Browsing by Author "Narsingh, Udi"

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    Block and graft copolymers as flocculants for wastewater treatment
    (Stellenbosch : Stellenbosch University, 2018-03) Narsingh, Udi; Klumperman, Lubertus; Pfukwa, Rueben; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
    ENGLISH ABSTRACT: Water pollution, due to toxic metals and organic compounds, remains a serious environmental problem. Many of the contaminants found in industrial and municipal wastewaters are known to be toxic or carcinogenic. Heavy metals are not biodegradable and tend to accumulate in living organisms, causing various diseases. The treatment of these wastewaters involves, among other steps, flocculation to remove, not only the suspended, colloidal particles but also heavy metals and other contaminants that get adsorbed on them. In this research, graft and triblock copolymer flocculants were synthesized to flocculate the suspended solids. For graft copolymerized flocculants, acrylamide was grafted onto cellulose. Cellulose is inexpensive and most abundantly available from plant and microbial resources. Polyacrylamide is a synthetic polymer that is polar and widely used for the treatment of wastewaters. Acrylamide was grafted onto cellulose using a conventional chemical free-radical initiation, as well as microwave-assisted and microwave- initiated methods. The synthesis procedure for each of the methods was optimized for percentage grafting using experimental design with response surface methodology. The optimally synthesized graft copolymer, Cell-g-PAM, from each of the synthesis methods was compared with highly recommended polyacrylamide based commercial flocculants for the flocculation of a model kaolinite suspension. The flocculant synthesized via the microwave-assisted method outperformed all flocculants tested. For triblock flocculants, two ABA type triblock copolymers were synthesized using single electron transfer living radical polymerization (SET-LRP). For both copolymers, the central block was poly(ethylene glycol) (PEG). PEG is a hydrophobic, pH insensitive polymer that adsorbs strongly onto colloidal particles. The first outer block was poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA). PDMAEMA is temperature and pH responsive and known to interact strongly with anionic colloidal particles and heavy metals. The second outer block was polyacrylamide. Various molecular weight triblock copolymers were synthesized and used for the flocculation of a kaolinite suspension. The mechanism of flocculation changed from patch to bridging as the length of the flocculants increased. The graft copolymer flocculants performed better than the block copolymer flocculants in the flocculation of kaolinite.