Water and Wastewater Quality Slide

8/13/2019 Water and Wastewater Quality Slide

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WATER AND WASTEWATER

QUALITY


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Causes of water pollution

Chemicalsmany are toxic

Pathogens produce waterborne disease in eitherhuman or animal hosts.

Physical or sensory changes (eg. Elevatedtemperature and discoloration)

Often, concentration is the key in determiningwhat is natural component of water and what is a

contaminant. Oxygen-depleting substances (plant matter) as

well as man-made chemicals cause turbidity


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PHYSICAL CHARACTERISTICS OF



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Solid typically includes

Inorganic solid (silt,sand gravel, and clay fromriverbanks)

Organic matter (plant fiber and microorganisms from

natural or man-made sources)Suspended material may

provide adsorption sites for biological and chemicalagents. These adsorption site provide attached

microorganisms a protective barrier against chemicalaction of chlorine.

Degraded biologically resulting in objectionalbyproducts.


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Turbidity

Is a measure if the extent to which light is eitheradsorbed or scattered by suspended material inwater.

Caused by

Algal blooms

In surface water, mostly related to smallerinorganic components of suspended solids,primarily clay particles.

Microorganisms and vegetable material

Detergents, soaps and various emulsifying agents


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Turbidity is useful in defining drinking water

quality

Turbidity measurements are important

whenever UV radiation is used in disinfection

process.

Turbidity high, UV disinfection low, colloidal

material provide adsorption site from

disinfection process.


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Temperature

Temperature increases in surface water affects

solubility of oxygen in water

Rate of bacterial activity

Rate at which gases are transferred to and from the water.

Temperature has effect on the rate of chemicals dissolve andreact.

When water is cold, more chemicals are required for efficientcoagulation and flocculation to take place.

When temp. high, higher chlorine demand because ofincreased reactivity and often increased level of algae andorganic matter in raw water.


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CHEMICAL CHARACTERISTICS OF



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Alkalinity

Definition: the quantity of ions in water that will reactto neutralize hydrogen ions. Thus, a measure of theability of a solution to neutralize acids.

Major chemical constituents of alkalinity in naturalwater supplies are the bicarbonate, carbonate, andhydroxyl ions of (Na,Potassium, Mg, and Ca)

These constituents originate from carbon dioxide (fromthe atmosphere and as a byproduct of microbial

decomposition of organic material) and from theirmineral origin (primarily from chemical compoundsdissolved from rocks and soil)


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Highly alkaline waters are unpalatable, this conditionhas little known significance for human health.

The principal problem with alkaline water is thereaction that occur between alkalinity and certaincations in the water. The resultant precipitate can foulpipes and other water-systems appurtenances.

Alkalinity is important to fish and aquatic life because itprotects or buffers against rapid Ph changes.

Alkalinity levels affect the efficiency of certain watertreatment processes, especially the coagulationprocess.


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Hardness

Hardness is due to presence of multivalent

metal ions that come from minerals dissolved

in water. Hardness is based on the ability of

these ions to react with soap to form a

precipitate or soap scum.

In fresh water, primary ions are calcium and

magnesium, iron and manganese may alsocontribute.


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Hardness classified as

Carbonate hardness (equal to alkalinity)

Noncarbonate hardness (may include nitratesand chlorides)

Hardness is either

Temporary (can be removed by boiling) Permanent (cannot be removed by boiling)


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When washing with a bar of soap, there is a need to usemore soap to get a lather whenever washing in hard water.

The problem is the precipitate formed by the hardness andsoap adheres to just about anything (tubes,sink,dishwashers) and may stain clothing, dishes, and otheritem.

Today, synthetic soap and detergents that do not react withhardness are developed.

Scaling occurs when carbonate hard water is heated and

calcium carbonate and magnesium hydroxide areprecipitated out of solution, forming a rock-hard scale thatclogs hot water pipes and reducing the efficiency ofboilers,water heaters and heat exchangers.


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Organics Substances

Carbohydrates are widely distributed in nature and found inwastewater, are organic substances that includestarch,cellulose,sugars, and wood fibers; they containcarbon, hydrogen and oxygen

In lower organisms(eg.bacteria), carbohydrates are utilizedto synthesize fats, protein and energy.

In absence of oxygen, end products of decomposition ofcarbohydrates are organic acids,alcohols and gases such ascarbon dioxide and hydrogen sulfide.

The formation of large quantities of organic acids can affecttreatment process by overtaxing the buffering capacity ofwastewater, resulting in a drop in Ph and a cessation ofbiological activity.


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Detergents (surfactants) are large molecules that areslightly soluble in water and cause foaming inwastewater treatment plants and in the surface watersinto which the effluents is discharged.

Detergents affects wastewater treatment processes by

Lowering surface tension of water and increase itsability to wet surface with which they come in contact

Emulsify grease and oil, deflocculate colloids

Induce flotation of solids and give rise to foam

May kill useful bacteria and other living organisms


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BIOLOGICAL CHARACTERISTICS

OF WATER AND WASTEWATER


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VIRUSES

Viruses are smallest biological structure known sothey can only be seen with the aid of an electronmicroscope.

Testing for viruses in water is difficult because: They are small

They are of low concentration in natural waters

They are numerous varieties They are unstable

They are limited identification methods available


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Equalization

Flow equalization

Constituents equalization

Flow equalization refer to changing the variation in rateof flow throughout the processing and cleanup cycles

to a more steady flow rate that is more nearly equal toaverage flow rate for that period of time

Constituents equalization refer to the concentration ofthe target pollutants in the wastewater stream.Throughout 24hour day, the concentrations ofindividual constituents in a given industrial wastestream typically vary over wide ranges, as processstarted,operated,shut down, and cleaned.


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Equalization can be either offline or online

Online flow equalization is accomplished byallowing the waste stream to flow into a basin.

The waste is then transferred from basin(large and containing enough waste) to thetreatment system at a constant rate.

Offline equalization is accomplished byrestricting the flow-regulating valve or aconstant speed pump.


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Chemical Methods of Wastewater

TreatmentChemical methods of wastewater treatment take advantage of two types ofproperties:

The chemical characteristics of pollutants

The chemical characteristics of the products of reaction between pollutants andtreatment chemicals.

There are 6 methods:

Reaction to produce an insoluble solid Reaction to produce an insoluble gas

Reaction to produce a biologically degradable substance

Reduction of surface charge to produce coagulation

Oxidation or reduction reaction.

Reaction to destroy or deactivate chelating agent

Chelating agents form multiple bonds with a single metal ions. Chelants are chemicalsthat form soluble complex molecules with certain metal ions, inactivating the ions sothat they cannot normally react with other elements or ions to produce precipitates orscale


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Jar Test Apparatus

To determine the correct chemical dosage, a jartest is performed. Jar tests simulate full scalecoagulation and flocculation processes to

determine optimum chemical dosages.The test can be used to:

Select the most effective chemical

Select the optimum dosage Determine the value of a flocculant aid and

the proper dose.


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Coagulation

Chemical coagulation conditions water for furthertreatment by the removal of:

Turbidity,color and bacteria

Iron and manganese

Taste and odor and organic pollutantsChemical coagulation is usually accomplished by theaddition of metallic salts such as aluminium sulfate (alum)or ferric chloride.

Alum is the most commonly used coagulant in watertreatment and is most effective between Ph ranges of 5.0and 7.5


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Factors influence the chemical

coagulation

In addition to ph, a variety of other factorsinfluence the chemical coagulation processincluding:

Temperature Influent quality

Alkalinity

Type and amount of coagulant used

Type and length of flocculation

Type and length of mixing


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Water and Wastewater Quality Slide