Water quality, pollution and treatment units

• Introduce water quality standards • Introduce typical treatment processes and design flow rates • Present examples of flow sheet diagrams... Bacteriological limits for drinking waterUS

Water Quality, Pollution,

and Treatment Plants

• Introduce water quality standards

• Introduce typical treatment processes and design flow rates

• Present examples of flow sheet diagrams

Storm water pollution

Scale formation due to water hardness

Red tide due to algae contamination

Standards for

water usage

B

Discharge or effluentstandard

C

Water qualityobjective limit

A Drinking Water Standard

Inorganic Chemicals

Different countries may have different drinking water standards

A2 Bacteriological limits for drinking water

US EPA states that “bacterial quality criteria for

drinking water from public supplies require not more

than

than 1 total-coliform/100 ml as the arithmetic mean 1 total-coliform/100 ml as the arithmetic mean of all

water samples examined per month, with

water samples examined per month, with no more than 4 no more than 4

coliforms/100 ml in any sample if the number of samples

is ≤ 20/month , or no more than 4 per 100 ml in 5% of the , or no more than 4 per 100 ml in 5% of the

samples if the number of samples exceeds 20 if the number of samples exceeds 20 per month.

Bouwer, Groundwater Hydrology, McGraw-Hill, 1978.

Number of samples taken for coliform testing depends on the population served by the treatment facility

Water samples from the effluent of a water treatment plant of a town (39,000 people) were analyzed at regular intervals over a month period The numbers of coliform/100 ml sample were as shown below:

No Count No Count No Count No Count

samples (sample # 14, 25, and 38) that have more than 4 coliform/100ml

So this is a violation of the regulations

The population is 39,000, so the minimum number of samples should be

40 Since we have 40 samples then the number of samples taken is OK

The arithmetic average of coliform should not be more

than 1 Since the average number of coliform is 0.95

which is less than 1 then this condition is OK

A3 Secondary Standard for Drinking Water

BOD and SS removal > 85%

B1 US National Pollutant Discharge Elimination System

(NPDES )

B2 Discharge standard of wastewater into Jebel Ali Harbor

Total Suspended solids mg/l 50

C Water Quality Objective Limits

Temperature 2 o C from background level

Total dissolved solids 2% from background level

Jebel Ali Harbor water quality objective limits

Parameter/Problem Treatment Process

Large debris (particles) Screens (Physical)

Suspended solids Coagulation (Chemical)/flocculation

(Physical)/Sedimentation (Physical)Filtration (Physical)

ion exchange (Chemical), or precipitation (Chemical)

Trace organic

contaminants Activated carbon (Chemical) or air stripping (Chemical) if chemicals are volatile in nature

Typical Treatment of Contaminants

Water Treatment Plant (WTP

(

A WTP consists of processes to remove contaminants present in the water

such that produced water is suitable for drinking

Raw water

influent

Produced waterEffluentWTP

A flow sheet for the plant shows the sequence of the processes used:

The design of a WTP depends on (1) the quality of raw water, (2) the quality

of produced water and the (3) capacity of the plant

The capacity of the plant depends on the design period (15-25 yrs), the

population served, and the per capita water consumption

Wastewater Treatment Plant (WWTP

(

A WWTP consists of processes to remove contaminants present in the

wastewater such that produced water is suitable for discharge or reuse

Wastewater

Or influent

Treated wastewater orEffluentWWTP

A flow sheet for the plant shows the sequence of the processes used:

The design of a WWTP depends on (1) the characteristics of wastewater, (2)

the desired characteristics of treated wastewater and the (3) capacity of the plant

The capacity of the plant depends on the design period (15-25 yrs), the

population served, and the per capita wastewater generation

Design flow rate =per capita water consumption*population at the end

The percent increase in population = (150000-100000)/100000= 50%

Per capita consumption at the end of design period=500(100%

+50%*10%)=525 L/d

Design flow rate = 150,000 * 525 L/d= 78750 m3/d

Example

A small town with a population of 100,000 and a per capita water

consumption of 500 L/d A water treatment plant is to be built to serve this town for the coming 10 yrs Estimate the design flow rate assuming the population after 10 yrs is 150,000

Solution

Flow Rates: Water Treatment Plants

Minimum flow rate

:

Important for design of pipes and channels that carry wastewater with

suspended solids Minimum velocity to keep organic solids in suspension is 0.3 m/s and to keep silt and sand in suspension is about 0.6 m/s

.

Maximum flow rate

:

This is the peak hourly flow Such flow is used to determine the hydraulic

capacity of the treatment plant and collection system

Design flow rate:

Average daily flow at the end of the design period Usually the average daily flow is taken as the average over a continuous of 12 months period.

This design flow rate is used to determine organic loading and for sizing all

treatment units.

Flow Rates: Wastewater Treatment Plants

Flow Sheet Diagram

River Water Treatment Plant

Raw

water

Effluent

Chlorine solution

Filtration Settling

Flocculation Mixing

Traveling Screen

Bar Screen

Coagulant

Ground Water

Filter

Bottled Water

Bottle water Plant

Example Industrial Wastewater Treatment Plant

Equalization Tank

Settling Tank

Effluent Air

Return sludge

Dispersed plug-flow activated sludge plant for an industrial wastewater

Chlorination

Removal Efficiency

Treatment Unit

Q,

Co

Q, C