MINISTER FOR TRANSPORT AND TECHNICAL SERVICES
BELLOZANNE WASTE TREATMENT WORKS: PETITION
LODGED BY DEPUTY J.B. FOX on 28TH MARCH 2006 (P34/2006)
COMMENTS
Introduction
The Bellozanne Sewage Treatment Works was constructed in the mid-1950’s to have the potential for treating the entire Island’s sewage and waste water.
Over the last 50 years, the foul sewer network has gradually been extended to the point where approximately 87% of the Island is served with a foul drainage system. With the exception of one small “package treatment plant” at Bonne Nuit, all sewage is conveyed to Bellozanne via a network of gravity drains and pump systems.
The Sewage Works had very little upgrading from its original construction until the late 1980’s when a programme of refurbishment, replacement and upgrading commenced. As each element of the upgrade has been considered, the major obstacle that has been faced is that of space as the Works is contained within Bellozanne Valley. It has been extremely difficult to extend the Works with the exception of the “Digester Platform”, that was constructed on new land created by blasting rock from the hillside. Consequently, the upgrade programme has been difficult and work has had to be phased over many years. During this time it has also been necessary to provide additional treatment capacity within the existing footprint of the Works to cope with population increase on the Island.
Odour resulting from the biological treatment process has been a problem for many years and the residents living within the Bellozanne Valley area have complained on a regular basis. The accumulation of the odour appears to be a factor early in the morning following certain weather conditions the previous night and usually clear by mid-morning. For staff working on the Sewage Treatment Works in close proximity to the treatment process, odour is a regular problem that has to be encountered.
Management and abatement of odour is a difficult and complex problem to deal with on a sewage works for a number of factors. Odour occurs as a result of the biological degradation of the sewage. As the sewage processing plant consists of a number of large open tanks and channels, the odour is generally liberated from the surface of the tanks. Unfortunately a by-product of sewage treatment is methane gas that if allowed to accumulate under covered tanks and not correctly managed can become explosive and create a serious health and safety risk. Part of the Sewage Treatment Works consists of specialist digester tanks built specifically for the breakdown of sewage sludge and generation of methane, this entire facility being classified as a hazardous zone.
The only practicable way to prevent odour being liberated from the Works is to effectively cover all of the tanks or enclose the tanks within a large building. As soon as this is done, all equipment within that structure has to undergo a full risk assessment to determine whether there is the likelihood of any gas generation and if so, what steps have to be taken to manage the associated risk.
Treatment Process
The sewage treatment process commences at First Tower where there is a large underground sewage pumping station that receives sewage from the east of the Island, town centre and west of the Island from where it is pumped under pressure to Bellozanne Valley Treatment Works. The incoming sewage then undergoes a series of screening and settlement in open tanks, the majority of which have the ability to liberate odour. The table below shows the treatment process and the areas of potential odour.
Process | Odour – Yes / No |
First Tower Pumping Station | Yes |
Inlet Works / Screens | Yes |
Grit / Grease Removal | Yes |
Grit Settlement Tank | Yes |
Channels | Yes |
Primary Settlement Tanks | Yes |
Digesters | Yes |
Sludge Treatment/Holding Tanks | Yes |
Secondary Treatment | No |
Final Settlement | No |
Ultra Violet Treatment | No |
From the above table it is apparent that there are eight definite areas that will need a thorough assessment. The remaining areas are not thought to be significant.
The first phase of establishing the scale of a problem will be to undertake an odour survey which will require specialist contractors to be brought in from the UK. Following assessment, a preliminary engineering appraisal will then have to be carried out to establish the scale of the enclosure required and whether it will merely consist of covers on top of a tank or whether a full building structure has to be constructed to enclose the entire facility.
The final and complex stage will be to undertake a full engineering and hazard assessment of each area to determine whether or not it has to be classified as a hazardous zone. It is only at this time that it will be possible to accurately determine the true financial cost of providing enclosures to the Works. Following this level of detail, the final stage will be then to design a large odour control unit with associated ducting to extract all foul air from within the enclosures through the odour control unit and then exhaust to atmosphere.
Timescale and Cost
The odour survey will be undertaken in 2006 together with the preliminary assessment of how any odours can be treated. It is estimated that the cost of this work will be in the order of £30,000, the cost of this work being met by the Transport and Technical Services Department as part of its ongoing maintenance programme.
With an outline for the size and scale of this project, it is proposed that a capital request is drawn up for inclusion in the 2012 capital programme. Subject to this scheme gaining early approval, funds for a full feasibility study will be requested from the Capital Planning Vote, subject to funds being available from within that Vote. Subject to funds being made available in 2012, the timeframe for completion of such works is currently estimated to be approximately 18 months to 2 years.
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