Management of Concentrate from Desalination Plants

Nikolay Voutchkov, Gisela Kaiser

• Publisher: Elsevier
• Year: 2020
• Print ISBN: 9780128180457
• eBook ISBN: 9780128180464
• Topic: Technology & Engineering
• Subtopic: Microbiology
• Index: Technology & Engineering

Management of Concentrate from Desalination Plants provides an overview of the alternatives for managing concentrate generated by brackish water and seawater desalination plants, as well as site-specific factors involved in the selection of the most viable alternative for a given project, and the environmental permitting requirements and studies associated with their implementation. The book focuses on widely used alternatives for disposal of concentrate, including discharge to surface water bodies; disposal to the wastewater collection system; deep well injection; land application; evaporation; and zero liquid discharge.Direct discharge through new outfall; discharge through existing wastewater treatment plant outfall; and co-disposal with the cooling water of existing coastal power plant are thoroughly described, and design guidance for the use of these concentrate disposal alternatives is presented with engineers and practitioners in the field of desalination in mind. Key advantages, disadvantages, environmental impact issues, and possible solutions are presented for each discharge alternative. Easy-to-use graphs depicting construction costs as a function of concentrate flow rate are provided for all key concentrate management alternatives.- Gives a critical overview of the latest practices and technological advancements in managing concentrate- Discusses the relationship between concentrate quality and quantity and other desalination processes- Provides design and cost guidance information to assist practitioners with the selection and sizing of the most commonly practiced concentrate disposal alternatives

Chapter 1

Introduction to concentrate management

Abstract

Desalination is becoming increasingly popular for the production of fresh potable water due to the elevated risk of water scarcity as a result of climate change and growth in demand, especially in highly urbanized coastal regions. As the number of plants and volumes of desalinated water increase, assurance must be provided for the environmental sustainability of such discharges over extended time periods. Potential environmental impacts can be minimized through treatment of concentrate and optimal discharge configuration and design, either directly into the water body, or disposed together with treated wastewater or cooling water from power plants. This chapter provides a brief introduction to the current status of desalination worldwide and an overview of the most commonly used concentrate management alternatives.

Keywords

Desalination status; water security; coastal population water demand; desalination production; energy demand; concentrate management practices; strategic water resources; surface water discharge; concentrate regulations; mega-project risks

Desalination is becoming increasingly popular for the production of fresh potable water since many inland and coastal municipalities and utilities in arid regions of the world are looking for new, reliable, and drought-proof local sources of water. Climate change increases the risks of water scarcity, which are amplified in vulnerable communities lacking essential infrastructure. Desalination is a tried-and-tested adaptation option to increase the reliability of water resources but has relatively higher production cost, energy demand, and carbon footprint as compared to conventional water supply alternatives. Similar to conventional water treatment plants and water reclamation facilities, desalination plants also generate discharge, which contains the plant’s source water treatment byproducts. For a desalination project to be viable, plant discharge has to be disposed of in an environmentally safe and sustainable manner that is compliant with all applicable governmental regulatory requirements.

One of the key limiting factors for the construction of new desalination plants is the availability of suitable conditions and location for disposal of the high-salinity waste stream generated during the desalination process, commonly referred to as concentrate or brine. Monitoring programs at existing plants worldwide have shown that impacts on the marine environment are nonexistent or very limited and localized with proper plant outfall configuration, siting, and design. Publicizing information of such monitoring programs have the capability of improving trust in desalination technology, and ensuring enhanced sustainability of future plant developments. This book provides an overview of existing concentrate management options, their advantages, disadvantages, and implementation constraints.

1.1 Current status of desalination

Accessible freshwater makes up only a fraction (<2.5%) of total water on the planet. Populations around the world historically relied on surface water (from rainfall) and groundwater, but both of these sources are vulnerable to changes in climate and variability in weather. As populations grew in locations where freshwater was scarce, new supply sources were pursued. The first thermal desalination plants were built in the beginning of the 20th century, while the first commercial brackish and seawater reverse osmosis (RO) plants came into operation in the 1960s and 1970s, respectively. With technology advancing, recycling and reuse of water is now also viable, expanding the options of potable water supply.

As the cost of water increases through diversification of supply beyond reliance on rainfall, so the value of water becomes more apparent. Sustainable water management requires that all water in the system is accounted for, and demand management forms an important aspect of reconciling demand and supply. Demand management should be the first, and is generally the least costly intervention to stretch available supply, but there are limits to efficiencies, beyond which additional water resources will inevitably be required.

While the value of water needs to be better appreciated, and the world aspires to a circular economy and closed-loop resource systems, growth in population and quality of life will require additional potable water in the foreseeable future. The ocean has two unique and distinctive features as a water supply source: It is drought-proof and is practically limitless. Over half of the world population lives in urban centers bordering the ocean. In many arid parts of the world such as the Middle East, Australia, Northern Africa, and Southern California, the population concentration along the coast exceeds 75%. Usually coastal zones have the highest population growth as well, resulting in seawater desalination being a logical solution for sustainable, longer-term water resource management to match growing water demand pressures in coastal areas.

Desalination removes the salts, pathogens and impurities from saline water to render it potable. Desalinated water is produced either from brackish water (saline water with total dissolved solids [TDS] content of less than 10,000 mg/L) or from seawater (TDS between 30,000 and 50,000 mg/L). Although brackish aquifers and surface waters have been used for production of fresh drinking water for over 50 years, these brackish water sources are of limited availability and have a long replenishment cycle resulting in limited long-term sustainability. In contrast, the world’s oceans contain over 97% of the planet’s water resources, providing an essentially unlimited raw material for seawater desalination. In most urban centers, the freshwater produced by desalination of seawater is returned back to the ocean in the form of treated wastewater. Usually wastewater treatment plants are within a 25–50 km radius of the desalination plants along the coast and the time to return over 80% of the desalinated seawater to the ocean as wastewater discharge is typically less than 1 week. Most of the remaining 20% of the desalinated water is lost to evaporation and ground percolation as drinking water and wastewater generated from it are mainly used for irrigation. This makes seawater desalination one of the water supply options with the shortest water cycle, shorter than lake, river, or brackish water sources.

With growing water scarcity and significantly reduced cost, interest in desalination has risen in recent decades. This is particularly true in the Middle East, where severe water scarcity and relatively low cost of energy have facilitated the early adoption of desalination as a main source of potable water supply. Driven by rising demand and commercial innovation, the cost of desalination has decreased significantly over time, and is becoming an increasingly feasible and sustainable option for most other countries worldwide.

At present, over 16,000 desalination plants worldwide provide drought-proof water supply for a large number of arid urban coastal municipalities of the Middle and Far East, Europe, Africa, Australia, and the Americas (Jones et al, 2018). Almost half of these plants (44%) are in the still fast-growing Middle East region. However, other regions of the world, notably Asia (in particular, China), the United States, and Latin America are also experiencing accelerated desalination plant capacity growth of 6%–8% per year, which far exceeds the growth rate of conventional water supply sources (2%–3% per year).

Production of freshwater by desalination in 2019 totaled approximately 95 million m³/day (24,300 MGD). The corresponding cumulative volume of concentrate generated by the desalination plants in operation at present is estimated to be 142 million m³/day (37,500 MGD). Approximately 74% of the existing desalination plants use membrane RO technology for salt separation; 21% apply thermal evaporation; and 5% use other salt separation technologies, such as electrodialysis (ED) and ion exchange (IX) to produce freshwater (see Fig. 1.1). After 2015, most Middle Eastern countries have drastically reduced the construction of new thermal desalination plants and have refocused on the use of membrane desalination due to its lower energy demand and operational flexibility.

Figure 1.1 Current status of worldwide desalination technology use. Data from IDA Desalination Yearbook 2018–19.

Desalination of brackish and seawater is becoming increasingly popular for production of fresh potable water in the United States. Based on a 2017 survey (Mickley, 2018) at present there are approximately 400 desalination plants in the United States and their number is growing steadily (see Fig. 1.2). Most desalination plants use nanofiltration (NF) and RO membranes for salt separation.

Figure 1.2 Cumulative number of municipal desalination plants in the United States.

The steady trend of reduction of desalinated water production energy and costs coupled with increasing costs of conventional water treatment and water reuse, driven by more stringent regulatory requirements, are expected to accelerate the current trend of reliance on the ocean as an attractive and competitive water source. This trend is likely to continue in the future and to further establish ocean water desalination as a reliable drought-proof alternative for a majority of coastal communities worldwide in the next 15 years. At present, desalination provides approximately 10% of the municipal water supply of the urban coastal centers in the United States, Europe, Israel, and Australia, and over 50% of the drinking water of the Gulf Cooperation Countries; by 2030 this percentage is expected to exceed 25% and 80%, respectively.

Increased reliance on seawater desalination is often paralleled with ongoing programs for enhanced water reuse and conservation with a long-term target of achieving a balance of conventional water supply sources, seawater and brackish water desalination, water reuse and conservation to the total water supply portfolio of large coastal communities. Surface water sources are usually significantly cheaper with well-developed management systems and operations in place. Adding more costly desalinated water to the supply mix requires improved demand management and deriving full value of reuse potential to optimize the value of potable water.

Near- and long-term desalination technology advances are projected to yield a significant decrease in costs of production of desalinated water by 2030. In desalination, innovative technologies have been addressing longstanding issues that have hampered the development of this alternative resource. New technologies such as nanoparticle enhanced membranes, biomimetic membranes and forward osmosis as well as beneficial extraction of rare metals from the brine generated by desalination plants are aimed at reducing energy consumption (by 20%–35%), reducing capital costs (by 20%–30%), improving process reliability and flexibility, and greatly reducing the volume of the concentrate discharge.

1.1.1 Desalination as a strategic water resource option

Despite signi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Acknowledgments
• Chapter 1. Introduction to concentrate management
• Chapter 2. Desalination plant discharge characterization
• Chapter 3. Surface water discharge of concentrate
• Chapter 4. Case studies for surface water discharge
• Chapter 5. Discharge to sanitary sewer
• Chapter 6. Deep well injection
• Chapter 7. Land application
• Chapter 8. Evaporation ponds
• Chapter 9. Zero-liquid discharge concentrate disposal systems
• Chapter 10. Beneficial use of concentrate
• Chapter 11. Regional concentrate management
• Chapter 12. Nonconcentrate residuals management
• Chapter 13. Selection of concentrate management approach
• Appendix 1
• Appendix 2
• Glossary
• Index