Biogas production and potential from U.S. Wastewater Treatment


How many wastewater treatment plants (WWTPs) have anaerobic digestion? How many are utilizing the biogas? What percentage of these facilities are feeding additional substrates into their digesters? How is the biogas being used — is it flared, used to drive process machinery, heat the digester, or injected into a natural gas pipeline? These are some of the questions asked of the approximately 1,200 wastewater treatment plants (WWTPs) currently operating anaerobic digesters across the United States during a survey conducted in the fall of 2011 and winter and spring of 2012. With seed funding from the Water Environment Federation (WEF), the North East Biosolids & Residuals Association (NEBRA) and Black & Veatch led a team of approximately 20 industry representatives to gather data, state-by-state, for what has become a free online database of biogas production at WWTPs.

Preliminary results of this survey were unveiled during the Northwest Biosolids Management Association’s (NBMA) 25th Anniversary BioFest in late August 2012; more complete data were presented at BioCycle’s 12th Annual Conference on Renewable Energy From Organics Recycling in late October, shortly after the launch of the new website created specifically for this project: The current initial website, version 1.1, was supported by Cambi, the New York State Energy Research & Development Authority (NYSERDA), and the National Biosolids Partnership and produced by 350 Technologies LLC.

The data gathering and resulting website are intended to provide policymakers, market analysts, project developers and water quality professionals with key information about the potential for biogas production at WWTPs as a renewable fuel. Biogas can be used in place of natural gas in boilers and engines to produce heat and electricity in combined heat and power (CHP) systems. “The goal was to develop and present a consensus-driven data set — data that everyone in the field could rely on,” says Lori Stone, Global Practice and Technology Leader at Black & Veatch, one of the principal investigators on the project. “It took hundreds of phone calls to wastewater treatment facilities to ensure the accuracy of the data. The teamwork made the daunting task more manageable.” In addition to NEBRA and Black & Veatch, the core project team included the Mid-Atlantic Biosolids Association (MABA), American Biogas Council, California Association of Sanitation Agencies, NBMA and BioCycle, with help from engineers at HDR and Hazen & Sawyer.

The Need for Better Biogas Data

There are four major sources of biogas production: landfills, farm digesters, industrial facilities (e.g. food processors such as Stonyfield and Tropicana) and WWTPs. In recent years, data have been compiled and reported regarding two of these sources: U.S.EPA Landfill Methane Outreach Program (LMOP), which tracks projects using methane from landfills across the U. S. (594 operational projects as of June 2012;; and U.S.EPA AgStar program, which provides information on farm-based digestion projects (an estimated 192 as of September 2012;

But information on industrial digestion projects is difficult to compile, in part because of proprietary information. And, until now, estimates of biogas production at WWTPs have been only approximate. For example, in 2007 and 2011, the U.S.EPA-led Combined Heat & Power Partnership reported its estimates of biogas production and potential from the nation’s WWTPs, which was the best information available at the time. According to its analyses, as of June 2011, “CHP systems using biogas were in place at 104 WWTFs, representing 248 megawatts (MW) of capacity.”

While further data analysis is needed to understand what the new data can add to improving this kind of information, it is at least clear from this most recent undertaking that there are nearly 300 electricity generating systems in operation at WWTPs in the U. S., most of which involve utilization of heat (i.e., are CHP systems) — far more than EPA had estimated. Project team members noted that even EPA’s estimates of the number of WWTPs with operating anaerobic digesters seemed to be low.

Compiling the Data

The biogas data project started in the fall of 2011, with $25,000 from WEF and a spreadsheet of WWTPs with AD, donated by InSinkErator. The company had hired a summer intern to check websites of WWTPs greater than 5 MGD, to confirm if they had operating AD; 858 were confirmed (although some of these data later proved wrong as websites are often not up-to-date). Conference calls were held with the project team and an advisory group convened by WEF in order to reach consensus on what data were to be collected initially (Phase 1 data) and what the “wish list” for additional data might contain.

An initial online database into which project team members could enter data was created. Over the next eight months, the project team worked to confirm the list of all WWTPs in their assigned state(s). The data collection protocol included these steps:

  1. Contact the regional U.S.EPA biosolids coordinator and/or the state biosolids coordinator and obtain any data they may have. It is rare to have lists of AD facilities, but sometimes there are lists of all WWTPs in the state, with critical contact information. Also inquire about other people in the state who may be familiar with AD facilities at WWTPs (e.g., consulting engineers).
  2. Using the list in the initial online database which indicated which WWTPs were thought to have AD, start calling the largest of the facilities, not only to obtain their data, but also to see if they know about other AD operations in the state.
  3. Continue calling all WWTPs thought to have AD, to confirm and collect data about what they do with the biogas (Phase 1 data). Also contact all or some of the largest facilities thought not to have AD, to confirm. The data collectors thus built an understanding of AD and biogas use in each state.
  4. For a few states, project team members contacted all facilities greater than 1 MGD or greater than 5 MGD, including those with AD and those without AD. Thus, the level of confidence in the final data from such states is very high. Other data collectors went only so far as to confirm the complete list of WWTPs with operating AD

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