Microbiological quality of spinach irrigated with reclaimed wastewater and roof-harvest water

Abstract

Aims: The effect of reclaimed wastewater (RCW) and roof-harvest rainwater (RHW) on the microbiological quality of irrigated spinach was investigated.

Methods and results: Spinach grown in the controlled environment chamber was irrigated by RCW, RHW or creek water (CW; control water) for 4 weeks, and then six replicate spinach samples from each treatment were collected weekly at 0 h and 24 h postirrigation. Spinach samples were analysed for populations of faecal bacterial indicators and pathogens. Bacterial populations in alternative irrigation water samples were determined by the membrane filtration technique. The RCW samples contained the highest faecal bacterial indicator populations, followed by the CW and RHW throughout the entire study. Irrigation waters containing higher populations of total and faecal coliforms did not necessarily result in higher populations of these bacteria on the irrigated spinach. Higher numbers of E. coli-positive spinach samples were reported from RCW-irrigated spinach, especially with repeated irrigation. Pathogens were not detected from any water or spinach samples.

Conclusions: Spinach irrigated with RHW did not significantly affect the populations of faecal indicator bacteria when compared with CW-irrigated spinach. Repeat irrigation with RCW is not recommended due to the increased contamination of E. coli on spinach leaves.

Significance and impact of the study: RHW may potentially be used as alternative irrigation water without deleteriously affecting the microbiological safety of the spinach.

Keywords: E. coli; microbial water quality; reclaimed water; roof water; spinach.