Participatory Training in Small-scale Anaerobic Digestion of Agricultural Residues

Anaerobic digestion (AD) of organic residues is a globally expanding sustainable technology for generating biogas with a high methane content [1].  In the US, the number of municipal AD plants has almost doubled since 2010, and currently, over 8,000 large dairy and hog farms use AD to produce biogas from their manure, generating renewable energy [2].

Small-scale, low-tech AD systems for processing food and agricultural waste, often applied at the household scale and frequently using co-digestion of plant and animal residues, are becoming increasingly common in Asia [3-5], Africa [6], and Latin America [7, 8]. In contrast, commercial AD technologies used in most US farms are designed for large-scale livestock operations. Thus, the adaptation of low-tech AD technologies in the US would benefit small farms by making them economically resilient to volatile energy prices, while contributing to reducing their net methane emissions [9] and enhancing their soil nutrient management. For example, large-scale AD systems commonly do not use the digestate as biofertilizer. Biofertilizers are fermented animal and plant residues with elevated micro-nutrient content. They enhance the soil microflora and increase the soil organic matter content [8, 10]. Apart from using biofertilizers for their crops, there are also reports of small farms successfully selling this product.

A Western SARE on-farm biogas technology project completed by Washington State University demonstrated that AD is a technically and economically viable option for smaller farms. It involved the development of three easy-to-operate AD units at small farms in Washington which served as effective biogas reactors [9]. Also, a Southern SARE project in Florida focused on AD biofertilizer production on small farms. This effort emphasized the analysis of feedstock on small farms and the design of a biodigester [11]. Both SARE projects (Table 1) generated first-hand experience on the usability, benefits, and limitations of AD.

At Montana State University (MSU), members of the project team are currently collaborating with extension specialists in an EPA-funded project dedicated to the use of small-scale biodigesters for processing household food waste [12]. 

The present project by MSU researchers and collaborating farmers and extension agents builds on the experience gained in Washington and Florida and aims at generating professional development activities to enhance the proper adoption of AD technologies. We will develop a series of instructional videos where an experienced Montana farmer facilitates small-scale, on-farm AD solutions for farms in the Western region. We will generate a manual and organize a webinar for extension agents across the Western region. We will also conduct field demonstrations to facilitate the use of AD digestate as a biofertilizer, combining the results of the previously funded SARE project with experience from our EPA project. We expect that the successful implementation of our project will benefit from the currently favorable interest regarding AD [12] and enhance the environmental, social, and economic sustainability of small-scale farms. We do not expect natural or regulative limitations for generating and distributing our outreach material.

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