Transcript Sewage Treatment Des..

NH International
(Caribbean) Ltd
Penal Rock Hindu School
Presented by : Sudesh Ramroop
DESIGN BRIEF

The proposed Sewerage Treatment Plant is sized
in accordance with the following guidelines:
Capacity x Average Daily Flow Rate

Example:300 x (55 Liters per Person /3.78) =
4365.07 Gallon of Waste Water per day
INLET & OUTLET QUALITY
 The proposed Sewerage Treatment Plant is designed to treat domestic
wastewater. Domestic Wastewater is essentially the spent or used water of a
community, emanating from personal, sanitation and domestic uses. It is
intended for the discharge from the treatment process to be integrated into
inland surface water according to TTS 417:1993.
 Influent waste water BOD
=
280 mg/l
 Maximum Permissible Levels of Key Parameters for Liquid Effluent from
Domestic Wastewater Treatment Plants
 Point of Discharge:
Inland Surface Waters
 5 Day BOD (mg/l)
25
 Suspended Solids
30
 pH
6-9
 Faecal Coliform
4000
 Total Residual Chlorine
 (mg/l)
0.1
 Source: Trinidad & Tobago Standards- Specifications for the Liquid
Effluent from Domestic Wastewater Treatment Plants into the
Environment. TTS 417:1993
WASA GUIDLINES

WASA requires that you allow 280 Liters per person and 4.5 persons per
house in all design calculations per details below- However, a study was
completed by ECO Projects Limited verifying the capacity used per
household and a figure of 250 Liters was recommended.
INNFLUENT QUALITY
EFFLUENT QUALITY
TREATMENT STAGES
SEPTIC TANK
SECONDARY
TREATMENT
TERTIARY TREATMENT
AEROBIC TREATMENT UNIT

An aerobic treatment unit (ATU) pretreats wastewater
by adding air to break down organic matter, reduce
pathogens, and transform nutrients. Compared to
conventional septic tanks, ATUs break down organic
matter more efficiently, achieve quicker decomposition
of organic solids, and reduce the concentration of
pathogens in the wastewater. More than 20 brands of
ATUs are available, but efficiency varies widely. A
properly operating ATU should produce high-quality
effluent with less than 30 mg/liter BOD (biochemical
oxygen demand, a measure of the organic matter), 25
mg/liter TSS (total suspended solids), and 10,000
cfu/100mL fecal coliform bacteria, an indicator of
pathogens and viruses.
How Do Aerobic Treatment Units Work?

By bubbling compressed air through liquid
effluent in a tank, ATUs create a highly
oxygenated (aerobic) environment for bacteria,
which uses the organic matter as an energy
source. In another stage bacteria and solids settle
out of the wastewater and the cleaner effluent is
distributed to a soil treatment system or water
course.


ATUs are more complicated than septic tanks. In a
septic tank, solids are constantly separating from liquid.
As individual bacterial cells grow, they sink to the
bottom, along with less decomposed solids, to form a
layer of sludge. Floating materials, such as fats and
toilet paper, form a scum layer at the top of the tank.
In an ATU, the bubbler agitates the water so solids
cannot settle out, and floating materials stay mixed in
the liquid. Well-designed ATUs allow time and space
for settling, while providing oxygen to the bacteria and
mixing the bacteria and its food source (sewerage). Any
settled bacteria must be returned to the aerobic portion
of the tank for mixing and treatment.