Skip to main content


Buy Article:

$17.50 plus tax (Refund Policy)

Or sign up for a free trial


The Laguna Subregional Water Reclamation Facility (LSWRF) is a 20-mgd nitrification activated sludge facility owned and operated by the City of Santa Rosa, California. The activated sludge facility includes five circular, 115-feet (ft) diameter secondary clarifiers. The plant has historically experienced problems with solids washout in the secondary clarifiers during peak wet-weather events. A previous study of the problem had prescribed an increase in return activated sludge (RAS) pumping capacity as the solution to the problem. Accordingly, the City had embarked on a RAS Capacity Upgrade project to increase the RAS pumping capacity from 23 mgd to 55 mgd, at an estimated construction cost of approximately 3.3 million. A diagnostic evaluation of the problem using the State Point Analysis (SPA) technique revealed that the clarifier operational problems were caused not by RAS pumping capacity limitations, but by a Criterion II solids flux overload. The evaluation further showed that increasing RAS capacity would not address the problem with solids washout in the clarifiers. Instead, an operational strategy for wet-weather MLSS control was prescribed and used to successfully solve the problem. By allowing for an accurate diagnosis, the application of the SPA technique helped solved a troublesome operational problem, at the same time saving the City an estimated 3.3 million in construction cost.

Document Type: Research Article


Publication date: January 1, 2001

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 These proceedings are not peer reviewed.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
  • ingentaconnect 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
Subscribed Content
Subscribed content
Free Trial Content
Free trial content
Cookie Policy
Cookie Policy
ingentaconnect 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