CE 428 Water and Wastewater Treatment Design
Lecture 2 - Water Quality Parameters
S.K. Ong
Water Quality Parameters
May be divided up into the following categories:
1. Physical
2. Chemical
3. Biological
4. Radiological
I. Physical
1. Temperature - no standard in the drinking water standards
- affects solubility of dissolved oxygen and other gases, accelerates biological action.
- affects chemical equilibrium and kinetics
2. Turbidity - measurement of interference of passage of light through a liquid caused by suspended material
in the liquid. Origins of suspended materials include:
- silt and clay from soil erosion, microorganisms, organic compounds - proteinaceous, pulp
fibers, organic matter
Two methods of measurement - by monitoring the amount of light scattered or transmitted
(a) light source illuminates the sample and one or more photoelectric detectors are used with a
readout device to indicate the intensity of scattered light at right angles to the path of the
incident light
- Expressed in NTU or Nephelometric Turbidity Units. Standards used are known
amounts of formazin polymer (1% hydrazine sulfate and 10% hexamethylenetetramine) suspensions.
(b) interference to the passage of light caused by suspended materials
- visual methods such as the Jackson candle turbidimeter
- units in Jackson Turbidity Units (JTU), range 25-1000 (long tube), and 100 -1000 (short tube)
or compared against an arbitrary scale of turbidity units such as Formazin or pure silica suspensions (see
attached note)
3. Color - Caused by:
1) colloidal organic matter, e.g., extracts of decaying vegetation such as tannin, humic acid,
lignin giving a yellowish-brown hues or
2) dissolved material such as iron salts or from dyeing operations and pulp and paper mill (lignin)
(generally negatively charged colloidal materials therefore removed using coagulation methods)
Apparent Color - also caused by suspended matter such as red clays
True color is due to vegetable or organics extracts that are colloidal
Methods of determination: by comparison against an arbitrary scale developed using different amounts of
potassium chloroplatinate (K2PtCl6) - 1 standard color unit = 1 mg/L of platinum (as K2PtCl6).
4. Taste and Odor - subjective evaluation
Taste and smell are closely related, substances that produce an odor will almost invariably
impart a taste as well. The converse is not true; there are mineral substances that impart taste
but not odor.
Sources - could be anything from inorganic salts, e.g., alkaline materials imparts a bitter taste
while metallic salts impart a salty or bitter taste.
- organics - may impart both taste and odor, e.g., petroleum products
- biological decomposition of sulfur produces hydrogen sulfide - rotten egg odor.
Measurement - use of human senses of tastes and smell
Threshold odor number (TON) - varying amount of odorous water diluted with enough odor-free water to
make a 200 mL mixture. A panel of 5 to 10 noses is used to determine the mixture in which the odor is just
barely detectable
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TON = (A + B)/A
where A = volume of odorous water (mL), B = Volume of odor-less water required to make up to 200 mL.
5. Solids
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1 m
Molecules
Colloids
Viruses
Suspended particles
Bacteria
Filter papers
Algae
Sand
Membrane
Sources:
- silts and clays and other soil constituents from erosion
- organic matter such as plant fibers, leaves; biological solids such as bacteria, algae cells, etc. from
industrial sources or from domestic wastewater
Measurements:
Total Solids (TS) = Total Suspended Solids (TSS) + Total Dissolved Solids (TDS)
= Total Fixed + Total Volatile
Total Suspended Solids = Fixed Suspended + Volatile Suspended Solids (VSS)
Suspended - known as nonfilterable residues
Dissolved - known as filterable residues (colloidal and dissolved)
II. Chemical Water Quality Parameter
1. pH - defined as the intensity of the acid or alkaline condition of the solution - a way of expressing the hydrogenion concentration (more precisely activity).
pH = - log[H+]
2. Alkalinity - measures the capacity of a sample to neutralize acids and hence a measure of the resistance to
change in pH
- salts of weak acids, weak and strong bases may contribute towards alkalinity
- three major sources of alkalinity: hydroxide (OH-); carbonates and bicarbonates
others include silicates and phosphates, organic acids such as salts of humic acid
salts of weak organic acids such as acetic, propionic, hydrosulfuric acid, ammonia and hydroxides
Measurement - by titrating the water with an acid usually 0.02N sulfuric acid to pH 4.5 (with 0.02N sulfuric
acid - 1 mL of the acid will neutralize 1 mg of alkalinity as CaC03)
3. Cations - positively charged ions:
(i) Iron and Manganese
Sources - in soil - ferric oxide and iron sulfide (pyrite); manganese as manganese dioxide
Concerns - no harmful effects, except that causes water to be turbid in color, interfere
with laundry, aesthetic value
(ii) Metals - of concern are lead, arsenic, copper, chrome, zinc and cadmium, selenium
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Sources - generally introduced from industrial wastewater, pipings, fittings and solders
that are lead or zinc based
Concerns - metals are toxic if consumed in sufficient quantities e.g. lead - damage to the brain
(iii) Hardness - concentration of multivalent metallic cations in solution, e.g., most common are
Ca2+, Mg2+ (include Fe2+, Mn2+, A13+. For all purposes hardness is usually represented
by the sum of Ca2+ and Mg2+ ions.
- hardness can be classified as: carbonate hardness - hardness that is equivalent to the
alkalinity concentration while the rest is noncarbonate hardness
- carbonate hardness is sensitive to heat and precipitates out
Concerns:
- consumption of soap - an economic loss to user; boiler scale; magnesium hardness
associated with sulfate ions has a laxative effectiveness on those who are not accustomed
to it. Hard water is apparently beneficial to the human cardiovascular system.
4. Anions - negatively charged ions
(i) Chlorides - Cl- , indication of salinity
Sources - chlorides from top soil and deeper formation
- salt spray from the ocean
Concerns - high concentration > 250 mg/L give a salty taste.
(ii) Sulfates - S042Concerns - excessive amounts cause laxative effects
- concerns with odor and corrosion problems in sewers
(iii) Nitrate - NO3- (See nitrogen)
5. Nitrogen - in forms such as NO3-, NO2-, NH3, organic nitrogen (such as in organic matter, proteins)
- Total Kjeldahl Nitrogen - organic nitrogen + free ammonia NH4+
- is a nutrient for algal growth - eutrophication
- exerts oxygen demand e.g., NH3 ----> NO3- Nitrate toxic to new born infants - methemoglobinemia; nitrate is reduced to nitrite in the
gastrointestinal tract - nitrite gets in the blood stream and reacts directly with the hemoglobin to
produce methemogloblin resulting in an impairment in oxygen transport (blue babies). can be
hazardous for babies less than 3 months.
6. Phosphorus - orthophosphates (e.g., PO43-, HPO42-, H2PO4-) polyphosphates(e.g., P2O7), - Inorganic phosphorus,
Organic phosphorus, total phosphorus
Concerns - nutrients for algal growth - algal bloom
7. Fluoride - demonstrated reduction in dental cavities in children. Approx. desired level = 1 mg/L
High concentration can cause mottling of teeth (brown spots)
8. Organic compounds - a range of different type of compounds:
Humic material - imparts color and is a precursor for the formation of trihalomethanes (THMs) during
chlorination. THMs are low molecular weight organic halides such as chloroform, dichlorobromoforms,
etc. Some of these compounds have been found to be cancer causing.
Volatile organic compounds (VOCs) and synthetic organic compounds (SOCs) - such as benzene, xylenes,
pesticides and herbicides (some are carcinogenic)
9. Surrogate or Aggregate Parameters
(i) Electrical conductivity (EC) - units - millisiemens/m (mS/m) or micromhos/cm (mho/cm)
- 1 mS/m = 10 mho/cm
- measure of the ability of a solution to conduct an electrical current
- conductivity increases with the concentrations of ions
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TDS (mg/L)

(0.55 to 0.70) X EC (in mho/cm)
- may not be applicable for high strength wastewater
(ii) Biochemical Oxidation Demand (BOD)
- measurement of dissolved oxygen used by microorganisms in the biochemical ozidation of
organic matter
(iii) Chemical Oxidation Demand (COD)
- measure the oxygen equivalent of the organic material in water that can be oxidized chemically
using chromate in an acid solution
(iv) Total Organic Carbon (TOC)
- heat and oxygen or UV radiation or chemical oxidants are used to convert organic carbon to
carbon dioxide whixh is measured by infrared analyzer
(v) UV absorbing organic constituents
- assessment of aggregate presence of UV absorbing compounds in water and wastewater
- typical wavelength - 254 nm
(vi) Oil and Grease
- fats, oils, waxes
- determined by extraction of waste sample with trichlorotrifluoroethane or mineral oils
III.
Biological Water Quality
- Thousands of biological species present in bodies of water - ranging in size and complexity.
- From the perspective of human use and consumption of water, the most important biological
organisms in water are pathogens. These are organisms that are capable of infecting or of
transmitting diseases to humans
- analysis of all the known pathogens would be time consuming and expensive.
- purity of water can be checked rapidly using an indicator organisms
Indicator Microorganisms - presence of indicator microorganism presumes that contamination has
occurred.
The ideal pathogen indicator should:
1) be applicable to all types of water,
2) be present when pathogens are present, be absent when pathogens are absent, be
proportional to concentration of pathogen,
3) same origin,
4) no interference from other extraneous organisms and should survive in a habitat as
long as the pathogen,
5) should not be a pathogen, i.e., for the safety of the laboratory personnel
The organisms meeting some of the above criteria are the fecal coliform group, native to the intestinal tract of
humans. Reasons:
1) coliforms are present in the faces of all-warm blooded animals and are very abundant,
2) coliforms are excreted in high numbers and coliform concentration >> pathogens,
3) Coliforms are slightly hardier than pathogens - if coliforms are gone, chances are pathogens are gone too, 4) Test
to determine coliforms is simple
Disadvantages
1) Some coliform species are found in soils and plants not related to pollution by human wastes
2) the multiple fermentation tube tests may take too much time
3) may not bear any relationship to virus content
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Test Methods
1) Multiple tube technique (MPN)
- coliforms are known to ferment lactose with one of the end products being a gas.
- a broth containing lactose and other substances which inhibit noncoliform organisms is placed in a
series of
test tubes which are then inoculated with a decimal fraction of 1 mL. These tubes are
incubated at 35° C and
inspected for gas production. The test is conducted in three stages. The number of coliforms present is then
determined statistically from the number of tubes that were
tested positive for gas or fermentation of lactose.
Steps of the test include:
a) Presumptive test - incubate in lactose broth at 35° C and check for production of gas
b) Confirmed test - incubate in brilliant green bile broth and check for gas
c) Completed test - incubate from confirmed test and check gram stain.
2) Membrane Filter Technique
- a faster technique and be used to analyze larger volumes. Procedures:
1) filter known volume of sample or sample dilutions through a membrane filter (0.45 microns)
2) incubate filter for 24 hours on top of a pad with appropriate medium at selected temperature
Test
Medium
Temperature
Total Coliform M-Endo Broth
35° C
Fecal Coliform M-FC Broth
45.5° C
3) Identify coliform colonies by characteristic color and/or metallic sheen and count them
3) Quanti-Tray/2000 System
- reagent is added to the sample and sealed in a sterile Quanti-Tray/2000 sample tray and incubate
- count the number of colored or fluorescent wells and estimate coliforms using a table
- reagent used is Colilert, Colilert-18 or Colisure which can quantify over 2,000 coliforms and E.Coli.
- counting range is 3,000% greater than that of the membrane filtration and minimizes serial dilutions
There are also tests that are conducted to test specific microorganisms such as Giardia (see Drinking Water
Standards)
IV
Water Quality - Radiological
Radiation Damage
1) Genetic hazards to offsprings (mutagenic)
2) Shortening of life spans
3) Physiological effects on individuals
Units
1) Amount of radioactive material - 1 curie (Ci) = 3.7 x 1010 disintegrations/sec. When we say a Cobalt-60
radiation source has an activity or strength of 1,000 Ci it means that the decay rate is 1000 x 3.7 x 10 10 =
3.7 x 1013 disintegrations/sec.
2) Radiation intensity:
Roentgen - amount of X-radiation if fully adsorbed in air would produce energy
loss of 83 ergs/gram
Rad (roentgen-adsorption-man)
- energy adsorption per kilogram of tissue weight
1 rad = 0.01 watt-second (J) energy adsorbed per kilogram of tissue weight
Rem (Roentgen-equivalent-man)- radiation equivalent that takes into account the
biological effect of radiation and the type of radiation =
(Rads) x (quality factor) x (Dose Distribution Factor)
or corresponds to the amount of radiation that will produce an energy dissipation
in the human body that is biologically equivalent to one roentgen of radiation of
X rays or approximately 100 ergs/gm.
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Sources of Radiation Exposure
Radon
200 mrems
Cosmic
27
Rocks and Soil
28
Inside human body
40
Medical X-ray
39
Nuclear Medicine
14
Consumer Products
10
Others
4
Total
360 mrems - annual dose to an average American
Concerns: radium 226, radium 228, radon, alpha emitters
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