On-farm Evaluation and Demonstration of Small-scale Biogas Technology

View the project final report

• 2008 annual report

Commodities

Practices

• Education and Training: demonstration, display, extension, farmer to farmer, on-farm/ranch research, participatory research
• Energy: bioenergy and biofuels

This project supported the development, fabrication and demonstration of a biogas technology application for small farms. Biogas technology has been used globally for decades, with primary applications for large-scale, high-tech commercial systems in Europe (and limited penetration in the US) and small-scale, low-tech “household” scale systems in Asia. The potential for application of biogas technology on small-scale farms in the US is great for providing alternative means for managing on-farm organic wastes (manure, on-farm food processing) and providing a clean, renewable source of energy for on-farm applications (thermal energy for water heating, food processing, etc.). Making biogas technology a viable option for small farms requires the development of reliable, effective biogas reactors that can be readily fabricated and maintained by farmers. This project evaluated existing designs, developed design recommendations that would overcome performance problems with existing designs, and fabricated three demonstration units for experimentation on farm. The final design selected for fabrication was a simple “plug-flow” reactor that combined elements to improve feedstock mixing and flow and retention of bacteria over the existing designs while maintaining simplicity for fabrication with readily available materials.

Introduction

Rapidly rising costs for energy and agricultural inputs produced from non-renewable sources pose a critical threat to the economic viability of US farms. Small diversified and organic farms, while more insulated than chemically intensive farms, are still not immune to the effects of volatile energy markets and stand to gain considerably from the use of renewable energy technologies on farm. In particular, energy technologies focused on waste biomass – or bioenergy technologies – hold great promise for efficiently and inexpensively treating organic farm wastes, reducing odor and methane emissions (a powerful greenhouse gas), providing nutrient-rich material for land application, as well as producing renewable energy for use on farm. Biogas technology, also known as anaerobic digestion, is a natural, biological process that has been used worldwide for the treatment of wet, organic wastes and the production of biogas which is a form of renewable energy. Currently, less than 100 US farms use the technology.

Eighty seven percent of Washington’s farmers are classified as “small farms.” Many of these farms have shown a significant interest in the adoption of small-scale on-farm technologies for production and use of bioenergy and related co-products. These farmers are underserved by existing biogas technology providers as no commercially available technologies are suited to small-farm applications in the northern latitudes of the US. Currently available commercial biogas technologies of US or European design have limited applicability on small farms – they are primarily designed for digesting manure from large Confined Animal Feedlot Operations (CAFO’s) – and do not meet the technical or economic needs of the majority of small farmers in Washington State. Several small-scale biogas technologies are currently available from Asia. Three primary technologies are the Chinese fixed dome digester (Figure 1), the Indian floating cover digester (Figure 2), and the Taiwanese polyethylene tubular digester (Figure 3). Each of these technologies has been used successfully by subsistence farmers in the developing world, but could be improved with additional research and development. Furthermore, commercial application of these technologies in northern latitude, cold-climate regions such as Washington State will require improvements in engineering and design as these existing technologies were developed for tropical and sub-tropical application. Washington’s small farmers have requested research, education, and technology development in regard to small-scale biogas technology.

Refinement of small-scale biogas technology will improve the resiliency of small farms in the Western region to volatile energy prices and ultimately improve their sustainability. Key challenges for deploying commercially appropriate biogas technology on small-scale farms in the region include developing climate appropriate applications of the technology and financially appropriate turn-key packages, evaluating the role of biogas technology in the farming systems (including trade-offs with other waste-management practices, such as composting), education on use and maintenance of the systems, and identification of technologies for making the most valuable uses of the biogas (i.e. water heaters and stoves, small generators, liquid fuel conversions, etc.). The development of successful, small-scale biogas technology has tremendous application for farms throughout the Western region for improved waste management and as a substitute for non-renewable sources of energy. For example, the average cost/person for heating water in California in 2003 ranged from $163 (natural gas) to $488 (electricity) (California Energy Commission). As prices for non-renewable energy continue to rise, the use of on-farm biogas could provide a significant financial savings.

• to introduce farmers to the potential opportunities of small-scale biogas technology applications

  to develop an improved/modified design based on the various Asian technologies

  to deploy and evaluate pilot plants on three farms.