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8/13/2019 Wastewater Characteristics Physical Chemical
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Lecture 2:
Wastewater CharacteristicsPhysical and Chemical
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Lecture 2 Outcomes
The students should be able to:
Recognize the various important Wastewater characteristics
Importance of each parameters
Impacts of each Wastewater parameters to Environment
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Whats in Wastewater? Contaminants
Definition of Contaminant:
constituents of air, water, or soil which render them
unsuitable for their intended use.
chemical or biological in nature
from natural forces, life processes of other species, our
own activities
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Principal contaminants of concern
Contaminants Impact
Suspended solids Materials that resis settling may remain suspended in wastewater.Suspended solids in wastewater
must be treated, or they will clog soil absorption systems or reduce the
effective-ness of disinfection systems.
Biodegradable organics If discharged to the environment, their biological stabilisation can
lead to the depletion of natural oxygen resources and development
of septic conditions.
Pathogens Communicable diseases can be transmitted.
Nutrients Discharged in large amount can lead the growth of undesirable
aquatic life and pollution of groundwater.
Priority pollutants Organic & inorganic compounds selected on the basis of their
known or suspected carcinogenicity, mutagenicity, teratogenicity or
high acute toxicity.
Refractory organics Organics that resist conventional methods of wastewater
treatment. E.g. surfactants, phenols & agriculture pesticides
Heavy metals Toxic to human organs, some can cause cancer, metabolism
failure, neurological problems.
Dissolved inorganics
Calcium, sodium & sulfate must be removed if the water is to bereused.
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Wastewater
Physical Characteristics
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Solids
Solids is one of the most common assessments of water quality.
Solids 3 categories
Dissolved
Truly in solution and pass through a filter.
Homogenous and of a single phase
Colloidal
Uniformly dispersed in solution
But form a solid phase that is distinct from the water phase.
Suspended Separate from the solution.
Some are settleable.
Method of analysis is given in APHA Method 2540.
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Solids
Three types of solids measured:
Suspended solids
Dissolved solids
Volatiles suspended solids
Filtration is used to separate suspended
and dissolved solids.
Commonly used filter paper is
Whatman glass fiber filter (1.58 m,
47 mm).
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Solids
Volatile solid
(VS) isassumed to be
organic.
Fixed solid (FS)
is assumed to
be inorganic.
Ratio of VS toFS gives an
approximate
amount of
organic matter
present in
wastewater.
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Chemical Constituents
OrganicInorganic
Oxygen demand
parameter
Oil and grease
Single organic
constituent
Total organic carbon
(TOC)
Aggregate organic
constituents
Nitrogen
Phosphorus
Gases
Trace metals
Alkalinity
Hardness
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Temperature
oxygen is less soluble at hightemperature
increase in biochemical reactions rate
at high temperature
DO (mg/L)
Temperature (C)
KT/K20
Temperature (C)
Temperature
Oxygen
demand
Oxygen
replenishment
Dissolved
oxygen
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Temperature
Other effects
change in fish species
mortality of fishes (thermal shock)
increase growth of water plants and wastewater fungus.
The best temperatures for wastewater treatment probably rangefrom 77 to 95 degrees Fahrenheit. In general, biologicaltreatment activity accelerates in warm temperatures and slows
in cool tempera-tures, but extreme hot or cold can stoptreatment processes altogether.
Therefore, some systems are less effective during cold weatherand some may not be appropriate for very cold climates.
Wastewater temperature also affects receiving waters. Hotwater, for example, which is a byproduct of many manufactur-
ing processes, can be a pollutant.
When discharged in large quantities, it can raise thetemperature of receiving streams locally and disrupt the naturalbalance of aquatic life.
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Taste & Odour
Caused by the presence of decomposed organic material and
volatile chemicals.
Drinking water should be practically free from colour,
tastes,and odour.
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pH
Intensity of acid or alkaline condition of a water
pH = - log [H+] = log 1/[H+]
The acidic or alkaline of wastewater affects both treatment andthe environ-ment.
Low pH indicates increasing acidic while a high pH indicatesincreasing alka-line nature (a pH of 7 is neutral). The pH ofwastewater needs to remain between 6 and 9 to protectorganisms.
Acids and other substances that alter pH can inactivatetreatment processes when they enter waste-water from
industrial or commercial sources.
-14 = log H+
H+= 1 x 10 -14
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pH
Toxicity of many compounds is affected by pH.
H2S ~ toxicity to fish increases as pH is lowered.
Solubility of heavy metals
Lower pH increases solubility of metals
Metals leaches from soil and sediment into surface water
Accumulate to fish gills or cause deformity ~ death
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Hardness
characteristic of water that causes it to require considerable
amounts of soap to produce a lather and that also producesscale in hot-water pipes, heaters, & boilers;
it is caused by divalent metallic cations such as calcium &magnesium.
Hardness is expressed in mg/l of equivalent calcium carbonate.
eg Ca = 200 mg/L ;
mol wt of CaCO3= 100 mg/L; mol wt of Ca = 40equiv. Wt of Ca = 40/2 = 20
equiv. Wt of CaCO3= 100/2 = 50
Ca = 200/20 *50 = 500 mg/L as CaCO3
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Alkalinity
Measure of the capacity of a water to neutralize acids or
capacity to accept protons;
In natural waters, the alkalinity is related to the bicarbonate,carbonate, and hydroxide concentration.
It is primarily caused by HCO3-, CO3
2-, and OH-alkalinity.
Total alkalinityis usually expressed in terms of equivalentcalcium carbonate in mg/l or meq/l.
Carbonate hardness is that part of the total hardness that ischemically equivalent to the bicarbonate and carbonatealkalinities.
Noncarbonate hardness (NCH) is equal to the total hardness
(TH) minus the carbonate hardness (CH).
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Conductivity
Determined by measuring its electrical resistance between two
electrodes and comparing this resistance with the resistanceof a standard solution of potassium chloride at 25C.Most waters, TDS (mg/l) = 0.55~0.7 x conductivity ( s/cm at25C)
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Iron and Manganese
Iron and manganese either dissolved or suspended in any
oxidation state.
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Sulfates
a major anion in natural waters, it can cause cathartic effect
upon humans and can form hard scales in boilers when it ispresent in excessive amounts.
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Fluorides
can cause dental cavities if too high; if too low, may be added
to water for prevention of cavities
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Nitrogen
essential to growth of prostita and plants; too little N will inhibit
biological treatment, too much can cause O2demand andexcessive algae growth in receiving stream
Total Kjeldahl Nitrogen = Organic N + Ammonia N
Ammonia N : toxic to fish
O2demandEutrophication
Nitrite N
Nitrate N : stimulates algal & aquatic growth
Blue babies syndrome (methemoglobenemia)
Phosphorusessential to growth of microorganisms; necessarynutrient for biological treatment; too much can cause
eutrophication
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Nitrogen and Phosphorus
From fertilizer, laundry detergent etc.
Excess nitrate in drinking water cancause BLUE BABY SYNDROME.
Excess nitrogen and phosphorus can
cause EUTROPHICATION or ALGAE
BLOOM.
Eutrophication is
apparent as
increased turbidity
in the northern partof the Caspian Sea,
imaged from orbit.
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Eutrophication
Source : www.bbc.co.uk
Note the bright green colour caused
by algae stimulated by the
experimental addition of nutrient for
the 26th consecutive year. The lake
in the background is unfertilized.
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Trace metals
Affect flora and fauna through bioaccumulation
Affect human organs
Arsenic mutagen and carcinogen
Cadmium carcinogen, accumulates in liver and kidney
Chromium carcinogen, corrosive and skin sensitizer
Lead brain and kidney damage
Mercury highly toxic, damage to nervous system
Selenium weakness, depression and red staining
Silver grey colouration of skin
But minute amount of heavy metal is essential for human health
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Single OrganicsPriority Pollutants
www.epa.gov/NE/npdes/permits/generic/prioritypollutants.pdf
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Single Organics
Priority pollutants - based on their known or suspected
carcinogenicity, mutagenicity, tetratogenicity or high acute toxicity.
Volatile organic carbons (VOC) - some are listed as priority
pollutants. In total they cause a great concern because:
in vapour state, they are much more mobile and more likely to bereleased to the environment
the presence of some VOC may pose significant public health
risk
they contribute to a general increase in reactive hydrocarbons in
the atmosphere, which lead to the formation of photochemicaloxidants.
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Single Organics
Disinfection byproducts- some are known or suspected potential
human carcinogens such as trihalomethanes (THMs), haloacticacids (HAAs), trichlorophenol and aldehydes.
Pesticides and Agricultural Chemicals- most are toxic to many
organisms.
Emerging Organic Compounds- veterinary and human antibiotics,
industrial and household wastewater products, human prescriptionand non-prescription drugs and sex and steroidal hormones.
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Typical Pollutants by Industry Sector
Reforming
Derivatives
Hydrocarbons Other pollutants
Methanol, Ammonia, Urea Methanol, heavy alcohols Ammonia, Urea
Hydrocarbons Other pollutants
MTBE Methanol, isobutene
Ethylene OxideEthylene Glycol, CO2, acetaldehyde,
hydrocarbons
Acetic Acid Formic acid, acetates, acetone
Acidic water, iodides,
rhodium
Vinyl Chloride Dichloroethane, hydrocarbons HCl, NaCl
Polyethylene Oil, TSS, catalysts
PVC Methanol, acetates Acidic water, TSS
Source: Degremont Water Treatment Handbook