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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]

California is the leading dairy state in the United States. The total sale of milk and its products represents about $6.3 billion annually out of the $50 billion generated from all agricultural production in the state. However, methane emissions from dairy manure and enteric fermentation represented nearly half of all annual methane emissions in California, with dairy manure accounting for 25%, and enteric fermentation for 20%. Methane emissions originating from manure are produced primarily from anaerobic settling basins and lagoons, which are the most common manure storage systems in the state. To achieve sustainability on dairy farms and to comply with state regulations for air and climate pollutants, dairy farms have implemented technologies such as anaerobic digestion and alternative manure management technologies. In addition, governmental incentive programs have been deployed to partially fund these technologies for eligible dairies in the state. The present article reviews the design and operations, effectiveness, and economics of the most common technologies employed in Californian dairies in reducing methane emissions. The technologies studied include anaerobic digesters, mechanical separators, compost-bedded pack barns, manure vacuuming followed by drying, and weeping walls. The current status and estimated effectiveness of government incentive programs are reviewed and recommendations for improvements presented. Finally, future trends and research needs for mitigating the emissions in Californian dairies are identified. [ABSTRACT FROM AUTHOR]

This study quantifies the financial and environmental impacts of a microalgal bioenergy system that attempts to maximize circular flows by recovering and reusing the carbon, nutrients, and water within the system. The system produces microalgal biomass using liquid digestate of an anaerobic digester that processes 45 metric tons of food waste and generates 28.6 m3 of permeate daily in California, and three energy production scenarios from the biomass are considered: producing biodiesel, electricity, and both. In all scenarios, the resulting energy products delivered only modest reductions in environmental impacts as measured by carbon dioxide equivalent emissions. The carbon intensities (CIs) of biodiesel from this study were 91.0 gCO 2 e/MJ and 93.3 gCO 2 e/MJ, which were lower than 94.71 gCO 2 e/MJ of conventional petroleum diesel, and the CI of electricity from this study was 70.6 gCO 2 e/MJ, lower than the average electricity grid CI in California (82.92 gCO 2 e/MJ). The economic analysis results show that generating electricity alone can be profitable, while biodiesel produced via this system is not cost competitive with conventional diesel due to high capital expenses. Thus, generating electricity in lieu of biodiesel appears to be a better option to maximize the use of waste flows and supply lower-carbon energy. [Display omitted] • Permeate from a digester had sufficient nutrients for microalgae cultivation. • Combining anaerobic digestion and microalgae limitedly reduced environmental impacts. • Electricity generation better than biodiesel financially and environmentally. [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]