Study On The Efficiency Of Treating Marine Aquaculture Wastewater By PSBBR System With Bacterial And Algal Symbiosi

In recent years,with the increasing demand for Marine products by Chinese residents,the pattern of intensive and high production industrial cycle aquaculture will become a new focus in the development of mariculture industry.The tail water discharge of high-density aquaculture will bring serious harm to the Marine ecological environment.Microalgal-bacterial Biofilm technology(microalgal-bacterial Biofilm)is a new sewage treatment technology that combines microalgae and bacteria together,which can remove pollutants in aquaculture wastewater in a non-aerated state and realize the recycling of biomass resources.Under the background of "carbon neutrality",which emphasizes energy conservation,environmental protection and resource utilization,bacteria-algal symbiotic biofilm technology has a very wide range of social demands as an environmentally friendly technology.Therefore,this study aims to construct a symbiotic biofilm system for the treatment of mariculture wastewater.In this paper,the treatment efficiency of common biofilm,microalgae and bacterialalgae biofilm on mariculture wastewater was compared,and the advantages of bacterialalgae biofilm(PSBBR)in the treatment of mariculture wastewater were clarified.On this basis,the effects of hanging membrane of algal mud at the same time and hanging membrane of mud before hanging algae on the formation of biofilm were compared,so as to obtain a more appropriate hanging membrane and realize the construction of symbiotic biofilm system of algal bacteria.Finally,by exploring the effects of light intensity,light period and carrier filling ratio on PSBBR operation,the PSBBR process operating parameters were optimized to realize the efficient treatment of mariculture wastewater by bacteria-algae symbiotic biofilm system.The main research results are as follows:(1)Comparing the operation efficiency of common biofilm,microalgae and bacteria-algae biofilm in the treatment of mariculture wastewater: In terms of pollutant removal load,bacteria-algae biofilm has a good removal effect on COD,TN,TP and SMX in aquaculture wastewater.The average removal loads were 74.259,8.334,0.361 and 0.825g/(kg MLSS.d)in stable operation for 7 days,respectively.However,the degradation ability of common biofilm to TP was almost 0.The removal load of microalgae on SMX was low,only 0.0139g/(kg MLSS.d).In terms of operational stability,bacteria-algal biofilm has better operational stability than microalgal action alone.In terms of energy consumption,PSBBR reactor generates oxygen through microalgae photosynthesis without aeration,which reduces energy consumption compared with SBBR mode operation.Therefore,bacteria and algae biofilms have obvious advantages in the treatment of mariculture wastewater.(2)The algal mud membrane hanging method leads to sludge granulation due to salinity stress,and the sludge shading to microalgae reduces the activity of bacteria and algae,which makes bacteria and algae unable to attach to the filler effectively and difficult to form bacteria and algae biofilm.The method of hanging mud first and then algae can effectively construct the symbiotic biofilm system.Under this hanging mode,the group with an initial bacteria-algal ratio of 3:1 successfully started within 7days and realized stable operation,and the startup time was the shortest for each group.(3)Optimal operating light intensity of PSBBR reactor operation: 6500lux;Optimum operating light cycle: photoperiod is 6h,dark period is 6h,light to dark ratio is 1.Under the illumination condition,the start-up time of the reactor is the fastest,and stable operation can be achieved on the 6d.In terms of pollutant removal effect at stable stage,under the condition of light intensity of 6500 lux and light period of L6:D6,the removal rates of TN,TP and SMX in the system can reach 91%,38% and82%,respectively.Too high or too low light intensity(2500lux and 8500lux)and too long or too short photoperiod(L4/D8 and L8/D8)would inhibit the activity of microalgae and bacteria on the biofilm.Analysis of inhibition reasons: under low light intensity and short photoperiod,low activity of microalgae led to low photosynthetic oxygen production rate,and DO restriction was the main reason.The main reasons are the direct stress of light energy radiation under high light intensity and long light period,inhibition of reactive oxygen ROS in cells,system DO and high p H.(4)When the SBBR operating mode with aeration is switched to the PSBBR operating mode with restricted aeration,the microbial diversity of biofilm will be lower.At the phyla level,Proteobacteria and Bacteroidetes were the dominant phyla of bacteria-algal biofilms.AOB was proved to accelerate the degradation of SMX.High light intensity(8500lux)reduced the abundance of α-deformationclass and γ-deformationclass,which were rich in AOB,NOB and denitrifying bacteria,and affected the system nitrogen removal and SMX degradation process.Under different light intensity and light cycle,different aerobic denitrifying bacteria genera Denitromonass,Planktosalinus high relative abundance,unclassified_f__Rhodobacteraceae,Halomonas has the ability to degrade aromatic compounds,It is presumed to be SMX-degrading bacteria.(5)The optimal carrier filling ratio for the treatment of mariculture wastewater by PSBBR reactor was 12%.Under this filling ratio,the PSBBR reactor can make TN reach the standard of primary effluent and remove the highest load.PSBBR is not ideal for TN removal when the fill ratio is less than 12%.When the filling ratio is higher than 12%,although effluent TN can reach the first grade standard,excessive filling will cause the increase of operation cost.PSBBR effluent TP does not reach the level 1 standard of tailwater discharge,and further treatment of TP shall be carried out by other means.