Irrigation water is one of the main sources of microbial contamination for produce. When irrigation water is obtained from a surface water reservoir, it is considered as a high risk for foodborne pathogen contamination, this is the case of most of the irrigation water used in the south-east production area of Spain. For this reason, water treatment is one of the most recommended mitigation options and prevention strategies of contamination for irrigation water, particularly for surface water in reservoirs.Commercial available solutions for these concerns are chemicals such as sodium hypochlorite and calcium hypochlorite, UV-C light, filtration, electrochemical disinfection and ultrasounds (US). Among these methods, chlorination is the main technology used for the removal of biohazards to disinfect irrigation water, however, the limitations of chlorine in terms of byproducts and the potential negative effect on the environment have limited its use in agricultural water. Recently, US treatments have been introduced as a greener technology based on the cavitation and sonolysis phenomenons.
Spanish scientists evaluated the disinfection capacity of two commercially available water treatment technologies (chlorine tablets at 1–2 ppm and US at 745 J/L), each one applied to a different water reservoir used to irrigate commercial growing fields of green peppers and artichokes. Correlations between physicochemical and microbial indicators were determined. The suitability of two US treatments (20 kHz: US20 and 40 kHz: US40 at a specific energy of 745 J/L) and one chlorine treatment (1–2 ppm free chlorine) was evaluated and compared to the untreated control. Five water reservoirs belonging to five commercial intensive farms were selected as representative of irrigation practices generally used in south of Europe, particularly in the southeast of Spain, one of the main vegetable producer areas in Europe.
All tested water treatments resulted in being able to reduce microbial loads, including Escherichia coli (0.5–0.6 log units), to values that were accepted in most of the recommended guidelines of good agricultural practices (≤2 log units). No significant differences were observed between total coliforms and E. coli loads in irrigation water treated with US and chlorine. All water treatments were able to reduce COD (= chemical oxygen demand) of irrigation water when compared to the untreated control. COD reductions obtained using chlorine (≥430 mg/L) and US 20 (~100 mg/L) were higher than those observed using US 40 (<50 mg/L).
The impact of the water quality on the disinfection capacity of 20 kHz US was tested in two different water reservoirs. It was found that the quality of the irrigation water significantly influences the efficacy of the ultrasound treatment. Based on the obtained results, more studies should be done to clarify the impact of the organic matter on the microbial inactivation capacity of US. Correlations between physicochemical and microbial indicators were also determined. Micro algae levels were well correlated with total coliforms and E. coli counts. Although the levels of E. coli spp. present in the untreated irrigation water were within the local E. coli criteria or some standards included in GAP guidelines (≤100 cfu/100 mL), the obtained results suggest the use of US as a potential alternative to reduce microbial risks of irrigation water.
The full study is available online at:
http://www.sciencedirect.com/science/article/pii/S0963996915300260
Source: Maria V. Villanueva, Maria C. Luna, Maria I. Gil, Ana Allende, 'Ultrasound treatments improve the microbiological quality of water reservoirs used for the irrigation of fresh produce', September 2015, Food Research International, Vol. 75, pages 140–147.
Contacts:
Ana Allende
Research Group on Quality, Safety and Bioactivity of Plant Foods, Department of Food Science and Technology, CEBAS-CSIC
Campus de Espinardo, 25, Murcia E-30100, Spain
Email: aallende@cebas.csic.es