Research in the use of ozone in water treatment conducted by many authors support the idea that
the nature and characteristics of natural organic matter (NOM) present in raw water determines the
efficiency of ozonation in water purification.
An ozone contact chamber was designed and made to allow pre-ozonation of water to take place.
The concentration of ozone in the chamber was determined using the Indigo method. For the
duration of one year, water samples were collected from four different sampling sites and analyzed
to determine their overall ecological status with regard to several variables such as pH, chlorophyll-a,
SAC254, turbidity, DOC, algal species composition and sum of NOM. Two dams sites and two
riverine sites were chosen, Hartbeespoort Dam (a hyper-eutrophic impoundment), Boskop Dam (a
mesotrophic impoundment), Midvaal Water Company at Orkney and Sedibeng Water at Bothaville.
The samples were treated in Jar Tests with FeCI3 and the same variables were measured. Preozonation
followed by Jar Tests was performed on each sample at twoconcentrations of ozone and
the variables were measured to examine the efficiency of ozonation.
In general, the ph was high and stayed the same for all the samples and for all the treatments.
DOC was variable and showed no relationship to any other variable or to the treatments.
Hartbeespoort Dam was found to be a eutrophic impoundment characterized by high algal bloom of
the cyanobacteria Microcystis sp., Turbidity, SAC254, and the sum of NOM were lower than for the
riverine sites but higher than for Boskop Dam. The NOM constituted more intermediate molecular
weight(1MW)and low molecular weight (LMW) fractions than the riverine sites. Ozone was effective
in reducing chlorophyll-a, turbidity and SAC254 from Hartbeespoort Dam, but the presence of large
numbers of algal cells interferes with its efficiency. Release of cell-bound organics after ozonation
can lead to increases instead of decreases in these variables. Jar Test results demonstrate that
ozonation improves water quality when compared to conventional treatment although the
interference of algal cells can alter results.
Boskop Dam is a mesotrophic impoundment characterised by low productivity, low SAC254, tow
turbidity and low sum of NOM. However, it has a large portion of the LMW fraction of NOM present.
This LMW fraction affects the treatment process as this fraction is not acted upon by ozone.
Therefore it was found that ozonation did not improve the quality of the water when compared to
conventional treatment.
The two riverine sites, Midvaal and Sedibeng were similar to each other. Both sites had high algal
productivity with high chlorophyll-a values indicative of algal blooms observed at certain times.
These blooms consisted either of members of Bacillariophyceae or Chlorophyceae. High turbidity
and SAC254 was observed during the rainy season and was related to the high percentage HMW
and IMW fractions of NOM present. There was correlation between the turbidity and SAC254 of
these sites leading to the assumption that the turbidity of the river is due to the presence of HMW
humic fractions of NOM. Ozonation was effective in improving water quality with respect to turbidity,
SAC254 and chlorophyll-a removal, both on its own and after conventional treatment when
combined with a coagulant. However, the species of algae present affects ozonation as members
of Bacillariophyceae are not affected by the actions of ozone because of the presence of a silica
frustule whereas members of Chlorophyceae are easily removed by ozone.
In general, ozone acts upon the HMW and LMW fractions of NOM causing them to breakdown into
smaller fractions. Ozone has no effect on samples that have a high percentage of the LMW fraction
of NOM. This LMW fraction is more readily removed by conventional treatment than by ozonation.
The presence of large numbers of algal cells as well as the species of cells can negatively affect
the treatment process with regard to ozone. / Thesis (M. Environmental Science (Water Science))--North-West University, Potchefstroom Campus, 2007.
| Identifer | oai:union.ndltd.org:NWUBOLOKA1/oai:dspace.nwu.ac.za:10394/21 |
| Date | January 2006 |
| Creators | Carrim, Ayesha Hamid |
| Publisher | North-West University |
| Source Sets | North-West University |
| Detected Language | English |
| Type | Thesis |
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