Transcript Document

Urban Landscape Irrigation with Recycled
Wastewater:
Water Quality and Salinity Issues
Yaling Qian
Colorado State University
Water Reuse
In dry and highly populated
metropolitan areas, where water is a
limited natural resource, water reuse
is a viable means of coping with
potable water shortages.
 Without doubt, water reuse for
landscape irrigation will increase in
the future.

Benefits of Recycle Water
Irrigation
Water conservation;
 Always available;
 Water reclamation;
 Nutrient recycling.

Water Source for Golf Courses in
Colorado - In 2000
Potable Water
11%
Well Water
18%
Surface Water
61%
Reclaimed
Wastewater
10%
Using recycled wastewater for landscape irrigation in Colorado
started in the 1960’s to irrigate golf courses.
Water Source for Golf Course in
Colorado: In 2002
Potable Water
12%
Well Water
16%
Surface Water
52%
Recycled
Wastewater
20%
Water reuse practice has increased dramatically recently.
Successful Recycled Wastewater Reuse Cases
Olympic Club
Castle Pine International
Challenges

Sodicity and salinity problems;
Residential use of water typically adds about 200-400
mg/L of dissolved salts. Those salts have relatively high
Na content that remain after wastewater treatment.
Nutrient issues;
 Groundwater quality.

Water Quality
Parameter
Unit
Value Salt load
Total dissolved salts (TDS)
ppm or mg/L
540
Electrical conductivity (EC) dS/m or mmho/cm
0.84
Sodium
ppm or mg/L
99
Calcium
ppm or mg/L
61
Magnesium
ppm or mg/L
15
Sodium adsorption ratio
3.1
Adjusted SAR
5.0
Bicarbonate
ppm or mg/L
112
Chloride
ppm or mg/L
95
Boron
Nitrogen
ppm or mg/L
ppm or mg/L
0.23
10.3
Phosphorus
ppm or mg/L
0.8
0.448 lb/100 gal
Effects of salinity on landscape plants

Physiological drought:
Plants cannot take up enough water due to
salts.
Turf Injury
Salinity caution levels in irrigation water:
EC > 0.75 mmho/cm
or
TDS > 500 ppm.

Salinity problems
areInjury
functions of:
Turf




soil type,
management,
shallow water table will reduce
leaching and introduce salts to the
root zone,
salinity of irrigation water.
Susceptible sites for salt
accumulation:
Shallow water table,
High clay content,
Poorly drained sites,
Compacted sites.
To reduce salt accumulation in
the soil
Improve irrigation uniformity;
Improve drainage;
Leach and flush periodically.
Water Quality
Parameter
RWW
Total dissolved salts (ppm)
514
Conductivity (dS/m)
0.84
Sodium (ppm)
99
Calcium (ppm)
61
Magnesium (ppm)
15
Sodium adsorption ratio (SAR)
3.1
Sodium
absorption ratio
(SAR)
[Na]
SAR = [Ca]+[Mg]/2
Sodium Problems
Sodium
Effect on
Soil Structure
Sodium permeability hazard:
High SAR (> 12) can induce soil structure
deterioration, including soil sealing,
crusting, and reduced water penetration.
 For fine textured soil and heavy traffic
areas, irrigation water SAR as low as 6-9
can cause problems.

Sodium Management
I. Chemical amendments of water and soil
Water Treatments
Soil Treatments
Calcium
nitrate;

Lime + sulfuric acid injection;
Gypsum
(calcium sulfate);

Gypsum
Calcium
chloride;

Calcium nitrate

Calcium chloride
Water Quality
Parameter
RWW
Total dissolved salts (ppm)
614
Conductivity (dS/m)
0.84
Sodium (ppm)
99
Calcium (ppm)
61
Magnesium (ppm)
15
Sodium adsorption ratio
3.1
Adjusted SAR
5.0
Bicarbonate (ppm)
112
Adjusted SAR:
Adjusted by considering bicarbonate, carbonate, and the water’s total
salinity, in addition to water’s calcium, magnesium, and sodium content.
Bicarbonate and Adjusted SAR
• Bicarbonate can combine with Ca++ and
Mg++ to precipitate them out and increase
the water SAR;
• Bicarbonate can also raise water pH to
undesirable levels;
• If recycled wastewater has high
bicarbonate (> 120 mg/L), it is
recommended that SAR be adjusted to
consider bicarbonate content in the water
- SARadj.
To reduce bicarbonate in
irrigation water

Acidification of irrigation water (to 6.5 –7.0
pH) is effective in converting bicarbonate to
CO2 and H2O.
Water Quality
Parameter
RWW
Total dissolved salts (ppm)
614
Conductivity (dS/m)
0.84
Sodium (ppm)
99
Calcium (ppm)
61
Magnesium (ppm)
15
Sodium adsorption ratio
3.1
Adjusted SAR
5.0
Bicarbonate (ppm)
112
Chloride (ppm)
95
Sodium (ppm)
99
Boron (ppm)
0.23
Specific ion toxicities/problems
Trees are more sensitive to salts
especially sodium and chloride are
sprayed directly onto plant leaves
through irrigation water.
 If irrigation water is applied to roots
rather than leaves, plant tolerance level
to Cl and Na will increase.
 B is usually absorbed by roots.


Use low angle nozzle to reduce leaf ion
toxicity on trees and shrubs.
Declines of conifer trees have been observed under
prolonged use of RWW
Mineral Concentration
in Ponderosa Pine Needles
Parameters
Firing (0-100%)
Surface Water
Irrigation
3.17****
Recycled Water
Irrigation
33.58
B
35.69***
50.27
K
2298
2128
Na
237****
2750
K/Na
9.7****
0.8
Cl
1383
3248
*, ***, **** Significant at P0.05, 0.001, and 0.0001
respectively.
Pine needle burn and Na+ in the needles
60
Leaf firing (0-100% scale)
50
40
30
20
y = 0.0096x + 4.6998
R2 = 0.7661
10
0
0
1000
2000
3000
4000
5000
Sodium Concentration in needles (ppm)
6000
Water Quality
Parameter
RWW
Total dissolved salts (ppm)
614
Conductivity (dS/m)
0.84
Sodium (ppm)
99
Calcium (ppm)
61
Magnesium (ppm)
15
Sodium adsorption ratio
3.1
Adjusted SAR
5.0
Bicarbonate (ppm)
112
Chloride (ppm)
95
Boron (ppm)
Nitrogen (ppm)
0.23
10.3
Phosphorus (ppm)
0.8
Nutrients in Irrigation Pond



Test recycled wastewater on regular basis, and
calculate N and P input via irrigation. These
amounts of N and P should be deducted from the
fertilization program.
Increased nutrient content will increase algae
population in irrigation ponds, which will result in
secondary problems, such as decreased clarity and
aesthetic appearance. Some algal metabolites are
toxic.
Irrigation pond maintenance level will increase,
needing additional aeration and chemical
modification.
To make water reuse a success:
Support water reuse;
 Recognize that reused water and fresh water
are not of equal value and quality;
 Yes, we can manage aesthetic appealing
landscapes, but hidden costs exist.

What should be done to manage landscapes
receiving recycled wastewater?
Irrigation
 Regularly monitor water quality.
 More vigorous aeration in irrigation pond;
 Improve irrigation uniformity;
 Irrigate based on ET with additional periodic
leaching and flushing;
 Improve drainage;
 Conversion to low angle nozzles to reduce leaf
damage of trees.
What should be done to manage landscapes
receiving recycled wastewater?
Compaction control
More intensive cultivation programs (deep
aeration and water injection) to maintain
oxygen diffusion and water movement;
 More vigorous traffic control.
What should be done to manage landscapes
receiving recycled wastewater?
Fertilization and Amendments
 Reduce N and P fertilization;
 Fertilize to alleviate nutrient imbalance;
 Additional chemical amendments to displace Na;
Add to soil
Add to water
 Leaching to remove excess Na after soil
amendment treatment;
What should be done to manage landscapes
receiving recycled wastewater?
Plant Selection
Replace with more salt tolerant species
and cultivars.
Deciduous Woody Plants
Salinity Tolerance
High
Pear
Cottonwood
Siberian Elm
Green Ash
Red Maple
Amur Maple
Littleleaf Linden
Low
Cool Season Turfgrasses
High
Alkaligrass
Creeping bentgrass
Tall fescue
Fine fescues
Perennial ryegrass
Kentucky bluegrass
Low
Related Research at CSU
Research Project at CSU
Management Options for Mitigating Sodium
Stress in Effluent Irrigated Turfgrass Systems
Sponsored by the City of Westminster, Denver Water,
Plum Creek Water Authority, and Castle Pine Golf Club
Treatments:
1
2
Treatment
Gypsum
Calcium
chloride
Application
Rate
50 lb/
1000 ft2
1qt/ 1000
ft2
3
4
5
6
7
Humate
+
Gypsum
VAM
+
Gypsum
Control
1+4
No
amendment
Humate
Mycorrhizae
(VAM)
15 lb/
1000 ft2
1.4 lb/1000
ft2
1+3
Preliminary Findings




Soil texture is playing a dominant role;
Mycorrhizae treatment did not help to reduce
sodium problems and improve turf quality, but
enhanced soil redox status;
Gypsum (CaSO4) treatment enhanced leaching of
Na, but did not improve turfgrass quality;
Calcium chloride treatment helped to reduce Na
accumulation and increased turf quality in both
greenhouse and field studies.
Warren et al.
(2005)
Development and Selection of
Salt Tolerant Plants
Sponsored by US Golf Association
New saltgrass nursery at Colorado State Univ.
that contains 3000+ accessions and progenies
Four acres of saltgrass plots at CSU (containing 250
accessions and progenies.)
Selecting Conifers Trees For Landscapes With
Recycled Wastewater Irrigation
Sponsored by Denver Water