Laboratory analysis for irrigation water


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Sampling and monitoring of irrigation water

Before supplying recycled water for irrigation purpose, there should be performed an  analysis of the quality of this water, interpreting results, search for solutions (i.e. good management practice, use of water treatment solutions and technology as provided by Lenntech) and monitoring frequently.

For example, water with low quality and big concentration of salt may require a reverse osmosis treatment system. Water with only minor quality problems may only require slight changes in supplemental fertility.

The procedure to take samples will affect the precision and reliability of the water quality data and determine its interpretation. it is important to monitor quality standards on a frequent basis to avoid potential problems.
 

Some general considerations to take into account when making lab test of irrigation water are listed below:

- Usually 1L of sample is sufficient

- All samples should be labelled to indicate date, location, time and other pertinent data.

- Take seasonal samples for representative data due to variation of water quality by climate conditions

- Take samples before and after the treatment plant for recycled water and other representative samples when appropriate such as after the storage tank, etc.

Recommendations for samples preparation & conservation

The following table compile the recommendations for samples preparation & conservation

ParameterType of bottle1Addition of chemicalsConservation Comments
Anions and cations (Chloride, sulphate, etc.), all forms of nitrogen and phosphorus, as well as general physicochemical parameters (PH, SS, conductivity, etc.)1 L plastic, with or without airNo additiveDark, 4°CTemperature and dissolved oxygen should be measure on site
COD100 mL, plastic, no airSulphuric acidDark, 4°CNo additive is needed if the samples are analyzed within 48h
BOD500 mL, plastic, no airNo additiveDark, 4°C 
Trace elements250mL, plastic, with or without airNitric acidDark, 4°CA special bottle and additive is needed for the analysis of mercury (Hg)
Trace organics and pesticides1L, dark glass bottle, no airNo additiveDark, 4°C 
Microbiological parameters (total and faecal coliforms, heminths, viruses, etc.)1-5L, sterile plastic bottle, with airNo additiveDark, 4°CAdditive should be added only to disinfected effluent (sodium thiosulfate in presence of residual chlorine)

Source of information: Valentina Lazarova Akiçca Bahri; Water Reuse for irrigation: agriculture, landscapes, and turf grass; CRC Press.

1. Plastic bottles are preferred because glass bottles may introduce boron to the samples.

The following table compile the recommendations for samples preparation & conservation:
 

Monitored parametersRaw wastewater & recycled waterReceiving soilsGroundwater
Shallow aquifers      Deep aquifers
Coliforms
 
Weekly to monthly-Bi-annualAnnual
TurbidityOn-line for unrestricted irrigation---
Chlorine residualOn-line for unrestricted irrigation---
Volume
 
Monthly ---
Water level
 
--Bi-annual-
PHMonthly AnnualBi-annualAnnual
Suspended SolidsMonthly ---
Total dissolved solids Monthly -Bi-annualAnnual
Conductivity (ECi)
 
Monthly Bi-annual (ECe)Bi-annualAnnual
BOD
 
Monthly ---
Ammonia
 
Monthly -Bi-annualAnnual
Nitrites
 
Monthly -Bi-annualAnnual
Nitrates
 
Monthly Annual (exchangeable NO3)Bi-annualAnnual
Total Nitrogen
 
Monthly Bi-annualBi-annualAnnual
Total phosphorusMonthly Bi-annual (extractable P)Bi-annualAnnual
Phosphates (soluble)Monthly Bi-annualBi-annualAnnual
Major solutes (Na, Ca, Mg, K, Cl, SO4, HCO3, CO3)QuarterlyBi-annualBi-annualBi-annual
Exchangeable cations (Na, Ca, Mg, K, Al) Annual--
Trace elements ---

Source of information: Valentina Lazarova Akiçca Bahri; Water Reuse for irrigation: agriculture, landscapes, and turf grass; CRC Press.



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