Unmasking air quality: A novel image-based approach to align public perception with pollution levels

In the quest to reconcile public perception of air pollution with scientific measurements, our study introduced a pioneering method involving a gradient boost-regression tree model integrating PM2.5 concentration, visibility, and image-based data. Traditional stationary monitoring often falls short of accurately capturing public air quality perceptions, prompting the need for alternative strategies. Leveraging an extensive dataset of over 20,000 public visibility perception evaluations and over 8,000 stationary images, our models effectively quantify diverse air quality perceptions. The predictive prowess of our models was validated by strong performance metrics for perceived visibility (R = 0.98, RMSE = 0.19), all-day PM2.5 concentrations (R: 0.77-0.78, RMSE: 8.31-9.40), and Central Weather Bureau visibility records (R = 0.82, RMSE = 9.00). Interestingly, image contrast and light intensity hold greater importance than scenery clarity in the visibility perception model. However, clarity is prioritized in PM2.5 and Central Weather Bureau models. Our research also unveiled spatial limitations in stationary monitoring and outlined the variations in predictive image features between near and far stations. Crucially, all models benefit from the characterization of atmospheric light sources through defogging techniques. The image-based insights highlight the disparity between public perception of air pollution and current policy implementation. In other words, policymakers should shift from solely emphasizing the reduction of PM2.5 levels to also incorporating the public's perception of visibility into their strategies. Our findings have broad implications for air quality evaluation, image mining in specific areas, and formulating air quality management strategies that account for public perception.

Dynamic life cycle assessment for water treatment implications

Long-term impact tracking of urban water services is an important scientific basis for the sustainable development goals of future foreground systems. This study developed a dynamic life cycle assessment (DLCA) method that considers temporal variation and the resulting impacts to address the challenges of water treatment facilities based on the principles of life cycle assessment (LCA) and system dynamics (SD) models. The model was then demonstrated and validated for a water treatment facility in the Kinmen Islands, Taiwan. The SD model simulates long-term water demand in terms of growth in the domestic, agriculture, livestock, and manufacturing sectors, which provides specific inventory data for LCA calculations, with the aim of showing the impact change for future water treatment scenarios. The results showed that using imported water and reclaimed water reduced Kinmen's reliance on groundwater from 77 % to 43 % and reduced the vulnerability of urban water services. The environmental impact of water treatment plants is determined to be strongly related to the efficiency of water treatment. In the long run, wastewater treatment plants can reduce their impacts with an increase in efficiency (3.7 % impact reduction). Additionally, the development of reclaimed water technology and water savings can reduce the impact by 19 % and 13.7 %, respectively, compared to the implementation of desalination. In terms of energy policy, more profound energy savings were observed when energy saving and structure transformation were simultaneously carried out. On the other hand, desalination poses the most political risk and has energy-associated environmental impacts. The DLCA results from this study showcase the trend of impact variation over time and thus provide valuable insights for future policy-making in mapping out the benefits and priorities of policy promotion.

Spatial allocation of LID practices with a water footprint approach

Urban water problems due to stormwater have been aggravated by the higher frequency of high-intensity precipitation events and the increase of paved surfaces. However, with appropriate stormwater management practices, such as low-impact development (LID), stormwater can provide an additional urban water resources rather than cause damage. This study aims to apply a water footprint to location determination of LID practices in the urban area. The LID planning procedure was demonstrated with the highest population density region in Taipei, Taiwan. In order to improve the spatial resolution of LID allocation, the "first-level dissemination area" with 450 residents was used as a spatial unit. The performance of LID practices was then evaluated with the simulation using the Storm Water Management Model (SWMM). Three LID practices, rainwater harvesting systems, permeable pavements, and bioretention systems, were selected. After the water footprint accounting, ten sites were suggested for LID implementation. The runoff reduction rate reached up to 65 % by rainwater harvesting systems or at least 3 % by permeable pavements. This study provides a simpler and more effective approach to ways of integrating an urban water footprint into LID planning and stormwater management in urban areas.

Carbon capture of biochar produced by microwave co-pyrolysis: adsorption capacity, kinetics, and benefits

Microwave co-pyrolysis of sewage sludge and leucaena wood was conducted to produce biochar as an adsorbent for CO₂ capture. Both microwave power level and blending ratio were crucial factors affecting the CO₂ adsorption capacity of biochar. At a power level of 150 W, the biochar produced by microwave co-pyrolysis of 25% sewage sludge and 75% leucaena wood possessed the highest CO₂ adsorption capacity. When the biochar was produced at 100 W, its CO₂ adsorption capacity was higher than predicted. Based on the proximate and elemental compositions of biochar, two equations were obtained to predict CO₂ adsorption capacity. The proximate composition of biochar can provide more precise prediction of CO₂ adsorption capacity than elemental composition according to the higher R² value provided. The blending ratio of 50% would be most appropriate to produce the biochar with acceptable reduction in CO₂ adsorption capacity and loss of quantity. The pseudo-second-order model would be most suitable for simulating the kinetic of CO₂ adsorption. The biochar produced from 1 metric tonne of sewage sludge and leucaena wood can offset carbon tax by 83 US dollars. Based on experimental results and findings, microwave co-pyrolysis should be a feasible technique to produce biochar possessing high CO₂ adsorption capacity.

Spatiotemporal impact of COVID-19 on Taiwan air quality in the absence of a lockdown: Influence of urban public transportation use and meteorological conditions

The unprecedented outbreak of COVID-19 significantly improved the atmospheric environment for lockdown-imposed regions; however, scant evidence exists on its impacts on regions without lockdown. A novel research framework is proposed to evaluate the long-term monthly spatiotemporal impact of COVID-19 on Taiwan air quality through different statistical analyses, including geostatistical analysis, change detection analysis and identification of nonattainment pollutant occurrence between the average mean air pollutant concentrations from 2018-2019 and 2020, considering both meteorological and public transportation impacts. Contrary to lockdown-imposed regions, insignificant or worsened air quality conditions were observed at the beginning of COVID-19, but a delayed improvement occurred after April in Taiwan. The annual mean concentrations of PM₁₀, PM_2.5, SO₂, NO₂, CO and O₃ in 2020 were reduced by 24%, 18%, 15%, 9.6%, 7.4% and 1.3%, respectively (relative to 2018-2019), and the overall occurrence frequency of nonattainment air pollutants declined by over 30%. Backward stepwise regression models for each air pollutant were successfully constructed utilizing 12 meteorological parameters (R² > 0.8 except for SO₂) to simulate the meteorological normalized business-as-usual concentration. The hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model simulated the fate of air pollutants (e.g., local emissions or transboundary pollution) for anomalous months. The changes in different public transportation usage volumes (e.g., roadway, railway, air, and waterway) moderately reduced air pollution, particularly CO and NO₂. Reduced public transportation use had a more significant impact than meteorology on air quality improvement in Taiwan, highlighting the importance of proper public transportation management for air pollution control and paving a new path for sustainable air quality management even in the absence of a lockdown.

Nature-based solutions for securing contributions of water, food, and energy in an urban environment

There is growing awareness that nature-based solutions (NBS) prevent negative effects and secure ecosystem services. However, the potential of NBS to provide intended benefits has not been rigorously assessed. Water, food, and energy (WFE) are essential for human well-being. This study highlights the importance of NBS in terms of water, food, and energy. A set of on-site NBS that includes permeable pavements, plant microbial fuel cells, bio-filtration basins, and rain gardens is used to determine the contribution of NBS to the environmental and economic development of urban environments. The results of this study show that NBSs benefit an urban environment in terms of water treatment, stormwater retention, food production and energy generation, carbon sequestration, pollination, sedimentation retention, and cultural services dimension. This research highlights an urgent need for the integration of water, food, and energy plans to ensure that NBSs contribute to the environment and for the conservation of ecosystem services.

Improving urban sustainability and resilience with the optimal arrangement of water-energy-food related practices

Water-, energy-, and food (WEF) related practices, such as low impact development (LID), residential solar panels, and rooftop urban agriculture, have been applied to improve urban sustainability and resilience under climate change and urbanization. However, most practices require space. This requirement may result in competition for land. In addition, not all newly built practices benefit the environment from the life cycle perspective. Therefore, this study aims to develop a systematic WEF-related practice planning method to improve urban sustainability and resilience in a limited space. The core method is a multi-objective optimization model that considers the performance and environmental impacts of the selected practices. The assessment was conducted in a densely populated area in Taipei, the capital city of Taiwan, to describe the planning processes and demonstrate the feasibility of the methods. In the Taipei case, five goals were defined: the supply of WEF, the sponge city development target, and the greenhouse gas reduction target. The optimal results of the multi-objective optimization model indicated the closeness of the optimal implementation of WEF-related practices to achieving the goals. The results showed that the optimal arrangement of WEF-related practices could provide water supply benefits and was favorable for developing a sponge city. According to the sensitivities, to achieve urban sustainability and resilience, the priorities in order of importance are as follows: establish a rainwater harvesting system for buildings, encourage the implementation of rooftop photovoltaic systems, and improve the materials and processes used solar panel and bioretention cell production. The systematic planning method provides a quantitative assessment and delivers practical cross-sectoral integrated strategies for decision-making.

Deployment of a mobile platform to characterize spatial and temporal variation of on-road fine particles in an urban area

Traffic-related air pollutants (TRAPs) pose a serious health hazard for residents and commuters in urban areas. In this study, a real-time mobile monitoring system was deployed in Taipei, a typical East Asian city with an overlap of high population density, traffic, and special structures (e.g., viaducts), to capture the on-road TRAPs at different times of the day. In general, black carbon, ultrafine particles (UFPs), CO concentrations, and lung deposition surface area (LDSA) were positively correlated with traffic flow, and for PM_2.5, a more independent fluctuating concentration was observed. During rush-hour periods, the mean concentrations of UFPs, PM_2.5, and LDSA were 6.12 × 10⁴ ± 3.83 × 10⁴ cm^-3, 23 ± 8 μg/m³, and 2.29 × 10² ± 1.20 × 10² μm²/cm³, respectively. Additionally, the UFP number concentration and LDSA were two times higher along the high-traffic commuting route than along the lower traffic route. Pollutants tended to accumulate at sites near viaducts and high buildings and were significantly influenced by vehicle composition. In this study, the ratio of LDSA to total particle surface area concentration was used as an indicator of the degree of particle irregularity, which was directly related to aging during transport.

Creating ecosystem services assessment models incorporating land use impacts based on soil quality

Life cycle assessment (LCA) is a widely applied approach used to evaluate the environmental impacts of a product or service across its life cycle stages; however, the impacts of land use on ecosystem services are less addressed in most LCA studies. This study, therefore, aims to improve the LCA model by incorporating a new impact category of land use on ecosystem services at both midpoint and endpoint levels in the existing ReCiPe2016 impact assessment method. The impacts of land use in the LCA model included land occupation and land transformation. The soil quality-based indicator, soil organic carbon (SOC), was adopted to quantify the soil quality change in ecosystem services caused by land use. A site with contaminated soils was adopted to validate the proposed impact assessment approach and to compare the results of various remediation practices. Our results revealed that the characterization factors (CFs) varied with the type of land use intervention, with land occupation of settlements presenting the highest CFs and land occupation of forest presenting the most negative CFs and thus benefitting ecosystem services. These results were well reflected in the case study, while the type of land intervention was the key factor determining the impact level. The results suggested that long-term occupation, high contamination levels, and high material or energy use contributed to relatively higher impacts of land use on ecosystem services. The proposed approach enables the quantification of land use impacts on ecosystem services as expressed in monetary loss or benefit at the endpoint resource level. The impact assessment results indicated that the in situ bioremediation scenario contributed relatively higher impacts ($12,667 USD) than the excavation and thermal treatment scenario ($-37 USD). These monetary assessment results are informative and are expected to be used in the decision-making process towards achieving beneficial environmental outcomes.

Energy recovery from sewage sludge: Product characteristics, heating value prediction and reaction kinetics

Energy recovery from sewage sludge was carried out by using microwave and conventional torrefaction. The microwave torrefaction was carried out by using a laboratory-scale microwave oven that provides single-mode microwave irradiation at 2.45 GHz, and the amount of sewage sludge for each experiment was approximately 20 g. The efficiency of microwave heating can be substantially promoted at higher power level, resulting in higher heating rate and maximum temperature. According to higher energy yield and heating value of torrefied sewage sludge, the optimum power level for bioenergy produced by microwave torrefaction of sewage sludge should be 200 W. Because of lower mass yield and temperature required to obtain the same yield, microwave heating can be more effective than conventional heating for sewage sludge torrefaction. The elemental composition of torrefied sewage sludge at 400 W was similar to that of anthracite, and its low hydrogen and oxygen contents could prevent excessive formation of smoke. Two correlations were obtained to predict the HHV of SS based on proximate and elemental compositions. With the recovery of liquid and gas products as bioenergy, the energy return on investment for microwave torrefaction of sewage sludge can be up to 16.4, much higher than the minimum value required for a sustainable society. Because of lower activation energy but higher pre-exponential factor, microwave heating can be approximately five times faster than conventional heating.

Measuring urban food-energy-water nexus sustainability: Finding solutions for cities

A city is the place where food, energy, and water consumption happen. This consumption leads to challenges and has a strong impact on natural sources. Although researchers broadly agree on the importance of incorporating the concept of the food, energy, and water nexus into policy strategies and decision-making, the assessment system for how governance methods can improve the provision of these three essential services is relatively blank. To clarify the policy mechanisms and heterogeneity of sustainability issues related to the food, energy and water nexus at the city level, this study develops an indicator system to guide the implementations and optimize urban sustainability. A qualitative approach is employed to form the priority strategies in in four selected cities: Amsterdam, Eindhoven, Taipei, and Tainan. The results show that renewable energy plays an essential role in the food-energy-water nexus. In addition, we also observed that future work should focus on technological innovation. These observations imply that the unique combination of influence factors in food-energy-water sustainability offers a comprehensive outlook of the broad and complex challenges that a city faces due to resource limitations, which can help inform future governance practices. Finally, some policy recommendations are made for highlighting and the activities needed to work. The results of the present evaluation could be used as a tool to strengthen food-energy-water management in the future. They can guide managers to develop possible solutions that ensure resources are applied successfully according to the visions of multiple perspectives and help the relevant ministries to improve future consultation plans.

Heterogeneous Fenton oxidation of trichloroethylene catalyzed by sewage sludge biochar: Experimental study and life cycle assessment

Heterogeneous Fenton oxidation of trichloroethylene (TCE) catalyzed by sewage sludge biochar was studied. The highest TCE removal efficiency was 83% at pH 3.1, catalyzed by 300 W biochar. The biochars produced at higher microwave power levels provided better catalytic effect, due to higher iron contents and specific surface areas. Reactivity of sewage sludge biochar maintained after several uses, which provides an advantage for using as a permeable reactive barrier to remediate groundwater pollution. Chromium, copper, nickel, lead, and zinc were found in the leachate generated from sewage sludge biochar, and most of the concentrations were lower than the standards for non-drinking water use. Besides, copper, zinc, and iron were found in the reaction solutions of Fenton oxidation. Because of the highest dosage required for Fenton oxidation, the environmental impact caused by 200 W biochar is highest. The environmental impact caused by 300 W biochar is lowest. Among the four endpoint impact categories in the life cycle assessment (LCA), human health is the highest concern, whereas ecosystem quality is the least. According to experimental and LCA results, the optimum microwave power level would be 300 W. The primary impact source is microwave pyrolysis because of high energy usage.

Membrane capacitive deionization for low-salinity desalination in the reclamation of domestic wastewater effluents

This study aims to investigate the feasibility of desalinating secondary effluent from a domestic wastewater treatment plant (DWTP) using membrane capacitive deionization (MCDI) for reclamation purposes. The desalination performance of a MCDI stack with 10 pairs of 20 cm × 20 cm activated carbon electrodes was evaluated in single-pass mode. As evidenced, the MCDI stack outperformed the capacitive deionization stack. The water quality characteristics of the inflows and product water were also analyzed. Our results revealed that MCDI can effectively remove undesired ions such as calcium and nitrate from the DWTP effluent for water reclamation. In particular, the solution conductivity of the product water was observed to be as low as 1.27 μS/cm. Removal of the ions was easily performed by the electrostatic field-assisted deionization process. The use of MCDI for low-salinity wastewater reclamation demonstrated favorable energy performance with a low volumetric energy input and a molar energy input of 0.12 kWh/m³ and 0.03 kWh/mole, respectively; and the energy efficiency of this system is expected to be further improved by energy recovery or incorporation of energy-producing processes. These results are indicative of the benefits of using MCDI as part of the treatment processes for the reclamation of wastewater with low salinity.

Understanding synergies and trade-offs between water and energy production at landfill sites

Landfills provide the most commonly used waste disposal solution. They are designed to reduce the risk of environmental or public health hazards due to waste disposal, and are used for waste management purposes in many places around the world. Depending on the design of the site and recovery methods, landfill sites can work as a potential reserve of energy and water for society. Landfill biogas is a source of renewable energy, and surface water can be collected in a retention pond. Although researchers broadly agree on the importance of incorporating the concept of the energy and water nexus into policy strategies and decision-making, the lack of studies focused on how governance methods that incorporate energy-water linkages at landfill sites can improve the provision of these two essential services has hindered progress in this direction. This study analyzes the links between water-energy nexus at a restored landfill site in Taipei City, Taiwan. The study tracks leachate and methane production at the site over the time periods when the landfill was actively receiving waste and after its closure and since its restoration. The results of model simulation of leachate yield and methane collection under different conditions show that energy and water production changed considerably during the time span under consideration. We identified an increasing trend of water and energy production in the landfill operation phase and a decreasing trend of water and energy production in the landfill restoration phase. In addition, we also identify a synergy between energy generation and water volume during the operation phase, and show that no trade-offs between energy generation and water volume were observed during any of the phases studied. These observations imply that greater water volumes will always lead to greater energy production, which can help inform future landfill design and governance practices.

Framework for determining optimal strategy for sustainable remediation of contaminated sediment: A case study in Northern Taiwan

Contaminated sediment may pose a serious threat to human health and ecosystems. However, sediment remediation is typically an expensive and time-consuming process. Therefore, an effective decision-making process for the remediation of contaminated sediment is essential for identifying the optimal approach. Since a single assessment for sediment remediation may be insufficient, combining different analytical approaches is highly recommended. The objective of this study was to develop a comprehensive assessment framework based on the concept of green and sustainable remediation that considers various environmental, economic, and social aspects for the management of contaminated sediment. We propose a framework based on human health risk assessment (HHRA) and cost-benefit analysis (CBA) and apply the multicriteria decision analysis (MCDA) technique to implement integrated and sustainable strategies for sediment management. We used the framework to determine the best alternative for managing heavy-metal-contaminated sediment in a river in Northern Taiwan. The results of the pre-remediation HHRA indicated an unacceptably high cancer risk to children, while the CBA revealed that a remediation project was economically feasible. Moreover, the results of the MCDA revealed that a strategy involving in-situ capping with anthracite-based activated carbon would be relatively inexpensive and result in low risk to human health. In addition, this strategy would have a higher environmental impact and greater public acceptance as compared to a method involving the dredging and washing of soil. Thus, in this case study, in-situ capping using anthracite-based activated carbon was identified as the preferable remediation alternative from multiple perspectives. The proposed framework should allow decision-makers to choose the optimal integrated management strategy for similar river sites with contaminated sediment.

Sector-wise midpoint characterization factors for impact assessment of regional consumptive and degradative water use

Water availability, resulting from either a lack of water or poor water quality is a key factor contributing to regional water stress. This study proposes a set of sector-wise characterization factors (CFs), namely consumptive and degradative water stresses, to assess the impact of water withdrawals with a life cycle assessment approach. These CFs consider water availability, water quality, and competition for water between domestic, agricultural and industrial sectors and ecosystem at the watershed level. CFs were applied to a case study of regional water management of industrial water withdrawals in Taiwan to show that both regional or seasonal decrease in water availability contributes to a high consumptive water stress, whereas water scarcity due to degraded water quality not meeting sector standards has little influence on increased degradative water stress. Degradative water stress was observed more in the agricultural sector than in the industrial sector, which implies that the agriculture sector may have water quality concerns. Reducing water intensity and alleviating regional scale water stresses of watersheds are suggested as approaches to decrease the impact of both consumptive and degradative water use. The results from this study may enable a more detailed sector-wise analysis of water stress and influence water resource management policies.

Assessment of different route choice on commuters' exposure to air pollution in Taipei, Taiwan

The purposes of this study are to develop a healthy commute map indicating cleanest route in Taipei metropolitan area for any given journey and to evaluate the pollutant doses exposed in different commuting modes. In Taiwan, there are more than 13.6 million motorcycles and 7.7 million vehicles among the 23 million people. Exposure to traffic-related air pollutants can thus cause adverse health effects. Moreover, increasing the level of physical activity during commuting and longer distances will result in inhalation of more polluted air. In this study, we utilized air pollution monitoring data (CO, SO₂, NO₂, PM₁₀, and PM_2.5) from Taiwan EPA's air quality monitoring stations in Taipei metropolitan area to estimate each pollutant exposure while commuting by different modes (motorcycling, bicycling, and walking). Spatial interpolation methods such as inverse distance weighting (IDW) were used to estimate each pollutant's distribution in Taipei metropolitan area. Three routes were selected to represent the variety of different daily commuting pathways. The cleanest route choice was based upon Dijkstra's algorithm to find the lowest cumulative pollutant exposure. The IDW interpolated values of CO, SO₂, NO₂, PM₁₀, and PM_2.5 ranged from 0.42-2.2 (ppm), 2.6-4.8 (ppb), 17.8-42.9 (ppb), 32.4-65.6 (μg/m³), and 14.2-38.9 (μg/m³), respectively. To compare with the IDW results, concentration of particulate matter (PM₁₀, PM_2.5, and PM₁) along the motorcycle route was measured in real time. In conclusion, the results showed that the shortest commuting route for motorcyclists resulted in a much higher cumulative dose (PM_2.5 3340.8 μg/m³) than the cleanest route (PM_2.5 912.5 μg/m³). The mobile personal monitoring indicated that the motorcyclists inhaled significant high pollutants during commuting as a result of high-concentration exposure and short-duration peaks. The study could effectively present less polluted commuting routes for citizen health benefits.

Sustainability assessment and prioritisation of bottom ash management in Macao

In Macao, about 7200 t yr^-1 of bottom ash (BA) is generated and conventionally landfilled with construction waste. Because the properties of BA are similar to those of natural aggregates, it is suitable to be recycled as construction material. However, pre-treatment processes for BA reuse may require more resource input and may generate additional environmental impacts. Life cycle assessment, multi-media transport model analysis, cost-benefit analysis and the analytical hierarchy process were conducted to evaluate the impacts of current and potential BA management scenarios regarding environmental, economic, social and regulatory aspects. The five analysed scenarios are as follows: (0) BA buried with construction and demolition waste (current system); (1) pre-treated BA used to replace 25% of the natural aggregate in asphalt concrete; (2) pre-treated BA used to replace 25% of the natural aggregate in cement concrete; (3) pre-treated BA used to replace 25% of cement in cement concrete; and (4) pre-treated BA sent to China, blended with municipal solid waste for landfill. The results reveal the following ranking of the scenarios: 3 > 2 > 0 > 1 > 4. Scenario 3 shows the best conditions for BA recycling, because the quantity of cement concrete output is the highest and this brings the greatest economic benefits. Our use of integrated analysis provides multi-aspect investigations for BA management systems, particularly in accounting for site-specific characteristics. This approach is suitable for application in other non-western regions.

Microwave pyrolysis of rice straw: products, mechanism, and kinetics

Rice straw is an abundant resource for the production of biofuels and bio-based products. How to convert the recalcitrant lignocellulose effectually is a critical issue. The objective of this study was to investigate the products, mechanism, and kinetics of rice straw pyrolysis by using microwave heating. The highest energy densification ratio of solid residues was achieved at the microwave power level of 300 W. The atomic H/C and O/C ratios of solid residues were much lower than those of rice straw. The primary components of gaseous product were CO, H2, CO2, and CH4, whose molecular fractions were 57%, 21%, 14%, and 8%, respectively. The more gaseous product and the less solid residues were obtained at higher microwave power levels, while the liquid production remained the same and showed a maximum of about 50 wt.%. The kinetic parameters of rice straw pyrolysis were increased with increasing microwave power level.

Life cycle assessment of biochar cofiring with coal

This study used life cycle assessment software SimaPro 7.2 and impact assessment model IMPACT 2002+ to evaluate the environmental impact and benefits of a biochar cofiring supply chain used for electricity generation. The biochar was assumed to be produced by rice straw torrefaction and the case study was located in Taoyuan County, Taiwan. This supply chain may provide impact reduction benefits in five categories (aquatic ecotoxicity, terrestrial ecotoxicity, land occupation, global warming, and non-renewable energy) but cause higher impacts than coal firing systems in other categories. Damage assessment of cofiring systems indicated that damage to human health was higher while the damage categories of ecosystem quality, climate change, and resources were lower. Carbon reduction could be 4.32 and 4.68metric tons CO2eq/ha/yr at 10% and 20% cofiring ratios, respectively. The improvement of electricity generation efficiency of cofiring systems may be the most important factor for reducing its environmental impact.

Microwave torrefaction of rice straw and Pennisetum

Microwave torrefaction of rice straw and pennisetum was researched in this article. Higher microwave power levels contributed to higher heating rate and reaction temperature, and thus produced the torrefied biomass with higher heating value and lower H/C and O/C ratios. Kinetic parameters were determined with good coefficients of determination, so the microwave torrefaction of biomass might be very close to first-order reaction. Only 150W microwave power levels and 10min processing time were needed to meet about 70% mass yield and 80% energy yield for torrefied biomass. The energy density of torrefied biomass was about 14% higher than that of raw biomass. The byproducts (liquid and gas) possessed about 30% mass and 20% energy of raw biomass, and they can be seen as energy sources for heat or electricity. Microwave torrefaction of biomass could be a competitive technology to employ the least energy and to retain the most bioenergy.

Implications of biomass pretreatment to cost and carbon emissions: case study of rice straw and Pennisetum in Taiwan

The purpose of this study was to explore the impact of feedstock collection and torrefaction pretreatment on the efficiency of a biomass co-firing system. Considering the transformation of existing municipal solid waste incinerators, several scenarios in which biomass supply chains depend on centralised pretreatment and transportation alternatives are presented. The cost, net energy output, and greenhouse gas effects of these scenarios were analysed using a spreadsheet model. Based on the Taoyuan County case in Taiwan, the mitigation costs of carbon emissions for rice straw and Pennisetum are 77.0 $/Mg CO(2) and 63.8 $/Mg CO(2), respectively. Results indicate that transporting feedstock from its source to the pretreatment and co-firing stations contributes the most to logistical costs for both straw and Pennisetum, regardless of whether torrefaction was adopted. Nonetheless, torrefaction requires more demonstrated cases at various scales to obtain the technical and economic data required for further analysis.

A sequential method to analyze the kinetics of biomass pyrolysis

The kinetics of biomass pyrolysis was studied via a sequential method including two stages. Stage one is to analyze the kinetics of biomass pyrolysis and starts with the determination of unreacted fraction of sample at the maximum reaction rate, (1-α)(m). Stage two provides a way to simulate the reaction rate profile and to verify the appropriateness of kinetic parameters calculated in the previous stage. Filter paper, xylan, and alkali lignin were used as representatives of cellulose, hemicellulose, and lignin whose pyrolysis was analyzed with the assumption of the orders of reaction being 1, 2, and 3, respectively. For most of the biomass pyrolysis, kinetic parameters were properly determined and reaction rate profiles were adequately simulated by regarding the order of reaction as 1. This new method should be applicable to most of the biomass pyrolysis and similar reactions whose (1-α)(m) is acquirable, representative, and reliable.

Assessing the environmental impact of five Pd-based catalytic technologies in removing of nitrates

Emerging technologies involving chemical catalytic processes to remove nitrate from water have proven efficient and cost-effective. However, the environmental impact of noble metals and metals at the nanoscale used in these processes has become a topic of serious concern. The aim of this research was to develop a system for evaluating the environmental impact of technologies associated with Pd-based catalytic denitrification. This research performed life cycle assessment (LCA) based on a detailed analysis of the technologies to examine the environmental burden associated with all stages of the removal process. We then applied analytical hierarchy process (AHP) to determine the weights of various burdens. We implemented the proposed system to determine the relative environmental friendliness of 5 processes used for the removal of nitrate. These five methods use Cu-Pd/TNTs, H(2)+Pd-Cu/TiO(2), Pd-Cu/TiO(2), Pd/ZnO, and Pd-Cu/FeO as catalysts for the removal of nitrate. The results indicate that the use of palladium and the consumption of electricity have a major environmental impact; while the use of Pd-Cu/TiO(2) as catalyst was the most environmentally friendly of the five processes evaluated.

Pyrolysis of biomass by thermal analysis-mass spectrometry (TA-MS)

The kinetic parameters such as pre-exponential factor and activation energy of hemicellulose, cellulose, and lignin were well determined by the linear regressions of selected, sufficient thermogravimetric data, and close to literature values. The pyrolysis of biomass can be divided into four stages. There was only drying in the zeroth stage (<150°C). In the first stage (150-250°C), some light hydrocarbons were produced with the early pyrolysis of biomass. The biomass was mainly pyrolyzed in the second stage (250-500°C) with higher reaction rates than those of other stages. The productions of H(2) and CO(2) in the third stage (>500°C) may be able to be the evidence of self-gasification of char existing at higher temperatures.

Microwave-hydrothermal decomposition of perfluorooctanoic acid in water by iron-activated persulfate oxidation

The microwave-hydrothermal decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in aqueous solution using persulfate activated by zero-valent iron (ZVI) at 60 and 90 degrees C was examined. The results of laboratory study reveal that when PFOA is treated with 5mM persulfate (PS) and ZVI at 90 degrees C for 2h, 67.6% of PFOA is effectively decomposed to form shorter-chain perfluorinated carboxylic acids (PFCAs) and fluoride ions, with 22.5% defluorination efficiency. Introducing ZVI into the PFOA solution with PS addition will lead to synergetic effect that accelerates the PFOA decomposition rate, and reduces the reaction time. ZVI not only decomposes PFOA, but also releases ferrous ions to lower the activation energy of PS while forming sulfate free radicals at a lower reaction temperature. The combined use of ZVI and persulfate will lead to significant savings in energy consumption and reduction of process time.

Efficient decomposition of perfluorocarboxylic acids in aqueous solution using microwave-induced persulfate

The microwave-hydrothermal decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water with persulfate (S(2)O(8)(2-)) at 60, 90, and 130 degrees C was examined to develop an effective technology for treating PFOA pollution. S(2)O(8)(2-) is an efficient oxidant for degrading PFOA even at the room temperature of 27 degrees C. Higher temperature accelerates the PFOA decomposition rate, but an extremely high temperature (130 degrees C) will lead to the formation of significant amounts of radical oxidants that are released rapidly to consume most remaining persulfate thus causing a lower mineralization efficiency. The solution pH value is another important factor to influence the degradation rate; there is almost no PFOA decomposition reaction under alkaline conditions. The decomposition rate in acidic conditions is 1.1-7.4 times faster than in alkaline condition. Additionally, the proposed method is also effective in decomposing other PFCA species such as the C2-C7 perfluoroalkyl groups.

A GIS-based system for allocating municipal solid waste incinerator compensatory fund

To ease the NIMBY (not in my back yard) syndrome of constructing municipal solid waste (MSW) incinerators in Taiwan, compensatory funding is widely allocated to the impacted communities to gain the acceptance and support of residents living the impacted areas. This paper presents a spatial methodology for distributing a compensatory fund more logically based on the environmental impact on each neighborhood in Taipei City. This method integrates ten impact factors, which have been proposed by a local committee, to evaluate all neighborhoods using mathematical models combined with spatial analyses in an analytic hierarchy process. The compensatory fund is distributed according to the resulting final scores. A GIS (geographic information systems)-based system has been developed to assist in assigning the final scores to the neighborhoods impacted. Results on impact factors and fund distributions are combined; they are included in an information system and displayed in spatial scales. For Taipei City, the impact of air quality during the incinerator operating period is the item of greatest concern to the surrounding residents and thus, it receives a relatively higher weight of 0.2894. As a result, high impact scores were assigned to not only those neighborhoods hosting the incinerators, but also the neighborhoods where the maximum particulate air pollutants occurred. This approach could be applicable to other MSW incinerators with similar environmental impact problems and interest in compensation schemes.

A vulnerability analysis in the Fei-tsui reservoir watershed in Taiwan

The vulnerability analysis method has been widely used in many environmental fields. In recent years, the tool has succeeded in comprehensive assessment of environmental problems. This study applied the vulnerability and resilience analysis method on watershed conservation and grasped the environmental change capacity that watershed could bear. The Fei-tsui reservoir watershed in Northern Taiwan provided the setting for the case study reported herein. This study considered both internal and external effect factors, including watershed vulnerability, rainfall energy and the distances between the outlet and subbasins, and developed a new index, WP, for the priority restraints strategies on the land-use activities. The land-use restraint index can be a significant criterion for watershed protection and management strategies.

Effect of spatial variability of storm on the optimal placement of best management practices (BMPs)

It is significant to design best management practices (BMPs) and determine the proper BMPs placement for the purpose that can not only satisfy the water quantity and water quality standard, but also lower the total cost of BMPs. The spatial rainfall variability can have much effect on its relative runoff and non-point source pollution (NPSP). Meantime, the optimal design and placement of BMPs would be different as well. The objective of this study was to discuss the relationship between the spatial variability of rainfall and the optimal BMPs placements. Three synthetic rainfall storms with varied spatial distributions, including uniform rainfall, downstream rainfall and upstream rainfall, were designed. WinVAST model was applied to predict runoff and NPSP. Additionally, detention pond and swale were selected for being structural BMPs. Scatter search was applied to find the optimal BMPs placement. The results show that mostly the total cost of BMPs is higher in downstream rainfall than in upstream rainfall or uniform rainfall. Moreover, the cost of detention pond is much higher than swale. Thus, even though detention pond has larger efficiency for lowering peak flow and pollutant exports, it is not always the determined set in each subbasin.

The assistance of microwave process in sludge stabilization with sodium sulfide and sodium phosphate

After industrial wastewater sludge passed through an acid-extraction process to reclaim most of the copper ions in it, the residue may still need to be treated by stabilization technologies. The common method for the stabilization of hazardous waste in Taiwan is by cement solidification. However, this method has the disadvantage of an increase in waste volume. In this study, it was tried to combine the advantages of sulfur anions and phosphate anions with the characteristics of microwave energy to offer a new method which can avoid the disadvantage of cement solidification. From the results, it was found that the assistance of heating in sludge stabilization with additives was effective. Huge amounts of additives were saved. Compared with the assistance of the traditional electrical-heating in sludge stabilization with additives, that of the microwave process saved much time and was more powerful. However, when the reaction time was longer, a re-leaching situation would occur. The hybrid microwave process, a procedure of leading an inert gas into the microwave process, could overcome the disadvantage of the microwave process with regard to the long reaction time. Finally, a modified hybrid microwave process which reduced the use of gas was performed and recommended.

Microwave enhanced stabilization of heavy metal sludge

A microwave process can be utilized to stabilize the copper ions in heavy metal sludge. The effects of microwave processing on stabilization of heavy metal sludge were studied as a function of additive, power, process time, reaction atmosphere, cooling gas, organic substance, and temperature. Copper leach resistance increased with addition of aluminum metal powder, with increased microwave power, increased processing time, and using a gaseous environment of nitrogen for processing and air for cooling [N2/air]. The organic in the sludge affected stabilization, whether or not the organic smoldered. During heating in conventional ovens, exothermic oxidation of the organic resulted in sludge temperatures of about 500 degrees C for oven control temperatures of 200-500 degrees C. After microwave heating dried the sludge, the sludge temperature rose to 500 degrees C. The reaction between copper ions and metal aluminum in the dried sludge should be regarded as a solid phase reaction. Adding aluminum metal powder and reaction temperature were the key parameters in stabilizing copper in the heavy metal sludge, whether heated by microwave radiation or conventional oven. The mass balance indicates insignificant volatization of the copper during heating.