Systematic mineralogical and chemical changes occur in the ash or slag of biomass during combustion. These changes are a function of fuelcomposition, firing temperature, and firing duration. Controlled temperature experiments were conducted using clean samples of wood, rice straw, and wheat straw to evaluate trace element mobility as a function of firing temperature. The concentrations of major and trace elements in ash and slag were analyzed using various multi-element instrumental techniques. The recommended analytical methods and element combinations consists of X-ray fluorescence (XRF) (or similar methods) for major and minor elements, the majority of trace elements using inductively coupled plasma mass spectroscopy (ICPMS), and short irradiation duration instrumental neutron activation analysis (INAA) for the alkali metals and chlorine. There are distinct differences between the individual fuel ash types that easily allow fuel sources to be identified based on knowledge of ash compositions. A general increase occurs in residual concentrations of many elements with the removal of volatile constituents and increasing temperature. Depletion with increasing firing temperature was in this study particularly observed for the alkali metals (Na, K, Rb, Cs), but could also be seen for other elements (Cl, Ag, Cd, As, Se, and Pb). Fly ash from fuel-intake controlled experiments was also analyzed. Observations include: 1) strong fractionation occurs during combustion; 2) trace element concentrations are often strongly affected by contamination from plant construction materials; and 3) incorporation of urban fuel types can strongly affect many heavy metal concentrations. Among the fuel samples tested, enrichment of both barium and lead in wood ash resulted in concentrations slightly exceeding US Environmental Protection Agency’s (EPA) total constituent analysis limits for heavy metals. In ashes and fly ashes for which a significant component of urban wood material is involved, As, Cr, and Pb may variably exceed EPA limits. Metals in allstraw ashes tested were below the permitted limits. Leaching of straw ashes also depletes many alkali major and trace elements, although concerns may then arise as to concentrations in water or other solvent employed.

Escalating demands for infrastructure materials and energy worldwide necessitate exploration of means to efficiently utilize resources to support growing consumption. This work evaluates the potential symbiotic relationship between cultivation of an agricultural product (namely, rice), energy conversion, and utilization of bioash in the production of cement-based materials to improve the sustainability across multiple industries. Primarily, leaching methods of biomass that benefit energy conversion are evaluated as a means to simultaneously improve ash properties for use in cement-based materials. Specifically, this study considers water leaching and H3PO4 leaching of rice hulls and rice straw, which were subsequently ashed at three different temperatures, 600, 850, and 1100 °C. The effects of leaching on the ash characteristics, on the performance of ash-cement mortars, and on the greenhouse gas (GHG) emissions from both the mortars and energy produced are quantified. Findings showed that while acid leaching led to higher GHG emissions for electricity generation, leaching decreased concentrations of undesirable alkali metals and chlorides in the ash. Regardless of treatment and ashing temperature, the inclusion of bioash delayed the early strength development of the cement-based mortars. Yet, several permutations of treatment, feedstock type, and ashing temperature were found to contribute to the later-age strength development of cement-based materials while reducing related GHG emissions. Specifically, after 28 days of curing, mortars containing 15% cement replacement with unleached ash prepared at 600 °C had 1-5% lower compressive strength, and after 56 days, mortars with leached rice hull ash prepared at 600 °C had 5-6% lower compressive strengths. Further, the use of unleached and water-leached ashes in mortar led to reductions in GHG emissions up to 15%. Hence, this work shows that pretreatment methods applied to rice biomass residues may contribute to desirable cobenefits for energy and materials production.

Fresh-harvested, air-dried rice straw was pretreated at a water content of 5 g H2O/g straw using sodium hydroxide (NaOH) and compared to pretreatment at 10 g H2O/g straw by hydrated lime (Ca(OH)2). Full factorial experiments including parallel wash-only treatments were completed with both sources of alkali. The experiments were designed to measure the effects of alkaline loading and pretreatment time on delignification and sugar yield upon enzymatic hydrolysis. Reaction temperature was held constant at 95°C for lime pretreatment and 55°C for NaOH pretreatment. The range of delignification was 13.1% to 27.0% for lime pretreatments and was 8.6% to 23.1% for NaOH pretreatments. Both alkaline loading and reaction time had significant positive effects (p < 0.001) on delignification under the design conditions, but only alkaline loading had a significant positive effect on enzymatic hydrolysis. Treatment at higher temperature also improved delignification; delignification with water alone ranged from 9.9% to 14.5% for pretreatment at 95°C, but there was little effect observed at 55°C. Post-pretreatment washing of biomass was not necessary for subsequent enzymatic hydrolysis. Maximum glucose yields were 176.3 mg/g dried biomass (48.5% conversion efficiency of total glucose) in lime-pretreated and unwashed biomass and were 142.3 mg/g dried biomass (39.2% conversion efficiency of total glucose) in NaOH-pretreated and unwashed biomass.

Biofuels are expected to play a major role in meeting California's long-term energy needs, but many factors influence the commercial viability of the various feedstock and production technology options. We developed a spatially explicit analytic framework that integrates models of plant growth, crop adoption, feedstock location, transportation logistics, economic impact, biorefinery costs and biorefinery energy use and emissions. We used this framework to assess the economic potential of hybrid poplar as a feedstock for jet fuel production in Northern California. Results suggest that the region has sufficient suitable croplands (2.3 million acres) and nonarable lands (1.5 million acres) for poplar cultivation to produce as much as 2.26 billion gallons of jet fuel annually. However, there are major obstacles to such large-scale production, including, on nonarable lands, low poplar yields and broad spatial distribution and, on croplands, competition with existing crops. We estimated the production cost of jet fuel to be $4.40 to $5.40 per gallon for poplar biomass grown on nonarable lands and $3.60 to $4.50 per gallon for biomass grown on irrigated cropland; the current market price is $2.12 per gallon. Improved poplar yields, use of supplementary feedstocks at the biorefinery and economic supports such as carbon credits could help to overcome these barriers.

Biogas consisting primarily of methane (CH₄) and carbon dioxide (CO₂) can be upgraded to a transportation fuel referred to as renewable natural gas (RNG) by removing CO₂ and other impurities. RNG has energy content comparable to fossil compressed natural gas (CNG) but with lower life-cycle greenhouse gas (GHG) emissions. In this study, a light-duty cargo van was tested with CNG and two RNG blends on a chassis dynamometer in order to compare the toxicity of the resulting exhaust. Tests for reactive oxygen species (ROS), biomarker expressions (CYP1A1, IL8, COX-2), and mutagenicity (Ames) show that RNG exhaust has toxicity that is comparable or lower than CNG exhaust. Statistical analysis reveals associations between toxicity and tailpipe emissions of benzene, dibenzofuran, and dihydroperoxide dimethyl hexane (the last identification is considered tentative/uncertain). Further gas-phase toxicity may be associated with tailpipe emissions of formaldehyde, dimethyl sulfide, propene, and methyl ketene. CNG exhaust contained higher concentrations of these potentially toxic chemical constituents than RNG exhaust in all of the current tests. Photochemical aging of the vehicle exhaust did not alter these trends. These preliminary results suggest that RNG adoption may be a useful strategy to reduce the carbon intensity of transportation fuels without increasing the toxicity of the vehicle exhaust.

Agriculture in California contributes 8% of the state's greenhouse gas (GHG) emissions. To inform the state's policy and program strategy to meet climate targets, we review recent research on practices that can reduce emissions, sequester carbon and provide other co-benefits to producers and the environment across agriculture and rangeland systems. Importantly, the research reviewed here was conducted in California and addresses practices in our specific agricultural, socioeconomic and biophysical environment. Farmland conversion and the dairy and intensive livestock sector are the largest contributors to GHG emissions and offer the greatest opportunities for avoided emissions. We also identify a range of other opportunities including soil and nutrient management, integrated and diversified farming systems, rangeland management, and biomass-based energy generation. Additional research to replicate and quantify the emissions reduction or carbon sequestration potential of these practices will strengthen the evidence base for California climate policy.

Biogas is a renewable energy source composed of methane, carbon dioxide, and other trace compounds produced from anaerobic digestion of organic matter. A variety of feedstocks can be combined with different digestion techniques that each yields biogas with different trace compositions. California is expanding biogas production systems to help meet greenhouse gas reduction goals. Here, we report the composition of six California biogas streams from three different feedstocks (dairy manure, food waste, and municipal solid waste). The chemical and biological composition of raw biogas is reported, and the toxicity of combusted biogas is tested under fresh and photochemically aged conditions. Results show that municipal waste biogas contained elevated levels of chemicals associated with volatile chemical products such as aromatic hydrocarbons, siloxanes, and certain halogenated hydrocarbons. Food waste biogas contained elevated levels of sulfur-containing compounds including hydrogen sulfide, mercaptans, and sulfur dioxide. Biogas produced from dairy manure generally had lower concentrations of trace chemicals, but the combustion products had slightly higher toxicity response compared to the other feedstocks. Atmospheric aging performed in a photochemical smog chamber did not strongly change the toxicity (oxidative capacity or mutagenicity) of biogas combustion exhaust.

Background: Climate-smart agriculture (CSA) addresses the challenge of meeting the growing demand for food, fibre and fuel, despite the changing climate and fewer opportunities for agricultural expansion on additional lands. CSA focuses on contributing to economic development, poverty reduction and food security; maintaining and enhancing the productivity and resilience of natural and agricultural ecosystem functions, thus building natural capital; and reducing trade-offs involved in meeting these goals. Current gaps in knowledge, work within CSA, and agendas for interdisciplinary research and science-based actions identified at the 2013 Global Science Conference on Climate-Smart Agriculture (Davis, CA, USA) are described here within three themes: (1) farm and food systems, (2) landscape and regional issues and (3) institutional and policy aspects. The first two themes comprise crop physiology and genetics, mitigation and adaptation for livestock and agriculture, barriers to adoption of CSA practices, climate risk management and energy and biofuels (theme 1); and modelling adaptation and uncertainty, achieving multifunctionality, food and fishery systems, forest biodiversity and ecosystem services, rural migration from climate change and metrics (theme 2). Theme 3 comprises designing research that bridges disciplines, integrating stakeholder input to directly link science, action and governance. Outcomes: In addition to interdisciplinary research among these themes, imperatives include developing (1) models that include adaptation and transformation at either the farm or landscape level; (2) capacity approaches to examine multifunctional solutions for agronomic, ecological and socioeconomic challenges; (3) scenarios that are validated by direct evidence and metrics to support behaviours that foster resilience and natural capital; (4) reductions in the risk that can present formidable barriers for farmers during adoption of new technology and practices; and (5) an understanding of how climate affects the rural labour force, land tenure and cultural integrity, and thus the stability of food production. Effective work in CSA will involve stakeholders, address governance issues, examine uncertainties, incorporate social benefits with technological change, and establish climate finance within a green development framework. Here, the socioecological approach is intended to reduce development controversies associated with CSA and to identify technologies, policies and approaches leading to sustainable food production and consumption patterns in a changing climate.