By Martin Hildebrand and Merle Kroeker,
Nelson Environmental Inc.
Direct injection of UV produced oxygen radicals into a
lift station wet well.
Hydrogen sulphide (H2S) based odours emanating
from wastewater treatment plants and lift stations
are not only a source of concern for operator safety,
but are an extreme nuisance for homeowners or
users of near-by public facilities or property. The negative
publicity and hassle caused by persistent nuisance odour
complaints are costly in both time and money for cities or
industries that own the odour-producing infrastructure.
H2S, as well as numerous other odour-causing compounds,
is generated as a result of organic material decomposition in
an anaerobic environment such as sewer force mains, lift stations,
digesters, or wastewater treatment plant headworks.
The distinctive odour (rotten egg smell) of H2S gas is
easily perceptible at very low levels (< 1 ppm in air).
Exposure to moderate H2S levels (10-50 ppm) can cause
headaches, dizziness, nausea and vomiting, coughing and
breathing difficulty. Exposure to H2S levels above 50 ppm
can result in severe respiratory tract and eye irritation and,
in extreme cases, even death.
In addition to safety and nuisance odour concerns, the
H2S can lead to the formation of sulphuric acid, which is
very corrosive to all exposed steel and can lead to reduced
life of concrete piping and structures.
UV odour control process
Various technologies and processes such as ozone generators,
chemical oxidizers (hydrogen peroxide, chlorine, etc.)
activated charcoal filters, essential oils (masking agents), and
biofilters have been used in an attempt to reduce H2S levels. Problems associated with these processes
typically revolve around high capital
or operation costs and, in some cases,
limited effectiveness.
Nelson Environmental Inc.’s Sol-Air
UV-based odour control system is a
compact footprint process that utilizes
patented multi–frequency Ultraviolet
(UV) light. The technology harnesses
the UV light in the UV-C and UV-V
frequencies. Wavelength frequency is
particularly “tuned” to produce highly
radical hydroxyls, which rapidly oxidize
a wide range of airborne odour
producing compounds such as ammonia,
H2S and mercaptans.
Ambient air is directed through the
system’s UV chamber. The ultraviolet
light acts as a catalyst, breaking down
the ambient oxygen and water vapour
molecules into O– and OH– (hydroxyl)
radicals. These short-lived free radicals
go on to oxidize the more complex
molecules found in the contaminant,
while the radicals themselves are
used up in the process. The end result
is a sequential and instantaneous gas
breakdown with very little by-product,
in the form of odour and elemental
traces, but mostly simple, harmless
CO2, water vapour, molecular oxygen,
trace ozone, elemental forms of N, S,
CL, and weak mineral acids.
Because of the way that UV reacts
with the water in the ambient air (to
form oxygen radicals), it is not necessary
to pass the contaminated air
through the unit. The hydroxyls
formed by passing ambient air through
the system are dispersed throughout
the contaminated air, either by injecting
them into a lift station, or by placing
the unit inside an odour filled room
in a wastewater treatment plant. In some
cases, such as a gas collection system,
the contaminated air may be passed
through the UV unit, but since the
process relies only on moisture in the
air passing through the UV lamps, the
method of treatment remains the same.
In this way, a relatively small unit can
treat the air in a large space, since a full
air exchange is not required.
The UV process is easily adaptable
for use in existing treatment plants or
lift stations. It is also ideal in the treatment
of odours originating in urban
collection systems.
For typical lift station applications,
the footprint of the process requires
less than one square metre of floor
space. The unit can either be installed
inside a building or, in most cases, the
system can simply be set outside with
treated air injection piping running to
the lift station or manhole. A standard
30-amp 110V electrical service is adequate
to operate all but the largest custom
built units. The system does not
require any on-going chemical costs or
disposal of contaminated odour
adsorption media.
Wastewater treatment plant
odour control case study
A 13,000 m3/day wastewater treatment
plant in Vernon, British
Columbia, experienced citizen complaints
regarding offensive odours. The
headworks area and the trickling filter
were identified as the sources of H2S.
In 2001, eight Sol-Air UV units were
installed in the City of Vernon
Reclamation Plant. Four modified offthe-
shelf units were installed in the grit
room and headworks, which re-circulate
the air in each room. Four larger custom
units were installed around the perimeter
of the trickling filter, exhausting
processed air to the atmosphere.
The UV process proved to be extremely
effective in reducing odour
levels at these locations, at a fraction
of the cost of other odour control technologies
considered. Offensive odours
were eliminated from the grit room/
compressor and the trickling filter.
Lift station odour control
case study
An existing lift station in
Kamloops, British Columbia, is located
several metres from a new condominium
development. Sulphurous
odours were escaping from the lift station
into the development, prompting
complaints by neighbours. The odours
were so severe, that the condominium
developer temporarily relocated condo
owners to local hotels.
The City purchased an eight-lamp
UV odour control unit for the lift station.
It was installed in an existing
building, and brought the odour under
control very quickly. Reduced odours
were reported within minutes of turning
on the system. Residents are back
in their condominiums and odour complaints
have ceased.
