Investigating the efficacy of medium pressure UV and hydrogen peroxide as on-farm treatment methods to reduce the microbial load of irrigation water

[摘要] ENGLISH ABSTRACT: Many South African farmers are forced to use water from nearby rivers for crop irrigation, since it isthe most affordable and sometimes only source of water available to them. During this researchproject, a baseline study was performed on a farm irrigating fresh produce with water obtainedfrom the Eerste River. The baseline study was done over a five month period, at six preselectedsampling points, to determine the microbial and physico-chemical parameters of the water so abaseline could be established to compare the results to when the ultraviolet (UV) apparatus wasinstalled (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 analysiscomprised of temperature, pH, conductivity, chemical oxygen demand (COD), alkalinity and totalsoluble solids (TSS). The UV treatment study was also performed over a five month timeline, ateight different sampling points (original six sampling points, with additional sampling points beforeand after UV). The same microbiological tests were performed during the UV treatment study, butturbidity and percentage ultraviolet transmittance (% UVT) were performed additionally duringphysico-chemical analysis.During the baseline study ACC, TC and E. coli counts as high as 9 600 cfu.mL-1, 13 799MPN.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 aresult it was concluded that the Eerste River was mostly unsuitable for irrigation of fresh producethat are consumed raw. The higher counts in the river, during the UV treatment study might beattributed 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 passingthrough sand filters and the addition of hydrogen peroxide (current mode of treatment) or afterpassing through the UV in the UV treatment study. The ACC, TC and E. coli counts during thebaseline study were as high as 8 800 cfu.mL-1, 24 196 MPN.100 mL-1 and 85 MPN.100 mL-1 at thepoint of irrigation (Sampling Point 6), respectively. After hydrogen peroxide addition average logreductionsranging 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 riverdue to contamination that occurred at the sand filters, making the water unsuitable for irrigation offresh produce in terms of ACC and TC counts. In the UV treatment study ACC, TC and E. colicounts were as high as 35 000 cfu.mL-1, 10 462 MPN.100 mL-1 and 63 MPN.100 mL-1 at the pointof irrigation (Sampling Point 8), respectively. Average log-reductions in the range of 0.90 to 1.25were achieved, but it was inconsistent. After treatment with chlorine and re-sanding of the sandfilters, no further contamination occurred and counts decreased to below guideline limits, makingthe water safe for irrigational use in terms of all of the microbiological parameters. Not only is UV treatment more effective in reducing microbiological counts than H2O2, it is also relatively lessexpensive in the long term. Hydrogen peroxide treatment of water amounts to a very high capitalexpense every month, whereas UV may seem expensive when starting up, but the monthlyoperating cost thereafter is marginally less than for H2O2.It is of great importance to farmers to find a treatment that would reduce the counts in theriver water to below the guideline limits required for safe irrigation since pathogens can be carriedover from water onto fresh produce, resulting in an increase in produce-associated foodborneoutbreaks and loss of consumer trust.

[发布机构] Stellenbosch University