Decontamination of irrigation water using a combined sand filtration and UV-C light treatment

Surface irrigation water is a food safety risk due to susceptibility to contamination and varying turbidity that affects chlorination efficacy. Effectiveness of a combined high-throughput, commercially available sand filter and UV-C system to inactivate Escherichia coli (K12, and attenuated O157:H7) in simulated irrigation water of varying turbidity and actual irrigation water was investigated. Sand filtration reduced the water turbidity from 600 nephelometric turbidity units (NTU) to 200 NTU but did not effectively filter out E. coli (K12) [<1 log colony forming units (CFU)/ml]. UV-C-induced inactivation of E. coli (attenuated O157:H7) was modeled for various levels of turbidity (0-500 NTU), and the relationship between the D value for inactivation and turbidity was found to be linear (R-2 > .97). Predicted UV treatment time to achieve 5 log reduction in water with turbidities of 100 and 300 NTU was 110 and 370 s, respectively. Validation performed with irrigation water (turbidity of 330 +/- 82 NTU) showed that sand filtration reduced turbidity to 180 +/- 57 NTU. Based on this, the duration of UV treatment required for 5 log reduction of E. coli O157:H7 was calculated (average of 237 s). Observed levels of inactivation, 4.7 +/- 0.31 log CFU/ml, were not significantly different (p > .05) from the predicted level, 5 log CFU/ml, indicating a good model fit.