode was proposed.In order to realize continuous pre-harvest culture mode,a column PBR for S.platensis cultivation with overflow device was designed,and the biomass concentration in the PBR was controlled by adjusting the pre-harvesting rate.The optimal biomass concentration was determined to be 1.8 g L-1,the pre-harvesting rate was 0.228 mL min-1,and the maximum biomass accumulation was 4.893 g L-1.Compared with the batch cultivation and periodically pre-harvesting cultivation mode,the biomass concentration was increased by 44.6%and 10.98%,respectively.The mathematical model of the continuously pre-harvesting cultivation mode was established by material balance and polynomial fitting.(2)A S.platensis strain with high concentration of nitrite tolerance was cultured to treat nitrite nitrogen in wastewater.After domestication,the maximum tolerance concentration of S.platensis was up to 100 mM,and the S.platensis grew well with high concentration of nitrite as a single nitrogen source.The maximum biomass concentration and the maximum protein concentration were respectively realized when the nitrite concentration was 5 mM and 10 mM(total nitrogen source was 30 mM)in the batch cultivation,and the nitrite was prior to the nitrate as the nitrogen source.Microalgae treated nitrite in wastewater by the continuously pre-harvesting cultivation mode,the removal rate of nitrite from wastewater was 78.73%when nitrite concentration was 30 mM as a single nitrogen source.The maximum biomass of 5.223 g L-1 and the total nitrogen removal rate of 87.83%were realized at the culture condition of 10 mM nitrite concentration(nitrate concentration of 20 mM).(3)NO in the flue gas was treated by the domesticated S.platensis strains,and the optimal flue gas concentration and biomass concentration were determined to be 0.25%?0.50%and 1.5?2.Og L-1,respectively.NO directly enters algal cells and were as nitrogen sources by S.platensis cell membrane.Study on the removal of 0.5%NO in the flue gas from S.platensis by continuously pre-harvesting(the gas flow was 10 mL min-1,and the algal liquid volume was 1L),the removal rate of NO changed with the growth of S.platensis,and the highest was 99%,and the maximum biomass accumulation was 6.120g L-1 after 14 days.