Water that has been used by people and is disposed into a receiving water body with
altered physical and/or chemical parameters is defined as wastewater. If only the
physical parameters of the water were changed, e.g., resulting in an elevated temperature
after use as a coolant, treatment before final disposal into a surface water
may require only cooling close to its initial temperature. If the water, however, has
been contaminated with soluble or insoluble organic or inorganic material, a combination
of mechanical, chemical, and/or biological purification procedures may be
required to protect the environment from periodic or permanent pollution or damage.
For this reason, legislation in industrialized and in many developing countries
has reinforced environmental laws that regulate the maximum allowed residual
concentrations of carbon, nitrogen, and phosphorous compounds in purified wastewater,
before it is disposed into a river or into any other receiving water body However,
enforcement of these laws is not always very strict. Enforcement seems to be
related to the economy of the country and thus differs significantly between wealthy
industrialized and poor developing countries. In this chapter basic processes for biological
treatment of waste or wastewater to eliminate organic and inorganic pollutants
are summarized.
