Assessment and Modeling of a Sequential Process for Water Treatment—Adsorption and Batch CWAO Regeneration of Activated Carbon

Abstract

A new sequential process -AD-OX -for (post)treatment of water polluted by poorly biodegradable organic compounds has been investigated. It is based on hybridizing classical adsorption on a fixed bed of activated carbon (AC) followed by batch wet catalytic oxidation at higher temperature and pressure on the same bed of AC, which is then regenerated in situ. The basic idea is to take advantage of both operations: 1-efficient water purification at room temperature by adsorption, 2-effective concentrated pollutant degradation by batch air oxidation achieving simultaneously AC regeneration.A small fixed bed reactor, 10 mm diameter, 0.18 m long, filled with granular activated carbon and equipped with convenient 3 way valves, may achieve successively the two main steps. Several AD-OX cycles have been performed with a phenol solution to quantify the regeneration of the activated carbon adsorption capacity. Results show that activated carbon is fast damaged during the first cycles, due to oxidative coupling, but then a quasi steady state is obtained proving that significant oxidative regeneration has been achieved.A dynamic model of the adsorption step has been first developed, including intraparticle diffusion, liquidsolid external mass transfer and axial dispersion of the liquid phase. It has been applied to simulate the performance of the regenerated activated carbon.Using oxidation kinetics over this aged carbon and its adsorption isotherm, separately determined in autoclave at reaction temperature, the oxidation step after several cycles has been simulated including the heating period, where desorption and oxidation simultaneously occur. The proposed model conveniently predicts the complex phenol concentration-time profile and gives insight to the hydrodynamic behavior of the recycle reactor and the role of mass transfer resistances.

Photocatalytic degradation of an azo-dye on TiO2/activated carbon composite material

“…It was a preliminary investigation towards a new version of the AD-OX process [36,37] by replacing wet catalytic air oxidation by photocatalysis. The water treatment was not achieved by oxidation but by adsorption, the oxidative step being needed only for pollutant degradation and subsequent AC regeneration.…”

Treatment of Wastewater by Material Based on Dates Rods

“…Other studies have also shown that the carboxyl and hydroxyl groups inhibit the adsorption of phenol by increasing the adsorbent affinity for water. These groups have a tendency to form hydrogen bonds with the molecules water promoting their competitive adsorption and leading to the formation of true aggregates that block access of molecules pollutants to micro pores [14]. The phenomenon can be explained by the steric effect and also the difference between diffusivities of copper ions and phenol which makes copper ions more adsorbed than phenol [15].…”

Improvement of (transition metal-modified) activated carbon regeneration by H2O2-promoted catalytic wet air oxidation

“…About 7 g of catalyst was packed in a small fixed bed reactor (18 cm high and 1 cm internal diameter) for successive adsorption-oxidation cycles. The corresponding setup was described in Julcour-Lebigue et al [32]. In these assays, phenol solution (0.5 g/L) was circulated through the AC bed at 0.23 L/h until saturation of the adsorbent.…”