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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
WATER AND WASTEWATER
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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
WATER AND WASTEWATER
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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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