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States of Jersey
Liquid Waste Strategy
Technical Note on Deep Shaft ASP Reactors
April 2010
Prepared for:
States of Jersey
Transport and Technical Services
PO Box 412 States Offices South Hill
St Helier Jersey
JE4 8UY
Prepared by:
Grontmij
Grove House Mansion Gate Drive Leeds
LS7 4DN
T +44 (0)113 262 0000
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Report Status: Draft
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Name Signature Date Prepared By: Oliver Grievson
Checked By: | Harold Buckland |
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Approved By: | Chris Wotherspoon |
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© Grontmij 2010 This document is a Grontmij confidential document; it may not be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, photocopying, recording or otherwise disclosed in whole or in part to any third party without our express prior written consent. It should be used by you and the permitted discloses for the purpose for which it has been submitted and for no other.
States of Jersey
Liquid Waste Strategy
Technical Note on Deep Shaft ASP Reactors Technical Note on Deep Shaft ASP Reactors
- INTRODUCTION ............................................................................................... 1
- DEEP SHAFT ASP TREATMENT..................................................................... 1
- CONCLUSIONS ................................................................................................ 3 APPENDIX 1 – DEEPSHAFT MARKETING BROCHURE.............................................. 4
1 INTRODUCTION
This technical briefing note examines the feasibility of using DeepShaft technology to replace the current secondary treatment process at Bellozanne Sewage Treatment Works. It focuses primarily on process issues and should be read in conjunction with our previous report entitled "Jersey Treatment Process Review Report" of September 2009.
2 DEEP SHAFT ASP TREATMENT
The DeepShaft activated sludge system was invented by ICI as a spin-off from the manufacture of Pruteen, which is a microbial protein grown on methanol. The patent for the process is currently held by Aker Kvaerner. A brochure for the system is included in Appendix 1.
The DeepShaft is essentially a high rate activated sludge system which is able to run at higher mixed liquor concentrations and at loading rates 5 to 10 times greater than conventional systems. The aeration requirement is also reduced by the nature of the process because it has a greater efficiency of oxygen transfer into solution.
The DeepShaft system works by drilling a shaft typically 40 to 100m deep, using techniques from the oil industry. Raw sewage enters a holding tank where it is mixed with return activated sludge. This mixture of raw sewage and return activated sludge is passed down the centre of the shaft and re-circulates back up the outside with the aid of compressed air. This typically takes between 2 to 6 minutes and the sewage is circulated around 20 to 40 times prior to discharge. After treatment the effluent is clarified by flotation or sedimentation. Figure 2.1 shows a typical DeepShaft system.
Figure 2.1 - DeepShaft Activated Sludge System.
The technology is not in widespread use with only 80 works in operation world-wide and only three in the UK namely, Tilbury, Southport and Billingham. Of these, Billingham treats solely industrial flows and Tilbury has a high proportion of industrial flow. Southport was constructed due to land constraints.
There are a number of advantages of the DeepShaft system and the principal generic ones can be summarised as follows: -
• No primary settlement stage is required
• High energy efficiency with removal rates of 1 to 4kg/BOD Kwhr
• Higher efficiency of oxygen transfer requiring less aeration for the same function
• Process is unaffected by temperature changes
• Smaller footprint compared to conventional activated sludge
• Resistant to hydraulic or loading variations
• Less potential for filamentous growth
• Typically reduced seeding period
• Initial start-up of the activated sludge process is reduced to 3 to 4 days in comparison to approximately 18 to 20 days for conventional processes.
As would be anticipated, there would be a number of disadvantages with respect to its use at Bellozanne and these are highlighted in Table 2.1.
Table 2.1 - Disadvantages of DeepShaft Activated Sludge System Disadvantages Relevance to Bellozanne
High capital cost of drilling and lining the deep The more difficult the ground conditions, shaft, depending on the underlying geological such as Jersey where there is rock, the conditions. greater the capital cost.
Due to the sub-surface nature of the deep There have been issues with the current shaft, it is not possible to observe the mixed secondary process at Bellozanne and liquor and thus more difficult to operate or additional operational risks are to be diagnose problems. avoided.
The efficiencies and cost savings of the system The raw sewage is domestic in nature and are only realised where the influent BOD does not contain any high strength industrial strength is greater than approximately 500mg/l loads
No nitrification or denitrification A separate treatment process would be
required.
The effluent normally requires de-gassing. High Required quantities of carbon dioxide and nitrogen can
be released out of solution with the rapid
reduction in pressure as the mixed liquor rises
to the top of the shaft
Maintenance of the high pressure blowers is Refer to above comment about operational more onerous than a conventional system risks
3 CONCLUSIONS
The DeepShaft process is an alternative to activated sludge systems. To date, its principal uses in the UK have been to treat high strength industrial flows or where space for a conventional works has been insufficient. The strength of the sewage at Bellozanne is not high, which means that the operational cost savings are unlikely to materialise. Whilst the area at Bellozanne is limited, it is possible to accommodate a conventional works. The DeepShaft process would eliminate the need for new primary tanks but additional processes would be required to nitrify and denitrify to achieve the Total Nitrogen consent for the works.
The lack of a significant track record in the UK for this process means that there would be increased operational risks, which would be compounded given the island setting and the past problems with the current process at Bellozanne.
In view of the above, we would not recommend the use of the DeepShaft activated sludge system at Bellozanne.
APPENDIX 1 – DEEPSHAFT MARKETING BROCHURE
