Agriculture Reference
In-Depth Information
Table 5.11
Composition of Wastewater Typical of a Large Winery
Measured component
Value
a
Biological oxygen demand
1000-12000 mg/L
pH
5-7.5
Electrical conductivity
1.5-3 dS/m
b
Total nitrogen (mainly organic)
25-50 mg/L
Total phosphorus (mainly organic)
5-20 mg/L
Calcium
40-450 mg/L
Magnesium
15-60 mg/L
Sodium
40-150 mg/L
Sodium adsorption ratio
0.5-5 (mmol charge (+))
1/2
a
The variation occurs both within and between seasons.
b
Multiply by 640 to give total dissolved salts in milligrams per liter.
the soil solution is decreased, ideally to less than 3 (corresponding to an exchange-
able sodium percentage <6). Another approach is to use K-based chemicals for
cleaning and to recover much of the K as potassium tartrate from the marc (this
requires the separated solids be sent away for treatment, see box 5.5).
Additionally, wastewater contains a small concentration of cationic poly-
mers that are used in winemaking to remove suspended colloids. These polymers
(possibly alum, a complex aluminum sulfate) can adversely affect soil biological
health. However, if the wastewater pH is adjusted to 7 or above with lime, the
polymers are precipitated; also, any zinc (Zn) and Cu contaminants are precipi-
tated as hydroxides. Such pH adjustment can also eliminate the offensive odor of
hydrogen sulfide (H
2
S) gas emitted from the settling and storage ponds.
Measurements of microbial activity at long-term disposal sites (with pastures
more than 20 years old) have shown that soil health is not impaired, provided
the wastewater is properly treated initially. Similarly, in the McLaren Vale region,
South Australia, reclaimed sewage water has been used to irrigate vineyards since
1999 and is now second only to bore water in its number of users. Tests have
shown that microbial activity in these soils has not suffered compared to soils irri-
gated with “mains” water. Figure 5.14 shows an example of healthy vines that are
drip irrigated with reclaimed water in McLaren Vale.
Leaching Requirement for Salt Control
When wastewater is used for productive irrigation, the amount applied should be
determined by the
ET
demand of the crop (see “Evaporation and Transpiration,”
chapter 4). However, repeated applications of wastewater will gradually increase
salts in the soil and restrict the range of plants that can be grown. To avoid this
problem, a leaching requirement should be incorporated into the irrigation sched-
ule, as discussed in box 4.11, chapter 4.
