In many developing countries, sewage is the sole source of water for drinking, cooking and bathing. Unfortunately, it also contains disease-causing pathogens and other contaminants which could harm public health. Thus, understanding how much sewage is produced per person is essential when managing and planning water resources.
How much sewage is produced depends on the type and quality of wastewater in each country. Wastewater contains both organics and non-organic compounds, such as proteins, carbohydrates, oils and grease; urea, surfactants, phenols, pesticides and other chemicals; these all contribute to its composition.
Sewage is generated from various sources, such as homes, businesses, schools and farms. In urban areas, sewage is collected and treated at public sewers while in rural areas it may be treated on-site in septic systems or other small on-site treatment plants.
The amount of wastewater treated and reused depends on economic development. This can vary significantly across regions or even within a single country within an area. Generally speaking, higher economic output per capita typically translates to higher wastewater collection and treatment rates.
Economic output per capita in high-income economies allows them to invest more resources in wastewater collection, treatment and reuse – leading to an overall higher percentage of wastewater being collected, treated and recycled. Furthermore, higher treatment rates are usually achieved through better pollutant loading reduction through better wastewater collection and recycling (see the section on pollution per capita below).
Globally, total wastewater production is highest in North America at 209.5 m3 yr-1 followed by western Europe at 91.7 m3 yr-1. Sub-Saharan Africa produces significantly less wastewater at 11.0 m3 yr-1.
According to its characteristics, wastewater can be classified as either sewage or industrial. The former tends to be less polluted with organics and chemically neutral while the latter contains more odours and nutrients. Furthermore, industrial wastewater tends to have greater corrosive potential than sewage which could result in damage to piping or other infrastructure.
In general, sewage is treated more thoroughly than industrial wastewater due to its usually smaller volume of pollutants and ease of treatment. In some instances, industrial wastewater may be mixed with sewage in order to reduce chemical concentrations in the mixed liquid; however, this practice should not be done as it could further pollute receiving water bodies.
The volume of industrial wastewater discharged into the environment is a crucial factor in whether or not it can be recycled. Furthermore, how well treated it is depends on local water supply availability. In some instances, no wastewater collection or treatment takes place at all; in others, wastewater may still be collected and treated at an abandoned plant due to lack of funding or maintenance.
Detergent production, collection, treatment and reuse worldwide must be assessed in order to monitor progress towards SDG 6, which seeks to reduce untreated wastewater by half while encouraging safe reuse globally. Furthermore, it helps identify hotspots where effective wastewater management is most needed.