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Critical Review

The Global Rise of Zero Liquid Discharge for Wastewater Management: Drivers, Technologies, and Future Directions Tiezheng Tong, and Menachem Elimelech Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b01000 • Publication Date (Web): 08 Jun 2016 Downloaded from http://pubs.acs.org on June 12, 2016

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Environmental Science & Technology

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Critical Review

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The Global Rise of Zero Liquid Discharge for Wastewater Management: Drivers, Technologies, and Future Directions

Tiezheng Tong† and Menachem Elimelech*,†,‡ †

Department of Chemical and Environmental Engineering, Yale University, New Haven, Connecticut 06520-8286, United States ‡ Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment (NEWT), Yale University

*Corresponding author: Menachem Elimelech Email: [email protected]; Phone: +1 (203) 432-2789

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ACS Paragon Plus Environment


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ABSTRACT

37

Zero liquid discharge (ZLD) — a wastewater management strategy that eliminates liquid waste

38

and maximizes water usage efficiency — has attracted renewed interest worldwide in recent

39

years. Although implementation of ZLD reduces water pollution and augments water supply, the

40

technology is constrained by high cost and intensive energy consumption. In this critical review,

41

we discuss the drivers, incentives, technologies, and environmental impacts of ZLD. Within this

42

framework, the global applications of ZLD in the United States and emerging economies such as

43

China and India are examined. We highlight the evolution of ZLD from thermal- to membrane-

44

based processes, and analyze the advantages and limitations of existing and emerging ZLD

45

technologies. The potential environmental impacts of ZLD, notably greenhouse gas emission and

46

generation of solid waste, are discussed and the prospects of ZLD technologies and research

47

needs are highlighted.

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TOC ART

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51

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INTRODUCTION

53

Freshwater scarcity, one of the most critical global challenges of our time, poses a major threat to

54

economic growth, water security, and ecosystem health 1-3. The challenge of providing adequate

55

and safe drinking water is further complicated by climate change and the pressures of economic

56

development and industrialization. The public and industrial sectors consume substantial

57

amounts of freshwater while producing vast quantities of wastewater. If inadequately treated,

58

wastewater discharge into the aquatic environment causes severe pollution that adversely

59

impacts aquatic ecosystems and public health 4.

60

Recovery and recycling of wastewater has become a growing trend in the past decade due to

61

rising water demand 3. Wastewater reuse not only minimizes the volume and environmental risk

62

of discharged wastewater, but also alleviates the pressure on ecosystems resulting from

63

freshwater withdrawal. Through reuse, wastewater is no longer considered a “pure waste” that

64

potentially harms the environment, but rather an additional resource that can be harnessed to

65

achieve water sustainability.

66

Zero liquid discharge (ZLD) is an ambitious wastewater management strategy that

67

eliminates any liquid waste leaving the plant or facility boundary, with the majority of water

68

being recovered for reuse. ZLD obviates the risk of pollution associated with wastewater

69

discharge and maximizes water usage efficiency, thereby striking a balance between exploitation

70

of freshwater resources and preservation of aquatic environments. Achieving ZLD, however, is

71

generally characterized by intensive use of energy and high cost. As a result, ZLD has long been

72

considered not viable and has been applied only in limited cases 5.

73

In recent years, greater recognition of the dual challenges of water scarcity and pollution of

74

aquatic environments has revived global interest in ZLD. More stringent regulations, rising

75

expenses for wastewater disposal, and increasing value of freshwater are driving ZLD to become

76

a beneficial or even a necessary option for wastewater management. The global market for ZLD

77

is estimated to reach an annual investment of at least $100-200 million

78

from developed countries in North America and Europe to emerging economies such as China

79

and India.

6, 7

, spreading rapidly

80

Early ZLD systems were based on stand-alone thermal processes, where wastewater was

81

typically evaporated in a brine concentrator followed by a brine crystallizer or an evaporation 3



82

pond. The condensed distillate water in ZLD systems is collected for reuse, while the produced

83

solids are either sent to a landfill or recovered as valuable salt byproducts. Such systems, which

84

have been in successful operation for 40 years and are still being built, require considerable

85

energy and capital.

86

Reverse osmosis (RO), a membrane-based technology widely applied in desalination 8, has

87

been incorporated into ZLD systems to improve energy and cost efficiencies. However, RO,

88

although much more energy efficient than thermal evaporation, can be applied only to feedwaters

89

with a limited salinity range. Accordingly, other salt-concentrating technologies that can treat

90

higher salinity feedwaters, such as electrodialysis (ED), forward osmosis (FO), and membrane

91

distillation (MD), have emerged recently as alternative ZLD technologies to further concentrate

92

wastewater beyond RO.

93

Although ZLD holds great promise to reduce water pollution and augment water supply, its

94

viability is determined by a balance among the benefits associated with ZLD, energy

95

consumption, and capital/operation costs. Therefore, it is imperative to understand the drivers

96

and benefits that make ZLD a realistic option. Incorporating new technologies, such as emerging

97

membrane-based processes, provides opportunities to reduce the associated energy consumption

98

and costs and to expand the applicability of ZLD.

99

In this critical review, we discuss the drivers, incentives, technologies, and environmental

100

impacts of ZLD as an important strategy for wastewater management. We highlight the evolution

101

of ZLD from thermal to membrane-based processes, with a detailed analysis of the advantages

102

and limitations of both existing and emerging ZLD technologies. Lastly, we discuss the

103

environmental impacts of ZLD, the prospects of ZLD technologies, and research needs for

104

improving its feasibility and sustainability.

105 106

ACHIEVING ZERO: DRIVERS AND BENEFITS

107

Why ZLD? Figure 1 describes the major drivers and benefits of ZLD implementation. Stricter

108

regulations for wastewater disposal are the primary driver for ZLD. More costly non-compliance

109

penalties along with increasing costs for wastewater disposal can outweigh the high expenses of

110

ZLD installation. As water scarcity intensifies globally, the capability of ZLD to recover

111

wastewater to the largest extent further enhances its prospects. Increased public environmental

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awareness constitutes an additional driver, as ZLD avoids negative environmental impacts of

113

wastewater discharge and reduces the corresponding public concerns.

114

[FIGURE 1]

115

In practice, the incentives behind ZLD implementation vary depending on its application

116

and geographical location. Therefore, the drivers and benefits of ZLD are discussed in this

117

section in the context of its global applications. Although ZLD has been applied in places such as

118

the European Union, Australia, Canada, the Middle East, and Mexico 6, 7, 9, 10, examples from the

119

United States, China, and India are highlighted, as they represent the major ZLD markets with

120

the largest served populations and economic power.

121

The United States. The birth of ZLD dates back to the 1970s when the increased salinity

122

of the Colorado River led to a regulatory mandate of ZLD for nearby power plants 6, 11. In those

123

days, obtaining approval for discharge agreements for new industrial projects required several

124

years, whereas adoption of ZLD reduced this period to only a few months

125

plants remain the major domain of ZLD implementation in the U.S., where feedwaters, such as

126

flue gas desulfurization (FGD) wastewater and cooling tower blowdown, are treated and

127

recycled. For example, ZLD has been adopted at the Dallman Power Plant in Illinois to avoid the

128

environmental impacts of boron from the FGD wastewater 13. Among the 82 ZLD plants listed in

129

a survey by Mickley in 2008 11, more than 60 plants were associated with the power industry; the

130

rest were distributed across areas such as electronics, fertilizer, mining, and chemical industries.

131

6, 12

. Today, power

The U.S. EPA recently completed its guidelines revising the existing regulations on 14

132

wastewater discharge from thermal power plants

133

limits on the level of toxic metals and other harmful pollutants in wastewater discharged from

134

power plants, considers zero discharge as the preferred option for pollutants in fly ash transport

135

water, bottom ash transport water, and wastewater from flue gas mercury control systems

136

Compliance with these tighter wastewater discharge standards provides new regulatory

137

incentives for ZLD installation in U.S. power plants.

138

. This new rule, which sets the first federal

15

.

ZLD can also be used for brine management in inland desalination plants. Compared to 16

139

seawater desalination, brackish water desalination requires much less energy

140

particularly suitable for semi-arid inland regions where seawater is inaccessible 17. However, the

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management of concentrated brines represents one of the biggest challenges for inland

142

desalination. Traditional brine management practices, including direct discharge into surface

143

water or publicly owned treatment works (POTW) as well as deep-well injection

144

excluded, due to potentially adverse impacts on surface water and groundwater, insufficient

145

POTW capacity, geological and legal restrictions, and increasing disposal costs. As a result,

146

inland desalination is still not installed at many locations where water is critically needed, such

147

as Las Vegas, Phoenix, and Denver 11.

11, 18

, can be

148

ZLD overcomes the challenge of brine discharge, thereby enabling inland desalination in

149

water-scarce areas. So far, multiple governmental agencies and organizations, including the U.S.

150

Bureau of Reclamation and California Energy Commission, have investigated ZLD application

151

to inland desalination under hypothetical scenarios in Arizona, California, Colorado, Nevada,

152

and Texas 11, 19-22. These pioneering studies, however, have not resulted in full-scale ZLD inland

153

desalination plants in the U.S., with cost and energy consumption providing the main barriers to

154

implementation.

155

China. Rapid economic development and urbanization have led to rising water

156

consumption and rampant pollution in China. In response to this great challenge, China recently

157

announced a new Action Plan to tackle water pollution, aiming to largely improve the quality of

158

local water resources and ecosystems by 2020 23. This plan, enforced by the central government,

159

emphasizes rigorous control of pollutant discharge and promotes water recycling and reuse,

160

thereby providing regulatory support for ZLD installation.

161

As in the U.S., the power industry is an important contributor to the Chinese ZLD market.

162

Although coal-fired power plants provide more than 70% of the total electricity generated in

163

China

164

owned companies are located in regions that suffer water scarcity or deficit 25. This sharp conflict

165

between energy demand and water deficiency makes ZLD one of the few sustainable solutions at

166

the energy-water nexus in China. Although no data have been revealed on the overall ZLD

167

installation in Chinese power industry, a rising trend of ZLD adoption is indicated by the recent

168

construction of the world’s first FO-based ZLD system at the Changxing coal-fired power plant

169

in Zhejiang Province 26.

24

, 65-84% of water-intensive thermal power plants operated by the five largest state-

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The recent boom of the coal-to-chemicals industry in China generates another promising

171

niche for ZLD application. The coal-to-chemicals industry, utilizing coal rather than oil or

172

natural gas to produce raw materials for chemical production, is currently under pressure to

173

reduce dependence on imported energy

174

amount of freshwater but are often located in water-stressed areas, such as Inner Mongolia where

175

ample coal reserves and environmentally sensitive grassland coexist. As a consequence, ZLD is

176

mandatory at coal-to-chemicals plants in those areas to preserve both local water resources and

177

ecosystems 28. Several ZLD facilities are already installed or in the stage of design/construction

178

at Chinese coal-to-chemicals plants, with a wide range of feedwater salinities (2,000-16,000

179

mg/L of total dissolved salts, TDS) and treatment capacity (110-2,300 m3/hour) 29-32.

180

27

. Coal-to-chemicals plants consume a considerable

In addition, greater public awareness of water pollution may facilitate ZLD implementation 33

181

in China. Multiple projects, including several para-xylene (PX) chemical plants

and a

182

wastewater discharge pipeline for a paper mill 34, have been recently suspended or canceled as a

183

result of public protests. The growing influence of public concern may force industries to adopt

184

ZLD as a necessary solution to gaining public acceptance.

185

India. Facing a situation similar to that in China, India is taking aggressive actions to curb

186

severe water pollution, even in the Holy River Ganga. The recent three-year target set by the

187

Indian government, known as the “Clean Ganga” project, imposes stricter regulations on

188

wastewater discharge and moves high-polluting industries towards ZLD

189

government issued a draft policy that requires all textile plants generating more than 25 m3 of

190

wastewater effluent per day to install ZLD facilities

191

dyeing plants in the city of Tirupur had already implemented ZLD by 2008, which recovered not

192

only water but also valuable salts from textile wastewater for direct reuse in the dyeing process.

193

According to a recent technical report 39, the ZLD market in India was valued at $39 million in

194

2012 and is expected to grow continuously at a rate of 7% from 2012 to 2017. In this market, the

195

textile, brewing and distilling, power, and petrochemical industries are the major application

196

areas 39.

36, 37

CONVENTIONAL ZLD SYSTEMS

7

. In 2015, the

. As reported by Vishnu et al.

197 198

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38

, 29


199

Thermal ZLD Systems. Early ZLD systems were typically based on a series of thermal

200

processes (Figure 2A). In such systems, the feed wastewater undergoes a pretreatment step that

201

reduces scaling potential, and is then concentrated sequentially by two core elements ⎯ a brine

202

concentrator and a brine crystallizer (or an evaporation pond). The distillates generated by the

203

brine concentrator and crystallizer units are reused as clean product water, whereas the solids

204

produced are either stored (in evaporation ponds), further processed for landfill disposal, or

205

reused as valuable byproducts.

206

[FIGURE 2]

207

Brine concentrators commonly use mechanical vapor compression (MVC) for water

208

evaporation. Although other thermal desalination technologies, such as multi-effect distillation

209

(MED) and multi-stage flash (MSF), have been extensively used in seawater desalination 40, their

210

applications in ZLD systems have not been reported in literature. In MVC, the feedwater is

211

preheated by heat exchangers utilizing the sensible heat from the distillate product water, and

212

then mixed with the recirculating brine slurry at the sump of the brine concentrator. The brine

213

slurry is conveyed to the top of the concentrator and flows down inside a bundle of heat transfer

214

tubes. The flowing brine forms a thin film on the internal tube surface where water evaporation

215

occurs. Calcium sulfate seeds are often added into the recirculating brine to provide preferential

216

precipitation sites, which keep precipitating salts in suspension and prevent scale formation on

217

the heat transfer tubes

218

delivers the compressed vapor to the external surface of the heat transfer tubes. The superheated

219

vapor condenses, transferring its latent heat to vaporize the falling brine slurry. The condensate

220

travels down the heat transfer tubes and is collected as distillate that preheats the incoming

221

feedwater before being reused.

11, 41

. The produced water vapor flows to the vapor compressor, which

222

The formation of a falling thin film enhances the heat transfer rate, thereby reducing the

223

compression ratio and required energy of the compressor 42. The use of energy recovery devices

224

(e.g., heat exchangers) further decreases the energy consumption. Even so, MVC brine

225

concentrators are still very energy-intensive and require high-grade electric energy. They

226

typically consume 20-25 kWhe/m3 of treated feedwater

227

kWhe/m3 of feedwater) reported in the literature

228

applied successfully in ZLD processes for decades 41, MVC brine concentrators set a benchmark

8

43

11, 22

, with higher values (up to 39

. As an established technology that has been


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for energy comparison with other technologies, which guides efforts to reduce energy

230

consumption in ZLD. Further, brine concentrators are able to reach salinity concentrations of

231

250,000 mg/L, with a water recovery of 90-98%, and produce high-quality product water (TDS
90%

298

for brackish water 48). The HERO process has been applied in multiple full-scale ZLD systems

299

worldwide

300

treatment capacity of 2300 m3/h 31.

301

29, 31, 49

22, 47, 48

. The feedwater is treated by a weakly acidic cation exchange

, including a recent project for a Chinese coal-to-liquids plant with a high

Current RO membrane modules cannot operate at very high hydraulic pressure, which 42

302

typically corresponds to a salinity of ~70,000 mg/L of the RO exit brine

303

RO systems imposes a ceiling on the salinity of water that can be treated by RO in ZLD systems.

304

This salinity limit is much lower than that achieved by brine concentrators (i.e., up to 250,000

305

mg/L). Thus, a stand-alone RO system is not able to reduce the volume of concentrated brine to

306

the same extent as brine concentrators. Accordingly, RO is usually followed by a brine

307

concentrator in ZLD processes

308

salinities than RO and consume less energy than brine concentrators (as highlighted in Figure 3),

309

is of paramount importance for advancing ZLD technology.

11, 19, 20

. This restriction of

. Developing new technologies, which tolerate higher

310 311 312

BEYOND THERMAL EVAPORATORS: EMERGING MEMBRANE-BASED ZLD TECHNOLOGIES

313

Three membrane-based processes ⎯ ED, FO, and MD ⎯ emerge as alternative ZLD

314

technologies to brine concentrators to further concentrate the wastewater after the RO stage. The

315

produced brine from these processes serves as a feed to the crystallizer or evaporation pond. A

316

schematic illustration of ZLD systems incorporating these technologies is shown in Figure 4.

317

Their advantages, limitations, and energy consumption, along with those of RO and MVC brine

318

concentrators, are summarized in Table 1. Some of these technologies (i.e., thermolytic FO and

11



319

MD) are hybrids of both thermal- and membrane-based processes. While the energy input to

320

these processes is thermal, membranes are the core separation components of these technologies.

321

[FIGURE 4]

322

[TABLE 1]

323

Electrodialysis. ED applies an electric potential as the driving force to remove dissolved

324

ions through ion exchange membranes. In contrast to RO membranes that reject all ions, ion

325

exchange membranes selectively permit the transport of counter ions but prevent the passage of

326

co-ions

327

passing through cation-exchange membranes, whereas anions migrate in the opposite direction

328

through anion-exchange membranes. These concurrent processes generate two streams ⎯ salt-

329

depleted diluate and concentrated brine. In a modified form of ED, electrodialysis reversal

330

(EDR), the polarity of the electrodes is reversed frequently for minimizing fouling and scaling 20,

331

thereby requiring much less pretreatment than RO

332

propensity for silica-enriched feedwaters (e.g., BWRO brines), as neutral silica is not

333

accumulated in the brine stream 20.

334

50

. As shown in Figure 4A, cations move towards the negatively charged cathode by

51

. ED and EDR also have a low scaling

Compared to RO, ED and EDR are able to concentrate feed waters to higher salinity 5, 52-54

335

(>100,000 mg/L)

336

consume 7-15 kWhe/m3 of feedwater

337

concentrators. Also, the total cost for equipment and energy by ED was estimated to be lower

338

than that of MVC

339

concentrators and RO, the salinity of ED/EDR effluent can be much higher (e.g., TDS>10,000

340

mg/L

341

energy consumption and capital cost.

53

56

. When concentrating brines to such high salinities, ED and EDR 52-55

, which is less than that required by MVC brine

. However, in contrast to the very low TDS of water produced by brine

), indicating a trade-off between the quality of the desired product water and overall

342

For ED/EDR treating concentrated feedwater in ZLD systems, low-salinity product water

343

results in a large voltage drop, high electric resistance, low current efficiency, and diluate loss,

344

further increasing the energy consumption

345

reduces the limiting current density, which increases the required membrane area and

346

capital/operation cost 51. As estimated by McGovern et al. 56, the cost of salt removal by ED is

347

higher at lower diluate salinities. As such, a stand-alone, single-stage ED/EDR system is not

57, 58

12

. Furthermore, a decrease of diluate salinity


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suitable for reaching ZLD in most cases, since one of the benefits of ZLD is the production of

349

usable water. A multi-stage configuration is a feasible solution

350

cost.

56-58

, but it increases the capital

351

As a partial desalination process, ED/EDR has been applied in combination with RO in

352

several ZLD systems. Such systems achieved the dual function of extending the salinity limit of

353

RO and reducing the energy consumption relative to brine concentrators. For example, Oren et al.

354

demonstrated a pilot RO-EDR system for brackish water desalination with a water recovery of

355

97-98% 5. In that system, EDR concentrated the RO brine to a salinity of 100,000-200,000 mg/L

356

prior to a side-loop crystallizer and wind-aided intensified evaporation. In another pilot study 53,

357

EDR effectively removed hardness to reduce the scaling potential of saline basal aquifer water,

358

thereby improving the subsequent RO recovery without chemical addition. The EDR brine could

359

reach a salinity of 125,000 mg/L and was further concentrated by a brine crystallizer to approach

360

ZLD. In both cases, the EDR effluent was further desalinated by RO or partially blended with

361

RO permeate to attain a desired product water quality 5, 53.

362

Forward Osmosis. Unlike hydraulic pressure-driven RO, FO utilizes an osmotic pressure 59

363

difference to drive water permeation across a semipermeable membrane

. In FO, water flows

364

from the feedwater to a concentrated draw solution with a higher osmotic pressure (Figure 4B).

365

The produced brine is sent to a brine crystallizer or an evaporation pond, whereas the draw

366

solutes are separated from the desalinated water to regenerate the concentrated draw solution.

367

Since the driving force in FO is osmotic pressure, FO can treat waters with much higher salinity

368

than RO. When using FO to concentrate feedwater beyond the salinity limit of RO, the osmotic

369

pressure of diluted draw solution will surpass the bearable pressure limit of RO. Hence, in this

370

case, draw solutes that depend on RO for regeneration (e.g., NaCl and MgSO4,

371

suitable.

60

) will not be

372

The development of thermolytic draw solutes, such as the ammonia−carbon dioxide

373

(NH3/CO2), paved the way for FO-incorporated ZLD systems. The NH3/CO2 draw solution

374

generates very high osmotic pressure-driving forces and can be regenerated by low-temperature

375

distillation

376

solution to concentrate produced water from the Marcellus shale region to an average salinity of

377

180,000 mg/L 43.

61, 62

. A recent pilot study demonstrated the application of FO with NH3/CO2 draw

13



378

Because the thermolytic NH3/CO2 draw solution decomposes at moderate temperature

379

(approximately 60 °C at atmospheric pressure) 61, low-grade thermal energy, including industrial

380

waste heat and geothermal energy, can be utilized to regenerate the concentrated draw solution.

381

A recent study estimated that U.S. power plants produced 803 million GJ of waste heat at

382

temperatures greater than 90 °C in 2012

383

NH3/CO2 FO, could potentially produce a maximum of 1.9 billion m3 of water annually, which

384

would meet the treatment demands for boiler water makeup and FGD wastewater systems of all

385

U.S. power plants

386

such as the U.S. and China 42, 65, 66.

64

63

. This amount of heat, if utilized to power the

. Also, geothermal energy is abundantly available in major ZLD markets

387

FO operates at low pressure, resulting in foulant layers that are less compact and more

388

reversible than in hydraulic pressure-driven RO systems. Accordingly, FO has a much lower

389

fouling propensity than RO 59, which not only reduces the operation cost for fouling control but

390

also extends the applicability of ZLD to wastewaters with high fouling potential.

391

The thermolytic FO process can be used as a brine concentrator after the RO stage.

392

Compared to MVC brine concentrators, the NH3/CO2 FO can be competitive because a small

393

volume of the more volatile draw solutes (i.e., NH3 and CO2), instead of water, is vaporized to

394

regenerate the concentrated draw solution

395

smaller area footprint and also renders ZLD systems more adaptable to fluctuations in the flow

396

rate and quality of feedwater 67.

397

43

. Furthermore, the modularity of FO results in

Recently, the world’s first FO-based ZLD system was constructed at the Changxing power 26, 67

398

plant in Zhejiang Province, China

. The system treats a mixture of FGD wastewater and

399

cooling tower blowdown at 650 m3/day. The feedwater is first concentrated by RO to a

400

concentration of ~60,000 mg/L. The NH3/CO2 FO process is then used as a brine concentrator to

401

further concentrate the RO brine to above 220,000 mg/L TDS. As the last step, the FO brine is

402

fed to a crystallizer for further concentration, while a high-quality product water (TDS < 100

403

mg/L after polishing by a secondary RO) is produced for reuse as boiler makeup water 67.

404

Membrane Distillation. MD is a thermal, membrane-based desalination process, in which

405

a partial vapor pressure difference drives water vapor across a hydrophobic, microporous

406

membrane

407

the hot feedwater (typically 60-90 °C

68

. In MD, the feedwater is heated and the resultant temperature difference between 69, 70

) and colder permeate side creates a vapor pressure

14


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difference to drive the water vapor flux (Figure 4C). The aqueous permeate can be in direct

409

contact with the membrane (direct contact membrane distillation, DCMD). Alternatively, the

410

water vapor can be collected on a condensation surface separated from the membrane, such as in

411

air gap membrane distillation (AGMD), vacuum membrane distillation (VMD), or sweeping gas

412

membrane distillation (SGMD) 68, 71-74.

413

MD is more energy intensive than RO and ED/EDR, because water separation by MD

414

requires liquid-vapor phase transition. The theoretical minimum energy of seawater desalination

415

by single-pass DCMD with heat recovery and a feed temperature at 60 °C is 27.6 MJ/m3 of

416

product water

417

MJ/m3 of product water) 8. In practical use, DCMD was estimated to consume 143-162 MJ (40-

418

45 kWht) per m3 of product water for seawater desalination 76, and a comparable value of 80-240

419

MJ (22-67 kWht)/m3 of product water was reported for AGMD 72. However, this thermal-based

420

energy consumption cannot be directly compared with the energy consumption of electricity-

421

driven technologies (RO, ED/EDR, and MVC brine concentrators), because the efficiency of

422

electricity generation from thermal energy varies with the quality (temperature) of the thermal

423

energy. Compared to MVC brine concentrators with well-designed energy recovery devices,

424

efficient heat recovery (e.g., use of heat exchangers 75 or brine recycling 77) is critical to improve

425

the energy competitiveness of MD.

75

, which is much higher than that by RO with a typical recovery of 50% (3.8

426

Similar to thermolytic FO, MD is beneficial due to its ability to treat high salinity feed

427

waters that cannot be desalinated by RO, and MD’s potential to leverage low-grade thermal

428

energy. When low-grade energy is available, MD achieves both cost saving and a reduced carbon

429

footprint relative to electricity-driven desalination technologies. Furthermore, MD is modular,

430

can operate at low pressure and temperature, and has low fouling propensity 70, 72, 76, 78. However,

431

when volatile pollutants or surfactants are present in the feedwater (e.g., in coal-to-chemical 79,

432

brewery 80, and shale gas industries 42), MD suffers from membrane wetting and the passage of

433

volatile compounds into the permeate, which deteriorate product water quality and cause process

434

downtime 42, 70, 81.

435

The potential application of MD in ZLD inland desalination has been demonstrated at the 82

436

bench scale

. When applying MD to further concentrate a secondary RO brine (with TDS of

437

~17,500 mg/L), a total water recovery of >98% was obtained for a brackish groundwater in

15



82

Page 16 of 29

438

California

. Recently, a conceptual near-ZLD system incorporating MD with reverse

439

electrodialysis (RED) was shown to achieve both water and energy production in seawater

440

desalination 83. In that system, MD reduced the volume of simulated SWRO brine (1 M NaCl) by

441

more than 80%. The produced MD brine was then mixed with seawater in a RED stack to

442

generate electrochemical energy. To date, however, large-scale applications of MD are still

443

hindered by its technical immaturity and low single-pass, single-module water recovery 20, 75. No

444

pilot-scale applications of MD in ZLD have been reported in the literature.

445 446

ENVIRONMENTAL IMPACTS

447

Despite the main goal of ZLD to reduce water pollution and improve water sustainability,

448

application of ZLD also results in unintended environmental impacts. One risk stems from the

449

produced solid wastes. For example, solid wastes stored in evaporation ponds have raised

450

concerns about their odors, potentially negative impact on wildlife, and risk of leakage

451

Similarly, solid wastes disposed in landfills may result in leaching of chemicals into groundwater

452

84

453

prevent potential contamination from solid wastes.

22

.

. Accordingly, impervious liners and reliable monitoring systems are typically required to

454

As discussed earlier, ZLD consumes large amounts of energy, leading to significant

455

emission of greenhouse gases (GHG). Some pretreatment methods, such as acidification

456

followed by degasification, release CO2 from the feedwater into the atmosphere. For example,

457

the application of ED in concentrating RO brine increases CO2 emission via both energy

458

consumption and decarbonation for scaling control

459

emission would increase by 50% if California water supply was switched from imported water to

460

BWRO inland desalination 86. According to the U.S. Energy Information Administration 87, the

461

amount of CO2 produced by electricity generation varies depending on the fuel type. Assuming

462

939 g of CO2 per kWhe generated by bituminous coal 87, MVC brine concentrators will typically

463

produce 19-23 kg of CO2 per m3 of treated feedwater solely from electricity usage

464

(corresponding to energy consumption of 20-25 kWhe/m3

465

higher energy efficiency, such as RO, will significantly reduce the GHG emission. In addition,

466

emerging ZLD technologies that can utilize low-grade or renewable energy (e.g., waste heat,

16

85

. A life-cycle study showed that GHG

11, 22

). Incorporating technologies with


Page 17 of 29


467

solar energy, geothermal energy

468

systems.

18, 42, 63, 64

) enable further reduction of GHG footprint of ZLD

469 470

OUTLOOK

471

ZLD implementation is growing globally as an important wastewater management strategy to

472

reduce water pollution and augment water supply. However, high cost and intensive energy

473

consumption will remain the main barriers to ZLD adoption. As the feedwater becomes more

474

concentrated along the ZLD treatment train, its salinity increases and so does the minimum

475

energy required for desalination 8. Therefore, the energy demand of ZLD, along with its

476

associated costs, will still be higher than that of conventional wastewater treatment or disposal

477

options.

478

Future growth of the ZLD market will heavily rely on regulatory incentives that outweigh its

479

economic disadvantages. As the severe consequences of water pollution are increasingly

480

recognized and attract more public attention, stricter environmental regulations on wastewater

481

discharge are expected, which will push more high-polluting industries towards ZLD. Intensified

482

freshwater scarcity, caused by both climate change and freshwater overexploitation, will likely

483

facilitate ZLD implementation. The prolonged drought in the Southwest U.S. 88 and accelerating

484

growth of water-intensive industries (e.g., coal-fired power plants) in China

485

worldwide freshwater deficiency. In such cases, a water quota may be imposed to limit the total

486

freshwater withdrawal by high water-consuming industries 90. In this case, ZLD may be a needed

487

strategy to guarantee sustainable water supply.

89

exemplify a

488

Due to the unrivaled energy efficiency of RO, expanding the salinity range of RO is of

489

paramount importance in ZLD systems. A robust RO system with higher resistance to hydraulic

490

pressure and fouling/scaling will effectively improve the energy efficiency and economic

491

feasibility of ZLD. At the core of such systems are fouling mitigation technologies, such as

492

fouling- and scaling-resistant membranes, which will reduce the operation cost through less

493

extensive pretreatment and cleaning needs

494

reuse 93. Major progress has been made to develop RO membranes with resistance to organic and

495

biological fouling

94-96

91, 92

and enhance the quality of the product water for

, but more remains to be done to test their performance in ZLD systems

17



Page 18 of 29

496

with various feedwater composition and very high concentration factors. Membranes with low

497

propensity to inorganic scaling (e.g., gypsum and silica scaling) are particularly desirable.

498

We have reviewed three membrane-based technologies ⎯ ED/EDR, thermolytic FO, and

499

MD ⎯ as three emerging ZLD technologies to further concentrate the feedwater after the RO

500

stage. However, compared to the technical maturity of RO and MVC brine concentrators, these

501

technologies are less established. More pilot or field studies are desirable to validate their large-

502

scale performance and viability in pursuing ZLD. Especially, their energy consumption and cost

503

need to be further evaluated to make a direct comparison with MVC brine concentrators. For MD

504

and thermolytic FO, their capability of harnessing low-grade energy will significantly reduce the

505

prime energy demand, operation cost, and GHG footprint of ZLD.

506

Resource recovery may provide an additional economic incentive for ZLD. Beneficial

507

components in the feedwater (e.g., valuable salts, nutrients, critical metals and elements) can

508

precipitate or be largely enriched when the feedwater is concentrated. For example, a proprietary

509

technology has been used for sequential salt recovery while achieving ZLD

510

technology involves multiple mineral precipitation and crystallization steps, producing useful

511

salts such as gypsum-magnesium hydroxide, magnesium hydroxide, and precipitated calcium

512

carbonate

513

carbonate 11) can partially compensate for the operation cost of ZLD. Further, the emerging ZLD

514

technologies reviewed in this article can recover various nutrients from wastewater

515

harvesting critical metals and elements from ZLD desalination systems has been recently

516

proposed 99.

11, 97

11, 97

. This

. The economic values of these byproducts (e.g., $350/ton of precipitated calcium 98

, and

517

In addition, the environmental impacts of ZLD need to be better understood. A life-cycle

518

assessment analysis of the energy demand and GHG emission will provide additional insights

519

into the cost-benefit balancing of ZLD. Along with advances in improving the energy and cost

520

efficiencies of ZLD technologies, particularly by incorporating membrane-based processes, ZLD

521

may become more feasible and sustainable in the future.

522 523

ACKNOWLEDGEMENT

524

We acknowledge the support received from the National Science Foundation through the

525

Engineering Research Center for Nanotechnology-Enabled Water Treatment (ERC-1449500). 18


Page 19 of 29


526 527

REFERENCES

528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570

1. Hoekstra, A. Y., Water scarcity challenges to business. Nat Clim Change 2014, 4, (5), 318-320. 2. Vorosmarty, C. J.; McIntyre, P. B.; Gessner, M. O.; Dudgeon, D.; Prusevich, A.; Green, P.; Glidden, S.; Bunn, S. E.; Sullivan, C. A.; Liermann, C. R.; Davies, P. M., Global threats to human water security and river biodiversity. Nature 2010, 467, (7315), 555-561. 3. Grant, S. B.; Saphores, J. D.; Feldman, D. L.; Hamilton, A. J.; Fletcher, T. D.; Cook, P. L. M.; Stewardson, M.; Sanders, B. F.; Levin, L. A.; Ambrose, R. F.; Deletic, A.; Brown, R.; Jiang, S. C.; Rosso, D.; Cooper, W. J.; Marusic, I., Taking the "waste" out of "wastewater" for human water security and ecosystem sustainability. Science 2012, 337, (6095), 681-686. 4. Schwarzenbach, R. P.; Egli, T.; Hofstetter, T. B.; von Gunten, U.; Wehrli, B., Global water pollution and human health. Annu Rev Env Resour 2010, 35, 109-136. 5. Oren, Y.; Korngold, E.; Daltrophe, N.; Messalem, R.; Volkman, Y.; Aronov, L.; Weismann, M.; Bouriakov, N.; Glueckstern, P.; Gilron, J., Pilot studies on high recovery BWRO-EDR for near zero liquid discharge approach. Desalination 2010, 261, (3), 321-330. 6. The global push for zero. http://www.waterworld.com/articles/wwi/print/volume30/issue-1/technology-case-studies/the-global-push-for-zero.html (accessed June 6 2016) 7. From zero to hero – the rise of ZLD. https://www.globalwaterintel.com/global-waterintelligence-magazine/10/12/market-insight/from-zero-to-hero-the-rise-of-zld (accessed June 6 2016) 8. Elimelech, M.; Phillip, W. A., The future of seawater desalination: Energy, technology, and the environment. Science 2011, 333, (6043), 712-717. 9. Durham, B.; Mierzelewski, M., Water reuse and zero liquid discharge: a sustainable water resource solution. Water Sci Technol 2003, 3, (4), 97-103. 10. Heins, W.; Schooley, K., Achieving zero liquid discharge in SAGD heavy oil recovery. J Can Petrol Technol 2004, 43, (8), 37-42. 11. Mickley, M. Survey of High-Recovery and Zero Liquid Discharge Technologies for Water Utilities; WRF-02-006a; WateReuse Foundation: Alexandria, VA, 2008. 12. Zero liquid discharge – A real solution? http://chinawaterrisk.org/resources/analysisreviews/zero-liquid-discharge-a-real-solution/ (accessed June 6 2016) 13. Aquatech secures order for FGD waste water treatment ZLD. http://www.wateronline.com/doc/aquatech-secures-order-for-fgd-waste-water-tr-0001 (accessed June 6 2016) 14. U.S. Environmental Protection Agency. Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category; Final Rule; 40 CFR Part 423, 2015. 15. Technical Development Document for the Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category; EPA-821-R-15-007; U.S. Environmental Protection Agency: Washington, DC, 2015. 16. Al-Karaghouli, A.; Kazmerski, L. L., Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes. Renew Sust Energ Rev 2013, 24, 343-356. 17. Brady, P. V.; J., K. R.; M., M. T.; Hightower, M. M., Inland desalination: Challenges and research needs. Journal of Contemporary Water Research & Education 2005, 132, 46-51.

19



571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616

18. Xevgenos, D.; Moustakas, K.; Malamis, D.; Loizidou, M., An overview on desalination & sustainability: renewable energy-driven desalination and brine management. Desalin Water Treat 2016, 57, (5), 2304-2314. 19. Bond, R.; Veerapaneni, S., Zeroing in on ZLD technologies for inland desalination. J Am Water Works Ass 2008, 100, (9), 76-89. 20. Eastern Municipal Water District and Carollo Engineers. Evaluation and Selection of Available Processes for a Zero-Liquid Discharge System for the Perris, California, Ground Water Basin; DWPR No. 149; U.S. Department of the Interior, Bureau of Reclamation: Denver, CO, 2008. 21. Bond, R.; Veerapaneni, S. Zero Liquid Discharge for Inland Desalination; No. 500-01040; Awwa Research Foundation: Denver, CO, 2007. 22. Burbano, A.; Brankhuber, P. Demonstration of Membrane Zero Liquid Discharge for Drinking Water Systems - A Literature Review; WERF5T10a; Water Environment Research Foundation: Alexandria, VA, 2012. 23. The State Council, the People's Republic of China. China announces action plan to tackle water pollution. http://english.gov.cn/policies/latest_releases/2015/04/16/content_281475090170164.htm (accessed June 6 2016) 24. Jiang, Y., China's water security: Current status, emerging challenges and future prospects. Environ Sci Policy 2015, 54, 106-125. 25. China's Power Utilities in Hot Water: Executive Summary; Bloomberg New Energy Finance: 2013. 26. Oasys applies FO to treat wastewater from China's growing power market. Membrane Technology 2014, 2014, (11), 2-3. 27. Xie, K. C.; Li, W. Y.; Zhao, W., Coal chemical industry and its sustainable development in China. Energy 2010, 35, (11), 4349-4355. 28. Coal-to-chemicals an emerging opportunity in China. http://usedtouseful.com/post/108284189605/coal-to-chemicals-an-emerging-opportunity-inchina (accessed June 6 2016) 29. Zero liquid discharge, membrane hybrid excels in China. http://www.waterworld.com/articles/wwi/print/volume-26/issue-4/editorial-focus/sludgeprocessing/zero-liquid-discharge-membrane.html (accessed June 6 2016) 30. Protecting China’s water supply. http://www.wwdmag.com/industrial/protectingchina%E2%80%99s-water-supply (accessed June 6 2016) 31. Aquatech awarded zero liquid discharge project for coal-to-liquids plant in China. http://finance.yahoo.com/news/aquatech-awarded-zero-liquid-discharge-124000102.html (accessed June 6 2016) 32. Mongolia coal to chemicals project to reuse wastewater using Aquatech’s ZLD. http://www.waterworld.com/articles/wwi/2015/11/mongolia-coal-to-chemicals-project-to-reusewastewater-using-aquatech-s-zld.html (accessed June 6 2016) 33. Para-xylene plants face uphill struggle for acceptance in China. http://www.rsc.org/chemistryworld/2014/04/para-xylene-px-plants-face-continued-oppositionchina (accessed June 6 2016) 34. Protest stops China sewage pipeline project. http://www.cnn.com/2012/07/28/world/asia/china-sewage-pipeline/ (accessed June 6 2016)

20


Page 20 of 29

Page 21 of 29

617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662


35. India uses zero liquid discharge (ZLD) to clean the Ganges River. http://inspiredeconomist.com/2015/01/14/india-uses-zld-ganges-river/ (accessed June 6 2016) 36. Environment (Protection) - Amendment Rules. Government of India, Ministry of Environment, Forest & Climate Change, Notification, 2015. http://www.moef.nic.in/sites/default/files/Effluents%20from%20textile%20Industry.PDF (accessed June 6 2016) 37. Government of India rolls out ‘ZLD’ norms for textile industry. http://news.apparelresources.com/sustainability-news/government-of-india-rolls-out-zld-normsfor-textile-industry/ (accessed June 6 2016) 38. Vishnu, G.; Palanisamy, S.; Joseph, K., Assessment of fieldscale zero liquid discharge treatment systems for recovery of water and salt from textile effluents. J Clean Prod 2008, 16, (10), 1081-1089. 39. Frost & Sullivan. Outlook on Zero Liquid Discharge (ZLD) Market in India; 2013. http://cds.frost.com/p/67599/#!/nts/c?id=9835-00-59-00-00 (accessed June 6 2016) 40. Ghaffour, N.; Missimer, T. M.; Amy, G. L., Technical review and evaluation of the economics of water desalination: Current and future challenges for better water supply sustainability. Desalination 2013, 309, 197-207. 41. Bostjancic, J.; Ludlum, R. Getting to Zero Discharge: How to Recycle That Last Bit of Really Bad Wastewater; GE's Water & Process Technologies: 2013. 42. Shaffer, D. L.; Chavez, L. H. A.; Ben-Sasson, M.; Castrillon, S. R. V.; Yip, N. Y.; Elimelech, M., Desalination and reuse of high-salinity shale gas produced water: Drivers, technologies, and future directions. Environ Sci Technol 2013, 47, (17), 9569-9583. 43. McGinnis, R. L.; Hancock, N. T.; Nowosielski-Slepowron, M. S.; McGurgan, G. D., Pilot demonstration of the NH3/CO2 forward osmosis desalination process on high salinity brines. Desalination 2013, 312, 67-74. 44. Stanford, B. D.; Leising, J. F.; Bond, R. G.; Snyder, S. A., Inland desalination: Current practices, environmental implications, and case studies in Las Vegas, NV. Sustain Sci Eng 2010, 2, 327-350. 45. Prihasto, N.; Liu, Q. F.; Kim, S. H., Pre-treatment strategies for seawater desalination by reverse osmosis system. Desalination 2009, 249, (1), 308-316. 46. Loganathan, K.; Chelme-Ayala, P.; El-Din, M. G., Pilot-scale study on the treatment of basal aquifer water using ultrafiltration, reverse osmosis and evaporation/crystallization to achieve zero-liquid discharge. J Environ Manage 2016, 165, 213-223. 47. Subramani, A.; Jacangelo, J. G., Treatment technologies for reverse osmosis concentrate volume minimization: A review. Sep Purif Technol 2014, 122, 472-489. 48. Mukhopadhyay, D. Method and apparatus for high efficiency reverse osmosis operation. US Patent 6537456 B2, Mar 25, 2003. 49. Aquatech awarded zero liquid discharge contract. http://www.wateronline.com/doc/aquatech-awarded-zero-liquid-discharge-contra-0001 (accessed June 6 2016) 50. Xu, T. W.; Huang, C. H., Electrodialysis-based separation technologies: A critical review. AICHE J 2008, 54, (12), 3147-3159. 51. Strathmann, H., Electrodialysis, a mature technology with a multitude of new applications. Desalination 2010, 264, (3), 268-288. 52. Korngold, E.; Aronov, L.; Daltrophe, N., Electrodialysis of brine solutions discharged from an RO plant. Desalination 2009, 242, (1-3), 215-227.

21



663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707

53. Loganathan, K.; Chelme-Ayala, P.; El-Din, M. G., Treatment of basal water using a hybrid electrodialysis reversal-reverse osmosis system combined with a low-temperature crystallizer for near-zero liquid discharge. Desalination 2015, 363, 92-98. 54. Turek, M.; Dydo, P.; Klimek, R., Salt production from coal-mine brine in EDevaporation-crystallization system. Desalination 2005, 184, (1-3), 439-446. 55. Turek, M., Electrodialytic desalination and concentration of coal-mine brine. Desalination 2004, 162, (1-3), 355-359. 56. McGovern, R. K.; Weiner, A. M.; Sun, L. G.; Chambers, C. G.; Zubair, S. M.; Lienhard, J. H., On the cost of electrodialysis for the desalination of high salinity feeds. Appl Energ 2014, 136, 649-661. 57. Turek, M., Cost effective electrodialytic seawater desalination. Desalination 2003, 153, (1-3), 371-376. 58. Wang, M.; Xing, H. B.; Jia, Y. X.; Ren, Q. C., A zero-liquid-discharge scheme for vanadium extraction process by electrodialysis-based technology. J Hazard Mater 2015, 300, 322-8. 59. Shaffer, D. L.; Werber, J. R.; Jaramillo, H.; Lin, S. H.; Elimelech, M., Forward osmosis: Where are we now? Desalination 2015, 356, 271-284. 60. Cath, T. Y.; Childress, A. E.; Elimelech, M., Forward osmosis: Principles, applications, and recent developments. J Membrane Sci 2006, 281, (1-2), 70-87. 61. McGinnis, R. L.; Elimelech, M., Energy requirements of ammonia-carbon dioxide forward osmosis desalination. Desalination 2007, 207, (1-3), 370-382. 62. McCutcheon, J. R.; McGinnis, R. L.; Elimelech, M., A novel ammonia-carbon dioxide forward (direct) osmosis desalination process. Desalination 2005, 174, (1), 1-11. 63. Gingerich, D. B.; Mauter, M. S., Quantity, quality, and availability of waste heat from United States thermal power generation. Environ Sci Technol 2015, 49, (14), 8297-8306. 64. Zhou, X. S.; Gingerich, D. B.; Mauter, M. S., Water treatment capacity of forwardosmosis systems utilizing power-plant waste heat. Ind Eng Chem Res 2015, 54, (24), 6378-6389. 65. Zhu, J.; Hu., K.; Lu., X.; Huang, X.; Liu, K.; Wu, X., A review of geothermal energy resources, development, and applications in China: Current status and prospects. Energy 2015, 93, 466-483. 66. Lund, J. W.; Freeston, D. H.; Boyd, T. L., Direct application of geothermal energy: 2005 Worldwide review. Geothermics 2005, 34, (6), 691-727. 67. Changxing power plant debuts the world's first forward osmosis-based zero liquid discharge application. http://www.wateronline.com/doc/changxing-power-plant-debuts-theworld-s-first-forward-osmosis-based-zero-liquid-discharge-application-0001 (accessed June 6 2016) 68. Camacho, L. M.; Dumee, L.; Zhang, J. H.; Li, J. D.; Duke, M.; Gomez, J.; Gray, S., Advances in membrane distillation for water desalination and purification applications. Water 2013, 5, (1), 94-196. 69. Alklaibi, A. M.; Lior, N., Membrane-distillation desalination: Status and potential. Desalination 2005, 171, (2), 111-131. 70. Lawson, K. W.; Lloyd, D. R., Membrane distillation. J Membrane Sci 1997, 124, (1), 125. 71. Curcio, E.; Drioli, E., Membrane distillation and related operations - A review. Sep Purif Rev 2005, 34, (1), 35-86.

22


Page 22 of 29

Page 23 of 29

708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752


72. Meindersma, G. W.; Guijt, C. M.; de Haan, A. B., Desalination and water recycling by air gap membrane distillation. Desalination 2006, 187, (1-3), 291-301. 73. Tijing, L. D.; Choi, J. S.; Lee, S.; Kim, S. H.; Shon, H. K., Recent progress of membrane distillation using electrospun nanofibrous membrane. J Membrane Sci 2014, 453, 435-462. 74. Subramani, A.; Jacangelo, J. G., Emerging desalination technologies for water treatment: A critical review. Water Res 2015, 75, 164-187. 75. Lin, S. H.; Yip, N. Y.; Elimelech, M., Direct contact membrane distillation with heat recovery: Thermodynamic insights from module scale modeling. J Membrane Sci 2014, 453, 498-515. 76. Al-Obaidani, S.; Curcio, E.; Macedonio, F.; Di Profio, G.; Ai-Hinai, H.; Drioli, E., Potential of membrane distillation in seawater desalination: Thermal efficiency, sensitivity study and cost estimation. J Membrane Sci 2008, 323, (1), 85-98. 77. Duong, H. C.; Cooper, P.; Nelemans, B.; Cath, T. Y.; Nghiem, L. D., Optimising thermal efficiency of direct contact membrane distillation by brine recycling for small-scale seawater desalination. Desalination 2015, 374, 1-9. 78. Alkhudhiri, A.; Darwish, N.; Hilal, N., Membrane distillation: A comprehensive review. Desalination 2012, 287, 2-18. 79. Zhang, W. Q.; Ma, J.; Yang, S. D.; Zhang, T.; Li, Y. F., Pretreatment of coal gasification wastewater by acidification demulsion. Chinese J Chem Eng 2006, 14, (3), 398-401. 80. Simate, G. S.; Cluett, J.; Iyuke, S. E.; Musapatika, E. T.; Ndlovu, S.; Walubita, L. F.; Alvarez, A. E., The treatment of brewery wastewater for reuse: State of the art. Desalination 2011, 273, (2-3), 235-247. 81. El-Bourawi, M. S.; Ding, Z.; Ma, R.; Khayet, M., A framework for better understanding membrane distillation separation process. J Membrane Sci 2006, 285, (1-2), 4-29. 82. Martinetti, C. R.; Childress, A. E.; Cath, T. Y., High recovery of concentrated RO brines using forward osmosis and membrane distillation. J Membrane Sci 2009, 331, (1-2), 31-39. 83. Tufa, R. A.; Curcio, E.; Brauns, E.; van Baak, W.; Fontananova, E.; Di Profio, G., Membrane distillation and reverse electrodialysis for near-zero liquid discharge and low energy seawater desalination. J Membrane Sci 2015, 496, 325-333. 84. Younos, T., Environmental issues of desalination. Journal of Contemporary Water Research & Education 2005, 132, (1), 11-18. 85. Zhang, Y.; Ghyselbrecht, K.; Vanherpe, R.; Meesschaert, B.; Pinoy, L.; Van der Bruggen, B., RO concentrate minimization by electrodialysis: Techno-economic analysis and environmental concerns. Journal of Environmental Management 2012, 107, 28-36. 86. Stokes, J. R.; Horvath, A., Energy and air emission effects of water supply. Environ Sci Technol 2009, 43, (8), 2680-2687. 87. U.S. Energy Information Administration. How much carbon dioxide is produced per kilowatthour when generating electricity with fossil fuels? http://www.eia.gov/tools/faqs/faq.cfm?id=74&t=11 (accessed June 6 2016) 88. Cook, B. I.; Ault, T. R.; Smerdon, J. E., Unprecedented 21st century drought risk in the American Southwest and Central Plains. Sci Adv 2015, 1, (1), e1400082. 89. Zhang, C.; Zhong, L.; Fu, X.; Wang, J.; Wu, Z., Revealing water stress by the thermal power industry in China based on a high spatial resolution water withdrawal and consumption inventory. Environ Sci Technol 2016, 50, (4), 1642-1652.

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90. Jiang, Y. L.; Chen, Y. S.; Younos, T.; Huang, H. Q.; He, J. P., Urban water resources quota management: The core strategy for water demand management in China. Ambio 2010, 39, (7), 467-475. 91. Fritzmann, C.; Lowenberg, J.; Wintgens, T.; Melin, T., State-of-the-art of reverse osmosis desalination. Desalination 2007, 216, (1-3), 1-76. 92. Greenlee, L. F.; Lawler, D. F.; Freeman, B. D.; Marrot, B.; Moulin, P., Reverse osmosis desalination: Water sources, technology, and today's challenges. Water Res 2009, 43, (9), 23172348. 93. Lee, S.; Cho, J.; Elimelech, M., Influence of colloidal fouling and feed water recovery on salt rejection of RO and NF membranes. Desalination 2004, 160, (1), 1-12. 94. Perreault, F.; Tousley, M. E.; Elimelech, M., Thin-film composite polyamide membranes functionalized with biocidal graphene oxide nanosheets. Environ Sci Tech Let 2014, 1, (1), 7176. 95. Rana, D.; Matsuura, T., Surface modifications for antifouling membranes. Chem Rev 2010, 110, (4), 2448-2471. 96. Ye, G.; Lee, J. H.; Perreault, F.; Elimelech, M., Controlled architecture of dual-functional block copolymer brushes on thin-film composite membranes for integrated "defending" and "attacking" strategies against biofouling. Acs Applied Materials & Interfaces 2015, 7, (41), 23069-23079. 97. Neilly, A.; Jegatheesan, V.; Shu, L., Evaluating the potential for zero discharge from reverse osmosis desalination using integrated processes - A review. Desalin Water Treat 2009, 11, (1-3), 58-65. 98. Xie, M.; Shon, H. K.; Gray, S. R.; Elimelech, M., Membrane-based processes for wastewater nutrient recovery: Technology, challenges, and future directio. Water Res 2016, 89, 210-221. 99. Diallo, M. S.; Kotte, M. R.; Cho, M., Mining critical metals and elements from seawater: Opportunities and challenges. Environ Sci Technol 2015, 49, (16), 9390-9399.

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Page 24 of 29


eu

sa W W

ZLD

y/r er

ov

No

Benefits

ec

dis

rr

po

Drivers

se

•  Stricter regulations on wastewater (WW) disposal •  Intensified freshwater scarcity •  High cost of WW disposal •  WW disposal options may not be feasible •  Public environmental awareness

ate W

l

Page 25 of 29

Valuable salt recovery

FIGURE 1. Drivers and benefits of zero liquid discharge (ZLD).

25


•  Compliance with environmental regulation •  No cost on WW disposal •  Augmenting water supply •  Protecting the environment


Page 26 of 29

Water reuse

(A) Wastewater

Wastewater

Filtration pH adjustment Deaeration Anti-scalant

Pretreatment

(B)

Solid disposal/ recovery

Brine concentrator

Brine crystallizer

or

Water reuse Evaporation pond

Softening Filtration Ion exchange pH adjustment Deaeration

Pretreatment

or Solid disposal/ recovery

RO Brine

RO

Brine concentrator

Brine crystallizer

FIGURE 2. Schematic illustration of (A) thermal and (B) RO-incorporated ZLD systems. Incorporation of RO, an energy-efficient technology, into ZLD reduces the volume of wastewater entering the brine concentrator, which consumes much higher energy per volume of treated water than RO.

26


Page 27 of 29


FIGURE 3. Specific energy consumption by RO, brine concentrator, and brine crystallizer. Although RO is energy efficient, its limited salinity range (typically with an upper concentration of ~70,000 mg/L) provides opportunities for other technologies to be applied in ZLD systems. The specific energies shown in the figure are in kWhe per cubic meter of feedwater.

27



Page 28 of 29

Reverse Osmosis Feedwater

Permeate Water reuse

RO Brine Thermal energy (e.g., low-grade heat)

Electricity + + + + + +

_ _ +

_ _

_ +

_

+

_

+

_ +

+

_ +

_

+ +

_ +

+

Brine

_ _ _ _ _ _

HOT

Diluted draw solution Brine Brine Brine Diluate Diluate

Draw solutes regeneration

Concentrated draw solution

Water reuse or back to RO Thermal energy (e.g., low-grade heat)

Back to RO

(A) ED/EDR-incorporated system

Brine

Cold water Permeate for water reuse

(C) MD-incorporated system

(B) FO-incorporated system

FIGURE 4. Schematic illustration of emerging membrane-based ZLD technologies in which (A) ED/EDR, (B) FO, or (C) MD is incorporated. ED/EDR uses an array of cation-exchange (green) and anion-exchange (orange) membranes that selectively reject anions and cations, respectively; FO employs a semipermeable membrane that allows water to pass through but ideally rejects all salts; MD employs a porous hydrophobic membrane that allows passage of water vapor through the membrane (as indicated by the blue curved arrows) but not liquid or salt. The produced brine is further concentrated by brine crystallizers or evaporation ponds to achieve ZLD.

28


Page 29 of 29


TABLE 1. Advantages, limitations, and energy consumption of different salt concentrating technologies used in ZLD operations Technology

Advantages

Limitations

Energy consumption

Energy efficient Modular Technical maturity

Limited salinity range (upper concentration ~75,000 mg/L) High fouling propensity

Seawater: 2-6 kWhe/m3 of product water 8, 16; Brackish water: 1.5-2.5 kWhe/m3 of product water 16

ED/EDR

High salinity limit (upper concentration > 100,000 mg/L) Low fouling propensity (especially for silica-enriched feedwater) Modular

High energy consumption and cost when treating high salinity feedwater with high-quality water product Incapability of removing noncharged contaminants Using only prime energy

7-15 kWhe/m3 of feedwater (with feed salinity > 15,000 mg/L) 52-55

FO (with NH3/CO2 thermolytic draw solution)

High salinity limit (upper concentration > 200,000 ppm) Utilization of low-grade heat Low fouling propensity Modular

Low water flux at very high feed salinities Reverse solute flux (NH3 may contaminate product water) Emerging technology with limited field performance data

21 kWhe/m3 of feedwater (with feed salinity of 73,000 mg/L and recovery of 64% in average) 43

MD

High salinity limit (upper concentration > 200,000 ppm) Utilization of low-grade heat Low fouling propensity Modular

Low water flux and water recovery Potential of membrane wetting Post-treatment is needed if volatile pollutants are present Emerging technology with limited field performance data

40-45 kWht/m3 of product water 76 22-67 kWht/m3 of product water 72

RO

MVC brine concentrator

Technical maturity High energy consumption High salinity limit (upper High capital and O&M costs concentration > 200,000 ppm) Operating at high temperature Using only prime energy ACS Paragon Plus Environment Not modular

20-25 kWhe/m3 of feedwater 11, 22 28-39 kWhe/m3 of feedwater 43

The Global Rise of Zero Liquid Discharge for ... - ACS Publications

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