A flowering water-purifying plant (Iris pseudacorus)
Most organisms involved in water purification originate from the waste, wastewater
or water stream itself or arrive as resting spore of some form from the
atmosphere. In a very few cases, mostly associated with constructed wetlands, specific organisms are planted to maximise the efficiency of the process.
Role of biota
Biota are an essential component of most sewage treatment processes and many water purification systems. Most of the organisms involved are derived from the waste, wastewater
or water stream itself or from the atmosphere or soil water. However
some processes, especially those involved in removing very low
concentrations of contaminants, may use engineered eco-systems created
by the introduction of specific plants and sometimes animals. Some full
scale sewage treatment plants also use constructed wetlands to provide treatmen.
Pollutants in wastewater
Pathogens
Parasites, bacteria and viruses may be injurious to the health of people or livestock ingesting the polluted water. These pathogens may have originated from sewage or from domestic or wild bird or mammal feces. Pathogens may be killed by ingestion by larger organisms, oxidation, infection by phages or irradiation by ultraviolet sunlight unless that sunlight is blocked by plants or suspended solids.
Suspended solids
Particles of soil or organic matter may be suspended in the water. Such materials may give the water a cloudy or turbid
appearance. The anoxic decomposition of some organic materials may
give rise to obnoxious or unpleasant smells as sulphur containing
compounds are released.
Nutrients
Compounds containing nitrogen, potassium or phosphorus
may encourage growth of aquatic plants and thus increase the available
energy in the local food-web. this can lead to increased concentrations
of suspended organic material. In some cases specific micro-nutrients
may be required to allow the available nutrients to be fully utilised by
living organisms. In other cases, the presence of specific chemical
species may produce toxic effects limiting growth and abundance of
living matter.
Metals
Many
dissolved or suspended metal salts exert harmful effects in the
environment sometimes at very low concentrations. Some aquatic plants
are able to remove very low metal concentrations, with the metals ending
up bound to clay or other mineral particles.
Organisms
Saprophytic bacteria and fungi
can convert organic matter into living cell mass, carbon dioxide, water
and a range of metabolic by-products. These saprophytic organisms may
then be predated upon by protozoa, rotifers and, in cleaner waters, Bryozoa
which consume suspended organic particles including viruses and
pathogenic bacteria. Clarity of the water may begin to improve as the protozoa are subsequently consumed by rotifers and cladocera.
Purifying bacteria, protozoa, and rotifers must either be mixed
throughout the water or have the water circulated past them to be
effective. Sewage treatment plants mix these organisms as activated sludge or circulate water past organisms living on trickling filters or rotating biological contactors.
Aquatic vegetation may provide similar surface habitat for
purifying bacteria, protozoa, and rotifers in a pond or marsh setting;
although water circulation is often less effective. Plants and algae
have the additional advantage of removing nutrients from the water; but
some of those nutrients will be returned to the water when the plants
die unless the plants are removed from the water. Because of the
complex chemistry of Phosphorus
much of this element is in an unavailable form unless decomposition
creates anoxic conditions which render the phosphorus available for
re-uptake. Plants also provide shade, a refuge for fish, and oxygen for aerobic bacteria. In addition, fish can limit pests such as mosquitoes. Fish and waterfowl feces return waste to the water, and their feeding habits may increase turbidity. Cyanobacteria have the disadvantageous ability to add nutrients from the air to the water being purified and to generate toxins in some cases.
The choice of organism depends on the local climate different species and other factors. Indigenous species usually tend to be better adapted to the local environment.
Macrophytes
A water-purifying plant (Iris pseudacorus) in growth after winter (leaves die at that time of year)
The choice of plants in engineered wet-lands or managed lagoons is
dependent on the purification requirements of the system and this may
involve plantings of varying plant species at a range of depths to
achieve the required goal.
Plants purify water by consuming excess nutrients
and by providing surfaces upon which a wide range of other purifying
organisms can live. They also are effective oxygenators in sunlight.
They also have the ability to translocate chemicals between their
submerged foliage and their root systems and this is of significance in
engineered wet-lands designed to de-toxify waste waters. Plants that
have been used in temperate climates include Nymphea alba, Phragmites australis, Sparganium erectum, Iris pseudacorus, Schoenoplectus lacustris and Carex acutiformis.
Fish are
frequently the top level predators in a managed treatment eco-system and
in some case may simply be a mono-culture of herbivorous species.
Management of multi-species fisheries requires careful management and
may involve a range of fish species including bottom-feeders and
predatory species to limit population growth of the herbivorous fish.
Rotifers
Rotifers
are microscopic complex organisms and are filter feeders removing fine
particulate matter from water. They occur naturally in aerobic lagoons,
activated sludge processes, in trickling filters and in final settlement
tanks and are a significant factor in removing suspended bacterial
cells and algae from the water column.
Annelids
Annelid worms are essential to the effective operation of trickling filters
helping to remove excess bio-mass and enhancing natural sloughing of
the bio-film. Supernumerary worms are very commonly found in the
drainage troughs around trickling filters and in the final settlement
sludge. Annelids also play a key role in lagoon treatment systems and in
the effective working or engineered wet-lands. In this environment
worms are a principal force in mixing in the upper few centimetres of
the sediment layer exposing organic material to both oxidative and
anoxic environments aiding the complete breakdown of most organics. They
are also a key ingredient in the food-chain transferring energy upwards
to fish and aquatic birds.
Protozoa
The range of protozoan species found is very wide but may include species of the following genera:
Dalecarlia Water Treatment Plant, Washington, D.C.
Water treatment is any process that improves the quality of water to make it more acceptable for a specific end-use. The end use may be drinking, industrial water supply, irrigation,
river flow maintenance, water recreation or many other uses, including
being safely returned to the environment. Water treatment removes contaminants
and undesirable components, or reduces their concentration so that the
water becomes fit for its desired end-use. This treatment is crucial to
human health and allows humans to benefit from both drinking and
irrigation use.
Drinking water treatment
Treatment for drinking water production involves the removal of contaminants from raw water to produce water that is pure
enough for human consumption without any short term or long term risk
of any adverse health effect. In general terms, the greatest microbial
risks are associated with ingestion of water
that is contaminated with human or animal (including bird) faeces.
Faeces can be a
source of pathogenic bacteria, viruses, protozoa and helminths.
[Guidelines for Drinking-water quality]. Substances that are removed
during the process of drinking water treatment, Disinfection is of
unquestionable importance in the supply of safe drinking-water.
The destruction of microbial pathogens is essential and very commonly
involves the
use of reactive chemical agents such suspended solids, bacteria, algae, viruses, fungi, and minerals such as iron and manganese.
These substances continue to cause great harm to several lower
developed countries who do not have access to water purification.
Measures taken to ensure water quality not only relate to the
treatment of the water, but to its conveyance and distribution after
treatment. It is therefore common practice to keep residual
disinfectants in the treated water to kill bacteriological contamination
during distribution.
Water supplied to domestic properties, for tap water or other uses, may be further treated before use, often using an in-line treatment process. Such treatments can include water softening or ion exchange. Many proprietary systems also claim to remove residual disinfectants and heavy metal ions.
A combination selected from the following processes is used for municipal drinking water treatment worldwide.
Chemical
Tanks with sand filters to remove precipitated iron (not working at the time)
Pre-chlorination for algae control and arresting biological growth.
Aeration along with pre-chlorination for removal of dissolved iron when present with small amounts relatively of manganese.
Coagulation for flocculation or slow-sand filtration.
Coagulant aids, also known as polyelectrolytes – to improve coagulation and for more robust floc formation.
Disinfection for killing bacteria, viruses and other pathogens.
Physical
Sedimentation for solids separation that is the removal of suspended solids trapped in the floc.
Filtration
to remove particles from water either by passage through a sand bed
that can be washed and reused or by passage through a purpose designed
filter that may be washable.
Technologies
Technologies
for potable water and other uses are well-developed, and generalized
designs are available from which treatment processes can be selected for
pilot testing on the specific source water. In addition, a number of
private companies provide patented technological solutions for the
treatment of specific contaminants. Automation of water treatment is
common in the developed world. Source water quality through the seasons,
scale, and environmental impact can dictate capital costs and operating
costs. End use of the treated water dictates the necessary quality
monitoring technologies, and locally available skills typically dictate
the level of automation adopted.
Desalination
Saline water can be treated to yield fresh water. Two main processes are used, reverse osmosis or distillation.
Both methods require more energy than water treatment of local surface
waters, and are usually only used in coastal areas or where water such
as groundwater has high salinity.
Portable Water Purification
Living
away from drinking water supplies often requires some form of portable
water treatment process. These can vary in complexity from the simple
addition of a disinfectant tablet in a hiker's water bottle through to
complex multi-stage processes carried by boat or plane to disaster
areas.
Where drinking water quality standards do exist, most are
expressed as guidelines or targets rather than requirements, and very
few water standards have any legal basis or, are subject to enforcement.
Two exceptions are the European Drinking Water Directive and the Safe
Drinking Water Act in the United States, which require legal compliance
with specific standards.
Industrial water treatment
Processes
Two of the main processes of industrial water treatment are boiler water treatment and cooling water treatment.
A large amount of proper water treatment can lead to the reaction of
solids and bacteria within pipe work and boiler housing. Steam boilers
can suffer from scale or corrosion
when left untreated. Scale deposits can lead to weak and dangerous
machinery, while additional fuel is required to heat the same level of
water because of the rise in thermal resistance. Poor quality dirty
water can become a breeding ground for bacteria such as Legionella causing a risk to public health.
Corrosion in low pressure boilers can be caused by dissolved
oxygen, acidity and excessive alkalinity. Water treatment therefore
should remove the dissolved oxygen and maintain the boiler water with
the appropriate pH and alkalinity levels.
Without effective water treatment, a cooling water system can suffer
from scale formation, corrosion and fouling and may become a breeding
ground for harmful bacteria. This reduces efficiency, shortens plant
life and makes operations unreliable and unsafe.
Boiler water treatment
Boiler water treatment is a type of industrial water treatment
focused on removal or chemical modification of substances potentially
damaging to the boiler. Varying types of treatment are used at different
locations to avoid scale, corrosion, or foaming.
External treatment of raw water supplies intended for use within a
boiler is focused on removal of impurities before they reach the boiler.
Internal treatment within the boiler is focused on limiting the
tendency of water to dissolve the boiler, and maintaining impurities in
forms least likely to cause trouble before they can be removed from the
boiler in boiler blowdown.
Cooling water treatment
Water cooling is a method of heat removal from components and industrial equipment. Water may be a more efficient heat transfer fluid where air cooling is ineffective. In most occupied climates water offers the thermal conductivity advantages of a liquid with unusually high specific heat capacity
and the option of evaporative cooling. Low cost often allows rejection
as waste after a single use, but recycling coolant loops may be
pressurized to eliminate evaporative loss and offer greater portability
and improved cleanliness. Unpressurized recycling coolant loops using
evaporative cooling require a blowdown waste stream to remove impurities
concentrated by evaporation. Disadvantages of water cooling systems
include accelerated corrosion and maintenance requirements to prevent heat transfer reductions from biofouling or scale
formation. Chemical additives to reduce these disadvantages may
introduce toxicity to wastewater. Water cooling is commonly used for
cooling automobileinternal combustion engines and large industrial facilities such as nuclear and steam electric power plants, hydroelectricgenerators, petroleum refineries and chemical plants.
Technologies
*Chemical treatment
Chemical
treatments are techniques adopted to make industrial water suitable for
discharge. These include chemical coagulation, chemical precipitation,
chemical disinfection, chemical oxidation, advanced oxidation, ion
exchange, and chemical neutralization.
Developing countries
Appropriate technology options in water treatment include both community-scale and household-scale point-of-use (POU) or self-supply designs. Such designs may employ solar water disinfection
methods, using solar irradiation to inactivate harmful waterborne
microorganisms directly, mainly by the UV-A component of the solar
spectrum, or indirectly through the presence of an oxide photocatalyst, typically supported TiO2 in its anatase or rutile phases. Despite progress in SODIS technology, military surplus water treatment units like the ERDLator are still frequently used in developing countries. Newer military style Reverse Osmosis Water Purification Units (ROWPU) are portable, self-contained water treatment plants are becoming more available for public use.
For waterborne disease reduction to last, water treatment programs that research and development groups start in developing countries
must be sustainable by the citizens of those countries. This can ensure
the efficiency of such programs after the departure of the research
team, as monitoring is difficult because of the remoteness of many
locations.
Energy Consumption: Water treatment plants can be significant
consumers of energy. In California, more than 4% of the state's
electricity consumption goes towards transporting moderate quality water
over long distances, treating that water to a high standard.
In areas with high quality water sources which flow by gravity to the
point of consumption, costs will be much lower.
Much of the energy requirements are in pumping. Processes that avoid the
need for pumping tend to have overall low energy demands. Those water
treatment technologies that have very low energy requirements including trickling filters, slow sand filters, gravity aqueducts.
Regulation
United States
The Safe Drinking Water Act requires the U.S. Environmental Protection Agency (EPA) to set standards for drinking water quality in public water systems (entities that provide water for human consumption to at least 25 people for at least 60 days a year). Enforcement of the standards is mostly carried out by state health agencies. States may set standards that are more stringent than the federal standards.
EPA has set standards for over 90 contaminants organized into six
groups: microorganisms, disinfectants, disinfection byproducts,
inorganic chemicals, organic chemicals and radionuclides.
EPA also identifies and lists unregulated contaminants which may require regulation. The Contaminant Candidate List is published every five years, and EPA is required to decide whether to regulate at least five or more listed contaminants.
Local drinking water utilities may apply for low interest loans,
to make facility improvements, through the Drinking Water State
Revolving Fund
Therapsida (not to be confused with Theropsida, which is a broader group) is a group of eupelycosauriansynapsids that includes mammals and their ancestors.
Many of the traits today seen as unique to mammals had their origin
within early therapsids, including having their four limbs extend
vertically beneath the body, as opposed to the sprawling posture of reptiles. The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian.
Therapsids evolved from "pelycosaurs", specifically within the Sphenacodontia,
more than 275 million years ago. They replaced the "pelycosaurs" as the
dominant large land animals in the Middle Permian and were largely
replaced, in turn, by the archosauromorphs in the Triassic, although one group of therapsids, the kannemeyeriiforms, remained diverse in the Late Triassic.
The therapsids included the cynodonts, the group that gave rise to mammals in the Late Triassic around 225 million years ago. Of the non-mammalian therapsids, only cynodonts survived the Triassic–Jurassic extinction event. The last of the non-mammalian therapsids, the tritylodontid cynodonts, became extinct in the Early Cretaceous, approximately 100 million years ago.
Therapsid legs were positioned more vertically beneath their bodies than were the sprawling legs of reptiles
and pelycosaurs. Also compared to these groups, the feet were more
symmetrical, with the first and last toes short and the middle toes
long, an indication that the foot's axis was placed parallel to that of the animal, not sprawling out sideways. This orientation would have given a more mammal-like gait than the lizard-like gait of the pelycosaurs.
Jaw and teeth
Therapsids' temporal fenestrae were larger than those of the pelycosaurs. The jaws of some therapsids were more complex and powerful, and the teeth were differentiated into frontal incisors for nipping, great lateral canines for puncturing and tearing, and molars for shearing and chopping food.
Fur and endothermy
Several characteristics in therapsids have been noted as being consistent with the development of endothermy: the presence of turbinates, erect limbs, highly vascularized bones, limb and tail proportions conducive to the preservation of body heat, and the absence of growth rings in bones. Therefore, like modern mammals, non-mammalian therapsids were most likely warm-blooded.
Therapsids evolved from a group of pelycosaurs called sphenacodonts. Therapsids became the dominant land animals in the Middle Permian, displacing the pelycosaurs. Therapsida consists of four major clades: the dinocephalians, the herbivorous anomodonts, the carnivorous biarmosuchians, and the mostly carnivorous theriodonts. After a brief burst of evolutionary diversity, the dinocephalians died out in the later Middle Permian (Guadalupian) but the anomodont dicynodonts as well as the theriodont gorgonopsians and therocephalians flourished, being joined at the very end of the Permian by the first of the cynodonts.
Like all land animals, the therapsids were seriously affected by the Permian–Triassic extinction event; the very successful gorgonopsians dying out altogether and the remaining groups - dicynodonts, therocephalians, and cynodonts - reduced to a handful of species each by the earliest Triassic. The dicynodonts, now represented by a single family of large stocky herbivores, the Kannemeyeridae,
and the medium-sized cynodonts (including both carnivorous and
herbivorous forms), flourished worldwide throughout the Early and Middle
Triassic. They disappear from the fossil record across much of Pangea at the end of the Carnian (Late Triassic), although they continued for some time longer in the wet equatorial band and the south.
Some exceptions were the still further derived eucynodonts. At least three groups of them survived. They all appeared in the Late Triassic period. The extremely mammal-like family, Tritylodontidae, survived into the Early Cretaceous. Another extremely mammal-like family, Tritheledontidae, are unknown later than the Early Jurassic. Mammaliaformes was the third group, including Morganucodon and similar animals. Many taxonomists refer to these animals as "mammals", though some limit the term to the mammalian crown group.
The therocephalians, relatives of the cynodonts, managed to survive the Permian-Triassic extinction and continued to diversify through the Early Triassic
period. Approaching the end of the period, however, the therocephalians
were in decline to eventual extinction, likely outcompeted by the
rapidly diversifying Saurian lineage of diapsids, equipped with sophisticated respiratory systems better suited to the very hot, dry and oxygen-poor world of the End-Triassic.
Dicynodonts were long thought to have become extinct near the end of the Triassic, but there is evidence that they survived into the Cretaceous. Their fossils have been found in Gondwana.[9] This is an example of Lazarus taxon. Other animals that were common in the Triassic also took refuge here, such as the temnospondyls.
Mammals are the only living therapsids. The mammalian crown group, which evolved in the Early Jurassic period, radiated from a group of mammaliaforms that included the docodonts. The mammaliaforms themselves evolved from probainognathians, a lineage of the eucynodont suborder.
The Russian domesticated red fox is a form of the wild red fox (Vulpes vulpes) which has been domesticated to an extent, under laboratory conditions. They are the result of an experiment which was designed to demonstrate the power of selective breeding to transform species, as described by Charles Darwin in On the Origin of Species. The experiment was purposely designed to replicate the process that had produced dogs from wolves, by recording the changes in foxes, when in each generation only the most tame foxes were allowed to breed. In short order, the descendant foxes became tamer and more dog-like in their behavior.
The experiment was initiated by scientists who were interested in the topic of domestication and the process by which wolves became domesticated dogs. They saw some retention of juvenile traits by adult dogs, both morphological ones, such as skulls that were unusually broad for their length, and behavioral ones, such as whining, barking, and submission.
In a time when centralized political control in the fields of genetics and agriculture promoted Lysenkoism as an official state doctrine, Belyayev's commitment to classical genetics
had cost him his job as head of the Department of Fur Animal Breeding
at the Central Research Laboratory of Fur Breeding in Moscow in 1948. During the 1950s, he continued to conduct genetic research under the guise of studying animal physiology.
Belyayev believed that the key factor selected for in the
domestication of dogs was not size or fertility, but behavior:
specifically, tameability. Since behavior is rooted in biology, selecting for tameness and against aggression means selecting for physiological changes in the systems that govern the body's hormones and neurochemicals.
Experimentation
Belyayev decided to test his theory by domesticating foxes, in particular, the silver fox, a dark color mutation of the red fox. He placed a population of them under strong selection pressure for inherent tameness. According to Trut:
The
least domesticated foxes, those that flee from experimenters or bite
when stroked or handled, are assigned to Class III. Foxes in Class II
let themselves be petted and handled but show no emotionally friendly
response to experimenters. Foxes in Class I are friendly toward
experimenters, wagging their tails and whining. In the sixth generation
bred for tameness we had to add an even higher-scoring category. Members
of Class IE, the "domesticated elite", are eager to establish human
contact, whimpering to attract attention and sniffing and licking
experimenters like dogs. They start displaying this kind of behavior
before they are one month old. By the tenth generation, 18 percent of
fox pups were elite; by the 20th, the figure had reached 35 percent.
Today elite foxes make up 70 to 80 percent of our experimentally
selected population.
Belyayev and Trut believed that selecting for tameness mimics the
natural selection that must have occurred in the ancestral past of dogs,
and, more than any other quality, must have determined how well an
animal would adapt to life among humans.
Results
Russian scientists achieved a population of domesticated foxes that are fundamentally different in temperament and behavior from their wild forebears. Some important changes in physiology and morphology became visible, such as mottled or spotted colored fur. Some scientists believe that these changes obtained from selection for tameness are caused by lower adrenaline production in the new population,
causing physiological changes within relatively few generations
yielding genetic combinations not present in the original species. This
indicates that selection for tameness, e.g. did not flee, produces
changes that are related to the emergence of other dog-like traits, e.g.
raised tail, coming into heat every six months rather than annually. These seemingly unrelated changes are a result of pleiotropy.
The project also bred the least-tameable foxes to study social
behavior in canids. These foxes avoided human contact as do their wild
behavioral phenotypes.
Similar research was carried out in Denmark with American mink.
Current project status
Following
the demise of the Soviet Union, the project ran into serious financial
problems. In 2014, officials stated that the number of foxes was never
reduced and is still stable at about 2,000. As of August 2016, there are 270 tame vixens and 70 tame males on the farm.
In another published study, a system of measuring fox behavior was described that is expected to be useful in QTL mapping to explore the genetic basis of tame and aggressive behavior in foxes.
The sculpture "Dmitriy Belyaev and the Domesticated Fox" was
built near Institute of Cytology and Genetics (Novosibirsk) the honor of
the 100th anniversary of the birth of Dmitry Konstantinovich Belyaev.
The tamed fox gives the scientist a paw and wags its tail. Konstantin
Zinich, sculptor (Krasnoyarsk) says "The philosophy of touching a fox
and a man is rapprochement, kindness, there is no aggression from the
fox – it was wild, and he made it genetically domesticated."
Morphology
Russian domesticated foxes exhibit a variety of coat color mutations,
including red, silver (black), platinum, cross, and Georgian white, the
lattermost being a color exclusive to the Russian breeding project.
Ancient attempts
Archaeologists have discovered evidence of fox breeding in the late Iron Age on Orkney,
off the northern coast of Scotland. After the attack of the Vikings in
Scotland around A.D. 800, the breeding is said to have stopped.
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