Green News

 

Click here

to see how the WRF is
committed to energy conservation

           

Des Moines Metropolitan
Wastewater Reclamation Authority
3000 Vandalia Road
Des Moines, IA 50317
515-323-8000

News

2015 Excellence in Environmental Engineering and Science Competition Winner

08/11/2015

Bookmark and Share

www.aaees.org/e3competition-winners-2015gp-design2.php

 

Entrant Profile

Des Moines Wastewater Reclamation Authority (WRA) in Des Moines, Iowa, operates a 97-million gallon-per-day wastewater treatment facility that produces high-quality treated wastewater discharged into the Des Moines River, biosolids used for agricultural fertilizer, and biogas used for electricity and heat.

WRA also accepts hauled non-hazardous waste from utility and industrial customers in Des Moines, surrounding communities and neighboring states. Using anaerobic digestion, the WRA facility processes sludge from the wastewater treatment process and treats wastes generated from outside the plant. Over the past 10 years, WRA's hauled-waste program has evolved from a pilot facility to a full-scale operation that receives as many as 70 tankers of hauled waste per day.

CDM Smith partnered with WRA to create a bioenergy master plan, using lifecycle analysis to upgrade the waste-receiving facilities and the anaerobic-treatment process used to treat sludge and trucked wastes. The project team provided design, construction services and training for the improvements, also developing a process-economics model to help WRA assess the economic benefits of different wastes and alternative uses for the biogas. These improvements will expand, improve and support efficient operations and maintenance for the next 20 years.

CDM Smith provides lasting and integrated solutions in water, environment, transportation, energy and facilities to public and private clients worldwide. The full-service engineering and construction firm is headquartered in Cambridge, Massachusetts, USA.

Project Description

Overview

Des Moines, Iowa, is the state's most populous city and the seat of Polk County. Approximately 600,000 people live in the metropolitan area, which is a growing regional hub for industries, including finance, insurance, transportation and agriculture.

Des Moines Metropolitan Wastewater Reclamation Authority (WRA) operates a 97-million gallon-per-day wastewater treatment facility that produces high-quality treated wastewater discharged into the Des Moines River, biosolids used for agricultural fertilizer, and biogas used for electricity and heat.

In addition to treating wastewater, WRA accepts hauled non-hazardous waste from utility and industrial customers in Des Moines, surrounding communities and adjacent states. Using anaerobic digestion, the WRA facility processes sludge from the wastewater treatment process and treats wastes generated from outside the plant. This includes fats/oils/grease (FOG), dairy, biodiesel, ethanol production byproducts and other municipal and industrial wastes that are hauled to the facility and processed to produce high-quality biosolids and biogas.

Over the past 10 years, WRA's hauled-waste program has evolved from a pilot facility to a full-scale operation that receives as many as 70 tankers of hauled waste per day. This critical service supports businesses that lack the technology or resources to process their own waste. An environmentally responsible alternative to typical waste removal, it creates valuable energy, minimizes pollution and reduces carbon emissions.

CDM Smith partnered with WRA to create a bioenergy master plan, using life cycle analysis to upgrade the waste-receiving facilities and the anaerobic-treatment process used to treat sludge and trucked wastes. The project team provided design, construction services and training for the improvements, also developing a process-economics model to help WRA assess the economic benefits of different wastes and alternative uses for the biogas. These improvements will expand, improve and support efficient operations and maintenance for the next 20 years.

Integrated Approach

  • Operating a central facility streamlines costs and benefits the environment - Consolidating hauled-waste and wastewater processing to a single central facility minimizes trucking of hauled waste, reduces energy use and associated carbon emissions, and produces biogas from hauled waste-generating more than 40 percent of the facility's energy.
  • Developing a bioenergy plan integrates planning, technical and operations processes- A holistic plan outlines improvements for the existing facility and evaluates potential for implementing the advanced digestion process. Evaluating technologies and selecting the optimal system for the solids handling facilities maximizes efficiency. Finally, the plan's process-economic model helps WRA evaluate wastes to determine effects on the process and economic value.

Quality

  • Improving digester performance better serves customers - Upgrading and expanding digester capacity at the existing WRA facility helps meet the region's growing demand for waste removal and processing. Maximizing the existing facility's performance helps reduce the cost of building additional waste-treatment facilities throughout the state.
  • Enhancing biogas production generates energy and revenue - Biogas produced onsite offsets energy used by the WRA facility and is sold to neighboring businesses for heating. The result is an environmentally friendly, renewable energy source that reduces strain on the electrical grid and creates an additional revenue stream.

Originality and Innovation

  • Improving digester-cover design makes digesters more versatile - Design includes concrete, submerged-fixed covers that accommodate various high-strength wastes, including FOG, dairy, biodiesel and ethanol production byproducts. Hauled wastes can generate excessive foam in the digestion process, and submerged covers help control and remove the foam-reducing its impact on the process. The covers maximize digester tank volume and allow WRA to serve a wide range of utility and industrial customers.
  • Applying an economic/process model optimizes performance and profit - The modeling component of the project improves overall management of the wastes program, helping WRA evaluate various outside waste streams and effects on the facility's digestion and biogas produc- tion. It also helps the utility assess tipping fees-ensuring that waste is processed correctly and biogas is optimally used-and provides a lifecycle-cost assessment for future uses of biogas.

Complexity

  • Complex cover design requires robust support system - To support the 115-foot diameter concrete digester covers and center dome system, an extensive column support system was designed, including four center columns to support the dome system and eight columns placed around the internal perimeter.
  • Providing biogas storage ensures optimal energy reuse - A gas membrane cover and mixing system were provided for the secondary digester. The largest membrane cover installed in the United States, this feature provides optimum biogas storage capacity-allowing WRA the greatest flexibility in operating the downstream solids dewatering system and beneficially using biogas produced at the facility.
  • Advanced mixing systems serve multiples uses to process a wide range of waste - An efficient mixing system was critical to the project because the anaerobic digesters process a variety of wastes from utilities and industries in the region. Computational fluid dynamic (CFD) modeling was used to evaluate multiple mixing systems for the five primary digesters and optimize the size of the selected stream. The design team used CFD modeling to help size the mixers, rather than using industry standard rules that would have resulted in larger, more expensive mixers-and consumed more electric power.

Contribution to Social or Economic Advancement

  • Optimizing performance at the WRA facility provides lasting environmental benefits-Ensuring that WRA remains the preferred hauled - in waste facility in Iowa means that less waste will be discharged to collections systems. Instead, more of the region's waste is handled responsibly and reused in the form of biosolids and biogas-creating valuable energy, minimizing carbon emissions and reducing pollution.
  • Providing cost-effective, sustainable waste management supports economic growth in the region - Affordable, reliable waste removal systems mean that companies without their own waste-processing capabilities can operate and thrive in the Des Moines metro area and the surrounding region-becoming profitable, providing valuable products and services, and hiring locally.
  • Operating a sustainable waste-to-energy program provides a model for other cities - The facility and program improvements demonstrate an economically viable, socially responsible way to handle growth in an expanding metro region. The utility's successful waste-to-energy program provides a model for other cities and municipalities looking for sustainable waste solutions.

Return to the News Listing