Degradation Of Aqueous Atrazine With Zero-Valent Aluminum And/or Zero-Valent Zinc And Their Mechanism

Atrazine was classified as one of the most common chloro-s-triazine herbicides in agricultural and forestry applications in the worldwide. For its widespread use and high mobility, moderate water solubility and high persistence in water, atrazine appears as one of the most commonly detected herbicides in ecological systems, which caused seriously pollution to soil and natural waters. Animals and humans experiments found atrazine could feminize amphibians and decreased semen quality due to its presumptive endocrine disrupter and human carcinogen nature. However, removal of atrazine from aqueous phase presents a significant challenge because it is recalcitrant to biodegradation, does not adsorb strongly on activated carbon or undergo chemical oxidation easily. Although advanced oxidation processes have been currently employed for the atrazine removal, most of them suffered from strict reaction conditions and/or high energy consumption. Continuous improvements in development of effecient treatment processes are still in demand.In this study, we investigated the oxidative/reductive degradation of atrazine using zero-valent aluminum and zero-valent zinc under acidic condition. Not only the affecting factors were investigated, but also the theoretical explanations for the above phenomena were conducted in the objectives. Finally LC/MS and GC/MS identifications were used to deduce the degradation pathway of atrazine.In the first part, we investigated the oxidative removal of atrazine by zero-valent aluminum in the presence of dissolved oxygen (ZVAl/H+/O2 system). The results showed that more than 95% of atrazine was removed within 7 h in pH 2.0 solutions initially containing 30.0 g/L of Al and 20 mg/L of atrazine in 25 ℃. A higher loading of Al accelerated removal of atrazine. Atrazine removal in the ZVAI/H+/O2 system followed the order of pH 2.0>pH 3.0>pH 3.5>pH 4.0>pH 4.5. The reduction of dioxygen to H2O2 by Al could be only achieved under pH<4.0 conditions. The atrazine was oxidized by the situ generated ·OH from H2O2. The transformation of atrazine was apparently accompanied by the release of Cl- and NH4+. Eight primary intermediates were found by LC-MS.In the second part, we investigated the reductive removal of atrazine by ZVZn/H+ system. Results showed that atrazine was degraded effectively by anoxic zero-valent zinc process. The dissolved oxygen and initial atrazine concentration did not affect the reduction of atrazine significantly, while the pH and temperature of solution impacted the reduction of atrazine by zinc. The atrazine removal could be inhibited by the co-existed aqueous anions and cations. Zero-valent zinc corrosion process was accompanied by electronic transfer, the electrons binding the H+ in the solution were excited to generate ·H, the reductive dechlorination of atrazine was the major pathway for its degradation. Triazine ring was hydrogenated by ·H when prolonging the reaction time, thus a novel atrazine degradation mechanism was proposed in the ZVZn/H+ system.