Final Report: Shock-Resistant Biogas Digester for Cookstove Fuel

EPA Grant Number: SU836795
Title: Shock-Resistant Biogas Digester for Cookstove Fuel
Investigators: Newton, Susan , Song, Ted , Bearden, Thomas , Belvardi, Mark , Clemenger, Anne , Perkins, Kyle , Terry, Grey , Keller, Joel , Gallegos, Fidel , Arauz, Kevin Mata , Magana, Vanessa , Cabral, Valeria Armendariz , Shorey, Wesley , Friesen, Alison
Institution: John Brown University
EPA Project Officer: Keating, Terry
Phase: I
Project Period: November 1, 2016 through October 31, 2017 (Extended to October 31, 2018)
Project Amount: $14,999
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2016) RFA Text |  Recipients Lists
Research Category: Sustainable and Healthy Communities , P3 Awards , P3 Challenge Area - Air Quality

Objective:

Every day guajeros scavenge throughout the Chimaltenango open dump, less than ten miles from the Guatemala City dump of Guatemala. Often these workers will stop at the end of their day to buy tortillas for their families from a street corner entrepreneur cooking over a makeshift stove. Burning whatever is flammable, often including toxin-infused trash, these stoves permeate the air of their already-polluted living quarters. Even entrepreneurs who can afford expensive firewood to cook tortillas breathe smoke-filled air for hours daily, resulting in chronic health issues, such as bronchitis, pneumonia, and chronic lung disease. This lack of clean fuel can be remedied by efficiently using methane gas with a simple biogas digester system. In order to guarantee the long-term viability of this system, operating conditions must be maintained to ensure the functionality of the biodigester.

The objective of the John Brown University (JBU) biogas team is to collaborate with a local not-for-profit (NFP) in Guatemala to create a user manual and training program based on an uniquely designed prototype. The key component of the biodigester designed by the JBU team is a monitoring system that allows users to efficiently observe and maintain operating conditions. The user manual and training program will assist local entrepreneurs in building and operating their own biodigesters. This program will provide locals with the opportunity to develop a marketable education focused on creating a sustainable and environmentally beneficial energy source for their community. The team will determine the contents of the manual by collecting data from several pilot projects, both in Guatemala and at the university.

The intended beneficiaries of this project are the impoverished communities living in the immediate vicinity of the dump. The solution will improve not only the living conditions in these communities but also provide them with increased economic opportunities. In order to empower these people, the JBU team will be operating through trusted NFP groups already working in the area.

Initially, the team will fund pilot projects at organizations such as the My Special Treasure (Mi Especial Tesoro), a home for young women who have come out of abusive situations in the Chimaltenango area. These projects will be sustained through constant long distance communication as well as periodic trips throughout the year. JBU has an established relationship with the Mi Especial Tesoro ministry, and JBU affiliates consistently travel there providing this partnership with a solid foundation.

The team will initially use the grant money to fund the purchase and construction of 3-5 biogas digesters for the local NFP groups and John Brown University's research team. The long-term goal of the project will be to supply the intended beneficiaries with knowledge through basic training, essential supplies, and an initial business plan. Through providing these materials, the JBU team hopes to establish a network of stable biogas producers that provide the community with a clean alternative fuel source for the future.

The vision of this project is to lower the number of deaths and diseases induced by air pollution while simultaneously boosting the economic health of the community by the founding of a locally sustained micro-biogas industry. The team hopes to do this through educating the local population on how to take advantage of alternative energy sources available in existing resources. As a side effect, this team will provide these communities a way to safely and effectively reallocate the waste contained in the dump.

Summary/Accomplishments (Outputs/Outcomes):

The goal for Phase I was to design a working prototype out of inexpensive, globally available components, alongside a kit of electrical components that compose the monitoring system. This prototype will be used for preliminary testing and providing a framework for future designs to be scaled to the needs of the users. The team examined existing data and literature regarding biogas digestion technology in order to find ways to improve on existing designs. From this study, the benefits of existing biodigester styles were compared to the requirements specified by the original partner organization in Ethiopia. After the biodigester style was selected, the remaining requirements were defined to fill the needs of the project.

To validate our design hypotheses, computer-aided analysis and manual calculations were completed. The results of this analysis drove the decisions that eventually led to the design constructed. The prototype became a platform for the team to perform data collection and testing. Challenges encountered during the testing phase pointed to a lack of scientific data available on small-scale biodigester projects and led to the compilation of necessary future improvements.

After construction of the prototype, the initial challenge involved the logistics of filling a 250-gallon tank with manure and water. Substrate to water ratios previously used in larger tanks proved to be crippling to this model. Due to time constraints, the biodigester was only in operation for a short period. Infrared spectrometry of the resulting gas indicated that methane was produced but the feedstock composition, water ratios, and start up conditions will be optimized in phase II.

Collected data from the monitoring system showed that the temperature of the biodigester changed less than 0.5 degrees Celsius over the period of an hour, and the pH did not alter more than 0.2 over the course of operation, meeting the requirements for bacterial growth. After a change in substrate, the monitoring system detected pH below 6.2, which could have a toxic effect on the methanogenic bacteria.

Several design problems were noticeable in the finished product. The time granted by a no-cost extension was used to redesign certain aspects of the equipment. The tank was resized to enable repositioning when full as the initial tank was too heavy to be moved without heavy equipment. The smaller size and thus lower capacity of the new tank motivated a shift to a thermophilic system instead of a lower temperature mesophilic system, as was originally proposed, as a way to approach the gas production capability of the larger tank. A gas tight manual stirring system was developed to eliminate the troublesome accumulation of solidified mass. The last major change was a heating system as this unit was built and tested in coldĀ conditions while expected to perform in tropical areas. Students also evaluated various initialization feed stocks to determine the most effective start up conditions.

Conclusions:

The first phase of the project was acutely beneficial in providing the team with direction for future improvements. Due to the limited information resources on small-scale biodigestion, the team encountered roadblocks necessitating innovation in the design of the prototype. An example is the design of a unique, easy-to-implement sealing system for the gas output resolving the common issue of leakage in biodigester units by providing a component customized for this application. The restrictive size of the prototype upflow system resulted in inadequate mixing for the digestion process. Investigating the benefits of incorporating a mixing system led the team to propose the addition of a leak-resistant mechanism to the phase II prototype.

The monitoring system designed was proven to be accurate, reliable, and showed us that both the temperature and the pH of our system remained relatively constant over extended periods. A functional monitoring system will allow large amounts of data to be collected by the pilot projects during Phase II of this project. In the future, the team will process collected information from both Guatemala and the university in order to make informed conclusions about operation procedures, particularly in how certain substrates affect gas production. Publication on small-scale, upflow biodigesters, particularly in Guatemala, will supplement the deficiency in existing academic publications on the subject.

The modifications to the original design allowed by a no-cost extension, resulted in a far more practical working prototype.

Journal Articles:

No journal articles submitted with this report: View all 3 publications for this project

Supplemental Keywords:

Anaerobic digestion, biogas production, microprocessor controls, temperature sensing, pH sensing, respiratory health, renewable energy, Guatemala City Dump (GCD), not-for-profit

Progress and Final Reports:

Original Abstract
  • 2017 Progress Report