Biomethane for Transportation: Upgrading Dairy Anaerobic Biogas Using Microbial MatsEPA Grant Number: SU835689
Title: Biomethane for Transportation: Upgrading Dairy Anaerobic Biogas Using Microbial Mats
Investigators: Leonhardt, Eric , Moyer, Craig L.
Institution: Western Washington University
EPA Project Officer: Hahn, Intaek
Project Period: August 15, 2014 through August 14, 2015
Project Amount: $14,600
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2014) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Agriculture , P3 Challenge Area - Energy , P3 Awards , Sustainability
The Biomethane for Transportation project demonstrates the viability of utilizing renewable natural gas or biomethane derived from dairy farming anaerobic digesters. This waste to energy project reduces the global warming potential of dairy farming while providing an alternative vehicle fuel market to electrical power generation projects. The project offsets conventional petroleum vehicle fuel including natural gas with a renewable fuel. The team has been developing a biogas upgrading solution that uses microbial mats to remove hydrogen sulfide from the biogas stream. Dairy anaerobic digester biogas contains roughly 40% carbon dioxide, 60% methane and up to 4000 ppm of hydrogen sulfide. Several technologies exist for upgrading biogas into renewable biomethane including membranes, water tower scrubbing, amine based scrubbers, and pressure swing absorbers. Most of these systems remove carbon dioxide and then require a second system to remove hydrogen sulfide. The hydrogen sulfide is often removed using an iron impregnated media that can be regenerated in an exothermic reaction. At some point all of the systems reject the hydrogen sulfide either from an exothermic reaction (iron impregnated wood chips) or as a waste biogas stream (amine and water tower scrubbing). As a result, all of the systems become point source pollution for hydrogen sulfide. A novel, microbial mat solution can remove the hydrogen sulfide from either the incoming biogas stream or a process gas waste stream. The hydrogen sulfide is then biologically converted into forms of sulfur, including elemental sulfur that can be more easily handled and used as a fertilizer. This project will help to determine the volume and mass of microbial mats required to process biogas with concentrations of hydrogen sulfide associated with dairy farming. The project supports the desire of the dairy industry to reduce farming impacts to the air, watershed, and global warming potential.
A sample biogas input stream will be filtered through the microbial mat in a bench scale biological filter system. The input and output gas levels of hydrogen sulfide will be monitored along with the microbial mat mass changes. The monitoring of gas samples will be performed using conventional Druegger Tubes and sensors. A novel approach using low-cost photospectrometry with light emitting diodes and photo diodes to produce a unique spectral identifier of target gases will also be used.
Microbial mats have been used to remove hydrogen sulfide from a biogas stream. Existing results identify that the process is effective and can be performed within process parameters such as temperature and salinity. Microbial mat growth rates and mass requirements will be identified for effective and sustainable biogas processing. Testing with bench scale equipment will help assess the effectiveness of the system in a proposed integration with an amine based scrubbing system located on a dairy farm.