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Session 22A: Facility Operations and Maintenance: Process Optimization
1:15pm - 2:45pm
Session Chair: Doug Berschauer, Parametrix;
1:15pm - 2:00pm
Simulating Advanced Controls using Integrated Modeling
Tom Johnson, William Leaf
Jacobs, United States of America;
Advanced control schemes such as Ammonia-based aeration control (ABAC) or Ammonia-Over-Nitrate (AVN) has become increasingly recommended options for plants who want to save energy and optimize nutrient removal. Testing and optimization of the control logic is critical in insuring the process is implemented successfully. Integrated modeling using hydraulics and process simulators provides an opportunity to pre-test the control logic, tune, and optimize prior to implementation. Communication between the two simulators starts with water quality and process parameters from the wastewater process model being passed to the dynamic simulation model to provide the necessary feedback information (DO, NH3-N, etc) for the advanced control strategies. The dynamic simulation model, with its ability to simulate hydraulics, instrumentation, controls, and equipment behaviors, predicts the resulting air flow rate which is passed back to the wastewater simulator. This enabled detailed control loops to be analyzed, control strategies to vetted, and optimized tuning parameters to be identified prior to implementation. This not only verifies the control strategy, but also aims to accelerate project startup by minimizing the post-tuning for functional acceptance testing.
This presentation will focus the discussion on how an integrated modelling approach using the wastewater process and dynamic simulation models was utilized to develop and verify operational strategies for the San Diego North City Water Reclamation Facility upgrade. Modelling approach will describe each of the two model programs, the construction of the associated models, and how the linkage was developed and integrated. Lastly, this presentation will discuss the results from the modeling efforts and lessons learned in respect to both the project itself as well as implications for the industry as whole with the desire to practically automate, decrease energy consumption, and accelerate project implementation from study to startup.
This integrated modelling work highlights how the gap between process design and control sysetm optimization can be mitigated prior to startup and commissioning.
2:00pm - 2:45pm
Balancing Chloramination for DBP Control With Tight Effluent Ammonia Permit Limits
Rachel Golda, Adrienne Menniti, Peter Schauer, Bob Baumgartner, Rajeev Kapur
Clean Water Services, United States of America;
Disinfection byproducts (DBPs) are formed from the reaction of chlorine with organic compounds. Effluent characterization performed by Clean Water Services (CWS) as part of NPDES permit-required monitoring identified the presence of two DBPs - bromodichloromethane (BDCM) and chlorodibromomethane (CDBM) - in effluent from the Durham and Rock Creek Advanced Wastewater Treatment Facilities (AWTFs) during full nitrification. CWS is taking proactive action to address this issue, identifying chloramination as a strategy to mitigate DBP formation. Chloramines are formed by the reaction of ammonia with free chlorine therefore, low concentrations of ammonia are needed in the secondary effluent. However, CWS also operates under stringent ammonia limits during the summer months. This poses a challenge for chloramination, as DBP formation control, effluent ammonia, and disinfection efficiency all must be balanced in order to meet current ammonia limits and potential future DBP limits.
CWS evaluated the chloramination approach at the Durham AWTF in summer 2018. The goal was to determine if chloramination could achieve the operational target of 0.5 mg/L for BDCM and CDBM while maintaining the effluent ammonia below 1.5 mg/L N. Full scale testing showed that chloramination successfully reduced CDBM to below the operating target. BDCM was reduced by an order of magnitude, but the operating target of 0.5 mg/L was not achieved.
Further testing in summer 2019 will be focused on optimizing chlorine dosage and mixing in an effort to further reduce DBP formation potential and achieve the operational target. The fate of DBPs and ammonia through sand filtration, reaeration and bisulfite dechlorination will also be investigated. Ammonia-based aeration control is currently being optimized to bleed the needed ammonia from secondary treatment rather than removing it fully through nitrification and adding external ammonia for chloramination. This presentation will summarize the results of the summer 2019 testing.