An efficient and economic disposal strategy for effluents from hydroponics culture in Mauritius

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An efficient and economic disposal strategy for
effluents from hydroponics culture in Mauritius

• By Prathima SEECHURN
• Supervisor Dr B. Lalljee Associate Professor,
  University of Mauritius

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STATEMENT OF PROBLEM
Intensive Agriculture
Open field
Hydroponics Culture
Heavy use of fertiliser /agrochemicals
Only 50 of fertiliser absorbed by plants 50
lost
Excess leachate dispose in environment
Groundwater, surface water, soil contamination
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STATEMENT OF PROBLEM

• Local Studies E.g Nitrate concentration
• Values measured from boreholes of Choisy and
  Poudre Dor between 10-20 mg/L with occasional
  peaks exceeding 40mg/L at times
• At Fond du Sac, Riche Terre and Petite Rivière
  concentrations measured oscillated between 20 to
  40 mg/L

A sign of warning
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Flow of excess solution from greenhouse
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RATIONALE OF THE STUDY

• Today, public is much concerned about protecting
  our environment for future generation
• Sustainability
• Sustainable production using Good Agricultural
  Practices (GAP)
• Optimise use of fertiliser/water i.e reduce
  wastage
• price of fertiliser escalating and water becoming
  a scarce resource

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AIMS OBJECTIVES

• To assess the potential risk associated with
  hydroponics effluents and evaluate the potential
  of using it as a source of nutrients and water in
  crop production

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ACTIVITIES

• To carry out survey among hydroponics growers
• To assess the amount of liquid effluent discharge
  from hydroponics system
• Characterisation of hydroponics effluents
• To assess the performance of crops fertilised
  with hydroponics effluents - pot trials

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METHODOLOGY

• Activity 1 Survey among hydroponics growers
• Face to face interview
• Activity 2 Assessing the amount of liquid
  effluent discharge
• from hydroponics system
• To record the amount of effluents for the whole
  crop cycle at different greenhouses for different
  crops

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METHODOLOGY Activity 3 Characterisation of
Hydroponics Effluents

• To conduct a preliminary analysis
• Leaching of nutrients at different substrates
• Collecting samples at three times interval to
  evaluate for any variation in concentration
• To collect effluents from different greenhouses
• Tomato
• Sweet Pepper
• Cucumber
• others

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METHODOLOGY

• Activity 3 (Contd) Characterisation of
  Hydroponics Effluents
• Plastic tank of 50 litres capacity buried outside
  the greenhouse to collect the over drain
  solution.
• Collection of
  effluents from greenhouse

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METHODOLOGY

• Activity 3 (Contd) Characterisation of
  Hydroponics Effluents
• HYDROPONICS EFFLUENTS ANALYSIS
• Determination of
• pH
• Electrical Conductivity
• Nitrate
• Phosphate
• Macro micro elements

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METHODOLOGY

• Activity 4 Assessing the performance of crops
  fertilised with hydroponics effluents - pot
  trials (bean)
• EXPERIMENTAL DESIGN
• Randomised complete Block Design - 6 treatments
  replicated 4 times
• TREATMENTS
• T1 No fertiliser and no hydroponics effluents
• T2 Hydroponics effluents only
• T3 25 mineral fertiliser hydroponics
  effluents
• T4 50 mineral fertiliser hydroponics effluents
• T5 75 mineral fertiliser hydroponics
  effluents
• T6 100 mineral fertiliser as per recommended
  rate

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METHODOLOGY

• Activity 4 (Contd) Assessing the performance of
  crops fertilised with hydroponics effluents - pot
  trials (bean)
• PARAMETERS RECORDED
• Plant height
• Full weight of pods at maturity per plant
• Weight of whole plant
• Percentage dry matter

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RESULTSActivity 1 Survey among hydroponics
growers

• Note
• Question 1
• How do you dispose the Hydroponics
  Effluents?
• Question 2
• Are you aware of the economic value of the
  Hydroponics Effluents?
• Question 3
• Do you know that this solution can be used
  alternatively for crop production?
• Question 4
• Have you ever thought of having your
  hydroponics culture along with a small plot in
  field where hydroponics effluents is used as
  fertiliser?
• Question 5
• Will you be interested in investing in
  such technology?

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RESULTSActivity 2 Assessing the amount of
liquid effluent discharge from hydroponics system

• Under normal condition, out of an average of 100
  ml of nutrient solution provided per plant around
  60 of solution is absorbed by the plant and the
  rest are leached out as hydroponics effluents.
• On average, the amount of hydroponics effluents
  collected per day from a greenhouse is around 1
  litre per square metre and has a nitrate
  concentration of 108 mg/L.
• Hence, the amount of nitrogen lost for a
  greenhouse of 250 m2 is 27 g per day.
• Work still under progress

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RESULTSActivity 3 Characterisation of
hydroponics effluentsPreliminary Observation

• Forecast
• Area of 20 hectares under Hydroponics Culture
  22 Kg of nitrogen will be lost to the environment
  per day

Solution lost from different substrates
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RESULTSActivity 3 (Contd) Preliminary
Observation
Mean Nitrate concentration at
different time interval
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• RESULTSActivity 3 (Contd) Preliminary
  Observation

Concentration 7.30 a.m 10.30 a.m 13.30 p.m
IN 151.88 167.47 155.45
OUT 140.92 152.66 181.80
Absorbed 7.2 8.8 0
leached 92.8 91.2 116
At 13.30 p.m the plants did not absorb nitrate
nutrients. This could be explained by the fact
that in afternoon the demand for water is higher
than that of fertiliser. As such it can be
concluded that hydroponics effluents do
contribute partially to environmental pollution.
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RESULTSActivity 4 Assessing the performance of
crops fertilised with hydroponics effluents - pot
trials (bean)

• Analysis under process

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DISCUSSION

• Savings on purchase of fertilisers price of
  fertiliser escalating year by year (30 increase
  over the last year)
• Environmental cost lesser contribution to
  pollution as compared to disposal in drains

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CONCLUSION

• The use of Hydroponics Effluents for crop
  production can help to make savings on fertiliser
  and be considered as a practical alternative to
  prevent further environmental damage.
• Further research needs to be undertaken to
  understand the fate of hydroponics effluents to
  the soil/water profile

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RECOMMENDATION

• Strategies to minimise possible damage caused by
  Hydroponics Effluents would be
• - sensitization of farmers on the potential
  risk of disposing Hydroponics Effluents in
  drain,
• - Training of farmers
• - Use of Hydroponics Effluents in an integrated
  system
• - Reset fertigation time
• - Electrical Conductivity Meter to be at
  disposal of each planter
• - Review of Chemical Fertiliser Control Act
• To be worked out

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Reference

• Agricultural Research and Extension Unit (2004).
  Cultures légumières. In Le Guide Agricole.
  Published by Agricultural Research and Extension
  Unit/Food and Agricultural Research Council.
• Hochmuth. R. C and M.S Sweat, (1999).
  Hydroponics Nutrient Effluent, A recoverable
  Energy Resource. University of Florida.
• Howard M. Resh, Ph.D, (1998). A definitive
  Guidebook for the Advanced Home Gardener and the
  Commercial Hydroponics Grower, fifth edition.
• Ministry of Environment and National Development
  Unit, Government of Mauritius. (2005). Threat to
  freshwater resources. In Mauritius staking out
  the Future.
• Ministry of Environment and National Development
  Unit, Government of Mauritius. (1991). State of
  Environment Report. pp 12, 63, 72 91.

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Acknowledgements

• Field workers from AREU Crop Research Station
• Hydroponics growers
• Technical staff of the University of Mauritius
• MRC for funding.

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