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