PRIMARY WATER TREATMENT

History of Water Treatment

WATER TREATMENTThe process of making water suitable for certain use such as domestic, industrial or any other use.

Drinking water must be free of organisms and chemical concentrations that are hazardous to human health.

Water should be free of :Suspended ParticlesBad TastesColors and Smells And should not damage a water supply system.

Levels of Water Treatment

Preliminary and Primary Water Treatment

Primary treatment is any physical, chemical or mechanical process used on water before it undergoes the main treatment process.

Preliminary Water TreatmentAim: To remove the easily separated components (mainly bulky solids and grit) to protect the principal treatment processes which follow.

Bulky suspended or floating solids are removed by screens or are chopped up by macerators or comminutors.

Grit is removed by grit channels.

Primary Water TreatmentPrimary treatment generally refers to a sedimentation process.- light solids to sink to the base of the storage tank as sludge and floating materials to rise to the surface as scum.

Preliminary and primary processes will remove approximately 25 percent of the organic load and virtually all of the nonorganic solids.

SCREENING

Usually the first step in water treatment.

Screening removes or reduces the size of trash and large solids that get into the sewage system.

The solids collected by screening are called screenings.

A screen is a device with uniform openings through which raw sewage is passed. Sloping bar screens are used to remove larger solid materials, such as pieces of wood, which can be intercepted by bars.

Types of Screens

Types of Screens

Types of Screens

Types of Screens

GRIT REMOVAL

Grit represents the heavier matter in wastewater which will not decompose in treatment processes.

Grit chamber design is based on the removal of all particles of about 0.011 inch or larger.

Grit removal is practiced to prevent its accumulation in other parts of the treatment system, to reduce clogging of pipes and other parts, and to protect moving parts from abrasion and wear.

PLAIN SEDIMENTATION

Sedimentation is a treatment process in which suspended particles are removed from the water.

In this facility, settleable solids and most suspended solids settle to the bottom of the basin.

Removals from domestic wastewaters undergoing plain sedimentation will range from about 30 to 40 percent for BOD and in the range of 40 to 70 percent for suspended solids.

Factors that influence the Sedimentation Process:DensitySizeTemperatureTurbulenceStability

Wastewater is usually retained in a primary sedimentation tank for a minimum period of two hours, by which time most settlement has been achieved.

Types of Sedimentation TanksRectangular Tank

Circular Tank

Four StagesInlet zoneSettlement zoneOutlet weir Zone for the collection and storage of the sludge.

SEDIMENTATION WITH COAGULATION

If the suspended solids of water are fine or colloidal in size, chemicals are often used to effect more complete removal of the suspended matter.

During coagulation, chemicals (coagulant) are added in a mixing tank to encourage the small solids (suspended solids) to coagulate into large particles (chemical flocs) that will more easily settle.

The positive charge of the coagulant neutralizes the negative charge of suspended particles in the water. When this reaction occurs, the particles bind together and become heavy and quickly settle to the bottom of the water supply.

CoagulantSuspended Particle

Common Coagulants

Common Coagulants

After the primary treatment, the water now undergoes the Secondary (Biological) Treatment whichremoves the dissolved organic matter that escapes primary treatment.

PRIMARY WATER TREATMENT - is any physical, chemical or mechanical process used on water before it undergoes the main treatment process.SCREENINGGRIT REMOVALPLAIN SEDIMENTATIONSEDIMENTAION WITH COAGULATION

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