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389
Evaluation of the Performance of an Ozonization System for the
Disinfection of the Nutrient Solution of a Greenhouse Tomato Crop
M.A. Laplante1), D. Brisson1), C. Boivin2), D. Doiron2), L. Gaudreau2), M. Dorais3),
M. Lacroix4), C. Martinez1), R. Tweddell1) and A. Gosselin1)
1)Centre de recherche en horticulture, pavillon Envirotron, Université Laval, Québec,
Canada, G1K 7P4
2)Les Serres du St-Laurent inc., 700 rue Thibodeau, Portneuf, Québec, Canada G0A 2Y0
3)Agriculture and Agrifood Canada, pavillon Envirotron, Université Laval, Québec,
Canada G1K 7P4
4)Laboratoire de diagnostic en phytoprotection, MAPAQ, 2700 rue Einstein, Ste-Foy,
Québec, Canada G1P 3W8
1)Corresponding author
Keywords: nutrient solution, Lycopersicon esculentum Mill. Cv Trust, disinfection,
ozone, root diseases, recirculation
Abstract
An ozonization system (Ozomax OZO 6VTT, IGT limited, Ontario, Canada)
was installed in a commercial plastic-covered greenhouse in Danville, Quebec, Canada
(www.savoura.com) to study the effects of the disinfection and recirculation of the
nutrient solution in a tomato crop. The ozonization system was compared to a conven-
tional growing system where the nutrient solution was not treated, neither recircu-
lated. Samples of both treated and non-treated nutrient solutions were analysed for
the presence of 38 potential pathogens using DNA Multiscan Technology. Detailed
measurements of the presence of Pythium spp. and Fusarium spp. in the nutrient
solutions, the growing media and the root system were achieved at various periods. We
also determined the evolution of bacteria in the treated and non-treated nutrient
solutions. A weekly complete mineral analysis, including pH and EC of both treated
and non-treated nutrient solutions was done. For both treatments, plant growth and
development were measured on a weekly basis while fruit yield and quality were
determined for every harvest.
INTRODUCTION
Protection of the underground water and of the environment requires that nutrient
solutions used for greenhouse tomato production are recuperated and recirculated. Various
systems using heat or UV radiation are commonly employed mainly in northern Europe to
treat nutrient solutions (Runia, 1994, 2001). These systems were shown to be very
efficient to eliminate pathogens in the nutrient solutions, but relatively expensive to
operate (0.15-0.25 Can$/m3) (Le Quillec, 2002). Other systems, using strong oxidants
such as ozone, peroxide or chloride to destroy pathogens were experimented (Rey, 2001;
Poncet et al., 2001; Runia, 1994, Vanacher, 1988). The addition of chloride to the nutrient
solutions caused symptoms of phytotoxicity to tomato plants when concentration
exceeded 2-4 ppm (Le Quillec, 2002). A French company (Trailigaz, Garges-lès-Gonesse)
developed an ozonization system to disinfect nutrient solutions using ozone and peroxide.
In Canada, IGT Ltd developed and commercialized an ozonization system coupled with a
bubbling system to increase oxygen concentration in the nutrient solution and potentially
improve its efficiency. This project aims at measuring the efficiency and the agronomic
performance of the latter system.
MATERIALS AND METHODS
The experiment was conducted in a 27 000 m2 double polyethylene greenhouse
equipped with a HPS supplemental lighting system supplying 120 µmol.m-2.s-1. Tomato
plants Cv Trust were grown at a plant density of 2,4 plants/m2 in rockwool slabs (Grodan
master type) placed on gutters located 1 m. high. Standard cultural practices were used for
Proc. IC on Greensys
Eds.: G. van Straten et al.
Acta Hort. 691, ISHS 2005
390
nutrition, irrigation and plant training. Biological control of insects was primarily achieved
by introducing predators such as Eretmocerus spp. and Dicyphus spp. Before being reused,
the nutrient solution from 50% of the growing area was recuperated and treated with the
ozonization system (Ozomax OZO 6VTT, IGT limited, Ontario, Canada) initially able to
produce 40 g and later upgraded to produce 60 g of O3 per hour. The rate of nutrient
solution treated was adjusted between 3 to 10 m3 per hour. It was consequently possible to
compare the effects of 3.0 , 5.3 , 7.7 and 14.1 g of ozone per m3of nutrient solution. The
capacity of the ozonization system related to each treatment rate is described in Table 1.
The nutrient solution of the other half of the growing area was neither recuperated, nor
recirculated. In each section of the greenhouse, three bays of 337 m2 were selected to
measure growth, development, yields and fruit quality (Dorais, 2001). Samples of the
nutrient solutions were taken before and after ozonization and analysed for their mineral
contents.
Four additional experiments were conducted. First, we treated nutrient solutions
for 30, 60, 90 or 120 minutes with ozone. Second, we sampled treated and non-treated
nutrient solutions with ozone at 14.1 ppm and we later treated both of them with 0, 1, 2, 3,
4 or 5 ppm of peroxide. Thirdly, recirculated nutrient solutions were treated with both
ozone (7.7 and 14.1 ppm) and peroxide at 5 ppm. Finally, nutrient solutions were treated
with ozone at 7,7 ppm, peroxide at 5 ppm and chloride at 1, 2 or 5 ppm. For all four
experiments, we counted bacteria on petri dishes as described further.
Microbial analysis were achieved by Relab den Haan in The Netherlands, the
Laboratoire de diagnostic en phytoprotection of MAPAQ and by the Centre de recherche
en horticulture (CRH) at université Laval. Relab den Haan uses DNA technology to detect
for the presence of 38 pathogens in the nutrient solutions. Nutrients solutions and root
samples were analysed for the presence of fungi by the Laboratoire de diagnostic en
phytoprotection of MAPAQ. Root segments or 100 µL of nutrient solutions were spread
on three different media: Synthetic nutrient agar with antibiotics, P5ARP specific for
Pythium and P5ARPH specific for Phytophthora. Bacterial counts were made at
Université Laval using 50 µL of nutrient solution spread in petri dishes containing a
tryptic soy agar. Nutrient solutions were sampled before the ozonization treatment,
immediately after and 18 hours after in the storage reservoir.
RESULTS AND DISCUSSION
Data measured by Relab Den Haan from DNA analysis (Table 2) indicate that the
treatment of ozonization did not eliminate all pathogens from the nutrient solutions, even
at the highest concentrations. However, ozonization reduced the level of infection in the
nutrient solutions for many pathogens, especially Pythium spp., Pythium dissocutum and
Fusarium oxysporum. In some cases, the level of infection was not reduced at all and in a
few cases, it was even increased for unknown reasons. An experiment will be conducted
shortly to verify if the sand filter located before the ozonization system was the source of
sporadic contamination.
Analysis of fungi (data not presented) in the nutrient solutions and in roots by the
Laboratoire de diagnostic en phytoprotection of MAPAQ indicated the presence of
Plectosporium spp., Fusarium oxysporum, and Cladosporium spp. in similar amounts in
both the treated and non-treated nutrient solutions. Fungi were also found in root
segments.
The increase in the duration of ozonization from 30 to 120 minutes improved the
efficiency of the disinfection treatment by reducing the number of bacteria present in the
nutrient solutions (Table 3). These results may be explained by either a longer period of
treatment and/or an increase in the oxydo-reduction potential caused by higher
concentration of ozone in the nutrient solutions.
Data presented in table 4 clearly indicate the effectiveness of peroxide to reduce
the number of bacteria in the nutrient solutions. The best results were obtained at the
highest peroxide concentrations (4-5 ppm). Peroxide appears to be more efficient when
added after the ozonization treatments (Table 5) when we sampled the treated nutrient
391
solutions in the storage tank. We however measured an increase in the bacterial counts
18H00 after storage. Our data support the strategy of Trailigaz to combine ozone and
peroxide to disinfect nutrient solutions. Our results also lead to an experiment on the
addition of chloride for a better disinfection.
Data presented in table 6 indicate that the addition of chloride in the nutrient
solutions following disinfestation with ozone and peroxide was very effective not only at
low concentrations (1-2 ppm), but also after a period of storage. The highest chloride
concentration (5 ppm) cannot be recommended as it was shown to be toxic to various
crops. This strategy seems to improve greatly the effects of ozone and peroxide, but also
appears to offer an interesting alternative to inhibit bacterial development in the storage
tank.
Ozonization did not affect the composition of the nutrient solutions as shown in
table 7. In fact, EC stayed quite constant at around 4.0 mmhos/cm, while pH varied very
slightly between 5.8 and 6.0. Major elements such as N, P, K, Ca and Mg were very
constant following ozonization at either 5.3 or 14.1 ppm. Although Fe and Mn concentra-
tions were shown to be reduced by ozonization (Vanachter et al., 1988), our data indicate
that their concentrations in the nutrient solutions were not affected.
After 12 weeks of recirculation, ozonization did not affect growth and develop-
ment (data not presented) of tomato as measured by stem diameter, leaf length, height of
the first cluster or fruit number on the plants. Yields were neither affected by the recircu-
lation and the ozonization of the nutrient solutions. Leaching of the nutrient solutions
averaged 36 and 38 % for the recirculated and the not-recirculated treatments,
respectively. The percentage of recirculation was satisfactory, being most of the time
above 80% for the first 10 weeks of the experiments.
CONCLUSION
Our data agree with those of Runia (1994) and Rey et al. (2001) indicating that
ozonization would reduce significantly the number of microorganisms in the nutrient
solutions. However, it seems that the highest concentration of ozone alone was not
sufficient to completely eliminate bacteria and fungi in the nutrient solutions. The
addition of peroxide and/or the increase in the duration of the ozonization did improve the
efficiency of the process, without obtaining complete disinfection. Complete disinfection
was only achieved with the combination of ozone, peroxide and chloride. Further research
will study the best combinations of ozone, peroxide and/or chloride to obtain complete
and lasting disinfection at the lowest cost.
ACKNOWLEDGMENTS
The authors thank the Ministère de l’Agriculture, des Pêcheries et de
l’Alimentation du Québec (CORPAQ) and Savoura for their financial support as well as
the technical staff at Savoura, the Laboratoire de diagnostic en phytoprotection of
Agriculture Québec and the CRH at université Laval.
Literature Cited
Dorais, M., Papadopoulos, A.P. and Gosselin, A. 2001. Greenhouse tomato fruit quality.
Horticultural Review, Vol 26 : 239-319.
Le Quillec, S. et al. 2002. Gestion des effluents des cultures maraîchères sur substrat.
CTIFL. France.
Poncet, C. et al. 2001. Desinfection systems of recycled effluents in flower crops. Acta
Horticulturae Vol 554: 349-354.
Rey, P. et al. 2001. Evolution of pythium spp. population in soilless cultivation and their
control by active disinfecting methods. Acta Hort. Vol. 554: 341-348.
Runia, W.T. 1994, Desinfection of recirculation water from closed cultivation systems
with ozone, Acta Hort. Vol. 382: 221-229
Runia, W.T. 2001. Desinfection of recirculation water from closed cultivation systems by
heat treatments. Acta Hort. Vol. 548: 215-222.
392
Vanacher, L.T., Wanbeke, E.V. and Van Assche, C. 1988. Possible use of ozone for dis-
infection of plant nutrient solutions. Acta Hort. Vol. 221: 295-302.
Tab l e s
Table 1. Ozone concentration in the nutrient solutions according to different production
capacity and treatment rates.
Ozone production*
(g O3 / hr)
Treatment rate
( m3 of water/hr)
or ppm)
Estimated ozone
concentration
(g O3/m3)
Duration of O3 injection*
(min / m3 of water)
32-40 9.1 3.5 7
40-60 9.1 5.3 7
40-60 6.2 7.7 10
40-60 3.4 14.1 18
* According to the manufacturer, the system produces 8-10 g of ozone per corona lamp. We assumed 8 g of
ozone in our experiments * O3 half-life is estimated to 30 minutes. After injection, O3 continues to react
until its breakdown.
Table 2. Influence of ozonization treatments on the detection of various fungi.
3.5 ppm* 5.3 ppm 14.1 ppm
Fungi Non-Treated Treated Non-Treated Treated Non-Treated Treated
________ __________ ______ __________ ______ __________ ______
Oomycetes 3** 1 2 3 2 3
Botrytis cinerea 0 2 0 1 3 1
Fusarium spp. 3 2 1 3 5 4
F. oxysporum 1 1 0 1 2 1
Pythium spp. 3 0 4 0 2 2
P. dissocutum 1 0 3 0 4 0
• *Calculated concentrations of ozone according to the power of the generator and the rates of the nutrient
solution
• ** 0 = not infected; 1 = starting infection; 2 = light infection; 3 = moderate infection; 4 = infected; 5 =
severely infected; 6 = very severely infected
Table 3. Influence of the duration of ozonization of the nutrient solution on the number of
bacteria in petri dishes.
Duration of
ozonization (min)
Total O3 injected
(g O3 / m3)
ORP* (mV) Number of bacteria
(CFU/ml)
Non-treated --- --- 4906
30 11.5 494 187
60 23.1 615 80
90 34.6 740 40
120 46.2 819 20
* Oxydo-reduction potential measured in the nutrient solutions in millivolts
393
Table 4. Influence of ozonization and peroxide concentration in the nutrient solutions on
the number of bacteria in petri dishes.
Number of bacteria (CFU/ml)
Peroxide concentration (ppm) Treated* Non-treated
0 3706 5653
1 800 2693
2 500 1467
3 566 1960
4 133 1413
5 80 1466
________________________________________________________________________
* Ozonization occurred at an estimated concentration of 14.1 ppm for a period of 18 min/m3.
Table 5. Influence of ozonization followed by peroxide treatment (5 ppm) of the nutrient
solutions on the number of bacteria and fungi (CFU/ml) in petri dishes.
Ozonization (ppm)
Sampling sites* 7.7 * 14.1
Bacteria Fungi Bacteria Fungi
In the ozonization reservoir 1866 19 826 27
At the exit of the ozonization reservoir 113 13 266 13
Immediately in the storage tank 26 16 13 30
After 18H00 in the storage tank 260 24 N/A N/A
________________________________________________________________________
*Counts of bacteria and fungi for the non-treated (no O3, no peroxide) nutrient solution were 6296 and 56,
respectively.
Table 6. Influence of chloride addition following ozone and peroxide treatments of the
nutrient solutions on the number of bacteria (CFU/ml) in petri dishes.
Time of sampling
Chloride concentrations (ppm) After treatment after 16H00 of storage
0 973 720
1 0 46
2 0 0
5 0 0
________________________________________________________________________
* Ozonization occurred at 7.7 ppm at a rate of 9,6 min/m3 and 5 ppm of peroxide was added
394
Table 7. Influence of ozonization on the mineral concentration of the nutrient solutions.
Elements Non-treated Treated Non-treated Treated
(7.7 ppm) ( 14.1 ppm)
________________________________________________________________________
EC* 4,02 4,15 3,89 3,90
pH 6,1 6,0 5,8 6,0
N 238 263 239 241
P 38 43 44 43
K 227 248 395 402
Ca 471 500 374 382
Mg 151 150 92 92
Sulphates 717 692 527 536
Na 25 25 17 17
Fe 1.68 1.88 116 1.23
Mn 0.93 1.84 0.86 1.25
________________________________________________________________________
* EC as electric conductivity in mmhos/cm
