| In recent years,the rapid development of mariculture industry has stimulated economic growth,but also produced a large number of mariculture wastewater containing organic matter,ammonia nitrogen,nitrate nitrogen,phosphate and other pollutants.If directly discharged into the water,it will cause serious damage to the ecological environment.The high salinity environment of mariculture wastewater has a negative impact on the traditional biochemical treatment process.In addition,poor phosphorus removal efficiency is also a major drawback of activated sludge process.The combination of microalgae and membrane reactor can effectively remove carbon,nitrogen and phosphorus from wastewater,ensure the quality of effluent,and achieve the goal of biomass accumulation by intercepting microalgae.Firstly,four kinds of marine microalgae were selected to compare the removal efficiency of pollutants from aquaculture wastewater,and the biomass growth of microalgae was also monitored.The results showed that the removal efficiency of ammonia nitrogen by Chlorella vulgaris was the best.The removal efficiency of ammonia nitrogen was 79%.The removal efficiency of phosphorus and ammonia nitrogen by Platymonas helgolandica tsingtaoensis was the best,and the removal efficiency of ammonia nitrogen was 68%.Due to the poor phosphorus removal efficiency is a major drawback of the traditional process,so the following research used Platymonas helgolandica tsingtaoensis as a microalgae species.On the basis of the above,the microalgae membrane reactor was started with Platymonas helgolandica tsingtaoensis as the algae species.When ordinary membrane reactor was used to treat wastewater,it was observed that uneven aeration resulted in microalgae precipitation,which resulted in slow growth of microalgae and poor removal efficiency.Therefore,a microalgae fluidized bed membrane reactor was designed to enhance internal circulation.After 60 days of operation,the removal rates of total nitrogen and total phosphorus in the fluidized bed membrane reactor were 73.6% and 77.9%,respectively.The removal rates were 15 g/(m~3·d)and 2.8 g/(m~3·d),and the biomass of microalgae was 1.4 g/L.The maximum average growth rate was 53.3 mg/(L·d).In addition,microalgae were harvested twice during operation,and the harvesting of microalgae did not affect the treatment efficiency of the reactor too much.Several fluidized bed membrane reactors were built to investigate the effects of different culture modes,influent TOC,p H and N/P on the microalgae membrane reactor.The results showed that under the mixed culture mode,the growth rate of microalgae was faster and the removal efficiency of pollutants was better than that of photoautotrophic culture.When the TOC concentration of influent in mixed culture mode was 40 mg/L,80 mg/L and 120 mg/L,the growth of microalgae and removal efficiency of nitrogen and phosphorus increased with the increase of TOC concentration.When the influent p H was 8,the best removal rates of ammonia nitrogen and total phosphorus were 11.7 g/(m~3·d)and 1.19 g/(m~3·d),respectively,which were higher than those of other experimental groups.When the influent p H was 9,the removal efficiency of pollutants and the growth of microalgae were inhibited.The growth rate of microalgae and the ability of nitrogen and phosphorus removal of the reactor increased gradually when the N/P ratio of influent increased from 5 to 20.When the N/P ratio was higher than 20,the removal efficiency of the reactor tended to be stable,and no longer changed with the increase of N/P.Through continuous monitoring of transmembrane pressure difference,the characteristics of membrane fouling in microalgae membrane reactor were investigated in a membrane fouling cycle.The results show that compared with traditional MBR,the membrane fouling cycle of microalgae membrane reactor is longer,and the trend of membrane fouling conforms to the three-stage theory,and the membrane fouling cycle is longer.The content of EPS and SMP increased significantly with the growth of microalgae.The results of three-dimensional fluorescence spectroscopy showed that tryptophan and aromatic proteins were important factors causing membrane fouling. |
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