MODELING AND CONTROL OF DISINFECTION BY-PRODUCTS IN WATER DISTRIBUTION SYSTEMS

Abstract

Adsorbable organic halide (AOX) compounds known with their toxic effect, produced as by-product for drinking water disinfection. The present work studied the control of pentachlorophenol (PCP) as a model AOX compound in water by adsorption using activated carbon. Date-pit is an agriculture waste used as a precursor for locally production of date-pit activated carbon (DPAC) using a low-cost production technique, which is a sustainable waste management. Many physical and chemical techniques used to characterize the prepared activated carbon (SEM, EDX, FTIR and elemental analysis) The surface properties of DPAC as well as the total surface area (SBET), total pore volume (VT), solid-phase density (ρs), particle density (ρp) and particle porosity (εp) have been determined. Effect of Contact time and initial concentration on the equilibrium adsorption capacity of PCP onto DPAC were investigated. Over pH range of (2-11), the uptake amounts of PCP adsorbed qe (µg.g-1), at acidic pH remained constant or decreased slightly with the pH, and at pH= 9 there was a decrease in the value of qe (µg.g-1). Temperature plays an interesting role in the adsorption of PCP onto DPAC. The adsorption capacities decreased from 412.5 to 259.5 (µg.g-1) with increasing temperature from 25 to 55°. These show that the adsorption processes are exothermic equilibrium modeling has been carried out using the Langmuir, the Freundlich, the Temkin and the Redlich-Peterson isotherms. The Langmuir isotherm of minimum value of error analyzed by error function provide the best fit of the experimental data. Mass transfer and kinetics study for the adsorption of PCP onto DPAC using slurry batch adsorber, with mechanical stirring techniques, have been investigated. Effects of different variables such as agitation speed, initial concentration, dose of carbon and temperature have been studied. The experimental results have been analyzed using external mass transfer and intraparticle diffusion models as mass transfer models and pseudo first-order and pseudo second-order as kinetic models. The values of macropore parameter (KI) have been determined and correlated with the design variables. The constant values of pseudo first-order and pseudo second-order model have also been determined. Pseudo second-order model fitted the experimental data better than the other model for all design variables system. In laboratory-scale studies, the experimental results indicated that the use of a locally prepared date-pit activated carbon (DPAC) as adsorbent of pentachlorophenol (PCP) from aqueous solutions was proved to be effective.

KEYWORDS: Disinfection by-products; Pentachlorophenol; Date-pit activated carbon; Adsorption; single-stage batch adsorber