Environmental Engineering Reference
In-Depth Information
In arid climatic conditions, which are typical for many countries in the Southern
African region, where water resources are scarce, the wastewater reuse practice in
general, and the wastewater reuse for irrigation purposes in particular, should be
encouraged and should be viewed as an alternative source of water. Such practice has the
following benefits:
• Reduces the volumes of fresh water resources needed for different irrigational activities;
• Reduces the need of fertilizers;
• Improves the soils' quality due to the addition of organic materials;
• Reduces the cost of wastewater treatment, in cases where high effluent standards are
required for discharge into natural water bodies.
The practice of wastewater and sludge reuse has limitations, which need to be considered
in order to prevent undesirable impacts on human health and the environment, which
could be summarized as follows:
• The volumes of wastewater and sludge produced are relatively constant with no time
interruption throughout the year and with a relatively low diurnal and seasonal
variation, while the demand for any beneficial use of the treated effluent and sludge
usually varies, and this is very much pronounced in the case of irrigation. Therefore,
this practice requires a proper consideration and management of the irrigation process
and the provision of storage volumes or other alternatives.
• The wastewater reuse practice should comply with specified requirements with respect
to the quality of the treated effluent and sludge, corresponding to each specific type of
use. The compliance with these requirements must be very strict and should be backed
up by an appropriate monitoring process. Thus, the practice requires a high standard of
operation and maintenance during the wastewater treatment process.
1.2
Land application of wastewater and sludge
Land application of municipal sludge is one of the beneficial and successful options for
sludge disposal, which has been practiced since ancient times, and recently in many cities
in Europe and North America. The banning of ocean disposal and strict regulations on
landfills has seen land application, particularly for agricultural use, increasing (Pescod
1992). USEPA (1995) gives agricultural land, strip-mined land, forests, parks and
gardens as some of the land application options, whereas Pescod (1992), provides four
major categories: agricultural utilization, forest utilization, land reclamation and land
disposal.
The advantages of land application systems are:
• Water conservation;
• Easy and inexpensive maintenance;
• Provision of plant nutrients.
The limitations of land application methods are connected with risks to public health and
environmental pollution. However, the disposal of sludge on land is also a type of sludge
treatment method, close to natural treatment processes. Studies have shown that
wastewater parameters such as BOD
5
, suspended solids and fecal indicator organisms are
