Disposal by dilution is a process where treated sewage or effluent is discharged into a river or stream. For dilution to be an effective means of disposal, certain conditions must be met, such as the sewage being relatively fresh, the receiving water having a high dissolved oxygen content, and the receiving water not being used for navigation downstream. The amount of treatment required depends on the dilution factor - a higher dilution factor means less treatment is required. Natural processes like dilution, sedimentation, sunlight, oxidation, and reduction help purify the sewage over time as it mixes with the receiving water.

1. DISPOSAL BY DILUTION

2. 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.

3. Disposal By Dilution
This 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

4. Disposal of sewage effluents
 Dilution 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}

5. Conditions favoring Disposal By Dilution
 When 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

6. 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

7. 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

8. 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

9. BIS STANDARD FOR DISCHARGE OF SEWAGE AND INDUSTRIAL
EFFLUENT IN SURFACE WATER SOURCE AND PUBLIC SEWERS:

10. GENARAL STANDARDS FOR DISCHARGE OF ENVIRONMENT POLLUTANT
FROM EFFLUENT INTO SURFACE WATER SOURCE, PUBLIC SEWERS, AND
MARINE COASTS UNDER ENVIRONMENT(PROTECTION) RULE, 1986

11. Natural Forces of Purification
 Physical Forces
 Dilution and dispersion
 Sedimentation
 Sunlight
 Chemical Forces
 Oxidation(bio)
 Reduction

12. Dilution and dispersion
 When 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)

13. Sedimentation
 The settle able solids, if present in sewage
effluents ,will settle down into the bed of
river, near the outfall of sewage.

14. Sunlight
 The sunlight has a bleaching and stabilizing
effect of bacteria .It also helps Certain
micro – organisms to derive energy, and it’s
called photo synthesis

15. 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

16. 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.