PHOTOCATALYTIC PURIFICATION OF DRINKING WATER
Report No: 834/1/00

EXECUTIVE SUMMARY

Background and Motivation of Project

Raw surface and groundwater can contain a wide range of materials that are detrimental to human health. These material can be classified as:

1. Natural organic materials (NOM), which represent a complex variety of organic molecules characteristic of the vegetation in a catchment area.
2. A variety of material resulting from the excreta of humans and animals.
3. Breakdown products of algae (not necessarily toxic) causing a bad odour and taste, specifically geosmin and 2-methyl-isoborneol (2-MIB).
4. Microcystin toxins produced by the blue-green algae that present a serious health hazard to humans and animals.
5. A variety of organic molecules of industrial and agricultural origin that can produce adverse health effects.
6. A wide range of micro-organisms causing human disorders.
7. Inorganic species.

The traditional flocculation/coagulation process has proved not to be completely efficient in removing all the combinations of material that can occur in raw water. These combinations can vary on an hourly basis, which complicates the flocculation/coagulation procedure even further.

Various other processes are under investigation elsewhere e.g. ozonation, treatment by hydrogen peroxide, ultraviolet irradiation treatment, microfiltration, Ti0₂ photocatalysis etc. Some of these techniques have found application especially in urban areas. Application of these techniques in isolated rural communities however, poses a serious problem. This WRC sponsored project was undertaken to assess the effectiveness of Ti02 photocatalysis for the oxidative removal of some of the above mentioned groups of compounds( 1, 4 and 5 ) from raw water. The project comprised two phases: an initial screening phase (August 1995 to December 1997) and a follow-up phase (January 1998 to June 2000). Experimental research was jointly conducted by the Department of Chemistry (University of Stellenbosch) and the Programme on Mycotoxins and Experimental Carcinogenesis (PROMEC) at the Medical Research Council (based in Tygerberg).

Project objectives

The objectives of this research programme were to:

• Develop and establish the optimum performance characteristics of a novel design of photocatalytic reactors for purification of raw drinking water containing humic acids, clay colloids and other organic pollutants.
• Evaluate and establish the optimum performance characteristics of photocatalytic reactor designs for the decomposition of microcystins in various raw water samples.
• Establish optimal growth conditions for the microcystins by toxic cultures of cyanobacteria.
• Isolate and purify known and novel microcystin variants from freeze-dried culture material.
• Apply pure microcystin variants to the photocatalytic reactor(s), using the optimised conditions determined under the second objective.
• Identify the decomposition products derived from individual pure microcystin variants.

Copies of this report are available from the Foundation, price £20.00, less 20% to FWR members.