State-of-the-Art Odor Control at the Brightwater Wastewater Treatment Plant

The Brightwater Treatment Plant (Brightwater) is a 136 million liters per day (ML/d) (36 million gallons per day [mgd]) state-of-the-art wastewater treatment and reclamation facility built to meet the growing service demands of the Puget Sound region. The plant is a key element of King County’s regional treatment system, and was designed and constructed with the objective of protecting Puget Sound and minimizing impacts on the environment and community. Initial planning of the plant began in 1991, with groundbreaking in 2006 and plant commissioning in 2011.Building a new wastewater treatment plant near homes and businesses requires a superior commitment to odor control. King County worked with the local permitting jurisdictions and community stakeholders to develop aggressive fence-line odor limits in keeping with “No Odor” commitments made during the design and permitting process. The Brightwater odor control system was designed to meet stringent odor control property boundary limits, specifically:• 1 dilution to threshold (D/T) odor• 0.8 parts per billion by volume (ppbV) hydrogen sulfide (H2S)• 2.8 parts per million by volume (ppmV) ammoniaTo meet these strict criteria, key features were implemented into the design scheme including covering or enclosing all wastewater processes for containing and capturing odors, treating foul air at best available control technology (BACT) multi-stage vapor phase odor control systems, implementing liquid phase treatment upstream of the plant, and covering of biosolids trucks to prevent odor emissions during transport.The vapor phase odor control systems consist of three localized scrubber complexes treating a total of 189 cubic meters per second (m3/s) (400,000 cubic feet per minute [cfm]) of foul air. Additional capacity of 57 m3/s (120,000 cfm) is also provided for redundant units and for handling dedicated ventilation during tank maintenance operations.Vapor phase odor control consists of a roughing stage biotower followed by single-stage chemical scrubber plus activated carbon at the two facilities that handle the higher odor loadings from the primary treatment and solids handling areas. For the aeration and membrane bioreactor (MBR) basins, which typically emit lower odor loadings, a single-stage chemical scrubber plus activated carbon is provided. This multiple stage approach treats a full range of odor-causing compounds while the biotowers reduce the chemical demand, making the systems safer for workers and the environment with fewer chemical truck deliveries to the site.The journey from conceptual design through construction included several key decision points. Major design decisions included selection of the best technical approach, the preferred number and size of treatment stages, the best scrubbant recirculation approach, and the best carbon change-out approach. With multiple scrubber trains, a detailed evaluation was conducted to select between a common basin scrubbant pumping approach versus an independent scrubbant pumping approach. A detailed evaluation of carbon systems and handling approaches was conducted including manual carbon replacement, outsourcing of carbon replacement, and plantwide dense phase carbon conveyance system and vacuum system.Multiple unique challenges had to be addressed during the design, construction, start-up and commissioning phases of the project. These included inherent challenges associated with large vapor phase odor control systems, state-of-the-art low detection level odor monitoring, noise attenuation challenges, and implementation of very large buried ductwork around the site for aesthetic improvement.Testing of the scrubber systems took place in November 2011 and October 2012. Each odor control train tested at each facility met the overall maximum discharge limit at the stack of 8 ppbV H2S. Similarly, odor levels in the treated air from the three facilities’ odor control systems were all below 10 D/T.Since September 2011 when the treatment plant began treating sewage, the odor control system has operated continuously and achieved compliance with odor control objectives. The few odor complaints received have been thoroughly investigated and verified as not attributable to Brightwater. Monitoring of treated air at the stack and regular monitoring with low level H2S monitors at the property boundary have confirmed that the plant is achieving the high “no detectable odor” standards agreed to.King County’s commitment to odor control has enhanced Brightwater’s image as a great community asset.