20 ENVIRONMENT AND ENERGY
Wastewater: technical aspects
Although the exact composition of wastewater obviously varies between diverse sources and also over time, water remains, by far, its principal constituent.
By Extracted from the United Nations World Water Development Report 2017
Table 1: Advantages and disadvantages of selected types of wastewater treatment systems
WASTEWATER SOURCES AND COMPONENTS There is an often-cited statistic that wastewater is roughly composed of 99 % water and 1 % suspended, colloidal and dissolved solids. Different sources of wastewater can present other types of components in varying concentrations( see Table 1).
Domestic and municipal wastewater is likely to contain high bacterial loads, though most of the bacteria present in human faeces are not inherently pathogenic. However, when an infection occurs, a large number of pathogenic microorganisms( such as bacteria, viruses, protozoa and helminths) are spread in the environment through faeces.
In order to reduce the disease burden, the removal of pathogens is often the primary objective of wastewater treatment systems. Wastewater from industrial and mining activities, as well as from solid waste management( for example landfill leachate), may also contain toxic organic compounds such as hydrocarbons, polychlorinated biphenyls( PCBs), persistent organic pollutants( POPs), volatile organic compound( VOCs) and chlorinated solvents. Very small amounts of certain organic compounds can contaminate large volumes of water.
One litre of gasoline, for example, is enough to contaminate one million litres of groundwater. Emerging pollutants( see Box 1) can be defined as“ Any synthetic or naturally occurring chemical or any microorganism that is not commonly monitored in the environment, but has the potential to enter the environment and cause adverse ecological and( or) human health effects.”
The main categories of emerging pollutants present in wastewater are pharmaceuticals( for example antibiotics, analgesics, anti-inflammatory drugs, and psychiatric drugs), steroids and hormones( for example contraceptive drugs), personal care products( for example fragrances, sunscreen agents, insect repellents, microbeads, and antiseptics), pesticides and herbicides, surfactants and surfactant metabolites, flame retardants, industrial additives and chemicals, and plasticizers and gasoline additives.
Emerging pollutants are rarely controlled or monitored, and further research is needed to assess their impacts on human health and the environment. It is possible to reduce / mitigate the use and release of certain types of emerging pollutants through government regulation( see Box 2) and private sector engagement.
January 2018 Volume 23 I Number 11 www. plumbingafrica. co. za