[Emergent treatment of source water contaminated by representative herbicide molinate and ametryn]

Emergent treatment of source water polluted by representative herbicide molinate and ametryn was researched. The results indicate that activated carbon adsorption and prechlorination could achieve high efficiencies to remove the herbicides. The pseudo second-order adsorption kinetic model and Freundlich adsorption isotherm model can be used to describe the adsorption process and the adsorption equilibrium of molinate and ametryn adsorbed by powdered activated carbon (PAC) in raw water respectively. Either molinate or ametryn of about 200 microg/L in water could be completely removed by 40 mg/L PAC. The best PAC adding point was 20 min before coagulation. The two herbicides were easily removed by granular activated carbon (GAC) column (20 cm high) which can be the available supplement of PAC treatment to strengthen safety. The Cl2 dosage of 2.5 mg/L could oxidize the two herbicides completely, but the chlorination products as well as their toxicity need further study. PAC adsorption combined with 1 mg/L KMnO4 preoxidation didn't improve the removal efficiencies of molinate and ametryn. The effect of PAC adsorption combined with 1.5 mg/L prechlorination depends on their adding sequence. When source water was simultaneously contaminated by the two herbicides both about 200 microg/L, the PAC and Cl2 dosage have to be increased to 50 mg/L and 3 mg/L respectively, then both herbicides can be removed or oxidized fully.