Degradation Of Phenolic Organic Compounds By Cathode/PDS/Fe³⁺ System

Phenolic wastewater is extremely harmful and it's source is very wide,but it is so difficult to deal with them,thus causing great concern.The target of this paper is the simplest and most representative phenol in phenolic compounds,and the4-bromophenol and 4-chlorophenol.The degradation of these three phenols is investigated.Now the persulfate technology,one of the advanced oxidation processes,has been rapidly developed,so this paper uses the way of ferrous ions activated persulfate,and then the introduction of electrochemical cathodic effect will continue to reduce the ferric ions into ferrous ions,finally formed Cathode/PDS/Fe³⁺system.The degradation of phenol,4-bromophenol and 4-chlorophenol were carried out by using Cathode/PDS/Fe³⁺system respectively.The target concentration was 1 mM.The results showed that phenol was completely removed at 120 min,and 4-bromophenol and 4-chlorophenol removal was completely removed at 90 min,indicating that Cathode/PDS/Fe³⁺system can effectively deal with phenolic organic compounds.The influencing factors showed that the three phenolic compounds have similarity,and the influence of each factor on the degradation of the target was similar.The optimum concentration of PDS is 10mM,the removal rate of target decreased with the decreasing of PDS concentration,but increasing the concentration does not increase the target degradation rate,and the decomposition rate of PDS does not matter much with its concentration.The optimum concentration of ferric ions is 2.0mM,the decomposition rate of PDS and the removal rate of target decreased with the decreasing of ferric ions concentration,but increasing the concentration does not increase the target degradation rate and the PDS decomposition.The optimum of the current density is0.50mA/cm²,the removal rate of target decreased with the decreasing of current density,but increasing current density does not increase the target degradation rate,and the decomposition rate of PDS increased with the increasing of current density.The optimum concentration of sodium sulfate is 50mM,the decomposition rate of PDS and the degradation rate of the target are not related to the concentration of sodium sulfate.The optimum pH of the solution is about 2.0,and if the pH is too high,ferric ions will precipitate,thus making the target almost no degradation effect.The reaction rate of halogen-containing phenols is faster than halogen-free phenols,while the decomposition rate of PDS is almost the same.Ferrous iron concentrations are increased first and then decreased in the process of three kinds of phenolic degradation,and the solution is mainly in the form of ferric iron,ferrous iron accounted for only about 2.5%.COD removal rate of three kinds of phenols are relatively high,about 80%to 85%,and TOC removal rate also have 70%to 75%.Ion chromatography analysis showed that the Cathode/PDS/Fe³⁺system had a dehalogenation effect on the halogenated phenol.The results of free radical identification showed that there were two kinds of free radicals in the degradation process of the three phenolic compounds,such as·OH and SO4·.