Shifts in structure and dynamics of the soil microbiome in biofuel/fuel blend-affected areas triggered by different bioremediation treatments.

The use of biofuels has grown in the last decades as a consequence of the direct environmental impacts of fossil fuel use. Elucidating structure, diversity, species interactions, and assembly mechanisms of microbiomes is crucial for understanding the influence of environmental disturbances. However, little is known about how contamination with biofuel/petrofuel blends alters the soil microbiome. Here, we studied the dynamics in the soil microbiome structure and composition of four field areas under long-term contamination with biofuel/fossil fuel blends (ethanol 10% and gasoline 90%-E10; ethanol 25% and gasoline 75%-E25; soybean biodiesel 20% and diesel 80%-B20) submitted to different bioremediation treatments along a temporal gradient. Soil microbiomes from biodiesel-polluted areas exhibited higher richness and diversity index values and more complex microbial communities than ethanol-polluted areas. Additionally, monitored natural attenuation B20-polluted areas were less affected by perturbations caused by bioremediation treatments. As a consequence, once biostimulation was applied, the degradation was slower compared with areas previously actively treated. In soils with low diversity and richness, the impact of bioremediation treatments on the microbiomes was greater, and as a result, the hydrocarbon degradation extent was higher. The network analysis showed that all abundant keystone taxa corresponded to well-known degraders, suggesting that the abundant species are core targets for biostimulation in soil remediation processes. Altogether, these findings showed that the knowledge gained through the study of microbiomes in contaminated areas may help design and conduct optimized bioremediation approaches, paving the way for future rationalized and efficient pollutant mitigation strategies.

Evolution of Vehicle Emission Factors in a Megacity Affected by Extensive Biofuel Use: Results of Tunnel Measurements in São Paulo, Brazil.

Since 2001, four emission measurement campaigns have been conducted in multiple traffic tunnels in the megacity of São Paulo, Brazil, an area with a fleet of more than 7 million vehicles running on fuels with high biofuel contents: gasoline + ethanol for light-duty vehicles (LDVs) and diesel + biodiesel for heavy-duty vehicles (HDVs). Emission factors for LDVs and HDVs were calculated using a carbon balance method, the pollutants considered including nitrogen oxides (NOx), carbon monoxide (CO), and sulfur dioxide, as well as carbon dioxide and ethanol. From 2001 to 2018, fleet-average emission factors for LDVs and HDVs, respectively, were found to decrease by 4.9 and 5.1% per year for CO and by 5.5 and 4.2% per year for NOx. These reductions demonstrate that regulations for vehicle emissions adopted in Brazil in the last 30 years improved air quality in the megacity of São Paulo significantly, albeit with a clear delay. These findings, especially those for CO, indicate that official emission inventories underestimate vehicle emissions. Here, we demonstrated that the adoption of emission factors calculated under real-world conditions can dramatically improve air quality modeling in the region.

Anaerobic biodegradation of dissolved ethanol in a pilot-scale sand aquifer: Gas phase dynamics.

Groundwater contamination from ethanol (e.g., alternative fuels) can support vigorous biodegradation, with many possible reactions producing dissolved gases. The objective of this study was to improve the understanding of the development and evolution of trapped gas phase changes occurring within an ethanol plume undergoing biodegradation. The experiment performed involved highly detailed spatial and temporal monitoring of gas phase saturations using Time Domain Reflectometry probes embedded in a 2-dimensional (175 cm high × 525 cm long) synthetic aquifer (homogeneous sand tank with horizontal groundwater flow). Ethanol injection immediately promoted gas-producing reactions, including: fermentation, denitrification, sulphate-reduction and iron(III)-reduction, with methanogenesis developing between 69 and 109 days. Substantial in situ increases in trapped gas were observed over ~330 days, with maximum gas saturations reaching 27% of the pore volume. Despite sustained gas production, this maximum was never exceeded, likely due to the onset of gas phase mobilization (i.e., ebullition) upon reaching a buoyancy-capillarity threshold. Reductions in the quasi-saturated hydraulic conductivity, resulting from the gas phase accumulation, were restricted by ebullition to a factor of ≤2; but still appeared to alter the groundwater flow field. Overall, trapped gas saturations exhibited high spatial and temporal variability, including declines within the plume and increases outside of the plume. Influential factors included vertically-shifting ethanol inputs and resultant secondary redox reactions, microbial controls on redox zonation, ebullition, and altered groundwater flows. These observations have implications for the transport of gases and volatile compounds within plumes and above the water table at sites with groundwater contamination from ethanol or other highly degradable organics.

Anaerobic biodegradation of dissolved ethanol in a pilot-scale sand aquifer: Variability in plume (redox) biogeochemistry.

The use of ethanol in alternative fuels has led to contamination of groundwater with high concentrations of this easily biodegradable organic compound. Previous laboratory and field studies have shown vigorous biodegradation of ethanol plumes, with prevalence of reducing conditions and methanogenesis. The objective of this study was to further our understanding of the dynamic biogeochemistry processes, especially dissolved gas production, that may occur in developing and aging plume cores at sites with ethanol or other organic contamination of groundwater. The experiment performed involved highly-detailed spatial and temporal monitoring of ethanol biodegradation in a 2-dimensional (175cm high×525cm long) sand aquifer tank for 330days, with a vertical shift in plume position and increased nutrient inputs occurring at ~Day 100. Rapid onset of fermentation, denitrification, sulphate-reduction and iron(III)-reduction occurred following dissolved ethanol addition, with the eventual widespread development of methanogenesis. The detailed observations also demonstrate a redox zonation that supports the plume fringe concept, secondary reactions resulting from a changing/moving plume, and time lags for the various biodegradation processes. Additional highlights include: i) the highest dissolved H2 concentrations yet reported for groundwater, possibly linked to vigorous fermentation in the absence of common terminal electron-acceptors (i.e., dissolved oxygen, nitrate, and sulphate, and iron(III)-minerals) and methanogenesis; ii) evidence of phosphorus nutrient limitation, which stalled ethanol biodegradation and perhaps delayed the onset of methanogenesis; and iii) the occurrence of dissimilatory nitrate reduction to ammonium, which has not been reported for ethanol biodegradation to date.

Importância do etanol na atenuação natural de águas subterrâneas impactadas por gasolina / Importance of ethanol on natural attenuation of groundwater impacted by gasohol

Nesse estudo, foram avaliados os resultados de um experimento de derramamento controlado de gasolina brasileira em água subterrânea durante 6,5 anos de monitoramento. A exaustão do etanol, aos 32 meses de monitoramento, e a significativa redução de mais de 90 por cento da massa máxima dos compostos BTEX dissolvidos no meio, aos 79 meses, associadas ao uso dos receptores de elétrons e acúmulo de seus subprodutos metabólicos, demonstraram a eficácia da atenuação natural monitorada para contaminações de águas subterrâneas sem riscos imediatos a receptores críticos. Constatou-se ainda que a biodegradação do etanol permitiu a formação de uma biobarreira natural que, após a sua completa degradação, acelerou a taxa de biodegradação dos BTEX e impediu o avanço da pluma destes contaminantes.

In this study, results of 6.5 years of a controlled release experiment with Brazilian gasoline in groundwater were evaluated. Ethanol exhaustion after 32 months and the significant dissolved BTEX mass reduction of more than 90 percent after 79 months, associated with the electron acceptors use and their metabolic byproducts accumulation, demonstrated the efficiency of monitored natural attenuation for groundwater contamination without immediate risk to receptors. Moreover, ethanol degradation provided a natural biobarrier formation that increased BTEX biodegradation rate and prevented the BTEX plume expansion.