Proceedings

The Use of Ionised Air as a Supplementary Treatment Stage to Bring About Improved Odour and General Working Conditions at Swansea Bay Wastewater Treatment Works

O’Malley, D., and Bowen, A., Imtech Process Ltd

(free)

Swansea Bay Waste Water Treatment Works (WwTW) was built in 1997 within the docks
area to the east of Swansea, South Wales. It serves a population equivalent (PE) of
approximately 165,000 and was designed to treat a maximum flow to treatment of 1300 l/s. In
order to comply with the Local Authority planning conditions, the works was designed and
built with specific up-to-date techniques’ to ensure that it met a “no nuisance” criteria set by
the Swansea Borough Council.

The mitigation measures employed at the time of design included the provision of bespoke
enclosures over certain treatment processes, which were identified as being a potential
source of odour emission within the enclosed works. The odours generated from these
contained areas were extracted, combined and finally directed for treatment to a three stage
chemical scrubber arranged into two streams running in parallel.

Over the years of operation, enclosures over certain processes were removed and never
replaced by the operator. This need to remove the covers was due primarily to the operators
being unable to successfully carry out regular and essential maintenance of critical treatment
processes. As a result, the atmosphere within the working area of the enclosed works has
gradually deteriorated due to the presence of increased concentrations of organic and
inorganic chemicals released to the air during the treatment of the incoming sewage flows. In
addition, the release of high levels of biological contaminants from the sewage flows into the
working atmosphere necessitated the introduction of a controlled working environment based
on a traffic light system.

As part of the Dŵr Cymru AMP4 Odour Delivery program, the works at Swansea Bay was
identified as a named odour output due to the increased level of complaints being received by
the company from residents in the area local to the works. Subsequent discussions with the
local authority Environmental Health Practitioners, followed by odour monitoring, and
olfactometric sampling of the site during its normal operation identified that the main
contributing processes to the odorous releases were predominately those which were
previously designed with covers, but had these covers removed due to operational difficulties.
Although the works is fully enclosed and had forced building ventilation and extraction, the
resultant poor quality working atmosphere within the building forced the operators to regularly
open the large access doors to naturally ventilate the working areas. This resulted in the
untreated odours escaping from the buildings to the outside of the works, which resulted in
complaints from receptors beyond the site boundary.

This paper discusses the phased approach that was undertaken to resolve both the issues of
foul odour being produced and the heightened biological exposure of the operating workforce
as a result of the normal operation of the treatment plant at Swansea Bay. It explores the
findings of the trials that were undertaken with the supplier to determine the level of
effectiveness of using an ionised air process to reduce the odour and biological contaminants
in the air within the building.

KEY WORDS
Odour; Hydrogen sulphide; Ionised air; Ionisation; Micro-organism; Ventilation; Extraction

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