Study On The Purification Technology Of Artificial Mariculture Wastewater By Monoculture And Symbiosis Of Microalgae-bacteria

Microalgae-bacteria symbiosis system cultivation using mariculture wastewater is a promising biorefinary concept for integrated biomass generation and subsequent nutrients removal.In this study,the field investigation was done in Wenchang,an important mariculture producing city in Hainan Province,P.R.China.According to the current mariculturing status and the indicator values in mariculture wastewater,an artificial mariculture wastewater(AWW)was simulated on a basis of the investigation results of the main pollutants and pollutant concentrations in Wenchang.Additionally,in indoor experiments,the adaptability of six monoculture microalgae species were evaluated in f/2 medium.AWW and actual shrimp culturing wastewater,respectively.Then,Chlorella vulgaris,Platymonas suhcordiformis and Chaetoceros muelleri were selected to study the cell density generation and biodegradability of main pollutants in AWW.The results indicated that C.vulgaris is the optimal strain for removing NH4+-N,NO2--N,Tn and PO43--P with the inoculation ratio of 25%.After that,C.vulgaris-Bacillus spp.symbiosis with C.vulgaris of the initial concentration of 2.5 × 105 cells/mL and Bacillus spp.inoculated 5 mL,10 mL and 25 mL(OD600=1.8)were cultured in AWW.The accumulation of microalgae cells and the removal efficiency of pollutants are determined and the optimal microalgae-bacteria symbiosis was screened.Finally,this study investigated two modes of mariculture wastewater bioremediation(i.e.free-state mode and immobilized mode)with monoculture and symbiotic system of microalgae Chlorella vulgaris and bacteria Bacillus spp.The cell growth and removal of wastewater nutrients such as NH4+-N,PO43--P,total phosphate(TP)and chemistry oxygen demand(CODMn)were tested.In conculsion,this study is designed in order to explore an efficient and feasible treatment technology of mariculture wastewater,with a win-win strategy of achieving the remediation of mariculture wastewater,and meanwhile accumulating microalgae biomass,so as to provide scientific basis for the utilization of mariculture wastewater and the control of marine pollution in Wenchang.The main conclusions were shown as following:(1)Six microalgae species,C vulgaris,Chlorella sp.,T.suhcordiformis,C.muelleri.Skeletonema coslatum and Streptococcus westermani grow well in.f/2 medium.In AWW and shrimp mariculturing wastewater,the microalgae growth cycle is shortened,cell accumulation is reduced and even partly microalgae is dead,such as Skeletonema costatum.(2)The dry cell weight accumulation of C.vulgaris,T.suhcordiformis and C.muelleri in AWW was relatively small and the removal efficiencies of PO43--P was about 98%;the removal efficiencies of NH4+-N was 96%-100%;the NO2--N in wastewater is completely removed and the removal efficiencies of TN was about 90%.C vulgaris has the fastest removal rate,the largest cell growth value and the optimal purification ability.(3)The dry weight of microalgae-bacteria symbiosis was relatively greater than that of the monoculture microalgae system.Comparing the purification ability of monoculture microalgae,bacteria and the microalgae-bacteria symbiosis in different inoculation ratio,the microalgae(i.e.C.vulgaris)and bacteria(i.e.Bacillus spp.)symbiosis with 25%C.vulgaris+5 mL Bacillus spp.treatment was the optimal treatment for purifying tropical mariculture wastewater,with 100%removal efficiency of both NH4+-N and PO43--P,and approximate 36%removal efficiency of CODMn in the first 72 h of cultivation time.(4)Comparing the treatment of AWW with monoculture microalgae,bacteria and microalgae-bacteria symbiosis system in free or immobilized state,the cell density of microalgae in free state is larger than that in iminobilized state.Overall,the highest removal efficiency of NH4+-N,PO43--P,TP and CODMn of 96.57%,98.62%,89.89%and 39.09%,respectively,was achieved under the biorenediation of co-immobilization of C.vulgaris and Bacillus spp.The concentration of NH4+-N and PO43--P in effluent reached the national second-level standards of“Water Drainage Standards for Sea Water Mariculture,,while the value of CODMn meets the second-level of“Water Drainage Standard for Sea Water Mariculture”.