Wastewater –Its Journey to Treatment and Return to the Environment

ESI

Where does it all go!Where does the water from the washer go?

When you flush the toilet where does the contents go?

By gravity flow, the waste is on its way to your local wastewater treatment plant!

Why treat wastewater?• Causes a demand for dissolved oxygen

(lower DO levels of streams)

• Adds nutrients (nitrate and phosphate) to cause excessive growth

• Increases suspended solids or sediments in streams (turbidity increase)

Western Branch WWTP

Blue Plains WWTP

Mattawoman WWTP

Sewagesheds

Piscataway WWTP

Parkway WWTP

Marlboro Meadows WWTP

Bowie WWTP

approximate boundaries

- an area where sewage is collected and delivered to a WWPT

Where do you locate the WWTP in the watershed?A

B

C

DConsider the four possible sites.

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Parkwa

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ie

Western

Branc

h

Piscat

away

Mar lbor

o Mead

ows

Mat tawom

an

WWTP

millio

n gall

on/d

ay

CapacityAverage Flow

The volume of wastewater

PGC 1992 Comprehensive Ten Year Water and Sewerage Plan

Levels of TreatmentPrimary– removal by physical separation of grit and

large objects (material to landfill for disposal)

Secondary– aerobic microbiological process (sludge)

organic matter + O2 CO2 + NH3 + H2ONH3 NO3

-

- lowers suspended solids content (into sludge)

aquatic nutrient

Mostly dead microbes

Aeration and

rapid mixing

Settlingcollects sludge

on bottom

Secondary process

airdiffuser

From

prim

ary

proc

ess

To tertiary process

Levels of Treatment continuedTertiary (advanced)– anaerobic microbiological process with a

different microbe where O2 is toxic (more sludge)NO3

- N2 (escapes to atmosphere)

– PO4-3 if not removed in sludge in secondary

processPO4

-3 + Al+3 AlPO4 (s) (into sludge)

- aeration to strip N2 and re-oxygenate (add DO)

Slow mixingto keep

suspended and O2 out

Settlingcollects sludge

on bottom

Tertiary processFr

om se

cond

ary

proc

ess

Effluent

add methanol as food source

When the treatment is done…

• Effluent back to stream after– a final carbon filtration and– chlorination/dechlorination

• Sludge – very nutrient rich– applied directly to land as fertilizer– incinerated (good fuel after drying)– composted (Compro® from WSSC)

Note – Leafgro® is composted leaves and grass from MES