Degradation Of PCP In Red Soils Under Waterlogged Conditions

China is severe problem of soil pollution. And the situation becomes more serious, due to presence of the organic pollutants, especially POPs (Persistent Organic Pollutants), which stay in the environment for a longer time. Organochlorine pesticides are highly toxic and residual, causing heavy pollution of the soil environment. For long period of time PCP (Pentachlorophenol) has been used as a pesticide and preservative. It has been attracted extensive attention on adsorption behavior in water and soil, because of the largest toxicity in all the Chlorophenols.Study was conducted to find the effects of adding electron donors such as sodium acetate (NaAc), glucose (Glu) and oxalate (Oxa) on PCP contaminated upland latosol, derived from basalt and Quaternary red clay. The soil samples were collected from Hainan province (HNL) and Hunan province (CSR). Appropriate pollution soil improver was sought, carrying out a laboratory experiment on the process of dissimilatory Fe(III) reduction by comparing the4kinds of electron donors’ differences. Reductive reaction process produced free iron, Fenton-like reaction was started by further addition of hydrogen peroxide to oxygenate PCP. To seek the optimum criteria under this condition in this degradation reaction, scientific based approach has been provided to recover PCP contaminated soils. The main results obtained from the experiments were as follows:1) Under the condition of soil water ratio1:1(W/V) flooding anaerobic incubation, pH and Eh values of2soils reduced significantly. The values of PCP contaminated soils decreased more sharply than that of non-PCP soils for HNL soil, especially oxalate treatment. While it was not obvious for CSR soil, but the values of pH and Eh of oxalate treatment were found to be significantly lower in other treatments.2) Under the condition of waterlogging and addition of electron donors, the reduction rates and yield of iron were not identical in2soils. The order of HNL soil from high to low were in the sequenced Glu> Oxa> NaAc> CK and the order of CSR soil from high to low were:Oxa> Glu> CK> NaAc, respectively. While significantly higher Fe(II) content was observed in the oxalate treatment in the PCP contaminated soils. 3) The experiment results of PCP reductive dechlorination showed that PCP degradation was most apparent effected by adding oxalic acid among these electron donors. In HNL soil removal rate of PCP reached up to34.8%, after6d of incubation, the degradation kinetic constant (k value) of PCP raised from0.0241to0.0537. The half-life was reduced to12.9d and concentration of chloride ion increased from23.41mg/L to32.43mg/L. While in CSR soil PCP removal rate was50.1%, the k value was lifted from0.0597to0.1035, the half-life was reduced to6.7d and concentration of chloride ion increased from16.62mg/L to31.26mg/L.4) The best initial soil water ratio of PCP degradation with addition of hydrogen peroxide oxidation was1:1(W/V). Optimum reaction time was50min. The lower mass fraction of hydrogen peroxide, degradation efficiency of PCP was not obvious and slow down the reaction rate. Under the condition of1:1water-logged incubation, degradation effect was found the best by using30%hydrogen peroxide. Initial concentration of PCP was higher in soil, the degradation rate was lower. The initial concentrations of PCP and degradation rates were followed by2g/kg,6g/kg,10g/kg,16g/kg, and86.3%,66.3%,47.8%,15.5%, respectively, after1h of treatment.5) The dosage of hydrogen peroxide, soil pH value and the PCP degradation rate was positive significant relationship (p<0.05). The influence of hydrogen peroxide dose effect was greater than that of pH value. The result revealed that there was weak negative correlation (p>0.25) between degradation rate of PCP and reaction time. The degradation rate of PCP was as high as21.9%, under the condition of addition6mL hydrogen peroxide to5g PCP (10g/kg) contaminated soil sample, pH7.26, and5min of reaction.6) By waterlogging and adding oxalic acid after6d of anaerobic incubation, PCP removal rates of HNL and CSR were35.3%and48.7%respectively and then kept stable. Further treatment of adding hydrogen peroxide, after1h of reaction, PCP removal rates respectively were raised to63.7%(HNL),81.4%(CSR), and at last it reached to steady condition.