Removal Of Refractory Organic Contaminants By Cobalt(?)Mediated Electrochemical Oxidation Process Under Usual PH Value

Mediated electrochemical oxidation?MEO?process is a promising technology for organic contaminants removal.It can effectively degrade environmental organic contaminants at normal temperature and pressure using electrogenerated strong oxidizing mediator ions.And it has already been identified as one of the most promising future technology in developing countries by UNEP.In MEO process,high-valency mediator ions will return back to low-valent mediator ions after oxidizing organic contaminants and.Therefore,mediator ions can be recycled,which greatly saved chemical drugs.The most widely used mediators are Ag⁺/Ag²⁺,Ce³⁺/Ce⁴⁺and Co²⁺/Co³⁺.MEO processes based on Co?MEO/Co?are very promising because Co²⁺/Co³⁺couple has a higher oxidation ability than Ce³⁺/Ce⁴⁺couple and it will not react with halide ion to form precipitates.However,the Co³⁺ions were all produced in strong acid medium?sulfuric acid or nitric acid?in present studies.And contaminants removal tests were conducted after the production of Co³⁺ions by mixing contaminants with the solutions containing Co³⁺ions.No works have been carried to produce Co³⁺ions in situ at usual pH?2-10?and degrade contaminants synchronously.Therefore,this study evaluated the oxidation ability of MEO/Co process at usual pH and the efficiency in tap water and tipaical surface water.Moreover,the key influence factors and contaminants remocal mechanism were also investigated in detail.This study evaluated the removal efficiency by MEO/Co process for six common organic contaminants,including sulfamethoxazole?SMX?,carbamazepine?CBZ?,phenol,ciprofloxacin?CIP?,tetracycline?TC?and nitrobenzene?NB?.The results demonstrated that MEO/Co process was efficient in removing all target contaminants except for NB.Several key operating parameters had great impact on the oxidation ability of the MEO/Co process,which included current density,initial Co²⁺concentration,initial pH,and electrolyte.The experiments data demonstrated that higher current density and initial Co²⁺concentration and lower initial pH value were beneficial for MEO/Co process.The concentration of Na₂SO₄ had negligible impact on MEO/Co process.However,NaNO₃ significantly weakened the oxidation ability of the process and the negative effect could be enhanced by increasing NaNO₃ concentration.Moreover,chloridion ion and phosphate ion could enhance the oxidation ability of MEO/Co process but bicarbonate could hinder its oxidation ability.The degradation efficiency for target contaminants by MEO/Co process would declined in surface water,but increased a little in tap water.The minerlization ability of MEO/Co process was evaluated by UV-vis spectrum scaning and TOC removal experiments.The results indicated that MEO/Co process possessed a fairly strong minerlization ability at usual pH.The degradation mechanism for organics by MEO/Co process was investigated by ammonia complexing experiments and radical scavenging experiments.Results indicated that the main oxidizing substance in MEO/Co process was Co³⁺ion rather than hydroxyl radical and sulfate radical.In MEO/Co process,the removal of organic contaminants was achieved by direct electrochemical oxidation and Co³⁺oxidation.