Connections: The Gold Standard

Sally Brown

Sally Brown
BioCycle September 2013, Vol. 54, No. 9, p. 69
For more on the “Gold Standard”:

Anaerobic Digestion Of High Strength Organics Solves Treatment Plant Challenges
Improving Economics Of Codigestion
Codigestion Research Builds Facility Operator Confidence
Analyzing Food Waste Management Methods
Food To Fuel Demonstration At US Air Force Academy

Everybody agrees that controlled anaerobic digestion is a terrific way to produce green energy from a wide range of residuals. And everyone agrees that losing a little weight, quitting smoking and exercising regularly are terrific goals.

Then why is it that so many operating digesters are still flaring their gas and so many of us are not going to the gym? What these two seemingly disparate things have in common is the need for a little push — some type of incentive to take them from terrific concept to reality.

One example of an incentive is in King County, Washington, where the county offered employees the option of sticking with the traditional health care plan or joining the “Healthy Incentives” version. The latter focuses on improved wellness and shared costs; participants are rewarded by lower out of pocket expenses if they meet wellness goals. In return, the county is rewarded by a healthier group of employees leading to reduced medical expenses. In the first six years, the smoking rate dropped by 40 percent, and employees classified as obese dropped 5 percent of their weight. This has ended up saving the county many millions.

Unfortunately no such incentive plan exists for anaerobic digesters. A significant number of the operating digesters in the U.S. are located at municipal wastewater treatment plants, where anaerobic digestion has been one of the standard technologies used to meet regulatory requirements for volatile solids and pathogen reduction. It should be mentioned here that wastewater treatment is the single largest point source of electricity use for municipalities. Using the methane generated during anaerobic digestion can typically meet about 50 percent of the energy needs of a wastewater plant. Despite this, according to a recent report from the U.S. EPA’s Combined Heat and Power Partnership, only 43 percent of the facilities that treat greater than one million gallons per day use digesters.

While this is disturbing, it is critical to remember that the municipal employees running these digesters are mandated to treat wastewater to make it safe for human health and the environment. There is a strict regulatory structure to make sure they fulfill their mission. By and large, treatment plant staff does an excellent job in meeting this mandate. However, their mandate does not include producing green energy. In fact, of that 43 percent with AD, only 8 percent actually do anything with the methane that they produce other than flare it. In our current environment, that is the equivalent of a pack a day habit.

So why are these plants not doing anything with their biogas? A recent survey conducted by the Water Environment Research Foundation (WERF) came up with a number of excuses, sorry, reasons. Here they are in bullet form:

• Cost: Capital resources at these facilities are limited and other projects take priority. This use of gas is not seen as a good investment of limited resources.

• Hurdles: Obstacles put up by power and gas utilities to selling this power to the grid.

• Regulatory: Air permitting regulations and uncertainties on meeting these regulations are a region-specific barrier.

• Size: Here the opposite of Goldilocks appears to be in play. While many smaller (5-10 million gallons/ day or mgd) and larger plants (> 25 mgd) use their gas, most mid-sized plants (10-25 mgd) included in the survey did not feel that sufficient gas could be produced to merit collection.

The survey found that in cases where using the gas had an internal champion, all of the hurdles could be overcome. Innovative solutions were often identified. These included combining residuals from a number of small plants or accepting high strength organic materials from external sources. For other plants, it was often a case of one group (the engineers) identifying one set of obstacles, with another group (the operators) identifying a different set of concerns. All of this while gas was being flared rather than used.

Biogas Utilization Incentives

It seems to me that, just like the King County health care system, this is a great idea in desperate need of an incentive program. Here is the tricky part though. In private enterprise, financial rewards are a clear and easy incentive. In the municipal sector it is not so simple. The core mission of these facilities is to treat wastewater. To change, we must find a way to redefine the core or to incentivize collection and use of digester gas.

This could easily be done on a federal level. You may recall that the Clean Water Act provided financing and grants for treatment plants to upgrade to meet new regulatory standards. For digester biogas, funds could be provided for plant upgrades, training for operators, and purchase of different types of engines to transform the gas into electricity. In addition, special exemptions could be made to existing regulations to allow a fixed number of violations while plants learn how to operate new systems. While I say that is an easy and clear way to make that happen, I also recognize that it is an unlikely way to get much done in our current political climate.

State governments however, are a different story and could provide much of the necessary leadership. This could involve partnering with utilities to support a feed-in tariff — an extra sum paid to utilities that reduce their own energy consumption through use of internal power or sell that energy back to the grid. This system has been used to support similar projects in Europe. Low interest loans could be provided to municipalities to allow for system upgrades.

Here we are talking about using the gas that these facilities already produce. What was not even discussed in detail in the WERF survey was the potential for codigestion. Taking in external residuals is an option for municipalities that are not using their digesters to full capacity. A select number of wastewater treatment plants in the country are accepting a range of high strength organics directly at the plant and adding them to digesters, avoiding both the primary settling step and the high energy secondary aeration phase. This creates even more energy than traditional digestion and may result in a more robust microbial population in the digesters.

There also have been reports of enhanced volatile solids reduction in plants that codigest alternative feedstocks. This is the equivalent of quitting smoking and doing a triathlon. However, this requires an even greater redefinition of the core mission from protection of public and environmental health to resource recovery. Plants that are already doing this are realizing a different incentive: a better bottom line. Taking in these feedstocks not only results in additional energy production, it typically involves a tipping fee. This tipping fee can dramatically improve the economics of wastewater treatment. The plants that are doing this are the gold standard and should be an example for us all. And the wonderful thing about it is, unlike those health plans where you are expected to give up the ice cream, here you get to go looking for more.

Sally Brown — Research Associate Professor at the University of Washington in Seattle — authors this regular column. Email Dr. Brown at

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