Occurrence of cyanobacteria toxins viz microcystins, nodularis and cylindrospermopsin in wastewater

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