Author: Almotasembellah Abushaban
Publisher: CRC Press
ISBN: 1000034704
Category : Science
Languages : en
Pages : 146
Book Description
Seawater desalination is increasingly being used as a means to augment freshwater supplies in regions with high water stress, and reverse osmosis is increasingly the technology of choice because of the low energy consumption. However, seawater reverse osmosis (SWRO) systems suffer from various types of fouling, which can increase energy consumption and the use of chemicals during SWRO operation. In practice, pre-treatment systems are put in place to reduce the particulate and biological fouling potential of SWRO feed water. However, simple, reliable and accurate methods to assess the extent to which biological fouling potential is reduced during pre-treatment are not available for seawater. This research developed a new method to measure bacterial growth potential (BGP) using the native bacterial consortium in seawater. New reagents to extract and detect ATP in microbial cells were specifically developed for seawater. The new lysis and detection reagents overcame the salt interference in seawater and allow low detection of total ATP, free ATP and microbial ATP in seawater. Incorporating a filtration step further increased the sensitivity of the method six fold, enabling ATP detection of ultra-low levels of microbial ATP in seawater. The newly developed ATP-based BGP method was applied to monitor and assess the pre-treatment of five full-scale seawater desalination plants around the world. A good correlation was observed between BGP measured in SWRO feed water and the pressure drop increase in the SWRO systems, suggesting the applicability of using the ATP-based BGP method as a biofouling indicator in SWRO. Furthermore, a safe level of BGP ( In the future, on-line monitoring of BGP in SWRO feed water may further reduce the consumption of chemicals and energy and improve the overall sustainability of seawater desalination by reverse osmosis.
Assessing Bacterial Growth Potential in Seawater Reverse Osmosis Pretreatment
Author: Almotasembellah Abushaban
Publisher: CRC Press
ISBN: 1000034704
Category : Science
Languages : en
Pages : 146
Book Description
Seawater desalination is increasingly being used as a means to augment freshwater supplies in regions with high water stress, and reverse osmosis is increasingly the technology of choice because of the low energy consumption. However, seawater reverse osmosis (SWRO) systems suffer from various types of fouling, which can increase energy consumption and the use of chemicals during SWRO operation. In practice, pre-treatment systems are put in place to reduce the particulate and biological fouling potential of SWRO feed water. However, simple, reliable and accurate methods to assess the extent to which biological fouling potential is reduced during pre-treatment are not available for seawater. This research developed a new method to measure bacterial growth potential (BGP) using the native bacterial consortium in seawater. New reagents to extract and detect ATP in microbial cells were specifically developed for seawater. The new lysis and detection reagents overcame the salt interference in seawater and allow low detection of total ATP, free ATP and microbial ATP in seawater. Incorporating a filtration step further increased the sensitivity of the method six fold, enabling ATP detection of ultra-low levels of microbial ATP in seawater. The newly developed ATP-based BGP method was applied to monitor and assess the pre-treatment of five full-scale seawater desalination plants around the world. A good correlation was observed between BGP measured in SWRO feed water and the pressure drop increase in the SWRO systems, suggesting the applicability of using the ATP-based BGP method as a biofouling indicator in SWRO. Furthermore, a safe level of BGP ( In the future, on-line monitoring of BGP in SWRO feed water may further reduce the consumption of chemicals and energy and improve the overall sustainability of seawater desalination by reverse osmosis.
Publisher: CRC Press
ISBN: 1000034704
Category : Science
Languages : en
Pages : 146
Book Description
Seawater desalination is increasingly being used as a means to augment freshwater supplies in regions with high water stress, and reverse osmosis is increasingly the technology of choice because of the low energy consumption. However, seawater reverse osmosis (SWRO) systems suffer from various types of fouling, which can increase energy consumption and the use of chemicals during SWRO operation. In practice, pre-treatment systems are put in place to reduce the particulate and biological fouling potential of SWRO feed water. However, simple, reliable and accurate methods to assess the extent to which biological fouling potential is reduced during pre-treatment are not available for seawater. This research developed a new method to measure bacterial growth potential (BGP) using the native bacterial consortium in seawater. New reagents to extract and detect ATP in microbial cells were specifically developed for seawater. The new lysis and detection reagents overcame the salt interference in seawater and allow low detection of total ATP, free ATP and microbial ATP in seawater. Incorporating a filtration step further increased the sensitivity of the method six fold, enabling ATP detection of ultra-low levels of microbial ATP in seawater. The newly developed ATP-based BGP method was applied to monitor and assess the pre-treatment of five full-scale seawater desalination plants around the world. A good correlation was observed between BGP measured in SWRO feed water and the pressure drop increase in the SWRO systems, suggesting the applicability of using the ATP-based BGP method as a biofouling indicator in SWRO. Furthermore, a safe level of BGP ( In the future, on-line monitoring of BGP in SWRO feed water may further reduce the consumption of chemicals and energy and improve the overall sustainability of seawater desalination by reverse osmosis.
Removal of Pollutants from Saline Water
Author: Shaik Feroz
Publisher: CRC Press
ISBN: 1000520625
Category : Technology & Engineering
Languages : en
Pages : 438
Book Description
Removal of Pollutants from Saline Water: Treatment Technologies provides a comprehensive understanding of technologies that are currently adopted in the treatment of pollutants present in saline water systems. It provides information on the treatment technologies for saline water systems, including seawater, brackish water, oil-produced water, and other industrial saline wastewaters. FEATURES Presents information exclusively for saline water pollutant removal Introduces current treatment technologies and addresses why and how the techniques differ between fresh and salt water Offers an inclusive overview of physicochemical, biological, membrane, and advanced oxidation treatment technologies Features various perspectives and case studies from relevant global experts Provides a comprehensive one-stop source for the treatment of pollutants in all saline water systems Aimed at students, academicians, researchers, and practicing engineers in the fields of chemical, civil, marine, and environmental engineering who wish to be acquainted with the most recent developments in the treatment of pollutants present in saline water systems. Prof. Dr. Shaik Feroz works at Prince Mohammad Bin Fahd University, Kingdom of Saudi Arabia. He has 30 years of experience in teaching, research, and industry. He has more than 190 publications to his credit in journals and conferences of international repute. He was awarded "Best Researcher" by Caledonian College of Engineering for the year 2014. Prof. Dr. Detlef W. Bahnemann is Head of the Research Unit, Photocatalysis and Nanotechnology at Leibniz University Hannover (Germany), Director of the Research Institute "Nanocomposite Materials for Photonic Applications" at Saint Petersburg State University (Russian Federation), and Distinguished Professor at Shaanxi University of Science and Technology in Xi’an (People's Republic of China). His research topics include photocatalysis, photoelectrochemistry, solar chemistry, and photochemistry focused on synthesis and physical-chemical properties of semiconductor and metal nanoparticles. His 500-plus publications have been cited more than 65,000 times (h-index: 100).
Publisher: CRC Press
ISBN: 1000520625
Category : Technology & Engineering
Languages : en
Pages : 438
Book Description
Removal of Pollutants from Saline Water: Treatment Technologies provides a comprehensive understanding of technologies that are currently adopted in the treatment of pollutants present in saline water systems. It provides information on the treatment technologies for saline water systems, including seawater, brackish water, oil-produced water, and other industrial saline wastewaters. FEATURES Presents information exclusively for saline water pollutant removal Introduces current treatment technologies and addresses why and how the techniques differ between fresh and salt water Offers an inclusive overview of physicochemical, biological, membrane, and advanced oxidation treatment technologies Features various perspectives and case studies from relevant global experts Provides a comprehensive one-stop source for the treatment of pollutants in all saline water systems Aimed at students, academicians, researchers, and practicing engineers in the fields of chemical, civil, marine, and environmental engineering who wish to be acquainted with the most recent developments in the treatment of pollutants present in saline water systems. Prof. Dr. Shaik Feroz works at Prince Mohammad Bin Fahd University, Kingdom of Saudi Arabia. He has 30 years of experience in teaching, research, and industry. He has more than 190 publications to his credit in journals and conferences of international repute. He was awarded "Best Researcher" by Caledonian College of Engineering for the year 2014. Prof. Dr. Detlef W. Bahnemann is Head of the Research Unit, Photocatalysis and Nanotechnology at Leibniz University Hannover (Germany), Director of the Research Institute "Nanocomposite Materials for Photonic Applications" at Saint Petersburg State University (Russian Federation), and Distinguished Professor at Shaanxi University of Science and Technology in Xi’an (People's Republic of China). His research topics include photocatalysis, photoelectrochemistry, solar chemistry, and photochemistry focused on synthesis and physical-chemical properties of semiconductor and metal nanoparticles. His 500-plus publications have been cited more than 65,000 times (h-index: 100).
Membrane Desalination
Author: Andreas Sapalidis
Publisher: CRC Press
ISBN: 0429672055
Category : Science
Languages : en
Pages : 401
Book Description
This book aims to provide details about membrane desalination processes, starting from basic concepts leading to real world implementation. Chapters cover novel research topics such as biomimetic and nanocomposite membranes, nanostructured fillers for mixed matrix membranes, advanced characterization techniques and molecular modeling. Additionally, engineering and economical aspects of desalination as well as the exploitation of green energy sources are thoroughly presented. This books targets bridging the gap between the everyday research laboratory practices with practical application demands, so that the readers gain a global perspective of all desalination challenges.
Publisher: CRC Press
ISBN: 0429672055
Category : Science
Languages : en
Pages : 401
Book Description
This book aims to provide details about membrane desalination processes, starting from basic concepts leading to real world implementation. Chapters cover novel research topics such as biomimetic and nanocomposite membranes, nanostructured fillers for mixed matrix membranes, advanced characterization techniques and molecular modeling. Additionally, engineering and economical aspects of desalination as well as the exploitation of green energy sources are thoroughly presented. This books targets bridging the gap between the everyday research laboratory practices with practical application demands, so that the readers gain a global perspective of all desalination challenges.
Gas Hydrate in Water Treatment
Author: Bhajan Lal
Publisher: John Wiley & Sons
ISBN: 1119866073
Category : Science
Languages : en
Pages : 340
Book Description
GAS HYDRATE IN WATER TREATMENT Explores current progress in the expanding field of gas hydrate-based desalination As potable water shortages continue to affect billions of people worldwide, seawater desalination and wastewater treatment have the potential to meet freshwater demands in the near future. Gas hydrate-based desalination, a process which requires CO2 and water as solvent, has become an increasingly popular approach—desalination with hydrates is environmentally friendly and can produce cheaper desalted water than other existing conventional technologies. Gas Hydrate in Water Treatment: Technological, Economic, and Industrial Aspects provides detailed, up-to-date reference to the application of gas hydrates in wastewater and seawater desalination treatment. Edited by experienced researchers in the field, this comprehensive volume describes the fundamental aspects of desalination and summarizes the latest research on gas hydrate-based desalination. The authors address a broad range of key topics, including issues related to water scarcity, post-treatment of desalinated water using both conventional and new technologies, hydrate-based desalination methods driven by renewable energy sources, and more. Provides thorough coverage of the technological, waste brine management, economic, and renewable energy and remineralization aspects of gas hydrate-based wastewater treatment Describes the energetic, economic, and environmental impact of gas hydrate desalination Explains the core concepts of gas hydrate-based desalination to help readers evaluate the performance of existing desalination processes Discusses the advantages and challenges of hydrate-based water treatment Compares conventional and gas hydrate technologies used in water treatment Reviews the most recent research in gas hydrate-based desalination Gas Hydrate in Water Treatment: Technological, Economic, and Industrial Aspects is an essential resource for all academics, researchers, process engineers, designers, industry professionals, and advanced students in the field.
Publisher: John Wiley & Sons
ISBN: 1119866073
Category : Science
Languages : en
Pages : 340
Book Description
GAS HYDRATE IN WATER TREATMENT Explores current progress in the expanding field of gas hydrate-based desalination As potable water shortages continue to affect billions of people worldwide, seawater desalination and wastewater treatment have the potential to meet freshwater demands in the near future. Gas hydrate-based desalination, a process which requires CO2 and water as solvent, has become an increasingly popular approach—desalination with hydrates is environmentally friendly and can produce cheaper desalted water than other existing conventional technologies. Gas Hydrate in Water Treatment: Technological, Economic, and Industrial Aspects provides detailed, up-to-date reference to the application of gas hydrates in wastewater and seawater desalination treatment. Edited by experienced researchers in the field, this comprehensive volume describes the fundamental aspects of desalination and summarizes the latest research on gas hydrate-based desalination. The authors address a broad range of key topics, including issues related to water scarcity, post-treatment of desalinated water using both conventional and new technologies, hydrate-based desalination methods driven by renewable energy sources, and more. Provides thorough coverage of the technological, waste brine management, economic, and renewable energy and remineralization aspects of gas hydrate-based wastewater treatment Describes the energetic, economic, and environmental impact of gas hydrate desalination Explains the core concepts of gas hydrate-based desalination to help readers evaluate the performance of existing desalination processes Discusses the advantages and challenges of hydrate-based water treatment Compares conventional and gas hydrate technologies used in water treatment Reviews the most recent research in gas hydrate-based desalination Gas Hydrate in Water Treatment: Technological, Economic, and Industrial Aspects is an essential resource for all academics, researchers, process engineers, designers, industry professionals, and advanced students in the field.
Seawater Pretreatment
Author: Nikolay Voutchkov
Publisher:
ISBN: 9789744017956
Category : Membranes (Technology).
Languages : en
Pages : 173
Book Description
Publisher:
ISBN: 9789744017956
Category : Membranes (Technology).
Languages : en
Pages : 173
Book Description
Recent Trends in Biofilm Science and Technology
Author: Manuel Simoes
Publisher: Academic Press
ISBN: 0128194987
Category : Science
Languages : en
Pages : 418
Book Description
Recent Trends in Biofilm Science and Technology helps researchers working on fundamental aspects of biofilm formation and control conduct biofilm studies and interpret results. The book provides a remarkable amount of knowledge on the processes that regulate biofilm formation, the methods used, monitoring characterization and mathematical modeling, the problems/advantages caused by their presence in the food industry, environment and medical fields, and the current and emergent strategies for their control. Research on biofilms has progressed rapidly in the last decade due to the fact that biofilms have required the development of new analytical tools and new collaborations between biologists, engineers and mathematicians. - Presents an overview of the process of biofilm formation and its implications - Provides a clearer understanding of the role of biofilms in infections - Creates a foundation for further research on novel control strategies - Updates readers on the remarkable amount of knowledge on the processes that regulate biofilm formation
Publisher: Academic Press
ISBN: 0128194987
Category : Science
Languages : en
Pages : 418
Book Description
Recent Trends in Biofilm Science and Technology helps researchers working on fundamental aspects of biofilm formation and control conduct biofilm studies and interpret results. The book provides a remarkable amount of knowledge on the processes that regulate biofilm formation, the methods used, monitoring characterization and mathematical modeling, the problems/advantages caused by their presence in the food industry, environment and medical fields, and the current and emergent strategies for their control. Research on biofilms has progressed rapidly in the last decade due to the fact that biofilms have required the development of new analytical tools and new collaborations between biologists, engineers and mathematicians. - Presents an overview of the process of biofilm formation and its implications - Provides a clearer understanding of the role of biofilms in infections - Creates a foundation for further research on novel control strategies - Updates readers on the remarkable amount of knowledge on the processes that regulate biofilm formation
Controlling Biofouling in Seawater Reverse Osmosis Membrane Systems
Author: Nirajan Dhakal
Publisher: CRC Press
ISBN: 1351056085
Category : Science
Languages : en
Pages : 175
Book Description
Seawater desalination is a rapidly growing coastal industry that is increasingly threatened by algal blooms. Depending on the severity of algal blooms, desalination systems may be forced to shut down because of clogging and/or poor feed water quality. To maintain stable operation and provide good feed water quality to seawater reverse osmosis (SWRO) systems, ultrafiltration (UF) pre-treatment is proposed. This research focused on assessing the ability of UF and other pre-treatment technologies to reduce biofouling in SWRO systems. An improved method to measure bacterial regrowth potential (BRP) was developed and applied at laboratory, pilot and full scale to assess the ability of conventional UF (150 kDa) and tight UF (10 kDa) alone and in combination with a phosphate adsorbent to reduce regrowth potential and delay the onset of biofouling in SWRO. The improved bacterial regrowth potential method employs a natural consortium of marine bacteria as inoculum and flow cytometry. The limit of detection of the BRP method was lowered to 43,000 ± 12,000 cells/mL, which is equivalent to 9.3 ± 2.6 μg-Cglucose/L. The reduction in bacterial regrowth potential after tight UF (10 kDa) was 3 to 4 times higher than with conventional UF (150 kDa). It was further reduced after the application of a phosphate adsorbent, independent of pore size of the UF membrane. Pilot studies demonstrated that the application of tight UF (10 kDa) coupled with a phosphate adsorbent consistently lowered the bacterial regrowth potential and no feed channel pressure drop increase was observed in membrane fouling simulators (MFS) over a period of 21 days. The study also showed that non-backwashable fouling of UF membranes varied strongly with the type of algal species and the algal organic matter (AOM) they release. The presence of polysaccharide (stretching -OH) and sugar ester groups (stretching S=O) was the main cause of non-backwashable fouling. In conclusion, this study showed that an improved BRP method is suitable for the assessment of SWRO pre-treatment systems and it can be a useful tool to develop potential strategies to mitigate biofouling and improve the sustainability of SWRO systems.
Publisher: CRC Press
ISBN: 1351056085
Category : Science
Languages : en
Pages : 175
Book Description
Seawater desalination is a rapidly growing coastal industry that is increasingly threatened by algal blooms. Depending on the severity of algal blooms, desalination systems may be forced to shut down because of clogging and/or poor feed water quality. To maintain stable operation and provide good feed water quality to seawater reverse osmosis (SWRO) systems, ultrafiltration (UF) pre-treatment is proposed. This research focused on assessing the ability of UF and other pre-treatment technologies to reduce biofouling in SWRO systems. An improved method to measure bacterial regrowth potential (BRP) was developed and applied at laboratory, pilot and full scale to assess the ability of conventional UF (150 kDa) and tight UF (10 kDa) alone and in combination with a phosphate adsorbent to reduce regrowth potential and delay the onset of biofouling in SWRO. The improved bacterial regrowth potential method employs a natural consortium of marine bacteria as inoculum and flow cytometry. The limit of detection of the BRP method was lowered to 43,000 ± 12,000 cells/mL, which is equivalent to 9.3 ± 2.6 μg-Cglucose/L. The reduction in bacterial regrowth potential after tight UF (10 kDa) was 3 to 4 times higher than with conventional UF (150 kDa). It was further reduced after the application of a phosphate adsorbent, independent of pore size of the UF membrane. Pilot studies demonstrated that the application of tight UF (10 kDa) coupled with a phosphate adsorbent consistently lowered the bacterial regrowth potential and no feed channel pressure drop increase was observed in membrane fouling simulators (MFS) over a period of 21 days. The study also showed that non-backwashable fouling of UF membranes varied strongly with the type of algal species and the algal organic matter (AOM) they release. The presence of polysaccharide (stretching -OH) and sugar ester groups (stretching S=O) was the main cause of non-backwashable fouling. In conclusion, this study showed that an improved BRP method is suitable for the assessment of SWRO pre-treatment systems and it can be a useful tool to develop potential strategies to mitigate biofouling and improve the sustainability of SWRO systems.
Pretreatment for Reverse Osmosis Desalination
Author: Nikolay Voutchkov
Publisher: Elsevier
ISBN: 0128099453
Category : Science
Languages : en
Pages : 308
Book Description
Pretreatment for Reverse Osmosis Desalination is a comprehensive reference on all existing and emerging seawater pretreatment technologies used for desalination. The book focuses on reverse osmosis membrane desalination, which at present is the most widely applied technology for the production of fresh drinking water from highly saline water sources (brackish water and seawater). Each chapter contains examples illustrating various pretreatment technologies and their practical implementation. - Provides in-depth overview of the key theoretical concepts associated with desalination pre-treatment - Gives insight into the latest trends in membrane separation technology - Incorporates analytical methods and guidelines for monitoring pretreatment systems
Publisher: Elsevier
ISBN: 0128099453
Category : Science
Languages : en
Pages : 308
Book Description
Pretreatment for Reverse Osmosis Desalination is a comprehensive reference on all existing and emerging seawater pretreatment technologies used for desalination. The book focuses on reverse osmosis membrane desalination, which at present is the most widely applied technology for the production of fresh drinking water from highly saline water sources (brackish water and seawater). Each chapter contains examples illustrating various pretreatment technologies and their practical implementation. - Provides in-depth overview of the key theoretical concepts associated with desalination pre-treatment - Gives insight into the latest trends in membrane separation technology - Incorporates analytical methods and guidelines for monitoring pretreatment systems
Comprehensive Membrane Science and Engineering
Author: Enrico Drioli
Publisher: Elsevier
ISBN: 0444637966
Category : Science
Languages : en
Pages : 1709
Book Description
Comprehensive Membrane Science and Engineering, Second Edition, Four Volume Set is an interdisciplinary and innovative reference work on membrane science and technology. Written by leading researchers and industry professionals from a range of backgrounds, chapters elaborate on recent and future developments in the field of membrane science and explore how the field has advanced since the previous edition published in 2010. Chapters are written by academics and practitioners across a variety of fields, including chemistry, chemical engineering, material science, physics, biology and food science. Each volume covers a wide spectrum of applications and advanced technologies, such as new membrane materials (e.g. thermally rearranged polymers, polymers of intrinsic microporosity and new hydrophobic fluoropolymer) and processes (e.g. reverse electrodialysis, membrane contractors, membrane crystallization, membrane condenser, membrane dryers and membrane emulsifiers) that have only recently proved their full potential for industrial application. This work covers the latest advances in membrane science, linking fundamental research with real-life practical applications using specially selected case studies of medium and large-scale membrane operations to demonstrate successes and failures with a look to future developments in the field. Contains comprehensive, cutting-edge coverage, helping readers understand the latest theory Offers readers a variety of perspectives on how membrane science and engineering research can be best applied in practice across a range of industries Provides the theory behind the limits, advantages, future developments and failure expectations of local membrane operations in emerging countries
Publisher: Elsevier
ISBN: 0444637966
Category : Science
Languages : en
Pages : 1709
Book Description
Comprehensive Membrane Science and Engineering, Second Edition, Four Volume Set is an interdisciplinary and innovative reference work on membrane science and technology. Written by leading researchers and industry professionals from a range of backgrounds, chapters elaborate on recent and future developments in the field of membrane science and explore how the field has advanced since the previous edition published in 2010. Chapters are written by academics and practitioners across a variety of fields, including chemistry, chemical engineering, material science, physics, biology and food science. Each volume covers a wide spectrum of applications and advanced technologies, such as new membrane materials (e.g. thermally rearranged polymers, polymers of intrinsic microporosity and new hydrophobic fluoropolymer) and processes (e.g. reverse electrodialysis, membrane contractors, membrane crystallization, membrane condenser, membrane dryers and membrane emulsifiers) that have only recently proved their full potential for industrial application. This work covers the latest advances in membrane science, linking fundamental research with real-life practical applications using specially selected case studies of medium and large-scale membrane operations to demonstrate successes and failures with a look to future developments in the field. Contains comprehensive, cutting-edge coverage, helping readers understand the latest theory Offers readers a variety of perspectives on how membrane science and engineering research can be best applied in practice across a range of industries Provides the theory behind the limits, advantages, future developments and failure expectations of local membrane operations in emerging countries
Reverse Osmosis Seawater Desalination Volume 2
Author: Heinz Ludwig
Publisher: Springer Nature
ISBN: 3030819272
Category : Science
Languages : en
Pages : 641
Book Description
Seawater reverse osmosis (SWRO) is the dominant desalination process worldwide for obtaining fresh water from the sea. The subject matter and scope of this book is the conceptual and advanced planning, design and engineering of plants of this desalination process together with the associated facilities for seawater pretreatment, post-treatment of the product water, wastewater treatment, seawater extraction and plant discharge. The book is intended to be used by technicians, engineers, economists and ecologists in the planning, design and operation of SWRO plants, as an educational and training tool, as well as an aid in environmental licensing of membrane desalination plants, and by interested laypersons for information about this process. The two volumes are also available as a set.
Publisher: Springer Nature
ISBN: 3030819272
Category : Science
Languages : en
Pages : 641
Book Description
Seawater reverse osmosis (SWRO) is the dominant desalination process worldwide for obtaining fresh water from the sea. The subject matter and scope of this book is the conceptual and advanced planning, design and engineering of plants of this desalination process together with the associated facilities for seawater pretreatment, post-treatment of the product water, wastewater treatment, seawater extraction and plant discharge. The book is intended to be used by technicians, engineers, economists and ecologists in the planning, design and operation of SWRO plants, as an educational and training tool, as well as an aid in environmental licensing of membrane desalination plants, and by interested laypersons for information about this process. The two volumes are also available as a set.