Water and waste water Engineering

1. CHARECTERISTICS OF
WASTEWATER

2. Physical characteristics
1. Solids
Composed of floating matter, settleable matter, colloidal matter and
matter in solution.
Total Suspended Solids (TSS)
 Total suspended solids (TSS) include all particles suspended in water
which will not pass through a filter.
 As levels of TSS increase, a water body begins to lose its ability to
support a diversity of aquatic life.
 Suspended solids absorb heat from sunlight, which increases water
temperature and subsequently decreases levels of dissolved oxygen

3. Total Dissolved Solids (TDS)
TDS are passed through the filter. TDS comprised of colloidal and dissolved
solids. Colloids are typically in the size range from 0.001 to 1μm.
Volatile Suspended Solids (VSS)
Those solids that can be volatilized and burned off when the TSS are ignited.
Volatile suspended solids data is critical in determining the operational behavior
and biological concentration throughout the system.
2. Turbidity
Measure of the light-transmitting properties of water, is another
test used to indicate the quality of waste discharges and natural waters
with respect to colloidal and residual suspended matter.
Units – NTU (Nephelometric Turbidity Units)
Equipment using to measure - electronic turbidity meter or a turbidity tube

4. 3. Colour
 Age of the waste water is determined qualitatively by its colour and
odour.
 Fresh wastewater is usually a light brownish- gray colour.
 Travel time of the collection system increases anaerobic conditions develop and
colour of the waste water changes sequentially for gray to dark gray, and
ultimately to black.
 This black colour is due to the metallic sulfides which formed under the
anaerobic conditions.
4. Absorption / Transmittance
 This is measure of the amount of light, of a specified wave length, that is
absorbed by the constituents in a solution.
 Absorbance measure using the spectrophotometer.
5. Temperature
 The temperature of waste water is commonly higher due to the addition of
warm water from households and industrial activities.
 Temp. is effects on chemical reactions and reaction rates, aquatic life and the
suitability of the water.

5. 6. Electrical Conductivity
 It is measure of the ability of a solution to conduct an electric current.
 EC is one of the important parameter used to determine the suitability of the
water for irrigation.
SI units – millisiemens per meter (mS/m) or micromhos per centimeter (μmhoms/cm)
Equipment use to measure – Electrical conductivity meters.

6. Chemical characteristics
1. pH
 This represent the hydrogen ion concentration.
 Waste water with an extreme concentration of hydrogen ion is difficult to treat
by biological means.
 For treated effluent discharged to the environment the allowable ph range usually
varies from 6.5 to 8.5.
1. Chlorides
 Human excreta, contain 6g of chlorides per person par day.
 Infiltration of salty water into sewers is also a potential source of high chlorides
3. Alkalinity
 Alkalinity in waste water results from the presence of the
 hydroxides (OH-), carbonates (CO3
2-), and bicarbonates (HCO3
-) of elements
 such as Calcium, Magnesium, etc….
 Waste water is normally alkaline, receiving its alkalinity from material added
during domestic use.
 The alkalinity in waste water helps to resist changes in pH caused by the addition
of acids.

7. 4. Nitrogen and Phosphorous
 Elements Nitrogen and Phosphorous, essential to the growth of microorganisms,
 plants, and animals are known as nutrient or bio-stimulants.
 These are required to evaluate the treatability of of waste water by biological
processes.
 Insufficient Nitrogen and phosphorous can necessitate the addition of nitrogen to
make the waste treatable.
 But if control of algal growth in the receiving water is necessary, removal or
reduction of nitrogen in waste water prior to discharge may be desirable.
5. Metallic constituents
 Trace quantities of many metals such as Cadmium (Cd), Chromium(Cr),
 Copper(Cu), Iron (Fe), lead (Pb), Manganese (Mn), Mercury (Hg), Nickel (Ni)
 and Zinc(Zn) are important constituents of most waters.

8. Measurement of Organic Content
Methods used to measure the aggregate organic material can be divided
into two groups.
1. Methods used to measure the gross concentration of organic matter greater
than about 1.0mg/l. – BOD, COD, Total Organic Carbon (TOC)
2. Methods used to measure trace concentration in the range of 10-12 to 100 mg/l -
Determined using instrumental methods including gas chromotography and
mass spectroscopy.

9. Biological Oxygen Demand (BOD)
BOD5 - 5 day, 20oC
BOD3 - 3 day, 27oC
The most wildly used parameter of organic pollution applied to both waste water
and surface water is the 5 day BOD (BOD5). BOD test results are used to;
 Determine the approximate quantity of oxygen that will be required to
biologically oxidized (Stabilized) the organic matter.
 To determine the size of waste treatment facilities
 Measure the efficiency of some treatment processes.
 Determine the compliance with wastewater discharge permits.

10. Chemical Oxygen Demand (COD)
COD test is used to measure the oxygen equivalent of the organic materials in
waste water that can be oxidized chemically. Normally use the dichromate in an
acid solution. The reasons for difference between the BOD and COD are as follows;
1. Many Organic substances which are difficult to oxidize biologically such as
lignin can be oxidized chemically.
2. Certain organic substances that are toxic to microorganisms use in BOD test
oxidize by chemicals.
Total Organic Carbon (TOC)
The TOC of a wastewater can be used as a measure of its pollution characteristics
and in some cases it has been possible to relate to TOC to BOD and COD values.
This test is done instrumentally by converting organic carbon into carbon dioxide
which is measured with an infrared analyzer.

11. Units of measurement for physical and chemical parameters
Measurements of chemical parameters are usually expressed in
“milligrams per liter (mg/L )”
or
“grams per cubic meter (g/m3)”
Concentrations also can be expressed as part per million (ppm).
ppm = mg/L
Specific gravity of fluid

12. Biological Characteristics
Organisms found in surface water and waste water include bacteria, fungi, algae,
protozoa, plants and viruses. Above some types can only be observed
microscopically.
Pathogenic Organisms
Pathogenic organisms found in waste water may be excreted by human beings
and animals who are infected with disease or who carriers of a particular infection
disease. These organisms can four broad categories bacteria, protozoa,
helminthes (worms) and viruses.