Individual Household Treatment Systems Septic Tanks

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Individual Household Treatment Systems (Septic
Tanks)
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Sizing Septic Tank Volume Vol (Average Flow
Rate per hour)(1 hr)
Size of Tile Field Determined by perc test
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Centralized Wastewater Treatment System
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Sedimentation Tank Principles
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The trajectories of particles entering the top of
the tank at depth h 0 are illustrated below.
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Clarifier (Sedimentation Tank) Design Primary
Hydraulic detention time 2 hrs
Overflow rate 40 m3/m2-day Secondary
Overflow rate 15 m3/m2-day
Depth 1.3 m
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Biological Treatment Principles
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The quantity of new biomass produced is a
function of the growth rate of the
microbes. Under aerobic conditions cell yield
varies from about 0.1 to 0.4 g cells per g of
BOD5 used. Under anaerobic conditions cell
yield is much lower 0.05 g cells per g BOD5
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Essential Elements of Activated Sludge Process
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Activated Sludge Design Parameters F/M 0.3
kg BOD5/kg MLSS-day Volumetric loading 0.8 kg
BOD5/m3-day Hydraulic residence time 5
hrs Air supplied 60 m3/kg BOD5
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Biofilm Systems

• Biofilm
• a biological slime layer
• bacteria in biofilm
• degrade organics
• biofilm will develop
• on almost anything

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Trickling filter
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Trickling Filter Design Parameters Hydraulic
loading 10 m3/m2-day Depth 2 m
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Anaerobic Digestion
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Anaerobic Digester Design Parameters Solids
loading 2 kg/m3-day Solids retention time 20
hrs Note that anaerobic digestion is considered
to be a mesophilic process where optimum
temperature is 350C ( 90oF)
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Gas (methane) production rate in anaerobic
digesters 0.4 m3 per kg biomass
digested (biomass digested waste biomass from
aerobic process, i.e., activated sludge,
trickling filter) This methane can be used to
heat the digester.
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