Desalination technologies can utilize various forms of energy to produce freshwater. The first law of thermodynamics (energy) analysis is used commonly to determine the process efficiency, which is not a true measure of the process performance because it does not account for all losses of energy. The second law of thermodynamics (exergy) is an efficient tool to evaluate the performance of desalination systems. This method accounts for all forms of available energy in the process streams and energy sources with a reference environment to identify the major losses of exergy destruction to aid in resource-efficient desalination system design. Due to changing climate concerns and dwindling conventional energy sources, renewable energy has been identified as a sustainable alternative to supply the energy demands for desalination processes. Desalination processes can be powered by solar, wind, geothermal, and tidal energy sources depending on the process type and configuration. This paper elaborates on use of exergy tools to evaluate renewable energy powered desalination processes to evaluate their thermodynamic efficiency. Illustrations are provided to identify the major components and process streams that contribute to major exergy destruction and to suggest suitable operating conditions that minimize exergy losses. Well-established MSF, MED, RO, Solar distillation and membrane distillation technologies were discussed with case studies to illustrate their exergy performances. Single (water only) and dual (water and power) purpose desalination plants were discussed. Cogeneration, trigeneration (water, power, and heating/cooling) and polygeneration schemes and their exergy performance were also included.
Many municipal wastewater treatment plants (WWTPs) or water and resource recovery facilities (WRRFs) are striving to achieve energy self-sufficiency in their process operations, while simultaneously complying with permit requirements. Currently, less than 10% of U.S. WWTPs or WRRFs produce energy for beneficial use and only a handful of these plants are actually energy self-sufficient. This research seeks to assess the current state-of-knowledge on energy-positive WWTPs or WRRFs, based on the treatment train classification named as “Basic”, “Moderate”, and “Advanced”. A simple quantitative mass-balance model (SQMM) is developed to evaluate the treatment train or technology classification in terms of removal and recovery of carbon-nutrient-energy components of municipal wastewater(s). The goal of this research is to identify potential challenges in the selection and implementation of resource and energy recovery process configurations and, propose practically feasible, energy-positive WWTP process configurations. Currently, energy recovery through biogas production, and aeration energy optimization are the two main approaches to achieve energy self-sufficiency. The main alternative strategy to enhance energy recovery in the near future is by co-digestion of wastewater biosolids and locally available biodegradable wastes. A hypothetical (but practically feasible) WWTP or WRRF configuration proposed in this work represents an alternative energy self-sufficient wastewater process train for future designs. A detailed quantitative analysis will be developed to recommend the ways in which WTTPs or WRRFs could become energy-positive and achieve maximum resource recovery.
Current wastewater treatment processes such as activated sludge process and other aeration technologies are resource-consuming and are unsustainable. Novel and integrated processes are crucial to the development of sustainable wastewater treatment systems. In this context, anaerobic treatment technologies provide numerous opportunities for minimization of energy and resource consumption and maximization of beneficial products. Further, integration of anaerobic digestion augmented by co-digestion, fermentation, dark fermentation or photo-fermentation and other bioelectrochemical systems may result in resource-efficient waste management and environmental protection. This mini-review discusses various possibilities and highlights recent developments of integrated aerobic and anaerobic technologies with bioelectrochemical systems for sustainable wastewater treatment.
A microbial desalination process with microalgae biocathode using sodium bicarbonate as an inorganic carbon sourcePublished: 01 May 2018 by Elsevier BV in International Biodeterioration & Biodegradation
This research investigates a novel platform for an energy-yielding wastewater treatment and desalination scheme in which the organic matter present in wastewater is purposely fed to the exoelectrogenic bacteria to produce bioelectricity in a three-compartment bioelectrochemical system called photosynthetic microbial desalination cell (PMDC). The role of an inorganic carbon source in the microalgae biocathode was studied. Addition of sodium bicarbonate (NaHCO3) increased power production, microalgae growth and desalination rate. A power density of 660 mW/m3 was measured which is about 7.5 times higher than the PMDCs without NaHCO3. Desalination rate was more than 40% after 72 h. Overall, the process could be energy-positive while producing 4.21 kWh per m3 of wastewater treated including desalination energy savings and microalgae biomass energy potential.
Bioelectricity production in photosynthetic microbial desalination cells under different flow configurationsPublished: 01 February 2018 by Elsevier BV in Journal of Industrial and Engineering Chemistry
Optimization of wet microalgal FAME production from Nannochloropsis sp. under the synergistic microwave and ultrasound e...Published: 19 January 2018 by Wiley in International Journal of Energy Research
The synergistic effect of microwave and ultrasound irradiations was evaluated for biodiesel production from microalgae biomass (Nannochloropsis sp.) as raw material. A response surface methodology technique based on central composite design was used to understand the process parametric interdependence and optimize the process reaction variables. Reaction kinetics of algal fatty acid methyl ester (FAME) production was also studied. The optimum reaction conditions were determined as wet algal biomass to methanol ratio of 20 g to 30 mL, 1 wt% catalyst concentration, and 7-minute reaction time at 140 W of microwave power and 140 W of ultrasound power. The estimated activation energy was 17,298 J/mol−1 K−1 for a first-order reaction kinetics. This study revealed that microwave energy dissipation at a low rate of 140 W combined with 140 W of ultrasound intensity is adequate to produce FAMEs at a maximum yield of 48.2%. Results from this optimization study suggest that a more detailed and mechanistic energy optimization study is critical to increase the FAME yield and maximize energy benefits.
Providing clean water for human consumption has become a major challenge at local, regional, national, and global levels due to excess population growth. The direct domestic water demand and the indirect industrial, agricultural, and environmental water needs to sustain this growth is expected to place serious strains on the currently available water resources. Water reuse and desalination technologies can provide a solution to this issue if implemented in a sustainable manner. Provision of clean water inevitably requires energy, which is currently being provided essentially by nonrenewable fossil fuels which is not a sustainable approach. This chapter discusses various options available for enhancing water supply in drought regions. Water reuse and desalination technologies have been discussed in detail. Energy needs and integration of renewable energy sources, energy recovery and process integration concepts have been discussed. Future research directions to develop energy-efficient water supply technologies are provided.
The act of ensuring freshwater is considered the most essential and basic need for humanity. Although the planet is water-rich in some terms, the freshwater sources available for human consumption and beneficial uses are very limited. Excess population growth, industrial development coupled with improving living standards have caused an unprecedented need for freshwater supplies all over the world. Regions once rich in water resources are struggling to meet the ever increasing demands in recent years. In addition, climate change and unsustainable water resource management practices have led to situation called “drought” in many regions. Water supplies in drought conditions can be addressed by taking two major approaches related to management and technology development. The management approaches include demand mitigation and supply enhancement. Demand mitigation can be done by implementing water conservation practices and by enforcing a mechanism to influence user-responsible behavior through higher water fares and other billing routes. Supply enhancement can be achieved by utilizing the methods available for water reclamation, reuse, and recycle including rain harvesting. This chapter provides a critical insight of the causes for drought and the issues caused by persistent drought conditions followed by discussion of management approaches required to maintain adequate water resources in these regions.
Decentralized and onsite wastewater management issues of small communities in Jourdan River Watershed, MississippiPublished: 24 November 2016 by MDPI AG in The 1st International Electronic Conference on Water Sciences
<p>Wastewater treatment and nutrient removal alternatives for large size communities are very<br />well-established and are feasible in many cases. When it comes to the small rural and especially<br />for low-income disadvantaged communities, this is not the case, particularly with regard to nutrient<br />removal. The alternatives for small communities are often viewed as cost-prohibitive and<br />unreliable. While this is partly true, careful selection and implementation of appropriate<br />technologies can result in high performance, energy and cost efficient and environmental-friendly<br />solutions.<br />Assessment of water and wastewater is very crucial to safeguard public health and the<br />environment. However, water quality data on fresh and marine waters in the Mississippi coastal<br />region, especially in Jourdan watershed are still sparse and uncoordinated. Therefore, monitoring<br />these parameters is important for safety assessment of the environment and human public health<br />and the water bodies. We have identified a few small and decentralized communities in the Jourdan<br />River watershed area to assess the current wastewater treatment and management practices and<br />their impacts on the receiving water bodies. This paper will discuss our preliminary<br />evaluation and understanding on the local water quality issues of the watershed.</p>
<p>Microbial desalination cells (MDCs), a recent technological discovery, allow for simultaneous wastewater treatment and desalination of saline water with concurrent electricity production. The premise for MDC performance is based on the principles that bioelectrochemical (BES) systems convert wastewaters into treated effluents accompanied by electricity production and the ionic species migration (i.e. protons) within the system facilitates desalination. One major drawback with microbial desalination cells (MDCs) technology is its unsustainable cathode chamber where expensive catalysts and toxic chemicals are employed for electricity generation. Introducing biological cathodes may enhance the system performance in an environmentally-sustainable manner. This study describes the use of autothrophic microorganism such as algae and Anammox bacteria as sustainable biocatalyst/biocathode in MDCs. Three different process configurations of photosynthetic MDCs (using Chlorella vulgaris) were evaluated for their performance and energy generation potentials. Static (fed-batch, SPMDC), continuous flow (CFPMDC) and a photobioreactor MDC (PBMDC, resembling lagoon type PMDCs) were developed to study the impact of process design on wastewater treatment, electricity generation, nutrient removal, and biomass production and the results indicate that PMDCs can be configured with the aim of maximizing the energy recovery through either biomass production or bioelectricity production. In addition, the microbial community analysis of seven different samples from different parts of the anode chamber, disclosed considerable spatial diversity in microbial communities which is a critical factor in sustaining the operation of MDCs. This study provides the first proof of concept that anammox mechanism can be beneficial in enhancing the sustainability of microbial desalination cells to provide simultaneous removal of ammonium from wastewater and contribute in energy generation.</p>
<p>The presence of pollutants known as emerging contaminants in water and wastewater is a topic of growing interest. Emerging contaminants, which include endocrine disrupting chemicals (EDCs) and pharmaceutical and personal care products (PPCPs), are compounds that remain relatively unknown, although their adverse effects have been proven. Emerging contaminants are not satisfactorily removed by traditional treatment methods; therefore, there is a need for innovative techniques. Advanced oxidation processes (AOPs) have been recognized as successful removal methods for these problematic pollutants. However, technical success is not the only factor that must be considered. Process engineering, environmental, and economic and social parameters were considered. A holistic analysis was completed using a ranking system to determine the performance of several AOPs (ozonation, UV, photocatalysis, the Fenton reaction, and integrated processes). Ultimately, H2O2/O3 presented the highest average ranking (3.45), with the other processes showing similar performance, with the exception of TiO2 photocatalysis (2.11).</p>
<p>The need for freshwater can never be over-stressed. Global agencies (including WHO, UNDP, UNICEF etc.) expect that 24 of the least developed countries, many of them along coastal areas without access to water and electricity, need to more than double their current efforts to reach the Millennium Development Goals for basic health, sanitation, and welfare. Desalination of available brackish or seawater sources is an ideal option for freshwater production. However, existing desalination technologies are energy-intensive and cost-prohibitive. Low temperature desalination using waste heat sources or solar collectors is an attractive option. Because the energy demands can be provided at low costs and with minimum environmental pollution. The main objective of this research is to investigate the technical feasibility of a multi-effect low temperature desalination process with higher thermodynamic efficiency and low environmental impact. Principles of operation, theoretical analyzes and experimental studies will be discussed in detail.</p>
<p>The impetus for new tools for a comprehensive and accurate analysis of energy utilization and industrial systems comes from the need for sustainable development that could be impeded by exhausting energy sources and deteriorating environment. Exergy evaluation provides insight to achieve highest technological efficiency at the lowest cost while meeting the social and legal conditions. Desalination processes are known as major energy consumers and exergy destruction and entropy of these processes is essential for their sustainable development. This paper identifies important areas of exergy destruction and entropy generation in desalination processes including multi-effect distillation (MED), multistage flash (MSF) and reverse osmosis (RO) with case studies and offers recommendations for future efforts in research and development.</p>
Direct use and power generation based on geothermal sources are growing at a steadfast pace around the world. Although available abundantly in many parts of the world, geothermal energy sources have been under-utilized in desalination applications. Geothermal sources have the potential to serve as excellent heat sources for thermal desalination processes. Since thermal desalination processes require large quantities of heat sources, geothermal based energy source represents a feasible, sustainable, and an environmentally friendly option. The advantage with geothermal source is that it can act as a heat source and a storage medium for process energy utilization. If these water sources have high dissolved solids, then they can serve as feed water for the desalination process. Since external energy consumption is minimized except for the mechanical energy requirements, geothermal enabled desalination processes could have less environmental impacts when compared to other nonrenewable energy driven desalination processes. Cogeneration schemes for simultaneous water and power production are also possible with geothermal sources as well as poly generation with multiple process benefits involving cooling and heating applications. This paper provides the present state-of-the-art of geothermal desalination with discussion on the benefits of geothermal desalination over other renewable and nonrenewable energy driven desalination configurations. Present status of the worldwide geothermal desalination and the potential for future developments in this technological area were discussed in detail with case studies for Australia, Caribbean Islands, Central America (Coasta Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama), India, Israel, the Kingdom of Saudi Arabia, UAE, USA, and Sub-Saharan Africa.
Highlights•Microbial fuel cell is a promising technology to mitigate environmental pollution.•Water sanitation coupled with electricity generation in MFCs is critically reviewed.•Electron release-transfer-acceptance mechanisms are key to MFC enhanced performance.•Various environmental pollutants can be removed or transformed into useful products.•MFCs integrated systems design might benefit from higher energy and water recovery. AbstractEnvironmental issues associated with water sanitation are not confined to developing countries alone but are the most basic human and environmental necessities all over the world. Wastewater sources are major causes for environmental pollution in surface and ground water bodies. Current wastewater treatment technologies are not sustainable to meet the ever growing water sanitation needs due to rapid industrialization and population growth, simply because they are energy and cost intensive leaving latitude for development of technologies that are energy conservative or energy yielding. For the present and future context, microbial fuel cells technology may present a sustainable and an environmentally friendly route to meet the water sanitation needs. Microbial fuel cell based wastewater systems employ bioelectrochemical catalytic activity of microbes to produce electricity from the oxidation of organic, and in some cases inorganic, substrates present in urban sewage, agricultural, dairy, food and industrial wastewaters. This article presents the potential for energy generation and comprehensive wastewater treatment in microbial fuel cells. The article provides an overview of recent literature with two specific aims. First, it provides an overview of current energy needs for wastewater treatment and potential energy recovery options followed by a comprehensive review of the principles of wastewater treatment, substrate utilization (organic removal), recent process developments, nutrient and metal removal capacities in microbial fuel cells. Several issues related to process performance, organic removal capacities and potential environmental impacts were discussed in detail. From the economic and life cycle assessment point of view, although recent developments in power production are encouraging, important discoveries in electrode materials, innovative and integrated process configurations along with experience in pilot scale studies are urgently required to determine the real potential of the microbial fuel cell technology to provide sustainable and energy positive wastewater treatment. Graphical abstract
Highlights•Effect of pulse sonication in transesterification of used vegetable oil was studied.•7 s ON/2 s OFF pulse mode resulted in a maximum biodiesel conversion of 99%.•Ethanol–methanol mixture provides high quality and quantity biodiesel.•Avoiding alcohol boiling temperatures may improve biodiesel yield.•Duty cycle is less important when compared to the optimum pulse mode operation. AbstractThis study evaluated the most suitable pulse mode (pulse ON–OFF pattern) for transesterification of waste cooking oil (WCO) using sodium hydroxide. Pulse sonication effect was investigated using ethanol, methanol, and ethanol–methanol mixtures to convert waste cooking oil into biodiesel. The importance of duty cycle (pulse-mode operation) and the role of reaction temperature during the conversion process were discussed. A maximum biodiesel yield of 99% was obtained for a pulse ON–OFF combination of 7 s–2 s at 150 W power output, and the optimum reaction conditions of 9:1 alcohol-to-oil molar ratio (50%-ethanol, 50%-methanol), 1 wt.% of NaOH, and 1.5 min reaction time. Graphical abstract
Highlights•Sustainability of desalination was appraised and a current perspective was elaborated.•A comparison with other water supply and wastewater treatment alternatives presented.•Recent developments around the world in desalination applications were discussed.•Driving factors for desalination market and sensitive, futuristic issues discussed.•Socio-economic, energy and environmental components of desalination were discussed. AbstractDesalination technologies have evolved and advanced rapidly along with increasing water demands around the world since 1950s. Many reviews have focused on the techno-economic and environmental and ecological issues of the desalination technologies and emphasized the feasibility of desalination industry as an alternative to meet the water demands in many water scarce regions. Despite these efforts, many perceptions about desalination processes hinder their applications for potential water supplies. This article has two specific aims: 1) provide an overview of the desalination trends around the world and discuss the sustainability components of desalination processes in comparison with other water supply alternatives; and 2) discuss case studies for desalination, and drivers and factors that influence sustainable desalination and other alternative water sources for desalination to increase our current understanding on the sensitive and futuristic issues of water supply and resource management options for drought facing regions. Although some of the facts and recent developments discussed here show that desalination can be affordable and potentially sustainable, contributions that meaningfully address socio-economic and ecological and environmental issues of desalination processes are urgently required in this critical era of severe water stress for the present context and the future development of desalination technologies. Graphical abstract
Conventional energy sources are limited and non-renewable and their consumption contributes to greenhouse gas emissions. The world is in need of advanced biorefineries to meet ever growing energy demands associated with population growth and economic development. An advanced biorefinery should use renewable and sustainable (both in quality and quantity) feedstock that gives rise to higher energy gains with minimum non-renewable energy and resource consumption. Development of advanced biorefineries is currently encircled by two major issues. The first issue is to ensure adequate biofuel feedstock supplies while the second issue is to develop resource-efficient technologies for the feedstock conversion to maximize energy and economic and environmental benefits. While microalgae, microbial derived oils, and agricultural biomass and other energy crops show great potential for meeting current energy demands in a sustainable manner, process intensification and associated synergism can improve the resource utilization efficiency. Synergism of process intensification tools is important to increase energy efficiency, reduce chemical utilization and associated environmental impacts, and finally process economics. Among the many process intensification methods, this commentary provides a perspective on the essential role of MWs and US and their synergy in biofuel production. Individual, sequential, and simultaneous applications of MWs and US irradiations can be utilized for process intensification of various biofuels production and selective recovery of high value bioproducts. Process related barriers, namely mass and heat transfer limitations, can be eliminated by this synergism while improving the reaction efficiency and overall process economics significantly. In this article, a brief review focused on recent developments in MW and US mediated process intensification for biofuel synthesis and associated issues in their synergism followed by a discussion on current challenges and future prospective is presented. Graphical Figure optionsDownload full-size imageDownload as PowerPoint slide
Thermodynamic and resource utilization efficiency analysis of a low temperature water desalination systemPublished: 05 November 2015 by MDPI AG in 2nd International Electronic Conference on Entropy and Its Applications
<p>A new low-temperature phase-change desalination process was studied in which, saline water is desalinated by evaporation at near-ambient temperatures under low pressures. The low pressure is achieved naturally in the head space of water columns of a height equal to the local barometric head. We present the energy, exergy and emergy analysis of this process to evaluate the thermodynamic efficiency of its major components and to identify suitable operating conditions to minimize exergy destruction and maximize resource utilization (emergy). For energy and exergy analysis, three different heat sources such as direct solar (SSV), photovoltaic energy (SSPV) as well as a low grade heat source (SSL) were considered. Exergy analysis showed that the major exergy destruction occurs in the condenser where the latent heat of the water vapor is lost to the environment. The overall exergy efficiencies were 0.04%, 0.051%, and 0.78% respectively for SSV, SSP, and SSL configurations. Exergy performance of individual process components and recommendations to further improve the exergy efficiency of the proposed process were discussed.</p> <p>Emergy analysis was performed on the three different configurations to assess their resource utilization efficiencies, environmental impacts, and sustainability. Six different indices based on the emergy approach took into account factors such as renewable and non-renewable energy used by the process, benefit of the process to society, and the cost of the process. Based on the indices estimated in this study, the configuration utilizing thermal energy from low grade heat source (such as a solar water heater) was found to be the most promising sustainable technology. Results of this study indicate that future research and development work on the barometric distillation process should focus on further refining the configuration utilizing thermal energy from a solar water heater.</p>
Synergistic effect of simultaneous microwave and ultrasound irradiations on transesterification of waste vegetable oilPublished: 01 December 2014 by Elsevier BV in Fuel
Transesterification of used vegetable oil catalyzed by barium oxide under simultaneous microwave and ultrasound irradiat...Published: 01 December 2014 by Elsevier BV in Energy Conversion and Management
Transesterification of waste vegetable oil under pulse sonication using ethanol, methanol and ethanol–methanol mixturesPublished: 01 December 2014 by Elsevier BV in Waste Management
This study reports on the effects of direct pulse sonication and the type of alcohol (methanol and ethanol) on the transesterification reaction of waste vegetable oil without any external heating or mechanical mixing. Biodiesel yields and optimum process conditions for the transesterification reaction involving ethanol, methanol, and ethanol-methanol mixtures were evaluated. The effects of ultrasonic power densities (by varying sample volumes), power output rates (in W), and ultrasonic intensities (by varying the reactor size) were studied for transesterification reaction with ethanol, methanol and ethanol-methanol (50%-50%) mixtures. The optimum process conditions for ethanol or methanol based transesterification reaction of waste vegetable oil were determined as: 9:1 alcohol to oil ratio, 1% wt. catalyst amount, 1-2 min reaction time at a power output rate between 75 and 150 W. It was shown that the transesterification reactions using ethanol-methanol mixtures resulted in biodiesel yields as high as >99% at lower power density and ultrasound intensity when compared to ethanol or methanol based transesterification reactions.
The use of non-conventional methods namely microwaves and ultrasound for extractive-transesterification of algal lipids (Chlorella, sp.) using ethanol as a solvent was investigated. Microwaves and ultrasound possess unique enhancing (thermal and non-thermal) mechanisms that can assist in successful and simultaneous extraction and transesterification of algal lipids in a very short reaction time. This paper presents a comparative study of microwave and ultrasound effects on the algal biodiesel production. The following conditions were determined as optimum through experimental studies: (1) microwaves – 1:12 algae to ethanol (wt./vol.) or 1:500 (molar) ratio; 2 wt.% catalyst; 5–6 min reaction time at 350 W microwave power; and (2) ultrasound – 1:6–9 algae to ethanol (wt./vol.) or 1:250–375 (molar) ratio; 2 wt.% catalyst; 6 min reaction time at 490 W ultrasound power. The highest fatty acid ethyl ester (FAEE) yields and conversions for microwave and ultrasound methods were 18.8%; 18.5% (yields) and 96.2%; 95.0% (conversions) respectively. In comparison, ultrasound method resulted in higher FAEE yield and conversion at low solvent ratios while microwaves were able to produce better results at lower power levels compared to ultrasound. The two methods performed better than the conventional bench-top Bligh and Dyer method which followed a two-step extraction and transesterification method with FAEE yields and conversions of 13.9% and 78.1% respectively.
Chitosan enhanced coagulation of algal turbid waters – Comparison between rapid mix and ultrasound coagulation methodsPublished: 01 May 2014 by Elsevier BV in Chemical Engineering Journal
This study describes the use of microwaves (MW) for enhanced extractive-transesterification of algal lipids from dry algal biomass (Chlorella sp.). Two different single-step extractive-transesterification methods under MW irradiation were evaluated: (1) with ethanol as solvent/reactant and sodium hydroxide catalyst; and (2) with ethanol as reactant and hexane as solvent (sodium hydroxide catalyst). Biodiesel (fatty-acid-ethyl-esters, FAEE) yields from these two methods were compared with the conventional Bligh and Dyer (BD) method which followed a two-step extraction-transesterification process. The maximum lipid yields for MW, MW with hexane and BD methods were 20.1%, 20.1%, and 13.9%, respectively; while the FAEE conversion of the algal lipids were 96.2%, 94.3%, and 78.1%, respectively. The algae-biomass:ethanol molar ratio of 1:250–500 and 2.0–2.5% catalyst with reaction times around 6 min were determined as optimum conditions for both methods. This study confers that the single-step non-conventional methods can contribute to higher algal lipid and FAEE yields.
This study reports the kinetics of ultrasonic transesterification of waste cooking oil into fatty acid methyl esters (FAMEs). Direct sonication of waste cooking oil under controlled external temperatures was performed. Transesterification kinetics under the influence of direct sonication was studied using eight different individual reaction orders with respect to waste cooking oil and methanol. The results show that reaction temperature has a very small effect on the transesterification reaction under direct sonication. The reaction rate constants for different temperatures (35, 45, 55, and 65°C) are determined as: 10.642 g2 mol−2 min−1; 7.053; 7.9727; 10.971 g mol−1 min−1 respectively and the activation energy of the ultrasonic transesterification of waste cooking oil was 19,645 J mol−1 K−1. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1051–1058, 2014
Microwave energy based chemical synthesis has several merits and is important from both scientific and engineering standpoints. Microwaves have been applied in numerous inorganic and organic chemical syntheses; perhaps, from the time their ability to work as heat source was discovered. Recent laboratory scale microwave applications in biodiesel production proved the potential of the technology to achieve superior results over conventional techniques. Short reaction time, cleaner reaction products, and reduced separation-purification times are the key observations reported by many researchers. Energy utilization and specific energy requirements for microwave based biodiesel synthesis are reportedly better than conventional techniques. Microwaves can be very well utilized in feedstock preparation, extraction and transesterification stages of the biodiesel production process. Although microwave technology has advanced in other food, pharmaceutical and polymer chemistry related research and industry, it has yet to prove its potential in the biodiesel industry at large scale applications. This paper reviews principles and practices of microwave energy technology as applied in biodiesel feedstock preparation and processing. Analysis of laboratory scale studies, potential design and operation challenges for developing large scale biodiesel production systems are discussed in detail.
Sustainable biodiesel production should: a) utilize low cost renewable feedstock; b) utilize energy-efficient, nonconventional heating and mixing techniques; c) increase net energy benefit of the process; and d) utilize renewable feedstock/energy sources where possible. In this paper, we discuss the merits of biodiesel production following these criteria supported by the experimental results obtained from the process optimization studies. Waste cooking oil, non-edible (low-cost) oils (Jatropha curcas and Camelina Sativa) and algae were used as feedstock for biodiesel process optimization. A comparison between conventional and non-conventional methods such as microwaves and ultrasound was reported. Finally, net energy scenarios for different biodiesel feedstock options and algae are presented.
Current microbial desalination cell (MDC) performances are evaluated with chemical catalysts such as ferricyanide, platinum catalyzed air-cathodes or aerated cathodes. All of these methods improve power generation potential in MDCs, however, they are not preferable for large scale applications due to cost, energy and environmental toxicity issues. In this study, performance of microbial desalination cells with an air cathode and an algae biocathode (Photosynthetic MDC – PMDC) were evaluated, both under passive conditions (no mechanical aeration or mixing). The results indicate that passive algae biocathodes perform better than air cathodes and enhance COD removal and utilize treated wastewater as the growth medium to obtain valuable biomass for high value bioproducts. Maximum power densities of 84 mW m−3 (anode volume) or 151 mW m−3 (biocathode volume) and a desalination rate of 40% were measured with 0.9:1:0.5 volumetric ratios of anode, desalination and algae biocathode chambers respectively. This first proof-of-concept study proves that the passive mechanisms can be beneficial in enhancing the sustainability of microbial desalination cells.
A new low-temperature phase-change desalination process has been presented where saline water is desalinated by evaporation at near-ambient temperatures under low pressures. The low pressure is achieved naturally in the head space of water columns of a height equal to the local barometric head. By connecting the head space of such a saline water column to that of a distilled water column, and by maintaining the temperature of the former about 15–20°C above that of the latter, fresh water is evaporated from the saline column and condensed in the distilled water column. This paper presents an exergy analysis of this process to evaluate the thermodynamic efficiency of its major components and to identify suitable operating conditions to minimize exergy destruction. Three different heat sources such as direct solar, photovoltaic energy as well as a low grade heat source were considered. It was found that the major exergy destruction occurs in the condenser where the latent heat of the water vapor is lost to the environment. Exergy performance of individual process components and recommendations to further improve the exergy efficiency of the proposed process are presented.