Treated water for irrigation (I). WWTPs

More and more sports facilities are being supplied with treated water from wastewater treatment plants, WWTP.

WWTPs are facilities that receive waste water which reach it through the sewage network and where, through a series of treatments and processes, their contamination is eliminated, making it possible for them to be reused in our sports surfaces (fields of golf, fields of footballetc.). The processes that take place in the WWTPs reduce the consumption of dissolved oxygen in the water by decomposing the organic matter in the wastewater, and therefore the anaerobiosis that would cause bad smells, pathogenic microorganisms, etc., on our golf courses.

The most important parameters to be taken into account in relation to the quality of the WWTP supplying the irrigation water are the following:

1. Suspended solidsSolid matter larger than 1 micron in size. Easily separable from waste water if left to stand for a period of time. Limit: 35 mg/l
2. Biological Oxygen Demand (BOD5)Oxygen needed by the micro-organisms in the water to stabilise the water within a standardised time of 5 days. The higher the value, the poorer the quality of the discharge. Limit: 25 mg/l
3. Chemical Oxygen Demand (COD)Oxygen equivalent to stabilise (oxidise) pollutants in water by chemical oxidants. Limit: 125 mg/l
4. Nitrogen (these inputs have to be subtracted from the monthly fertiliser plan), ammonia, organic nitrogen, nitrates and nitrites
5. Phosphorus (inputs to be subtracted from the monthly fertilisation plan), total phosphorus, dissolved orthophosphate
6. Heavy metals
7. acidity/alkalinity
8. conductivity

The reuse of treated water requires compliance with Royal Decree 1620/2007, of 7 December, which establishes the Legal Regime for the reuse of treated water in Spain. In the case of sports fields it is given by the following:

1. Nematodes intestinal: 1 egg/10L
2. Escherichia coli: 200 CFU/100mL
3. Suspended solids: 20 mg/L
4. Turbidity: 10 UNT
5. Legionella spp: 100 CFU/L

In general, the processes that take place in WWTPs are:

1. Physical processes (decantation, thickening, drying)
2. Chemical processes (coagulation, flocculation)
3. Biological processes (aerobic, anaerobic, anoxic)

And the operations are:

1. Pre-treatment (pre-treatment, roughing)
2. Primary Treatments (physical, chemical)
3. Secondary (biological) treatments
4. Tertiary treatments (disinfection)
5. Sludge treatment (thickening, digestion, drying)

The use of stabilised sludge is an important resource that we can count on as a fertiliser in our sports facilities.