Wastewater (or waste water) is any water that has been negatively impacted by human use. Wastewater is a result of domestic, industrial, commercial or agricultural activities. In other words: Wastewater is "used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff or stormwater, and any sewer inflow or sewer infiltration". Wastewater contains a large number of physical, chemical and biological pollutants at varying concentration levels.
Wastewater produced by households or communities is also called municial wastewater or sewage. Households produce wastewater by using flush toilets, sinks, dishwashers, washing machines, bath tubs, showers.
Wastewater may be conveyed in a combined sewer (which includes runoff water from storms) or a sanitary sewer (which conveys only sewage). Once transported to a wastewater treatment plant, the treated wastewater (also called effluent) is discharged to a receiving water body. Treated wastewater can also be reused for various purposes - an approach also called "water reclamation".
In developing countries and in low-density rural areas, wastewater is often not collected in centralized sewer systems but rather dealt with by various on-site sanitation systems. This can include septic tanks connected to drain fields, pit latrines, dry toilets, vermifilter systems and many more.
Terminology
The overarching term sanitation includes the management of wastewater, human excreta, solid waste and storm water. The term sewerage refers to the physical infrastructure required for transporting and treating wastewater.
Sources
Wastewater can come from:
- Human excreta (feces and urine) often mixed with used toilet paper or wipes; this is known as blackwater if it is collected with flush toilets
- Washing water (personal, clothes, floors, dishes, cars, etc.), also known as greywater or sullage
- Surplus manufactured liquids from domestic sources (drinks, cooking oil, pesticides, lubricating oil, paint, cleaning liquids, etc.)
- Urban runoff from highways, roads, carparks, roofs, sidewalks/pavements (contains oils, animal feces, litter, gasoline/petrol, diesel or rubber residues from tires, soapscum, metals from vehicle exhausts, de-icing agents, etc.)
- Storm drains (may include trash)
- Manmade liquids (illegal disposal of pesticides, used oils, etc.)
- Industrial waste
- Industrial site drainage (silt, sand, alkali, oil, chemical residues);
- Industrial cooling waters (biocides, heat, slimes, silt)
- Industrial process waters
- Organic or biodegradable waste, including waste from abattoirs, creameries, and ice cream manufacture
- Organic or non bio-degradable/difficult-to-treat waste (pharmaceutical or pesticide manufacturing)
- Extreme pH waste (from acid/alkali manufacturing, metal plating)
- Toxic waste (metal plating, cyanide production, pesticide manufacturing, etc.)
- Solids and emulsions (paper manufacturing, foodstuffs, lubricating and hydraulic oil manufacturing, etc.)
- Hydraulic fracturing
- Produced water from oil & natural gas production
- Agricultural pollution, direct and diffuse
Wastewater can be diluted or mixed with other types of water in the form of:
- Seawater ingress (high volumes of salt and microbes)
- Direct ingress of river water
- Rainfall collected on roofs, yards, hard-standings, etc. (generally clean with traces of oils and fuel)
- Groundwater infiltrated into sewage
After it has undergone some treatment, the "treated wastewater" remains, e.g.:
- Septic tank discharge
- Sewage treatment plant discharge
Pollutants
The composition of wastewater varies widely. This is a partial list of pollutants that may be contained in wastewater:
Chemical or physical pollutants
- Heavy metals, including mercury, lead, and chromium
- Organic particles such as feces, hairs, food, vomit, paper fibers, plant material, humus, etc.;
- Soluble organic material such as urea, fruit sugars, soluble proteins, drugs, pharmaceuticals, etc.;
- Inorganic particles such as sand, grit, metal particles, ceramics, etc.;
- Soluble inorganic material such as ammonia, road-salt, sea-salt, cyanide, hydrogen sulfide, thiocyanates, thiosulfates, etc.;
- Macro-solids such as sanitary napkins, nappies/diapers, condoms, needles, children's toys, dead animals or plants, etc.;
- Gases such as hydrogen sulfide, carbon dioxide, methane, etc.;
- Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils, etc.;
- Toxins such as pesticides, poisons, herbicides, etc.
- Pharmaceuticals and hormones and other hazardous substances
- Thermal pollution from power stations and industrial manufacturers
Biological pollutants
If the wastewater contains human feces, as is the case for sewage, then it may also contain pathogens of one of the four types:
- Bacteria (for example Salmonella, Shigella, Campylobacter, Vibrio cholera),
- Viruses (for example hepatitis A, rotavirus, enteroviruses),
- Protozoa (for example Entamoeba histolytica, Giardia lamblia, Cryptosporidium parvum) and
- Parasites such as helminths and their eggs (e.g. ascaris (roundworm), ancylostoma (hookworm), trichuris (whipworm));
It can also contain non-pathogenic bacteria and animals such as insects, arthropods, small fish.
Quality indicators
Any oxidizable material present in an aerobic natural waterway or in an industrial wastewater will be oxidized both by biochemical (bacterial) or chemical processes. The result is that the oxygen content of the water will be decreased.
Since all natural waterways contain bacteria and nutrients, almost any waste compounds introduced into such waterways will initiate biochemical reactions (such as shown above). Those biochemical reactions create what is measured in the laboratory as the biochemical oxygen demand (BOD). Such chemicals are also liable to be broken down using strong oxidizing agents and these chemical reactions create what is measured in the laboratory as the chemical oxygen demand (COD). Both the BOD and COD tests are a measure of the relative oxygen-depletion effect of a waste contaminant. Both have been widely adopted as a measure of pollution effect. The BOD test measures the oxygen demand of biodegradable pollutants whereas the COD test measures the oxygen demand of oxidizable pollutants.
Treatment
At a global level, around 80% of wastewater produced is discharged into the environment untreated, causing widespread water pollution.
There are numerous processes that can be used to clean up wastewaters depending on the type and extent of contamination. Wastewater can be treated in wastewater treatment plants which include physical, chemical and biological treatment processes. Municipal wastewater is treated in sewage treatment plants (which may also be referred to as wastewater treatment plants). Agricultural wastewater may be treated in agricultural wastewater treatment processes, whereas industrial wastewater is treated in industrial wastewater treatment processes.
For municipal wastewater the use of septic tanks and other On-Site Sewage Facilities (OSSF) is widespread in some rural areas, for example serving up to 20 percent of the homes in the U.S.
One type of aerobic treatment system is the activated sludge process, based on the maintenance and recirculation of a complex biomass composed of micro-organisms able to absorb and adsorb the organic matter carried in the wastewater. Anaerobic wastewater treatment processes (UASB, EGSB) are also widely applied in the treatment of industrial wastewaters and biological sludge. Some wastewater may be highly treated and reused as reclaimed water. Constructed wetlands are also being used.
Disposal
In some urban areas, municipal wastewater is carried separately in sanitary sewers and runoff from streets is carried in storm drains. Access to either of these systems is typically through a manhole.
During high precipitation periods a combined sewer system may experience a combined sewer overflow event, which forces untreated sewage to flow directly to receiving waters. This can pose a serious threat to public health and the surrounding environment.
Sewage may drain directly into major watersheds with minimal or no treatment but this usually has serious impacts on the quality of an environment and on the health of people. Pathogens can cause a variety of illnesses. Some chemicals pose risks even at very low concentrations and can remain a threat for long periods of time because of bioaccumulation in animal or human tissue.
Wastewater may be pumped underground through an injection well.
Reuse
Treated wastewater can be reused in industry (for example in cooling towers), in artificial recharge of aquifers, in agriculture and in the rehabilitation of natural ecosystems (for example in wetlands). In rarer cases it is also used to augment drinking water supplies. There are several technologies used to treat wastewater for reuse. A combination of these technologies can meet strict treatment standards and make sure that the processed water is hygienically safe, meaning free from bacteria and viruses. The following are some of the typical technologies: Ozonation, ultrafiltration, aerobic treatment (membrane bioreactor), forward osmosis, reverse osmosis, advanced oxidation.
Some water demanding activities do not require high grade water. In this case, wastewater can be reused with little or no treatment. One example of this scenario is in the domestic environment where toilets can be flushed using greywater from baths and showers with little or no treatment.
Irrigation with recycled wastewater can also serve to fertilize plants if it contains nutrients, such as nitrogen, phosphorus and potassium. In developing countries, agriculture is using untreated wastewater for irrigation - often in an unsafe manner. There can be significant health hazards related to using untreated wastewater in agriculture. The World Health Organization developed guidelines for safe use of wastewater in 2006.
Legislation
Australia
As part of the Environmental Protection Act 1994, the Environmental Protection (Water) Policy 2009 is responsible for the water management of Queensland, Australia.
Nigeria
In Nigeria, the Water Resources Act of 1993 is the law responsible for all kinds of water management.
Philippines
In the Philippines, Republic Act 9275, otherwise known as the Philippine Clean Water Act of 2004, is the governing law on wastewater management. It states that it is the country's policy to protect, preserve and revive the quality of its fresh, brackish and marine waters, for which wastewater management plays a particular role.
United States
The Clean Water Act is the primary federal law in the United States governing water pollution.
See also
- List of waste-water treatment technologies
- Sanitation
- Waste management
- Water management
- Water pollution
References
