The Case for Anaerobic Digestion in North America

By Douglas Kemp | January 07, 2013

Despite the significant economic and environmental benefits of generating renewable energy from the anaerobic digestion (AD) of organic waste streams, North America, with fewer than 200 AD installations, has lagged behind other parts of the world. Europe has more than 8,000 AD installations, and, according to the German Biogas Association, the number of AD installations in Europe is projected to grow to nearly 25,000 by 2020.

For environmental reasons, Europe has regulated the diversion of organic waste away from landfills to other solutions such as composting and the production of biogas for power and renewable natural gas. To ensure the economic viability and funding of these renewable energy projects, European governments provide economic support with long-term subsidized power purchase agreements (PPAs). This is not the case in North America, where government support to divert organic waste and provide economic subsidies is not widespread. In order for the AD industry to rapidly develop in North America, solutions must be found to address these issues.

AD projects typically earn revenue from three sources: converting the biogas into electricity for sale to the grid, charging tipping fees for the processing of the organic waste, and selling the digestate as bio-fertilizer. Even with these combined revenue streams, a typical AD project’s payback is five to seven years. In order to attract capital, these projects must find additional revenue streams to reduce the payback to less than three years. To meet current air and water quality standards, these projects must find solutions for sequestering the carbon dioxide (CO2) and hydrogen sulfide (H2S) found in biogas, and reuse the production water from the AD.

Solutions4CO2’s Integrated Biogas Refinery provides AD developers with solutions to these economic and environmental challenges. The IBR platform’s enhanced recycling and reuse of the CO2, H2S, digestate and production water from the AD creates additional value-added nutra/pharma coproducts from the production of microalgae. Project paybacks are significantly reduced to less than three years.

The continuous-flow and modular IBR consists of a biogas purifier and infusion system, algae cultivation system and harvesting and extraction system, which can be integrated with any AD technology. Here’s how it works: the AD processes organic waste to produce biogas containing roughly 60 percent methane, 39 percent CO2 and less than 1 percent H2S as well as waste water and digestate. The biogas purifier and infusion system separates over 85 percent of the CO2 and 95 percent of the H2S from the biogas by infusing and dissolving these gasses into water for use in the algae cultivation system, in which the microalgae assimilate over 95 percent of the dissolved gasses over the course of their growth cycle. The purified 90 percent methane stream is used to power a combined-heat-and-power unit, which more than offsets the parasitic load of the entire IBR, and provides some surplus power for sale to the grid. The harvesting and extraction system harvests and dewaters the algae biomass and extracts the oil containing high-value coproducts for sale in the nutraceutical and pharmaceutical markets, and the production water from the system is then recycled and reused in the biogas purifier and infusion system. The residual algae biomass can be sold as bio-fertilizer.

The potential market for biogas projects in North America is significant, and more realizable now that solutions exist to address the economic and environmental hurdles that have historically faced the industry. An integrated biorefinery platform unlocks this potential.

Author: Douglas Kemp
CEO, Solutions4 CO2