Water & Wastewater Asia September/October 2019

24 | INSIGHT
Efficient sludge thickening
and dewatering: How to find
the right parameters for
choosing the ideal solution
By Christian Dousset, Process Technology Manager, ANDRITZ
Sludge thickening and dewatering are key process steps when treating wastewater. Numerous suppliers
provide dozens of different machines to make this process easier – all claiming that their solution is
the best, but often not taking account of the fact that several given parameters in a plant determine
the success of the equipment chosen and consequently, the efficiency and profitability of operations.
With no one-size-fit-all solution, how do plants find the one to fit their specific requirements?
THE BEST SOLUTION – CONSIDER
IT NOT ALWAYS BEING BEST FOR
YOU
In wastewater treatment, plants will most
likely be challenged to find an efficient,
reliable, and safe wastewater treatment
solution that is also less costly to install,
operate, and maintain, all while meeting
the strictest local requirements. This
challenge has not become easier, as dozens
of suppliers are pushing various machines
for thickening and dewatering, claiming
that their technology is the best. Obviously,
there is no ideal, universal solution because
not every wastewater treatment process and
its preconditions are the same, and every
technology comes with process-related
advantages and disadvantages alike.
Even if only the economic arguments
are considered, every project is specific,
and nothing is set in stone. The variable
elements could be the cost of sludge
transport, the sludge’s final destination,
the structure and quality in which it has
to be transported, special treatment of
sludges in a wastewater treatment plant
requiring dedicated equipment, the plant’s
geographical location, whether or not a
building already exists, specific constraints
such as noise or odour, energy costs,
availability of special reagents like powder
and emulsion polymer, as well as qualitative
discharge constraints like granulation or
storage capabilities.
SIZE DOES MATTER – CONSIDER
YOUR SURROUNDINGS
The required footprint of a machine is an
essential factor in wastewater treatment
plants, both those in planning and also those
that are already up and running. When space
is limited, a decanter centrifuge presents
itself as a potential solution: Not only is the
space required to install these machines
smaller than for all other dewatering and/
or thickening units (which has an impact on
the civil engineering costs), this technology
also features an excellent capacity/size
ratio. Its versatility in the treatment of
various types of sludge, combined with
this advantage, make it a popular solution –
also for mobile dewatering units.
But if conditions like a municipality’s
population and the wastewater it produces
are likely to change in the future, a gravity
belt table seems to be a good thickening
solution thanks to its high hydraulic capacity.
Another thing to consider when checking
whether a machine fits into a plant is the
surroundings. Depending on the location
and the neighbouring buildings, the noise
from the machine as well as the ability to
reduce the often-terrible odour coming
from the treated sludge should not be left
unconsidered when choosing the right
technology. When noise and especially
odour are of concern, it is better to choose
a closed system instead of an open one –
the reasoning behind this is simple: Foul
odours and distractive sounds are contained
if the system is enclosed. A common closed
system for thickening with verified benefits
in clean rooms and odour prevention is the
drum thickener – which is also very compact
in terms of capacity. When searching for
a closed system for dewatering, a screw
Water & Wastewater Asia • September / October 2019