Effluent Decontamination Systems (EDS) - The Process
1) Filling
The vessel is in Receiving Mode. Waste effluent is either pumped or gravity
flows into the receiving tank via the inlet waste line, shown in orange
above. Of the two remaining tanks in the system, at least one will be available
for service. As the tank fills with effluent, the dirty air is vented out
via a double bank of HEPA filters. While filling, any large solids shall
be retained in the inlet collection basket, as illustrated above, if applicable.
When the effluent reaches the high level sensor a sterilization cycle is
automatically initiated.
2) Commencement of Sterilization Cycle
The inlet ‘Trash Valve’ will close diverting any further waste effluent
to one of the remaining two tanks in the system (commencement of a sterilization
cycle in one tank automatically sets the next tank in sequence to Receiving
Mode). When the inlet trash valve is fully closed, the valve on the power
flush water line will open for approximately 20 seconds. This allows a powerful
flow of water to pass through the inlet ball valve, removing any solid particles
that may be present. These particles could potentially damage the valve
seals, which are essential in maintaining pressure. After the power flush
of water the now clean inlet valve will close and the vessel will move into
Heating Mode.
3) Heating
To ensure a uniform temperature rise across the system, the recirculation
pump will start, providing agitation to the vessel contents. This not only
ensures that no ‘cold spots’ are present, but also prevents solids build
up on the bottom surface of the vessel. Furthermore, as the liquid from
the recirculation loop re-enters the vessels it passes through a static
jet pump, which applies a venturi effect to further amplify agitation. The
steam valve will open allowing flow of steam through the vessel jacket or
heating coils, which will heat the vessel contents. The vessel will continue
to heat and recirculate until a temperature of 270˚F (132°C) is reached,
at which point the system will proceed into Sterilizing Mode.
4) Sterilizing
During this phase the vessel contents will be held at (or slightly above)
270˚F (132°C) for a period of one hour. These parameters are specifically
selected by WR2 to guarantee complete sterilization
of the entire vessel contents in all circumstances. The temperature and
pressure are measured by redundant sensors both inside the vessel and in
the recirculation loop. Throughout the sterilization phase, the recirculation
pump continues to provide agitation to the system for uniform mixing.
5) Cooling
After sterilization conditions have been achieved, then (and only then)
the system will automatically proceed into Cooling Mode. WR2
EDS typically cool in one of two ways depending on each individual facility
and its corresponding waste effluent stream. Where there is not a relatively
large amount of particulate solids, the effluent can be passed through a
shell and tube heat exchanger. In other circumstances the sterile effluent
is cooled by passing cold water through the vessel jacket or heating coils.
When the internal vessel pressure has dropped to zero and the vessel contents
have reached an acceptable temperature to go to the local sewer, the tank
system will go into Draining Mode.
6) Draining
When the sterile effluent has cooled to the desired temperature, it is then
pumped to the drain. When the pump loses suction (ie. the vessel is empty)
it automatically shuts down and the vessel will go into Stand by Mode. It
will remain in Stand by Mode until the other processing vessels in the system
have completed a cycle, at which point the Trash and Inlet ball valves will
again open and the tank will proceed back into Receiving Mode. If routine
or emergency maintenance is required on the vessel or the solids collection
basket is required to be emptied, then while in Stand by Mode the vessel
can be manually entered into Service Mode. It is now safe to carry out maintenance
procedures and open the man-way if necessary.