Restoration Of Black And Odorous Waterbody By Layer Double Hydroxides/Microorganisms Composite Materials

Due to the random discharge of domestic sewage and industrial waste water,a large number of nutrients and pollutants are discharged into the river water body,which cause the water body to be black and smelly.The reasons of black and odor in the river are complex and the environmental conditions are changeable,so repairing black and odor water bodies is hard to be satisfactory.Taking advantage of the positive charge on the surface of hydrotalcite-like materials and the exchangeability of interlayer anions,this paper studies its adsorption of phosphate ions in black and odorous water and the corresponding adsorption mechanism.On this basis,we developed a hydrotalcite-like/microbial co-processing system,investigated the evolution of microbial communities,and repaired an actual black and odorous water body in Xiangtan.The main research results obtained are in the following:(1)ZnFe-LDHs with a metal ion ratio of 3:1 was optimized through phosphate adsorption experiments,which phosphate removal rate can reach up to more than 95%at a phosphate concentration of 6-10 mg/L.The effect of p H and coexisting ions in the water body on the adsorption capacity was explored.The adsorption capacity of phosphate will decrease with the increase of p H between the p H of 3?10,and the cations such as Ca²⁺and Mg²⁺promoted the removal of phosphate ion.The coexisting anions reduced the phosphate removal,in which the order of influence was CO₃^2->SO₄^2->NO₃^->Cl^-,while the influence increased as the increase of the coexisting ions concentration,Under the condition of 100mg/L CO₃^2-,the phosphate adsorption capacity of ZnFe-LDHs was only 33%of the original adsorption capacity.Using adsorption isotherms to fit the experimental data found that ZnFe-LDHs was more in line with the Langmuir model,indicating that monolayer adsorption was dominant.Through BET,SEM and XRD characterization,it was found that the material mainly exists in the form of Zn O and Zn(OH)₂,so the removal mechanism of phosphate radical by the material was mainly surface precipitation.Through the ion dissolution test,it was found that the dissolution amount of Zn²⁺was higher under acidic conditions,which will cause secondary pollution to the environment.Acute toxicity test data of algae show that the inhibition rate of ZnFe-LDHs on Chlorella after 1 day is 100%.(2)CuFe-LDHs with a metal ion ratio of 2:1 was optimized through phosphate adsorption experiments,which phosphate removal rate can reach up to more than 98%at a phosphate concentration of 1-5 mg/L The single-factor control experiment was used to explore the influence of coexisting ions and p H on the phosphate adsorption effect.The experimental rule was similar to that of ZnFe-LDHs,but CuFe-LDHs had a larger p H range than ZnFe-LDHs.When the p H value is in the range of 3?10,the adsorption capacity is above 13mg/g,maintaining 77%of the highest adsorption capacity.It was also relatively less affected by the competitive adsorption of coexisting anions.it can still maintain the original 75%adsorption capacity Under the condition of 100mg/L CO₃^2-,the sewage treatment had a wide range of applications.After the adsorption isotherm and adsorption kinetics,the experimental data was fitted and found to be in line with the Langmuir model and the pseudo-second-order kinetic model,indicating that it is a single-layer adsorption dominated by chemical adsorption.Through characterization methods such as SEM,XRD,FTIR,XPS and Zeta potential,it can be seen that CuFe-LDHs mainly adsorb phosphate through physical adsorption,ligand exchange and interlayer ion exchange.According to the results of the acute toxicity test of algae,it can be seen that the inhibition rate of CuFe-LDHs on Chlorella after 7 days is 18.7%,and the toxicity is relatively small.(3)The actual black and smelly water was treated by three materials:CuFe-LDHs,ZnFe-LDHs and Al₂(SO₄)₃,The dissolved oxygen and total phosphorus content in actual water are 1.08mg/L and 3.64mg/L respectively,The results shown that the content of dissolved oxygen can be increased after adding the materials to 3.4,3.8 and2.3mg/L respectively.The removal rate of total phosphorus is 93.7%,92.6%and86.3%respectively,so CuFe-LDHs and ZnFe-LDHs were better than Al₂(SO₄)₃for the promotion of dissolved oxygen and the removal of total phosphorus.On this basis,the repair performance of the sediment group,microbe group,CuFe-LDHs group and microorganism+CuFe-LDHs group on the actual black and smelly water body was studied,Compared with the experimental group without CuFe-LDHs,the dissolved oxygen in the LDHs experimental group increased faster.The the microbe+CuFe-LDHs group could be converted to aerobic state in 26 days,respectively.Under ensuring the stable removal of other indicators,the microorganism+CuFe-LDHs group can maintain the total phosphorus effluent index below 0.3mg/L,which reaching the surface water quality standard IV.Characterization methods such as SEM and FTIR confirmed that CuFe-LDHs were adsorbed on the microbial micelles by virtue of surface electrostatic adsorption and ion complexation.The EPS results showed that the addition of microorganisms increased the PN content of the system,while the addition of CuFe-LDHs promoted the electron transfer between systems without affecting the stability of the microbial structure.The electron transport chain activity experiment shown that the addition of microorganisms and CuFe-LDHs will increase the electron transport chain activity of the system,and the activity of the experimental group with CuFe-LDHs was relatively higher.According to the analysis of microbial community,the addition of microorganisms and CuFe-LDHs increased the abundance of bacteria related to denitrification and phosphorus removal in the system,while the addition of CuFe-LDHs significantly increased the abundance of related bacteria for phosphorus removal.The abundance of Proteobacteria increased from 31%to 41%,48%,55%and 54%.The abundance of the Actinomycota was dominated by saprophytes,decreased from 24%(in the original sludge)to 22%,24%,13%and 18%,so the addition of CuFe-LDHs had a positive effect on the treatment of black and odorous water.At the same time,it ensured the stability of the removal of other microbial communities and indicators related to COD and NH₃-N,and provided ideas for the treatment of black and odorous water pollution.