Environmental Engineering Reference
In-Depth Information
irrigation water demand forms by far the most substantial water use activity in a
catchment. Therefore, the reuse of treated wastewater and sludge for irrigation of
different types of agricultural products could contribute to an improved water demand
management practice and could save a considerable amount of fresh water resources for
other beneficial activities. This is of specific importance for arid countries, which have
limited water resources. Irrigation with treated sewage and sludge, as an effluent and
sludge disposal option, has the advantages of:
• Polishing the effluent through the application of natural soil filtration and purification
methods;
• Being an additional source of nutrients to the plants,
• Providing a soil building capacity and improving the organic content of soils;
• Being a cheap, easy to operate and maintain, and a cost effective technology;
• Requiring less energy, compared to other alternative sludge treatment and disposal
options;
• Conserving natural water resources; and
• Attaining an economic return from crops.
Use of sewage in agriculture is limited by several public health and environmental risks,
such as possible transmission of diseases through pollution of water resources or through
the food chain of the crops irrigated with sludge. Also, the pollution of ground water and
soils could limit their future use and pose an environmental threat for future generations.
However, an adequate design and operation practice, together with regular monitoring
could reduce to a minimum level such risks. Other limitations for the application of such
practice could be that:
• Large areas are required, due to the low reaction rate of the purification process and the
plant waterrequirements;
• Soil conditions are not suitable;
• Long transportation and energy cost might be involved, if the irrigation field is located
faraway from the treatment plant, correspondingly more intensive sludge treatment
disposal options might be economically viable, compared to disposal on land or
irrigation;
• Large storage facilities are required, especially in countries with temperate and cold
climates, in order to store the volumes, which will be released, when water is not
required for irrigation.
Sludge and effluent disposal on land, together or as separate entities, is a preferred
practice of sludge treatment and disposal in the region. This is due to the specific climatic
conditions, which allow disposal throughout the year. Sewage effluent, treated in
conventional treatment plants, could be a source of enhanced eutrophication of surface
waters, due to a high nutrient content of the effluents and sludge. Reusing the effluent
and sludge for irrigation purposes has the double effect of utilizing in an optimal way, the
already used water, and protecting the natural water resources. Land availability is also a
conducing factor, together with the relatively low-skills and low-cost operational
requirements.
The problems associated with the risks of application of this practice and possible
adverse effects on the environment have been discussed in the previous chapter. In this
