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Hypochlorite Application for Controlling Algae Biofilm Formation, Microorganisms and Tomato Production in Recirculating Systems


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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.
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Eingegangen: 3. September 2015 / Angenommen: 21. September 2015
© Springer-Verlag Berlin Heidelberg 2015
DOI 10.1007/s10343-015-0351-3
plants exposed to the treatment D I showed a comparable
plant height to the control plants after 7 weeks, whereas
However, the formation of leaves was more pronounced
by treatment D I. After a growing period of 7 weeks, a
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 promi-
sing effects of ClO as a disinfectant for hydroponic sys-
tems were achieved with a free chlorine concentration of
1 mg L1 (D I), where phytotoxic effects can be excluded.
.H\ZRUGV Potassium hypochlorite · Disinfectant ·
Hydroponic systems · Algae · Microorganisms · Plant
development · Tomato yield .
=XVDPPHQIDVVXQJ Physikalische und chemische Desin-
den sich in ihrer Effektivität unterscheiden, sind mehr
$EVWUDFW Physical and chemical disinfection methods are
used or are under investigation in greenhouse facilities to
of pesticides in recirculating systems. Since the most of
these methods differ in their effectiveness, more investiga-
tion is needed to produce healthy plants in a sustainable
way. Therefore, the present study is focused on the identi-
as a disinfectant for a recirculating system and algae for-
mation, spread of microorganisms, as well as plant devel-
opment. As such, on-site produced potassium hypochlorite
(1 % KClO) solution were supplemented using proportional
into a recirculating tomato production system (NFT) until a
free chlorine concentration of 1 mg L1 (D I) and 2 mg L1
(D II) were reached, respectively.
15 % (D I) and 48 % (D II). These treatments also sup-
pressed cultivated microorganisms up to 100 %. Tomato
D. Dannehl () · I. Schuch · U. Schmidt
Faculty of Life Sciences, Albrecht Daniel Thaer – Institute of
Agricultural and Horticultural Sciences, Division Biosystems
Albrecht-Thaer-Weg 3,
Y. G ao
newtec Umwelttechnik GmbH,
Am Borsigturm 62,
13507 Berlin, Germany
S. Cordiner
The New Zealand Institute for Plant and Food Research Ltd.,
Private Bag 11600,
Palmerston North 4442, New Zealand
1 3
... Hypochlorite (CLO-) used for preharvest processes can eliminate organic substances and kill pathogens (Cayanan et al., 2009). Studies also show its utility to control algae biofilm formation in greenhouses (Dannehl et al., 2015). Nevertheless, a drawback of this disinfection method is possible initiation of unwanted chlorate in fruits such as tomatoes (Dannehl et al., 2016). ...
... The dry weight of the algae on the fleece in the disinfection row is 0.166 g in comparison to the one on the fleece from the control row with 0.363 g. This is similar to results of Dannehl et al. (2015) and Yiasoumi (2005) that also show an increasing efficacy against algae biofilm formation with increasing dosages of potassium hypochlorite in irrigation water. Xin et al. (2010) showed that algae growth requires nutrients like phosphorous and nitrogen. ...
... Xin et al. (2010) showed that algae growth requires nutrients like phosphorous and nitrogen. Stemming algae formation with hypochlorite can therefore attend more nutrients of irrigation water being available for plants and such fertilizers can be reduced (Dannehl et al., 2015). Algae biofilm is also a platform for pathogens. ...
Tested in experimental scale, an innovative system for electrolytic water disinfection in greenhouses (SeWiG) was very efficient. It was developed by Humboldt-Universität zu Berlin and newtec Umwelttechnik GmbH. With scaling up this system for industrial greenhouses, the new technology will be tested, validated and optimized under practical conditions. The implemented technology will be incrementally scaled-up. After successful installation of the disinfection system within a separated part of an industrial greenhouse, two large-scaled greenhouses will use the on-site produced hypochlorite as a disinfectant for irrigation or drain water applied for vegetables and ornamental plants. The effects on plant growth, yield and product quality will be controlled and particular attention is paid to chlorate and perchlorate. Due to the first results, both pesticides are under the limits given by the European Commission. This can be related to the short dwell time of the disinfectant before dosing based on the on-demand production of fresh hypochlorite. Hypochlorite is dosed by the method of shock disinfection, which might decrease the accumulation of unwanted ingredients in plants. The special feature of the new system for electrolytic water disinfection is the functional superiority over common methods such as filtration, ultraviolet irradiation, heating, ozonation or chlorine dioxide. Worth highlighting is its high effectiveness against plant viruses and the reduced risk for users, plants and the environment while less energy is needed, compared to other disinfection systems. Besides a reduced formation of algae biofilm, a reduced application of fertilizers is expected. All parameters mentioned before will be monitored within this study.
... 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 irrigation 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 tomatoes of < 532 mg chloride/l (SOnneVelD and StraVer 1988) was undersupplied, even after three months without water change. ...
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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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:Hydrogen peroxide has been used as a sanitation agent for many years. Recently, hydrogen peroxide products have been used to remove algae from irrigation lines and sanitize hydroponic systems between uses. However, hydrogen peroxide can have phytotoxic effects on plants at high concentrations. The goal of this research was to determine if hydrogen peroxide treatments affected plant and algae growth in the ebb and flow hydroponic systems. The research was conducted at the Department of Horticulture and Landscape Architecture greenhouses in Stillwater, OK. Two cultivars of lettuce, ‘Green Forest’ and ‘Tropicana’, and two cultivars of basil, ‘Aroma II’ and ‘Genovese’, were transplanted into the ebb and flow hydroponic systems, and three different hydrogen peroxide products, PERpose Plus, ZeroTol, and 3% hydrogen peroxide, were applied at different rates and combinations in two experiments. Shoot fresh weight in lettuce was found to be significantly greater in control and 3% hydrogen peroxide treatments for both cultivars; however, in ‘Tropicana’ those treatments were not different from any other treatment. Greater amounts of PERpose Plus and ZeroTol, such as 60 mL, restricted plant growth in lettuce, whereas only cultivar differences for SPAD and plant width were reported for basil. Algae growth was not significantly controlled by any treatment in this research based on algae counts, weights, or spectrometer readings. However, algae species quantification did show that Microspora tumidula was found in the greatest concentrations in control, with a 96.0%, 99.2%, 94.0%, and 97.9% reduction in the 15 mL ZeroTol, 60 mL ZeroTol, 15 mL PERpose Plus, and 3% hydrogen peroxide treatments, respectively. Other algae genera identified included Scenedesmus, Chlamydomonas, Gloeocystis, Tetraspora, Leptolyngbya, Pennate diatoms, and Centric diatoms.
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Technical Report
Im Produktionsgartenbau besteht bei geschlossener Bewässerung ein erhöhtes Verbreitungsrisiko von wasserübertragbaren Pflanzenkrankheitserregern. Hierzu weisen die gängigen Verfahren zur Wasserdesinfektion zwar eine hohe Effizienz bei der Eliminierung von Pilzen und Bakterien auf, können aber Viren nur mit hohem Energieaufwand (Wärmebehandlung > 90 °C) zuverlässig inaktivieren. Daher wurde das System zur elektrolytischen Wasserdesinfektion in Gewächshäusern (SeWiG) entwickelt und im Rahmen einer DIP-Förderung auf große Praxisgewächshäuser skaliert und optimiert. Das zum Einsatz kommende Desinfektionsmittel wird vor Ort während eines elektrochemischen Prozesses (Salzelektrolyse) erzeugt. Die eigentliche Wasserbehandlung erfolgt durch eine sensorgesteuerte Applizierung mit diskontinuierlicher Dosierstrategie (2-3/Woche), wobei ein desinfektionswirksamer Puffereffekt zur Verringerung des Energie- und Desinfektionsmitteleinsatzes führt. Unter Praxisbedingungen beträgt der Energieverbrauch des Verfahrens lediglich 0,5 kWhel/m³. Zudem ist die Wirksamkeit gegen Pflanzenviren wie Tobacco mosaic virus und Pepino mosaic virus hervorzuheben. Am Beispiel eines tomatenproduzierenden Gewächshausbetriebs ließen sich die mikrobielle Belastung im Drain und der Biofilm in den Bewässerungsrinnen deutlich reduzieren. Hinsichtlich des Einflusses auf die Pflanze trat unter den geprüften Bedingungen keine Ertragsminderung auf und die toxikologisch unbedenkliche Menge an Desinfektionsnebenprodukten (Chlorat, Perchlorat) wurde nicht überschritten (gemäß EFSA-Berechnungsmodell). Mit Projektende sind die Voraussetzungen zur Marktetablierung des Desinfektionsverfahrens gegeben.
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Technical Report
Bei der Nutzung von Oberflächenwasser zur Bewässerung und einer Wiederverwendung des überschüssigen Wassers ist das Verbreitungsrisiko von Pflanzenkrankheitserregern erhöht. Dies bedingt eine effektive Wasserdesinfektion. Hierzu wurde zunächst in vitro die Wirksamkeit einer durch Salzelektrolyse erzeugten Desinfektionslösung zur Inaktivierung von pilzlichen, bakteriellen und viralen Erregern geprüft. Erwartungsgemäß variieren die erforderlichen Chlorkonzentrationen und Einwirkzeiten in Abhängigkeit von der Erregerart. Anschließend wurde die Wirksamkeit in vivo bei Tomatenpflanzen unter Einsatz einer Mess- und Dosieranlage getestet, wobei eine diskontinuierliche Applizierung (1/Woche) des hypochlorithaltigen Desinfektionsmittels zur Unterbindung der Virusverbreitung und zum deutlichen Rückgang von Mikroorganismen im Wasser führte ohne phytotoxische Reaktionen hervorzurufen. Ferner wurde ein Zusammenhang zwischen der Akkumulation von Chlorat und Carotinoiden in Tomaten und der elektrolytischen Wasserdesinfektion festgestellt, wobei nach dem aktuellen Kenntnisstand der Frischgemüseverzehr unter den geprüften Desinfektionsbedingungen als unbedenklich eingestuft werden kann. Das System zur elektrolytischen Wasserdesinfektion in Gewächshäusern (SeWiG) muss nun unter kommerziellen Bedingungen getestet werden und seine Effizienz im Praxisbetrieb unter Beweis stellen. Grundvoraussetzung zur Anwendung im Pflanzenbau ist, dass die toxikologisch unbedenkliche Menge an Desinfektionsnebenprodukten nicht überschritten wird.
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Die Minimierung von Chlorat bei der elektrolytischen Gießwasserdesinfektion ist aufgrund problematischer Chloratrückstände in pflanzlichen Lebensmitteln von Bedeutung. Im Hinblick auf verfahrenstechnische Optimierungsvorschläge wurde daher am Beispiel einer Salzelektrolyseanlage (Einkammersystem) geprüft, wie viel Chlorat beim Herstellungsprozess des Desinfektionsmittels entsteht und wie sich dessen Anteil bei einer Lagerung unter warmen Temperaturbedingungen im Gewächshaus verändert. Zudem wurde untersucht, wie sich der Pflanzendünger Ammonium auf das Desinfektionsmittel auswirkt. Dabei ergab sich, dass die Chloratbildung durch eine Kühlung des Elektrolysereaktors sowie des Desinfektionsmitteltanks und durch ein zur Kurzzeitlagerung ausgelegtes Bevorratungssystem von Desinfektionsmittel minimiert werden könnte. Ferner wurde bestätigt, dass Ammonium den Desinfektionsmittelverbrauch bzw. Chlorateintrag deutlich erhöht. Daher empfiehlt sich eine sensorbasierte Dosierung, um sich ändernde chemische Vorgänge im Gießwasser (Chlorzehrung) zu berücksichtigen.
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Indiscriminate agricultural activities have led to the spread of saline lands both in Iran and around the world, thus making it impossible to produce agricultural crops. The identification of varieties which are resistant to salinity is one approach that can be taken to maintain production under stress conditions. Therefore to analyze the effects of salinity on growth and photosynthetic features of tomatoes, an experiment was conducted using a completely randomized design in greenhouse conditions. The treatments used consisted of 0, 25 and 50 mM concentrations of NaCl, each in four replication. Results showed that salinity had a decreasing effect on all the features studied. The shoots’ fresh weights were significantly reduced with the 50 mM sodium chloride treatment showing the least fresh weight. Photosynthetic indexes such as the rate of photosynthesis, stomatal conductance and the efficiency of photosynthetic water were significantly reduced with the least amount again seen in the 50 mM Sodium chloride concentration. In this treatment, the photosynthetic rate was 53% lower than that of the control treatment and the efficiency of photosynthetic water consumption was 29% less than treatment.
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Recycled irrigation water is one of the major sources of inoculum and may spread plant pathogens throughout the nursery or greenhouse operation. Chlorination is the most economical method of disinfecting water and has been adopted by some North American commercial growers. However, chlorine has not been assessed as a disinfectant for the common plant pathogens Phytophthora infestans, Phytophthora cactorum, Pythium aphanidermatum, Fusarium oxysporum, and Rhizoctonia solani. These pathogens were exposed to five different initially free chlorine solution concentrations ranging from 0.3 to 14 mg·L -1 in combination with five contact times of 0.5, 1.5, 3, 6, and 10 min to determine the free chlorine threshold and critical contact time required to kill each pathogen. Results indicated that the free chlorine threshold and critical contact time for control of P. infestans, P. cactorum, P. aphanidermatum, F. oxysporum, and R. solani were 1, 0.3, 2, 14, and 12 mg·L-1 for 3, 6, 3, 6, and 10 min, respectively.
Dutch greenhouse growers are obliged to invest in environmental friendly cropping systems, in order to comply with new legislation. Closed soilless growing systems may lead to environmental friendly systems and thus to a sustainable horticultural sector. This paper encompasses the change from general to specific legislation, the availability of good water and the developments in disinfection of nutrient solutions. For the latter, the interest of growers in the possibilities of slow sand filtration to disinfect the nutrient solution will be discussed. In the last ten years there has been an awakening of environmental consciousness in society. Agriculture and horticulture have had to face their polluting aspects too, such as the discharge of nutrients, the emission of pesticides and the waste of materials such as plastics and substrates for cultivation. Initial legislation was rather rough and not based on research. Later, forced by court judgments and social pressure, new regulations have set a timetable for all nurseries to adopt specific measures in order to decrease the leaching of water and fertilisers into the environment. A recent covenant between horticultural employers and the Dutch government for a sustainable development of greenhouse horticulture between 2000 and 2010 enables the growers to achieve the environmental targets in their own way, if they make a specific plan for their nurseries. Closed growing systems prevent the leaching of chemicals into the environment; in Dutch situations leaching into ground and surface water. Studies showed savings of up to 30% of water and up to 40% of fertilisers in closed systems compared to traditional open systems. A 100% efficiency of water and nutrients often cannot be achieved, because of the relatively poor water quality of the supply water. Mostly the sodium content of the water eventually becomes too high, and, consequently, part of the nutrient solution should be discharged. Closed growing systems bear the risk of dispersal of pathogens all over the nursery. Therefore, it is always said in the Netherlands that disinfection of the recirculating nutrient solution is a necessity for long-term crops to avoid a disaster due to an outbreak of root-borne diseases. However, existing, active, sterilisation systems are not always applied, mainly because of the high costs. Now, developments in passive disinfection equipment focus on the removal of pathogens without a complete sterilisation of the nutrient solution. Investigations into the prospects of slow sand filtration as a cheap, robust disinfection method for a number of major pathogens have proved its feasibility on a small scale. Future trends are scaling-up and inter-farm co-operation to achieve a sustainable use of water and nutrients to minimise contamination of ground and surface water. Economic prospects are still the most important motive to change the traditional way of growing.
Greenhouse tomato production is valued at about 250 million dollars annually in southwestern Ontario. The tomatoes are grown hydroponically and mainly in a rockwool pouch system where their root systems are partially submerged in the nutrient solution. Such growing conditions are highly conducive to the development and the spread of Pythium root rot disease because the recirculating nutrient solution can carry the pathogen and spread the disease. Therefore, it is imperative to disinfest the run-off nutrient solution before recirculating it. This paper reports the successful application of leak-proof, micropore, modern filters to remove Pythium zoospores from the recirculating nutrient solution. The two filters used are (a) Membrane Module Filter that consisted of numerous hollow fibre membrane strands and (b) Sediment Filter Cartridge that was constructed with pleated cellulose/polyester materials. The former has a porosity of 0.01 μm which can completely remove zoospores and bacteria, and the latter has a porosity of 0.5 μm which can completely remove zoospores, but not bacteria. Both filters can withstand pressure up to 2.5 kg cm-2 and deliver a flow rate of 50 L min-1. In both cases, a prefiltration using a 20Φ pore size pleated cellulose/polyester cartridge along with a 100-mesh strainer can drastically increase the life span of the filters. The filter systems are highly effective and economical and require minimal infrastructure as compared to other disinfestation systems such as UV, heat, ozone, ultrasonication and sand or volcanic lava filtration systems.
Trials were conducted to optimize slow sand filtration by varying filter material, depth of the filter bed and flow rate. Recirculated nutrient solutions from Dracaena marginata and Aglaonema commutatum pot plants grown hydroponically in expanded clay on ebb/flow benches were inoculated with Xanthomonas campestris pv. pelargonii as the test organism. Four completely separated systems were used each consisting of one hydroculture bench (approx. 3 m2) and one filter unit (approx. 0.2 m2 filter surface). Granulated rockwool in comparison to sand, pumice or anthracite has been shown to be the most efficient filter material. The efficiency of a rockwool filter with a depth of 90 cm was only slightly and not significantly higher than that of a 60 cm filter. However, both efficiency rates were significantly higher than that of a 30 cm filter. The differences of the mean efficiency rates at flow rates of 100, 200 and 300 L/m2h were not as high as expected (99.76, 99.41 and 98.85 % respectively). A regression analysis revealed a significant correlation of -0.5 between flow rate and efficiency rate.
EU legislation, laid down in the Water Framework Directive, demands to minimize emissions of nitrogen, phosphate and crop protection products to achieve an excellent chemical and ecological quality in 2015. The aim is to force growers to a better water and disease management. Supply water of excellent chemical quality will have to be recirculated as long as possible, for which adequate disinfection equipment have to be used. Several sources of water are used as supply water. Rainwater is chemically best, followed by reverse osmosis water. However, the latter is rather expensive. Tap water and surface water often have a too high salinity, while well water may vary dramatically from place to place. Rainwater and surface water are potential risk factors for importing soil-borne pathogens. Disinfection of the recirculating nutrient solution can be done adequately by heat treatment and UV radiation. Membrane filtration performs well, but is mostly too costly. Chemical treatments as sodium hypochlorite, chlorine dioxide and copper silver ionization may partly solve the pathogen problem, but introduce a potential accumulation of other elements in closed systems. Hydrogen peroxide, chlorine dioxide and sodium hypochlorite perform better to clean pipe work instead of soil-borne pathogens.