Water  pollution :  Sources, effects and control measures

Sources of surface water pollution are generally grouped into two categories based on their origin.

Point sources:- (contaminants that enter a waterway from a single, identifiable source, such as a pipe or ditch) . Ex. discharge from a sewage treatment plant, a factory, or a city storm drain.

Non–point sources (NPS) :- (diffuse contamination that does not originate from a single discrete source). NPS pollution is often the cumulative effect of small amounts of contaminants gathered from a large area. Ex. leaching out of N compounds from fertilized agricultural lands. Contaminated storm water washed off of parking lots, roads and highways, called urban runoff.

Types

Oxygen-depleting substances

Oxygen-depleting substances may be natural materials, such as plant matter (e.g. leaves and grass) as well as man-made chemicals. Other natural and anthropogenic substances may cause turbidity (cloudiness) which blocks light and disrupts plant growth, and clogs the gills of some fish species.

Many of the chemical substances are toxic. Pathogens can produce waterborne diseases in either human or animal hosts. Alteration of water's physical chemistry includes acidity (change in pH), electrical conductivity, temperature, and eutrophication. Eutrophication is an increase in the concentration of chemical nutrients in an ecosystem to an extent that increases in the primary productivity of the ecosystem. Depending on the degree of eutrophication, subsequent negative environmental effects such as anoxia (oxygen depletion) and severe reductions in water quality may occur, affecting fish and other animal populations.

Pathogens

Coliform bacteria are a commonly used bacterial indicator of water pollution, although not an actual cause of disease. Other microorganisms sometimes found in surface waters which have caused human health problems include Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia,Salmonella ,Novovirus and other viruses, Parasitic worms (helminths).

High levels of pathogens may result from inadequately treated sewage discharges. This can be caused by a sewage plant designed with less than secondary treatment (more typical in less-developed countries). In developed countries, older cities with aging infrastructure may have leaky sewage collection systems (pipes, pumps, valves), which can cause sanitary sewer overflows. Some cities also have combined sewers, which may discharge untreated sewage during rain storms. Pathogen discharges may also be caused by poorly managed livestock operations.

Chemical and other contaminants

Contaminants may include organic and inorganic substances.

Organic water pollutants include:

·         Detergents

·         Disinfection by-products found in chemically disinfected drinking water, such as chloroform

·         Food processing waste, which can include oxygen-demanding substances, fats and grease

·         Insecticides and herbicides, a huge range of organohalides and other chemical compounds

·         Petroleum hydrocarbons, including fuels (gasoline, diesel fuel, jet fuels, and fuel oil) and lubricants (motor oil), and fuel combustion byproducts, from stormwater runoff

·         Tree and bush debris from logging operations

·         Volatile organic compounds (VOCs), such as industrial solvents, from improper storage.

·         Chlorinated solvents, which are dense non-aqueous phase liquids (DNAPLs), may fall to the bottom of reservoirs, since they don't mix well with water and are denser.

o    Polychlorinated biphenyl (PCBs)

o    Trichloroethylene

·         Perchlorate

·         Various chemical compounds found in personal hygiene and cosmetic products

Inorganic water pollutants include:

·         Acidity caused by industrial discharges (especially sulfur dioxide from power plants)

·         Ammonia from food processing waste

·         Chemical waste as industrial by-products

·         Fertilizers containing nutrients--nitrates and phosphates--which are found in stormwater runoff from agriculture, as well as commercial and residential use

·         Heavy metals from motor vehicles (via urban stormwater runoff) and acid mine drainage

·         Silt (sediment) in runoff from construction sites, logging, slash and burn practices or land clearing sites

Macroscopic pollution—large visible items polluting the water—may be termed "floatables" in an urban stormwater context, or marine debris when found on the open seas, and can include such items as:

·         Trash or garbage (e.g. paper, plastic, or food waste) discarded by people on the ground, along with accidental or intentional dumping of rubbish, that are washed by rainfall into storm drains and eventually discharged into surface waters

·         Nurdles, small ubiquitous waterborne plastic pellets

·         Shipwrecks, large derelict ships

Thermal pollution

Thermal pollution is the rise or fall in the temperature of a natural body of water caused by human influence. Thermal pollution, unlike chemical pollution, results in a change in the physical properties of water. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. Elevated water temperatures decreases oxygen levels (which can kill fish) and affects ecosystem composition, such as invasion by new thermophilic species. Urban runoff may also elevate temperature in surface waters.

Thermal pollution can also be caused by the release of very cold water from the base of reservoirs into warmer rivers.

Effects

Water pollution affects our, rivers, lakes, oceans and drinking water. Some water pollution effects show up immediately where as others don’t show up for months or years. The water pollution has damaged the food chain and is very important for the food preparation of plants through photosynthesis. When Filth is thrown in water the toxins travel from the water and when the animals drink that water they get contaminated and when humans tend to eat the meat of the animals is infected by toxins it causes further damage to the humans. Infectious diseases such as cholera and typhoid can be contracted from drinking contaminated water. Our whole body system can have a lot of harm if polluted water is consumed regularly. Other health problems associated with polluted water are poor blood pressure, vomiting, skin lesions and damage to the nervous system. In fact the evil effects of water pollution are said to be the leading cause of death of humans across the globe. Pollutants in the water alter the overall chemistry of water, causing a lot of changes in temperature. These factors overall have had an adverse effect on marine life and pollutes and kills marine life. Marine life gets affected by the ecological balance in bodies of water, especially the rivers and the lakes.

Fish and shellfish kills have been reported, because toxins climb the food chain after small fish consume copepods, then large fish eat smaller fish, etc. Each successive step up the food chain causes a stepwise concentration of pollutants such as heavy metals (e.g. mercury) and persistent organic pollutants such as DDT. This is known as biomagnification, which is occasionally used interchangeably with bioaccumulation.

Large gyres (vortexes) in the oceans trap floating plastic debris. The North Pacific Gyre for example has collected the so-called "Great Pacific Garbage Patch" that is now estimated at 100 times the size of Texas. Many of these long-lasting pieces wind up in the stomachs of marine birds and animals. This results in obstruction of digestive pathways which leads to reduced appetite or even starvation.

Control

Domestic sewage

In urban areas, domestic sewage is typically treated by centralized sewage treatment plants. In the U.S., most of these plants are operated by local government agencies, frequently referred to as publicly owned treatment works (POTW). Municipal treatment plants are designed to control conventional pollutants: BOD and suspended solids. Well-designed and operated systems (i.e., secondary treatment or better) can remove 90 percent or more of these pollutants. Some plants have additional sub-systems to treat nutrients and pathogens.

A household or business not served by a municipal treatment plant may have an individual septic tank, which treats the wastewater on site and discharges into the soil. Alternatively, domestic wastewater may be sent to a nearby privately owned treatment system (e.g. in a rural community).

Industrial wastewater

Some industrial facilities generate ordinary domestic sewage that can be treated by municipal facilities. Industries that generate wastewater with high concentrations of conventional pollutants (e.g. oil and grease), toxic pollutants (e.g. heavy metals, volatile organic compounds) or other nonconventional pollutants such as ammonia, need specialized treatment systems. Some of these facilities can install a pre-treatment system to remove the toxic components, and then send the partially-treated wastewater to the municipal system. Industries generating large volumes of wastewater typically operate their own complete on-site treatment systems.

Some industries have been successful at redesigning their manufacturing processes to reduce or eliminate pollutants, through a process called pollution prevention.

Heated water generated by power plants or manufacturing plants may be controlled with:

·        cooling ponds, man-made bodies of water designed for cooling by evaporation, convection, and radiation

·        cooling towers, which transfer waste heat to the atmosphere through evaporation and/or heat transfer

·        cogeneration, a process where waste heat is recycled for domestic and/or industrial heating purposes.

Agricultural wastewater

Nonpoint source controls

Sediment (loose soil) washed off fields is the largest source of agricultural pollution in the United States. Farmers may utilize erosion controls to reduce runoff flows and retain soil on their fields. Common techniques include contour plowing, crop mulching, crop rotation, planting perennial crops and installing riparian buffers.

Nutrients (nitrogen and phosphorus) are typically applied to farmland as commercial fertilizer; animal manure; or spraying of municipal or industrial wastewater (effluent) or sludge. Nutrients may also enter runoff from crop residues, irrigation water, wildlife, and atmospheric deposition. Farmers can develop and implement nutrient management plans to reduce excess application of nutrients.

To minimize pesticide impacts, farmers may use Integrated Pest Management (IPM) techniques (which can include biological pest control) to maintain control over pests, reduce reliance on chemical pesticides, and protect water quality.

Point source wastewater treatment

Farms with large livestock and poultry operations, such as factory farms, are called concentrated animal feeding operations or confined animal feeding operations in the U.S. and are being subject to increasing Government regulation. Animal slurries are usually treated by containment in lagoons before disposal by spray or trickle application to grassland. Constructed wetlands are sometimes used to facilitate treatment of animal wastes, as are anaerobic lagoons. Some animal slurries are treated by mixing with straw and composted at high temperature to produce a bacteriologically sterile and friable manure for soil improvement.

Construction site stormwater

Sediment from construction sites is managed by installation of:

·        erosion controls, such as mulching and hydroseeding, and

·        sediment controls, such as sediment basins and silt fences.

Discharge of toxic chemicals such as motor fuels and concrete washout is prevented by use of:

·        spill prevention and control plans, and

·        specially designed containers (e.g. for concrete washout) and structures such as overflow controls and diversion beams.

 Urban runoff (storm water)

Effective control of urban runoff involves reducing the velocity and flow of storm water, as well as reducing pollutant discharges. Local Governments use a variety of stormwater management techniques to reduce the effects of urban runoff.

Pollution prevention practices include low impact development techniques, installation of green roofs and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides). Runoff mitigation systems include infiltration basins, bioretention systems, constructed wetlands, retention basins and similar devices.

Thermal pollution from runoff can be controlled by stormwater management facilities that absorb the runoff or direct it into groundwater, such as bioretention systems and infiltration basins. Retention basins tend to be less effective at reducing temperature, as the water may be heated by the sun before being discharged to a receiving stream.