Co-treatment of Animal Manure and Other Wastes
In the last two decades, the term, “Sustainable Agriculture”, has moved to the center stage of the agricultural economy and has topped the news headlines in both the US and the world, simply because it has become increasingly clear that the current development that aims to meet the needs of the present generation is compromising the ability of future generations to meet their own needs. To turn this trend around requires the agricultural community to ameliorate the negative impact of agricultural activities on the finite natural resources and the environment, so continued growth in food production and agricultural economy, and betterment in social well-beings as a whole can be sustained. To that end, effective technologies to improve our ability to not only reduce the polluting power of agricultural wastes, but also recycle them to the extent possible into renewable products that can offset the consumption of fossil fuel based energy and fertilizer have to be developed and put in use.
Literature information indicates that any single process of bioenergy production such as hydrogen fermentation or methane digestion will normally lead to either a net energy loss or underutilized substrates. However, a net energy gain may be achieved by forming a system that produces multiple renewable products with minimum emissions of greenhouse gases. For instance, methane production from swine manure has been studied at great length in the past and the technology has been well established. However, the vast majority, if not all, of the previous studies solely dealt with methane generation without considering hydrogen as an intermediate product during the digestion process. In other words, the focus of interest in the early studies is on the so called one-stage digestion process with one end product which is methane. According to the biochemistry of methane digestion, there are three major steps involved, i.e., hydrolysis, acidogenesis/acetogenesis, and methanogenesis, and hydrogen is produced during the second step together with various volatile fatty acids (VFAs) that are the precursors for methane generation in the third step (methanogenesis). A major drawback with the traditional one-stage process is that it cannot create an optimal environment simultaneously in a single reactor for both the acid-forming and methane-producing microbial consortia because these two groups of bacteria require totally different pH ranges (4.5-6 for the former and 6.5-7.5 for the latter). Therefore, in this project, a two-stage anaerobic configuration consisting of a hydrogen fermenter (first stage) and an anaerobic digester (second stage) will be proposed followed by a gas cleaning unit and a struvite precipitator to produce an organic fertilizer from the digester effluent. The long-term goal of this project is to promote and establish sustainable agriculture in Arkansas and the US by developing a novel treatment system to recycle agricultural wastes into renewable products, thus conserving natural resources and maintaining environmental sustainability.