Degradation of Hazardous Organic Contaminants using Ferrate(VI) Synthesized by Wet Oxidation Method

Abstract

Trichloroethylene (TCE) and perchloroethylene (PCE) are representative volatile organic compounds that the International Agency for Research on Cancer considers to be a likely carcinogen. Due to being non-inflammable, chemically stable, and an excellent washing solvent, TCE and PCE are frequently used in commercial processes such as machine manufacturing, metal degreasing, and dry cleaning; and as a result, many cases ground water and soil contamination have been reported. 2,4,6-trichlorophenol (TCP) is one of organic contaminants that present in wastewater. This compound is widely used in pesticides, antiseptics and wood preservation and can enter the environment when these products are being made or used. Toxicity studies showed that TCP was carcinogenic to three laboratory animals, causing liver tumors in mice and inducing forms of leukemia/lymphoma in male rats. TCP also classified as Group B2 (probable human carcinogen) by the United States Environmental Protection Agency. Advanced Oxidation Processes (AOP’s) has become interesting technology that many researchers try to develop and improve to overcome many contamination cases. Since late 90’s until nowadays ferrate(VI) technology has been developed and discussed as a hazardous organic contaminants degradation material. Degradation of TCE, PCE, and TCP using ferrate(VI) synthesized by wet oxidation method were conducted in closed free head-space reactor. In synthesis, several source of precursors, procedural variations in filtering and variation in concentration of sodium hydroxide (NaOH) were used to obtain the highest concentration of Ferrate(VI) can be produced by wet oxidation method. The Ferrate(VI) produced by optimum condition were applied in the degradation experiment with several parameters such as pH (acid, base and neutral), ferrate(VI) concentration (14, 28, 42, and 56 ppm), target compound initial concentration (0.1, 0.25, 0.5, and 1ppm) and temperature (10oC, 25oC, 35oC, and 45oC). A second order reaction was observed in the all target compound degradation processes with TCE have more rapidly degraded than PCE while TCP has the higher degradation efficiency. The kapp value of TCE was 1,029.8 M-1s-1, the kapp value of PCE was 315.19 M-1s-1, and TCP was 1489.7 M-1s-1. Even though activation energy showed that PCE has lower activation energy than TCE in acid condition, TCE was more degraded compare to PCE because PCE degradation product was TCE. In the pH experiment, neutral condition has identified as the optimum condition for degradation with 70% TCE and 60% PCE removed followed by acid and base condition. TCP optimum condition for degradation was in acid condition with 95% TCP removed. The efficiency of degradation were depend on the amount of ferrate(VI) available on the reactor, this trend was shown in the effect of ferrate(VI) dosage and initial concentration. Degradation efficiency increased as increasing of ferrate(VI) amount or decreasing of target compound concentration. Temperature parameter showed that degradation by ferrate(VI) was significantly affected, since temperature has been reported as one of the most significant parameters that increasing temperature caused an enhancement of the homogeneous ferrate(VI) decomposition kinetics. The optimum temperature was obtained in 25oC and degradation efficiency decreased as temperature increased. Degradation pathways were proposed based on intermediate product identified by GC/MS.