7. Water Pollution

Water treatment

The treatment of water, to bring it up to a standard, such that it is safe to drink

Wastewater treatment

The treatment of wastewater, to bring it up to a standard, such that it is safe to discharge back to the environment

Pathogenic organisms

Organisms that cause disease

Where do most pathogens originate from

faecal matter

What do analysts tend to count because they are particularly resistant to disinfection

coliform bacteria

What are the four categories of pathogenic organisms

viruses, bacteria, protozoa, helminths

What are TDS

Total dissolved solids which can be measured using a conductivity meter

What are trihalomethanes (THM)

A result of chlorination of organic matter

Why are THMs undesirable in drinking water

carcinogenic

How can THM production be reduced

removing organic matter prior to disinfection using various combinations of coagulation, flocculation, adsorption, sedimentation and filtration

When can Boron be a problem in water

Where drinking water is provided by seawater desalination and wastewater is reused for irrigation

How can Boron be removed

ion exchange

What can nitrate in drinking water lead to

methaemoglobinaemia in infants

Which forms methaemoglobin, which binds oxygen tightly and does not release it

How can nitrates be removed from water

ion exchanged, reverse osmosis, biological denitrification and/or electrodialysis

When is a TEP (trade effluent permit) not required for wastewater

when wastewater is discharged to wastewater treatment plants by sewer sysyem

What does BOD5 represent

the quantity of biodegradable matter present in the water in terms of the DO that would be consumed within a five day period due to its presence

What is the standard method for measuring BOD5

1. Place a sample of diluted water into a closed vessel

2. Measure the initial DO concentration of the sample

3. Leave for five days in darkness at 20 degrees

4. Measure the final DO concentration of the sample

5. The BOD5 of the diluted sample is the difference between the two DO measurements

6. The BOD5 of the original undiluted sample is obtained by volumetric scaling

What is the equation for Initial DO concentration

B(t)=U0-U=aC0(1-exp(-Kct))

What is the equation for ultimate BOD

L0=B(t)/1-expt(-Kct)

COD

Chemical oxygen demand: represents the amount of oxygen required to oxidise any organic matter in a water sample using chromic acid, a strong oxidising agent

SS

Suspended Solids: represent all undissolved material present in water

Turbidity

Measure of the amount of scattering that occurs when light passes through water

How can you remove SS

screening and clarification

Eutrophication

excessive levels of P and N in natural water systems

What does dead plant matter provide

additional BOD, which is consumed by benthic organisms, leading to DO depletion and anaertobic environments

What is the downstream concentration in terms of CU, CE,QU and QE

CD=QUCU+QECE/(QU+QE)

What does the graph of distance v biodegradable matter concentration look like

exponential decay graph

What does the graph of distance v DO concentration (discharge of biodegradable matter in a river)

oxygen sag curve

Can u draw the two film model

see image

What is the equation of the Net mass flux of CO2 from gas phase to liquid phase (JI(

JI=(bL/DEL + KbG/DEG)^-1 (KCG-CL)

What is the reaeration rate

ra=ka . (Us-U)

What is the empirical equation for DO solubility limit

lnUs= 4Ei=0 ai/Ti

What is the empirical equation for reaeration rate

ka=au^b /H^c

What is the equation for control-volume for biodegradable matter

Q dC/dc=-Arc

What is the equation for control volume for dissolved oxygen

Q dU/dx = A.(ra-arc)

What is the Streeter-Phelps equation

G=Us-U

What is the equation for minimum DO concentration

The location of the min DO conc, xmin, is found by setting dG/dx=0 at x=xmin and solving for xmin yielding…