Application Of Microbial Flocculant Cu²⁺ Trapping To Electrochemical Reduction Of Nitrate

With the rapid development of technology and industry,the constantly improving of human living standard has led to a substantial increase of daily water’s demand in society,as a result,the large amounts of municipal wastewater are generated.As a result,it has led to a sharp increase in the generation of residual activated sludge,which is the one of the wastes of domestic sewage treatment process.As a by-product of urban sewage treatment,the residual sludge has special biological composition（such as microorganisms,algae,pathogens,etc.）and complex composition（such as a large number of nitrogen,phosphorus and other organic components,silica,heavy metals,etc.）.Therefore,the treatment and disposal of residual sludge still face many chanllenges（such as lagging technology development,poor economic efficiency,waste of resources,and unfriendly to the environment,etc.）.For the special biological characteristics of sludge,the method of extracting organic matter（such as protein,polysaccharide,nucleic acid,etc.）from the biological phase of sludge has been widely paid attention to and studied in recent years.It can not only prevent the pathogens and other harmful bacteria in sludge from causing adverse effects on the ecological environment and human health,but also realize the harmless treatment and resource utilization of municipal residual sludge.In this paper,the microbial flocculants were prepared by extracting the organic matter in the residual activated sludge using the process of hydrochloric acid maceration.The flocculation adsorption and removal efficiency of Cu²⁺and[Cu（NH₃）₄]²⁺were evaluated by applying zeta potential analysis,FTIR and SEM.The microbial flocculant particles showed an irregular layered structure,the zero-charge potential point of the microbial flocculant was p H=5.2,and its functional groups for trapping Cu were mainly composing of proteins and polysaccharides.Conducted the experimental study of static adsorption for microbial flocculant traps copper ions,the influence of process conditions on its adsorption performance were analyzed.The adsorption kinetics and thermodynamic equations were resolved to investigate the adsorption mechanism.The results showed that the maximum Cu²⁺adsorption capacity of the microbial flocculant could be 150 mg/g at optimized conditions,and the removal rate of 50 mg/L Cu²⁺and[Cu（NH₃）₄]²⁺could be more than 90%in 30 min;the adsorption processes are performed more easily at p H=7.Among the five coexisting species,EDTA and TA interfer the Cu²⁺capture significantly.The pseudo-second-order kinetic model and the Langmuir isothermal adsorption model can describe the above adsorption process more accurately.The results showed that the adsorption process was a spontaneous exothermic reaction.Using the microbial flocculants that loaded with Cu²⁺/[Cu（NH₃）₄]²⁺as a raw material of nano copper-graphite carbon/carbon cloth catalytic electrode（Cu-GC/CC）,and the preparation parameters were optimized.The catalytic electrode was characterized by XRD,SEM,EDS and FTIR,and the electrochemical performance of the electrode was further assessed by LSV,CV and EIS.The performances for nitrate reduction of Cu-GC/CC electrodes were investigated under different operation parameters（electrolysis time,initial concentration,initial p H,current density,and Cl^-concentration）.The experimental results showed that the nitrate removal rate was 100%in 9h under optimal conditions,and the nitrogen selectivity could be more than 90%with the coexistence of Cl^-.This might be caused by the synergistic effect of cathodic reduction and anodic oxidation.The seven cycle experiments showed that it had a promising stability.In addition,the simulated wastewater treatment results showed that the nitrate removal rate could be 95%,and the total nitrogen removal rate could be 92.37%within 9h.The fabricated Cu-GC/CC electrode has good prospects for engineering applications in the field of water treatment.In summary,this paper realized the extraction of microbial flocculants from residual sludge and the adsorption capture of copper ions from the solution.The fabricated Cu-GC/CC functional electrode shows the highly efficient electrochemical reduction conversion of waste nitrate in aqueous solution.This study will provide firmly technical guideline for sludge resource utilization and the eutrophication pollution prevention of water bodies.