Studies On Removal Of Lead Wastewater By Fly Ash-microbial Flocculant

Along with social economy development,heavy metals are discharged into surface water increasingly.Pb²⁺ as one of most toxic heavy metals,exists in the wastewater of many industries.The compounds of Pb²⁺ can enter human body through the respiratory tract,the digestive tract and skin,and accumulate in the body.They may damage the human nervous system,hematopoietic system,digestive system,immune system,kidney and cardiovascular,etc.How to choose a method which may be efficient and can remove Pb²⁺ at the same time has becoming a hot topic.Microbial flocculants is biodegradable,safe,efficient,non-toxic,no secondary pollution,but its high production cost restriction limits its large-scale applications.Because of its high ion exchange capacity,specific surface area and other characteristics,fly ash gradually replaces natural zeolite used in waste water treatment,but there is a low utilization efficiency.Hence,this study proposes the use of fly ash and microbial flocculants to remove to Pb²⁺ improve efficiency of wastewater treatment.Firstly,the optimum conditions for the treatment of Pb²⁺ by fly ash and microbial flocculant were optimized separately,and the kinetic and thermodynamic models were constructed to reveal the reaction mechanism.On the basis of this,the optimal combination of fly ash and microbial flocculant was determined by surface optimization method.The main contents and results of the study are as follows:In this study,we have cultured and screened the active microbial flocculates through separating and purifying the effective flocculants from a salina area in Inner Mongolia.Based on 16 S rDNA gene sequence analysis,strain HG6 was classified as Oceanobacillus polygoni.We investigated the optimized production of the novel salt-tolerant,alkaliphilic bioflocculant MBF-HG6.The optimal carbon source,nitrogen source,metal ion,and initial pH of the medium for bioflocculant production were starch,urea,Fe²⁺,and pH 9.0,respectively.The resultant bioflocculant showed excellent stability over a temperature range of 0 °C to 60 °C.The purified MBF-HG6 contained 81.53% polysaccharides and 9.98% proteins.The fourier transform infrared spectrum indicated that the bioflocculant contained carboxyl,hydroxyl,and amino groups.The optimized bioflocculating activity was observed as 90.25% for 6.96 m L MBF-HG6,4.77 m L CaCl2?1%,m/v?,and 19.24 g/L NaCl dosages using the response surface methodology.The effects of fly ash and microbial flocculant MBF-HG6 on the removal of Pb²⁺ under different influencing factors were investigated,respectively.The adsorption isotherm model,kinetics and thermodynamics of fly ash and MBF-HG6 were studied.Fly ash and MBF-HG6 adsorption Pb²⁺ mechanism were discussed.On this basis,Pb²⁺ removal from wastewater was investigated by fly ash and MBF-HG6 using box-behnken design?BBD?method,In BBD method,Pb²⁺ removal efficiency was served as response value,results from the analysis of variance demonstrated that the model was highly significant,in which the Model F value was 17.30 and P value was 0.0005,and correlation coefficient was 0.9017.The optimum values of the variables were found to be of fly ash dosing quantity of 1.46 g/L,MBF-HG6 dosing quantity of 0.888 g/L and CaCl2 dosing quantity of 15.6 m L/L?1%,w/v?,respectively.Under the optimum conditions,it can reach 99.75% of Pb²⁺ removal efficiency.Compared with the removal of Pb²⁺ with fly ash alone and the removal of Pb²⁺ using MBF-HG6 alone,the dosage of fly ash and MBF-HG6 were saved.The effect of fly ash and MBF-HG6 on the removal of Pb²⁺ was studied by Zeta potential analysis.It was found that fly ash and MBF-HG6 had the effect of ionization and adsorption on the Pb²⁺ during the trapping process of fly ash and MBF-HG6.Adding MBF-HG6 and coagulant CaCl2 to fly ash,stable flocculation and adsorption bridging had a solid role to maximize the removal of heavy metals from leaded wastewater.