Peak ambient dusts levels in the San Joaquin Valley (SJV) are often coincident with peak agricultural harvest seasons, particularly for nut orchards. Federal reference methods (FRMs), consist of mass-based sampling techniques, are designated to measure and analyze ambient dust concentrations. However, FRMs generally require meticulous attention to sampling details, tedious labor and logistics, and time-consuming dispersion calculations. This study used opacity-based techniques - the U.S. Environmental Protection Agency (EPA) Method 9 and the Digital Compliance Opacity Technique (DCOT) - to quickly measure relative dust intensity at different harvester settings, and to evaluate visible dust emission reductions using a new/low-dust nut harvester. Results indicate that old/conventional harvester at standard settings (3 mph ground speed and 900 rpm blower speed) produced visible dusts with opacities ranging from 23.3% - 29.0%. The dust plume generated from new/low-dust harvesters at similar settings registered lower opacity readings, with an average of 13.94%. The lowest average dust opacity (7.8%) was achieved when the separation fan was turned off. The present results validated the previous FRM emission findings that an old/conventional harvester has the highest PM emissions, but with a potential to achieve 50% reduction by adopting new/low-dust harvesters. Compared to an old harvester, the relative intensity of dusts was reduced by 40% - 51% for low-dust harvesters operated at lower ground speeds. Further dust reductions could be achieved by lowering the fan speed (58%) and operating at no fan/blower setting (66.4%). Both visible emission evaluation (VEE) techniques were able to provide rapid quantitative feedback on the effects of operational changes on emitted harvest dusts. At this stage, opacity-based techniques can potentially be adapted as a screening tool for identifying best management practices (BMP) in reducing harvest dusts, rather than to solely rely on FRM mass-based techniques.

Converting heterogeneous waste streams into stable carbon materials while minimizing environmental risk is an important goal in sustainable waste management. In this study, waste-derived biochars produced at 500 °C from municipal solid waste (MSW), end-of-life rubber tires (RT), and wood waste (WW) were evaluated for long-term carbon stability and short-term soil chemical responses. Carbon stability was assessed using elemental ratios, fixed carbon content, carbon yield, and carbon sequestration efficiency. Biochars derived from MSW and RT showed low H/C and O/C ratios, high fixed carbon contents, and retained approximately one-third of their original feedstock carbon, indicating strong potential for long-term persistence in soil environments. Short-term soil chemical responses were characterized using a controlled soil incubation. Changes in soil chemistry were primarily associated with limited ash dissolution rather than nutrient enrichment. Electrical conductivity increased moderately but remained below salinity thresholds, and exchangeable calcium (Ca) increased consistently across treatments. Soil pH declined slightly in soils amended with MSW and RT biochars, while WW biochar caused minimal change. Micronutrient behavior varied by feedstock. Copper (Cu) and manganese (Mn) generally declined, suggesting immobilization on biochar surfaces, whereas zinc (Zn) decreased in soils amended with MSW and WW biochars but increased with RT biochar due to its inherent Zn content. Trace metal concentrations in all biochars were below international guideline values, although their long-term mobility under field-relevant dynamic conditions remains uncertain. Overall, the results indicate that waste-derived biochars provide chemically stable carbon inputs to soils, with short-term soil chemical responses serving as indicators of environmental compatibility.

End-of-life tires (ELTs) and refuse-derived fuel (RDF) produced from municipal solid waste (MSW) contain recoverable carbon (C), nitrogen (N), and chemical energy. This study evaluated pyrolysis as a resource-routing approach by comparing ELT and RDF under a common 500 °C batch condition. Product yields, elemental routing, energy retention, and downstream utilization potential were assessed across char, liquid, and gas streams. ELT retained 82.6% of feed carbon and 86.2% of feed energy in char and liquid products, whereas RDF retained 62.4% of feed carbon and 44.6% of feed energy in these condensed streams and produced a larger apparent gas fraction. Nitrogen routing also differed markedly: ELT distributed N relatively evenly between char and liquid, while RDF retained 61.3% of its initial N in char despite containing approximately seven times more N per unit mass of prepared feedstock. ELT produced carbon-rich char and an energy-dense liquid requiring upgrading, while RDF showed greater carbon and nitrogen retention in char and generated a predominantly aqueous condensate. Screening against published utilization studies and relevant product criteria identified plausible material, chemical, and energy-recovery pathways. Overall, the findings highlight the importance of feedstock-specific elemental routing and product quality in evaluating resource recovery, providing a practical basis for integrating thermochemical conversion into circular waste-management systems.