NITRIFICATION AND ACTIVATED SLUDGE FOAMING ...

METHODOLOGY
An integrated, hands-on operations approach was used to evaluate the issues of foaming and nitrification
performance at the WRF. The steps included:
• Defining the situation at the facility with regard to foaming and nitrification issues
• Understanding background information - assimilating process data and information resources
• Assessing the information, and
• Developing recommendations to address the issues
Background data used for the evaluation were historical operations and process data from operator
sampling, and archived and real-time data from SCADA via on-line analyzers. Key on-line monitoring
includes ammonia, pH and dissolved oxygen (DO). As the evaluation program progressed, additional online
analyzers for ammonia (primary effluent and aeration basins) and TSS (aeration basins and
secondary effluent) were installed for process/performance monitoring and data trending. To fully
understand the components of the foam to help establish the root causes, microscopic analyses of MLSS
and foam were conducted.
The initial review of historical data from periods of ammonia pass-through of the aeration basins was
somewhat puzzling as no critical process factors seemed to be askew – DO, MLSS/MCRT, alkalinity, and
temperature all appeared to be in good range for providing complete nitrification based on the flows and
loading conditions to the WRF. Short circuiting through the aeration basins was not a factor. From this
review, sample collection points were examined and additional MLSS sampling points along with
additional auto samplers for TSS (MLSS) were implemented to help with understanding the MLSS
concentration and profiles in the aeration basins and in aeration basin effluent. Grab samples from the
aeration basin were collected and analyzed for ammonia nitrogen to develop a nitrification profile along
the length of the aeration basins. From this work, additional ammonia on-line analyzers were installed to
track ammonia levels in the influent to and through the aeration basins, see Figure 3.
Figure 3 – On-line ammonia analyzer for secondary influent monitoring
RESULTS
The microscopic analyses of the MLSS and associated foam identified Nocardia sp. bacteria as the
agents promoting the foaming conditions. Figure 4 presents an example micrograph of Nocardia sp.
bacteria. Nocardial filaments cause foaming due to their hydrophobic nature. Their growth is promoted by
several conditions generally in combination including elevated mean cell residence time (MCRT), higher
levels of fats/oils/grease/fatty acids in the wastestream, acidic range pH levels, and foam trapping