Title: WHAT ARE THE WATER TREATMENT PLANT EFFECTS ON WASTEWATER IRRIGATION BENEFITS
1WHAT ARE THE WATER TREATMENT PLANT EFFECTS ON
WASTEWATER IRRIGATION BENEFITS?
- A revision of a case study in the water-short
Guanajuato river basin in west-central Mexico
Paula Silva and Christopher Scott
2Background
- In 1999 field research was carried out by IWMI to
explore the benefits and risks of urban
wastewater reuse for crop production along the
Guanajuato river. - According to the completed research report (Scott
et al, 2000), the benefits from wastewater
irrigation include - additional water value,
- nutrient value and
- reduced (foregone) cost of water treatment.
3NOM-001-1996 Water utility must pay fine of
USD 0.25/m3 for releasing untreated wastewater
into a water body
SIMAPAG (water supply utility) Water Treatment
Plant operating since June 2002
There are at least 140 hectares of land irrigated
with treated wastewater downstream of the city
of Guanajuato in two peri-urban communities San
Jose de Cervera and Santa Catarina
4Guanajuato River
- The Guanajuato river sub-basin encompasses the
townships of Guanajuato city, Silao, Irapuato and
Romita. The wastewater produced in these
cities is normally diverted untreated along the
whole sub-basin - Presence of multiple recycling loops. From the
total river discharge of 0.305 m3/s, over half
comprised of returns loops (multiple uses). - Diversion points for wastewater irrigation
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7SIMAPAG
- Record of highest financial surplus in
Guanajuato province - General characteristics
8Water treatment plant
- Type sludge wastewater treatment. Liquid
phase derivation box, mechanic sieve, raw
wastewater pumping station, fine sieve,
biological oxidation tank, secondary
clarification and chlorine tank. Solid phase
solid waste sludge management. - Investment cost USD 3.6 million (24 federal
government, 40 local government and 36 SIMAPAG)
- Plant layout
- Design parameters
- Treatment cost (production costs OM) USD
0.11 / m3 - Existing income 10 extra charge for
sanitation services to customers (domestic USD
0.04/m3, industrial and commercial USD
0.08/m3). No treated water or solid waste is
being sold
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10Only 70 of total discharge is treated
11Urban water reuse for crop production
- INDIRECT and INFORMAL wastewater irrigation
- Around 140 hectares of land irrigated with
treated wastewater (different points of
contamination and no water quality control at
farm level) - Alfalfa is the main cultivated crop
12What are the treatment plant effects on
wastewater irrigation benefits?
- Water value impacts
- The presence of the WTP gives the opportunity of
selling the treated water competition
among sectors likely (industrial price around
USD 0.5/m3) - Nutrient value impacts
- Existing concentration of Nitrogen and
Phosphorous in the outgoing flow are enough to
meet the Alfalfa requirements. No advantage of
solid waste of WTP is taking place (30 to 40 ha
could benefit).
13What are the treatment plant effects on
wastewater irrigation benefits?
- Water treatment cost impacts
- Wastewater irrigation was not considered as an
alternative method for wastewater treatment.
14Final comments
- The major impact of the WTP in wastewater
irrigation could be the reduction of water
availability if treated water is sold to
industry. The informal wastewater irrigation is
in a weak position for competition (only 30 to 40
have proper water right and lower water
productivity, USD 0.15/m3).
15- Enforcement of environmental regulations seem
very effective and encourage wastewater treatment
plants construction but wastewater irrigation
benefits are not promoted