A comparison between different advanced oxidation processes for the remediation of PCP contaminated wastewaters

In this paper a comparison between different advanced oxidation processes (AOP), for the remediation of a wastewater contaminated with 100 mg/l of pentachlorophenol (PCP), is proposed. The AOP chosen were: Fenton or Fentonlike reactions in which the soluble iron catalyst salt was added as Fe(II) or Fe(III) or a mixture of Fe(II) and Fe(III), and ozonation. In the latter case the effects of the presence of a solid iron oxide (hematite) were also evaluated. For the Fenton’s reactions, the investigated parameters were: pH (from pH=1.5 to pH=5), reaction time, H2O2/PCP ratio (from 5/1 to 20/1), Fe/H2O2 ratio (from 0 to 2/1) and the effect of a H2O2 stabilizer: KH2PO4. The highest TOC removal (75%) was reached, using stabilized H2O2 and Fe(II), when H2O2/PCP=5/1 and Fe/H2O2=1/1; in this case, dechlorination was 96% and KH2PO4 increased H2O2 lifetime significantly. Fe(III) or the mixture of Fe(II) and Fe(III), proved to be more efficient than Fe(II) when H2O2/PCP<15/1 and Fe/H2O2<1/1. For ozonation the effects of pH and of the ratio between airflow and the solution’s volume, were investigated. The highest efficiencies (TOC removal=35%, Cl- release=80%) were reached when O3=0.24 mg/l at pH=11; however diminishing the volume of treated solution, 47% TOC removal and stoichiometric Cl- release were observed. The addition of hematite resulted in a slight increase of TOC removal and Cl- release. By comparing the experimental results, among the tested AOP systems, Fenton’s reaction proved to be the most effective for PCP remediation.