Problems were encountered in the USA prompting the Environmental Agency to commission a number of reports. These reports identified a number of issues and criticized the RBC process. One author suggested that since manufacturers were aware of the problem, the problems would be resolved and suggested that design engineers should specify a long life.
However, this is only possible if the manufacturer is aware of the design problems and the stress to ensure a long life and since failures still occurred it is unlikely any design stresses were widely published assuming they were known.
Severn Trent Water Ltd, a large UK Water Company based in the Midlands, employed these as the preferred process for their small works which amount to over sites Consequently, long life is essential to compliance.
As a result, the issue of short life failure is now fully understood and is in the public domain and the correct process and hydraulic issues have been identified to produce a high quality nitrified effluent. One supplier went into liquidation leaving Severn Trent Water Ltd liable for a number of failed plants. Cranfield were commissioned to design replacement frames where were specified to be defect free for a minimum of 20 years.
The 20 year life was extended to about 30 following work at Copa Ltd. The Cranfield Plant is more robust and, since life is governed primarily by fatigue, last longer than slimmer plant However in capital costs terms it may be more expensive but in whole life costs significantly cheaper since it avoids replacement. This is discussed by Findlay in a paper below presented in Milan. Findlay also developed a system for repairing defective RBCs enabling shaft and frame life to be extended up to 30 years based on the Cranfield designed frame.
Where additional capacity was required intermediate frames are used maximising minimising the need for duplication. Secondary clarifiers following RBCs are identical in design to conventional humus tanks, as used downstream of trickling filters.
Sludge is generally removed daily, or pumped automatically to the primary settlement tank for co-settlement. Regular sludge removal reduces the risk of anaerobic conditions from developing within the sludge, with subsequent sludge flotation due to the release of gases. From Wikipedia, the free encyclopedia. This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed.
May Learn how and when to remove this template message. This article may require cleanup to meet Wikipedia's quality standards. The specific problem is: Requires citations, lacks flow and perhaps better in another section? Please help improve this article if you can. Leslie Grady, Glenn T. Daigger and Henry C. Biological wastewater Treatment 2nd ed. Handbook of Environmental Engineering Calculations 1st ed. Spellman's Standard Handbook for Wastewater Operators. Aqueous Wastes from Petroleum and Petrochemical Plants 1st ed.
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