Point Source Pollution

Point source pollution is contamination that enters the environment through any clear, specific location,

like smokestack, pipe, ditch, tunnel, or conduits. Point source pollution remains a major cause of pollution

to water. Point sources of water pollution include municipal sewage treatment plant discharges and

discharges from industrial plant.

Municipal sewage treatment plant point sources can contribute

pollution in the form of oxygen-depleting nutrients and in the

form of pathogens that cause serious health hazards in drinking

water and swimming areas. Industrial point sources can contribute

pollution in the form of toxic chemicals and heavy metals

. point sources of water pollution can be limited to ensure

protection of designated uses of a receiving water. Either standard

may be used to minimized the effluents concentration by proper

wastewater treatment processes like screening, grit chamber

sedimentation, flotation and biological treatment processes.

Point sources are as at specific locations, they are easy to identify, monitor and regulate. Developed world

control point source discharges of many harmful chemicals into aquatic system as well as in atmosphere.

Calculation of Point source Pollutions

In Point source pollution calculation law of conservation of mass can be used in any water or wastewater unit

operation. It relate influent flow rate and concentration to effluent flow rate and concentration by accounting for

removal or transformation phenomena. It can be applied to rivers, lakes, or other treatment basins, where the

problem is to find the concentration of a substance at a location or its rate of change in a section. According to this

law there are three general cases .

(i) Steady state conservative system: The simple system to analyze are the assumption that the substance is

conservative . It means the substance leave the system with out any change

Then input rate = output rate

Mathematically

(ii) Many contaminants undergo chemical, biological or nuclear reactions at

a rate sufficient to treat them non conservative substances. Then

Input = Out put + Decay rate . The decay rate is = -KC

where K is rate coefficient. The negative sign implies a loss of

substance with time or C = C0 e-Kt so Decay rate = KCV

Qw

QS

Cs

Cw Qm

Cm

Accumulation and Decayinput output

Non Point Source Pollution (NPSP)Non point source pollution can not be traced to any single site of discharge. They are usually large land areas that

pollute water by runoff, subsurface flow or deposition from the atmosphere. The runoff of chemicals into surface

water from cropland, live stocks feed lots, urban streets, lawns and parking lots, fugitive discharges from pipelines,

spraying, fertilizers, runoff from lands are the common examples of non point source pollution. There has been

little progress in controlling non point water pollution because of the difficulty extends of identifying and

controlling discharges from so many diffuse sources. Current concerns include the contamination of aquatic

environments by fertilizers and pesticides in runoff from agricultural lands, by oils and particulate matter from

urban streets and by atmospheric deposition of acids. The contamination of ground water resources, especially by

hazardous wastes is also of great concerns.

Major Non Point Source Pollution Categories

Categor S.S D. S BOD Nutrients Toxic Metals Pesticides Pathogens

Agriculture +++ +++ +++ +++ + +++ +++

Construction +++ n + + + n n n

Urban Runoff +++ ++ ++ +++ +++ +++ +++

Mining ++ ++ n n +++ n n

+++ = Potentially High Pollutant Source ++ = Moderate Pollutant Source

+ = Low pollutant Source and n = negligible pollutant source

Urban Non Point Source Pollution

Storm water runoff from urban areas contained higher concentration of different pollutants, like metals,

nutrients, oxygen demanding wastes and suspended solids. It also contains pathogenic microorganisms,

oil and petroleum hydrocarbons, pesticides and a variety of synthetic organics. The following measures

are help in reducing urban NPSP. (i) Public education and outreach (ii) Public participation (iii) Illicit

discharge determination and elimination (iv) Construction site runoff control (v) Post Construction runoff

to reduce soil erosion and (vi) Pollution prevention/ good house keeping to reduce pollution in runoff

from municipal operations. There are three major steps that can mitigate urban NPSP. (a) Reduce surface

runoff from urban sites (b) source control to reduce the amount of pollution pick up by runoff and © Best

management practices (BMP) to remove or treat pollutants in the runoff. Urban areas have a higher

percentage of impervious surfaces like roads side walls, driveways and parking lots. As a greater

percentage of precipitation falling in urban areas becomes surface runoff. Pollution control techniques

that reduce the amount of surface runoff can be effective at reducing erosion and pollution transport. In

addition to reducing surface runoff we can emphasize source control to reduce the amount of pollutants

deposited on impervious surfaces. Source control can be attained by increasing public education providing

waste disposal sites, introducing appropriate planning and regularity policy and enforcing pollution

control regulations. Streets sweeping least expensive source control techniques, reduces sediment loads

in runoff but fail to pick up the finer particles that are often the most significant source of pollution. Street

vacuuming is efficient in collecting the small particles, but expensive and often ineffective during wet

season. Street flushing is an effective way, but the catch basins have to cleaned periodically.

Mitigation Measure

Urban NPSP can be mitigated by the use of appropriate structural and non structural best management

practices. They are (i) Infiltration systems : Infiltration systems reduce the total amount of surface runoff

and the amount of sediment transport by increasing the amount of precipitation infiltrated into the soil.

(ii) Detention system: It reduce pollutant transport by retarding the rate of runoff and by encouraging the

settling of suspended solids. (iii) Retention system: Retention systems are wet ponds that are sized to

hold a typical (6 months) storm events. The ponds may be lined or unlined. The unlined ponds increase

infiltration and can help with ground water recharge. However, unlined ponds are not appropriate if the

surface runoff contains pollutants that could contaminate drinking water aquifer or in area where a high

water table would result in ground water flowing into ponds. (iv) constructed Wetlands: Constructed

wetlands are similar to retention system and wet ponds in that they have permanent standing water, but

have the added advantage that they incorporate biotic functions like nutrients uptake and microbial

degradation of pollutants. (v) Filtration System: Filtration systems use sand, soil, organic matter, carbon

or other materials to filter out pollutants. Filter systems can be incorporated into existing storm drainage

structures by adding underground vaults. (vi) Biofilter: Biofilter and other vegetated system such as grassy

swales and filter strips can be used to treat shallow flow or sheet flow by increasing infiltration and

reducing sediment transport. Large bioretention system add biological treatment such as nutrient uptake

and microbial degradation of pollutants. Most of the structural BMPs are designed to remove sediments

and pollutants that are transported in surface runoff along with sediments. The nonstructural BMPs focus

on reducing various pollutants. A public education program, with appropriate enforcement of pollution

control regulation is effective tools.

Mitigation Measure

Urban NPSP can be mitigated by the use of appropriate structural and non structural best management

practices. They are (i) Infiltration systems : Infiltration systems reduce the total amount of surface runoff

and the amount of sediment transport by increasing the amount of precipitation infiltrated into the soil.

(ii) Detention system: It reduce pollutant transport by retarding the rate of runoff and by encouraging the

settling of suspended solids. (iii) Retention system: Retention systems are wet ponds that are sized to

hold a typical (6 months) storm events. The ponds may be lined or unlined. The unlined ponds increase

infiltration and can help with ground water recharge. However, unlined ponds are not appropriate if the

surface runoff contains pollutants that could contaminate drinking water aquifer or in area where a high

water table would result in ground water flowing into ponds. (iv) constructed Wetlands: Constructed

wetlands are similar to retention system and wet ponds in that they have permanent standing water, but

have the added advantage that they incorporate biotic functions like nutrients uptake and microbial

degradation of pollutants. (v) Filtration System: Filtration systems use sand, soil, organic matter, carbon

or other materials to filter out pollutants. Filter systems can be incorporated into existing storm drainage

structures by adding underground vaults. (vi) Biofilter: Biofilter and other vegetated system such as grassy

swales and filter strips can be used to treat shallow flow or sheet flow by increasing infiltration and

reducing sediment transport. Large bioretention system add biological treatment such as nutrient uptake

and microbial degradation of pollutants. Most of the structural BMPs are designed to remove sediments

and pollutants that are transported in surface runoff along with sediments. The nonstructural BMPs focus

on reducing various pollutants. A public education program, with appropriate enforcement of pollution

control regulation is effective tools.