Mechanism of Effective Nocardioform Foam Control Measures for Non‐Selector Activated Sludge Systems

Abstract

Solids retention time (SRT), biological scum trapping and recycle, and the dynamic equilibrium between Nocardioform populations in the foam and the mixed liquor are the controlling factors in activated sludge foaming events caused by Nocardioform bacteria. For the operating modes described in this paper, a cured mixed liquor foaming condition (filament counts of approximately 10 5 intersections/g volatile suspended solids) was only achieved when SRT control, selective wasting, and polymer addition were in effect. Solids retention time control, with the SRT remaining below 1.5 days, and selective wasting will cure a severely foaming mixed liquor, but effects will only be observed after 3 or 4 months after implementation. The combined wastage of Nocardioform bacteria from selective wasting and SRT control can ensure long-term foam control to the operation of a pureoxygen activated sludge system with foam-trapping features. An SRT of 0.3 days will result in the complete washout of Nocardioform bacteria from the activated sludge system, which can then operate at an SRT of 3 days free of Nocardioform. Polymer addition to mixed liquor is only effective for foam control when a large portion of the system biomass exists as a heavy layer of foam above the mixed liquor. Water Environ. Res., 78, 920 (2006).

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

“…Combine Several Means of Control. Equivalent experience with another severe foam trapping process, the HPOAS process, indicates simultaneous application of several control measures at once could be successful, such as previously cited in this paper (Jolis, 2006). Also, the use of an anaerobic selector has been noted to reduce nocardioforms counts in the HPOAS process (Petit et al1997, Jolis et al 2005.…”

“…Anecdotally, it is reported that nuisance were avoided in the secondary clarifiers, but pumping nocardioforms to the digesters caused foaming there which required careful management of the problem (Parker et al, 2001 and. Selective Foam Wasting proved to be quite reliable in foam control when combined with SRT control and polymer addition measures in a later San Francisco HPOAS trial (Jolis et al, 2006).…”

Thermal Hydrolysis of Secondary Scum for Control of Biological Foam

“…Total control of biological foam in activated sludge systems is a rare event. A recent report ( Jolis et al, 2006 ) describes how it can be achieved through the combination of selective wasting and SRT control in the range 2 to 3 days. However, because biological nutrient removal plants typically operate at SRTs greater than 5 days, they cannot use SRT control.…”

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).…”