Archive record · Method record · 2020s · Saudi Arabia
Green cities in arid climates run on recycled water. Treated sewage effluent, TSE, is the irrigation supply behind large scale urban greening, and using it well is a discipline of its own. This record rebuilds an operations and maintenance briefing on treated water quality preserved in the company's Green Riyadh and Diplomatic Quarter files, alongside the irrigation standards work documented in the same program.
What recycled water carries
Recycled waters contain physical, chemical and biological constituents that can cumulatively clog the small orifices of an irrigation system, drip emitters above all.
- Physical: suspended solids, mainly sand fractions.
- Chemical: constituents that form precipitates, including calcium carbonate, iron and manganese hydroxides, and hydrogen sulfides.
- Biological: the products of microbial activity, hydroxides and sulfides generated by microbially mediated redox reactions.
The reassuring part: constituents in most recycled waters, especially waters receiving tertiary treatment, pose little restriction on use for virtually all parameters. The exception to watch is total dissolved solids, which may pose a slight to moderate restriction. There are no clear guidelines on the clogging potential of a given water type, so published values are a first approximation only: direct feedback from site managers is the best way to assess how a specific water behaves in a specific system.
The method, distilled
- Filter first: remove suspended material and organic matter from irrigation water before it reaches the system, so blockages stop before they start.
- Test on a calendar: measure the quality of every water source at least annually, covering salinity, acidity, sodium absorption ratio, suspended material, bicarbonates and elemental salts, and check pH and EC monthly.
- Design to standard: apply water evenly, with a mean application rate under 25 millimetres per hour and a coefficient of uniformity above 85 percent.
- Fertigate deliberately: nitrogen, phosphorus, potassium, sulphur, magnesium and calcium are the macronutrients to supply through soil, water and fertigation; molybdenum, copper, zinc, manganese, iron, nickel, boron and chlorine are the micronutrients. Let any of them run short and plant health and growth suffer seriously.
Why this record matters
Every ambitious greening program in an arid climate depends on recycled water, and the difference between a thriving landscape and a maintenance crisis is managed water quality: filtration, monitoring, even application and complete nutrition. The standards culture this record draws on is set out in our companion record, exporting a standard to the Gulf.
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