Making Classifying Selectors Work for Foam Elimination in the Activated‐Sludge Process

Abstract

Classifying selectors are used to control the population of foam-causing organisms in activated-sludge plants to prevent the development of nuisance foams. The term, classifying selector, refers to the physical mechanism by which these organisms are selected against; foam-causing organisms are enriched into the solids in the foam and their rapid removal controls their population at low levels in the mixed liquor. Foam-causing organisms are wasted "fi rst" rather than accumulating on the surface of tanks and thereby being wasted "last", which is typical of the process. This concept originated in South Africa, where pilot studies showed that placement of a fl otation tank for foam removal prior to secondary clarifi ers would eliminate foam-causing organisms. It was later simplifi ed in the United States by using the aeration in aeration tanks or aerated channels coupled with simple baffl ing and adjustable weirs to make continuous separation of nuisance organismsfromthemixedliquor. Water Environ. Res., 75, 83(2003).

Introduction of New Process Technology into the Wastewater Treatment Sector

“…Confirming work showed that an anaerobic selector seemed quite effective for nocardioform control, when combined with SRT control and with sufficiently low SRT (Jolis et al, 2005). Due to the high level of foam trapping in the compartmentalized HPOAS system, a classifying selector was only partly successful at Sacramento in its first HPOAS application (Parker et al, 2003b), but proved to be quite reliable when combined with other measures in a later San Francisco trial (Jolis et al, 2006).…”

“…This work put into better perspective what DO levels were appropriate for each process to prevent high F/M and low DO bulking. What followed were two decades of work on progressive improvements to bulking control in conventional activated sludge systems with improved reliability through the use of selectors (see Jenkins et al, 2004and Parker et al, 2003a, 2003b. This indirectly muted the argument that the HPOAS process produced mixed liquor with significantly better compaction and settleability.…”

“…The resolution of identified settleability problems by selector enhancements also came too late to reverse perceptions of the HPOAS process. Both anaerobic and classifying selectors (Pettit et al, 1997 andParker et al, 2003b) were tested and found effective, but this happened quite late in the development of the HPOAS process. Confirming work showed that an anaerobic selector seemed quite effective for nocardioform control, when combined with SRT control and with sufficiently low SRT (Jolis et al, 2005).…”

A Biological Selector for Preventing Nuisance Foam Formation in Nutrient Removal Plants

“…For example, only foam removal is discussed, rather than providing for a selector for foam elimination. In fact the single reference to our work in MOP 8 (page 14-213), states " Parker et al (2003) introduced the concept of adding mechanical skimming devices, such as a spiral or chain-and-flight blades to move floatables up a beach and into a hopper located at the end of the aerated channel." This fails to accurately and completely describe our work as the selection mechanism is not described nor are its mechanical features (we have never used any of the MOP 8 described equipment in our Classifying Selector designs).…”

Anoxic or Anaerobic Selectors: Which Is Better?

“…When designing inter-zone baffles it is important to provide a head loss which allows surface foam to pass freely. Since selectors have not generally provided consistent elimination of foam causing organisms, we have developed and provided classifying selectors at strategic locations within the reactor to eliminate or control foam-causing organisms, and thus avoid deterioration of effluent quality (Parker et al, 2003).…”