Continuous plug-flow dry anaerobic digestion
For both waste collection avenues, dry AD technology plays an important role in the processing of organic waste to energy and fertilizer. Dry AD technology can process many mixtures of organic material with average dry matter contents of 20% to 50%.
These “solid” waste streams would need to be diluted to be processed in larger volume “wet” AD reactors with dry matter contents of less than 15%. These wet systems, although designed as fully stirred reactor tanks, are subject to solids accumulation over time and related shutdowns to maintain active volume. Wet AD systems are typically designed for liquid or pumpable slurries and manure, wastewater treatment plant sludge, or liquid effluents from food or beverage producers.
Veolia has extensive global experience operating various AD, composting and MBT plants. Continuous thermophilic (53-55°C) AD technology employing horizontal plug-flow has proven to be particularly robust and efficient. This process type achieves a nearly perfect conversion of degradable organic matter into biogas, maximizing energy yield. Thermophilic AD also kills pathogens, seeds and germs in a very compact reactor.
In contrast, non-continuous or batch dry AD processes are not completely closed, potentially releasing both odours and methane gas. In terms of efficiency, batch dry AD processes may lose part of the methane while percolating, since only the organic “juices” are digested. This results in undigested organics attached to residual solids and explosion risks due to an oxygen rich environment.
The Kompogas® process
In 2012, Veolia Water Technologies Canada started to look for an appropriate technology for high solids AD applications. The selection criteria were: availability, efficiency, simplicity and safety. The Kompogas plug-flow AD best met these criteria, and has two decades of proven operation with over 75 installations.
A wide range of input materials can be processed in a Kompogas reactor module, such as:
• Bio-waste and food leftovers from households.
• Food waste from commercial caterers, including oils and fats from restaurants, cafeterias, etc.
• Unpacked organic waste from supermarkets and industrial food processors.
• Green waste from private yards and public works.
• Organic fraction of municipal solid waste.
This modular solution has a standard design and processing train for most SSO applications.