Study On Treatment Of HCB-containing Simulated Wastewater And Remediation Of HCB Contaminated Sediments

Hexachlorbenzene (HCB), one of the persistent organic pollutants (POPs), can led to many serious illnesses, such as endocrinopathy, maladjustment of procreation and immunity, heteroplasia, cancer and so on. It is benefit to environment protection; people's health keeping and the "Stockholm treaty for the reduction of persistent organic pollutants (POPs)" performing by study the remediation technologies for HCB contaminated water body and sediments. In this paper theEF-Feox, zero valent iron and electro kinetics technologies were used to treat the HCB-containing wastewater and/or sediments. The main research results of this paper include: 1. Establishment of HCB analytical methods in water body and sediments and analysis of degree of polluted level by HCB at target pollution source. High levels of HCB have been recently found in our study in one chemical plant wastewater ditch in Wuhan city. The HCB concentration was up to 200μg/L in the wastewater and 1200mg/kg (dry weight) in the sediments. Because of the bioaccumulation and persistence of HCB as well as its potential toxicity, HCB must be removed from wastewater and sediments. 2. Study on removal efficiency of HCB in simulated wastewater treated by Fenton reagent, EF-Feox and zero valent iron methods. The removal of HCB showed high efficiency by using Fenton reagent, EF-Feox and zero valent iron methods. In Fenton treatment process, it was found to be benefit to HCB removal at the conditions of lower pH, proper H₂O₂ and Fe²⁺ dosage and longer reaction time. HCB removal methodology follows pseudo-first-order decay kinetics. In EF-Feox treatment process, the removal efficiency of HCB increased with the dosage of H2O2 and operation voltage, but it increased at the beginning of the reaction and then decreased with the increase of Na2SO4 dosage. And in zero valent iron treatment process, the results showed that the HCB removal efficiency increased with the increasing reaction time, oscillated frequency of the shaker or iron and β-cyclodextrin(β-CD) dosage. The initial pH of reaction solution significantly influence on the dechlorination. It showed a higher HCB removal efficiency when initial pH changed between 3 and 6. The temperature of reaction had little effect to the HCB removal when it ranged from 20℃to 30℃. It also was found pH value a little increased with reaction time. Through experiment the removal efficiency of HCB was optimized in the Fenton and EF-Feox system. And the general removal kinetic model of HCB (dt? dC) was defined in the EF-Feox and zero valent iron processes. 3. The migration of HCB in the electro-kinetic system. The study results also showed that electro-kinetic transport processes can effectively stimulate the migration of HCB in the sediments,depending upon the reaction time, electrolysis voltage, initial pH and the dosage of sodium chloride (NaCl)and β-CD. It was found that the electro-kinetic process can change sediments properties. 4. Study on electro-kinetic and EF-Feox remediation of HCB contaminated sediments. The removal of HCB in the sediments was showed higher efficiency both in the electro-kinetic and EF-Feox remediation processes. In the electro-kinetic process, It was also found that the removal of HCB in sediments by uniform electro kinetics were increased with the increase of cell voltage and the dosage of NaCl; but it decreased with the increase of initial pH and distance between the electrodes. But the HCB removal in the EF-Feox was increased with the increase of the dosage of NaCl and H2O2; it was found the percentage of moisture decreased, the electrical current increased at the beginning of the reaction and then decreased.5. Removal mechanism of HCB in the zero valent iron and EF-Feox processes. From the removal mechanism study of HCB treated by zero valent iron and EF-Feox processes, new peaks of material were found in the gas chromatogram chart, and the kinds and content of the new materials changed during the reaction in the EF-Feox processes. It was further proved by the toxicity test that the new materials could come into being during the reaction of HCB in both zero valent iron and EF-Feox processes; and the new materials have less poisonous. Based on the above experimental results, the basic EF-Feox reactor was designed for HCB removal.