Grantee Research Project Results

Final Report: Development of an Affordable Family-Scale Biogas Generator

EPA Grant Number: SU834330
Title: Development of an Affordable Family-Scale Biogas Generator
Investigators: Meyer, W. Craig , Minkovsky, Alexandra , Nemeth, Amy , Oster, Brendan , Young, Chelsea , Mehta, Daniel , Nefcy, Dillion , Shoplyansky, Jessica , Woods, Jordan , Judy, Kaitlin , Pracher, Mark , Parisi, Nicholas , Layne, Zachary
Institution: Pierce College
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2009 through August 14, 2010
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2009) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Awards , P3 Challenge Area - Air Quality , P3 Challenge Area - Sustainable and Healthy Communities , Sustainable and Healthy Communities

Objective:

We will design a simple scalable biodigester system that will: a) generate enough biogas to cook a meal per day for a family of four, b) be constructed of local or scrap materials, c) be flexible in the type of wastes it uses, and d) be inexpensive enough to be affordable by the least affluent members of society with no technical training. The digester will be disseminated as a kit containing components not readily available and understandable assembly instructions with information regarding the best waste sources and mixes thereof. The kit will be constructed by local artisans as a cottage industry. Benefits of replacing wood and dung with biogas for cooking include: 1) reduced pressure on local forests; 2) reduced disease caused by pathogens in unused dung and indoor air pollutants from combustion of wood and dung for cooking; and 3) increased revenues through cottage industry and increased ecotourism. Local agriculture will benefit from use of the spent slurry as a nutrient-rich soil amendment.

Summary/Accomplishments (Outputs/Outcomes):

From laboratory experiments we calculated that our system would have to deliver 262 liters/hr of biogas to cook a meal. Biogas produced by slurries of various wastes was measured with a two liter bench-top digester system designed by the team. Gas volume was measured by displacement of water from a second flask attached to the generator. The results of duplicate batches of the various single wastes and mixtures run for 28 days revealed that cow manure produced the most biogas (7.34 liters), followed by goat manure (6.78 liters), green waste (3.25 liters), food waste (2.98 liters), and paper (2.98 liters). Mixtures of goat and cow manure produced more biogas (11.2 liters) than either waste alone as did mixtures of food and manure (10.3 liters). Interestingly, though paper was least effective at producing biogas alone, mixtures of small amounts of paper with manures produced more biogas than the same amount of manure alone. Spent cow manure slurry was analyzed for nutrients with the following results: B = 2 mg/kg; Fe = 272 mg/kg; P = 270 mg/kg; K = 170 mg/kg Zn = 7.1 mg/kg; pH = 7.1; Total N = 0.04; C:N = 22.8. This suggests that growth tests of the spent slurry are warranted in Phase II.

A prototype biogas burner was designed that will serve as a model for construction of a burner that can be made of scrap or local materials during Phase II. Burner parameters were determined by calculations using Bernoulli's equations augmented by laboratory experiments. It was determined that at our expected delivery pressure of 0.04 psi, the following values were found most effective: Orifice Area = 3.67 mm²; Air Inlet Area = 19.2 mm²; Tubular Mixing Chamber: Length = 10 cm, Diameter = 1.5 cm. Because we plan to examine the use of plastic garbage bags as bladders for digestion and gas storage, we tested five commercially available bags for strain in response to increasing stress and ultimate rupture strength. The results for maximum strain and failure strength are as follows: Ralph's Value Kitchen bags (0.4 mil): 327% elongation, 0.7 kg failure; Hefty white bags (0.9 mil): 570% elongation, 1.2 kg failure; Ralph's Value Black (0.5 mil): 468% elongation, 0.7 kg failure, Rite Aid Waste Basket (0.6 mil): 400% elongation, 0.8 kg failure; and Pro Value Clear (0.55 mil): 464% elongation, 1.55 kg failure. All were able to contain the maximum pressure (1.8 psi) generated by our bench-top generators.

Conclusions:

The conclusions drawn from Phase I research are: 1) our generator system must produce a minimum of 262 liters of biogas per hour; 2) manures (cow, goat) produce more biogas than food or green waste and mixes of wastes produce more than single wastes; 3) addition of paper to waste increases biogas output; 4) a variety of wastes will produce enough biogas to use in our digester; 5) the spent slurry has potential as a soil amendment; 6) it should be possible to design and build a simple burner that can be manufactured by local cottage industry; 7) plastic bags have sufficient strength to be used as bladders for digesters and gas storage; and 8) it should be possible to build a biogas system that is consistent with our objectives.

Proposed Phase II Objectives and Strategies: Our objective in Phase II is production of a final set of design parameters for a scalable, modular biodigester to meet our objectives. This will include: 1) confirming bench-top results by testing of various wastes and mixes on a full-scale floating drum digester; 2) confirming that addition of small amounts of paper to other wastes increases biogas production; 3) finalizing methods of burner construction from scrap and local materials; 4) finalizing design of a modular, scalable biodigester that can be made from scrap and local materials; 5) conducting growth tests to confirm the value of spent slurry as a soil amendment; 6) designing kits and manuals with the aid of a liaision from Tanzania to be used by end users to assemble their biodigester; and 7) transferring the technology, manuals, and materials to Tanzania for use by their government.

Supplemental Keywords:

Biogas, digester, affordable, scalable, family sized, waste to energy, agricultural byproducts, animal waste gasification, renewable feedstocks,

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.