Abstract
South Africa is facing an imminent threat to its water sources due the presence of
cyanotoxins; the growing incidence of cyanotoxins in different water matrices globally
poses major risks to the world and its inhabitants (humans and animals). For decades,
researchers have reported on the deaths of animals and humans due to cyanotoxins
poisoning, the world health organization (WHO) established guidelines to regulate these
toxins in our drinking water. Some of the health effects caused by cyanotoxins includes but
not limited to; liver failure, vomiting, skin irritation and cancer. The main concern about
cyanotoxins is that they are water soluble and studies have shown that conventional water
treatment methods are inadequate in removing cyanotoxins. Thus, this has since raised the
interest in finding cheaper alternative methods to remove cyanotoxins. Amongst other
alternatives, activated carbon was found to be one of the most studied and proved to be
adequate for removal of cyanotoxins. A few of the carbon precursors such as coal, coconut
and wood have been studied, but presented drawbacks such as the decrease in accessibility,
increase in mass production costs which resulted in commercial activated carbon being
expensive. Thus, the primary objective of this research was to examine the applicability of
waste tyre activated carbon (WTAC) as a cost effective carbon precursor used for the
removal of microcystin-leucine arginine (MC-LR), nodularin (NOD) and
cylindrospermopsin (CYN).
During this study, the adsorptive removal of MC-LR which is the most toxic of the
cyanotoxins was investigated. The detection of MC-LR in samples was achieved using
high performance liquid chromatography coupled with a photodiode array detector. The
factors affecting the removal of MC-LR with WTAC were studied using response surface
methodology to achieve maximum removal efficiency. Under optimal conditions, kinetic
and adsorption isotherms studies for adsorption process of MC-LR onto WTAC were
evaluated. The equilibrium data fitted best pseudo second-order rate and Langmuir
isotherm model, the maximum adsorption capacity was found to be 357 ug g−1. The
achieved optimum conditions were then further tested on both influent and effluent
samples collected from Daspoort wastewater treatment plants (Pretoria, South Africa) and
WTAC showed 100 % removal efficiency.
Moreover, to describe the competitive adsorption between cyanotoxins and dissolved
natural organic matter (NOM) onto WTAC, a simplified comparable background...
M.Sc. (Chemistry)