Search

This study was carried out in order to analyze characteristic and composition of crops, crop wastes, and residues including a variety of sugar beets and melons, tomato, Jose tall wheatgrass, wheat hay, and wheat straw in California. Ethanol potential was estimated from different scenarios in using carbon sources of feedstock during fermentation, including the new information of using pectin–derived galacturonic acid for ethanol production. Sugar beet appears more favorable than other feedstocks because of its high sugar content (67–75% dry basis, db) and the highest crop yield, resulting in the greatest ethanol potential of 591 m 3 Gg −1 db when all carbohydrates are used during fermentation, with the California area–based potential of 1273 m 3 km −2 . Fermentation of polygalacturonic acid can increase the ethanol potential of sugar beet leaves up to 30% over the fermentation of hexoses alone, increasing the theoretical ethanol potential to 340 m 3 Gg −1 and the area–based yield of 497 m 3 km −2 . Melons and tomato containing 42–69% by mass of soluble sugars showed ethanol potentials in a range of 448–545 m 3 Gg −1 db and the area–based yield of 25–53 m 3 km −2 . The theoretical ethanol yield from lignocellulosic feedstocks tested can be maximized up to 470–533 m 3 Gg −1 db and 291–300 m 3 km −2 when the primary components from cellulose (27–39% db) and hemicellulose (26–30% db) are utilized. The information on composition and ethanol potential is important for determining biofuel feedstock and developing technology for efficient use of bioresource. [ABSTRACT FROM AUTHOR]

A small-scale, transportable membrane upgrading system designed to purify biogas was tested at two food waste digesters and one dairy digester. The system had a rated capacity of 100 Nm3 h−1 raw biogas making it suitable for the many small-scale biogas production facilities being developed across California. The membrane removed a majority of the carbon dioxide from the biogas with performance matching expected targets. The membrane system also removed trace levels of aldehydes, ketones, siloxanes, halocarbons, and sulfur-containing compounds from the biogas, mainly because the pre-cleaning steps removed these contaminants from the gas stream. The average composition of upgraded biomethane produced by the membrane system satisfied the trace contaminant requirements for pipeline injection in California. Residual air in the biogas was not removed efficiently by the membrane system which prevented methane concentrations from reaching levels sufficient to meet the heating value requirements for pipeline injection. Dedicated upgrading plants could carefully eliminate air leakage to address this issue, and/or mix propane into the biomethane to achieve the target heating value. An economic model developed for small scale biogas production facilities predicted that capital costs for a typical small-scale membrane separation plant exceed $2.46 million and projects only become financially viable over a 15 year return period when natural gas prices exceed $21.92 GJ−1. Current market prices for petroleum natural gas are far below this level, and so financial incentives will be required to make small-scale biogas projects using membrane separation technology viable in the near term. • A small-scale membrane separation unit was tested for biogas upgrading in California. • Pre-cleaning steps removed most trace contaminants but breakthrough occurred. • Air injection used at most sites prevented upgrading gas to pipeline quality. • Upgrading at small-scales requires subsidies to be economically feasible. [ABSTRACT FROM AUTHOR]