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Sewage Treatment
What goes on at a sewage treatment plant
14
Environmental Studies
Graduate
12/01/2010

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Cards

Term
Exponential Growth
Definition
In reference to the test tube metaphor, species which exhibit this type of growth will reproduce geometrically until they have reached the limit of the resources present
Term
E-folding Residence Time
Definition
The time interval in which an exponentially-growing quantity increases by a factor of e
Term
Instantaneous Rate of Change
Definition
P=P0ekt  where P0 is initial concentration and P is concentration at time t
Term
Half-life
Definition

The period of time it takes for a substance undergoing decay to decrease by half (opposite of doubling time).

T1/2=ln(2)/λ=half-life

Term
Doubling Time/ Rule of 70
Definition
Doubling time equals 70/growth rate
Term
Sewage Treatment Goals
Definition
Removal of suspended sediments, biological oxygen demand, pathogens, and nutrients (nitrogen and phosphorus)
Term
Biochemical Oxygen Demand
Definition
A measure of the degree of organic pollution in the water-- milligrams of O2 consumed by one liter of sample during 5 days of incubation at 20o Celsius
Term
Primary Sewage Treatment
Definition

1. Inflow to course screening and grit removal

2. Primary clarifier

3. (Primary sludge to anaerobic digester)

 

At least 30% of BOD and SS must be removed at this stage

Term
Secondary Sewage Treatment
Definition

1. Sludge from primary clarifier to activated sludge or trickling filter

2. Sludge to secondary clarifier

3. Sludge back to activated sludge/trickling filter, to chlorination, or to anaerobic digester

4. Chlorinated sludge to effluent

 

85% of BOD and SS must be removed at this stage

Term
Grit Chamber
Definition
Remove heavy organic solids. Method: grit (sand, gravel, clay, metal filings) is heavier than the organic solids that should be kept in suspension for subsequent treatment. Centrifugal motion is used to separate the solids from the waste water.
Term
Primary Clarifier
Definition
Tank with residence time of a few hours, collects primary sludge for anaerobic digester.
Term
Trickling Filter
Definition
Fixed-film or attached growth systems-- 70% of organic waste from effluent of primary clarifier is oxidized here. 15-20% is converted to biomass. Characterized by resilient microbial community. Lower sludge production and cheaper to operate once built.
Term
Activated Sludge
Definition

A process for treating sewage using air and a biological floc composed of bacteria and protozoans.

Higher SS and BOD removal, cheaper to build.

Term
Anaerobic Digester
Definition
Results in 1/3 sludge reduction by weight due to methane and CO2 production, anaerobic catabolism, and dewatering. Methane production can provide energy to heat digester to 27-35oC
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