www.wwtonline.co.uk | WWT | JANUARY 2016 | 31
B
etween the 1960s and the 1990s,
wastewater treatment facilities
were encouraged to enclose
their digester tanks in a bid to control
the release of landfill gases into the
atmosphere. In the absence of gaseous
oxygen, conditions inside the tank
become anaerobic - a completely
natural process dramatically
intensified by the newly covered
conditions.
Whilst bio-fuel is a naturally
occurring by-product of the digestion
process, corrosion within the head-
space of the tank is a common
occurrence, affecting both the walls of
the structure and the tank lid.
In recent years, however, a far
more alarming corrosion hazard
has emerged, which if le untreated
will dramatically shorten the
life expectancy of digester tanks
throughout the UK. This hazard is
sulphuric acid corrosion – and it can
cause tank leakage, devastating asset
failure or even contamination.
What is actually happening?
When lids were originally placed on
digester tanks, the levels of hydrogen
sulphide (H²S) trebled from 500ppm
to 1500ppm, which at the time wasn't
considered a hazard.
Hydrogen sulphide is the
by-product of sulphur-reducing
bacteria found during the anaerobic
decomposition of organic waste in a
Marcus Lockett
MANAGING DIRECTOR
SPI PERfORMANCE COATINGS
acid damage
Decades a er enclosed
digester tanks became the
norm for UK wastewater
treatment facilities, a
previously undetected
hazard is beginning to
emerge – sulphuric acid
corrosion
In the know
Getting to grips with: tank corrosion
The effects of H
2
SO
4
on a digester tank
