Study On Microwave Assisted Wet Air Oxidation Of Biorefractory Organic Contaminant In Water

Wet air oxidation (WAO) is a promising method for the treatment of heavily contaminated wastewater. However, severe operation conditions (high pressure and high temperature) in WAO leads to the restriction against its wide application. In this paper, a new method, microwave (MW) assisted wet air oxidation (MAWAO) process was investigated aiming to treat biorefractory contaminated wastewater under milder conditions, where the treated solution was irradiated by MW, coupled with activated carbon (AC) added and airflow supplied. The results showed that H-acid (1-amino-8-naphthol-3, 6-disulfonic acid) in the solution was effectively degraded. TOC removal in the solution (20mL, 3000mg/L) reached 81.1% after 60min irradiation under the conditions of 800W of MW power, 10g of AC dose and 0.5L/min of airflow. AC dosage, airflow rate and MW power influenced TOC removal.From the analysis using HPLC and UV and the determination of pH, SO₄⁽2-_, NH₄⁺, NO_x¹ and biodegradability in the treated solution, the results showed that the structure of H-acid was destroyed and gradually mineralized after MAWAO, which resulted in a great increase in the biodegradability of the solution.From the determination of hydroxyl radical (OH) using HPLC and ESR (electron spin resonance), the results indicated that ·OH could be generated in the process. Its generation rate approximately ranged from 0.020 to 0.036μmol/s under the experimental conditions. The results also displayed that AC dosage, airflow rate and MW power had influence on its yield. The degradation of organic substances in this process was related to formation and function of ·OH.Temperature determination showed that rapid rising temperature of AC resultedin temperature gradient from AC to water, which possibly made the localization of AC reaching high temperature, providing the condition of OH generation. The data from determination of the SEM and surface physical properities of the AC after treatment proved that AC possibly suffered high termperature during the process.NiO-loaded AC could obviously promote the effect of MAWAO duo to the fact that load of NiO henced capacity of AC to absorb MW energy, as well as NiO functioned as catalyst. The results displayed that TOC removal in H-acid solution reached 87.4% in 20min. Increase of Ni amounts in AC favored TOC removal, but losing of Ni was obvious in the initial irradiation.A flow model in MAWAO was also investigated, where the decoloring rate of telon fast green 5G in aqueous solution reached 88% when HRT=10min. It indicated that the process could also be operated under flow model.The results indicated that under the relatively moderate conditions, MAWAO simulated the principle of conventional WAO, which made WAO operated under safer and more convenient conditions. It provided a new approach to treat biorefractory pollutants in water at the atmospheric pressure.