Environmental and Energy Assessment of Biomass Residues to Biochar as Fuel: A Brief Review with Recommendations for Future Bioenergy Systems

This study explores the environmental and energy benefits of biomass residues, including crop residues and agricultural waste, for the production of renewable energy in the form of biochar as fuel, in order to offer recommendations for policy makers, by reviewing information regarding the key environmental issues associated with the implementation of the systems. The highest environmental benefits for biochar-to-fuel systems were most observed in reduction of global warming potentials (i.e., carbon abatement), particularly for those integrated with combined heat and power technology, or for those incorporating electricity offsets from biochar combustion and co-firing. But all of these practices come at the cost of hidden environmental burdens, such as elevations in eutrophication, acidification, carcinogens and ecotoxicity impacts, as a consequence from land use change, additional infrastructure requirement or additional fertilizer application connected to biochar production or post-treatment. Other notable challenges, including regional availability of biomass residues, improper management of the residues, limited economic incentives, low energy efficiency and synergies, as well as mistreating adverse impacts from indirect land use change, were discussed. This suggests the flexibility to adjust the biomass-biochar ratio to optimize desired energy yields, carbon abatement and environmental beneficial objectives. Comprehensive analysis of the trade-offs between energy yields, carbon abatement and other associated environmental impacts is therefore recommended for future studies. Future studies in this field are also advised to explore the solution and to develop methodologies capable of quantifying the impacts and other equally relevant trade-offs, to better reflect the changes in real-world trends for decision making

Strategic Optimization of Water Reuse in Wafer Fabs via Multi-Constraint Linear Programming Technique

The risk of water shortage has been posing as a threat to water demanding industries in Taiwan, including the high-tech industries where ultrapure water is needed for the production of microchips. Such risks are especially unpredictable in the age of climate change, where more frequent extreme climate events such as prolonged droughts have sent these industries scrambling for securing water supply at a very high cost. The national policy also mandates strict water recycling standards for these high-tech plants, while the risk of water supply shortage also forces the industry to be water-conscious. However, most plants set their water recycling strategies based on experience or ‘‘rules of thumb” practices, without implementing optimization tools that can help making decisions in a more scientific approach. In this study we applied linear programming technique to optimize the water recovery path for a microchip assembly plant. A water balance diagram was formulated and completed to determine the existing water recycling performance, and the data was converted to a water flow network. The water flow network was then derived with a mathematical model to formulate a linear optimization problem. The proposed linear programming model is composed of mass balance constraints, unit specification constraints, capacity constraints as well as water quality constraints (discharge limits). The linear programming method was effectively applied to improve the efficiency of water reuse. With the installation of the regeneration units, an increase of 40.1% in the volume of reused water was predicted. The results from water cost structure also indicated that, at higher water tariff, water reuses through reclaiming and generating spent effluents can alleviate the overall water consumption costs

Integrated assessment of water conservation practices for sustainable management strategies

Miami-Dade County implemented a series of water conservation programs, which included rebate/exchange incentives to encourage the use of high efficiency aerators (AR), showerheads (SH), toilets (HET) and clothes washers (HEW), to respond to the environmental sustainability issue in urban areas. This study first used panel data analysis of water consumption to evaluate the performance and actual water savings of individual programs. Integrated water demand model has also been developed for incorporating property’s physical characteristics into the water consumption profiles. Life cycle assessment (with emphasis on end-use stage in water system) of water intense appliances was conducted to determine the environmental impacts brought by each practice. Approximately 6 to 10 % of water has been saved in the first and second year of implementation of high efficiency appliances, and with continuing savings in the third and fourth years. Water savings (gallons per household per day) for water efficiency appliances were observed at 28 (11.1%) for SH, 34.7 (13.3%) for HET, and 39.7 (14.5%) for HEW. Furthermore, the estimated contributions of high efficiency appliances for reducing water demand in the integrated water demand model were between 5 and 19% (highest in the AR program). Results indicated that adoption of more than one type of water efficiency appliance could significantly reduce residential water demand. For the sustainable water management strategies, the appropriate water conservation rate was projected to be 1 to 2 million gallons per day (MGD) through 2030. With 2 MGD of water savings, the estimated per capita water use (GPCD) could be reduced from approximately 140 to 122 GPCD. Additional efforts are needed to reduce the water demand to US EPA’s “Water Sense” conservation levels of 70 GPCD by 2030. Life cycle assessment results showed that environmental impacts (water and energy demands and greenhouse gas emissions) from end-use and demand phases are most significant within the water system, particularly due to water heating (73% for clothes washer and 93% for showerhead). Estimations of optimal lifespan for appliances (8 to 21 years) implied that earlier replacement with efficiency models is encouraged in order to minimize the environmental impacts brought by current practice

Chitosan as a Natural Polymer for Heterogeneous Catalysts Support: A Short Review on Its Applications

Chitosan, a bio-based polymer which has similar characteristics to those of cellulose, exhibits cationic behavior in acidic solutions and strong affinity for metals ions. Thus, it has received increased attention for the preparation of heterogeneous catalysts. Recent studies demonstrated that chitosan-based catalysts had high sorption capacities, chelating activities, stability and versatility, which could be potentially applied as green reactants in various scientific and engineering applications. This study intends to review the recent development of chitosan-based catalysts, particularly in the aspects of the main mechanisms for preparing the materials and their applications in environmental green chemistry. Studies on the preparation of catalyst nanoparticles/nanospheres supported on chitosan were also reviewed

Chitosan as a Natural Polymer for Heterogeneous Catalysts Support: A Short Review on Its Applications

Chitosan, a bio-based polymer which has similar characteristics to those of cellulose, exhibits cationic behavior in acidic solutions and strong affinity for metals ions. Thus, it has received increased attention for the preparation of heterogeneous catalysts. Recent studies demonstrated that chitosan-based catalysts had high sorption capacities, chelating activities, stability and versatility, which could be potentially applied as green reactants in various scientific and engineering applications. This study intends to review the recent development of chitosan-based catalysts, particularly in the aspects of the main mechanisms for preparing the materials and their applications in environmental green chemistry. Studies on the preparation of catalyst nanoparticles/nanospheres supported on chitosan were also reviewed

Water–Energy Nexus for Multi-Criteria Decision Making in Water Resource Management: A Case Study of Choshui River Basin in Taiwan

The Choshui river basin, the mother river in Taiwan, suffers from severe water shortage from extensive water use in irrigation as well as land subsidence from over-pumping of groundwater. To address these challenges, several water-related strategies and actions, including enhancement of water-use efficiency, development of alternative water sources, and improvement in effective water management, were proposed in this study to support sustainable water resource management in the watershed. Management of water resources in Taiwan is expected to confront not only freshwater resource but also energy source constraints. Multi-criteria decision analysis (MCDA), an approach for ranking overall performances of decision options, was then used to prioritize the water resource management strategies. The analysis considered economic (economic feasibility) and environmental (stability from the influence of climate change) criteria in the context of water⁻energy nexus (water supply/conservation potential and systemic energy efficiency). Our results indicated that, while economic feasibility was considered as the most important factor in implementation of the practices, improvement in groundwater pumping control and management was ranked as a high-priority water resource management action, followed by initiating water conservation programs for residential sector and reducing leakage rate for agricultural irrigation canals. The results from this study are expected to provide direction for future decision making in water resource management

Simultaneous Carbon Capture, Biomass Production, and Diary Wastewater Purification by Spirulina maxima Photobioreaction

The feasibility of a two-stage process involving carbon dioxide capturing and a photobioreaction (containing microalgae cells of Spirulina maxima) was investigated for the dual purpose of CO₂ sequestration and wastewater remediation. The study systematically demonstrated the capability of CO₂ removal through wet scrubbing using diluted wastewater as the scrubbing liquid and the potential of biomass growth in the CO₂-enriched wastewater. The NaOH-alkalized wastewater provided a CO₂ absorption capacity approximately equal to 0.5 g CO₂ g^–1 NaOH at 0.5 M, and the absorbed CO₂ was effectively converted into usable bicarbonate to support the growth of S. maxima. The biomass productivity using the CO₂-enriched wastewater (30% diluted) was 0.036 g L^–1 d^–1, which was in line with the productivity obtained from the controlled growth tests using NaHCO₃ as the carbon source. Dilution of raw dairy (milk processing) wastewater was necessary as high chemical oxygen demand (COD) loading inhibited the growth of S. maxima. However, with sufficient dilution, as the COD was less than 300 mg L^–1, the COD was effectively removed (79%) during the microalgae cultivation period, as were NH₄⁺ (51%) and PO₄^– (35%) to lesser extents. The uptake of organic carbon indicated that <i>Spirulina</i> grew mixotrophically in the wastewater. Furthermore, by virtue of the hydroxide reaction with CO₂ that form aqueous carbonates (lowering the pH) and the photosynthetic activity that consumes carbonates (increase the pH), the solution pH can effectively be used as the controlling parameter in operation of the system

Lignocellulosic Biomass Transformations via Greener Oxidative Pretreatment Processes: Access to Energy and Value-Added Chemicals

Anthropogenic climate change, principally induced by the large volume of carbon dioxide emission from the global economy driven by fossil fuels, has been observed and scientifically proven as a major threat to civilization. Meanwhile, fossil fuel depletion has been identified as a future challenge. Lignocellulosic biomass in the form of organic residues appears to be the most promising option as renewable feedstock for the generation of energy and platform chemicals. As of today, relatively little bioenergy comes from lignocellulosic biomass as compared to feedstock such as starch and sugarcane, primarily due to high cost of production involving pretreatment steps required to fragment biomass components via disruption of the natural recalcitrant structure of these rigid polymers; low efficiency of enzymatic hydrolysis of refractory feedstock presents a major challenge. The valorization of lignin and cellulose into energy products or chemical products is contingent on the effectiveness of selective depolymerization of the pretreatment regime which typically involve harsh pyrolytic and solvothermal processes assisted by corrosive acids or alkaline reagents. These unselective methods decompose lignin into many products that may not be energetically or chemically valuable, or even biologically inhibitory. Exploring milder, selective and greener processes, therefore, has become a critical subject of study for the valorization of these materials in the last decade. Efficient alternative activation processes such as microwave- and ultrasound irradiation are being explored as replacements for pyrolysis and hydrothermolysis, while milder options such as advanced oxidative and catalytic processes should be considered as choices to harsher acid and alkaline processes. Herein, we critically abridge the research on chemical oxidative techniques for the pretreatment of lignocellulosics with the explicit aim to rationalize the objectives of the biomass pretreatment step and the problems associated with the conventional processes. The mechanisms of reaction pathways, selectivity and efficiency of end-products obtained using greener processes such as ozonolysis, photocatalysis, oxidative catalysis, electrochemical oxidation, and Fenton or Fenton-like reactions, as applied to depolymerization of lignocellulosic biomass are summarized with deliberation on future prospects of biorefineries with greener pretreatment processes in the context of the life cycle assessment