The State of Colorado is tightening rules on nutrient levels in wastewater, and the City of Boulder will soon need to meet strict limits for phosphorus, in addition to its existing nitrogen limits. We supported the City with the design, construction, and start up of their Phosphorus Upgrades Project at the City’s Water Resource Recovery Facility (WRRF).
The improvements intensified the existing secondary activated sludge process adding enhanced biological phosphorus removal (EBPR) to the existing biological nitrogen removal process. The modified bioreactor configuration added anaerobic volume and a low-dissolved-oxygen (low DO) aerobic volume to achieve simultaneous nitrification/denitrification (SND). Online instrumentation controls the low-DO/SND aerobic volume using an ammonia-based aeration control (ABAC) strategy. These modifications, combined with densified activated sludge (DAS), allowed phosphorus removal to be added to the existing nitrogen removal without additional process tank volume.
Our team completed extensive biological and aeration control process modeling to set the design criteria for the improvements. Our modeling included BioWin, SUMO, and SIMBA# process modeling to confirm the ABAC and simultaneous nitrogen/denitrification removal processes.
The upgraded system also includes extensive air supply modifications such as new dual-core turboblowers with improved turndown, new advanced diaphragm airflow control valves, replaced ceramic diffusers with membrane diffusers, and a new large-bubble mixing system to carefully and efficiently control air delivery to the secondary process across a very wide range of airflow needs.
We worked with the City through construction, supporting their transition to a low DO/DAS process while maintaining daily maximum ammonia and total nitrogen. This $24 million project has been commissioned, and we are supporting the City with ongoing process optimization.
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