IWC 12‐69

a

Nalco and the logo are trademarks of Nalco Company

b

Ecolab is a trademark of Ecolab USA Inc.

C

All other trademarks are the property of their respective owners

Opportunities for Treatment and Reuse of 

Acid Mine Drainage and Produced Water in 

Oil and Gas Shale 

Timothy S. Keizer and Jason R. Burney 

Nalcoa

, An Ecolab Companyb 

1601 W. Diehl Rd. Naperville, IL 60563, USA 

Jarod C. Limke, Joon H. Min, and Young J. Eum 

BKT Co., Ltd.c

1225 N. Patt St. Anaheim, CA, 92801, USA 
IWC 12‐69

Keywords: Hydraulic fracturing, membrane, produced water, flowback water, Acid mine 

drainage, Mine influenced water, reuse 

ABSTRACT 

Hydraulic fracturing is a water intensive process that is used to release gas and oil from tight 

shale formations. The large demand for water on a well pad can significantly complicate 

sourcing and logistics for exploration companies. As such, locating an alternate source of 

water or reuse of produced water that could be accessed on site is very desirable. Acid Mine 

Drainage (AMD) and some surface waters could be accessed on site but can contain high 

amounts of sulfate, which will have an undesired reaction with Barium and Strontium present in 

the some shale formations. Likewise, sulfate metabolized by bacteria could sour the gas. 

Explorations of non-traditional treatment methods are being piloted. 

 
IWC 12‐69

INTRODUCTION 

Natural gas plays a large role in meeting 

the energy demands of the United 

States, supplying around 23 percent of 

the nation’s energy. (Newell 2010) 

According to the U.S. Energy 

Information Administration, in 2009 

shale gas represented approximately 14 

percent of the U.S. natural gas supply, a 

number that is expected to grow to 46 

percent by 2035. (Newell 2010) To 

enable this large growth in shale gas 

supply, numerous new wells will need to 

be drilled and stimulated via hydraulic 

fracturing. Hydraulic fracturing involves 

pumping a water-sand-chemical mixture 

into a well at high pressure to fracture 

the shale formation and allow the 

natural gas to flow to the wellbore. The 

water quantities needed for a well 

stimulation using the slickwater 

methodology range from 3 to 5 million 

gallons per well. The extensive water 

demands present a significant cost to 

well completions activities. The total 

cost of procuring and transporting the 

millions of gallons of water to a well site 

can run well over $1 million per well. 

Tightening water restrictions in some 

areas of the U.S. and the exorbitant cost 

of buying and moving the fracturing 

water makes the search for easily 

accessible alternate water sources 

highly desirable. 

A common side effect of sub-surface 

mining is Acid Mine Drainage (AMD). As 

the depth of the mine reaches below the 

water table, ground water seeps into the 

mine. This water must be removed from 

the mine-shaft in order for the mine to 

produce. In abandoned mines, the water 

is often left unchecked and the mine 

floods. AMD is highly concentrated with 

sulfates and metals which oxidize and 

pollute natural waterways. 

The Marcellus Shale region is uniquely 

situated in that a large natural gas 

bearing shale is located close to 

numerous abandoned mines, which 

could present a very attractive source of 

water. Ideally, a gas company could 

drill into an abandoned mine full of 

AMD, pump the water to the surface, 

treat the water, and use it for fracturing. 

One hurdle facing the feasibility of using 

AMD for fracturing in some shale is the 

high levels of sulfate present in the 

AMD. In particular the Marcellus Shale 

formation is rich in Barium and 

Strontium, which will react with sulfate in 

AMD and precipitate down hole and 

plug the well. Likewise, the sulfate may 

be metabolized and cause potential 

odor issues. The intent of implementing 

the anti-fouling system (Park 2010) 

developed by BKT with various 

nanofiltration (NF) membranes from 

commercial suppliers is to give value to 

this previously unusable water source. 

(Min 20113) The NF membranes should 

lower the sulfate levels in the AMD to a 

point where the treated AMD can be 

used in completions along with scale 

inhibitor chemistries. 

Treated Produced Water (PW) can be 

reused as fracturing water as long as 

the hardness, metals, and conductivity 

thresholds are within reuse limits after 

treatment. NF membranes are tested to 

evaluate rejection of the listed 

parameters in highly saline Marcellus 

PW. 

The unique design of the anti-fouling 

system should limit the amount of 

pretreatment needed for the AMD/PW 

and lower costs. 

 
IWC 12‐69

ACID MINE WATER 

The primary goal of the project is to use 

a NF membrane to remove sulfate 

(<100 ppm), conductivity, and 

suspended solids from AMD water. 

The results of the membrane selection 

trials are presented in Table 1. All data 

were obtained using a constant 

pressure of 170 PSI (12 kg/cm2) and an 

average temperature of 80oF (27oC). 

Table 1. AMD membrane selection 

results summary 

Membrane Sulfate Flux 

NF grade 

Feed Permeate Rej. Average 

ppm ppm % GFD 

(LMH) 

A 833 12 98.6 48 (81) 

B 562 3 99.5 45 (77) 

C 600 300 50 75 (128) 

D 613 3 99.5 70 (119) 

The results are consistent with the NF 

manufacturers guidelines; membrane A 

and B both yielded the highest rejection 

of monovalent ions (average 45 μS/cm 

conductivity), but the lowest flux of 47 

Gallons/Ft.2

/Day [GFD] (79 

Liters/M2

/Hr.[LMH]) average between 

each membrane. 

Membrane C and D both yielded higher 

average flux (average 73 GFD (125 

LMH)) but less rejection of conductivity. 

Sulfate rejection by membrane D was 

the highest among the tested 

membranes. Since membrane C did not 

reject sulfate below the threshold (100 

ppm) it was not considered for further 

testing. 

The membrane selected for the feed 

concentration trial was membrane D due 

to the highest rejection of sulfate, 

99.5%, and flux, 70 GFD (119 LMH). 

FEED CONCENTRATION FINDINGS―

The average flux of the AMD using 

membrane D was 65 GFD (110 LMH) 

after 92% recovery. 

The temperature range of the AMD feed 

water was broad, initially at 72o

F (22oC) 

and finishing at 92o

F (34oC). The 

increasing flux data shown in Figure 1 

(from 0% to 70% recovery) is attributed 

to the rise in temperature of the feed 

water. Temperature rise is attributable to 

energy transfer from the feed pump and 

high speed vortex generation inside the 

pilot unit. 

Figure 1. Filtering AMD with membrane 

D: Flux and feed temperature as a 

function of recovery 

 After removing 70% of the feed water 

as permeate, membrane flux began to 

decline due to TDS (sulfate, suspended 

solids, salts) buildup in the feed water. 

Both the rise in temperature and decline 

in flux are natural occurrences in batch 

mode filtration processes. 

Figure 2 shows the sulfate levels 

observed in both the feed water and 

permeate as the batch mode 

40

50

60

70

80

90

100

110

120

130

140

0% 20% 40% 60% 80% 100%

Flux (LMH) and Temperature 

(deg F)

Recovery (% water treated)

Flux as LMH

Temp as F
IWC 12‐69

concentration progressed. The upper 

sulfate concentration limit in the 

composite permeate is 100 ppm. Sulfate 

rejection was greater than 99% 

throughout the trial. Likewise, the 

conductivity in the permeate and feed 

display a similar trend and is shown in 

Figure 3. 

Figure 2. Sulfate concentration as 

function of % recovery 

The maximum measured sulfate 

concentration in the permeate was 32 

ppm, while the maximum measured 

sulfate concentration in the 

concentrated feed water was 14,000 

ppm. 

Figure 3. Conductivity as a function of 

% recovery 

 

Because the AMD permeate is to be 

reused as a product (fracturing water), a 

high recovery is important to the 

economics of the project. 

ACID MINE DRAINAGE WATER 

QUALITY ― Table 2 contains data 

obtained from an analytical laboratory. 

Membrane D shows hardness and 

sulfate removal rates of >98% and 

>99%, respectively. Iron and calcium 

rejection are >99% and >98%, 

respectively. A significant portion of the 

measured parameters, including 

hardness and heavy metals, were 

measured below 0.01 ppm in the 

permeate. 

Table 2. Filtering AMD with membrane 

D: Water quality analysis 

Metals 

Initial 

AMD 

Feed 

Final 

AMD 

Permeate 

Final 

AMD 

Concentrate

Rejection 

ppm ppm ppm % 

Ca 230 3.7 1200 98.4 

Fe 2.2 <0.02 21 99.1 

Mg 60 0.97 570 98.4 

Mn 0.3 <0.01 3.5 96.7 

K 6.9 1.6 57 76.8 

SiO2 10 8.2 26 18.0 

Na 410 100 3300 75.6 

Sr 2.5 0.04 17 98.4 

Hardness 

(CaCO3) 820 13 5500 98.4 

Figure 4. Feed and permeate samples 

for AMD pictured 

0

4000

8000

12000

16000

0

5

10

15

20

25

30

35

0 20 40 60 80 100

Feed (ppm)

Permeate (ppm)

Recovery (% water treated)

Permeate Sulfate

Feed Sulfate

0

2

4

6

8

10

12

14

16

0% 20% 40% 60% 80% 100%

Electrical Conductivity (mS/cm)

Recovery(% water treated)

Permeate EC, mS/cm

Feed EC, mS/cm

Feed Permeate
IWC 12‐69

Each membrane tested successfully 

removed all solids and color (turbidity 

<<1 NTU), as shown in Figure 4 and 5. 

Figure 5. Concentrate and permeate of 

AMD water in anti-fouling system feed 

and collection tanks 

Concentrated AMD AMD permeate

PRODUCED WATER 

The primary goal of the PW project is to 

use an NF membrane to remove sulfate, 

hardness, metals, conductivity, and 

solids from produced water. The sample 

received was exceptionally difficult to 

treat using NF membranes. The high 

conductivity (~50% higher than sea 

water) gave rise to charge balance 

phenomena which may explain the flux 

and rejection data in Table 3. The 

average flux of the batch was 22 GFD 

(37 LMH) after an 80% recovery using 

Membrane C. The turbidity in the 

composite PW permeate was 0.6 NTU, 

well below the target value. 

The temperature range was moderate, 

initially at 77o

F (25oC) and finishing at 

95o

F (35oC). The conductivity in both the 

feed tank and permeate remained 

constant throughout the trial, indicating 

stable, but low rejection. As shown in 

Table 3, conductivity rejection averaged 

14.4%, which may be attributed to the 

high concentration of salts in the water. 

The charge balance (i.e. high osmotic 

pressure) across the NF membrane is 

heavily polarized, and thus a viable 

explanation of the relatively low flux and 

low rejection for PW when using an NF 

membrane. 

These results are preliminary and may 

be refined with prolonged testing. 

Table 3. Filtering PW with membrane C: 

Water quality analysis 

Ions Initial PW 

Feed 

Final PW 

Permeate 

Final PW 

Concentrate Rejection 

ppm ppm ppm % 

Ba 2600 1400 4100 46.15 

B 21 19 19 9.52 

Ca 7700 5800 9400 24.68 

Fe 180 61 440 66.11 

Li 50 44 43 12.00 

Mg 710 440 1200 38.03 

Mn 4.2 3.1 6.4 26.19 

K 360 310 320 13.89 

SiO2 14 <7.5 47 N/A 

Na 24000 21000 23000 12.50 

Sr 2000 1100 3200 45.00 

Hardness 

(CaCO3) 22000 16000 29000 27.27 

TDS 97000 83000 110000 14.4 

EXPERIMENTAL 

ANTI-FOULING SYSTEM PILOT TRIAL 

PROCEDURE - A typical pilot trial 

procedure is divided into two major 

tasks: (1) membrane selection and (2) 

batch mode concentration. For each 

task, adequately mixed sample was 

transferred into the feed tank and the 

system was operated in recirculation 

mode (retain concentrate in closed loop) 

as depicted in Figure 6. 

MEMBRANE SELECTION ―

Determination of the optimal membrane 

is the most important aspect of the inhouse pilot trial. 
IWC 12‐69

Four NF grade membranes were tested 

using approximately 2.5 gallons of 

sample each; all permeate was returned 

to the feed tank to maintain the initial 

feed concentration. The filtration time for 

a membrane selection is typically 60-90 

minutes which allows adequate time for 

membrane stabilization and 

reproducible flux and rejection data.

Figure 6. PFD for anti-fouling system 

nanofiltration pilot of acid mine drainage 

BATCH MODE CONCENTRATION ― 

The most optimal membrane as 

determined by the membrane selection 

process is reused during the batch 

mode concentration. Approximately 60-

80 liters (16-21 gallons) of sample are 

transferred into the feed tank. Permeate 

is continuously removed allowing the 

concentration of rejected species to 

increase in the feed tank. Feed 

concentration time may vary greatly 

depending on initial feed volume and 

water quality. 

 Under these conditions, flux typically 

decreases as the filtration resistance 

(solids concentration) increases. Feed 

water temperature will increase due to 

mechanical energy transfer. 

The testing parameters used in each 

trial are summarized in Table 4. 

Table 4. Testing conditions for NF 

membranes with anti-fouling module 

Pilot Model Anti-fouling system 

Membrane Surface 

Area 0.94 ft2

 (0.087 m2) 

Operating Pressure 142 - 170 PSI (10 - 

12 kg/cm2

) 

Average Testing 

Temperature 84 o

F (29 oC) 

Vortex speed(1) 280 RPM 

 Note: (1) Vortex speeds differ according to scale-up 

factor, max industrial model speed is 270 RPM 

SUMMARY 

The membrane selected for further 

study for AMD was membrane D. This 

membrane yielded the highest rejection 

and flux among the tested membranes. 

Membrane D offered an average flux of 

65 GFD (110 LMH), 92% recovery, and 

sufficient sulfate rejection (>99%) during 

the 510 minute batch mode 

concentration. Each membrane 

successfully removed all solids and 

color (turbidity <<1 NTU) for each batch 

mode concentration. Preliminary results 

indicate that AMD permeate from 

membrane D can be reused as frac 

water due to 99.5% sulfate rejection (2 

ppm in permeate). For the PW 

membrane C yielded the highest 

rejection and flux among the tested 

membranes. Membrane C offered an 

average flux of 22 GFD (37 LMH) 

throughout an 80% recovery and low 

TDS (approximately 14.4%) during the 

1020 minute batch mode concentration 

based on the limited conditions tested. 

The anti-fouling system industrial unit 

has 1021 Ft2

 membrane surface thus 

the unit would have a permeate flux rate 

of 46 gpm for the AMD and 15.5 gpm for 

the PW. 

Future work may include long term pilot 

testing near production sites where 
IWC 12

‐69

treatment options and variables (i.e. 

different NF membranes, anti-scalant 

doses) can be evaluated with certainty. 

 
IWC 12‐69

Reference 

Min, J. H. et al., “Anti-fouling membrane system for industrial wastewater treatment 

and recovery”, International Water Conference, 2011. 

Newell, R., “Annual Energy Outlook 2011”, EIA, 2010. 

Park, G. T. and Kim, S. W., “Rotor for generating vortex water flow, and filtering 

apparatus employing the same”, U. S. Patent 7,666,305 B2, 2010.