Water waste management is the field of handling waste water to make it suitable to either be recycled into a water system or to be disposed of in an environmentally-conscious manner. This is one of the larger problems facing most major cities in the modern world, with overflow causing severe pollution problems and increasing population densities stretching existing infrastructure to the breaking point. Both mechanical and biological processes are used to manage waste water to get rid of undesirable particulate matter and to eliminate any potentially harmful pathogens.
One of the major fields in water waste management is that of sewage treatment. This covers domestic sewage, commercial runoff, environmental runoff, and more. Households produce sewage as waste from their toilets, showers, sinks, and baths, which is generally either pumped into a leech field on the premises, or else sent into a central sewage system. Industrial wastewater can be particularly dangerous, often with harmful pollutants added to the water and introduced into the sewage system. In some regions, this wastewater is specially regulated, and may require a special facility to process.
A substantial problem in modern management has arisen as existing sewage systems are filled close to capacity. Many modern cities allow runoff from rainstorms to filter directly into the sewage system, which adds a stress to an already stretched system. As a result, during particularly heavy storms or storms that last for long periods of time, the rainwater may cause the sewage system to exceed its capacity, creating what is called a combined sewer overflow, which can be a mess both within the cities and on the coastline.
Sewage in a major city is generally treated at a central facility, where it is sent by an extensive series of pipes and pumps. Most management systems have three distinct tiers, referred to simply as primary, secondary, and tertiary treatments. Primary treatment involves separating solids out of the water, generally through mechanical means such as settling and filtration. Secondary treatment involves using biological means, such as micro-organisms, to bring dissolved material out of solution and into a solid form. Tertiary treatment then involves removing these solids from the water, and treating the resulting water to purify it, generally through microfiltration or chemical additives.
On an individual level, water waste management may be used by households that are not on a sewage system or by households that wish to reduce the amount of waste it pumps into a sewage system. In recent years, many regions have allowed for the separation of wastewater into greywater and blackwater. Greywater is the relatively uncontaminated water that results from activities like doing laundry, showering, or washing dishes. Blackwater, on the other hand, is sewage from toilet systems.
While blackwater must, by law in most regions, be either sent into a sewage system or into a leech field, greywater is less regulated. Many modern homes use basic filtration systems to make it suitable for a number of water-intensive activities that do not require potable water. For example, people may use greywater to water their gardens or landscaping, or to refill the cisterns on toilets for flushing. This is a simple and effective form of water waste management that can save large amounts of water annually, as well as reducing the workload of sewage systems.