Neelancherry Remya

Carbofuran degradation by the application of MW-assisted H2O2 process

Carbofuran removal performance of a microwave (MW)-assisted H2O2 system under different MW-power levels (300-900 W) was investigated. Batch experiments were conducted at 100 mg/L carbofuran concentration using a modified-MW reactor with 2450 MHz of fixed frequency. As a precursor, control experiments were carried out with H2O2 alone, MW alone and conventional heating (CH). A maximum carbofuran removal of 14 % was observed in both H2O2 alone and CH systems. On the other hand, only 2 % removal was observed in the MW alone system irrespective of the operation-mode, i.e. continuous or pulsed. The combination of MW and H2O2 produced 100 % carbofuran removal in all the MW-assisted experiments. The MW-assisted system operated under continuous-mode and at 750 W has showed rapid carbofuran degradation, i.e. 30 sec, with the highest first-order removal rate constant of 25.82/min. However, 97 % carbon oxygen demand (COD) removal was observed in the same system only after 30 min. On the other hand, 100 % carbofuran removal and 49 % COD removal were observed in the pulsed-mode MW-assisted H2O2 system after 10 and 30 min, respectively. Carbofuran mineralization in the system was evidenced by the formation of ammonium and nitrate, and carbofuran intermediates.

Microwave-granular activated carbon (MW-GAC) system for carbofuran degradation: Analysis of characteristics and recyclability of the spent GAC

Granular activated carbon (GAC) is frequently used to remove pollutants from wastewater. However, the mechanism of pollutant removal by GAC is by adsorption and hence spent GAC should be regenerated and used for several cycles for minimizing the cost of treatment. In the present study, the characteristics of GAC and carbofuran removal mechanism were explored in a microwave-GAC (MW-GAC) system. Carbofuran removal by adsorption was 52% at a GAC loading of 0.8 g/L. However, complete carbofuran degradation from aqueous solution as well as from GAC surface was obtained within 30 min in a MW-GAC system. In addition, A COD removal efficiency of 72% was observed in the MW-GAC system at pH 8 and 80˚C after 30 min. The degradation occurred mainly through cleavage of carbamate group and oxidation of furan ring. Carbofuran removal by adsorption was enhanced with MW exposed GAC due to the improvement in the surface property on exposure to MW. On the other hand, recyclability of MW exposed GAC in the MW-GAC system indicated > 99% degradation of carbofuran in all the three cycles tested. As a whole, complete degradation of carbofuran and the effective recycling of the spent GAC could be achieved in the MW-GAC system.

Carbofuran removal in continuous-photocatalytic reactor: Reactor optimization, rate-constant determination and carbofuran degradation pathway analysis

ABSTRACT Carbofuran (CBF) removal in a continuous-flow photocatalytic reactor with granular activated carbon supported titanium dioxide (GAC-TiO2) catalyst was investigated. The effects of feed flow rate, TiO2 concentration and addition of supplementary oxidants on CBF removal were investigated. The central composite design (CCD) was used to design the experiments and to estimate the effects of feed flow rate and TiO2 concentration on CBF removal. The outcome of CCD experiments demonstrated that reactor performance was influenced mainly by feed flow rate compared to TiO2 concentration. A second-order polynomial model developed based on CCD experiments fitted the experimental data with good correlation (R2 ∼ 0.964). The addition of 1 mL min−1 hydrogen peroxide has shown complete CBF degradation and 76% chemical oxygen demand removal under the following operating conditions of CBF ∼50 mg L−1, TiO2 ∼5 mg L−1 and feed flow rate ∼82.5 mL min−1. Rate constant of the photodegradation process was also calculated by applying the kinetic data in pseudo-first-order kinetics. Four major degradation intermediates of CBF were identified using GC-MS analysis. As a whole, the reactor system and GAC-TiO2 catalyst used could be constructive in cost-effective CBF removal with no impact to receiving environment through getaway of photocatalyst.