Better Management
of
Nutrients in Sewage
Present Practice
• Present sewage treatment practice involves
oxidation by bacteria in presence of air
followed by bacterial denitrification.
Ammonia and sulphur compounds escape
giving a foul smell.
• Nitrogen in the sewage is lost to the
atmosphere mainly as nitrogen molecules
and to some extent as nitrous oxide.
• Nitrous oxide is 300 times more powerful
green house gas than carbon dioxide. It
contributes to climate change, ozone
depletion and to acid rain. Ammonia and
sulphur compounds contribute to fog
formation.
CLIMATE CHANGE
Hole in the ozone layer UV filter
FOG
Our Relation to Nitrogen
• We fix nitrogen by an industrial process to make
fertilizers and also by growing leguminous
plants.
• We use them to produce food in which nitrogen
is present in proteins. We eat the food.
LEGUMES
• We excrete. Most of the nitrogen excreted is present in urine.
Better Practice
• Separate the solids and make use for biogas
production. Biogas can be used as a source of
energy. Nutrients remaining in residue can be
used as fertilizer.
• Store liquids in a closed tank. The liquids give
off ammonia by natural bacterial
decomposition. By pumping air into the
liquid a major part of the ammonia can be
taken out and made to react with acids to
form ammonium salts. The latter can be used
as fertilizers.
• Suitable sea weeds can be grown in the
remaining liquids to further extract NPK etc
present in the liquid. The weeds can be
composted to make fertilizers. Only common
salt remains in the residual liquid which
should be disposed off suitably.
Seaweed
COMPOST
Advantages
1. Valuable fixed nitrogen and other nutrients
are recovered.
2. Pungent smell of ammonia and bad smell of
sulphur compounds are avoided.
3. Air, soil and water pollution is avoided.
4. Less disposal problem.
5. No health problems as there is no mix up with
industrial waste containing heavy metals etc.
6. Less dependence on natural gradients.
7. No contamination of crops and soil with E coli.
8. Reduced need for manufactured fertilizers.
Thank you for reading
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