Biogas through Anaerobic Digestion from Waste Streams as a Renewable Transportation Fuel - A Brief Review of Technology

Upgraded and purified biogas from anaerobic digestion, also known as biomethane, is an environmentally friendly renewable transportation fuel that is already commercially available for road transports. Biomethane shows low emissions of greenhouse gases compared to other transportation fuels, especially if waste streams are used as feedstock, and the emissions can even be negative in the case of manure. In this review, a technical overview is given for the available technology and how to process different organic waste streams and convert them to transportation fuel. The dry solids content (i.e. the viscosity) and particle size are the most important parameters determining the type of technology to be used: a sugar rich water stream is very different from agricultural crop residues. Another important aspect is the amount of contamination and unwanted material in the feedstock, since it is desirable to produce a high value digestate that can be used to fertilize agricultural land. The carbon dioxide separated from the biogas during the upgrading to biomethane can also be considered as a valuable by-product, and here there is room for development. It is also desirable to improve the productivity of the process by increased methane yield and higher energy efficiency, and there are opportunities for better overall resource efficiency and economy if the production is integrated with other processes.