Model A&B Type Plants (0 - 350m3/day)
General
The unit is a complete activated sludge treatment plant which is factory built
ready for installation on the purchaser's prepared foundations. The dimensions
of the plant and the design hydraulic and organic loadings are specified in the
technical data section of this description and drawing.
The unit comprises a mild steel welded tank suitable stiffened for burying or
standing at ground level and epoxy resin painted for corrosion protection,
together with the ancillary equipment detailed later. The tank is divided by
means of a partition wall into separate aeration and settlement or
clarification compartments.
The treatment plant is fabricated as a single structure. All side walls, bottom
and partition walls mild steel plate and all structural shapes used for
reinforcing and bracing will have a minimum thickness of 6mm.
General Arrangement
Inlet Box
A welded steel box is provided at the inlet end of the aeration
compartment to receive the incoming sewer.
Aeration Compartment
The aeration compartment is designed to provide a minimum of 24 hours
detention at dry weather flow, and to ensure an adequate circulation velocity.
Settlement Compartment
The settlement compartment is of the upward flow type with a hopper
bottom formed by sloping the end wall of the plant structure and by inclining
in the opposite direction the partition wall between the settlement compartment
and the aeration compartment.
Clarified liquid, after settlement, passes over the edge of the effluent weir
into the effluent trough and through the effluent pipe to the water treatment
plant outlet.
Sludge which settles to the bottom of the settlement compartment is returned to
the aeration compartment by an airlift pumping system which is also utilised to
waste sludge.
The effluent trough weir is formed from 6mm thick plate with a vee-notched
overflow edge and is mounted so as to permit easy adjustment of level and
height. A scum baffle is fitted in front of the effluent weir.
Automatic Skimming System
To provide continuous automatic removal of floating solids from the
settlement tank water surface, a hydraulic skimming device is incorporated
consisting of channels which draw the floating material from the surface of the
settling basin and does not require any direct power, the system operating
entirely on the hydraulic gradient developed between the settlement and
aeration compartment.
Outlet Box
A welded steel box is provided at the outlet end of the treatment
plant structure to permit connection of the effluent pipe to the outfall sewer.
Walkway
A walkway approximately 650mm wide, consisting of galvanised mesh
grating is installed across the aeration tank to provide access to air
diffusion equipment, the blower housing and the electrical control panel.
Aeration Equipment
Air Header
A square section of mild steel air distribution header is provided on which are
individual air diffusion drop pipes assemblies to permit introduction of the
maximum quantity of one side of the tank to the other with minimum end
clearance. The header is supported on the aeration tank by means of structural
framing.
Drop Pipes and Diffusers
Each air diffusion drop pipe assembly is formed from a 25mm diameter
galvanised mild steel pipe, which also serves as the air conduit. The drop pipe
is also connected to the air header as to permit the air diffusion disc at the
lower end to be raised above the water surface quickly and easily without
disturbing the air flow or the operation of any other weir diffuser. The air
diffusion discs are designed to ensure uniform bubble distribution of the air
over the entire width construction, removable for inspection and servicing as
required.
The air diffusion efficiency of the discs is such that an adequate supply of
oxygen is maintained in the aeration tank to meet the treatment requirements of
the sewerage load for which the plant is designed.
Blowers & Motors
Air Blowers
The air supply for the treatment plant is provided by a Roots-type
blower. The blower has cast iron rotors of a specially developed form to give
the highest efficiencies. The rotors are mounted on high-tensile steel shafts
keyed and locked in position and the shafts and tips of the rotors are ground
to fine limits. Each rotor assembly is supported by ball and roller bearings
located in the housings in the end plates. The rotors are linked by a pair of
timing gears mounted on a shaft. The design of the blower is such that there is
not internal contact between the rotors themselves or between them and the
rotor chamber.
The end covers enclose the bearings and gears and form reservoirs for
lubricating oil - in addition the driving end covers contain s supplementary
bearing supporting the output shaft. The lubrication required to the motor
shaft bearing and timing gears is supplied by splash feed from a self-contained
sump. The sump is fitted with level indicators. The oil sumps are completely
divorced from the working air chamber by a neutral chamber to prevent the
contamination of the air by lubricating oil, or conversely, the condensation of
water from the air in the lubricating oil system.
Motor & Driver
The motor is driven through a vee-belt drive by a horizontal spindle,
squirrel cage, totally enclosed fan cooled metric frame motor, rated at least
10% in excess of the maximum HP absorbed. The motor is mounted on slide rails
to facilitate driving belt adjustment.
Piping & Valves
Complete blower discharge piping of galvanised steel with galvanised
malleable iron fittings, flexible couplings and check valves are provided.
Control Panel
A weatherproof control panel is provided to be fixed onto the support
frame work. The panel is suitable for direct on-line starting and is equipped
with:
(a) An interlock isolator.
(b) Main circuit breaker.
(c) Triple pole thermal overload relays having inherent single phase
protection.
(d) Triple pole block type contactors having inherent under-voltage release.
(e) 0 - 24 Hour timer.
Corrosion Protection
This is provided to the Client's specification or our standard as
detailed below.
Structural Steelwork (Inside or Buried In Ground)
1. Structural members and plates will be treated inside and outside by
mechanical wire brush to remove scale and weld debris as well as rust.
2. 1 x Coat of Culturite primer to a minimum DFT of 50 microns.
3. 2 x Coats EPD 100 epoxy tar to a minimum DFT of 250 microns.
Structural Steelwork (External Exposed)
1. Structural members and plates will be treated inside and outside by
mechanical wire brush to remove scale and weld debris as well as rust.
2. 1 x Coat of High Zinc Rich Primer to a minimum DFT of 50 microns.
3. 2 x Coats of Alkyd Enamel to a minimum DFT of 100 microns.
Model R Type Plants (+350m3/day)
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General
Oxigest Sewage Treatment Plants of the Package and Site Erected type have been used successfully
all over the world over the past 50 years. They were developed in the U.S.A. for small and medium
sized communities and can be adapted to various process systems.
Although originally an excellent U.S.A. innovation, technology both inside and
outside the U.S.A. have taken the Oxigest Sewage Treatment Plant to a design and
cost level which is recognised as the ultimate in its field.
The Oxigest range of factory built and site erected plants are recognised as
the best, and most widely used diffused air/activated sludge sewage and
effluent treatment plants. They are self-contained and will treat domestic
sewage from 30 to 20 000 people.
The diffused air process is continuous, rapid and odourless. The capital cost
of Oxigest systems is about half of conventional plant and the time necessary
for erection and commissioning is substantially reduced. Only a
fraction of the land necessary for conventional plant is
required.
WEC Projects’ Model 'R' plant is designed to run as an extended aeration
activated sludge system using the parameters as laid down in the attached
specifications. The plant can be located above or below ground to suit gravity
flow or other site conditions.
The plant is of all steel construction located on steel channel rings cast
within the concrete base.
The unit consists of two concentric circular steel walls. The inner tank is the
clarifier whilst the space between the outer wall and the clarifier is the
reactor which contains the Aerobic zone as well as an Anoxic and/or Anaerobic zone
depending on the treatment requirements. The aeration basin is sized using well defined
parameters for retention and contact time. A fine bubble diffused air system, provides the
necessary oxygen required to facilitate biological treatment within the basin.
Construction
Steel channel rings are pre-rolled prior to delivery to site along
with the clarifier sludge hopper. The ring for
the outer tanks are positioned on and welded to support tubes
driven into the prepared ground. After external shuttering the concrete slab is
cast around the ring.
Pre-rolled Angle is fixed to the concrete to support the
inner tank. Pre-rolled and weld prepared plates are
end set and welded into position on the channel ring and angle to
form the outer tank and inner tank respectively.
Pre-rolled angle stiffening rings are
located around the top of the tanks. Onto this structure all ancillary
equipment such as clarifier overflow weirs, bridges and walkways are then located.
The floor of the clarifier is cast in concrete at the desired slope to the
centre within the inner tank walls and the central steel sludge hopper. The
sludge return pipe is laid within this mass concrete from the hopper to the
aeration compartment.
Air Distribution and Diffusion System
Air for the diffused air system and air lift pumps is supplied from a
Roots blower. Multiple and standby units can be supplied. The filtered and
silenced air is fed into a transfer header for distribution to the main air
header which runs at high level around the outside of the inner clarifier wall.
From this main air header dropper pipes are provided, with isolating valves
and disconnection unions. At the bottom of each drop pipe, a steel lateral header
feeds to a cluster of fine bubble diffusers. This system, whilst providing efficient
fine bubble diffused air has the ability to allow individual dropper pipes to be
removed for service without affecting the operation of the plant.
Clarifier
The clarifier is sized to accommodate peak flow at a conservative
overflow rate as indicated in the technical data sheets.
The unit has a centre driven rotating sludge scraper which directs the sludge into the
central hopper for transfer back to the aeration/anoxic/anaerobic compartment
(depending on the treatment process) using an air-lift pump.
An overflow launder with adjustable "V" notch weirs collects the final effluent
for transfer to the chlorine contact tank. Peripheral scum baffles and an automatic
scum discharge system is also provided.
A walkway from the plant edge extending over both walls of the clarifier
is provided both as a bridge for the clarifier drive mechanism and to provide general access.
The rotating sludge scraper assembly is suspended from drive on the clarifier bridge.
An annular walkway on the outside of the clarifier is also supplied giving access to the diffusers
and general plant access.
Air Blowers
A positive displacement Roots type blower provides the air supply for the treatment plant.
The blower has cast iron rotors of a specially developed form to give the highest efficiencies.
The rotors are mounted on high tensile steel shafts keyed and locked in position and the shafts and
tips of the rotors are ground to fine limits. Each rotor assembly is supported by ball bearings
located in housings in the end plates. A pair of timing gears mounted on the shafts links the rotors.
The design of the blower is such that there is no internal contact between the rotors themselves or
between them and the rotor chamber.
The end covers enclose the bearings and gears and form reservoirs for the lubricating oil.
The lubrication required for the rotor shaft bearings and timing gears is supplied by splash
feed from the self-contained sump. The sump is fitted with a level indicator and fill and drain plugs.
The oil sumps are completely divorced from the working air chamber to prevent
contamination of the air by lubricating oil, or conversely, the condensation of
water from the air in the lubricating oil system.
Motors and Drives
Each blower is mounted on a base plate and driven through a
Vee-belt drive by a horizontal spindle, squirrel cage, totally enclosed fan
cooled metric frame motor rated at least 10% in excess of the maximum power absorbed.
The motors are mounted on slide rails to facilitate driving belt adjustment.
Adequate safety guarding is supplied.
Control Panel
A weatherproof control panel is provided to be fixed to a supporting
framework. The panel is suitable for direct-on-line starting and is equipped
with:
| Door Interlocking Isolator : | Merlin Gerin Load Break Switch (IEC60947.2) |
| Circuit Breakers : | Merlin Gerin Multi 9 System (IEC60947.2) |
| Contactors : | Telemecanique D Range 3 Pole contactors |
| Overloads : | Telemecanique 3 Pole thermal Overloads |
| Control Relays : | Finder Plug in Relays |
| Pilot Lights : | Telemecanique 22 mm Pilot Lights with integral protected LED |
| Push Buttons : | Telemecanique 22 mm Metal Bezel |
| Enclosure : | Perano Mild steel wall mounted enclosures |
| Isolators’ at motors : | ABB Plastic enclosed load break switches (IP65) |
| Cable : | 4 core CU PVC SWA 600/1000V Cables |
| Cable tray : | HDG Hot dip galvanized |
Electrical Wiring
Unless otherwise specified only local wiring between the panel
and motors is provided. The wiring between the power supply and the control panel
shall be provided and installed by the purchaser.
Corrosion Protection
This is provided to the Client's specification or our standard as
detailed below.
Structural Steelwork
1.) Structural members and plates will be treated inside and outside by shot blasting to remove scale and weld debris as well as rust.
2.) 1 x Coat of Epoxy Tar to a minimum DFT of 125 microns for the outside of the tank.
3.) 2 x Coats Epoxy Tar to a minimum DFT of 250 microns for the inside of the tank.
Handrails & Walkways
All handrails and access walkways will be galvanised to SABS 763.
Drop Pipes
All drop pipes will be galvanised to SABS 763.
'V' Notch Weirs will be galvanised to SABS 763.
Bolts and Nuts
All bolts and nuts supplied will be a minimum of hot-dip
galvanised.
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