Block and graft copolymers as flocculants for wastewater treatment

Narsingh, Udi (2018-03)

Thesis (PhD)--Stellenbosch University, 2018.

Thesis

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.

AFRIKAANSE OPSOMMING: Waterbesoedeling, as gevolg van giftige metale en organiese verbindinge bly steeds 'n gevaarlike omgewingsprobleem. Baie van die besoedelingstowwe wat gevind word in industriële en munisipale afvalwater is giftig of kankeropwekkend. Swaarmetale kan nie biochemies afgebreek word nie en versamel in lewende organismes wat verskeie siektes veroorsaak. Die behandeling van hierdie afvalwater behels, benewens ander stappe, flokkulering om nie net die gesuspendeerde kolloïdale partikels te verwyder nie, maar ook ander gifstowwe wat daarop adsorbeer. In hierdie navorsing was ent en trippelblok kogepolimeriseerde flokmiddels gesintetiseer om die opgeskorte vastestowwe te flokkuleer. Vir die ert kopolimeerde flokmiddels, was akrielamied op sellulose ingeënt. Sellulose is goedkoop en geredelik beskikbaar vanaf plant en mikrobiese bronne. Poliakrielamied is 'n sintetiese polimeer en word algemeen gebruik vir die behandeling van afvalwater. Akrielamied is gebind op sellulose deur middel van 'n konvensionele chemiese vryradikaal inisiëring en ook aangehelp deur middel van mikrogolfgeïnisieerde metodes. Vir die sinteseprosesse van elk van die metodes is die optimale kondisies bepaal deur eksperimentele ontwerp deur gekose oppervlakmetodes. Die optimaal gesintetiseerde kopolimeer, Cell-g-PAM, vanaf elk van die metodes is vergelyk met die hoogs aangeskrewe poliakrielamied gebaseerde kommersiële flokkulante vir die flokkulering van 'n model kaolinitiese suspensie. Die gesintetiseerde flokkulant wat deur middel van die mikrogolf gebaseerde metodes vervaardig is het alle flokkulante wat ondersoek is oortref Vir trippelblok flokkulante is twee ABA tipe trippelblok koplimere gesintetiseer deur middel van enkel elektronoordrag lewende radikale polimerisasie (SET-LRP). Die sentrale blok van beide kopolimere was poliëtileenglikool (PEG). PEG is 'n hidrofobiese, pH onsensitiewe polimeer wat sterk aan kolloïdale deeltjies adsorbeer. Die buitenste blok was poli(N,N-dimetielamino-etielmetakrilaat) (PDMAEMA). PDMAEMA is temperatuur en pH afhanklik toon sterk interaksie met anioniese kolloïdale partikels en swaarmetale. Die blok aangrensend aan die buitenste blok was poliakrielamied. 'n Aantal trippelblok polimere met verskille molekulêre massas is gesintetiseer en gebruik vir die flokkulering van 'n kaolinietsuspensie. Die meganisme van flokkulasie het van kol na oorbrugging verander namate die lengte van die Flokmiddels verhoog. Die gebinde kopolimeer flokkulante het beter resultate gelewer as die blok kopolimeer flokkulante in die flokkulasie van kaoliniet.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103930
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