Several successful codigestion projects in North America involving small- and large- scale wastewater treatment facilities, as well as two recent conceptual design projects in Australia, demonstrate the feasibility of implementing new anaerobic digestion and resource recovery facilities at small-scale treatment plants.

By: John Kabouris Ph.D., P.E., CH2M HILL Senior Technologist

Dr. John Kabouris presented his paper “Positive Business Case for Small-Scale Codigestion and Resource Recovery Facilities Without Pre-Existing Anaerobic Digesters” on Tuesday, October 8, at 4 p.m. in TS414, during the 2013 Water Environment Federation Technical Exhibition and Conference (WEFTEC), in Chicago, Illinois. Learn more about CH2M HILL’s WEFTEC 2013 participation and technical sessions.

How big does a wastewater facility need to be in order to implement a successful codigestion project? The current perception is that smaller facilities (typically less than 5 mgd in size) are limited in their opportunities for beneficial biogas generation—an opportunity worth leveraging for power generation and potentially generous cost savings.

However, several successful codigestion projects involving both small- and large- scale facilities in North America, as well as two recent conceptual design projects in Victoria, Australia (Yarra Valley Water and City West Water) demonstrate this is simply not the case.

Yarra Valley Water (YVW) and CH2M HILL recently completed a project to determine the feasibility of renewable energy generation through anaerobic digestion of waste at four different sites. The project included:

  • Assessing the available biogas generation technologies and waste sources available
  • Recommending the preferred technology and waste sources
  • Conceptualizing likely biogas generation and development costs
  • Assessing likely revenue generation and payback period through export of power to the grid, funding, and other government incentives
  • Assessing likely risks, opportunities, and overall feasibility of a biogas generation plant

Size does not determine successful implementation, but rather the key factor is the codigestion of municipal treatment residual solids with high-strength waste stream (trucked process waste; fats, oils, grease; food waste, green waste, paper/pulp waste, etc.). Combining residual solids with waste efficiently produces large amounts of biogas that can be used for power cogeneration and power export to the grid.

At YVW, fats, oils and grease, as well as food wastes were identified as the best high-strength waste for biogas production when using two-phase acid-methane digestion.

A second case study was conducted for the City of West Water (CWW) to investigate the viability of building a green-field codigestion-based resource recovery center (RRC) to service industrial customers using meat processing and other industrial wastes codigested with municipal sludge for the generation of renewable products while reducing greenhouse gas emissions. The CWW RRC would produce electrical power and heat, high-quality reuse water and compost products. Key factors for generating the positive business case for the CWW RRC included the selection of the most promising higher strength wastes for maximizing annual income and high-efficiency low-footprint treatment processes for minimizing the land acquisition and facilities capital cost.

YVW and CWW are leading the way in implementing codigestion resource recovery facilities in Australia. In his presentation, John will use these two case studies as the foundation to show how codigestion can be economically viable for existing facilities, as well as at green-field facilities looking to implement an RRC. When utilities combine revenue achieved from codigestion with the income gained from accepting high-strength wastes, and possibly reclaimed water and composted biosolids, a positive business case can be developed even for small-scale facilities.

John Kabouris, Ph.D., P.E., is a Global Biosolids Technologist at CH2M HILL with expertise in process design, optimization, and high-stength wastes codigestion. He has led research and design projects on the codigestion of high-stength wastes using conventional and advanced digestion configurations and has co-authored the 2010 Water Environment Federation (WEF) Technical Practice Update document on codigestion of Fat Oil and Grease (FOG) and High Strength Wastes (HSW).