Brine management
Contributor: , , , , , , ,

Desalination brine is extremely concentrated saline water; it contains various salts, nutrients, heavy metals, organic contaminants, and microbial contaminants. Conventional disposal of desalination brine has negative impacts on natural and marine ecosystems that increase the levels of toxicity and salinity. These issues demand the development of brine management technologies that can lead to zero liquid discharge. Brine management can be productive by adopting economically feasible methodologies, which enables the recovery of valuable resources like freshwater, minerals, and energy.

• brine solution
• management
• sustainability

## 1. Introduction

Water scarcity has evolved into a global challenge with the population explosion and its demand for industrial and domestic applications. Research has been focused on the technological and material aspects to meet the growing water demand. With the exhaustion of freshwater sources and the abundance of seawater or brackish water, research has been focused on the production of clean water from these resources. Desalination has been an important advancement that has the potential to meet the water crisis, but with the advantages of this process there are disadvantages too. The large production of brine, i.e., the highly concentrated salt stream from the desalination plant, is a major concern as most of the desalination plants dispose of the brine into the original water source. The salt accumulation in brine increases the seawater salinity and consequently it increases the energy needed for desalination for a potable water supply. Brine also contains metals and chemicals (Table 1) that cause negative effects on marine ecosystems. The threats posed by brine discharge lead to socioeconomic and socio-political consequences such as energy demand, water stress, and negative health impacts. Therefore, the increasing pollution of the water resources has to be managed strategically to maintain the balance of the ecosystem.
However, there are socio-political and legal challenges that any management approach should address for the development and the proliferation of brine management. It is severely impacted by a variety of often neglected socio-political factors. These are major factors in the success or failure of many brine management projects around the world, and they are classified into four categories: strengths, weaknesses, opportunities, and dangers. There are links between brine management and society’s critical needs for political stability, better health, economic growth, and water security. For example, proper brine management can result in the commercialization of valuable resources like water, minerals, and energy, which will lower the overall cost and offer a business opportunity that definitely will ensure the economic, social, and environmental stability of countries.
This review focuses on the advancement in brine management and proposes future strategies to overcome the crisis. Hybrid technologies that can be utilized to develop a circular solution of waste to energy or value-added products will also be discussed.
There are several review articles in this area that presented discussions on brine management and treatment-based and technology-based solutions. Bello et al. have recently given an overview of brine management, desalination technologies, life cycle assessment, and recovery methods [1], while Al-Absi et al. provided an update on the use of adsorption processes as a recovery option and discussed the various brine management strategies and technologies [2]. Mavukkandy et al. reviewed recent research and technological development on recovering water, minerals, and energy from desalination brine [3]. Soliman et al. have presented a comprehensive review of the current technologies of various desalination processes and the detailed energy consumption and water production costs of these technologies [4]. However, previous reports lack detailed analysis of future prospects to achieve sustainable brine management. Hence, the present review focuses on the current brine disposal strategies, methods of treatment, hybrid methods for metal recovery, and zero liquid discharge (ZLD). More attention was given to analyzing futuristic developments of a sustainable hybrid strategy for brine management that could open gateways to remarkable water recovery and mineral recovery channels while attaining the near-ZLD approach.
Table 1. General characteristics of brine from seawater desalination plants [5,6,7].
Parameters Details
Physical characteristics Salinity: above 55,000 mg/L of TDS; conductivity: 0.6 W/mK at 25 °C; temperature: ambient seawater; pH: 7–8.
Inorganic salts Example: sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2) are the major constituents.
Metals caused by corrosion Brine might have high levels of iron, chromium, nickel, and molybdenum if the facility uses low-quality stainless steel.
Nutrients Ammonia, nitrate, and phosphorus.
Pretreatment chemicals Antiscale additive (ethylenediaminetetraacetic acid: EDTA, sodium hexameta phosphate).
Biofouling control additives such as chlorine (small quantities)—coagulants.
Halogenated organics Trihalomethanes are common byproducts of chlorine addition (low content).
Cleaning chemicals -Acidic solutions used to adjust the pH of the seawater.
-Detergent such as EDTA, oxidants (sodium perborate) and biocides (formaldehyde) are used to clean the membrane.

#### 1.1. Brine Solution and Characteristics

Brine is a by-product or the end product of a desalination process that consists of various components. A list of typical physical and chemical characteristics of desalination brine is given in Table 1. Brine has a salinity above 55,000 mg/L of total dissolved solids (TDS) in the stream [5]. The chemical characteristics of brine discharge depend on various factors such as the quality of feed water and permeate water, type of desalination process, pre-treatment method, and cleaning procedures used. Each plant has a diverse concentration and components of contaminants in it. The presence of heavy metals, organic contaminants, strong acids/base, antiscalants, coagulants, and biocides add to the complexity of the brine solution.

#### 1.2. Conventional Methodologies for Disposal of Brine

The conventional strategies involved in the disposal of brine from desalination processes can vary depending on the geographical location, quality, and volume of the brine. Some conventional disposal methods include surface water discharge, deep well injection, land application, evaporation ponds, and conventional crystallizers. There are several factors that influence which option of disposal method can be adopted such as quantity and quality of the brine, geographical location of discharge point, availability and authorization of dump sites, and operational and transportation costs. All these are critical factors to be addressed when a desalination plant needs to be installed. It has been reported that almost 5% to 33% of the total cost will be spent on the disposal processes for the brine. In addition, revenue that can be made from the brine, such as minerals recovery, waste-to-value-added products like fertilizers, etc., are alternatives for a more cost-effective model. The conventional brine disposal strategies have been tabulated in the Table 2.
Table 2. Conventional brine disposal strategies and its environmental impacts.

## 4. Brine Management: Resource Recovery Technologies

#### 4.1.1. Forward Osmosis

Forward osmosis, as the name implies, is an osmotic pressure-driven membrane process, unlike RO (which uses hydraulic pressure), it uses the osmotic pressure gradient across the membrane to separate the feed water and allow it to permeate. In brine treatment, this method is majorly adopted for water recovery. In principle, as shown in Figure 1, to attain an osmotic pressure gradient, a high-saline solution called a draw solution will be used. During the process, water from feed water (low saline) will pass through the semipermeable membrane to the draw solution (DS), which is highly saline, to achieve the osmotic equilibrium. As the process continues, there will a diluted draw solution and concentrated feed. The freshwater and draw solution can be separated via a regeneration process using RO/evaporation/mechanical methods. The remaining concentrated DS can be reused further. The obtained concentrated brine feed can be subjected to crystallizers/evaporators for minerals recovery.
Figure 1. Schematic diagram for forward osmosis.
In the FO process, the major role was given for a draw solution, since its characteristics will control the water transport through the membrane and the regeneration of potable water. Conventionally, NaCl and MgCl2 are used as DS in RO regeneration, till now, and numerous draw solutions of organic solutes, inorganic solutes, volatile salutes, polyelectrolytes, bio-waste materials, and nanoparticles were studied; however, there is a need to fill some voids to meet the ideal DS. The majorly governed factors for an ideal DS are availability, cost effectiveness, high flux rates, reduced fouling potential, low reverse solute diffusion, non-toxicity, and ease of recovery/regeneration [41]. Hence, most of the current research is focused on developing such an ideal draw solution for FO technology.
One of the main issues associated with DS is the energy utilized for recovery/regeneration; to alleviate this, studies on developing DS with thermolytic, mechanical, and magnetic responsiveness or hybrid solutions for those are under exploration. Recently, liquid fertilizers have also been used as draw solutions. The major goal of liquid fertilizers as DS is there is no need of regeneration; diluted DS can be directly used in irrigation. This technology is referred to as fertilizer-drawn forward osmosis. This methodology is found to be very effective to supply the essential nutrients to crops via irrigation. FO-related studies also paved the way to efficient FO membranes; the governing factors for the same are nature, surface characteristics, thickness modulation, wetting behavior, fouling resistance, etc. [42]. The recent studies on water recovery from brine using FO technology are illustrated in Table 3.
Table 3. Summary of water recovery studies recently reported using FO process.
Source of Brine Draw Solution and FO Membrane Water Recovery and Salinity Level Ref.
High-saline water NH3/CO2 as DS and polyamide FO thin film composite membrane 64% water recovery with 300 mg/L TDS [43]
Reverse osmosis brine NaCl as DS and flat-sheet cellulose triacetate membrane 90% water recovery [44]
NaCl-based synthetic brine Industrial-grade fertilizer ammonium sulfate as DS and commercial FO membrane 12.7% water recovery [45]
RO brine 3 M MgCl2 as DS; cellulose-based polymers with an embedded polyester mesh 50% water recovery [46]
Synthetic brine Fructose as DS; hydrophilic cotton-derived cellulose-ester plastics embedded on top of a microfiltration membrane 56.8% recovery with 5 M Fructose; 61.4% recovery with 6 M Fructose [47]
Brine from multi-effect distillation systems 3 mol/L NaCl as DS; cellulose triacetate membrane and polyamide thin film composite membranes Brine volume reduced to 54.9% [48]
Four source of high-saline wastewater Sodium alginate sulfate as DS - [49]
RO concentrate produced from coal chemical industry DS: NaCl; membrane: active rejection layer made of cellulose triacetate (CTA) as well as a polyester support layer 72.1% (4.6g/L TDS), 84.3%, 90.9% and 92.5% (17.4 g/L TDS) water recovery using 1 M, 2 M, 3 M and 4 M DS [50]
Anaerobic palm oil mill effluent DS: 3 reagent-grade fertilizers (i.e., (NH4)2SO4, monoammonium phosphate (MAP) and KCl) and three commercial grade chemical fertilizers (i.e., (NH4)2SO4-f, monoammonium phosphate-f and muriate of potash; membrane: cellulose triacetate Highest recovery with MAP, 5.9% for a 4 h operation [51]
Among the several brine treatment methods, being an energy-efficient methodology, FO has numerous advantages compared to RO, such as cost effectiveness, low energy consumption, reduced membrane fouling, high water flux, and remarkable rejection rates, and it can be applied to high-saline brine (<200 g/L). Generally, FO technology utilizes low energy (energy cost can be low as 0.02 kWh/m3) compared to other approaches such as RO (2–2.92 kWh/m3) and mechanical vapor compression (20 kWh/m3) [52,53,54]; further cost reduction can be achieved by using a more concentrated draw solution as suggested by Gulied et al. [55]. Therefore, FO is considered as the most suitable brine resource recovery method at present [45].
Although FO has several goals, there are several lab-scale implementations; however, full-scale implementation is still in the growing stage. The world’s first commercial FO plant based on ZLD was deployed in 2016 in China (the Changxing power plant in Zhejiang Province). The system transforms 630 m3/day of used industrial wastewater with the utilization of 90 kWht of energy per m3 of wastewater treatment. The feed wastewater from flue-gas desulfurization is subjected to pre-concentrating RO followed by a membrane brine concentrator (MBC) system. The pretreatment results in the concentration of ~60,000 mg/L; the FO MBC system further concentrates the RO brine to <220,000 mg/L using a NH3/CO2 draw solution. The MBC draw solution subjected to recovery and pass-through RO system finally produces high-quality product water of <100 mg/L TDS. The implemented MBC can recover up to 23 m3/h, having 87% recovery. In 2019, another FO plant was industrialized by Forward Water Technologies, Canada. They developed a thermolytic FO DS for wastewater treatment and achieved the treatment of 15 m3/day.

#### 4.1.2. Electrodialysis Technologies

In electrodialysis, an alternating series of cation and anion selective semipermeable membranes (ion exchange membranes—IEM) are placed in between cathode and anode; clean water is produced by the electrochemical separation of ions, i.e., ions in solution are separated by the influence of electric potential. A schematic diagram illustrating the principle of electrodialysis process is shown in Figure 2. The brine solution is passed through into the cells in the ED system; the voltage gradient makes the movement of anions and cations through the selective membranes to anode and cathode, respectively. The cation-exchange membranes (CEM) allow the cations to block the anions; similarly, anions get passed through anion-exchange membranes (AEM) and cations are blocked. This leads to the complete separation of ions in brine, and ends up in ion enrichment at one side and freshwater recovery in another side. All cations such as Na+, K+, Mg2+, and Ca2+ and all anions such as chlorides, sulfates, and nitrates are found to be separated effectively from brine using ED technology.
Figure 2. Schematic diagram for electrodialysis.
Compared to RO, ED has several advantages such as simple operation, high water-recovery rate, long life for membranes, low fouling (since it not pressure driven as RO), and no need of pre/post treatments. The performance of transporting ions in ED majorly depends on the characteristics of the exchange membranes, concentration and nature of ions in feeds, ion density, etc. The polymers such as polyethylene, polysulphone, and polystyrene with charged ions are commonly used as IEMs. The positive charges such as ammonium ions, amines, etc. are used for the preparation of AEM, and sulfonic acid, phosphonic acid, phosphoryl, and carboxylic acid groups are commonly seen in CEM. Depending upon the wetting behavior, electrical, and surface characteristics, IEMs can be homogenous and heterogenous in nature. Novel hybrid membranes such as bipolar membranes, monovalent selective membranes, etc. are emerged to extend the application scenario of ED in brine treatments [56,57].
The degradation/depletion of IEMs membranes over time is the major obstacle in the application of ED. It is found that suspended molecules with 200–700 Da, surface deposition of metal cations, etc. can induce clogging in IEMs, which reduces the overall separation efficiency. To reduce fouling and scaling, some modifications are adopted in ED, known as electrodialysis reversal (EDR) and electrodialysis metathesis. Increased resistance owing to fouling can be overcome by electrodialysis reversal. In EDR, for a certain time interval the electric polarity of the electrodes is reversed to have movement of deposited ions in opposite directions. As a result, clogging can be reduced by the reduction of polarization boundary-layer thickness, thereby improving the efficiency of the system. EDR is considered as ED/EDR and can be used for concentrating high salinity of approximately >100,000 mg/L, utilizing maximum energy of 15 kWh/m3 of feedwater; this energy is less compared to conventional methods [16].
Using ED systems, the water recovery rate is found to be 70–90% depending on the feed water. ED systems are also be used for treating RO concentrate; because of the high salinity of feed water, there is high electrical resistance, voltage drop, and also high energy consumption; hence, most of the studies suggest a hybrid system for a water recovery process. Recently, Bader et al. reported a case study in Kuwait utilizing a pilot-scale high-current-density electrodialysis-evaporator hybrid system for brine management; they reported a 77% water recovery rate [58]. The recent studies on water recovery from brine using ED are illustrated in Table 4.
Table 4. Summarized reports of ED systems utilized for water recovery from various sources of brine.
Source of Brine and Salinity Level IEMs and Conditions of ED Technologies Water Recovery Rate Ref.
RO concentrate discharged from RO plant Series of ion exchange membranes such as FAS-PET-130, FKS-PET-130, Neosepta-CMX, Neosepta-AMX, LabAM-NR, LabCM-NR were used 67.78% [56]
RO brine concentrate RO-ED integrated system 95% [59]
Brackish water RO concentrate Lab-scale EDR system with three cell pairs of AEM and CEM 85% [60]
Synthetic brine Electrodialyzer with 25 cell pairs of monovalent selective AEM and CEM 70% [58]
Brackish Water RO brine Bipolar membrane electrodialysis (BMED) Acid (0.7 mol/L) and base (0.6 mol/L) recovery [61]
Seawater reverse osmosis brine Monovalent selective electrodialysis (S-ED) 55% [62]

This entry is adapted from 10.3390/su14116752

This entry is offline, you can click here to edit this entry!
Feedback