An integrated approach to odour treatment

Mangawhai is a rapidly expanding town on the east coast north of Auckland. To cope with increasing population and to improve the condition of the harbor waters the Kaipara District Council let a contract to Water Infrastructure Group ( formerly Earth Tech) to design, build, transfer and operate a sewerage collection and treatment scheme for Mangawhai. Odour generation in the reticulation was recognized as a problem from the outset. This paper describes the approach taken to firstly identify sources of odour and to treat these sources to mitigate any adverse effects.

At the design stage low population densities for most of the year resulting in increased residence times in rising mains and the use of pressure sewer systems to service parts of the town were identified as posing particular problems. As a first stage odour reduction measures adopted at the design stage included close fitting covers on pump wet wells, and chemical dosing with calcium nitrate to prevent septicity developing. On commissioning some problem areas were identified where these measures were insufficient and proprietary vermiculite/hypochlorite filters were fitted to some household vent stacks. Specially developed carbon filters were fitted to two pump stations. This has proved to be a cost effective method of tackling odour problems and the end result is an essentially odour free system.