ABSTRACT

Land that is used for disposing biodegradable materials such as food, plant and paper wastes is effectively put out of use forever. A city of 150,000 effectively wastes about five acres per year to dispose its wastes in what is called, euphemistically, a “landfill”. In addition, such a landfill remains for centuries after closure a source of potent greenhouse gases (methane, etc.) and leachate solutions. This paper will discuss the design of a re-usable landfill: The Aerobic Bioconversion Cell. The preferred values of operating parameters and of the biochemical rate constants of oxidation to CO2 and H2O were identified. Energy and material balances were then constructed for a large, 3-m deep aerobic cell holding 1,440 tons of the ‘wet’ component of organic wastes (major organic constituent: [C6H10O4]n). It was found that conduction/convection and radiation losses to the surroundings amount to a relatively small fraction of the chemical heat released by oxidation. The excess heat must be removed by means of an upward water-saturated air flow that is several-fold the stoichiometric requirement for oxidation. From a process engineering viewpoint, the principal difference between anaerobic and aerobic biodegradation is that in the former much of the chemical heat contained in the wastes is transformed to methane and, if collected, can be used as a fuel elsewhere. In the case of aerobic oxidation in a packed bed reactor, this heat is released by oxidation and need to be removed by a very large flow of air through the bed.