Water & Wastewater Asia September/October 2019

INSIGHT | 25
press is the technology recommended. A
decanter centrifuge also achieves minimum
odour emissions and is suitable for both
thickening and dewatering, but it comes with
the disadvantage of being extremely loud in
comparison due to the high operating speed
required for centrifugation.
In adapting their machinery, technology
group ANDRITZ often manages to find
solutions that bypass some disadvantages.
A decanter centrifuge, for example, can be
upgraded with special casings to reduce
vibration and hence the noise it creates,
sometimes even down to less than 85 dB(A),
as a recent example from a desalination
plant in the Middle East shows (the
decanter centrifuge there is used for brine
dewatering). However, special modifications
and research come at an extra cost.
LITTLE THINGS ADD UP –
CONSIDER INVESTMENT AS WELL
AS TOTAL COST OF OWNERSHIP
A basic economic principle is never to forget
about the running costs in relation to the
investment costs and always to calculate
which technology is the most economically
efficient over time. The variable costs in
sludge treatment arise not only from energy
consumption and maintenance costs, but also
from consumables like wash water or polymer
– and you have to choose which of these
resources are the least expensive and most
easily accessible in your area of operation.
When choosing a thickening solution for
example, both a gravity belt table and a
drum thickener come at a moderate price,
but require a large amount of wash water and
polymer. When using a decanter centrifuge
for thickening, the need for both polymer
and wash water decreases significantly
compared to the other two technologies, but
this system requires more power to operate.
For dewatering, the belt press appears to
be an attractive solution cost-wise, with
low investment costs combined with low
energy consumption, but this technology is
not suited for regions where water is scarce
because of the high wash water consumption.
In this case, a screw press would be better
suited as its water and energy consumption
are minimal. On the other hand, this press
requires more polymer and has a high initial
investment cost for the capacity it provides.
A filter press may be intimidating at first due to
the relatively high investment costs, but it has
low polymer consumption and is very wash
water-efficient when used with one of the most
innovative control systems on the market
today – the Metris addIQ control system.
The addIQ control systems are a part
of Metris, the ANDRITZ brand for digital
solutions, and they try to reduce the total
cost of ownership in different ways – be
this with the automatic filter cloth washing
system for optimisation of the washing cycle
and water consumption in filter presses, or
an automated polymer measurement and
dosing system called Metris addIQ RheoScan
that can be used in different machines.
ANDRITZ Belt press; low-profile design for ease of maintenance