An introduction to Pollution control

Industry Homes Water distribution system Sanitary sewer WWTP treatment Pre-Characteristics Drinking water Standards Treatment Treatment processes Reuse or discharge Standards... Bacter

WATER POLLUTION CONTROL

Industry

Homes

Water distribution system

Sanitary sewer

WWTP

treatment

Pre-Characteristics

Drinking water Standards

Treatment

Treatment processes Reuse or discharge Standards

US Primary Drinking Water MCL in mg/L (partial list)

Inorganic Chemicals

Bacteriological limits

US EPA states that “bacterial quality criteria for

drinking water from public supplies require not more

than 1 total-coliform/100 ml as the arithmetic mean of all water samples examined per month, with 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 samples 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

Population served Number of samples/month

<100,000 100

<1 million 300

Secondary Standard for Drinking Water

Contaminant Level Effects

Foaming agents 0.5 mg/L Aesthetic

Sulfate 250 mg/L Taste, laxative effects

Water Treatment Plants (WTPs)

A WTP consists of processes to remove contaminants present in

the water such that produced water is suitable for drinking

Raw water

influent

Produced water Effluent WTP

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

Contaminant Treatment Process

Large debris Screens

Settalable solids Grit chamber

Suspended solids Coagulation/flocculation/

sedimentation (w/ or w/o filtration)Dissolved solids Desalination

Deficit fluoride Fluoridation

Excess fluoride Defluoridation

Undesirable gases Air Stripping

Organic contaminants Activated carbon

Microorganisms Disinfection

1 Lime Soda-Ash Method

A precipitation method through which Ca is removed as CaCO3 and Mg is removed as Mg(OH)2

Wastewater Treatment

System

Raw wastewater Treated

wastewater

Treatment Processes

Primary Treatment

Grit Chamber

Wastewater

influent

Effluent Disinfectant

Screens

Primary Settling tank

Contact tank

Primary treatment removes about 35% BOD and 60% SS

Secondary Treatment

Biological treatment

Effluent Contact

Advanced Treatment

May include:

Activated carbon to remove organic contaminants.

Filter to capture suspended solids.

Nitrate removal

Zakher Wastewater Treatment Plant

CIVL270-Maraqa

Remove large solids and rags that cause problems if passed through the plant

Grit Removal

Remove 95% of grit and stones, which could result in blockages and abrasive, wear on machinery and pipe works

Aeration Tanks

Incoming sewage, “seeded” with active organisms, passed through tanks with surface aerators to provide oxygen for the degradation process and to ensure mixing that would maintain sewage and organisms in suspension.

Settling Tanks

After the aeration process the

activated sludge is allowed to settle, leaving an effluent containing less

than 30 PPM of suspended solids

Return Activated Sludge:

Some of the sludge from the

settling tanks is returned to be

mixed with incoming sewage to

the aeration tanks, in order to

seed active organisms into the

process

Aeration tank

Return sludge

Settling tank

Sludge to digesters

To further processes

Filtration:

After secondary settling, treated

wastewater passes through sand

filters to reduce the suspended

solids to about 10 ppm

Disinfection

Chlorine gas is injected into

the final effluent before the

effluent is being reused

Residual chlorine content of 1

ppm is the desired final

concentration.

Treated effluent is pumped into an elevated tower about 12 km away from the works The tower supplies the roundabout and roadside

irrigation networks and is also used for irrigation of parks

Overall treatment efficiency

 BOD removal =98%

 TSS removal =99%