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Tshwane University of Technology (2010)

Functionalised natural zeolite and its potential for treating drinking water containing excess amount of nitrate

Masukume, Mike

Titre : Functionalised natural zeolite and its potential for treating drinking water containing excess amount of nitrate.

Auteur : Masukume, Mike.

Université de soutenance : Tshwane University of Technology

Grade : MAGISTER TECHNOLOGIAE : ENGINEERING : CHEMICAL 2010

Résumé
Excess levels of nitrate in drinking water is responsible for methemoglobinemia, or "blue baby" disease. Consequently, management of nitrate in drinking water is universally of public health interest. In this study, clinoptilolite functionalized with cationic surfactant hexadecyltrimethyl ammonium bromide (HDTMABr), was used for the removal of nitrate from drinking water. The adsorption media was characterized using relevant analytical techniques such as XRF, XRD, FTIR and SEM analysis. In one approach, the batch adsorption mode was used to study batch equilibrium and kinetics of nitrate adsorption while in another, column dynamic experiments were adopted. In the batch sorption mode, the effects of surfactant loading, adsorbent dosage, pH, coexisting ions, temperature and environmental water quality, on the adsorption of nitrate were investigated. As a result, it was found that nitrate adsorption was optimum when the initial concentration of the functionalizing surfactant was 300 0 ppm. An increase in adsorbent dosage raised the percentage removal of nitrate. The valency of the coexisting anion had a major effect on nitrate removal, with the presence of phosphate (a trivalent anion) giving the highest inhibiting effect. Temperature and pH had negligible effect on the adsorbent performance. Environmental water samples (natural groundwater samples from Limpopo province- South Africa) were tested and it was found that the South African regulatory compliance can be achieved especially when the initial nitrate concentration is slightly above 100 ppm. Equilibrium data was modeled using the Freundlich and Langmuir isotherms and the data conformed well to the Freundlich isotherm. This indicates that the adsorbent surface is heterogeneous in nature. Kinetically, nitrate adsorption was best described by the pseudo-second order rate equation. Meanwhile the column dynamic study and breakthrough analyses were carried out as a function of bed depth, flow rate and aspect ratio. Results revealed that as the adsorbent mass increased from 30 g to 90 g, the breakthrough time increased from around 7.5 to 18 hours. Flow rate had a major effect on the breakthrough behavior, with 5 mL/min giving the maximum adsorption capacity. Column aspect ratio had negligible effect on nitrate adsorption. Desorption and regeneration tests were also carried out to evaluate reusability of the adsorbent and cost implications . Clinoptilolite being a potentially low- cost natural adsorbent, it can be concluded therefore that its use may provide an alternative treatment solution to nitrate contaminated groundwater used for drinking purposes.

Mots Clés : Nitrate ; Methemoglobinaemia ; Surfactant modified zeolite ; Adsorption isotherms ; Kinetic and thermodynamic parameters ; Fixed bed adsorption and breakthrough analysis ; Modeling

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