Process Optimization Of Chitosan@Buckwheat Hull Biochar For The Removal Of Pb²⁺ From Lead-Acid Wastewater

Lead is one of the most common heavy metals in industry and when it accumulates to a certain level it can be harmful to the ecological environment and human health.How to economically and effectively remove lead ions from industrial wastewater is an urgent problem.A lead-acid battery enterprise in Chongzhou City adopts the inclined plate treatment system to treat the lead-containing wastewater generated during the manufacturing process of lead-acid batteries.The core process of the system is“primary p H adjustment tank-coagulation reaction tank-secondary p H adjustment tank-precipitation tank-acid re-conditioning”（referred to as the“coagulation-precipitation process”）.The major characteristics of the wastewater from the factory is strong acidity（p H=2.56）and Pb²⁺in relatively low concentration（3.87 mg/L）,and the treatment of“coagulation and precipitation process”requires large amount of precipitant and coagulant with complicated process and high cost.Given the characteristics of lead battery factory wastewater and the shortcomings of the“coagulation-precipitation process”,this study proposes a new process to replace the“coagulation-precipitation process”.Adsorption has been proven to be an effective method for removing heavy metal ions in low concentration in wastewater.This study used chitosan@buckwheat hull biochar as adsorbent to prepare a dynamic adsorption column,and the dynamic column adsorption process works as the core of the adsorption process（“dynamic adsorption process”）.The“dynamic adsorption process”could be applied to replace the“coagulation-precipitation process”to simplify the treatment process of the wastewater from the factory,reducing the cost and improving the Pb²⁺removal efficiency.The study intends to provide a technical reference for the wastewater treatment of lead-acid battery enterprises,and the main research results are as follows:（1）The chitosan@buckwheat hull biochar was selected as the adsorbent,and the adsorption parameters were optimized.The single-factor experiment and the response surface optimization experiment shows that the adsorption performance of Pb²⁺by chitosan@buckwheat hull biochar（KQB）was better,and the adsorption removal of Pb²⁺by KQB was about 35%higher than that of buckwheat hull biochar（QB）when the optimal parameter values were applied.The value of adsorption parameters were optimized as follows:p H=5.38,adsorbent dosage 1.06 g/L,and adsorption time 6.02 h.Using the optimized parameter values,the predicted adsorption removal of KQB on Pb²⁺was 96.10%,and the actual adsorption removal was 95.31%.（2）In the experiment applying“dynamic adsorption process”in the treatment of the wastewater from the factory,the process can improve the Pb²⁺removal and simplify the whole treatment process compared to the“coagulation-precipitation process.”By constructing a dynamic adsorption column with chitosan-buckwheat hull biochar as adsorbent for treating Pb²⁺in the factory wastewater,the adsorption process flow（lead acid wastewater-grease trap-p H adjustment tank-adsorption column-transparent water tank-discharge/reuse）was established.The Response Surface Methodology optimized the operating conditions of the adsorption column in the dynamic adsorption test.The test results showed that the“dynamic adsorption process”was more effective than the“coagulation-precipitation process”in treating Pb²⁺.The removal rate of Pb²⁺reached 92.01%,while the“coagulation-precipitation process”was only 85.92%.In addition,compared to the“coagulation-precipitation process”,the“dynamic adsorption process”requires no secondary p H adjustment and acid retreatment.（3）The process comparison and benefit analysis show that the“dynamic adsorption process”can achieve lower cost and better effluent quality than the“coagulation-precipitation process”.In terms of cost,the“dynamic adsorption process”can reduce chemical cost by reducing the use of p H adjustment agent Na OH,and reduce the operating cost of the process.In terms of effluent quality,according to the Nemero integrated contamination index method,the heavy metal contamination index for the“coagulation-precipitation process”effluent is 1<P_i=1.72<2,and there could be residual Al from the flocculant.However,the“dynamic adsorption process”has a P_i=0.56<0.7,and the effluent quality meets the clean level.The benefits of the two processes were evaluated using grey correlation analysis based on economic indicators,treatment effectiveness,and process maturity level.The correlation coefficient between the“coagulation-precipitation process”and ideal solution is 0.67,while the correlation coefficient between the“dynamic adsorption process”and ideal solution is 0.92.The higher correlation coefficient indicates that the adsorption process is a better solution.In summary,compared to“coagulation-precipitation process”,the proposed“dynamic adsorption process”using chitosan@buckwheat hull biochar can simplify the process flow,reduce the cost,and improve the Pb²⁺removal in the treatment of lead-acid wastewater from the lead acid battery factory.The process can be used as an alternative solution to the“coagulation-precipitation process”,and the study provides a technical reference for the treatment of similar lead-containing wastewater.