Accepted Manuscript

Title: Sustainable nitrate-contaminated water treatment usingmulti cycle ion-exchange/bioregeneration of nitrate selectiveresin

Author: Shelir Ebrahimi Deborah J. Roberts

PII: S0304-3894(13)00669-9DOI: http://dx.doi.org/doi:10.1016/j.jhazmat.2013.09.025Reference: HAZMAT 15405

To appear in: Journal of Hazardous Materials

Received date: 30-5-2013Revised date: 11-9-2013Accepted date: 12-9-2013

Please cite this article as: S. Ebrahimi, Sustainable nitrate-contaminated water treatmentusing multi cycle ion-exchange/bioregeneration of nitrate selective resin, Journal ofHazardous Materials (2013), http://dx.doi.org/10.1016/j.jhazmat.2013.09.025

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

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Sustainable nitrate-contaminated water treatment using multi cycle ion-1

exchange/bioregeneration of nitrate selective resin2

Shelir Ebrahimi1, Deborah J. Roberts1*3

1 School of Engineering, University of British Columbia, EME 3218, 3333 University Way, 4

Kelowna, BC Canada V1V 1V7. Shelir.ebrahimi@ubc.ca5

* Corresponding author: School of Engineering, University of British Columbia, EME 4261, 6

3333 University Way, Kelowna, BC Canada V1V 1V7. Deborah.roberts@ubc.ca, Phone (001)7

250 807-8722 | Fax (001) 250 807-98508

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Abstract10

The sustainability of ion-exchange treatment processes using high capacity single use 11

resins to remove nitrate from contaminated drinking water can be achieved by regenerating the 12

exhausted resin and reusing it multiple times. In this study, multi cycle loading and 13

bioregeneration of tributylamine strong base anion (SBA) exchange resin was studied. After each 14

cycle of exhaustion, biological regeneration of the resin was performed using a salt-tolerant, 15

nitrate-perchlorate-reducing culture for 48 hours. The resin was enclosed in a membrane to avoid 16

direct contact of the resin with the culture. The results show that the culture was capable of 17

regenerating the resin and allowing the resin to be used in multiple cycles. The concentrations of 18

nitrate in the samples reached a peak in first 0.5 to 1 hour after placing the resin in medium 19

because of desorption of nitrate from resin with desorption rate of 0.099±0.003 hr-1. After this 20

time, since microorganisms began to degrade the nitrate in the aqueous phase, the nitrate 21

concentration was generally non-detectable after 10 hours. The average of calculated specific 22

degradation rate of nitrate was -0.015 mg NO3- /mg VSS.hr.23

Applying 6 cycles of resin exhaustion/ regeneration shows resin can be used for 4 cycles 24

without a loss of capacity, after 6 cycles only 6% of the capacity was lost. This is the first 25

published research to examine the direct regeneration of a resin enclosed in a membrane, to 26

allow reuse without any disinfection or cleaning procedures. 27

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Keywords: Denitrification, drinking water, ion exchange, biological treatment, resin 29

regeneration30

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1. Introduction33

Nitrate contamination of groundwater from agricultural activities, discharges of 34

municipal and industrial wastewaters, processed food, dairy and meat products, and the 35

decomposition of decaying buried organic matter is a growing concern worldwide [1, 2, 3, 4, 5, 36

6]. Excess nitrate can cause several environmental and health problems [1]. An intake of high 37

concentrations of nitrate can cause many effects including birth defects, spontaneous abortions, 38

increased infant mortality, abdominal pains, diarrhea, vomiting, and changes to the immune 39

system. Nitrate is converted to nitrite in the stomach, which is the main cause of 40

methemoglobinemia and is suspected as a causative agent of human cancer. Methemoglobinemia 41

results in a lack of oxygen in body tissues, especially blood cells [2]. Additionally, nitrate can 42

cause heavy growth of algae in the water bodies ultimately resulting in eutrophication. Nitrate 43

has also been known to poison cattle if they ingest significant concentrations (3000 ppm nitrate 44

from food and water) [3]. To limit the risk to human health from nitrate in drinking water, the 45

maximum acceptable concentration (MAC) was set to be 10 mg-N/L (45 mg NO3-/L) in Canada 46

and the United States, while the World Health Organization (WHO) and the European 47

Community have set the MAC at 11.3 mg-N/L (50 mg NO3-/L) [7, 8].48

The most common treatment processes used to remove nitrate are zero-valent iron, zero-49

valent magnesium, reverse osmosis, ion exchange, electro dialysis, activated carbon adsorption 50

in conjunction with pH adjustment and biological treatments methods [9-12]. There are 51

disadvantages with many of these methods that limit their utility, such as, the expense of 52

operation, and the requirement for disposal of the waste brine or by-products. A sustainable 53

solution to the nitrate problem would most likely involve a combination of physical-chemical 54

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systems such as, reverse osmosis or ion exchange (IX) and a biological system to treat the 55

contaminated resin or brine of these systems [9-12].56

One of the most commonly used methods for the removal of nitrate from drinking water 57

is ion exchange [13-18]. Industry is trending toward the use of nitrate selective single use resins. 58

These resins have a great capacity for nitrate but since there are no economically viable methods 59

for regenerating them, they are replaced after exhaustion and incinerated or disposed of in a 60

landfill. The production of greenhouse gases and re-contamination of the environment are very61

important disadvantages of incineration and landfill, respectively, not to mention the 62

environmental cost of resin production, the cost of the resin itself, and the environmental costs of 63

shipping the resin to each treatment site.64

The wide use of ion-exchange processes to remove nitrate from drinking water creates 65

an urgency for development of a process for the regeneration of these resins. Since these resins 66

cost in the thousands of dollars per cubic foot, the ability to reuse the resin for even a few times, 67

will increase the economic viability and sustainability of nitrate-contaminated water treatment 68

processes. 69

Venkatesan et al. [19] and Xiao et al. [20] studied the direct bioregeneration of 70

perchlorate-selective resin. The resin was in direct contact with the culture in both of these 71

papers and so at the end of each cycle, bio-fouling removal and disinfection of resin was 72

performed before the resin was reused in another cycle. Also, because of the direct contact of 73

biomass with resin there is a possibility biomass effecting the desorption of perchlorate from the 74

resin. These factors result in increasing the cost and time required for each regeneration cycle75

[19].76

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In this study we perform multi-cycle exhaustion/ regeneration of trybutylamine strong 77

base anion (SBA) exchange resin with nitrate enclosed in a membrane to eliminate direct contact 78

of the biological system with the resin. The specific objectives of this research are to determine: 79

the feasibility of multi cycle regeneration of nitrate-selective resin, the capacity loss of the resin 80

after several IX/ bioregeneration cycles, the kinetics observed during each of the processes, and 81

to evaluate the results in the context of the literature to date. 82

2. Materials & Methods83

2.1. Resin84

This research was performed using ion exchange resin commercially available as highly 85

nitrate selective product (CalRez 2190). This resin is classified as a macroporous styrene strong 86

base anion (SBA) resin with N-tributylamine functional groups. The resin beads are 0.77±0.06 87

mm. Based on previous studies the nitrate-chloride separation factor and capacity of the resin 88

was identified as 780 and 1.48 meq/g, respectively [21]. The resin was conditioned and 89

converted to the chloride form using HCl (1N) and NaOH (1N) using 3 cycles of acid- base 90

cycling. One g of the washed resin was enclosed in a membrane (Spectrum Spectra/por 6RC91

Dialysis membrane tubing 50,000 Dalton molecular weight cut-off) to avoid direct contact of the 92

resin with the culture. Figure 1-a shows resin enclosed in the membrane (using clamps) in the 93

reactor (1 litre flask). The mass of resin was chosen to present as close to a monolayer of resin as 94

possible to maximize the transfer of nitrate out of the resin and in to the culture. 95

2.2. Culture96

A mixed perchlorate- and nitrate-reducing bacterial culture (NP30) was enriched from 97

marine sediment in previous research [22]. The culture was adapted to 6% salt and 500 mg/L 98

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nitrate using synthetic medium based on general marine medium composition with the addition 99

of a group of trace metals as reported previously [22]. The medium contained 23 g/L 100

MgCl2•6H2O, 1.4 g/L CaCl2•2H2O, 0.72 g/L KCl, 60 g/L NaCl, 3.9 g/L CH3COONa•3H2O, 0.3 101

g/L NaHCO3, 0.48 g/L NH4Cl, 1 mL/L 67 mM Na2S•9H2O, 1 mL/L phosphate solution (50 g/L 102

KH2PO4), 1 mL/L mineral solution (which contained 50 g/L (NH4)6Mo7O24•4H2O, 0.05 g/L 103

ZnCl2, 0.3 g/L H3BO3, 1.5 g/L FeCl2•4H2O, 10 g/L CoCl2•6H2O, 0.03 g/L MnCl2•6H2O, and 104

0.03 g/L NiCl2•6H2O). Acetate was applied to achieve 1.5 acetate to nitrate ratio as the carbon 105

and electron source. Strict anaerobic technique was used in medium preparation. 106

2.3. Exhaustion/ Regeneration107

In this research, 3 test (biological regeneration) and 3 control (salt only regeneration) 108

samples were studied using 6 cycles of exhaustion/ regeneration. Tests and controls were treated 109

identically during exhaustion. The resin was exhausted in glass columns in the first and last cycle 110

to reveal the breakthrough curve and capacity for this resin using glass columns with 5cm 111

diameter and 50cm length (figure 1-b). To do this, nitrate solution (500 mg/L) was used as 112

influent with a flow rate of 2.5 ml/min to obtain an empty bed contact time (EBCT) of 10 min. 113

Samples of the effluent were collected periodically and analysed for nitrate concentration. The 114

resin was considered as exhausted when nitrate appeared in the effluent. The resin operating 115

capacity was estimated from the breakthrough curve by calculating the area above the curve and 116

the mass of resin loaded. 117

Exhaustion for cycles 2-5 were done as a batch where both control and test samples 118

were enclosed in membranes and placed in 1 litre flasks with 300 ml of 700 mg/L nitrate solution 119

and mixed on a rotary shaker (110 RPM & 23°C) for 3 days to ensure complete exhaustion. A 120

sample of the aqueous phase was analysed for nitrate before and after exhaustion. 121

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During regeneration studies the test membranes containing resin were placed in 1 litre 122

flasks with 250 ml of mixed synthetic medium and culture (2500 mg/L VSS) and mixed by 123

shaking on a rotary shaker (110 RPM & 23°C) for 48 hours. In addition to the 3 replicates of test 124

conditions, 3 replicates of control conditions were placed in the same medium without the 125

culture to show nitrate desorption from resin due to the salt. For the controls the medium was 126

replaced with new medium at the beginning of each regeneration cycle. For the tests the culture 127

was settled and about 90% of the medium above the biomass was replaced with fresh medium. 128

Biomass concentrations were measured based on the volatile suspended solids (VSS) 129

before the first cycle and after the last cycle. Aqueous phase samples were taken in intervals 130

during regeneration for nitrate analysis. After each complete cycle, 0.1 g of resin was taken for 131

analysis of the nitrate attached to the resin.132

2.4. Analytical Methods133

Nitrate in the aqueous phase was measured using the nitrate test kit and an Orion 134

9512BNWP ammonia ion selective electrode (Thermo Fisher Scientific) when the concentration 135

of nitrate was higher than 1 mg/L. Lower concentrations of nitrate and chloride concentrations136

were measured using a Dionex ICS-2100 with KOH eluent using a multi-step gradient of 1, 1,137

30, 60, 1, and 1 mM respectively at time of 0, 8, 28, 38, 38, and 43 minutes and flow rate of 1.5 138

ml/min. Calibration curves were established using nitrate standard solutions of 250 µg/L, 500 139

µg/L, 750 µg/L and 1 mg/L and chloride standard solutions of 750 µg/L, l mg/L, 10 mg/L, 100 140

mg/L, and 500 mg/L.141

The measurement of nitrate attached to the resin was carried out by resin combustion in 142

a calorimeter (Bomb calorimeter). After combustion the combustion chamber was rinsed 143

thoroughly with Type 1 (18.2 MOhm/cm2) water. The rinsate was analysed using the IC and the 144

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difference of the chloride concentration in samples and samples from the resin in complete 145

chloride form was used to calculate the nitrate attached to the resin. The subtractive method was 146

applied because the nitrogen backbone of the resin formed nitrate on combustion and prevented 147

the direct measurement of nitrate on the resin. The method was verified by combustion of resin 148

with known nitrogen loading prior to the use of the technique for samples.149

Volatile suspended solids (VSS, biomass) was measured using Standard Methods 254-E 150

[23]. A sample volume of two ml was filtered through a glass fiber filter. The filter was dried and 151

then combusted. 152

2.5. Statistical Analysis153

Statistical analysis was performed to determine whether there is a significant difference 154

in nitrate concentration between the different processes. The statistical significance of the 155

differences was determined using one way ANOVA test (p=0.05) and a Student Neuman Keuls 156

test when the ANOVA showed significant differences using SPSS Statistic 20 software.157

3. Results158

3.1. Resin Exhaustion159

Before and after each exhaustion cycle nitrate was measured in the aqueous phase of 160

each test and control reactor. Based on the difference of nitrate concentration before and after 161

exhaustion and the mass of applied resin, the amount of nitrate absorbed on the resin was 162

calculated. Figure 2 presents the nitrate absorbed in test and control reactors for each cycle 163

compared to theoretical capacity. Since at the end of each cycle a sample was taken out from 164

resin absorbed nitrate has been normalized based on mass of resin at each cycle.165

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Statistical analysis revealed there was no significant difference in the absorbed nitrate 166

over the first 4 cycles. For cycle 5, the difference is significant, a 12% reduction in absorbed 167

nitrate was observed in cycle 5 compare to other cycles. There was also no significant difference 168

in absorbed nitrate in the controls in first 3 cycles, the amount of absorbed nitrate decreased 169

significantly in cycles 4 and 5. The statistical analysis also showed that there was significantly170

more nitrate adsorbed in the tests than in the controls for the 4th and 5th cycle. 171

3.2. Resin Bio-Regeneration172

During each bioregeneration cycle, the nitrate concentration in the aqueous phase was 173

measured periodically during the 48 hours of bioregeneration. Figure 3 shows the normalized 174

nitrate concentration (mg of nitrate per gram of dry resin) for test and control reactors in each 175

cycle. The concentrations of nitrate in the test reactors reached a peak in first 0.5 to 1 hour after 176

placing the resin in medium because of desorption of nitrate from resin. After this time the177

microorganisms began to degrade the nitrate in the aqueous phase and so the nitrate 178

concentration decreases rapidly over the next 9 hours. The nitrate concentration was generally 179

non-detectable after 10 hours. Although nitrate is no longer measurable in the aqueous phase, the 180

resin was left in flask for 48 hours to ensure that the nitrate attached to the resin had time to 181

completely desorb.182

In the control reactors, the nitrate concentration in the aqueous phase reached183

equilibrium by about 10 hours. A statistical analysis of the nitrate concentration in controls 184

showed that the equilibrium concentration in control samples in cycle 1 and 2 are not 185

significantly different but they are different from cycle 4 and 5. 186

The peak concentrations shown in Figure 3 decrease in each cycle because the 187

biodegradation rate is increasing. To further demonstrate this, the cultures were incubated with a 188

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direct nitrate spike with no resin. Biomass was spiked with nitrate to measure the direct nitrate 189

degradation rate of the biomass. Figure 4 presents the concentrations of nitrate removed. Initially 190

the culture was able to remove 500 mg/L of nitrate from the aqueous phase experiment in 12 191

hours and after using the culture for 6 bioregeneration cycles it was able to remove the same 192

amount of nitrate in <8 hours. This can be explained by an increase in biomass (VSS increased 193

from 2500 mg/L to 5400±600 mg/L). As the number of cycles increased the biomass also 194

increased the biodegradation of nitrate in the aqueous phase occurred before the first sampling 195

point. 196

At the end of each regeneration cycle, samples of resin were taken to determine the 197

mass of nitrate attached to the resin using the bomb calorimeter to combust the resin. Figure 5198

presents the results of these analyses. There was insignificant nitrate left on the resin in test 199

samples for the 1st three cycles. After cycle 4 some nitrate residual remained attached to the 200

resin. The culture achieved more than 94% and 78% nitrate removal from resin in cycle 4 and 5, 201

respectively. There was always some residual nitrate attached to the resin in control reactors. 202

This increased with each cycle. Through cycle 1-5, for control samples, removal of nitrate 203

attached to the resin was 99%, 96%, 89%, 79% & 59%, respectively. 204

3.3. Time Series Resin Analysis205

During regeneration, nitrate was removed from the aqueous phase within 10 hours, but 206

the samples were incubated for 48 hours as a factor of safety. In order to understand the exact 207

time when nitrate was completely removed from the resin (i.e. no new nitrate desorbed from the 208

resin) in cycle 6, samples of resin were taken at different times and analysed for nitrate attached 209

to the resin using the bomb calorimeter. The results (Figure 6) show that for fresh resin the 210

nitrate in the resin was removed to non-detectable levels within 10 hours, but after six cycles of 211

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exhaustion/bioregeneration the process was much slower. A projection of the slope of line 212

suggests that it would have taken 80 hours to completely regenerate the resin.213

3.4. Resin Capacity214

Column experiments were conducted as the first and last exhaustion cycle in order to 215

observe resin performance and determine resin capacity and obtain a breakthrough curve. The 216

result of the column exhaustion test is shown in Figure 7. The bed volume of the exhaustion 217

solution at which the nitrate concentration in the effluent was half of the influent, was considered 218

as the 50% breakthrough point of the resin. Table 1 summarizes the change in bed volume to the219

50% breakthrough point and the calculated capacity of resin. Initially the 50% breakthrough 220

point was at 68 bed volumes (BV) of resin. After using resin in 6 exhaustion/ bioregeneration 221

cycles, less than 6% of the resin capacity was lost while in the controls without bioregeneration, 222

the resin lost 20% of its capacity. 223

4. Discussion224

One major concern of multi-cycle use of resin in ion-exchange processes is resin 225

capacity loss. In this research the capacity of resin during 6 exhaustion/bioregeneration cycles 226

(test samples) was compared to the capacity of resin in control samples (no biological reduction).227

During regeneration cycles in control samples desorption of nitrate from the resin continued to 228

the point when the nitrate concentration in aqueous phase reached equilibrium with the nitrate 229

concentration on the resin. 230

The desorption rate can be presented by a single kinetic model for both test and control231

samples [20, 21, 24]:232

����������= ��������(����− ����) (1)233

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The difference between the final equilibrium concentration (Ce, mg/L) and the aqueous 234

phase concentration of nitrate at any time (Ct, mg/L) can be considered as the driving force, 235

which allows the incorporation of the concepts of kinetic limitations and end point equilibrium 236

(Kdes, t-1, is the desorption kinetic constant).237

In control samples, using equation 1 and based on the equilibrium concentration of 238

nitrate at each cycle an average kdes of 0.099±0.003 hr-1 was calculated. In test samples the 239

equilibrium concentration is changing continually as the desorption rate and the degradation rate 240

change due to the concentration in the aqueous phase. At low concentrations, and early in the 241

process, desorption is favored, as higher concentrations develop in the aqueous phase 242

degradation becomes favored. So the test samples never reach the equilibrium concentration of 243

control samples at each cycle.244

Additionally, nitrate was removed faster from the test samples with each test cycle. This 245

is reflected in the reduction in the peak concentration of nitrate in each cycle. It is generally 246

accepted that anion (nitrate, perchlorate) degradation follows Monod’s kinetics [19]:247

��������= − ������������+ �� (2)248

Where S is the nitrate concentration (mg/L); t is the time (hr); µm is the maximum specific nitrate249

removal rate (hr-1); Ks is the half saturation constant for nitrate (mg/L); and X is the microbial 250

concentration (mg VSS/L). A calculated specific degradation rate of - 0.017 and - 0.012 mg NO3-251

/mg VSS.hr respectively for initial and final tests shows that since the rates were very 252

comparable, the increasing biomass must be responsible for the increased removal from the 253

system. 254

Based on these results, the resin did not lose significant capacity until after 4 cycles. 255

The capacity in cycle 5 and 6 was still much better in biologically regenerated resin than for 256

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resin that had not undergone biological regeneration. There appears to be an increase in the non-257

regenerable sites in the resin in each cycle. Because of the degradation of nitrate in the aqueous 258

phase, the maximum concentration of nitrate in test samples never reaches the equilibrium 259

concentration of nitrate in controls. So, the nitrate accumulation in the less regenerable sites is 260

decreased and the capacity is maintained. Increasing the non-regenerable sites of the resin in 261

each cycle can also be explained based by the shrinking core model which was developed for ion 262

uptake by resins [19, 24]. The model shows that ions first occupy the outer region of the resin, 263

and progressively moves to the inner unused resin core with time. Based on this model, it is 264

reasonable to assume that nitrate ions in the outer region of the resin becomes available to 265

biomass more easily when compared to nitrate ions present in the inner core of the resin. So, in 266

each cycle, as more and more nitrate is loaded in to the core, more time is required for the nitrate 267

to dissolve out of the core. The calorimeter results suggest that leaving the resin in the bioreactor 268

for a longer time would allow complete regeneration of resin.269

Sharbatmaleki and Batista [24] reported that the capacity loss was more significant 270

through the first cycles and stabilized after a few cycles which differs significantly from the 271

results reported here. However, the results are difficult to compare directly since their272

experiment was done using perchlorate and the resin was in direct contact with the culture.273

The ultimate application of the process would see resin sold in membrane cartridges that 274

could be plugged in to the ion exchange column housing for exhaustion, then removed and put in 275

a bioregeneration tank for regeneration. This would probably be done in regional facilities where 276

the culture can be maintained, rather than at each site. This would require shipping the resin to 277

and from the regional facility and the treatment sites but would still result in a net savings due to 278

the ability to reuse the resin several times. A full cost benefit analysis would be performed for 279

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each site to account for the cost of using fresh resin for each use, as well as incineration or 280

transport of the exhausted resin to the landfill, as compared to the costs associated with housing 281

the resin in a membrane and applying bioregeneration process along with losing some capacity 282

of resin after 6 cycles. 283

5. Conclusion284

The main objective of this study was to investigate the potential of multi-cycle use of 285

resin for removal of nitrate from drinking water by bioregeneration of strong base nitrate 286

selective resin. The results of this research show:287

Nitrate selective resin can be bioregenerated and reloaded for at least 6 cycles,288

Nitrate can be removed from drinking water without producing any brine,289

Resin can be used in 4 cycles of IX/ bioregeneration for nitrate removal without losing 290

any capacity, and,291

Using resin in 6 cycles resulted in losing about 6% of the resin capacity.292

6. Acknowledgments293

This research was done in Biological Solutions Laboratory of University of British 294

Columbia. We thank Dr. Bailey from The Barber School of Arts and Sciences for providing the295

bomb calorimeter for this research and Dr. Xiao for his valuable assistance with process and data 296

evaluation. This research was funded by the Natural Sciences and Engineering Research Council 297

of Canada (NSERC) through the Discovery Grant Program.298

299

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299

Figure Captions300

Fig. 1. Schematic of exhaustion apparatus. a) resin enclosed in membrane in the reactor (1 liter 301

flask), b) column exhaustion used for the first and last cycle of exhaustion.302

Fig. 2. Nitrate absorbed onto the resin during exhaustion for each cycle for tests and controls. 303

The data are calculated from the difference between nitrate concentrations in the aqueous phase 304

before and after exhaustion. The bar heights indicate the average and the error bars indicate one 305

standard deviation of triplicate test or controls.306

Fig. 3. Nitrate concentration in the aqueous phase during regeneration a) test b) control; nitrate 307

concentrations in aqueous phase are normalized by dividing to the mass of resin in each sample. 308

The data points represent the average of three replicates of each test and control samples. The 309

error bars are omitted to avoid crowding in the figure. 310

Fig. 4. Nitrate degradation in aqueous phase cultures used during the initial and final cycle. 311

Fig. 5. Residual nitrate on resin after each cycle as determined from the rinsate from ignition of 312

the resin. The bar height presents the average and the error bars present one standard deviation of 313

triplicate results. 314

Fig. 6. Residual nitrate (as determined from the rinsate from ignition of the resin) on resin at 315

different intervals during the first and last regeneration cycle. 316

Fig. 7. Column exhaustion breakthrough curve. a) first cycle of all samples, b) last cycle of 317

control samples, c) last cycle of test samples. The data points represent the normalized (C/Co) 318

nitrate concentrations in the effluent of columns fed with 500 mg/L nitrate using an EBCT of 10 319

minutes. 320

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321

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Table 1377

Bed volumes required to 50% breakthrough point and resin capacity, initially and after 6 cycles.378

SampleBreakthrough point

(BV)BV Reduction

(%)Capacity

(meq/g of dry resin)Capacity reduction

(%)

Test 61±2 13 1.34±0.06 5.9

Control 48±2 33 1.15±0.08 19.7

Initial 68 - 1.43 -

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380

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Highlights381

IX/bioregeneration of resin is a sustainable method for nitrate removal382

Nitrate selective resin can be bioregenerated and reloaded for 6 IX cycles383

Nitrate can be removed from drinking water without producing any brine384

Resin can be used in 4 IX cycles without losing any capacity385

Using resin in 6 IX cycles resulted in losing less than 6% of the resin capacity386

387

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Figure 3

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Bioregenerated

Resin to

another IX

Process

Graphical Abstract.pdf