Sources of wastewater include the following
domestic or household activities:
Ø Human excreta (feces and urine) often mixed with used toilet paper or wipes; this is known as black water if it is collected with flush toilets
Ø Washing water (personal, clothes, floors, dishes, cars,
etc.), also known as grey water or sullage
Ø Surplus manufactured liquids from domestic sources
(drinks, cooking oil, pesticides, lubricating oil, paint, cleaning liquids, etc.)
Ø Activities producing industrial
Ø Industrial site
drainage (silt, sand, alkali, oil, chemical
Ø Industrial cooling waters (biocides, heat, slimes, silt)
Ø Industrial processing waters
Ø Organic or biodegradable waste, including waste from hospitals, abattoirs, creameries, and food factories.
Ø Organic or non bio-degradable waste that is
difficult-to-treat from pharmaceutical or pesticide manufacturing
Ø Extreme pH waste from acid and alkali manufacturing
Ø Toxic waste from metal plating, cyanide production, pesticide manufacturing, etc.
Ø Solids and emulsions from paper mills, factories producing lubricants or hydraulic oils, foodstuffs, etc.)
Ø Water used in hydraulic
Ø Produced water from oil & natural gas production
Ø Other activities or events:
Ø 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, herbicides and pesticides from gardens,etc.)
pollution, direct and diffuse
Ø Wastewater can be diluted or mixed with other types of
water by the following mechanisms:
Ø Seawater ingress (high volumes of salt and microbes)
Ø Direct ingress of river water
Ø Rainfall collected on roofs, yards, hard-standings, etc.
(generally clean with traces of oils and fuel)
Ø Groundwater infiltrated into sewage
Ø Mixing with other types of wastewater or fecal sludge
The composition of wastewater varies widely.
This is a partial list of pollutants that may be contained in wastewater:
Chemical or physical pollutants
Ø Heavy metals, including mercury, lead, and chromium
Ø Organic particles such as feces, hairs, food, vomit, paper fibers, plant material, humus, etc.;
Ø Soluble organic material such as urea, fruit sugars, soluble proteins, drugs, pharmaceuticals, etc.;
Ø Inorganic particles such as sand, grit, metal particles, ceramics, etc.;
Ø Soluble inorganic material such as ammonia, road-salt, sea-salt, cyanide, hydrogen sulfide, thiocyanates, thiosulfates, etc.;
Ø Macro-solids such as sanitary napkins, nappies/diapers, condoms, needles, children’s toys, dead animals or plants, etc.;
Ø Gases such as hydrogen sulfide, carbon dioxide, methane, etc.;
Ø Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils, etc.;
Ø Toxins such as pesticides, poisons, herbicides, etc.
Ø Pharmaceuticals and hormones and other hazardous substances
Ø Thermal pollution from power stations and industrial manufacturers
If the wastewater contains human feces, as is the case for sewage, then it may also contain pathogens of one of the four types:
Ø Bacteria (for example Salmonella, Shigella, Campylobacter, Vibrio cholerae),
Ø Viruses (for example hepatitis A, rotavirus, enteroviruses),
Ø Protozoa (for example Entamoeba
histolytica, Giardia lamblia, Cryptosporidium
Ø Parasites such as helminths and their eggs (e.g. Ascaris (roundworm), Ancylostoma (hookworm), Trichuris (whipworm));
Ø It can also contain non-pathogenic bacteria and animals
such as insects, arthropods, small fish.
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.
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.
At a global level, around 80% of wastewater
produced is discharged into the environment untreated, causing widespread water pollution.4:2
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.5
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.
Industrial wastewater effluent with
neutralized pH from tailing runoff in Peru.
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
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.