From Greenhouse Gas to Green Fuel

Paul L. Busch Award Winner Kartik Chandran has devised a novel technology to turn the methane in biogas into methanol

ImageBiogas holds tremendous potential as an energy resource. But the reality for many U.S. treatment plants is that biogas recovery processes can have drawbacks that make them either unaffordable or impractical for all but the largest facilities. Researcher Kartik Chandran, of Columbia University, is pursuing a promising new approach that could make affordable resource recovery from biogas a reality for plants of all sizes.

The WERF Endowment for Innovation in Applied Water Quality Research presented Chandran with its 2010 Paul L. Busch Award during WERF’s annual subscriber luncheon at WEFTEC.2010. The award carries with it a $100,000 research grant that will assist him in his efforts to develop a new technology that transforms plant-generated methane, a potent greenhouse gas, into the green fuel, methanol. The technology could offer wastewater treatment plants a more affordable, environmentally friendly process for producing this alternative fuel and help them address one of their top challenges – the reduction of nitrogen in effluents.

A New Role for Ammonia Oxidizing Bacteria

ImageCurrent methanol production in the United States occurs largely through an expensive conversion process that chemically catalyzes the oxidation of methane gas. Adding to the cost is the need to purify methane sources, such as digester gas, prior to conversion. Chandran’s research takes an alternative and more cost-effective approach to generating methanol through the development of autotrophic microbial reactors. These reactors, which plants can integrate into their normal biological treatment processes, convert the methane in digester gas straight to liquid methanol, avoiding purification and chemically catalyzed conversion. Success, however, hinges on Chandran’s ability to effectively employ specific ammonia oxidizing bacteria. These otherwise unremarkable bacteria will play a novel role in the reactor’s design.

Chandran has targeted ammonia oxidizing bacteria not for what they do well, which is, of course, oxidize ammonia, but for their inability to completely oxidize methane. (Figure 1) Methane oxidizing bacteria oxidize methane completely to carbon dioxide, which is a greenhouse gas. On the other hand, ammonia oxidizing bacteria partially oxidize methane, leaving methanol and trace amounts of formaldehyde, as well as biologically fixing the carbon dioxide.

The first goal of Chandran’s research will be to develop a bioreactor system using these ammonia oxidizing bacteria to generate methanol. Early research will focus on process stability and methanol yield using different nitrifying bacterial strains. Through the course of his work, he will also help clarify the mechanisms of autotrophic methane oxidation to methanol, and develop mathematical models that describe autotrophic methane to methanol oxidation. This will give us a better understanding of how these microbial communities work and provide a foundation for additional research and advances both within the treatment plant and beyond.

Good for Plants with Small Footprints

ImageProcesses and technologies already exist to harness biogas as a resource. Cogeneration, which uses biogas to generate heat and power, is well established and is in use at wastewater treatment plants. But cogeneration, as with any resource recovery technology, has its drawbacks. The cost of producing energy from biogas can be quite high relative to current energy prices, and the quantity of biogas required to make the process feasible often limits it to the largest treatment plants.

Industry experts find Chandran’s approach intriguing because of its reliance on biological processes to address the methane and carbon dioxide in biogas. Biological nutrient removal has a proven track record in wastewater systems, even smaller ones. Chandran’s process could easily fit into existing anaerobic treatment schemes and in so doing, yield additional benefits.

By integrating these bioreactors into the biological nutrient removal process it would be possible to enhance nitrogen removal by converting nitrogen to nitrite using the ammonia oxidizing bacteria, and then channeling the methanol these bacteria produce back into the system to serve as an external carbon source for denitrification of the nitrite produced.

Some of today’s largest and most advanced treatment plants rely on methanol addition to improve the performance of their denitrification processes. For example, Blue Plains Wastewater Treatment Facility, which serves the metropolitan Washington, D.C. area, was able to cut its nitrogen discharge in half thanks to methanol addition. The cost of methanol addition, however, is significant and recent domestic methanol prices recently reached their highest levels in three years. By providing the technology for plants to generate their own methanol, Chandran’s bioreactor could provide smaller treatment plants, as well, with a more cost-effective option while still realizing the benefits of increased denitrification rates and improved nitrogen removal.

Good for Reducing Greenhouse Gas Footprints

Biogas is a mixture of roughly 60% methane and 40% carbon dioxide. Both are greenhouse gases. And it is estimated that methane is 20 times more powerful a greenhouse gas than carbon dioxide.

Because the bacteria used in Chandran’s bioreactor are unable to oxidize methane completely, they lack the ability to produce carbon dioxide. As a result, the process could lower the overall greenhouse gas footprint of wastewater treatment plants by reducing both methane and carbon dioxide release, as well as recovering methanol.

The production of methanol and its subsequent use as a carbon source for denitrification could have the additional benefit of reducing yet another greenhouse gas – nitrous oxide. Incomplete denitrification can result in the release of increased levels of nitrous oxide, which is roughly 300 times more potent than carbon dioxide. The methanol addition would increase denitrification rates and assure more robust denitrification under varied conditions.

Chandran is leading an additional WERF project that is exploring the triggers for increased nitrous oxide emissions. In an upcoming phase of the research, the team will test their understanding of the mechanisms for the generation and release of nitrous oxide to demonstrate that modifications to process operations affect emissions and can lead to control strategies.

Beyond the Treatment Plant

Chandran’s ongoing research concerning biological nitrogen transformations has established him as a leader in the area of nitrogen cycling in wastewater treatment. The Paul L. Busch Award will help him explore new directions along the water-energy nexus and allow him to continue his work combining environmental engineering, environmental microbiology, and environmental sustainability into practical solutions for tomorrow’s wastewater treatment plants.

In addition to the Paul L. Busch Award, he has received numerous awards and honors, including the National Science Foundation’s CAREER award in 2009 for his ongoing efforts to characterize nitrous oxide and nitric oxide emissions from wastewater treatment plants at the molecular mechanism and metabolic modeling levels. Most recently, his work earned him yet another honor – appointment to the board of trustees at the Water Environment Federation.

Chandran is the director of Columbia University’s Biomolecular Environmental Sciences (CUBES) program, and he is the faculty advisor for the Columbia chapter of Engineers Without Borders, a nonprofit organization that pairs students with professional engineers and nongovernmental organizations in developing countries. It is with their work that Chandran’s bioreactors could realize their most lasting benefit.

Methane, which is generated by landfills and the breakdown of animal and human waste, has become a valuable resource for developing economies, as well as a cleaner, more environmentally friendly source of heating fuel for even the remotest villages. In Obodan, Ghana, members of the Columbia chapter of Engineers Without Borders are working on source separation toilets that allow urine to be used as fertilizer and solids for digester gas recovery. Chandran would like to incorporate his bioreactors into these systems providing valuable methanol to local villages. As a liquid, methanol allows for easier conveyance, and it’s also more socially acceptable as a cooking fuel. In this role alone, it could replace the enormous amounts of wood used for cooking in developing countries. Of greater significance to some is methanol’s value as a commodity in the fuel market. It is widely used in Asia and other parts of the world as a gasoline additive and alternative fuel.

It’s benefits such as these – benefits beyond the treatment plant -- which put the potential of Chandran’s research into proper perspective. To help wastewater treatment plants cut greenhouse gas emissions and reduce their annual nitrogen discharge would be a remarkable feat, but improving the way millions of people live would be extraordinary.

WERF is currently accepting nominations for the 2011 Paul L. Busch Award. To learn more, visit us online at www.werf.org/PaulLBusch.