Irrigation Water Disinfection Research Articles

Application of electrolysed water in the quality and safety control of fruits and vegetables: A review

SummaryFruits and vegetables (F&V) provide people with a variety of essential vitamins, antioxidants and dietary fibre, thus constituting integral components of human diet. With the surge of interest in F&V, their consumption ratio has kept increasing in recent years. Unfortunately, microorganisms and pesticide residues on the surfaces of F&V may be hazardous to humans. As an emerging technology, electrolysed water (EW) shows great application potential in reducing these hazards. EW treatment not only effectively removes microorganisms from F&V but also degrades pesticide residues on their surfaces. In addition, EW treatment affects the physiological metabolism of harvested F&V, which is conducive to maintain their sensory quality and nutritional value. This article reviews the principles of EW preparation, advantages and disadvantages, and the application of EW in F&V in the last decade, including disinfection of irrigation water, removal of pesticide residues, disinfection after harvest its effects on physicochemical parameters and enzyme activity of F&V, etc. Moreover, the combination of EW and other technology, including ozone, short‐time heat treatment, ultraviolet irradiation and ultrasound, to further improve the quality control effects of F&V is discussed.

Electrolytic Disinfection of Irrigation Water for Intensive Crop Production in Greenhouses as Demonstrated on Tomatoes (Solanum lycopersicum Mill)

Shortage of water availability and awareness of the need for sustainable resource management have generated a significant increase in the use of recycled water for irrigation and processing of crops and harvest products, respectively. As a result, irrigation systems face the challenge of neutralizing plant pathogens to reduce the risk of their dispersal and the subsequent occurrence of diseases with potentially high economic impacts. We evaluated the efficacy of an innovative electrolytic disinfection system based on potassium hypochlorite (KCLO) to inactivate major pathogens in hydroponically grown tomatoes: Fusarium oxysporum (Synder and Hans), Rizocthonia solani (Kühn), Tobacco mosaic virus (TMV) and Pepino mosaic virus (PepMV). The electrolytically derived disinfectant was prepared on-site and added to the recirculating fertigation solution once a week for 60 min in an automated manner using sensor technology at a dosage of 0.5 mg of free chlorine/L (fertigation solution at pH 6.0 ± 0.3 and ORP 780 ± 31 mV). Tomato fruit yield and pathogen dispersal were determined for 16 weeks. At the applied dosage, the disinfectant has been shown to inhibit the spread of plant pathogenic fungi and, remarkably, plant viruses in recirculating fertigation solutions. Phytotoxic effects did not occur.

Disinfection/ammonia removal from aquaculture wastewater and disinfection of irrigation water using electrochemical flow cells: A case study in Hawaii.

This field case study reports findings on disinfection/ammonia removal from aquaculture wastewater and disinfection of irrigation water carried out at an aquaculture farm and two irrigation locations in Hawaii. We used a flow cell incorporating PtRu/graphite anode and graphite cathode for the disinfection/ammonia removal from aquaculture wastewater, and a flow cell assembled with graphite plates as both anode and cathode for the disinfection of irrigation water. The removal of ammonia followed the indirect oxidation mechanism mediated by free chlorine electro-generated at the PtRu/graphite anode. Ammonia removal rate increased with the increase in NaCl concentration, applied current density, or flow rate. The disinfection of aquaculture wastewater can be readily achieved due to the presence of highly germicidal free chlorine species. The disinfection of irrigation water was realized without the addition of chemicals. The disinfection mechanism was attributed to the formation of free chlorine from the anodic oxidation of chloride ions naturally occurring in the water sources. The disinfection efficiency decreased with increasing organic matter concentration. In addition to the flow cell approach, we also successfully demonstrated the disinfection of irrigation water by adding electrolyzed NaCl solution or purging with a mixture of air and chlorine gas, both of which were generated on-site. PRACTITIONER POINTS: Field case study on disinfection/ammonia removal from aquaculture wastewater and disinfection of irrigation water was carried out in Hawaii. Electrochemical flow cell assembled with PtRu/graphite anode and graphite cathode effectively removes ammonia from aquaculture wastewater. Ammonia removal proceeds via the indirect oxidation mechanism mediated by free chlorine electro-generated at the PtRu/graphite anode. Electrochemical flow cell assembled with commercial graphite electrodes enables fast disinfection of coliform bacteria and E.coli. The primary disinfection mechanism is through chlorine species electro-generated from chloride oxidation at the graphite anode.

Effect of water compounds on photo-disinfection efficacy of TiO2 NP-embedded cellulose acetate film in natural water

Abstract Photocatalysis disinfection has great potential for irrigation water disinfection to improve fresh produce safety. Titanium dioxide (TiO2) nanoparticle (NP)-embedded cellulose acetate (CA) film has shown effectiveness against Escherichia coli (E. coli) O157:H7 in water. The current study evaluated the effect of natural water compounds on the photo-disinfection efficacy of TiO2 NP-embedded CA film. Humic acid, calcium carbonate (CaCO3), and kaolin clay solutions were prepared at four concentrations, respectively. When concentration increased from 0 to 20 ml/L, inactivation of E. coli O157:H7 in humic acid, CaCO3, and kaolin clay solutions decreased from 6 log to 5, 4, and 2 log CFU/ml, respectively after 3 h treatment. Turbidity, UVT-254, water hardness, total suspended solids (TSS), and total organic carbon (TOC) of the solutions were measured. UVT-254 and turbidity had the highest correlation with the inhibition effect of water compounds on photo-disinfection efficacy. A prediction equation was developed with UVT-254 and water hardness as independent variables to predict photo-disinfection efficacy in natural water. E. coli O157:H7 decreased by 1 and 2.5 log CFU/ml in unfiltered and filtered natural creek water samples after treatment. The results from this study showed promise in the use of TiO2 NP-embedded CA film to inactivate pathogens in natural water.

Electrochemical disinfection of irrigation water with a graphite electrode flow cell.

In this work, we report experimental studies on the disinfection of irrigation water using a flow cell assembled with low-cost graphite plates as both anode and cathode. Natural irrigation waters collected from two irrigation locations (Reservoir 225 and Bott Well Pond) in Hawaii were used, and synthetic irrigation waters were prepared based on the chemical analysis of natural irrigation waters. The concentration of chloride was 10.2mg/L in the synthetic Reservoir 225 water and 6.9mg/L in the synthetic Bott Well pond water. Escherichia coli K12 ER2738 was selected as a model bacterium to evaluate the disinfection capability of the flow cell. Experiments performed in the synthetic irrigation waters showed that E.coli was inactivated by free chlorine species electro-generated from oxidation of chloride ions at the graphite anode. Complete removal of E.coli was achieved within 10min in the synthetic irrigation waters. The disinfection of the natural irrigation waters took about four times longer than the disinfection of the synthetic irrigation waters. This result is most likely due to the presence of organic matter (and possibly other oxidizable species) in the natural irrigation waters. PRACTITIONER POINTS: Electrochemical flow cell disinfects to 99.9% with commercial graphite electrodes. E.coli is removed in 10min from synthetic irrigation water by a flow cell. E.coli removal takes 4× longer in natural irrigation water. A minimum current density of ≥1mA/cm2 is required for disinfection. The primary disinfection mechanism is through chlorine generated from chloride ions.

Modular, Off-Grid Electrochemical System for Disinfection of Irrigation Water and Disinfection/Ammonia Removal from Aquaculture Wastewater

Although food supply in the United States is one of the safest in the world, there are about 48 million cases of foodborne illness and an estimated death toll of 3,000 each year due to food contamination by disease-causing bacteria (e.g., Shiga toxin-producing E. coli) or pathogens.[ 1 ] It is estimated that agricultural water is the most important route of contamination.[ 2 ] The U.S. Food and Drug Administration has established microbiological water quality criteria for irrigation and other farm uses (e.g., washing hands and produce).[ 3 ] These criteria are based on the presence of generic E. coli as indicators of the presence of fecal contamination. Similarly, disinfection and ammonia removal are two major challenges in water reuse and recycling in aquaculture and aquaponics systems, where water reuse is crucial in order to reduce water consumption and improve nutrient recycling.[ 4 ] Therefore, energy-efficient, modular, and scalable systems that can achieve disinfection and ammonia removal are of particular importance. Remote farms in particular require a system that can be integrated with renewable, off-grid energy supply.In this work, we developed electrochemical flow cells for both disinfection of irrigation water and disinfection/ammonia removal from aquaculture wastewater. Both synthetic waters and natural waters, which were collected from Hawaii, were tested and dosed with certain amounts of ammonia-nitrogen (NH3-N) and E. coli bacteria to obtain different contamination levels. For disinfection of irrigation water, graphite plates were used as both anode and cathode, and a significant disinfection effect was achieved when electric current was applied between the two electrodes. Hydrogen peroxide was detected in the solution and its concentration increased with electrolysis time. Therefore, the disinfection effect was attributable to hydrogen peroxide formed as an intermediate during oxygen reduction at the graphite cathode. For disinfection/ammonia removal from aquaculture wastewater, a PtRu/graphite electrode prepared by pulsed electrodeposition was used as the anode and a graphite plate was used as the cathode. Ammonia removal was slow in natural aquaculture water, which contains 0.66mM NaCl; however, the addition of low levels of NaCl (e.g., 5mM) can dramatically increase disinfection and ammonia removal rate. The concentration of free (HOCl, ClO-) and combined (NH2Cl, NHCl2, NCl3) chlorine was monitored during the experiment. It was found that before the complete removal of ammonia, free chlorine was not found in the solution, while during ammonia oxidation, a relatively stable concentration of combined chlorine was measured. However, after the complete removal of ammonia, combined chlorine was no longer detectable in the solution, while free chlorine appeared and its concentration increased with electrolysis time. These results indicate an active chlorine-mediated ammonia oxidation mechanism.[ 5 ] In this mechanism, chloride ions were oxidized at the anode to form free chlorine, which reacts with ammonia (or ammonium) to form combined chlorine. With more free chlorine being produced at the anode, the combined chlorine was further oxidized to nitrogen gas until the complete removal of both ammonia and combined chlorine. Another finding is that the solution’s pH decreased until the complete removal of ammonia, and then increased with electrolysis time. Therefore, pH could be used as an indicator for determining complete ammonia removal. More experimental findings, including monitoring the concentrations of nitrate, chlorate, and disinfection byproducts, and field demonstration tests in Hawaii, will be presented. An economical assessment of the flow cell system will also be discussed.

Disinfection options for irrigation water: Reducing the risk of fresh produce contamination with human pathogens

The growing health and economic burden posed by foodborne pathogens has stimulated global interest in the development of safe, affordable, effective and environmentally-sustainable irrigation water treatment technologies. This review critically compares the potential of existing and emerging methods for disinfection of irrigation water to reduce pathogenic microbial loads on high-risk vegetables and minimally processed fresh produce. We explore electrochemical disinfection and electrolyzed oxidizing water as alternatives to traditional chlorination, and identify hydrodynamic cavitation as an emerging disinfection strategy worthy of further investigation in this context. In addition, we assess the state of the knowledge regarding the impact of current water sanitation strategies on the ecological dynamics of plant and soil microbes and the potential induction of viable but nonculturable cells. Increased research in these areas could translate into substantial improvement in the overall quality and value of fresh produce, while maintaining environmentally-sustainable irrigation water usage.

Comparative antibacterial activities of neutral electrolyzed oxidizing water and other chlorine-based sanitizers

There is increasing demand for safe and effective sanitizers for irrigation water disinfection to prevent transmission of foodborne pathogens to fresh produce. Here we compared the efficacy of pH-neutral electrolyzed oxidizing water (EOW), sodium hypochlorite (NaClO) and chlorine dioxide (ClO2) against single and mixed populations of E. coli, Listeria and Salmonella under a range of pH and organic matter content. EOW treatment of the mixed bacterial suspension resulted in a dose-dependent (<1 mg/L free chlorine), rapid (<2 min) and effective (4–6 Log10) reduction of the microbial load in water devoid of organic matter under the range of pH conditions tested (pH, 6.0, 7.0, 8.4 and 9.2). The efficacy of EOW containing 5 mg/L free chlorine was unaffected by increasing organic matter, and compared favourably with equivalent concentrations of NaClO and ClO2. EOW at 20 mg/L free chlorine was more effective than NaClO and ClO2 in reducing bacterial populations in the presence of high (20–100 mg/L) dissolved organic carbon, and no regrowth or metabolic activity was observed for EOW-treated bacteria at this concentration upon reculturing in rich media. Thus, EOW is as effective or more effective than other common chlorine-based sanitizers for pathogen reduction in contaminated water. EOW’s other characteristics, such as neutral pH and ease of handling, indicate its suitability for fresh produce sanitation.

Tomato Crop Improvement Using Ozone Disinfection of Irrigation Water

ABSTRACTPlant–parasitic nematodes diminish the yield of tomato crops worldwide. Irrigation water may be contaminated with such parasites, including Meloidogyne enterolobii. In this study, ozone treatment was applied to inactivate M. enterolobii eggs. Eggs were rendered inviable in water after exposure to 0.55 mgO3 L−1 ozone residual for 15 min. Additionally, the effect of temperature, alkalinity, and organic matter of the water were evaluated. The results showed that ozonation is an effective and promising alternative method for nematode control in irrigation water, which could reduce tomato crop infestation caused by plant–parasitic nematodes.

Impact of weather conditions, leaf age and irrigation water disinfection on the major epiphytic bacterial genera of baby spinach grown in an open field

The effects of factors such as weather conditions, leaf age and irrigation water disinfection on the main bacterial genera (total bacterial, Enterobacteriaceae and Pseudomonas) of baby spinach were studied. Culture-dependent and independent quantification techniques were compared. Cultivation was carried out over two consecutive trials in commercial open field divided in two plots: 1) baby spinach irrigated with untreated surface water and 2) baby spinach irrigated with chlorine dioxide (ClO2) treated water. In all the cases, higher concentrations of bacteria were detected using molecular quantification in comparison with culture dependent techniques. Based on the obtained results, wind speed, solar radiation and relative humidity seem to have an impact on the levels of total bacterial, Enterobacteriaceae and Pseudomonas during cultivation of baby spinach. However, further studies would be needed to confirm this tendency. Water disinfection treatments (ClO2), when applied to irrigation water, impacted differently the bacterial genera evaluated in the present study. Thus, although no significant effects were observed in total bacterial enumerations of baby spinach irrigated with ClO2 treated water; significant reductions were detected in Enterobacteriaceae (19%) and Pseudomonas spp. (14%) levels. These results were also confirmed using specific culture-dependent methods. On the other hand, leaf age did not influence the levels of the main bacterial genera of baby spinach. Considering that, a large proportion of foodborne and pathogenic bacteria associated to fresh produce belong to the Enterobacteriaceae family and Pseudomonas genera, reductions in these bacterial groups could be beneficial. However, these groups are very diverse, making difficult to link the measurement of Enterobacteriaceae and Pseudomonas levels with the presence/abundance of potential pathogenic and spoilage microorganisms.

Impact of chlorine dioxide disinfection of irrigation water on the epiphytic bacterial community of baby spinach and underlying soil.

The contamination of pathogenic bacteria through irrigation water is a recognized risk factor for fresh produce. Irrigation water disinfection is an intervention strategy that could be applied to reduce the probability of microbiological contamination of crops. Disinfection treatments should be applied ensuring minimum effective doses, which are efficient in inhibiting the microbial contamination while avoiding formation and accumulation of chemical residues. Among disinfection technologies available for growers, chlorine dioxide (ClO2) represents, after sodium hypochlorite, an alternative disinfection treatment, which is commercially applied by growers in the USA and Spain. However, in most of the cases, the suitability of this treatment has been tested against pathogenic bacteria and low attention have been given to the impact of chemical residues on the bacterial community of the vegetable tissue. The aim of this study was to (i) to evaluate the continual application of chlorine dioxide (ClO2) as a water disinfection treatment of irrigation water during baby spinach growth in commercial production open fields, and (ii) to determine the subsequent impact of these treatments on the bacterial communities in water, soil, and baby spinach. To gain insight into the changes in the bacterial community elicited by ClO2, samples of treated and untreated irrigation water as well as the irrigated soil and baby spinach were analyzed using Miseq® Illumina sequencing platform. Next generation sequencing and multivariate statistical analysis revealed that ClO2 treatment of irrigation water did not affect the diversity of the bacterial community of water, soil and crop, but significant differences were observed in the relative abundance of specific bacterial genera. This demonstrates the different susceptibility of the bacteria genera to the ClO2 treatment. Based on the obtained results it can be concluded that the phyllosphere bacterial community of baby spinach was more influenced by the soil bacteria community rather than that of irrigation water. In the case of baby spinach, the use of low residual ClO2 concentrations (approx. 0.25 mg/L) to treat irrigation water decreased the relative abundance of Pseudomonaceae (2.28-fold) and Enterobacteriaceae (2.5-fold) when comparing treated versus untreated baby spinach. Members of these two bacterial families are responsible for food spoilage and foodborne illnesses. Therefore, a reduction of these bacterial families might be beneficial for the crop and for food safety. In general it can be concluded that the constant application of ClO2 as a disinfection treatment for irrigation water only caused changes in two bacterial families of the baby spinach and soil microbiota, without affecting the major phyla and classes. The significance of these changes in the bacterial community should be further evaluated.

Disinfection by-products in baby lettuce irrigated with electrolysed water.

Irrigation water disinfection reduces the microbial load but it might lead to the formation and accumulation of disinfection by-products (DBPs) in the crop. If DBPs are present in the irrigation water, they can accumulate in the crop, particularly after the regrowth, and be affected by the postharvest handling such as washing and storage. To evaluate the potential accumulation of DBPs, baby lettuce was grown using irrigation water treated with electrolysed water (EW) in a commercial greenhouse over three consecutive harvests and regrowths. The impact of postharvest practices such as washing and storage on DBP content was also assessed. Use of EW caused the accumulation of chlorates in irrigation water (0.02-0.14 mg L-1 ), and in the fresh produce (0.05-0.10 mg kg-1 ). On the other hand, the disinfection treatment had minor impact regarding the presence of trihalomethanes (THMs) in water (0.3-8.7 μg L-1 max), and in baby lettuce (0.3-2.9 μg kg-1 max). Disinfection of irrigation water with EW caused the accumulation of chlorates in the crop reaching levels higher than the current maximum residual limit established in the EU legislation for leafy greens. © 2017 Society of Chemical Industry.

Demonstration tests of irrigation water disinfection with chlorine dioxide in open field cultivation of baby spinach

Treatments for the disinfection of irrigation water have to be evaluated by demonstration tests carried out under commercial settings taking into account not only their antimicrobial activity but also the potential phytotoxic effects on the crop. The consequences of the treatment of irrigation water with chlorine dioxide (ClO2 ) used for sprinkler irrigation of baby spinach in two commercial agricultural fields was assessed. Residual ClO2 levels at the sprinklers in the treated field were always below 1 mg L-1 . ClO2 treatment provoked limited but statistically significant reductions in culturable Escherichia coli counts (0.2-0.3 log reductions), but not in the viable E. coli counts in water, suggesting the presence of viable but non-culturable cells (VBNC). Although disinfected irrigation water did not have an impact on the microbial loads of Enterobacteriaceae nor on the quality characteristics of baby spinach, it caused the accumulation of chlorates (up to 0.99 mg kg-1 in plants) and the reduction of the photosynthetic efficiency of baby spinach. Low concentrations of ClO2 are effective in reducing the culturable E. coli present in irrigation water but it might induce the VBNC state. Presence of disinfection by-products and their accumulation in the crop must be considered to adjust doses in order to avoid crop damage and chemical safety risks. © 2017 Society of Chemical Industry.

Alternative methods of microorganism disruption for agricultural applications

This paper reviews various non-conventional techniques for microorganism disruption. Microorganism disruption plays a pivotal role in various agricultural applications such as disinfection of irrigation water, processing of crops and livestock products and the newly emerging area of bioenergy production for agricultural uses. Methods of treatment to destroy microorganisms for the purposes of disinfection or extraction of bio-products can be generally categorized as either thermal treatment methods or non-thermal treatment methods. The thermal methods for microbial disruption are not favorable in many applications such as food processing and water treatment due to its negative impact on product quality and process performance. The discussion of thermal methods for microorganism disruption will not be included in this review. Non-thermal treatments are divided into two groups; chemical and physical treatments. Owing to the concerns of the health organisations with regards to the use of chemical methods for microorganism disruption, the recent research efforts have been directed towards exploring alternative physical methods for rupturing microorganisms. The common alternative physical methods for microorganism disruption include mechanical and non-mechanical treatments. This paper discusses in details the use of the common mechanical treatments for cell disintegration. Such methods include ultrasound, shock wave, High Pressure Homogenization (HPH), Hydrodynamic Cavitation (HC), shear stress, bead milling and micro-fluidizer. The application of the non-mechanical methods for microbial disruption such as electrical treatment, non-thermal plasma, Ultra-Violet (UV), non-conventional chemical methods and some other treatments are also briefly addressed in this paper. Due to the importance of the mechanical methods in the current cell disruption research, more attention is directed to these methods in this work.

Resistance of Fusarium sp spores to solar TiO2 photocatalysis: influence of spore type and water (scaling‐up results)

AbstractBACKGROUND: Common irrigation water disinfection methods, which may be unable to inactivate all types of pathogens or even become phytotoxic themselves, are not very effective in controlling phytopathogens. Water disinfection by photocatalysis is a promising irrigation‐water treatment for destroying phytopathogens without the drawbacks of conventional disinfection methods. Previous research has shown that solar photocatalytic technology can be used in the disinfection treatment of bacteria, protozoa and fungi, either through solar disinfection only. The purpose of this work was evaluate the TiO2 photocatalysis process to inactivate Fusarium spores in distilled and well water.RESULTS: This paper reports on the ability of solar photocatalysis to inactivate Fusarium spores in a solar bottle reactor and in a new 60 L compound parabolic collector (CPC) prototype reactor. Inactivation of Fusarium sp spores by titanium dioxide (Degussa P25) was evaluated in distilled and natural well water. The experiments were carried out using 5 or 6 h exposure to natural sunlight at the Plataforma Solar de Almeria (Southeast Spain). The highest Fusarium spore inactivation rate during experiments was achieved with a 30 L min−1 flow rate and 100 mg L−1 TiO2 concentration. Three different Fusarium spores (microconidia, macroconidia and chlamydospores) were individually evaluated to determine whether there were differences in resistance to the photocatalytic treatment. The results showed that chlamydospores were the most resistant, followed by macroconidia, and finally microconidia were the most sensitive.CONCLUSIONS: Microconidia, macroconidia and chlamydospores in distilled and well water were inactivated with TiO2 slurry in a 60 L CPC photoreactor, demonstrating for the first time that it is possible to scale‐up photocatalytic treatment for use and reuse of water for irrigation. Copyright © 2010 Society of Chemical Industry

Towards In-Channel Irrigation Water Disinfection Using Solar Photocatalysis

The irrigation water used by Chilean producers must fulfill both national and international quality standards. However, producers are constantly facing microbiological quality problems in the irrigation water, mainly fecal bacteria in the irrigation channel network. Photocatalysis using titanium dioxide (TiO2) activated by solar radiation is an alternative to conventional water detoxification and disinfection technologies. Many publications show that this technique is effective, harmless, and has a low cost, but there are no reported applications for agricultural waters. The main focus of this research is the application of heterogeneous solar photocatalysis to decrease the microbiological load in irrigation water using a photocatalyst (TiO2) activated by sunlight UV radiation and supported in concrete mortar that could be used as a channel's lining. Laboratory tests were made in static reactors of low volume, in addition to tests done in controlled conditions of operation in a prototype channel of 104 meters in length. Low volume tests showed up to 100% removal for Escherichia Coli ATTCC 25922, with cumulative radiation energy of 1500 J/L, which allow the fulfillment of irrigation water quality standards. For the prototype channel, removal was 85% at 50 m and 90% at the end of the channel. These preliminary results indicate that the use of this technology in the irrigation water disinfection is feasible and low cost. Nevertheless, it is necessary to advance in the development of a design methodology for real-scale applications in a Good Agricultural Practices framework