Water & Wastewater Asia January/February 2022

IN THE FIELD
WASTE NOT, WANT NOT
Industrial water and wastewater
applications are ones where filter
presses have proven their worth
from day one. This is an application
where large volumes of solids and
liquids need to be separated on
a daily basis. The filter press is
ideal for this application because
of its method of operation. As the
solid-laden slurry is pumped into
the press, two chambers are filled,
which facilitates the formation
of thick slurry “cakes”. While the
chambers fill, the pressure inside the
system increases to the point that
when the chambers reach capacity,
the liquid is filtered out with the aid
of streams of compressed air or
water. This dewatering leaves behind
solid slurry or sludge cakes that are
ready for disposal.
An advantage in this cake-creation
process for the operators of water
and wastewater plants is that instead
of having to dispose large amounts
of wet slurry, the outcome is a flow of
neutralised water and a comparatively
small amount of cake, which reduces
disposal costs.
To operate properly, filter presses
require good filtration and constant
system pressure so that the flakes
that form the slurry cakes are not
destroyed. This means that pressures
of up to 100psi is generally required.
The filter-press process in water and
wastewater treatment also requires
that various types of ancillary liquids
be used. In many cases, these
liquids – including things like milk
of lime, which is very abrasive, and
a variety of alkaline – cannot be
released into the environment. This
necessitates the need for a reliably
leak-free pumping technology that is
compatible with a wide range of liquid
types.
All-Flo production line
CREATING A LESS-STICKY
SITUATION
Everyone has at least seen a depiction
of the manufacturing process for maple
syrup – a series of buckets connected
by plastic tubes are hung from maple
trees, which are trapped, allowing their
sap to flow into the buckets. When
enough is collected, the sap is boiled
until it reaches the point that can be
called pancake-ready maple syrup.
This is a time- and labour-intensive
process, but one that was performed in
that manner for hundreds of years.
That is until recently. It has only been
in the last two to three decades that
maple syrup production has become
fully mechanised and modernised,
with many producers now utilising a
reverse osmosis production process
that reduces the time and cost to
manufacture maple syrup. Enter the
filter press – or as syrup manufacturers
have begun calling it the “syrup press”.
Instead of repeatedly boiling the sap
to create syrup, today’s process sees
the sap passed through the filter
press in what is called the evaporation
stage. As evaporation occurs, the sap
is separated into the sticky, syrupy
solution widely recognised with a
water-like by-product that is removed.
To get the production process started,
pumps are used to transfer the raw sap
into the filter press at the beginning of
the production process.
SURVIVING THE DEEP FREEZE
There are some industrial production
processes that require the finished
products to be manufactured with the
aid of components that need to be
separated in extremely cold operating
conditions. In fact, in some cases this
requires the use of a liquid like ethanol
that has been cooled to a temperature
that can be as low as -40°C. It is at the
beginning of these types of processes
that pumps are used to push a mixture
of the raw material and the supercooled
ethanol through the filter press.
Because many of these types of
processes are also used in the
production of goods made for human
consumption, they must be produced
under the strict auspices of hygienic
or sanitary manufacturing regulations.
This means that the pumps must not
only be able to manage extremely low
temperatures, but also be compliant
with US Food & Drug Administration
edicts, as well as those of Europe’s
Restriction of Hazardous Substances
(RoHS) directive. Specifically, the RoHS
3 regulation lists the maximum levels –
less than 1,000 parts per million – that
can be present of such substances as
lead, mercury and cadmium in finished
consumable products.
Additionally, since ethanol is classified
as an explosive substance, the pumps
used in the production of goods that
WATER & WASTEWATER ASIA | JANUARY/FEBRUARY 2022 35