NITRIFICATION AND ACTIVATED SLUDGE FOAMING ...

nitrification performance. The WRF performance has become more consistent and with experience, the
plant staff has become keenly aware of how quickly the system can react to changes in WAS to promote
foam and scum increases.
Given this sensitivity which has been seen to be more pronounced in winter operations, additional means
to help reduce ammonia nitrogen pass-through during periods of higher foaming conditions were
investigated. Data from the on-line ammonia analyzer monitoring secondary influent provided information
that ammonia nitrogen concentrations in the influent after flow equalization varied significantly during a 24
hour period. Historically, the WRF has operated on the basis of equalized diurnal flow. This system is
automated through SCADA programming for control of flow equalization basins and pumping systems.
With the ammonia nitrogen concentration variability, a constant flow approach created a wide range of
actual ammonia nitrogen loading to the activated sludge system. Using the SCADA system, online
ammonia analyzer, and existing equalization system capabilities, an ammonia nitrogen load control
system was developed. Figure 7 provides a screen shot of the nitrogen load control “switch” which is now
used to target the ammonia load to the activated sludge system.
Figure 7 – SCADA load control screen shot
The ammonia loading control switch is located near the center of screen. As shown, the targeted
ammonia loading rate is 2,600 lb/day. The switch window also includes the actual current loading value.
Implementation of this control system to enable more equalized ammonia nitrogen loading provided
immediate positive impact to the WRF including:
• Reduced MCRT required to achieve nitrification (no need to maintain higher MCRT for the higher
loading periods)
• Reduced/eliminated nocardial foaming and scum – minimal Effective and Total MLSS differential
• Stable aeration system demands - more consistent loading creates aeration supply consistency
and lower peak power requirements; lower aeration intensity – lower foaming tendencies
• Stable alkalinity demands
• Stable anoxic selector operation