Aquaculture Wastewater Treatment By Microalgae Biofilm-membrane Photobioreactor(BMPBR)

With the rapid development of marine aquaculture in coastal areas,the effluent from the marine aquaculture industry,which is rich in nitrogen,phosphorus and some other pollutants,is increasingly polluting the marine environment,often causing problems such as water quality deterioration and water eutrophication in nearby sea areas.Using a cost-effective water purification technology has become an urgent problem to be solved in the current aquaculture industry.But at present,there are few technologies specifically for aquaculture wastewater,and most of them are treated by traditional methods such as biological nitrification and denitrification,which have widespread problems such as high energy consumption,incomplete removal of nitrogen and phosphorus,and in need of harmless treatment of by-product sludge.In this study,microalgae cultivation is used to treat aquaculture wastewater.Using wastewater as the cultivation medium can obtain amount of algae cells with high development value and then achieved deep denitrification and dephosphorization of wastewater.However,the nutrients in aquaculture wastewater are much lower than the traditional culture medium,making it difficult to support the efficient microalgae production,so that the traditional batch cultivation is not suitable to apply in aquaculture wastewater treatment and coupled to microalgae biomass production.In this study,the membrane concentration culture and immobilization culture methods are adopted to utilize the low-nutrients aquaculture wastewater in photobioreactor for high-efficiency microalgae cultivation and realize the deep removal of nutrients and other pollutants in wastewater simultaneously.Firstly,a new membrane photobioreactor?MPBR?with continuous water operation was constructed,and microalgae were cultured by low-nutrients aquaculture wastewater.The membrane module added to the reactor functions as a solid-liquid separation,which can completely intercept the microalgae cells in the effluent,and successfully realize the effective separation of hydraulic retention time?HRT?and microalgae biomass retention time?BRT?during the cultivation process.Thereby efficient cultivation of microalgae and efficient removal of nitrogen and phosphorus in wastewater were achieved.The results indicated that MPBR operated at an HRT=1.0 d obtained the largest algal biomass productivity of 1.13 g L^-1,and the highest removal rates for DIN and DIP of 4.30 g L^-1 d^-1and 3.96 g L^-11 d^-1,respectively,after 22 days of culture.After the first phase of cultivation,it was found that there was a high density phenomenon caused by the rapid growth of Chlorella vulgaris in the MPBR during the experiment,which restricted the photosynthesis of microalgae and the utilization of nitrogen and phosphorus.Therefore,this study decided to carry out further research by using the microalgae biofilm immobilization culture in the second phase.A microalgae biofilm-membrane photobioreactor?BMPBR?was constructed by adding fiber balls to the MPBR.Utilizing the adsorption of the microalgae by the filler realized the immobilization microalgae cultivation,thereby effectively prolonging the culture period of the reactor.The microalgae were cultured for 70 days in continuous water under different HRTs without harvesting the microalgae cells.According to the results,the BMPBR operated at an HRT=1.0 d obtained the highest microalgae fixation rate of 60.46%and the highest total microalgae biomass yield of 1.55 g L^-1.The average removal rate for DIN and DIP also reached the highest level,were 98.58%and 95.94%,respectively.Compared with MPBR,BMPBR achieved more stable culture and efficient contaminant removal after 70 days of culture.Based on the above research,BMPBR was selected to study the removal of sulfonamides in aquaculture wastewater.This study was mainly for the determination of three sulfa antibiotics?sulfadiazine SDZ,sulfamethazine SDME and sulfamethoxazole SMZ?.The results showed that under the three HRTs,Chlorella vulgaris all had a certain removal of the three sulfonamides,and Chlorella vulgaris had the strongest removal ability of SMZ under the same conditions,the highest removal rate was 78.79%of HRT=4.0 d.In summary,the MPBR with continuous water can obtain certain microalgae biomass yield and good nutrient removal effect,and the best effect was obtained of HRT=1.0 d.The BMPBR established on this basis can obtain more stable long-term operation through the adsorption of the filler,thereby obtaining higher microalgae biomass production and deeper wastewater purification,The effect is also optimal at HRT=1.0 d.In addition,the microalgae can remove the three sulfonamides in the wastewater due to the bioaccumulation,achieving the final low concentration of effluent.Therefore,it indicated that the presence of the microalgae biofilm in the reactor can increase the biomass production of the microalgae and the ability to remove pollutants from the wastewater.