Wwtp trestrail development proposal

1. WASTEWATER MANAGEMENT PROPOSAL
P R O J E C T : PROPOSED HOUSING DEVELOPMENT
TRESTRAIL LANDS, ARIMA
Prepared and Calculated by
JEFFREY A. JAMES Dip Pl Cr, Dip Env. Mgmt. MTPATT WPC

2. WSSM
PLUMBING PROFESSIONALS
TRESTRAIL LANDS HOUSING DEVELOPMENT
WASTEWATER MANAGEMENT PROPOSAL 2 ©WSSM Ltd
1
INTRODUCTION
A private enterprise proposes to develop 51 Hectares of land at Trestrail Lands,
Arima for the purposes of a RESIDENTIAL BUILDING DEVELOPMENT . This
development will consist among other things 1, 200 residential building units , a
Primary School , Police Post, Community Center and Recreational park with
washroom facilities
WSSM proposes to design, construct, fabricate and install a packaged Wastewater
Treatment Plant, to manage the Wastewater generated from this development . This
plant is to be capable of treating 4.5k m3
of wastewater per day.
ANTCIPATED WASTEWATER PEAK FLOW
Estimated Population
Total amt. of Residential units 1206 units Design
Amt. per Residential unit 4.5 persons
WASA - Guidelines for Design of
Water and Wastewater systems
Estimated Residential population 5427 persons calculated
Proposed WWTP capacity
Wastewater Discharge per person 280 litres/day
WASA - Guidelines for Design of
Water and Wastewater systems
Estimated Wastewater Discharge 1519560 litres/day calculated
Allow 5% for Wastewater Discharge from other sources
within the Development
75978 estimated
Total Wastewater Discharge from Development 968720 litres/day calculated
Allow Peak Factor 5/P 1/6 4
where P is population in
thousands.
Peak Wastewater Discharge 3874880 litres/day
Size of proposed Development 51 hectares
Allow for Ground Water Infiltration 255000 litres/day 5000 l/ha/day
Peak Flow
4129880 litres/day
4130 m
3
/day
The expected effluent when treated will be:
 20 mg/l Biochemical Oxygen Demand
 less than 30 mg/l of total solids
This meets the discharge standards set out by Environmental Management Authority
and Water and Sewerage Authority.

3. WSSM
PLUMBING PROFESSIONALS
TRESTRAIL LANDS HOUSING DEVELOPMENT
WASTEWATER MANAGEMENT PROPOSAL 2 ©WSSM Ltd
2
This Packaged Wastewater Treatment Plant will be designed using the EXTENDED
AREATION process which uses modified activated sludge procedures. In E xtended
Aeration, the raw sewage goes straight to the aeration tank for treatment. The
whole process is aerobic. This simplification implies longer aeration time which has
earned for the process the name "extended aeration". The BOD removal efficiency
of the extended aeration process is higher than activated sludge process which
makes it especially desirable to use where it is to be followed by UV tertiary
treatment before discharge.
WSSM Treatment System will comprise of components which will be imported from
the United States . This proposed WWTP must be located on the western perimeter
(down-wind) of the development on at least 3600m 2
of land, in close proximity to
either a natural or man -made water course
The plant shall be:
 Duplex Tank construction with each half capable of treating fifty percent of
the daily flow and allows for down time for cleaning and repairs. Each half
will have an ano xic, aeration, clarifier, and sludge digester compartment to
allow for treatment of wastewater
 Grit Chamber for removing grit ahead of pumps
 Sludge Drying beds (4 no.)
Figure 1 - Extended Aeration Process Flow diagram

4. WSSM
PLUMBING PROFESSIONALS
TRESTRAIL LANDS HOUSING DEVELOPMENT
WASTEWATER MANAGEMENT PROPOSAL 2 ©WSSM Ltd
3
DESCRIPTION OF PLANT
Duplex Tank
The process tank will be constructed of reinforced concrete or steel to
withstand the pressures generated by its contents. The process tank shall be of
duplex construction divided into five compartments. There is the anoxic
chamber into which the raw sewerage enters to start the treatment process by
removing nitrates. From this chamber the sewage flows into the aeration
chamber where air is bubbled to cause the tank’s contents to be aerated and
agitated to keep the contents in suspension. From this chamber the sewage
passes through a floating weir into the settling chamber. The floating weir
allows excess wastewater during pumping from wetwell to remain in the
aeration chamber and prevents upsets in the clarifier. In clarifier the quiescent
conditions allow the heavy solids to separate from its carrying liq uid and sink
to the bottom of the chamber, while the light solids float to the surface. The
heavy particles that sink to the bottom of the chamber are called sludge and
the solids that float to the surface are called scum. The sewage then flows
through a filter to remove any stray solids before it goes to the ultra violet
system for disinfection. The other compartment in the tank is called the sl udge
digester and is not inter -connected to the other compartments in the tank. Any
excess sludge to be wasted i s airlifted to this tank to be aerated before going
on to the sludge drying beds.
A Floating Weir between the aeration and settling compartment allow only the
normal flow through the system and stores the excess from pumping in the
aeration chamber and forms part of the aeration process . On the tank there is a
catwalk that allows access for the operations required in the plant. Along the
catwalk there are several galvanized steel pipes, called diffusers through which
air flows from the header for the aer ation process. The volume of air
discharged from each diffuser is regulated by a gate valve, while the check
valve allows air to flow in one direction only. There is a union on the diffuser
that allows for the separation of the pipe into the sewage and th e header pipe.
Along the length of the catwalk there are two steel 100 millimetre pipes, one
carries activated sludge to the beginning of the aeration process. The other
pipe carries from the settling chamber any excess sludge to the sludge digester
chamber to be aerated. The amount of sludge flowing in each pipe is adjusted
by opening and closing a 25 millimetre valve that controls them. Another valve
controls the skimmer which removes the scum that has accumulated on the
surface of the settling chamber. At the end of the settling chamber is the
overflow collection channel with an adjustable weir, over which flows the final
effluent which flows through a filter then through a 2.4 millimetre steel pipe
and polyvinylchloride pipe to the ultra violet disinfec ting system, before
discharging to drain. sludge discharge line to drying beds . Along the length and
width of the tank there will be three 100 millimetre valves. Each valve will be
connected to a compartment in the tank to allow for emptying for maintenanc e
of the plant if required. Each valve when opened allows the contents from the
compartment to empty onto the sludge drying bed through a common 100
millimetre PVC pipe. Just before the 100 millimetre PVC pipe enters the sludge
drying beds there are four 1 00 millimetre valves manifold to control the flow
from the tank into each or all beds simultaneously.

5. WSSM
PLUMBING PROFESSIONALS
TRESTRAIL LANDS HOUSING DEVELOPMENT
WASTEWATER MANAGEMENT PROPOSAL 2 ©WSSM Ltd
4
Grit Chamber
A grit chamber is placed ahead of the pumps to remove stones and other such
material that can damage the pumps impeller. A mechanical pump is provided
to remove accumulated grit from chamber.
Sludge Drying Beds
There will be four sludge drying beds each measures approximately ten
meters by five meters. The distribution polyvinylchloride pipes are under the
filter media. The media is made up of a 200millimeter of 12 to 18 millimetres
washed gravel, upon which is a 150 millimetre of 10 millimetres washed pea
gravel upon which is the 100 millimetre final layer of sharp sand. Each bed is
provided with a one meter square splash pad to prevent eros ion of the sand
where the sludge impacts. The filtrate from the sludge drying beds flow
through a 100 millimetre polyvinylchloride pipe to the wetwell for re -cycling
through the tank. The solids that remain on the beds are allowed to dry by
the sun. The dr ied matter is then bagged and removed or disposed by
appropriate disposal methods.
Equipment
The equipment on the plant will consist of:
QTY UNIT DESCRIPTION
EQUIPMENT
3 only
Gorman Rupp surface mounted pumps inclusive of anti-slam check valves, and
gate valves
3 only
Roots sound attenuated blowers complete with silencers, motors, belts, pulleys,
belt guard, pressure relief valve, gate valve and check valve
1 only Ultra Violet system complete with monitor - 360 USGPM
1 only Standby Generator - 170 KVA
PIPING
1 item Complete Piping system for air diffusers and air header
1 item Complete Piping system for pumps
1 item Complete Piping system for ultra violet system
1 item Complete Piping system for Skimmer and air pump
1 item
Complete Piping system for sludge return line, sludge digester line, Overflow
weirs and baffles
ELECTRICAL
1 item Electrical wiring throughout plant
1 item Electrical control panel for pumps, blowers
OTHER
1 item Process tanks
1 item Miscellaneous grating, railings, access stairway, painting, catwalk
TOTAL COST OF PLANT AND EQUIPMENT - 14.5M (TTD)

6. WSSM
PLUMBING PROFESSIONALS
TRESTRAIL LANDS HOUSING DEVELOPMENT
WASTEWATER MANAGEMENT PROPOSAL 2 ©WSSM Ltd
5
Electrical Control Panel and Automatic Transfer Switch
The equipment on the plant is controlled by a panel that has separate control for
each piece of equipment. Each blower has a timer mechanism that controls the on
and off running of each blower and also the length of time it runs/operates
automatically. Each pump is controlled by float switches located in the wetwell
that automatically turn each pump on and off as the level of the sewage in the
well rises and falls. Each piece of equipment has a manual, off and automatic
position on the switch located on the outside of the panel. Lights are provided to
indicate which blower or pump is running, is off or has tripped. The volt meter
indicates the voltage supplied by TTEC and ammeter measures current being used
by the equipment are on the outside of the panel. Inside the panel are breakers,
contractors, under/over voltage, phase failure relay, star delta starters
alternator for then pumps and timers for the blowers. The middle panel contains
the breakers for the supply to the panels and the main breaker. There is a
transformer to provide 110 Volt power supply. The next panel is the automatic
transfer switch. This device allows the standby generator to be turned on
automatically when the power source is removed, and turns off when power is
restored. On the front of this switch there are indica tor lights that indicate the
power source is from the mains or generator.
Electrical Wiring
All electrical wiring required for the operation of the plant is supplied from the
point of entry of TTEC power. The client is responsible for bringing the power
supply to the Operator’s Building.
ADDITIONAL REQUIREMENTS
The Developer will have to provide the following:
DESCRIPTION ESTIMATED COSTS
Fencing 300,000.00
Access roadway 500,000.00
Administration 352,000.00
Wetwell 600,000.00
Pump house 196,300.00
Operators building 356,890.00
Overflow line 75,000.00
Lifting mechanisms for pumps, blowers,
and generator
150,000.00
Landscaping 80,000.00
Estimated costs of additional requirements for the
plant to be borne by Developer
$ 2,610,190.00

7. WSSM
PLUMBING PROFESSIONALS
TRESTRAIL LANDS HOUSING DEVELOPMENT
WASTEWATER MANAGEMENT PROPOSAL 2 ©WSSM Ltd
6
The Compound
The compound should be at least 60 meters long by 60 meters wide of flat
topography. The area will be fenced with a 2.1 meter high chain link fence
upon which is placed 400 millimetres diameter razor wire for a total fence
height of 2.4 meters. The entrance gate to the compound is 5 meters wide
and 2.1 meters high inclusive of razor wire. There will be an asphalt paved
access roadway 5.0 meters wide to the tank, operator’s building and the
sludge drying beds with parki ng for three vehicles. The compound will be
grassed.
The pump house and wetwell
The pump house will house the control panel and surface mounted pumps.
Lights are provided in and outside the building. The wetwell will have a
screen for collecting trash and steps for accessing the wetwell. There are also
three float switches for the automatic control of the pumps. The building will
be constructed with a concrete foundation reinforced with BRC fabric. The
walls of the structure will be loaded with one hundred and fifty millimeters
concrete blocks with twelve millimeter steel at four hundred millimeter
centres. The roof of the building will be reinforced concrete and sloped to
allow for free flow of water off the roof.
The operators building
This building shal l be 14 metres long by 5 meters wide with the floor one
meter above the ground. The floor of the building is a reinforced concrete
slab. On this slab is placed 150mm x 200mm x 400mm concrete blocks
reinforced with 12 millimetre steel at 400 millimetres cen tre to centre and
filled with concrete. The roof of the building is a reinforced concrete slab
sloped, so that, water will run off the roof without settling. The building has
an office area, a toilet and shower whose walls are tiled to a height of 1.8
meters, an area to be used as a laboratory for carrying out tests, and
equipment and storage area. Adequate lights are provided in each area. In
the office area are the electrical controls for the equipment that operates
the plant.