Environmental Engineering Reference
In-Depth Information
Nickel (N)I
50.0
40 000
x
Lead (Pb)
6.6
10 100
x
Zinc (Zn)
46.5
70 700
x
Arsenic (As)
2.0
3 000
x
Selenium (Se)
2.0
3 000
x
Boron (B)
10.0
16 000
x
Fluoride (F)
100.0
80 000
x
• Risks, associated with the consumption of the products of the irrigated field;
• Risks, associated with the personnel, operating the field;
• Risks, associated with the soil conditions of the irrigated field.
The primary concern when sludge is used for irrigation is related to the health risks for
close-lying neighborhoods and for the consumers of the products, irrigated with reused
sewage. Sludge land disposal sites should be well protected to avoid the spreading of
sludge or effluent to the neighborhood or access of unauthorized persons to the site. For
these reasons, surface irrigation methods are preferred to spring irrigation, as the wind
could spread wastewater or sludge outside the protected areas. The risks vary greatly
depending on the local state of sanitation in the area, farming methods, customs and
climate. In general, sewage should not be used on or near crops that are eaten raw
.
The
use of sewage on hay meadows does not seem to pose any great problems, while for
grazed pastures, a proper rotating scheme of irrigation could considerably reduce the risk.
Cereals, beets and oleaginous crops are the types of cultivation more suited.
The main health risk of the sludge disposal on land technique is associated with the
personnel, which would operate the site and is exposed to direct contact with the sludge
or wastewater. A proper training program in respect to safety requirements, together with
proper protective clothing and good hygienic facilities at the site would help to prevent
the spreading of diseases among the personnel.
The main risk to soils, irrigated with treated sewage are clogging, increased salinity,
and the introduction of toxins. Land disposal can alter the physical properties of the soil.
In particular, the introduction of an excessive amount of sodium and the absence of
leaching can destroy the soil structure. An effluent that has a salinity level exceeding 2 g/l
also causes trouble and leads to a stricter control on the quantity of the water that is
spread and the level of salinity in the soil. The carbon/nitrate ratio remains one essential
crop requirement. One of the drawbacks of using sewage for irrigation is that it may raise
the nitrate level of ground water. Therefore, a specific monitoring program to control soil
characteristics during the operational life of the site is important and could prolong its
design life substantially. More information with respect to the control parameters and
maximum permissible criteria are presented in Chapter 9.
