The amount of sewage produced per person varies based on population size and economic and development factors in a country. Furthermore, how well-equipped each country is with wastewater treatment, collection, reuse and disposal options will determine how much waste is produced.
Water used for handwashing in homes, businesses and industries contains different substances than the water we drink or use to wash our hands with. It may contain organic matter, inorganic wastes, chemicals, bacteria and fungi, salts, heavy metals, toxins or other pollutants – making its management as efficiently as possible essential.
No matter where sewage is collected – in a septic tank or at a treatment plant – it must first be processed to meet certain standards before discharge into the environment. This includes reducing pollutants, disinfection and eliminating odours.
There are various methods for measuring the quality and strength of sewage, including laboratory tests such as dissolved oxygen concentrations, pH value, biochemical oxygen demand (BOD) and chemical oxygen demand (COD), nitrogen/phosphorus content and indicators of faecal contamination. These tests determine if sewage is suitable for disposal, treatment or reuse applications.
Sewage treatment can be challenging due to its high nutrient load, which encourages plant growth and causes excess nutrients in receiving waters to deplete or kill fish and other aquatic life. Severe cases may result in foul odors as well as environmental degradation.
Management of wastewater generated in homes, businesses and industry is essential to reduce risks to public health and the environment. Different methods are used for this task – from simple septic tanks and community sewage systems to large centralized treatment plants.
Wastewater treatment is the process of eliminating organic and inorganic wastes through biological media such as trickling filters, sand filters or soil. In community systems, activated sludge treatment is commonplace where wastewater is mixed with a sludge that has been fermented by microorganisms.
The treatment of sewage is a key aspect of wider sanitation policies and regulations, which may also encompass non-sewered waste management, solid waste management and stormwater management. In certain countries, specific sewage management regulations exist which mandate separation between household and commercial sewage for separate treatment.
This process is costly and complex, so there is a strong incentive to reduce both the total volume of sewage produced in the country as well as how much enters into the sewer system.
Sewage treatment options range from biological treatment for disposal to reuse of wastewater for agricultural purposes. Each has its own advantages and drawbacks. The two most widely-used procedures are biological treatment of sewage for disposal and reuse of wastewater for agricultural purposes.
Individual countries’ sewage production, collection, treatment and reuse levels differ considerably; they tend to cluster around urban centres with the lowest rates found in regions with high wastewater collection and treatment rates such as western Europe or Scandinavia. These regional trends have global implications and can be used as a springboard for developing sustainable wastewater management systems; they also inform water quality models and human health assessments.