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To the background of discussions on problematical residues in plant-derived foods, the procedure for minimising chlorate content in the electrolytic disinfection of irrigation water is of great importance. As a source of adjustment recommendations was investigated, on the basis of a brine electrolysis plant (single chamber system), how much chlorate is produced during the electrochemical production procedure for the disinfectant solution and how its proportion changes during storage under warm greenhouse conditions. Investigated additionally was the effect the plant fertiliser ammonia has on disinfectant substances. Consequently, minimising chlorate in the electrolytic water disinfection could be achieved by using a cooling system for the electrolysis reactor and the disinfectant storage tank. Additionally recommended is a short term storage tank for the disinfectant solution. Regarding dosage of disinfectant solution, it was shown that ammonia markedly increases usage of disinfectant or chlorate input into the irrigation water. It is therefore recommended that dosage be controlled by chlorine sensor so that alterations of chemical processes in water (e.g. chlorine loss) can be accounted.
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LANDTECHNIK 71(2), 2016, 25–33
Minimising chlorate in the electrolytic
disinfection of irrigation water
Ingo Schuch, Dennis Dannehl, Martina Bandte, Johanna Suhl, Yuan Gao, Uwe Schmidt
To the background of discussions on problematical residues in plant-derived foods, the pro-
cedure for minimising chlorate content in the electrolytic disinfection of irrigation water is of
great importance. As a source of adjustment recommendations was investigated, on the basis
of a brine electrolysis plant (single chamber system), how much chlorate is produced during
the electrochemical production procedure for the disinfectant solution and how its proportion
changes during storage under warm greenhouse conditions. Investigated additionally was the
effect the plant fertiliser ammonia has on disinfectant substances. Consequently, minimising
chlorate in the electrolytic water disinfection could be achieved by using a cooling system
for the electrolysis reactor and the disinfectant storage tank. Additionally recommended is a
short term storage tank for the disinfectant solution. Regarding dosage of disinfectant solu-
tion, it was shown that ammonia markedly increases usage of disinfectant or chlorate input
into the irrigation water. Thus, it is recommended that dosage is controlled by chlorine sensor
so that alterations of chemical processes in water (e.g. chlorine loss) can be accounted.
Keywords
Water disinfection, brine electrolysis, hypochlorite, chlorate, chlorine loss
Where using surface water (esp. stored rainwater) for irrigation, and re-using surplus irrigation wa-
ter (esp. in closed systems), the risk of spreading waterborne phytopathogens is increased (Sally
2011). For this reason, there already exist several procedures for water disinfection that, in principal,
are suitable for plant production. Hereby, we differentiate between physical disinfection procedures
(heat, UV radiation, filtration) and chemical procedures (ozone, hydrogen peroxide, copper/silver
ions, chlorine dioxide, chlorine) (Van OS 2010). Compared with the physical procedures, the chemical
procedures have the advantage of potential efficacy within the entire irrigation system and can thus
prevent disease spread from plant to plant (WOhanka et al. 2015).
However, problematical with chemical disinfection procedures is possible accumulation of unde-
sirable by-products in the water or in the plants cultivated with the help of this water, or in plant parts
washed by it. Thus, a comprehensive study with 1020 samples of plant-based foods showed that with
around 10 % of the samples, ≥ 0.01 mg chlorate (ClO3) per kg of food was detectable (kaufmann-hOr-
lacher 2014). Chlorates (e. g. sodium chlorate or potassium chlorate) were used as non-selective her-
bicides. Since 2010, these chemicals are no longer approved as herbicides within the European Union
(eurOpean cOmmiSSiOn 2008). Additionally, chlorate can cause damage to red blood cells and inhibit io-
dine uptake by humans (Bfr 2014). For this reason, the European Food Safety Authority published a
preliminary review of chlorate threshold values in food, based on an acute reference dose of 0.036 mg
per kg bodyweight and day (efSa 2015). The toxicological risk assessment is ongoing because the
knowledge collected up until now is not enough to support a conclusive health-based evaluation.
received 19 October 2015 | accepted 3 February 2016| published 4 March 2016
© 2016 by the authors. This is an open access article distributed under the terms and conditions of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/4.0).
DOI:10.15150/lt.2016.3119
landtechnik 71(2), 2016 26
As to how chlorate arrives in the food, among the reasons considered are application of chlorinated
irrigation and washing water in pre- and post-harvest periods (kaufmann-hOrlacher 2014). There is
already evidence in this respect that circulating irrigation water (NFT technique) with a chlorine dis-
infection using electrolytically produced hypochlorite (ClO) can lead to concentration of chlorate in
tomatoes (Dannehl et al. 2015a). The disinfection procedure applicable can feature application of com-
mercially available chlorine bleach liquor (sodium hypochlorite) delivered in barrels, as well as dis-
infectant substances produced via on-site systems. Hereby, the latter, so-called electrolysis systems,
have so far been mainly used for treatment of drinking and pool water (DygutSch and kramer 2012).
From salt (e. g. NaCl) water and electrical current is hereby produced a hypochlorite-content disin-
fectant solution with the necessary energy delivered into the brine (electrolyte or sole) via electrodes
(anode and cathode). During the resultant material conversion (redox reaction), electrons (e) are
transferred, whereby those from negatively charged ions (chloride) are deposited on the anode side
(Eq. 1), and those from positively charged ions or neutral substances (water) are received on the cath-
ode side (Eq. 2). Finally (Eq. 3), hydroxide (OH-) and chlorine (Cl2) react to give hypochlorite (ClO)
and chloride (Cl-).
2 Cl Cl2 + 2 e (Eq. 1)
2 H2O + 2 e 2 OH + H2 (Eq. 2)
2 OH + Cl2ClO + Cl + H2O (Eq. 3)
In the context of brine electrolysis, two different chlorine compounds can be formed, depending
on pH value of the water to be disinfected: hypochlorite (ClO) or hypochlorous acid (HClO). Both are,
however, designated as free chlorine (clark and SmajStrla 1992). The related dissociation reaction is
reversible (Eq. 4). Hereby, the hypochlorite proportion reduces as the hypochlorous acid proportion
increases, and vice versa. Furthermore, at pH < 6 the hypochlorous acid (HClO) has a high disinfec-
tion efficacy, and from pH > 6 the hypochlorite (ClO) increasingly has a reduced disinfection efficacy.
From a pH > 7.5 the disinfection effect is regarded as insufficient (meBalDS et al. 1996).
ClO + H+ HClO (Eq. 4)
In an aqueous solution the disproportionation of three parts hypochlorite (ClO) occurs in a multi-
stage reaction to one part chlorate (ClO3-) and two parts chloride (Cl). The overall reaction is given
by equation 5. This process is accelerated, especially through high hypochlorite concentrations, UV
radiation and heat (Strähle 1999, gaBriO et al. 2004). Additionally, even during the electrochemical
production of the solution, the reactions taking place through application of heat can produce a chlo-
rate content of 2 to 8 % (DygutSch and kramer 2012).
3 ClO ClO3 + 2 Cl (Eq. 5)
landtechnik 71(2), 2016 27
The water to be disinfected can be different according to its proposed use and its chemical param-
eters. Thus, circulating nutritional solutions for hydroponic vegetable crops such as tomatoes or cu-
cumbers, with 18 mg ammonia per litre (SOnneVelD and StraVer 1988) contains a much higher concen-
tration of plant nutrients compared to drinking water with < 0.05 mg ammonia per litre (BWB 2015).
Additionally, the nitrogen fertiliser ammonia (NH4+) increases the chlorine loss in the water and
oxidises with hypochlorous acid (HClO) in several partial steps, at first to chloramine (bound chlorine)
with reduced antimicrobial efficacy (uS natiOnal reSearch cOuncil 1987), then to nitrite and finally
further to nitrate (NO3-) (Bryant et al. 1992) which is a nitrogen source readily available to plants.
Hereby, 1 mg of ammonia nitrogen (NH4-N) binds around 10 mg of hypochlorous acid measurable as
free chlorine (WOhanka et al. 2015). The overall reaction is given by equation 6.
4 HClO + NH4+ NO3 + H2O + 6 H+ + 4 Cl (Eq. 6)
Focus of this paper is the procedural adaptation of the electrolysis technique, up until now mainly
applied for disinfection of drinking and pool water, for use as disinfectant in irrigation water (esp. in
closed irrigation systems). As a source of adjustment recommendations was investigated, on the basis
of a brine electrolysis plant (single chamber system), how much problematical chlorate is produced
during the production procedure for the disinfectant and how its proportion changes during storage
under warm greenhouse conditions (summer season). Investigated additionally was the effect the
plant fertiliser ammonia has on average disinfectant requirement, or chlorate input into the irrigation
water.
Materials and methods
Featured in the investigation is a single chamber brine electrolysis plant (nt-BlueBox mini nt-CLE,
newtec Umwelttechnik GmbH, Berlin, Germany) used for on-site disinfectant solution production in
the experimental greenhouse of the Humboldt University at Campus Berlin Dahlem.
Brine electrolysis
During the electrochemical procedure for production of the disinfectant solution in an electrolysis
reactor (Figure 1, C: single chamber system without membrane) a 3.5 % brine solution (sole) was
subjected to a redox reaction for a 15 minute period through application of an electrical direct current
(≈ 9 A) at a low voltage range (≈ 13 V). The brine solution (Figure 1, B) contained potassium chloride
(KCl ≥ 99,5 %, p. a., ACS, ISO, Carl Roth GmbH + Co. KG, Karlsruhe, Germany). Because this was
produced from the domestic water supply (≈ 16 °dH) the plant is equipped with an water softener
(Figure 1, A) to avoid lime deposition on the titanium coated electrodes. Disinfectant solution was
stored in a reserve tank (Figure 1, D) with content volume sensor. During withdrawal of the disin-
fectant solution (e. g. through a dosage system) this regulated the automatic refilling of the tank up to
a predetermined volume. The functioning of the brine electrolysis system was based on two patents
belonging to the plant constructor (gaO et al. 1997, gaO 2010).
landtechnik 71(2), 2016 28
Analysis of chlorate formation
To determine the influence of the length of time in storage on the chlorine and chlorate content of the
disinfectant solution under warm greenhouse conditions (summer season), this was stored after elec-
trolytically production for four weeks (August 2014) in the greenhouse. Hereby, it was assumed that
the average day temperature of the disinfectant solution was the same as the daily average air tem-
perature recorded at five-minute intervals within the greenhouse. Supplementing this, the set points
(day/night) of the heating temperature were 17/20 °C and ventilation air temperature was 24/24 °C.
The temperature recording in the greenhouse took place at 2 m height with a radiation-protected and
ventilated climate recorder (P-TF-30, Positronik, Au in der Hallertau, Germany). The determination
of free chlorine (Cl2) in the disinfectant solution took place at the beginning (n = 4, double sample
analysis), as well as at the end of storage via DPD method (cleScerl et al. 1999) and photometer (Pock-
et Colorimeter II, Hach Lange GmbH, Düsseldorf/Berlin, Germany). Similarly, chlorate recording was
via QuPPe method (anaStaSSiaDeS et al. 2013) and liquid chromatography coupled to mass spectro-
metry (1290 Infinity LC und 6460 Triple Quadrupole MS/MS, Agilent Technologies GmbH, Wald-
bronn, Germany).
Analysis of chlorine loss
In order to quantify the influence of ammonia on the chlorine loss in the irrigation water, a nutrient
solution with an ammonia content of 10 mg/l (± 0.5 mg/l) and a pH of 6 was produced (n = 2). For this
purpose, drinking water and rainwater (50 %/50 %) was dunged with a basic solution for hydroponic
crops (SOnneVelD anD StraVer 1988) and acidified with phosphoric acid (3 % H3PO4). Hereby, ammo-
nia content was recorded via Nessler method (hanna inStrumentS inc. 2010) as well as photometer
(HI 96733, Hanna Instruments GmbH, Vöhringen, Germany) and pH measurement via multi-parame-
ter meter (HI 9811, Hanna Instruments GmbH, Vöhringen, Germany). In conclusion, the disinfectant
solution was added to the nutrient solution in concentration steps of 5, 10, 50, 75 and 100 mg free
Figure 1: Brine electrolysis plant equipped with water softener (A), sole storage tank (B), electrolysis reactor (C),
disinfectant storage tank (D) and control module (E) (Photo: I. Schuch)
landtechnik 71(2), 2016 29
chlorine/l, so that after 10 minutes reaction time, the remaining free chlorine could be recorded us-
ing the DPD method (cleScerl et al. 1999) and photometer (Pocket Colorimeter II, Hach Lange GmbH,
Düsseldorf/Berlin, Germany). Similarly, comparisons were made with drinking water and an ammo-
nia content of < 0.05 mg/l (BWB 2015). All recording featured double sample analysis.
Results and discussion
The example of single chamber electrolysis plant used produced a disinfectant solution with an aver-
age free chlorine concentration of 4872 mg/l (± 612 mg/l) and 197 mg/l (± 154 mg/l) of chlorate (Fig-
ure 2), representing a limited chlorate proportion of around 4 % (based on the free chlorine). Hereby,
the chlorate formation was possibly attributable to the endothermic production process within the
electrolysis reactor (Strähle 1999, gaBriO et al. 2004). In comparison, similar plants show a chlorate
proportion of 2 to 8 % (DygutSch anD kramer 2012). After four weeks storage (summer season), the dis-
infectant solution in the greenhouse with a storage temperature averaging 22.4 °C in total, ranging
from 20.5 to 25.6 °C daily average (minimum 17 °C nights and 34.6 °C days according to the funda-
mental single measurements), showed a greater temperature divergence (ΔT = 17.6 K). The content of
free chlorine had decreased by almost 50 % to 2500 mg/l (± 375 mg/l). At the same time, the chlorate
content increased to 1412 mg/l (± 212 mg/l) (Figure 2). This represented a high chlorate proportion of
around 56 % (based on the free chlorine). This result should be checked for reproducibility and should
also be supplemented by results from experiments with storage at lower temperature fluctuations in
the greenhouse (e. g. winter season), as well as by any evidence of further by-products from the pro-
cedure such as chlorite (ClO2) and perchlorate (ClO4).
Figure 2: Influence of the length of time in storage on the free chlorine and chlorate content of the electrolytically
produced disinfectant solution under warm greenhouse conditions (summer season, Tmax = 34.6 °C); Mean values
(n = 4) with standard deviation (±) of the free chlorine and chlorate content in the disinfectant solution after produc-
tion (blue bars) and after 4 weeks storage (red bars)
landtechnik 71(2), 2016 30
According to the recordings, using fresh disinfectant solution and an antimicrobial dosage of 1 mg
free chlorine/l (clark and SmajStrla 1992) enables an arithmetical result of around 0.04 mg chlo-
rate/l (± 0.03 mg/l) in treated irrigation water to be reached. Hereby, increasing or decreasing the
disinfectant dose would influence the chlorate input to the same extent. On the other hand, should
the disinfectant solution be stored for four weeks in the greenhouse (summer season) whereby the
typical warm season temperature fluctuations occur within the greenhouse between day and night,
the chlorate input would rise, on an arithmetic basis using the given disinfectant dosage, to 0.56 mg/l
(± 0.08 mg/l).
The measured chlorine loss indicates a marked difference between the water with/without am-
monia. Thus, as opposed to drinking water (< 0.05 mg NH4+/l), in which the free chlorine was quite
near the dosage applied (Figure 3, blue line), in irrigation water (10 ± 0.5 mg NH4+/l) a rise in free
chlorine did not take place until the chlorine loss limit was reached (Figure 3, red dashed line). In this
respect, it is possible to deduce with the help of a regression line (Figure 3, red dotted line) supported
by the parallelism for recording without ammonia, a loss ratio of ammonia to chlorine of around 1 : 7
(after 10 min reaction time). This is under the result of 1 : 10 for ammonia-nitrogen (WOhanka et al.
2015) (without given reaction time). Hereby, we can assume that the period of time between chlorine
addition and sampling influenced the measured value. Thus, chlorine loss measurements need to be
supplemented with further reaction times (e.g. after 5, 20 and 30 min).
Figure 3: Chlorine loss, 10 min after dosage, in drinking water without ammonia (blue line) and irrigation water
with ammonia (red dashed line); Calculation of the chlorine loss limit (red dotted line) for chlorine dosage of 75 and
100 mg/l; Mean values (n = 2) with standard deviation (±) of free chlorine
landtechnik 71(2), 2016 31
Chloramine (bound chlorine) is produced during reactions between chlorine and ammonia. In
comparison with free chlorine this, however, has reduced antimicrobial efficacy (uS natiOnal re-
Search cOuncil 1987), although a longer half-life period whereby the chloramine decomposition under
UV radiation reached a maximum of 0.2 mg/l h (White 1992). Over and above this, the readily avail-
able nitrogen source for plants, nitrate (NO3-), can be produced from chloramine under nitrification
conditions (Bryant et al. 1992). In this respect, it can be assumed that continuous chlorination brings
the fundamental microbiological degradation process (nitrification) to a standstill more rapidly than
a discontinuous/sporadic disinfection of irrigation water.
With regard to the investigated loss ratio of ammonia to chlorine under nutrient recommendations
for tomato/cucumber irrigation of 18 mg NH4+/l (SOnneVelD and StraVer 1988) and a reference value
in irrigation water of 1 mg free chlorine/l, an increased requirement for disinfectant solution to the
factor of 126 (based on a chlorine loss ratio 1 : 7) is to be expected. The chlorate input in irrigation
water would be influenced to the same extent, whereby not a lot is known about chlorate uptake
by plants. Official food surveillance shows, however, that relatively high chlorate contents, e. g. in
tomatoes (0.2 mg/kg) and carrots (0.3 mg/kg), can occur (kaufmann-hOrlacher 2014). Hereby, it has
been proved in the meantime that the electrolytic disinfection of irrigation water can lead to chlo-
rate absorption by vegetables. In the corresponding study (Dannehl et al. 2015a), tomato plants were
continuously irrigated within a closed circuit on plastic channels (NFT) with a disinfectant solution
produced on site and dosed discontinuously over a period of three months (1/week for 90 min) in
concentrations of 1 mg (variant DI) or 2 mg free chlorine/l (variant DII) in fertiliser-containing irri-
gation water (contents including ammonia). In the result, no yield reduction was determined while
antimicrobial efficacy was found to be improved (Dannehl et al. 2015B). However, the chloride content
in water rose following discontinuous introduction of disinfectant by 14 mg/l (DI) on average, or
21 mg/l (DII) (Dannehl et al. 2015a), whereby the crop growing recommendation for hydroponic toma-
toes of < 532 mg chloride/l (SOnneVelD and StraVer 1988) was undersupplied, even after three months
without water change. All the same, the tomatoes also tolerated, compared to other hydroponic crops
(e.g. salad crops), higher chloride content in the irrigation water (SOnneVelD and StraVer 1988). Fur-
thermore, under the discontinuously applied disinfectant regime (as mentioned), chlorate content in
the tomatoes rose to 0.22 mg/kg (DII) or 0.25 mg/kg (DII) (Dannehl et al. 2015a) from which one can
deduce, based on current knowledge, a toxicologically safe daily consumption of up to 10 kg tomatoes
(based on a 70 kg bodyweight and in the absence of any other chlorate consumption) (efSa 2015).
Conclusions
In principle, brine electrolysis systems are suitable for disinfection of irrigation water, when proce-
dural techniques, storage conditions, dosage management and actual applications are coordinated.
Required in the future to help in this respect are case studies with different crops, cropping systems,
dosage scenarios and phytopathogens. The basic requirement for application in crop production is,
however, that amounts of disinfection by-products (esp. chloride, chlorite, chlorate, perchlorate) in
water, substrates and plants (esp. vegetable plants) do not exceed toxicologically acceptable limits.
During brine electrolysis, a certain amount of chlorate is produced by the electrochemical process
whenever heat is applied. Therefore techniques should be tested for conducting any produced heat
away from the procedure through e. g. fan, water-cooling or Peltier cooler.
landtechnik 71(2), 2016 32
A further procedure concerns storage of the disinfectant solution (esp. under warm conditions).
With increasing storage time, the effective disinfectant proportion of the free chlorine decreases and
the chlorate proportion increases. In the context of irrigation water disinfection it appears, that the
on-site production of a fresh disinfectant solution according to short term requirement (e. g. one day’s
supply) is advantageous compared to storing industrially produced large volumes delivered in bar-
rels. Additionally recommended is a cooling system for the disinfectant storage tank.
A further measure for minimising chlorate in water, or in the plants that are cultivated with the
help of the water, concerns dosage management. Thus, a discontinuous application of disinfectant
(e. g. 1 to 2 times per week) with higher doses of chorine could lead to less chlorate input compared
with continuous chlorine application at a lower dosage. Comparative tests on plant tolerance and in-
fection reduction have yet to be conducted, however.
Regarding dosage of electrolytically produced disinfectant solution, it is shown that the plant fer-
tiliser ammonia rapidly binds the free chlorine and thus markedly increases usage of disinfectant or
chlorate input up to the chlorine loss limit. Thus, it is recommended that dosage to according to solu-
tion concentration with this concentration level controlled by chlorine sensor so that alterations of
chemical processes in water (chlorine loss) can be accounted for when adjusting dosage. Additionally,
as little ammonia fertiliser as possible under plant development requirements should be applied with
substitution where required with other plant nutrient substances (e. g. nitrate).
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Authors
Dr. Ingo Schuch and Dr. Dennis Dannehl are postdoctoral researchers, Division Biosystems Engineering,
Humboldt University of Berlin, Albrecht-Thaer-Weg 3, 14195 Berlin, Germany, E-Mail: ingo.schuch@agrar.hu-berlin.de
Dr. Martina Bandte is postdoctoral researcher, Division Phytomedicine, Humboldt University of Berlin,
Lentzeallee 55/57, 14195 Berlin, Germany.
M.Sc. Johanna Suhl is research assistant, Division Biology and Ecology of Fishes, Leibniz-Institute of Freshwater Ecology
and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany.
Dipl.-Ing. Yuan Gao is managing director of newtec Umwelttechnik GmbH, Am Borsigturm 62, 13507 Berlin, Germany.
Prof. Dr. Uwe Schmidt is director of the Albrecht Daniel Thaer-Institute of Agricultural and Horticultural Sciences and is
head of the Division Biosystems Engineering, Humboldt University of Berlin, Albrecht-Thaer-Weg 3, 14195 Berlin, Germany.
Acknowledgments
The results originates from a research project (FKZ 2815502611) that was financed by the Federal Ministry of Food and
Agriculture (BMEL) with assistance of the Federal Office for Agriculture and Food (BLE).
The topic was presented at the 50th Horticultural Science Conference and the International WeGa Symposium,
Freising-Weihenstephan, Germany, 24–28 February 2015. An abstract was published in BHGL series (vol. 31, p. 34).
The authors are grateful to M.Sc. Janine Berberich and M.Sc. André Seyfarth for their support.
... A single chamber brine electrolysis plant was used to produce hypochlorite on-site (nt-BlueBox mini; newtec Umwelttechnik GmbH; 13507 Berlin, Germany), as previously described by Schuch et al. [46]. Chlorine (Cl 2 ) was formed with a 10 A direct current and a 13 V voltage applied with titanium electrodes to a brine solution containing potassium chloride (KCl) and fresh water. ...
... The maxim must consequently be: as little as possible, as much as necessary. Ref. [46] showed that ammonia rapidly binds the free chlorine and thus markedly increases the usage of disinfectant or chlorate input up to the chlorine loss limit. These changes in chemical processes in irrigation and fertigation solutions (e.g., chlorine losses) can be monitored and considered with the use of a chlorine sensor, administered as needed; overand under-dosing are thus avoided. ...
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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.
... Hypochlorite was produced on-site in a single chamber brine electrolysis plant (nt-BlueBox mini; newtec Umwelttechnik GmbH; Berlin, Germany) as described by Schuch et al. (2016). A direct current of 10 A with a voltage of 13 V was applied with titanium electrodes to a brine solution containing potassium chloride (KCl) and fresh water leading to the formation of chlorine (Cl 2 ). ...
... Recently, Dannehl et al. (2016) reported on a highly significant correlation between the chlorate-accumulation in tomatoes and the application of hypochlorite as a disinfectant for hydroponic systems, although they classified the consumption of those tomatoes as harmless because maximum residue levels for chlorate (EFSA, 2015) were not exceeded. Nevertheless, we demonstrate here that with the use of ORP sensor-controlled dosing application of hypochlorite can be optimised, and combined with following the recommendations of Schuch et al. (2016) for the generation of electrolytically-derived hypochlorite, this should keep risks of chlorate accumulation low. ...
Article
Demand for conservation and recycling of water has increased significantly. Therefore irrigation water used for horticultural or agricultural purposes needs to be treated before being reused to eradicate plant pathogens and thereby reducing the risk of pathogen dispersal and losses due to disease. The economically important fungal plant pathogens Fusarium oxysporum (Synder and Hans) and Rhizoctonia solani (Kühn) were selected to examine the efficacy of nutrient solution treatment by electrolytic disinfection to prevent the dispersal of these pathogens in the hydroponic production of tomatoes (Solanum lycopersicum Mill.). First, we determined the efficacy of the disinfectant to inactivate F. oxysporum and R. solani in vitro. The electrolytically generated potassium hypochlorite (KClO) was tested at five concentrations of free chlorine (0.2, 0.5, 0.8, 1.0, 2.0 mg/L) in nutrient solutions of pH 5.5, 6.0 and 6.5 with four contact times (5, 30, 60, 120 min). Best sanitation was achieved in nutrient solution at pH 6.0. In vitro, F. oxysporum required 2 mg/L at 30 min for complete inactivation whereas chlorination had only a minimal effect on viability of R. solani. Subsequent trials under practical conditions applied the disinfectant via a new sensor-based disinfection procedure. Potassium hypochlorite solution produced on site and injected into a recirculating nutrient solution once a week for 60 min at a free chlorine concentration of 0.5 mg/L (ORP 780 mV) inhibited the dispersal of F. oxysporum and R. solani during the entire test period of 16 weeks. In contrast all tomato test plants irrigated with untreated nutrient solution became infected with F. oxysporum and a third of them additionally with R. solani. At the applied dose no plant damage occurred. Thus, the treatment proved to be effective and applicable to prevent dispersal of fungal pathogens by nutrient solution under simulated field conditions.
... Hypochlorite was produced on-site in a single chamber brine electrolysis plant (nt-BlueBox mini; newtec Umwelttechnik GmbH; Berlin, Germany) as described by Schuch et al. (2016). A direct current of 10 A with a voltage of 13 V was applied with titanium electrodes to a brine solution containing potassium chloride (KCl) and fresh water leading to the formation of chlorine (Cl 2 ). ...
... Recently, Dannehl et al. (2016) reported on a highly significant correlation between the chlorate-accumulation in tomatoes and the application of hypochlorite as a disinfectant for hydroponic systems, although they classified the consumption of those tomatoes as harmless because maximum residue levels for chlorate (EFSA, 2015) were not exceeded. Nevertheless, we demonstrate here that with the use of ORP sensor-controlled dosing application of hypochlorite can be optimised, and combined with following the recommendations of Schuch et al. (2016) for the generation of electrolytically-derived hypochlorite, this should keep risks of chlorate accumulation low. ...
Article
Demand for conservation and recycling of water has increased significantly. Therefore irrigation water used for horticultural or agricultural purposes needs to be treated before being reused to eradicate plant pathogens and thereby reducing the risk of pathogen dispersal and losses due to disease. The economically important fungal plant pathogens Fusarium oxysporum (Synder and Hans) and Rhizoctonia solani (Kühn) were selected to examine the efficacy of nutrient solution treatment by electrolytic disinfection to prevent the dispersal of these pathogens in the hydroponic production of tomatoes (Solanum lycopersicum Mill.). First, we determined the efficacy of the disinfectant to inactivate F. oxysporum and R. solani in vitro. The electrolytically generated potassium hypochlorite (KClO) was tested at five concentrations of free chlorine (0.2, 0.5, 0.8, 1.0, 2.0 mg/L) in nutrient solutions of pH 5.5, 6.0 and 6.5 with four contact times (5, 30, 60, 120 min). Best sanitation was achieved in nutrient solution at pH 6.0. In vitro, F. oxysporum required 2 mg/L at 30 min for complete inactivation whereas chlorination had only a minimal effect on viability of R. solani. Subsequent trials under practical conditions applied the disinfectant via a new sensor-based disinfection procedure. Potassium hypochlorite solution produced on site and injected into a recirculating nutrient solution once a week for 60 min at a free chlorine concentration of 0.5 mg/L (ORP 780 mV) inhibited the dispersal of F. oxysporum and R. solani during the entire test period of 16 weeks. In contrast all tomato test plants irrigated with untreated nutrient solution became infected with F. oxysporum and a third of them additionally with R. solani. At the applied dose no plant damage occurred. Thus, the treatment proved to be effective and applicable to prevent dispersal of fungal pathogens by nutrient solution under simulated field conditions.
... Moreover, combined strong acidic electrolyzed water and alkaline electrolyzed water have stronger sterilization ability than single acidic electrolyzed water or slightly acidic electrolyzed water (51). A cooling system for the electrolysis reactor and cooling and control of chlorine storage are recommended to achieve production of minimal amounts of chlorine (104). ...
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Irrigation water can be a source of pathogenic contamination of fresh produce. Controlling the quality of the water used during primary production is important to ensure food safety and protect human health. Several measures to control the microbiological quality of irrigation water are available for growers, including preventative and mitigation strategies. However, clear guidance for growers on which strategies could be used to reduce microbiological contamination is needed. This study evaluates pathogenic microorganisms of concern in fresh produce and water, the microbiological criteria of water intended for agricultural purposes, and the preventative and mitigative microbial reduction strategies. This article provides suggestions for control measures that growers can take during primary production to reduce foodborne pathogenic contamination coming from irrigation water. Results show that controlling the water source, regime, and timing of irrigation may help to reduce the potential exposure of fresh produce to contamination. Moreover, mitigation strategies like electrolysis, ozone, UV, and photocatalysts hold promise either as a single treatment, with pretreatments that remove suspended material, or as combined treatments with another chemical or physical treatment(s). Based on the literature data, a decision tree was developed for growers, which describes preventative and mitigation strategies for irrigation-water disinfection based on the fecal coliform load of the irrigation water and the water turbidity. It helps guide growers when trying to evaluate possible control measures given the quality of the irrigation water available. Overall, the strategies available to control irrigation water used for fresh produce should be evaluated on a case-by-case basis because one strategy or technology does not apply to all scenarios. Highlights:
... 25 Apart from the formation of chlorate during the electrolysis used to produce EW, chlorate content can increase during storage of chlorinated disinfectant solutions, due to disproportionation of hypochlorite ion to chlorate and chloride ions. 26 Such disproportionation process is faster at higher temperatures. The container of the concentrated EW solution was located outside with no control of temperature conditions. ...
Article
Background: 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 electrolyzed 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. Results: Use of EW caused the accumulation of chlorates in irrigation water (0.02-0.14 mg/L), and in the fresh produce (0.05-0.10 mg/kg). On the other hand, the disinfection treatment had minor impact regarding the presence of trihalomethanes (THMs) in water (0.3-8.7 μg/L max), and in baby lettuce (0.3-2.9 μg/kg max). Conclusions: 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.
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Physical and chemical disinfection methods are used or are under investigation in greenhouse facilities to minimize the occurrence of pathogens and the application of pesticides in recirculating systems. Since the most of these methods differ in their effectiveness, more investigation is needed to produce healthy plants in a sustainable way. Therefore, the present study is focused on the identification of interactions between hypochlorite (ClO−) used as a disinfectant for a recirculating system and algae formation, spread of microorganisms, as well as plant development. As such, on-site produced potassium hypochlorite (1 % KClO) solution were supplemented using proportional injection control once a week for 90 min, as a disinfectant, into a recirculating tomato production system (NFT) until a free chlorine concentration of 1 mg L−1 (D I) and 2 mg L−1 (D II) were reached, respectively. The formation of the algae biofilm was reduced by 15 % (D I) and 48 % (D II). These treatments also suppressed cultivated microorganisms up to 100 %. Tomato plants exposed to the treatment D I showed a comparable plant height to the control plants after 7 weeks, whereas D II led to a significant increase in plant height of 12 cm. However, the formation of leaves was more pronounced by treatment D I. After a growing period of 7 weeks, a significant difference in leaf number up to 2.9 leaves per plant was calculated compared to the other treatments. The same treatment had the largest positively impact on the fruit yield and number of fruit, which were increased by 10 and 15 %, respectively, compared to the control plants. Under consideration of all results, the most promising effects of ClO− as a disinfectant for hydroponic systems were achieved with a free chlorine concentration of 1 mg L−1 (D I), where phytotoxic effects can be excluded. http://link.springer.com/article/10.1007%2Fs10343-015-0351-3
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With water conservation and reuse a priority for communities worldwide, recycling irrigation water in commercial plant nurseries and greenhouses is a logical measure. Plant pathogenic microorganisms may be present in the initial water source, or may accrue and disperse from various points throughout the irrigation system, constituting a risk of disease to irrigated plants. The continual recycling of this water is exacerbating this plant disease risk. Accurate and timely detection of plant pathogenic propagules in recycled irrigation water is required to assess disease risk. Both biological and economic thresholds must be established for important plant-pathosystems. Plant pathogens in recycled irrigation water can be managed by a variety of treatment methods that can be arranged in four broad categories: cultural, physical, chemical, and biological. An integrated approach using one or more techniques from each category is likely to be the most effective strategy in combating plant pathogens in recycled irrigation water.
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Revised! Circular 1039, a 7-page illustrated fact sheet by Kati W. Migliaccio, Brian Boman, and Gary A. Clark, provides a guide for using chlorine to treat inhibiting microorganism buildup in irrigation systems. Includes references. Published by the UF Department of Agricultural and Biological Engineering, May 2009.
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Recently, official food surveillance discovered high residues of chlorate (ClO3 −) and perchlorate (ClO4 −) in different plant-based foods, which was the start of a big discussion in the EU Commission. There is currently no knowledge about possible ClO3 − uptake quantities in vegetable, when hypochlorite (ClO−) is used as a disinfectant in plant production facilities. Therefore, the present study is focused on the identification of interactions between ClO− applications and ClO3 − accumulations in fruit, as well as findings in terms of suitable concentrations of ClO− to ensure food safety. Primary and secondary metabolites were analyzed as well. As such, on-site produced potassium hypochlorite (1 % KClO) solution was supplemented using proportional injection control once a week for 90 min, as a disinfectant, into a recirculating tomato production system (NFT) until a free chlorine concentration of 1 mg L−1 (D I) and 2 mg L−1 (D II) was reached, respectively. The chlorate (ClO3 −) content in fruit increased from 0.01 mg (Control) to 0.22 mg (D I) and 0.25 mg ClO3 − kg−1 FW (D II). A critical assessment of these values is given in the discussion section. Contrary to the expectations, a co-occurrence of ClO3 − and ClO4 − in fruit was not found. Compared to the control, the fruit contents of lycopene were increased by 21.3 % (D I) and 33.5 % (D II) and those of ß-carotene by 9.2 % (D I) and 23.9 % (D II), when calculated on a fresh weight basis. These results changed slightly when these substances were calculated on a dry weight basis. Furthermore, ClO3 − induced stress in fruit. In this context, a significant correlation (r) and a significantly increased slope (m) compared to zero were found between ClO3 − and lycopene (r = 0.74; m = 0.10), as well as ß-carotene (r = 0.70; m = 0.01). The content of soluble solids and that of titratable acids remained unaffected. http://rdcu.be/mHBZ