Brackish Water - an overview (original) (raw)

Chapters and Articles

You might find these chapters and articles relevant to this topic.

Water-Quality Engineering

S. Gray, ... Y. Cohen, in Treatise on Water Science, 2011

4.04.3.1 Brackish Water Desalination Applications

Brackish water, generally defined as water with TDS content between that of freshwater (≤500 mg l−1 TDS) and seawater (33 000–48 000 mg l−1 TDS), can occur naturally as brackish groundwater in subsurface saline aquifers, as surface water due to natural erosion, or as a result of seawater mixing with river water (in estuaries) or groundwater (in coastal aquifers). Natural brackish water, particularly brackish groundwater, exists in most continents in quantities almost equal to or more than fresh groundwater and surface waters combined (Shiklomanov, 1993). Human activities can also cause fresh surface water and groundwater resources to become brackish through consumptive use and increase in their salt loading. For example, excessive groundwater pumping from coastal aquifers can cause salt-water intrusion that extends the brackish water zone of mixing inland, while saline return flows from irrigated agricultural lands can increase the salt loading of surface waterways. Some agricultural irrigation practices such as subsurface tile drainage often generate agricultural drainage waters that are highly brackish. Similarly, mining activities can also generate mine-drainage waters that are brackish and contaminated with heavy metals.

In the past, brackish-water desalination applications have been limited to small-scale municipal and industrial applications. It is especially popular in the USA as it accounts for the majority (∼77%) of the nation's total online-desalination capacity (Committee on Advancing Desalination Technology, 2008). One of the early large-scale inland brackish-water desalting plant, the Yuma Desalting Plant in Arizona (USA) (Lohman, 2003), was completed in 1993 for the purpose of supplementing Colorado River water deliveries to Mexico (via desalting brackish agricultural water return flows; ∼2500 mg l−1 TDS). Although its production capacity remains the largest in the world for a brackish-water desalting plant (272 500 m3 d−1 or 72 million gallons a day (MGD)), the plant was operational for only two occasions in 1994 and has remained offline (although well maintained). With dwindling freshwater supplies and maturing RO/NF and ED/EDR process technologies, desalting of under-utilized brackish groundwater and surface-water resources has attracted significant interest. Some recent (2000–10) large-scale brackish-water desalting installations include the Aigües Ter-Llobregat's (ATLL) Plant (Spain; 220 000 m3 d−1), the Al Wasia Plant (Saudi Arabia; 200 000 m3 d−1), the El Atabal Plant (Spain; 165 000 m3 d−1), the Wadi Ma’in Plant (Jordan; 135 000 m3 d−1), and the K. B. Hutchison Plant (USA; 104 000 m3 d−1). All of these are RO plants, except for the ATLL plant, which is an EDR plant.

Feedwater quality plays a major role in both the design and operation of brackish-water desalination processes. Brackish waters vary greatly in ionic composition and content, both temporally and geographically, depending on hydrogeologic conditions and related human activities (i.e., industrial or agricultural). For example, in California's San Joaquin Valley, one of the most productive agricultural regions in the US, tile drainage of irrigated agricultural lands generates brackish waters with a wide salinity range (3000–30 000 mg l−1 TDS). In Texas (USA), subsurface aquifers with salinity ranging from 1000 to 10 000 mg l−1 TDS have been estimated to hold as much as 3 trillion m3 of brackish groundwater. Major solutes in brackish waters, such as sodium, chloride, calcium, sulfate, and bicarbonate ions, typically originate from water reactions with minerals such as halite, gypsum, anhydrite, calcite, and dolomite. Other common minor solutes include silicates, iron, strontium, barium, fluoride, selenium, and boron. Some examples of brackish-water composition are listed in Table 4.

Table 4. Composition of brackish water from a variety of sources (USA)

a

Data on ElPaso Water Utilities, TX and Indian Valley Water District, CA, form Committee on Advancing Desalination Technology (2008) Desalination a National Perspective, Science and Technology Board, National Research Council. Washington, DC: National Academies Press.

b

Data on Panoche Water District, CA, from Cohen Y and Christofides P (2010) Reverse Osmosis Field Study, Final Report, DWR-WRCD Agreement 46000534-03, Task Order No. 22, California Department of Water Resources, 16 June 2010.

c

Data on Colorado River Water, Yuma, AZ, from Rahardianto A, Gao J, Gabliech CJ, Williams MD, and Cohen Y (2007) High recovery membrane desalting of low-salinity brackish water: Integration of accelerated precipitation softening with membrane RO. Journal of Membrane Science 289: 123–137.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444531995000774

Trace Fossils as Indicators of Sedimentary Environments

Murray K. Gingras, ... S. George Pemberton, in Developments in Sedimentology, 2012

2.1 Brackish-Water Trace-Fossil Assemblages

Brackish-water trace-fossil assemblages are recognized on the basis of characteristic combinations of trace fossils, trace-fossil sizes, assemblage diversities, and distribution trends (Fig. 2). The fundamental characteristics of the brackish-water model were developed by Pemberton et al. (1982) and refined by Beynon et al. (1988). Working in the Mannville Group of the oil sands deposits of NE Alberta, they demonstrated that large parts of the succession were dominated by estuarine facies. Several important characteristics reported by Pemberton et al. (1982) are now routinely used as evidence for brackish-water sedimentation. These include the following:

Figure 2. Examples of brackish-water assemblages of trace fossils. (A) Nereid (ne) and capitellid (cp) polychaete burrows that resemble the ichnogenera Skolithos (Sk) and Trichichnus. Gironde Estuary, France. (B) Resin cast of a low-diversity trace assemblage comprising Polykladichnus made by nereid (ne) polychaetes. Kouchibouguac, New Brunswick, Canada. (C) Low-diversity suite of Arenicolites (Ar) and Trichichnus (Tr) from a tidally influenced bar deposit of the Fraser River delta. (D) Comparably robust Gyrolithes (Gy1) and more gracile examples (Gy2) in inclined heterolithic stratification (IHS) of the Cretaceous McMurray Formation. (E) Skolithos in cross-bedded sands of the inner Ogeechee estuary, Georgia, USA. (F) Monospecific assemblage of Arenicolites, Bay of Fundy, Canada. (G) Low-diversity trace assemblage comprising diminutive traces (Pl, Planolites; Ar, Arenicolites) from an upper point bar, inner estuary, Willapa Bay, Washington, USA.

The identification of ethological generalist behaviors derived from the marine realm. In brackish-water deposits, trace fossils record behaviors of animals that exploit food resources under a diverse range of environmental conditions (Fig. 2). These types of trace fossils are referred to as “facies-crossing” elements. Owing to the rich food resource associated with sedimentation in tidally influenced settings, traces that are the product of rapid once-over harvesting of food within the sediment are common (e.g., Planolites, Thalassinoides, and Protovirgularia). Likewise, burrow morphologies that suit head-down deposit-feeding, interface deposit-feeding, and/or subordinate suspension-feeding behaviors (e.g., Skolithos, Cylindrichnus, Arenicolites, Gyrolithes, and Siphonichnus) are exceedingly common in brackish-water strata. The behaviors employed in estuaries are primarily imported from adjacent marine environs; thus trace fossils not normally associated with freshwater (e.g., Thalassinoides-, Cylindrichnus-, Arenicolites-, and _Gyrolithes-_like traces) are common in low-salinity (i.e., < 10 psu [practical salinity units]) waters (e.g., Gingras et al., 1999).

Trace fossils are comparably diminutive in brackish water. In brackish-water deposits, diminution of trace fossils is interpreted to result from size selection and physiological duress, associated with low and/or fluctuating salinity (Fig. 2). A decrease in size may occur for two reasons: (1) a high body surface/volume ratio of the organism can be desirable for osmotic and ionic regulation (e.g., Moore and Francis, 1985); (2) owing to physiological stress, energy expenditure toward regulatory processes slows animal growth rates and reduces survival rates (e.g., Holste et al., 2009; Spaargaren, 1979, 1995). A high surface-area-to-volume ratio is required by animals that move solutes (such as salt or oxygen) or heat energy across their body membranes. We refer to this as “facilitative diminution”, which is prevalent in brackish-water settings (Gingras et al., 1999; MacEachern and Gingras, 2007). Diminution in response to physiological stress can be referred to as “enforced diminution” and can be ascribed to animals living in low- and fluctuating-salinity settings, as well as very warm waters, both of which lead to sustained high metabolism in animals (Remane and Schlieper, 1972; Roy and Martien, 2001; Spaargaren, 1979). Enforced diminution also may induce shortened lifecycles, thereby promoting elevated mortality rates. Such conditions lead to a predominance of juvenile tracemakers (Chapman and Brinkhurst, 1981) that produce comparably small traces.

Assemblage diversities in brackish-water strata are substantially lower than in equivalent marine strata (Fig. 2). Trace-fossil diversities are considerably lower in brackish-water strata than in marine units. Lower behavioral diversity may be ascribed to the importance of ethologically flexible feeding strategies needed to rapidly harvest the rich food resources in dynamic sedimentary conditions (see 1). Another consideration is that, for modern settings, these robust ethologies are mostly used by opportunistic, commonly brackish-water tolerant animals (e.g., nereid polychaetes, the bivalve Macoma balthica, arthropods such as Corophium volutator, and the lugworm Arenicola marina). As such, the traces produced by animals employing these generalist behaviors are rapidly and widely distributed in marginal-marine settings.

Common presence of high population densities. Although the diversity of trace fossils is lower in brackish-water settings, trace fossils are commonly present in high population densities, that is, with high bioturbation indices (BI) (Fig. 2A–D; MacEachern and Gingras, 2007; Pemberton et al., 1982). This characteristic is exemplified by the occurrence of mono-ichnospecific trace-fossil assemblages in highly burrowed strata (i.e., BI = 4 or 5). There are at least two likely reasons for this pattern. First, due to the presence of tidal transport from the marine realm and low overall energies in many brackish-water settings, food resources are comparably abundant on and in the sediment. As well, favorable physiological or behavioral adaptations by some animals enable them to outcompete others under stressful conditions (see 3). The successful animals are thereby able to flourish in the environment, with minimal interference from competitors.

Brackish-water environments tend to promote infaunal over epifaunal lifestyles. One reason for this may be that living within the sediment provides protection against high-frequency (daily or semi-daily) salinity fluctuations (Chapman, 1981; Knox, 1986). Interstitial waters show much more uniform salinities throughout the tidal cycle because they are buffered from the more variable surface waters by the sediment body. Infaunal lifestyles are also a consequence of the abundance of food resources in such regimes, encouraging deposit-feeding within the sediment (Gingras et al., 1999).

Longitudinal trends in brackish-water settings are indicative of landward freshening of the depositional waters (Fig. 3). Although not specifically outlined by Pemberton et al. (1982), it is derivative of their work (2 and 3). A similar trend was identified by Howard et al. (1975) and Howard and Frey (1975) from their work on the Ogeechee River estuary. Hauck et al. (2009) showed correspondence between the function ([maximum burrow size observed] × [diversity of macroscopic infauna]) and mean salinity within the modern estuary, Kouchibouguac Bay, New Brunswick, Canada. Similarly, Gingras et al. (1999) document a progressive diminution and diversity reduction at Willapa Bay, Washington. This work suggests that both animal sizes and burrow diversities show a crude relationship to salinity and that their product provides a logarithmic relationship. Although similar efforts have not been attempted in the stratigraphic record, this type of data-intensive analysis has excellent potential for the identification of various marginal-marine settings.

Figure 3. Conceptual framework for the distribution of trace-fossil characteristics in mixed-energy to tide-dominated (top row) and wave-dominated (bottom row) estuary settings. Broadly speaking, the mixed to tidal framework is based on personal observations and data from the Willapa and Tillamook bays, the Ogeechee River estuary and the Bay of Fundy. The wave-dominated framework is based on the Kouchibouguac-River estuary. These distributions are most sensitive to the amount of freshwater flux into the system: a higher fluvial discharge can significantly freshen the estuary.

Regarding criteria 2 and 3, it can be challenging to establish what is meant by the terms “diminutive trace fossil” and “low-diversity assemblage”. In practice, it is difficult to recognize trends in diminution and diversity, unless a fully marine baseline can be established from contemporaneous rocks in the associated sedimentary basin (cf. MacEachern and Gingras, 2007). In other words, workers must establish a case for relatively lower salinity as opposed to determining absolute salinity. This practice is important. The basin from which the “marine” ichnological suite is defined, may itself have contained brackish water (e.g., the Baltic Sea; Virtasalo et al., 2011), and the salinity of the basin may decrease rapidly into the adjoining bays and estuaries.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444538130000162

Aquatic Environments

Virginia I. Rich, Raina M. Maier, in Environmental Microbiology (Third Edition), 2015

6.6.1 Brackish Waters

Brackish water is a broad term used to describe water whose salinity is between that of fresh and marine water, and these are often transitional areas where such waters mix. An estuary, which is the part of a river that meets the sea, is the best-known example of brackish water. Estuaries are highly variable environments because the salinity can change drastically over a relatively short distance, ranging from 10‰ to 32‰ (Information Box 6.1), and over time of day due to tidal cycles (for example, high tide bringing saltier marine waters farther up into the estuary). Seasonal increases in freshwater due to rainfall or snowmelt will decrease the salinity at a given point in the estuary. In order to survive here, resident microbes must be adapted to these large fluctuations in salinity. Despite this challenge, estuaries are very productive environments. In general, estuarine primary production is low, due to poor sunlight penetration as a result of high turbidity, which occurs from suspended organic matter brought by river inflow and tidal mixing (Ducklow and Shiah, 1993). However, heterotrophic activity and secondary production are high. Primary and secondary production are decoupled in these systems, because of the large amounts of organic carbon brought by terrestrial runoff and river inflow. In fact, the supply of carbon and nutrients can be so great that in many cases estuaries can actually become anoxic for whole seasons during the year (Ducklow and Shiah, 1993).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123946263000065

Nitrogen Assessment and Management in Brackish-Water Aquaculture of India

M. Muralidhar, ... K.K. Vass, in The Indian Nitrogen Assessment, 2017

Brackish-Water Aquaculture and Culture Systems

Brackish-water aquaculture (BWA) requires natural resources such as land, water, and biological resources such as seed and feed. Shrimp farming, a biology-based production activity, is synonymous with BWA in India. The quality and quantity of available resources and their management therefore plays a key role in the economic success and long-term sustainability of coastal aquaculture. Shrimp culture technology and the system of culture to be undertaken depend entirely on the site characteristics. The natural resources, namely land and water, if poorly planned and managed, can result in irreversible environmental damage and may lead to ultimate loss in economic gains. Shrimp farming in India till now has three distinct phases. First, the “rising phase” with Penaeus monodon culture from late 80s to 1995, second, the “falling phase” during 1995–2001 affected with viral diseases, predominantly the “white spot syndrome virus” (WSSV) and monodon baculo virus (MBV), and from 2002 onward, the third phase during which the farming is “sustainable” due to involvement of research and development (R&D) institutions in the country (Kumaran et al., 2003). Since 2009 after the introduction of Penaeus v_annamei_, India witnessed rapid expansion of shrimp culture activity. The inland production of marine shrimp provides an alternative to traditional coastal aquaculture where land costs and user conflicts can inhibit commercial development.

The culture systems practiced vary depending on the availability of inputs and farmers capacity to invest in the farming. In low input farming systems, due to adoption of scientific principles of farming, 500–1500 kg crop ha−1 production is predictable. Surendran et al. (1991) demonstrated the technology of semi-intensive shrimp farming with 4–6 tons ha−1 production.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128118368000197

Aquatic Environments

Todd R. Sandrin, ... Raina M. Maier, in Environmental Microbiology (Second Edition), 2009

6.3.2 Brackish Water

Brackish water is a broad term used to describe water that is more saline than freshwater but less saline than true marine environments. Often these are transitional areas between fresh and marine waters. An estuary, which is the part of a river that meets the sea, is the best known example of brackish water. Estuaries are highly variable environments because the salinity can change drastically over a relatively short distance. Dramatic change can also occur at a given point in the estuary as a function of the time of day or season of the year. For example, at high tide, the salt content at a given spot in the estuary will increase as ocean water moves into the area. In contrast, seasonal increases in freshwater due to rainfall or snowmelt will decrease the salinity at a given point in the estuary. The variation in salinity can range from 10 to 32‰, with the average salinity of freshwater being 0.5‰ (Information Box 6.2). In order to survive in these environments, microbes and plants in an estuary must be adapted to the fluctuations in salinity. Despite this, estuaries are very productive environments. Specific examples of highly productive brackish water environments are mangrove swamps such as those found in the everglades of Florida. The salinity in these swamps is usually very close to that of seawater. Mangrove swamps are named for the characteristic trees that grow in the saturated soils of the swamp. These trees have specially adapted roots that grow up from the water to allow gas exchange above the water so that the trees can continue to obtain oxygen and “breathe.” A second important adaptation is that mangrove trees inhibit salt transport into the roots to avoid salt stress. Mangrove swamps are an important transition community because they help filter contaminants and nutrients from the water, they stabilize sediments, and they protect the shoreline from erosion. They also provide an active habitat for more than 250 animal and 180 bird species.

Information Box 6.2

What is Salinity?

The average salt concentration in the ocean is approximately 3.5‰. This is more precisely expressed in terms of salinity. Salinity ‰ is defined as the mass in grams of dissolved inorganic matter in 1 kg of seawater after all Br− and I− have been replaced by the equivalent quantity of Cl−, and all HCO3− and CO32 − have been converted to oxide. In terms of salinity, marine waters range from 33 to 37‰, with an average of 35‰.

In general, estuarine primary production (10 to 45 mg carbon/m3/day) is not always enough to support the secondary populations. Estuaries tend to be turbid because of the large amount of organic matter brought in by rivers and the mixing action of tides (Ducklow and Shiah, 1993). As a result, light penetration is poor. Numbers of primary producers are variable, ranging from 100 to 107 organisms/ml, and these populations also vary considerably in relation to depth and proximity to existing littoral zones. Despite low primary productivity, because availability of substrate is not limited, heterotrophic activity is high, ranging from 150 to 230 mg carbon/m3/day. Local runoff and organic carbon are brought in abundantly by the rivers that flow into the estuaries. In fact, the supply of nutrients can be so great that in many cases estuaries can actually become anoxic for whole seasons during the year (Ducklow and Shiah, 1993). As a result of the steady and abundant carbon supply, numbers of secondary producers fall into a much narrower range from 106 to 108 organisms/ml. Measured viral to bacteria ratios range from 0.4 to 50 (Wommack and Colwell, 2000).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780123705198000067

Impact of sea-level rise on shrimp farming

Takahiro Osawa, ... Dwi Puspa Arini, in Coastal Altimetry, 2023

2.1 Study location

Brackish water aquaculture is widespread in coastal Banyuwangi Regency. This study focused on the coastal waters of four subdistricts of Banyuwangi district in eastern Banyuwangi Regency: Muncar, Rogojampi, Kabat, and Banyuwangi subdistricts (Fig. 6.1). The Bali Strait, which forms the eastern border of Banyuwangi Regency, varies in depth; it gradually deepens eastward to up to 140 m where an elongated trough parallels the coast of Bali (Marine and Fisheries Agency Banyuwangi District, 2015) (Fig. 6.2). There is a dry season (June to October), influenced by the Australian continental air masses, and a rainy season (November to March) that is caused by Asia and Pacific Ocean air masses. Local wind patterns in general, sea surface temperature (SST), and sea surface salinity in the Bali Strait are higher during the west monsoon (wet) season (December, January, and February) and lower during the east monsoon (dry) season (June, July, and August). However, in 2010 and 2016, SST in the Bali Strait was much higher than in other years (Sukresno et al., 2019).

Figure 6.1. Study area in Banyuwangi district, Banyuwangi Regency, East Java Province, and the spatial distribution of shrimp farming areas (brackish water ponds).

Figure 6.2. Bathymetry map and survey locations along the coast of Banyuwangi district. The red (gray in print version) dots show the starting point of each survey line.

In general, the area used for shrimp farming in Banyuwangi district was stable from 2008 to 2016, although it increased to 1432 ha in 2011 (Report of the Banyuwangi District Marine and Fisheries Agency, 2015). In 2016, the aquaculture sector in Banyuwangi district accounted for approximately 30% of the total shrimp production of East Java Province; there were shrimp farms in 9 out of 25 subdistricts, and they occupied a total area of approximately 1381 ha (Fig. 6.3). Shrimp farming in Banyuwangi district is carried out mainly by using intensive (80–125 shrimp/m2, three pinwheel for 125.000 shrimp) and semiintensive (30–80 shrimp/m2, three pinwheel for 125.000 shrimp) shrimp cultivation techniques. In general, shrimp production is higher under intensive cultivation than under semiintensive or extensive (10 shrimp/m2, not using Pinwheel) cultivation. In Muncar subdistrict, semiintensive, extensive, and intensive pond systems are used, whereas in the Rogojampi, Kabat, and Banyuwangi subdistricts, intensive and semiintensive systems are dominant. The total pond area in these four subdistricts is 1457.72 ha (Table 6.1).

Figure 6.3. Area used for brackish water aquaculture (solid line) and shrimp production (dashed line) in Banyuwangi district from 2008 to 2016.

Table 6.1. Type and area of shrimp cultivation ponds in Banyuwangi district in 2015.

Source: Ministry of Marine Affairs and Fisheries, 2015. Marine and Fisheries in Figures 2015. The Center for Data, Statistics, and Information. Ministry of Marine Affaires and Fisheries of Indonesia (308 pp).

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780323917087000122

Assessing the impact of aquafarming on landscape dynamics of coastal West Bengal, India using remotely sensed data and spatial metrics

Asit Kumar Roy, ... Debajit Datta, in Remote Sensing of Ocean and Coastal Environments, 2021

4.2 Environmental impact of aquacultural spread

Coastal brackish water aquafarms are designed by modifying the lowlands through saline water intrusion as well as excavating and embanking them for artificial storage. Since these natural coastal depressions played a crucial role in groundwater recharging, their utilization for brackish water fisheries had resulted in the infiltration of dissolved salts in groundwater aquifers, causing an increase in pH of surface as well as groundwater. This artificially augmented salinity of the groundwater table may have eventually created an unfavorable condition for the coastal populace to use this water for drinking and irrigation purposes. In addition, the enormous amount of brackish water storage in the aquafarms also triggered the deteriorating state of physicochemical properties of the top soil layers of associated LULCs. Consequently, assemblage of salt-tolerant varieties of floral (i.e., P. coarctata, Sesuvium portulacastrum, A. ilicifolius, and P. tectorius) and faunal (i.e., S. serrata, Uca rosea, Oxudercinae, and Paguroidea) species have started to colonize around these aquafarms, even far away from the coast in some instances.

Formerly, croplands dominated this coastal region. At present, it is mostly utilized for paddy (Boro) cultivation during dry periods and partially used for paddy-cum-fish cultivation during wet periods. Although agriculture was the prime source of livelihood in this region since time immemorial, it still follows a traditional approach of production, neglecting the objectives of profit maximization and commercialization. Moreover, excessive groundwater irrigation has resulted in higher alkalinity and salinized surface soil, as a negative consequence of brackish water aquafarms, for acting together to degrade the natural environmental condition and decrease the agricultural yield rapidly (Dutta et al., 2016). Thus, the deteriorating hydroedaphic condition of this entire region minimizes the prospect of having sustainable agroecosystem and transforms it into a less synergetic ecosystem with minimum biodiversity.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128196045000081

Desalination and On-site Energy for Groundwater Treatment in Developing Countries Using Fuel Cells

Rajindar Singh, in Emerging Membrane Technology for Sustainable Water Treatment, 2016

6.4.3.1 RO Product Water Recovery

Since BWRO systems typically operate at 70–75% recovery, 25–30% of feedwater is wasted as concentrated brine (reject stream). Disposal of a large volume of concentrated brine is a problem. Further, it is vitally important to maximise recovery to conserve water. It is, therefore, desirable to treat the RO reject stream to address these two issues and is discussed in detail Chapters 7 and 12Chapter 7Chapter 12. For low- to mid-range-salinity brackish waters, it was shown that the overall product recovery could be increased to nearly 90% in certain cases using an RO + brine RO (BRO) system [34,35] (see Figure 6.10).

Figure 6.10. Schematic process flow diagram and mass balance of a high recovery reverse osmosis system (overall recovery = 88%). Remineralisation and pH adjustment of product water using calcite media filter.

The data in Table 6.5 show that the maximum BRO recovery for Site #1 is 50% resulting in an overall recovery (RO + BRO) of ∼88%. Similarly, in the case of higher TDS water (Site #2), the maximum BRO recovery is 40% resulting in an overall recovery (RO + BRO) of ∼85%. The overall product water TDS is 250 (Site #1) and 528 mg/L (Site #2). The SEC of the RO + BRO system increased to 0.38 kWh/m3 and 0.6 kWh/m3, respectively. Higher SEC values of 0.406 and 0.788 kWh/m3 are observed when tighter (higher rejection, lower productivity) Hydranautics CPA3 membranes are used instead of ESPA1 for primary RO desalination.

Table 6.5. Brine RO and overall (RO + BRO) performance

RO, reverse osmosis; BRO, brine RO; Feed water temperature = 35° C.

@Hydranautics TFC membranes, 10-cm diameter (BRO) spiral-wound elements.

RO membranes: ESPA1 (see Table 6.4).

BRO membranes: ESPA4 – higher productivity and lower rejection membrane than ESPA2 membrane.

a

PWR = product water recovery.

b

SEC = specific energy consumption.

c

Combined performance.

The data show that for these low- to mid-TDS brackish waters, recovery in the range of 85–88% can be achieved with little penalty in product water quality and energy consumption. However, since brackish water composition is highly variable and site specific unlike seawater, the maximum recovery that can be achieved may be lower or higher depending on the groundwater composition and feedwater pretreatment. For example, the maximum recovery achieved in pilot runs with high hardness and high silica brackish water was only 63–67% (TDS = 5067 mg/L, hardness = 2800 mg/L as CaCO3, alkalinity = 833 mg/L as CaCO3, silica = 70–100 mg/L) [36]. Hence, alternate processes are required to achieve higher recovery.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444633125000061

Ecology Processes

JoAnn M. Burkholder, Patricia M. Glibert, in Encyclopedia of Biodiversity (Third Edition), 2024

Estuarine and marine communities

Brackish waters are colonized by rooted, mostly freshwater species with moderate salt tolerance (as examples, certain Potamogeton spp., Valisneria americana, Zanichellia). In such habitats, light is often the primary resource limiting growth. Species with broader salt tolerance such as Ruppia maritima also can be abundant. Only about 50 species of angiosperms, mostly close relatives of freshwater Potamogeton spp., have the salt tolerance needed to thrive in marine habitats. Nearly all of these “seagrasses” (technically not grasses) grow in muddy substrata of shallow coastal lagoons and quiet embayments. As in freshwaters, estuarine and marine macrophytes tend to be highly sensitive to light reduction and, thus, susceptible to eutrophication-related turbidity from algal (phytoplankton, epiphyte, and macroalgae) overgrowth and sediment loading/ resuspension. Such shading causes gradual dieback and loss of most SAV, leading to dramatic declines, in turn, in the diversity and abundance of many plant and animal species that depend on the habitat provided by these plants.

More sensitive SAV species are replaced by others that are tolerant of eutrophic conditions – for example, among subtropical seagrasses, field observations and limited experiments have indicated that turtle grass (Thalassia testudinum) is more sensitive to eutrophication than shoal grass (Halodule wrightii) and manatee grass (Syringodium filiforme). Other regions may not have additional seagrass species available to replace more sensitive species and, even where such species are present, they typically offer less desirable fish nursery habitat than the former dominant. Thus, in seagrass meadows under nutrient over-enrichment, more oligotrophic seagrass species are replaced by less sensitive species when available. As eutrophication progresses the seagrasses are eliminated, and rapidly growing macroalgae and/or phytoplankton become the dominant flora.

Although light reduction is considered the major mechanism for seagrass decline under cultural eutrophication, excessive nutrients can act independently of light to promote seagrass loss (Fig. 13). The dominant north temperate species, eelgrass (Zostera marina), apparently lacks a physiological mechanism to down-regulate NO3− uptake through its leaves (see review by Burkholder et al., 2007a). Most plants take up NO3− during the day with energy from photosynthesis. In contrast, Z. marina takes up water-column NO3− day or night if it becomes available, as shown by Touchette and Burkholder (2000) (Fig. 14). This species is thought to have evolved in N-poor coastal waters, where sustained NO3− uptake under temporary enrichment would have been a highly advantageous competitive strategy. However, as coastal waters have become more eutrophic from sewage, septic effluent leachate, and other anthropogenic sources, sustained uptake of water-column NO3− has become a disadvantage. Nitrate enrichment to the sediments, under control by an abundant microbial consortium, does not cause a similar effect and can even be mildly stimulatory.

Fig. 13. The effects of water-column NO3− enrichment and light reduction on shoot production of the seagrass, Zostera marina. From author JB's outdoor mesocosm experiments, indicated as the percent decrease from shoot production of control plants that did not receive water-column NO3− additions or light reduction (except that plants in controls and treatments all received an additional 30% light reduction for 3 hours at 0900, 1200, and 1500 hours on a 3-day rotation using neutral density screens to stimulate conditions during high tide). Treatments were imposed for 10 weeks during the fall growing season for Z, marina. Controls were maintained at ambient natural light (except during simulated high tide) and NO3− (< 30 µg NO3−N L−1 or 2.1 µM). Treatments included low N (at 50 µg NO3−N L−1 or ~3.6 µM) and high N (at 100 µg NO3−N L−1 or ~7.1 µM); low and high NO3− additions were added in the morning as a pulse of enrichment) at each of three imposed light levels as 30, 50, or 70% reduction of ambient surface light (Io, accomplished using the neutral densityscreens, with additional shading to simulate high tide as noted). Water exchange (5–10% of the tank volumes per day replaced with fresh estuarine water) was done in late afternoons; see Burkholder et al. (1992) for further details about the mesocosm system. In all treatments with water-column NO3− enrichment, Z, marina declined in shoot production relative to shoot production of control plants, and the NO3− inhibition effect was exacerbated by light reduction (means ± 1 standard error, SE; P < 0.05, n = 3 mesocosms for controls and 3 for each treatment). These effects were not caused by algal overgrowth, which was maintained at low levels in controls and all treatments throughout the experiment.

Reproduced with permission from Burkholder, J. M., Mason, K. M. and Glasgow, H. (1992). Water-column nitrate enrichment promotes decline of eelgrass Zostera marina: Evidence from seasonal mesocosm experiments. Marine Ecology Progress Series 81, 163–178.

Fig. 14. The response of the seagrass Zostera marina to pulsed water-column NO3− enrichment in light and dark periods. Plant NO3− uptake is indicated as leaf activity of nitrate reductase (NR, the key enzyme used to actively take up NO3−) of previously unenriched shoots. A spike of NO3− (100 µg NO3−N L−1 or ~7.1 µM) was added in the morning (white arrow), or to a subsample of plants from the same population at night (black arrow). NR activity (plotted as micromoles of nitrite product produced per gram dry weight of plant leaf tissue per hour) indicated that Z. marina took up NO3− day or night, whenever a pulse was detected (data given as means ± 1 SE). In fact, maximal NR activity was significantly higher when NO3− was added during the dark period.

Reprinted from Touchette, B. W. and Burkholder, J. M. (2000). Overview of the physiological ecology of carbon metabolism in seagrasses. Journal of Experimental Marine Biology and Ecology 250, 169–205. With permission from Elsevier.

Nitrate uptake is a metabolically expensive process, requiring high cellular energy. Sustained water-column NO3− uptake by Z. marina leaves can promote severe internal carbon imbalances, apparently from the need to shunt carbon skeletons from photosynthesis for use in high amino acid synthesis to prevent internal accumulation of products such as NH3 at toxic levels. The physiological mechanism of an internal “carbon drain” from sustained NO3− uptake previously was documented for algae by Turpin (1991). A common trait of Z. marina shoots under excessive water-column NO3− enrichment is structurally weakened growing regions (e.g., the basal meristem), perhaps analogous to the above-mentioned loss of stem strength that has been reported in certain freshwater emergent macrophytes under NO3− enrichment. Excessive Ni enrichment has also promoted seagrass attack by pathogens (for example, the slime mold Labrynthula zosteroides), hypothesized to occur because N and carbon are internally shunted to amino acid production rather than to production of alkaloids and other anti-microbial compounds.

Another seagrass that has been examined for the NO3− inhibition phenomenon, Halodule wrightii, and certain macroalgae (e.g., Ulva lactuca) have shown depressed growth in response to water-column NO3−enrichment, although at much higher N levels than for Z. marina. The seagrass Ruppia maritima is stimulated by high water-column NO3− but inhibited by elevated Ni as NH4+. Z. marina has been experimentally inhibited by high NH4+ levels as well. In mesocosm experiments, light reduction has been shown to exacerbate the inhibitory effects of water-column NO3− enrichment on shoot production in Z. marina. Warm temperatures exacerbate water-column NO3− enrichment impacts on root growth of this seagrass as well, suggesting that warming trends in climate change will interact with eutrophication to exacerbate adverse impacts on this beneficial habitat species. Direct NO3− inhibition has also been suggested for some SAV in freshwater Florida springs (Osborne et al., 2017; and see section on Estuarine and Marine Macrophytes below).

Invasive macrophytes such as Hydrilla verticillata (hydrilla) or Egeria densa (Brazilian elodea) are another concern in systems altered by nutrient loading. These species appear to be most common in systems that have received excessive N loading relative to P, or systems in which much of the P has been removed but N loads remain high. Examples of ecosystems invaded by these plants after P removal include the Potomac River, a tributary of Chesapeake Bay, and the San Francisco Bay Delta, USA. Both systems receive (or historically received) high nutrient loads from sewage discharge, but have sustained less P loading due to improved effluent treatment and/or removal of Pi from laundry detergents. Such highly productive invasive plants have been characterized by Yarrow et al. (2009) as “ecological engineers”. They can thrive in turbid waters but also tend to trap sediments, thereby reducing turbidity. They also provide habitat for zooplankton and fish and, through their productivity, they alter pH and both water-column and sediment nutrient chemistry.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780128225622000529

Hybrid Membrane Systems – Applications and Case Studies

Rajindar Singh, in Membrane Technology and Engineering for Water Purification (Second Edition), 2015

3.2.2 Brackish water RO desalination

Brackish water RO (BWRO) plants tend to be smaller in production capacity than seawater RO plants, but a greater number of BW RO plants (48% of the total number of plants) are in operation worldwide than SWRO plants (25%) [3]. The feed water is either groundwater or surface water. Many plants produce between 500 and 10,000 m3/d of RO product water. The production range of BWRO plants in the US is 200–76,000 m3/d, and the range of feed water TDS is 500–8500 mg/l. More than 1200 desalination plants operate in the United States, which has 16% of the world’s desalination capacity [48]. Most of the brackish desalination plants (80%) in the US use RO technology. The remaining are divided between ED and NF. Ninety-six percent of the more than 300 municipal desalination plants in the US are located inland. The BWRO plants are typically single-pass and two-stage.

The largest brackish water RO (BWRO) plant in the US (Yuma, Arizona) was built in 1991 and operated in 1992. Although it has been on “ready reserve” since 1993, it was operated again in spring 2007 for 90 days successfully. The 270,000 m3/d BWRO plant is designed to treat agricultural drainage water and divert the RO product water to the Colorado River to lower the river’s salinity before it flows to Mexico [61]. The plant was reactivated in May 2010 to launch a 1-year pilot run. The RO plant consists of 9360 CA membrane elements as follows: approximately two-thirds of the spiral-wound elements are Koch (Fluid Systems), 30 cm diameter × 150 cm long with a surface area of 117 m2, and one-third are Hydranautics, 20 cm diameter × 100 cm long with a surface area of 33 m2.

Most brackish water RO plants require extensive pre-treatment as discussed in Chapter 2. Feed water quality of brackish waters in the US southwest is given in Table 3.4. The intensity of pre-treatment depends on the quality of feed water as detailed in Table 3.6. Feed water constituents that affect pre-treatment design are summarised below [62,63]:

Table 3.6. Pre-treatment options for brackish water desalting plantsa

a

Based on feed water chemical analysis in Table 3.4.

Ground waters usually have very low SDI values, and cartridge filtration is a generally sufficient pre-treatment. Cartridge filters of 5.0–10.0 μm nominal pore size are typically used. Increasingly, cross-flow MF and UF is being used. Surface waters may have SDI as high as 200 requiring more rigorous pre-treatment. A rough guide is that waters with SDI less than six can be passed through deep-bed media filters. SDI values in the 6–50 range require coagulation with cationic polyelectrolytes, followed by clarification. Coagulation with aluminium sulphate (alum) or ferric salts, followed by sedimentation and media filtration, is suitable pre-treatment when SDI is greater than 50.

The fouling tendency of colloids can be reduced in some instances by increasing their zeta potential, thus reducing their tendency to adhere to surfaces as discussed in Chapter 2. Methods used to achieve this include softening the feed water by IX, NF and/or dosing the feed with a polymeric dispersant.

The most common precipitates encountered in brackish water desalination are calcium and magnesium carbonate, sulphates of calcium, barium, and strontium, and silica. Well water may have special problems associated with components that are soluble under reducing conditions but form insoluble substances when oxidised by contact with air. Manganese, ferrous salts and hydrogen sulphide fit in this category.

Since brackish waters usually contain high levels of calcium, sulphuric acid dosing is commonly used to prevent calcium carbonate precipitation. This increases the potential for calcium sulphate scaling, which may become the limiting factor in determining product water recovery. If the calcium or magnesium concentrations are high, cation exchange or lime-precipitation softening should be employed before acid dosing.

Precipitation of sulphates can be prevented by dosing with polyelectrolyte crystallisation inhibitors such as SHMP. Its effect is to hinder the rate of crystallisation, rather than to prevent it altogether. SHMP is almost totally rejected by RO membranes and has little or no effect on the permeate quality. The RO module feed/reject channels must be flushed before shutting the RO system down.

Polymers are also used to inhibit calcium carbonate precipitation; for example, Flocon®, Aqua Feed®, Belgard®, and Aquakreen®. Use of these polymers can reduce the need for acid dosing. The advantages over SHMP are that they are more stable against thermal and hydrolytic degradation, making dilution procedures less critical. These advantages are particularly useful in small installations, but the use of such polymers has become established in large plants as well.

Silica precipitation is a serious problem. The formation of insoluble silica compounds is not easy to predict accurately, as the solubility is strongly dependent on temperature and pH, as discussed in Chapter 6. Silica compounds, once formed, are difficult to remove – particularly from CA membranes, which are not tolerant to high pH cleaning solutions. Silica, soluble and colloidal, can be removed by the lime-precipitation process, but because of the relative cost and complexity of the process, this is generally avoided if possible.

The concentration of ferrous ions that can be tolerated by most membranes depends on the concentration of dissolved oxygen. If dissolved oxygen is less than 0.1 mg/l, brine may contain up to 4 mg/l ferrous ions. If the brine is oxygenated, the iron concentration should be below 0.05 mg/l. Contact with air should be avoided or the water should be aerated followed by filtration or clarification.

Well water may contain dissolved hydrogen sulphide. At pH ≥ 8, a significant portion of the hydrogen sulphide is present as sulphide ions, which oxidise to elemental sulphur by either oxygen or chlorine. This can be prevented by acidifying the water. Under acid conditions, the hydrogen sulphide passes through the membrane into the product water, which then requires degasification. The release of hydrogen sulphide gas can cause corrosion and environmental problems.

Case studies

Feed water composition of several brackish waters in the southwest United States are given in Table 3.4. This region is drought prone, and with a rapid growth in population, the situation is worsening [3,48]. Membrane pre-treatment options for RO and ED designed plants operating at 70% and 80% water recovery are given in Table 3.6 [64]. The design data show that the pre-treatment required for Rio Grande, Coalinga and Orange County is minimal using in-line acid and anti-scalant dosage, whereas it is elaborate for Tularosa, Fort Morgan, and Welton Mohawk. The data also show that 80% recovery is achievable even in the case of the last three feed waters with well-designed pre-treatment systems. Process flow sheets based for these feed waters are shown in Figures 3.34–3.37. Sample RO performance process flow sheets based on the membrane manufacturer’s projections at 70% product water recovery for Welton-Mohawk and Rio Grande are shown in Figure 3.38, illustrative of RO unit design calculations.

Figure 3.34. Lime pre-treatment system plus a RO membrane brackish water desalination plant process flow sheet.

Source: Cabibbo et al.

Figure 3.35. Acid pre-treatment system plus a RO membrane brackish water desalination plant process flow sheet.

Source: Cabibbo et al.

Figure 3.36. Lime pre-treatment system plus an ED membrane brackish water desalination plant process flow sheet.

Source: Cabibbo et al.

Figure 3.37. Acid pre-treatment system plus an ED membrane brackish water desalination plant process flow sheet.

Source: Cabibbo et al.

Figure 3.38. (a) Process design flow schematic of a brackish water RO membrane system. Welton-Mohawk site. (b) Process design flow schematic of a brackish water RO membrane system. Rio Grande site.

The Welton-Mohawk RO unit is a two-stage array (29:15) comprised of 44 pressure vessels. Each pressure vessel contains six polyamide TFC water spiral-wound elements, 20 cm diameter × 100 cm long, producing 3820 m3/d (~ 700 gpm) permeate. The membrane (Hydranautics CPA2) average flux is 17.9 l/m2/h (lmh). The initial operating pressure is 17 bar g. The reject brine flow rate is 1636 m3/d (~ 300 gpm). The product water TDS is 90 mg/l and the pH is 4.9 units. The feed water pH is lowered to 6.0 with sulphuric acid to prevent calcium carbonate scaling. An anti-scalant (5–10 ppm) is also required to prevent calcium sulphate scaling. The product water is remineralised and pH is raised to 7.5 with lime or caustic soda.

The Rio Grande RO unit is a two-stage array (26:14) comprised of 40 pressure vessels. Each pressure vessel contains six polyamide TFC water spiral-wound elements, 20 cm diameter × 100 cm long, producing 3820 m3/d (~ 700 gpm) permeate. The membrane (Hydranautics ESPA4) average flux is 17.9 lmh. The initial operating pressure is 14 bar g. The reject brine flow rate is 1636 m3/d (~ 300 gpm). The product water TDS is 127 mg/l and the pH is 5.5 units. The product water is remineralised and pH is raised to 7.5 with lime or caustic soda.

Read full chapter

URL:

https://www.sciencedirect.com/science/article/pii/B9780444633620000033