8Apr2016

Anaerobic Digesters Reduce Fossil-Fuel DependencePosted by Sudhir

Engineers have experimented with anaerobic digestion as a way to create energy since the 1800s. For example, some British communities were using biogas captured from sewage treatment operations to power street lamps over 100 years ago. However, throughout the twentieth century, the abundance and relatively low cost of gas, oil, and coal has made it economically impractical to develop more advanced and larger-scale anaerobic digester technologies, especially in the U.S.

This is starting to change, however. Anaerobic digestion a straightforward, well-understood process that can now be cost-effective compared to fossil fuels. Its positive impacts on the environment are also desirable. Small-scale digesters have been used successfully for years to provide energy and heat in developing countries (more than 8 million small-scale digester systems are estimated to be in use in China). This overall increased awareness is leading to the establishment of larger-scale anaerobic digestion systems in Europe and North America that produce thousands of kWh of renewable electricity on a daily basis.

Straightforward Technology

Anaerobic digestion is a natural process by which bacteria break down organic matter in an oxygen-free environment to form biogas and a digestate. Feedstock can be food waste, manure, sewage, or other organic matter. Depending on the type of bacteria used, operating temperatures are typically 35° C (95° F) or 55° C (131° F). Precise temperature control is required to optimize the bacteria’s rate of activity. The final product is a biogas mixture of methane and carbon dioxide that can be used as a fuel for generating electricity; the digestate is usually spread on agricultural fields as a fertilizer.

Environmental benefits of anaerobic digestion include the capture and use of greenhouse gas emissions, reduced reliance on fossil fuels, and reduced volumes of stored waste, which lessens the environmental risks of manure run-off and groundwater contamination. Being able to process waste organic matter through anaerobic digestion also relieves disposal burden on municipal landfills.

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