DISPOSAL BY DILUTION

introduction

The study of the sources of disposal is

important, because the amount of

treatment required to be given to

sewage depends very much upon the

source of disposal.

Disposal By DilutionThis process where the treated sewage

or the effluent from the sewage

treatment plant is discharged into a river

stream.

The discharged sewage, in due course of

time is purified by what is known as self

purification process of natural waters

Disposal of sewage effluentsDilution i.e. disposal in water ; and

Effluent Irrigation or Broad Irrigation or Sewage

Farming i.e. disposal on land

{Disposal by dilution is common of these two}

Conditions favoring Disposal By DilutionWhen sewage comparatively fresh(4 - 5 hrs. old),

and free from floating and settle able solids.When the diluting water (i.e. the source of

disposal ) has a high dissolved oxygen (D.O) content.

Where diluting waters are not used for the purpose of navigation on the down stream from the point of sewage disposal

When the out fall sewer of the city or the treatment plant is situated near some natural waters having large volumes

The bureau of Indian Standards

(BIS),previously known as Indian

Standard Institution (ISI), has there for

laid don it’s guiding standards for

sewage effluents ,vide IS 4764 -

1973,and for industrial effluents vide IS

:2490-1974 as shown in the table

Bureau of Indian Standards

Standards of Dilution Based on Royal commission Report

Dilution Factor Standards of purification required

Above 500 No treatment is required .Raw sewage can be directly discharged into the volume of dilution water

Between 300 to 500 Primary treatment such as plain sedimentation should be given to the sewage

Between 150 to 300 Treatments such a sedimentation, screening and essentially chemical precipitation are required

Less than 150 Complete thorough treatment should be given to sewage

Dilution in Rivers and self Purification of Natural Streams

The automatic purification of

polluted water by dilution.

sedimentation, oxidation-reduction

in sunlight, etc in due course is

called Self Purification Phenomenon

BIS STANDARD FOR DISCHARGE OF SEWAGE AND INDUSTRIAL EFFLUENT IN SURFACE WATER SOURCE

AND PUBLIC SEWERS:

GENARAL STANDARDS FOR DISCHARGE OF ENVIRONMENT POLLUTANT FROM EFFLUENT INTO SURFACE WATER SOURCE,

PUBLIC SEWERS, AND MARINE COASTS UNDER ENVIRONMENT(PROTECTION) RULE, 1986

Natural Forces of PurificationPhysical Forces

Dilution and dispersion

Sedimentation

Sunlight

Chemical Forces

Oxidation(bio)

Reduction

Dilution and dispersionWhen the putrescible organic matter is discharged

into a large volume of water contained in the river

stream, it gets rapidly dispersed and diluted . this

results in diminishing conc. of organic matter

When sewage of concentration Cs flows at a rate

Qs in to a river stream with conc. Cr flowing at rate Qr

Cs Qs + Cr Qr = C ( Qs+Qr)

SedimentationThe settle able solids, if present in

sewage effluents ,will settle down

into the bed of river, near the outfall

of sewage.

SunlightThe sunlight has a bleaching and

stabilizing effect of bacteria .It also helps

Certain micro – organisms to derive

energy, and it’s called photo synthesis

OXIDATION

THE OXIDATION IS A ORGANIC MATTER

PRESENT SEWAGE EFFLUENT, WILL START

AS SOON AS THE SEWAGE OUTFALL INTO

THE RIVER WATER CONTAINING DISSOLVED

OXYGEN

REDUCTION

REDUCTION OCCURS DUE TO HYDROLYSISOF

ORGANIC MATTER SETTLED AT THE BOTTOM

EITHER CHMICALLY OR BIOLOGICALLY.

ANAEROBIC BACTERIA WILL HELP IN

SPLITTING THE COMPLEX ORGANIC

CONSTIUTUENT OF SEWAGE INTO LIQUID

AND GASES, AND THUS PAVING THE WAY FOR

THEIR ULTIMATE STABILIZATION BY

OXYDATION.