Enhancing the resource potential of anaerobic digestion

Anaerobic Digestion can provide a renewable source of acetic, propionic and butyric acids.  Prior research into the behavior of anaerobic digestion of sludge and food waste has focused on maximizing methane production.  This research studied the conditions of organic acid production that were optimal for methanogenesis.  Organic acids, such as acetic, propionic and butyric, have existing markets in the production of plastics, solvents, fuels, and pharmaceuticals and their values range from 4 to 16 times that of methane per unit mass if recovered and purified.  Research has demonstrated that there is a positive linear relationship between volatile solids loading of the substrate undergoing digestion and the resulting concentration of organic acids. However, loading rates above 60 g/L solids had yet to be examined.  Solids concentrations above 60 g/L for food waste and sludge were tested in acid phase digesters at varying pH, temperatures, and retention times.  The outcome of this research is a three-dimensional surface plot that indicates the best conditions for acetic, propionic, and butyric acid production.  The surface plots also include the concentration of methane, hydrogen, and carbon dioxide in the gas phase of the digester output.  The data collected in this study will be used to evaluate recovery methods for organic acids from a renewable source.