Skip to main content


The full text article is not available for purchase.

The publisher only permits individual articles to be downloaded by subscribers.

or click here to sign up for a free trial


In Australia and New Zealand, gravity thickening and dissolved air flotation are commonly used to thicken primary sludge and waste activated sludge respectively. For plants with anaerobic digestion, the feed concentration to the digesters is often set by the limiting thickening capability of these upstream thickening processes. In some cases this does not fully utilise the capacity of this high capital value asset. Rather than build additional digester capacity (and possibly additional dewatering hydraulic capacity), consideration should be given to increasing the feed concentration to existing digesters to maintain or even extend the HRT. This paper describes how secondary thickening of primary and waste activated sludge has been successfully implemented at the Mangere Wastewater Treatment Plant (WwTP) in Auckland, NZ, to maximise the capacity of existing anaerobic digesters and improve digestion performance. It identifies the limiting performance of the first stage thickening units and describes how the second stage thickening can provide constant digester HRT control, increasing digester VS destruction to 55%VSR in conventional mesophilic digesters. This secondary thickening approach has also been adopted at two other major wastewater plants in the region.

Document Type: Research Article


Publication date: January 1, 2007

More about this publication?
  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

    WEF Members: Sign in (right panel) with your IngentaConnect user name and password to receive complimentary access.
  • Subscribe to this Title
  • Membership Information
  • About WEF Proceedings
  • WEFTEC Conference Information
  • Ingenta Connect is not responsible for the content or availability of external websites

Access Key

Free Content
Free content
New Content
New content
Open Access Content
Open access content
Partial Open Access Content
Partial Open access content
Subscribed Content
Subscribed content
Free Trial Content
Free trial content
Cookie Policy
Cookie Policy
Ingenta Connect website makes use of cookies so as to keep track of data that you have filled in. I am Happy with this Find out more