INVESTIGATING THE EFFICACY OF MEDIUM PRESSURE UV AND HYDROGEN PEROXIDE AS ON-FARM TREATMENT METHODS TO REDUCE THE MICROBIAL LOAD OF IRRIGATION WATER

Many South African farmers are forced to use water from nearby rivers for crop irrigation, since it is the most affordable and sometimes only source of water available to them. During this research project, a baseline study was performed on a farm irrigating fresh produce with water obtained from the Eerste River. The baseline study was done over a five month period, at six preselected sampling points, to determine the microbial and physico-chemical parameters of the water so a baseline could be established to compare the results to when the ultraviolet (UV) apparatus was installed (February 2013). Aerobic colony count (ACC), total coliforms (TC) and Escherichia coli (E. coli) were tested for during the microbiological study, while the physico-chemical analysis comprised of temperature, pH, conductivity, chemical oxygen demand (COD), alkalinity and total soluble solids (TSS). The UV treatment study was also performed over a five month timeline, at eight different sampling points (original six sampling points, with additional sampling points before and after UV). The same microbiological tests were performed during the UV treatment study, but turbidity and percentage ultraviolet transmittance (% UVT) were performed additionally during physico-chemical analysis. During the baseline study ACC, TC and E. coli counts as high as 9 600 cfu.mL-1, 13 799 MPN.100 mL-1 and 2 098 MPN.100 mL-1 were isolated at the river (Sampling Point 1), respectively. While performing the UV treatment study ACC, TC and E. coli counts as high as 142 000 cfu.mL-1, 241 960 MPN.100 mL-1 and 6 867 MPN.100 mL-1 were isolated at the river, respectively. As a result it was concluded that the Eerste River was mostly unsuitable for irrigation of fresh produce that are consumed raw. The higher counts in the river, during the UV treatment study might be attributed to the increase in rainfall that occurred in the sampling months (March to July 2013). The counts as measured at the point of irrigation are considered of greater importance, since the counts present in the river might still decrease to below the guideline levels after passing through sand filters and the addition of hydrogen peroxide (current mode of treatment) or after passing through the UV in the UV treatment study. The ACC, TC and E. coli counts during the baseline study were as high as 8 800 cfu.mL-1, 24 196 MPN.100 mL-1 and 85 MPN.100 mL-1 at the point of irrigation (Sampling Point 6), respectively. After hydrogen peroxide addition average logreductions ranging between 0.65 and 1.13 were seen, but reduction was never constant. The counts at the point of irrigation remained more or less constant compared to the river due to contamination that occurred at the sand filters, making the water unsuitable for irrigation of fresh produce in terms of ACC and TC counts. In the UV treatment study ACC, TC and E. coli counts were as high as 35 000 cfu.mL-1, 10 462 MPN.100 mL-1 and 63 MPN.100 mL-1 at the point of irrigation (Sampling Point 8), respectively. Average log-reductions in the range of 0.90 to 1.25 were achieved, but it was inconsistent. After treatment with chlorine and re-sanding of the sand filters, no further contamination occurred and counts decreased to below guideline limits, making the water safe for irrigational use in terms of all of the microbiological parameters. Not only is UV Stellenbosch University https://scholar.sun.ac.za