Removal of an emerging contaminant (tris-2- chloroethyl phosphate) from water and wastewater through adsorption to zeolite beta

Emerging contaminants are becoming a global environmental problem as there is increasing information linking them to environmental and human health hazards. Identification and mitigation of these constituents at the source before entering the environment is crucial if impacts to the ecosystem and humans are to be eliminated. One emerging contaminant of interest is tris-2-chloroethyl phosphate (TCEP), an organo-phosphate ester used as a plasticizer and flame retardant. TCEP is of special interest due to potential toxicity, prevalence in the environment, and difficult to remove through conventional wastewater treatment operations. This work presents a methodology of zeolite material review and selection. Equilibrium capacity of TCEP using Zeolite beta was determined for both 25:1 and 300:1 silica:alumina ratios. Excellent removal (>97%) of TCEP from solution was achieved. Adsorption at an acidic initial solution pH (4.8 S.U.) exhibited the highest adsorption capacity compared to neutral or alkaline pH values. Maximum adsorption capacities of 77 mg/g (25:1) and 103 mg/g (300:1) were obtained. To describe a diffusion-limited adsorption uptake, a configurational diffusion (CD) model is proposed to simulate variable diffusivity in the uptake of TCEP in zeolite. The CD model showed flexibility to fit both materials better than existing models using constant or single diffusivity values. Fast diffusion (near equilibrium conditions were reached in <60 minutes) was observed. Both equilibrium and kinetics of TCEP adsorption were evaluated in surrogate background (natural organic material and salts) and in a competitive adsorption environment with methyl tert-butyl ether (MTBE). Natural organic material (NOM) and salt reduced maximum adsorption capacity by up to 30% compared to DI, but showed a negligible effect at equilibrium potential concentrations of environmental interest. MTBE reduced adsorption capacity of TCEP by approximately 30 to 50%. The CD model represented the diffusion in the surrogate water background well, showing that addition of MTBE decreased the mobility of TCEP during diffusion. The results show that Zeolite beta is a successful approach to remove TCEP from water and wastewater matrices and could be a useful technology to treat other hydrophilic persistent ECs.