Researcher Univeristy of Texas at Arlington Arlington, TX, United States
Lignocellulose comprises a significant portion of municipal solid waste (MSW) - 40-70% in developed countries, including paper, wood, yard waste, and textiles such as cotton fibers (Li et al., 2009). Cellulose, the main biodegradable plant polymer, is often shielded by lignin, as well as hemicellulose. Lignin is unfortunately resistant to microbial degradation under anaerobic conditions that normally occur in MSW landfills. Lignin destruction can make cellulose and hemicelluloses available for anaerobic microbial conversion to biogas. This could potentially increase a landfill’s methane production by a factor of 2-3, depending on waste composition. The Termite-associated Verrucomicrobium, strain TAV5, a microaerophilic bacterium isolated from the hindgut of the Reticulitermes flavipes termite, contains genes which code for enzymes that structurally modify lignin. The overall goal of this research was to increase lignin decomposition of MSW and boost methane production, via TAV5. Specific objectives were: 1. To determine the optimum ratio of TAV5 to traditional methane-producing microorganisms for waste degradation and methane production, using batch reactor tests. 2. To compare the effectiveness of TAV5 cultured at 2% oxygen and 40°C, to TAV5 cultured at 20% oxygen and room temperature, in breaking down lignin-containing waste for methane production, using batch reactor tests. 3. To test the effectiveness of the optimum ratio of TAV5 in degrading lignocellulose and generating methane at 40°C in lab-scale landfill reactors for separated types of waste and mixed waste.
To accomplish the objectives, three kinds of waste, including paper and cardboard, yard waste and wood, were collected. 72 batch scale reactors were prepared with selected MSW and different ratios of TAV5 to anaerobic digester microorganisms and incubated at 40º C. In the batch scale reactors, 3 different types of separated waste and 4 different ratios of mixed of waste were tested to see the effect of results of TAV5 ratios. Based on the preliminary studies on batch scale tests, five 6-gallon laboratory reactors were conducted for wood, mixed of waste with equal weight ratio and yard and incubated at 40º C, the leachate were recirculated, and the pH level were controlled in the recirculated leachate. Addition of TAV5 increased methane production from paper, yard, and wood waste, as well as reduced the lignin percent. At optimal ratios of TAV5, 49%, 34%, and 297% more methane was generated from mixed waste (paper, yard and wood), yard waste, and wood waste, respectively, compared to reactors seeded with anaerobic digester microorganisms alone (Fig. 1). TAV5 was most effective in facilitating acid-soluble lignin break-down for paper waste (additional 39%), followed by yard waste (additional 30–31%) and then wood waste (additional 7–30%).
