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

Authors: HSIN-BAI, YIN - UNIVERSITY OF MARYLAND; Nou, Xiangwu; Patel, Jitu; GU, GANYU - VIRGINIA TECH

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2018
Publication Date: 2/25/2018
Citation: Hsin-Bai, Y., Nou, X., Patel, J.R., Gu, G. 2018. Microbiological quality of spinach irrigated with reclaimed wastewater and roof-harvest water. Journal of Applied Microbiology. 125:133-141. https://doi.org/10.1111/jam.13746.
DOI: https://doi.org/10.1111/jam.13746

Interpretive Summary: Water scarcity is becoming a serious issue due to climate change and increasing urbanization, and poses significant risks to global food security. The use of alternative water such as wastewater and roof-harvested water has been considered as a potential approach to overcome the water scarcity as an environmentally sustainable practice for maintaining agricultural productivity and security of food supplies. We investigated microbial quality of spinach irrigated with reclaimed wastewater (RCW) and roof-harvest rainwater (RHW) to determine presence of fecal and pathogenic bacteria on spinach leaves. The RCW contained highest fecal bacteria indicators, followed by CW and RHW throughout the entire study. Spinach irrigated with these waters were free from pathogens: Salmonella, Listeria monocytogenes, or E. coli O157:H7. Total and fecal coliforms were detected in all spinach samples; however, irrigation water samples containing higher populations of total and fecal coliforms did not necessary result in higher populations of these bacteria in the irrigated spinach. Spinach irrigated with RHW did not significantly affect the populations of fecal indicator bacteria when compared to CW-irrigated spinach; however, the RCW may not be recommended to be used as irrigation water for fresh produce due to the high populations of the E. coli that exceeded the limit of FSMA regulation for fresh produce irrigation. The research helps produce growers in utilizing alternative water sources for irrigation of fresh produce.

Technical Abstract: Aims: The effect of reclaimed wastewater (RCW) and roof-harvest rainwater (RHW) on microbiological quality of irrigated spinach was investigated. Methods and Results: Spinach grown in controlled environment chamber was irrigated by RCW, RHW, or creek water (CW; control water) for four weeks, and then six replicate spinach samples from each treatment were assessed weekly at 0 h and 24 h post-irrigation. Spinach samples were analyzed for populations of fecal bacteria indicators and pathogenic bacteria. Bacterial populations in alternative irrigation water samples were assessed by membrane filtration technique. The RCW contained highest fecal bacteria indicators, followed by CW and RHW throughout the entire study. Total and fecal coliforms were detected in all spinach samples; however, irrigation water samples containing higher populations of total and fecal coliforms did not necessary result in higher populations of these bacteria in the irrigated spinach. Conclusions: Spinach irrigated with RHW did not significantly affect the populations of fecal indicator bacteria when compared to CW-irrigated spinach; however, RCW irrigation resulted in higher E. coli positive spinach samples than other water sources. Significance and Impact of the Study: RHW may potentially be used as alternative irrigation water without deleteriously affecting the microbiological safety of the spinach.