Investigation On Aquaculture Wastewater Pollution In The Pearl River Delta Region And Study On Heavy Metal Pollution By Immobilized Fungi

With the development of agricultural intensification,the problems of nitrogen,phosphorus and trace pollution in aquaculture wastewater have become increasingly prominent.Heavy metal pollution is characterized by its high toxicity,its inability to be biodegraded,and its enrichment through the food chain,which poses a serious threat to human and other biological health.Based on the background value survey of the environmental quality of aquaculture wastewater in the Pearl River Delta,this paper comprehensively considers the influence of pollutant content and pollutant type on the environment,and evaluates the potential hazard and ecological risk of pollutants to the environment.Enriched in a polluted environment to screen for environmentally friendly strains that are well tolerant to extreme environments,study their tolerance to heavy metals and mechanisms,and select dominant strains that are well tolerant to heavy metals as biosorbents.Adsorb heavy metals and study their adsorption characteristics and mechanisms.Biochar and sodium alginate were used as immobilized materials to immobilize dominant strains by embedding method and cross-linking method.For the problem of heavy metals in aquaculture wastewater in the Pearl River Delta region,Cr⁶⁺in bio-adsorbed wastewater,fitting adsorption kinetics model and isothermal adsorption The model describes the biosorption process of heavy metals by immobilized microorganisms,reveals its biosorption mechanism,and provides practical reference and theoretical basis for immobilized microorganisms to repair heavy metal pollution.The main conclusions of the paper are:?1?According to the statistical characteristics of aquaculture wastewater pollution indicators in Huizhou,Dongguan,Guangzhou,Zhaoqing and Foshan,the environmental risk is assessed by index evaluation method.The test results show that the main risk factors in aquaculture wastewater are FC,TP and NH₃-N.The comprehensive pollution indices of Huizhou,Dongguan,Guangzhou,Zhaoqing and Foshan in the Pearl River Delta region were 2.00,5.98,2.74,1.70 and 31.91.respectively.Excessive levels of heavy metals,due to the high biotoxicity of heavy metals,the harm can not be underestimated.?2?According to the characteristics of aquaculture wastewater pollution in the Pearl River Delta region,11 filamentous fungi were isolated from the polluted environment,and the effects and inhibitions of three heavy metal ions(Cr⁶⁺,Pb²⁺and Cd²⁺)on mycelial growth and expansion were studied.The results showed that during the observation period of 14 days,the MIC of Mucor sp.?Mu-tea1?with good tolerance to Cr⁶⁺was 220 mg·L^-1,and the colony diameter was 3.1 cm,compared with other treatment concentrations.There was a significant difference?P<0.05?.The MICs of the well-tolerant strains of Neofusicoccum sp.?Nf1172?and Penicillium sp.?Pe-soil2?were18 mM,and the colony diameters were 2.3 cm and 2.7 cm,respectively,compared with other treatment concentrations.There were significant differences?P<0.05?.The MIC of Penicillium sp.?Pe-soil2?with Pb²⁺was 18 mM,and the colony diameter was 4.3 cm at this concentration,which was significantly different from other treatment concentrations?P<0.05?.?3?Mucor sp.with good tolerance to Cr⁶⁺was prepared as an inactive microbial agent,and the adsorption test was carried out to establish the optimal adsorption conditions.The adsorption isotherm was adsorbed by adsorption isotherm and adsorption kinetics model.The results of single factor test showed that the lower pH favored the adsorption of Cr⁶⁺by Mucor sp.At pH 1 and 2,the removal rate of Cr⁶⁺by Mucor sp.was 92.83%and 85.08%,respectively.At the time,the removal rate of Cr⁶⁺was only 28.86%.When the amount of adsorbent is 0-0.8 g·L^-1,the removal rate of Cr⁶⁺in the solution increases with the increase of the amount of Mucor sp.,and the adsorption reaction exceeds 0.8 g·L^-1 tends to balance.When the adsorption time is from10 min to 24 h,the removal rate of Cr⁶⁺increases with time by Mucor sp.,and the adsorption tends to balance when the adsorption time exceeds 24 h.In the initial concentration of Cr⁶⁺10-80 mg·L^-1,the adsorption amount of Cr⁶⁺by Mucor sp.increased with the increase of initial concentration.When the concentration of Cr⁶⁺exceeded 80 mg·L^-1,the adsorption became saturated.Mucor sp.The maximum equilibrium adsorption capacity for Cr⁶⁺ is 20.90 mg·g^-1.Considering that the pH of the aquaculture wastewater in the Pearl River Delta is 5-8,the optimal adsorption conditions for the removal of Cr⁶⁺in the aquaculture wastewater by Mucor sp.are:pH 6,adsorption agent concentration 0.8 g·L^-1,adsorption time 24 h.The quasi-second-order kinetic model can better describe the adsorption process of Mucor sp.on Cr⁶⁺.The formation of chemical bonds has a significant effect on adsorption,mainly chemical adsorption.The Freundlich model can more accurately describe the adsorption process of Cr⁶⁺by Mucor sp.The adsorption is dominated by multi-molecular layer,and the maximum adsorption capacity after fitting can reach 20.99 mg·g^-1.The immobilized microorganism was prepared from biochar?ZL600?-sodium alginate?SA?-Mucor sp.,and the adsorption test was carried out to compare the difference between the adsorption of Cr⁶⁺by different materials?ZL600,SA,immobilized Mucor sp.?,and the adsorption isotherm was applied.The adsorption kinetic model was used to fit the immobilized mucormyc biosorption Cr⁶⁺process.The results showed that the removal effect of Cr⁶⁺was:immobilized Mucor sp.>free Mucor sp.>ZL600.In 0-8 d,the removal rate of Cr⁶⁺by immobilized Mucor sp.was increased with the increase of adsorption time.After 8 days,the adsorption tends to balance.When the initial concentration of Cr⁶⁺was 40 mg·L^-1,the removal rate of Cr⁶⁺by immobilized Mucor sp.was the highest,reaching 98.54%.When the initial concentration of heavy metals was increased to 100 mg·L^-1,the removal rate was62.53%.The quasi-first-order kinetic equation can better describe the biosorption process of immobilized microorganisms on Cr⁶⁺.Langmuir can better describe the biosorption process of immobilized microorganisms on Cr⁶⁺.The biosorption process is mainly monolayer,and the maximum adsorption capacity is 70.92 mg·g^-1.