Chelate based-Fenton reaction for the degradation of chlorinated aliphatic hydrocarbons by new polymeric chelating agent (cross-linked chitosan)

Abstract

Degradation of trichloroethylene (TCE) and tetrachloride (CT) by a modified Fenton reaction was investigated in aqueous solution. Fenton reaction can be significantly enhanced in the presence of Fe(II) chelated by cross-linked chitosan (CS) with glutaraldehyde (GLA) at near-neutral pH. A remarkable oxidative degradation of TCE ($1.838\h^{-1}$) was observed in modified Fenton system with Fe(II)-CS/GLA (10 mM and $2\g L^{-1}$, respectively) and $H_2 O_2$ (318 mM), while no significant degradation ($0.005\h^{-1}$) was observed in classic Fenton reaction system with Fe(II) (10 mM) and $H_2 O_2$ (318 mM) at pH 7 in 5 hrs. The kinetic rate constants for the degradation of TCE in modified Fenton system was dependent on the initial suspension pH, Fe(II) loading, CS/GLA dosage, and concentration of $H_2 O_2$. We have also observed 74.8 % of CT degradation by the Fe(II)-CS/GLA in modified Fenton system, while 43 % of CT degradation has been done in classic Fenton system in 10 hrs at pH 6. The degradation of CT in modified Fenton system was dependent on the concentration of $H_2 O_2$, Fe(II) loading, and concentration of CT. TCE and CT transformation was conducted by monitoring its disappearance and chloride ion ($Cl^{-}$) released with time. The concentration of $Cl^{-}$ was rapidly produced and its total mass recovery was reached more than 91 % during modified Fenton reaction. Addition of the hydroxyl radical scavenger 2-propanol to modified Fenton reactions significantly enhanced the CT degradation (removal efficiency from 57.2 % to 92.4 %), while TCE degradation was strongly inhibited in 5 hrs reaction time (removal efficiency from 74.7 % to 19.9 %). These results confirm the reductive reaction mechanism of CT by modified Fenton reaction with CS/GLA. Moreover, it shows that modified Fenton reaction with CS/GLA not only oxidizes TCE, but also effectively reduces CT at near-neutral pH. We observed the formation of surface Fe(II)-CS/GLA complex using microscopic analyses...