Several barriers exist that make many industries and farmers reluctant to imple­ment AD to convert their biomass wastes to methane biogas. Improvements in AD technologies with respect to efficiency, reliability, and cost-effectiveness will overcome some of the barriers related to the technologies. Other barriers can only be debased from policy and public supports. While it is broadly realized that the building of a sustainable society requires both renewable energy and protection of the environment, the valuation of such is incomplete. AD is one of the few tech­nologies that help achieve both goals. Even the bioethanol and biodiesel industries generate biomass wastes, which need AD to extract otherwise wasted energy and to reduce environmental pollution. Therefore, AD should be regarded as a unique, indispensable, renewable energy-producing biotechnology that protects the environ­ment. With continued improvement of AD technologies and supports from both the public and the government, AD will become more cost-effective, energy-efficient, reliable, and widely implemented. AD will evolve into one of the most environment — friendly biotechnologies that produce cost-effective bioenergy in the next five to ten years.

Acknowledgement Research in our laboratories is supported by grants awarded from DOE and the Ohio Third Frontier Project. We thank Dr. Mark Morrison for his helpful discussions during the preparation of this chapter.