Comparative study for the transformation of emerging contaminants and endocrine disrupting compounds : electrochemical oxidation and biological metabolism

Brocker, Johann Heinrich Ludwig (2020-03)

Thesis (MSc)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: As little as 1% of all water sources is fresh water accessible for use and it is increasingly be polluted by anthropogenic materials such as solid and chemical waste. Previous studies have shown that various organic micropollutants are not effectively removed by conventional water treatment processes and persist in natural water sources. The primary aim of this study was not to detect and monitor micropollutant distribution but rather to investigate two degradation processes, electrochemical oxidation and microbial degradation, as well as the resulting transformation products. It was hypothesized that microbial degradation will produce less toxic transformation products than the harsh process of chemical oxidation. Two micropollutants, sulfamethoxazole and carbamazepine, were chosen based on their widespread detected and persistence in the environment. The CabECO technology harnesses the process of electrochemical oxidation to produce ozone in the aqueous phase for water treatment and produced >2 mg/L of ozone at the suggested operating parameters. Ozonation of environmental water sources showed some success in reducing the microbial load, however, several orders of magnitude of microbes remained after treatment, especially in samples with high COD. It also proved effective in the abatement of SMX and CBZ, reducing the micropollutant concentration to below detection limits within 1 min. However, the endocrine disrupting effect of the compounds required up to 4 hours of exposure time to ozone to eliminate the estrogenic/anti-estrogenic activity. Although effective for SMX and CBZ, the CabECO technology is less effective against a broad suite of micropollutants and environmental samples, where non-target pollutants scavenge the ozone. Microbial degradation of SMX and CBZ was more effective by nutrient limited biofilms than by planktonic counterparts. Even though biodegradation was less effective than ozonation, the transformation products proved to be less toxic. Nutrient limited biofilms are scarce in natural system, as most natural and waste water is high in nutrients, therefore the application thereof for micropollutant removal would be a post-secondary treatment step or ‘polishing step’ for water treatment systems. The possibility of combinations of treatment processes should be further investigated to optimize a system that can effectively reduce micropollutants as well as the eco-toxicological footprint.

AFRIKAANSE OPSOMMING: Slegs 1% van alle water bronne is vars water wat toeganklik is vir gebruik en word al meer deur mens gemaakte materiale soos soliede en chemiese afval, besoedel. Vorige studies het gewys dat verskeie organiese mikro-besoedelstowwe nie deur konventionele water behandeling verwyder word nie en dat dit voortduur in natuurlike water bronne. Die primêre doel van hierdie studie was nie om mikro-besoedelstowwe te meet en te monitor nie, maar eerder om twee degradasie prosesse, elektrochemiese oksidasie en mikrobiese degradasie, asook die gevolgelike transformasie produkte te ondersoek. Die hipotese was die mikrobiese afbraak minder toksiese transformasie produkte gaan produseer as die sterk proses van chemise oksidasie. Twee mikro-besoedelstowwe, sulfamethoxazole en carbamazepine, was geselekteer op grond van hul wyd verspreide opsporing en voortdurendheid in die omgewing. Die CabECO tegnologie gebruik die proses van elektrochemiese oksidasie om osoon in die waterige fase met die doel vir water behandeling. Die CabECO tegnologie produseer >2 mg/L osoon en toon sommige effektiwiteit om die mikrobiese lading van omgewings water monsters meningsvol te verlaag, alhoewel veelvuldige ordegroottes van mikrobes steeds teenwoordig is, veral in monsters met hoë CSB. Dit was ook effektief in die afbraak van SMX en CBZ, deur dit te verwyder tot onder deteksie limiete binne 1 min se behandeling. Selfs met effektiewe afbraak binne 1 min, het die endokrien versteurende effek tot 4 ure se blootstelling geverg om die estrogeniese/anti-estrogeniese aktiwiteit te verwyder. Alhoewel effektief vir SMX en CBZ, is die CabECO tegnologie minder effektief teen ‘n wye reeks van mikro-besoedelstowwe en omgewings monster, waar nie-teiken stowwe die ozoon aas. Mikrobiese afbraak van SMX en CBZ was meer effektief deur nutriënt beperkte biofilms as deur planktoniese ewewigte. Selfs al was bio-afbraak minder effektief as osoon behandeling, was die transformasie produkte minder toksies. Nutriënt beperkte biofilms is skaars in natuurlike sisteme, aangesien meeste natuurlike en afval water hoog in nutriënte is. Daarom sal die toepassing daarvan vir mikro-besoedelaar verwydering toegepas word as ‘n na-sekondêre behandelings stap of ‘n ‘polishing’ stap in water behandelings sisteme. Die moontlikheid van gekombineerder behandelings prosesse moet verder ondersoek word om ‘n sisteem te ontwikke wat beide mikro-besoedelstowwe en die eko-toksilogiese voetspoor effektief verwyder.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/108029
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