Anaerobic digestion of solid wastes: process enhancements; synergistic effect of food waste on digestibility of lignocellulosic fibres

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Vast quantities of garbage are sent to landfill every day. A significant fraction of this waste is organic and decomposes naturally to produce leachate and landfill gas, both threats to the environment. Anaerobic digestion (AD) occurs naturally in the absence of oxygen as microbes break down organic materials to biogas, a mixture of methane (CH4) and carbon dioxide (CO2). Harnessing this process in engineered reactors captures biogas to make energy and reduces the amount of solid material for disposal. ****A new novel approach to AD has been designed explicitly to be versatile, robust, and affordable in North America. This AD approach features no energy-intensive mixing of the solid waste. A recently completed research program (supported by NSERC CRDPJ 459122-13) demonstrated that the technology is indeed robust and versatile, and capable of treating a wide range of organic wastes of variable composition. Two surprising findings came from this recently completed research: 1) that overall solid waste conversion to biogas (i.e., the biogas yield) was as high as that achieved in well-mixed stirred tank reactors, and 2) that digestion of lignocellulosic fibers in the waste was significantly enhanced by the presence and digestion of food waste. ****The objective of this new proposed CRD program is to investigate the fundamental principles that enabled such high biogas yields, and to determine the process variables of critical importance to the design and operation of a planned commercial demonstration project in east end of Ottawa. The same laboratory-scale two-stage anaerobic digester used in the initial research will be upgraded and recommissioned for this purpose, and a series of experiments will be conducted to establish the fundamental basis underlying good performance. Process modelling and verification in a scaled-up demonstration unit in Ottawa will enable a true validation of the results.