Starting up a 21st Century Nutrient Removal Process
Authors:
- Charless Bott, Rick Baumler, and Bill Balzer - Hampton Roads Sanitation District
- Katya Bilyk and Alan Stone - Hazen and Sawyer
This paper will discuss the startup of a 30-mgd, 5-stage BNR process with supplemental carbon addition to meet low nutrient standards (TN ≤ 8 mg/L and TP ≤ 1 mg/L) during the coldest part of the year. The plant has a state-of-the-art treatment and monitoring approach that utilizes six online Nitratax®sc analyzers, two each online Phosphax®sc and Amtax®sccolorimetric analyzers for orthophosphate and ammonia, and sidestream nitrogen and phosphorus recovery.
The first step of the transition from construction to startup of the BNR process involved optimizing the air distribution system. The new system was designed to use input from up to 21 dissolved oxygen (DO) probes to modulate 19 motorized butterfly valves based on air flow measurements from 19 flow tubes; and control DO in three separate zones among seven parallel and different sized BNR basins.
The second step involved starting up the supplemental carbon feed system. This involved thawing frozen pipelines; verifying feed algorithms were correctly programmed; verifying all existing and new flow splitting structures were at/in the appropriate elevations/positions; managing nitrification, nitrite accumulation, and carbon limitations; and optimizing the first anoxic zone.
Information sharing among plant staff and design engineerings was key to productive discussions, and everyone on the team had read-only remote access to the plant distributed control system, which is viewable over the internet using a secure VPN connection.
Other useful tools were nutrient profiles; the calibrated process model used to design the plant; and laboratory-scale sequencing batch reactors that parallel plant operations for comparison. Frequent nutrient profiles were conducted to elucidate system performance when information beyond that provided by the probes was needed. The process model was used to simulate quick “what if” scenarios.
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