Wastewater treatment plant enhances city’s sustainable image

Dubuque, Iowa — Sustainability is classically and creatively exemplified in the City of Dubuque’s recently completed Water and Resource Recovery Center (W&RRC) project. The project represents more than 20 years of collaborative civil engineering by the City of Dubuque, its citizens, and Strand Associates, Inc. After completion of a 20-year facilities plan, the city hired Strand to complete the design and construction of upgrades to the W&RRC.

The plant required a massive overhaul to meet not only the city’s growing population, but also its growing popularity as a sustainable, smarter city.

In 2006, the city, under Mayor Roy Buol’s lead, embarked on its Sustainable City program and in 2009 added a “smarter” element to the mix, thus becoming the Smarter Sustainable Dubuque Initiative. This program seeks to transform Dubuque into one of the first “smarter” sustainable cities in the United States. The “smarter” elements incorporate new technologies, community outreach, and implementation strategies to create a model of sustainability for smaller communities with a population of 200,000 or less. These communities represent 40 percent of the United States’ population. With projects like the W&RRC upgrade, Dubuque is setting a precedent for the nation’s population.

The W&RRC project presented a few challenges, namely in the design phase; 12 challenges to be exact. The design needed to adhere to the city’s 12 Sustainable principles, which include smart energy use, regional economy, resource management, community design, community knowledge, and clean water. The upgrades effectively maintained the integrity of the city’s sustainable principles by exploring and implementing only sustainable and economically viable solutions.

At the beginning of the design phase, the team examined seven possible solids management alternatives to replace the 40-year old incinerators the plant had previously used. The team examined incineration, anaerobic digestion, drying, composting, and various combinations of each.

However, with a keen eye on sustainability and the 12 principles, the design team chose anaerobic digestion as it presented the most beneficial and intuitive method to fulfill the city’s sustainability goals.

Additionally, with an unwavering dedication to sustainability, the city chose to construct digestion facilities to meet Class A biosolids requirements instead of previous Class B qualifications. Class A biosolids require that the resulting biosolids contain no pathogens. These Class A biosolids can then be used as fertilizer or as a soil amendment to enhance a soil’s physical properties. In addition, Class A biosolids can be used for residential gardening or landscaping whereas Class B biosolids cannot. In order to meet this new class, temperature-phase anaerobic digestion (TPAD) facilities were designed and constructed to not only meet the Class A requirements, but also to generate electricity.

The TPAD process produces a biogas that can be used in microturbines to produce electricity and heat. The TPAD process is housed in a repurposed building with an electrical generation capacity of 600 kilowatt (kW); however, it can easily expand to 1,000 kW. With the use of TPAD, the plant is able to reuse the resulting biogas to currently self-produce more than 50 percent of its electrical needs. It is anticipated that the plant will be electrically self-sufficient within five years.

Other upgrades and improvements include replacement of the plant’s supervisory control and data acquisition (SCADA) system, the addition of influent fine screening facilities, grit removal equipment, a new primary clarifier, weir covers for odor control on all four primary clarifiers, and new energy dissipating inlets on the clarifiers. An important improvement was the transition from chemical disinfection to Ultra Violet (UV) disinfection. UV disinfection uses UV lamps to neutralize the microorganisms in the water and does not rely on the addition of chemicals that could jeopardize compliance with effluent discharge requirements.

These improvements and upgrades not only produced sustainable solutions, but also impressive economic results for the city and the surrounding community.

“Innovative techniques in design, construction, and management of this facility are expected to cut heating and cooling usage by 25-30 percent compared to the former 40-year-old plant,” said Mayor Buol. “Investment in co-generation systems and improvements also lowered electrical energy demands from 950 kW to 600 kW – a 37-percent reduction! Through the use of captured methane gas and three electrical turbines, we will generate the full 600kW and realize a savings a $250,000 per year.”

Throughout the process, the collaborative efforts of the city, its citizens, and the Strand team required constant vigilance and adherence to the city’s sustainable initiative. Following the 12 principles, the team made sure to evaluate the progression of the project at various intervals as well as gain community input, understanding, and support through education and public involvement at each stage of the project.

The Dubuque W&RRC was completed in 2013 and is the first W&RRC in Iowa designed to meet Energy Star requirements. Additionally, this project represents sustainability at its finest as the city can now leave a sustainable legacy that will efficiently last for the next 20 to 40 years.

“This is a perfect example of how progressive communities are designing smarter, efficient municipal facilities now that will benefit the long-term sustainability of our community,” said Mayor Buol.


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