Selectors in Pulp and Paper Mill Activated Sludge Operations - Do They Work?, 1999 Environmental Conference Proceedings

Rick Marshall

Marshall Environmental Training and Consulting Group, Inc.

Michael Richard

The Sear Brown Group

A selector is a small mixing basin ahead of the main aeration basin where wastewater (food) and return activated sludge (bacteria) are mixed for a short time. This creates a short-term growth environment that favors floc-forming bacteria and disfavors the growth of filamentous bacteria, resulting in a good flocculating and good settling sludge.

Selectors have been widely used in municipal activated sludge systems with good success. However, selectors have only recently been used in pulp and paper activated sludge systems. This paper reviews the performance and evaluates the success of selectors in use at seven pulp and paper systems.

Three of four aerated selectors and two of three nonaerated selectors examined were successful at filament control. Successful selectors varied significantly in design. Selector hydraulic detention times ranging from 30 minutes to 2 hours were successful. The successful aerated selectors had a selector F/M in the range 0.5 to 4.4. The nonaerated selectors had a selector F/M in the range 10 - 14. Selectors were successful at several types of pulp and paper mills including: a groundwood and sulfite mill, a groundwood SCMP mill, and several deinking mills and TMP mills.