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ANAEROBIC SEWAGETREATMENT
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HISTORICAL PERSPECTS
1850:Louis H Mourac, France
Automatic scavengers for settled sewage sludge
1895:Donald Cameron
Built first septic tank, collected CH4 and used
it for street lighting
1904:
Travic hydrolytic tank achieving dust function
of sedimentation and digestion installed at
HAMPTON
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INTRODUCTION
DECOMPOSITION OF ORGANIC ANDINORGANIC MATTER WITHOUT MOLECULAR
OXYGEN
PROCESS DONE BY ANEROBIC BACTERIA
THREE TYPES
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PROCESSES INVOLVED
HYDROLYSIS
ACIDOGENESIS
METHANOGENESIS
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MICROBIOLOGY OF PROCESS
HYDROLYSIS:TRANSFORMATION OFCOMPLEX COMPOUNDS TO SIMPLER
COMPOUNDS.
ACIDOGENESIS:ACID FORMATION TAKESPLACE.
METHANOGENESIS:METHANE FORMATIONTAKES PLACE.
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STEPS IN ANAEROBIC DIGESTION
COMPLEX
ORGANICS
HIGHER
ORGANIC
ACIDS
ACETIC ACID
H2
CH4
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Complex organic material(starch, protein fats)
Simple organic material(sugar, amino acids)
Hydrolysis
Volatile fatty acids(propionate, butyrate etc.)
Acidogenesis
Acetogenesis
H2 + CO2 Acetate
CH4 + CO2
MethanogenesisMethanogenesis
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STANDARD RATE ASD
THE CONTENTS OF DIGESTER AREUSUALLY UNHEATED AND UNMIXED.
DETENTION TIME VARY FROM 30 TO
60 DAYS.
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MIXING OF FIRST STAGEDIGESTION CAN BE ACHIEVED BY
FOLLOWING METHODS:
Installing a draft tube mixer (commonlyused in India)
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Gas recirculation (practiced in USA)
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Sludge recirculation(practiced in UK,FRG)
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From maintenance point of view option3 is ideal since a pump can be easily
replaced /repaired without affectingdigester performance
From mixing consideration 1 and 2 are
comparable Option 2 needs an auxiliary storage of
gas for starting up a digester.
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STANDARD RATE SLUDGE DIGESTER
To pipeline
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HIGH RATE ASD
HERE THE SLUDGE IS HEATED AND
MIXED.
DETENTION TIME IS TYPICALLY 15 DAYS
OR LESS.
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HIGH RATE SLUDGE DIGESTER
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TWO STAGE SLUDGE DIGESTIONPROCESS
SCUM
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FACTORS AFFECTING ASD
DISSOLVED OXEGEN
pH (6.6 to 7.6)
NUTRIENTS AVAILABLITY.
OPTIMUM TEMPERATURE(85 TO 100 F)
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ADVANTAGES OF ASD
LOW CONCENTRATION OF BIO-MASS.
METHANE IS VERY USEFUL ENDPRODUCT.
RESULTING ORGANIC MATTER IS WELLSTABILIZED.
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LIMITATIONS OF ASD
SLOW GROWTH RATE(LONG DETENTION
TIME).
HIGH TEMPERATURE.
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QUESTIONS ?
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