lecture 04.pdf

Asif uz zaman(Lecturer)

Civil Engineering DepartmentFaculty of Engineering

RabighKing Abdulaziz University

Water Quality� Water quality can be defined as the current status or

condition of the water in a specific aquatic ecosystem.

� Activities such as fishing, swimming, boating, shipping,and waste disposal have different requirements for waterand waste disposal have different requirements for waterquality.

� Water of a particular high quality is needed for drinkingwater supplies.

� In many parts of the world, the introduction of pollutantsfrom human activity has seriously degraded water quality,even to the extent of turning clean streams into foul opensewers with few life forms and fewer beneficial uses.

Water quality� Water that does not impart a taste or odour and is,

therefore, pleasant to drink, is called palatable.

� Water that is free of chemicals, micro organisms, andother contaminants, and is, therefore, safe to drink, isother contaminants, and is, therefore, safe to drink, iscalled potable

� We expect our water to be both palatable and potable.

Drinking water qualityThe following four categories are used to describe

drinking-water quality.

1) Physical: Physical characteristics relate to the qualityof water for domestic use and are usually associatedwith the appearance of water, its colour or turbidity,with the appearance of water, its colour or turbidity,temperature, and, in particular, taste and odour.

2) Chemical: The chemical characterization ofdrinking water includes the identification of itscomponents and their concentration.

Contd..3) Microbiological: Microbiological agents are

important to public health and may also be significantin modifying the physical and chemicalcharacteristics of water.

4) Radiological: radiological factors must be considered4) Radiological: radiological factors must be consideredin areas where the water may have come in contactwith radioactive substances. The radioactivity of thewater is of public health concern.

Potable water classification� Potable water is most conveniently classified as to its source,

that is, ground water or surface water.

General characteristics of Ground water and Surface Water

Ground Water Surface Water

Constant Composition Varying CompositionConstant Composition Varying Composition

High mineral content Low mineral content

Low turbidity High turbidity

Low or no colour Colour

May be bacteriologically safe Microorganisms present

No dissolved Oxygen Dissolved oxygen

High hardness Low hardness

H2S, Fe, Mn Tastes and odours

Possible chemical toxicity Possible chemical toxicity

Water Quality Contd...� Water quality managers are concerned with controlling

pollution from human activity so as to ensure that thewater is suitable for its intended uses.

� Water quality management is also the science of knowinghow much waste is too much for a particular water body.how much waste is too much for a particular water body.

� To know how much waste can be tolerated(the technicalterm is assimilated) by a water body, water qualitymanagers must know the type of pollutants discharged andthe manner in which they affect water quality.

� They must also know how water quality is affected bynatural factors such as the mineral heritage of thewatershed, the geometry of the terrain, and the climate ofthe region.

Water pollutants and their sources� The wide range of pollutants discharged to surface waters

that is the source of pollutants can be grouped into twoclasses.

Point Sources:

� Domestic sewage and industrial wastes act as point� Domestic sewage and industrial wastes act as pointsources because they are generally collected by a networkof pipes or channels and conveyed to a single point ofdischarge into the receiving water.

� Domestic sewage consists of wastes from homes, schools,office buildings, and stores.

� The term municipal sewage includes domestic sewagealong with any industrial wastes that are permitted to bedischarged into the sanitary sewers.

Point sources� Point source pollution comes from a defined, specific

source such as a discharge pipe from a factory, amunicipal sewage treatment plant, or a powergenerating station.generating station.

� In general, point source pollution can be reduced oreliminated through waste minimization and properwastewater treatment prior to discharge to a naturalwater body.

Point sources

Point Sources

Non point sources� Urban and agricultural runoff are characterized by

multiple discharge points and are called non point sources.

� Much of non point source pollution occurs duringrainstorms or spring snowmelts, resulting in large flowrainstorms or spring snowmelts, resulting in large flowrates that make treatment even more difficult.

� Urban storm water runoff (including that from streets,parking lots, golf courses and lawns) can transportpollutants such as nitrogen and phosphorous fromfertilizers, herbicides applied to lawns and golf courses, oil,greases, ehylene glycol (used in antifreeze), and cut grassand other organic debris.

Non Point Sources