Optimizing the Treatment of Produced Water 

and Flowback for Reuse or Disposal

Brian A. Wrenn

PureLine
Produced Water and Flowback: 

Characteristics of Concern for Reuse and Disposal

• Dissolved solids

 soluble species like sodium, calcium, barium, chloride, sulfate

 processes or operations like reverse osmosis, ion exchange, and 

chemical precipitation are required to remove dissolved solids

• Suspended solids

 particles like sand, metal sulfides, clay, bacteria

 suspended solids may be either settleable (e.g., sand) or colloidal 

(e.g., clay, bacteria)

• Scale formation potential

 Examples: calcium carbonate (calcite), barium sulfate (barite)

• Iron and manganese

• pH
Treatment of Produced Water and Flowback by 

Coagulation-Flocculation-Sedimentation

• Settleable solids are large enough to be removed from water by 

settling under the influence of gravity (e.g., sand)

• Colloidal particles are too small to be removed from water by 

settling under the influence of gravity

 colloidal particles can be converted into settleable particles by 

coagulation and flocculation

• Coagulation is the process of destabilizing colloidal particles so 

they can grow into larger, settleable particles

 coagulation changes the surface chemistry of colloidal particles in a 

way that causes them to stick together when two particles collide

• Flocculation causes colloidal particles to grow into larger, 

settleable particles

 flocculation induces collisions between particles
Fe2+

ClO2 ClO2

-

3 H2O 3 H+

Fe(OH)3(s)

Step 1: Oxidation of Fe(II) Step 2: Coagulation Step 3: Flocculation

Removal of Colloidal Suspended Solids from Produced Water

Step 4: Sedimentation

high mixing energy
Fe2+

ClO2 ClO2

-

3 H2O 3 H+

Fe(OH)3(s)

Step 1: Oxidation of Fe(II) Step 2: Coagulation Step 3: Flocculation

Removal of Colloidal Suspended Solids from Produced Water

Step 4: Sedimentation

moderate mixing energy
Fe2+

ClO2 ClO2

-

3 H2O 3 H+

Fe(OH)3(s)

Step 1: Oxidation of Fe(II) Step 2: Coagulation Step 3: Flocculation

Removal of Colloidal Suspended Solids from Produced Water

Step 4: Sedimentation

low mixing energy
Conventional Process Flow

water

coagulant

to

filtration

Rapid Mix:

• high mixing energy

• mix coagulant with raw water

Flocculation:

• gentle mixing

• facilitate particle growth through 

particle-particle collisions

Sedimentation:

• quiescent, uniform, horizontal flow

• particle removal by settling under the 

influence of gravity
Oil-Field Implementation of Coagulation-Flocculation-Sedimentation

14 ft

10 ft

10 ft 40 ft

Floc 1

Floc 2

Sedimentation

Has been used successfully at 7,500 bbl/day

ClO2

oil recovery
Typical Footprint

9
Coagulation-Flocculation-Sedimentation Bench Tests

before

treatment

control 35 ppm 80 ppm 150 ppm 230 ppm

beginning of

flocculation

settle for

2 hours
Coagulation-Flocculation-Sedimentation Bench Test Results

flocculation sedimentation
treatment

parameter units untreated 230 mg ClO2/liter EC treated

sodium mg/liter 35,200 33,200 38,00

potassium mg/liter 422 370 330

calcium mg/liter 4,580 3,940 4,450

magnesium mg/liter 595 520 580

barium mg/liter 15.4 2.6 2.8

strontium mg/liter 1,050 870 1000

iron mg/liter 167 1.0 20

manganese mg/liter 1.1 0.1 1.0

chloride mg/liter 65,260 55,000 68,810

alkalinity mg/liter as CaCO3 335 118 189

sulfate mg/liter 164 188 340

total sulfides mg/liter 25 0 ND

total 

suspended 

solids

mg/liter 3,960 80 480

turbidity NTU >1100 6 125

pH 6.9 6.5 6.4

density mg/liter 1.07 1.07 1.08

Coagulation-Flocculation-Sedimentation Bench Test Results
Coagulation-Flocculation-Sedimentation Bench Test Results

flocculation sedimentation
treatment

parameter units untreated 40 mg ClO2/liter

sodium mg/liter 6,870 7,050

potassium mg/liter 5.8 5.8

calcium mg/liter 74.7 74.1

magnesium mg/liter 15.1 14.8

barium mg/liter 16.2 15.1

strontium mg/liter 3.0 3.0

iron mg/liter 42.7 1.2

manganese mg/liter 0.5 0.2

chloride mg/liter 9,910 9,760

alkalinity mg/liter as CaCO3 1,100 1,080

sulfate mg/liter 2.3 0.0

total suspended solids mg/liter 160 10

turbidity NTU 177 8

pH 8.1 8.1

density mg/liter 1.01 1.01

Coagulation-Flocculation-Sedimentation Bench Test Results
Coagulation-Flocculation-Sedimentation Bench Test Results

before

treatment

control 0 ppm 10 ppm 20 ppm 80 ppm

end of

flocculation

settle for

2 hours

40 ppm
Coagulation-Flocculation-Sedimentation Bench Test Results
treatment

parameter units no ClO2 20 mg ClO2/liter

sodium mg/liter 74,000 68,600

potassium mg/liter 5,480 5,570

calcium mg/liter 17,100 17,000

magnesium mg/liter 1,430 1,430

barium mg/liter 11.6 11.5

strontium mg/liter 1,500 1,450

iron mg/liter 24.7 2.5

manganese mg/liter 16.5 15.8

chloride mg/liter 162,000 165,000

alkalinity mg/liter as CaCO3 413 402

sulfate mg/liter 325 310

total suspended solids mg/liter 1,110 164

turbidity NTU 240 45

pH 6.9 6.9

density mg/liter 1.20 1.20

Coagulation-Flocculation-Sedimentation Bench Test Results
Conclusions

• Chlorine dioxide is an effective coagulant for removal of 

suspended solids from produced water and flowback

 ClO2 oxidizes dissolved iron (Fe2+) to form solid Fe(OH)3, which 

acts as coagulant

 turbidities <10 NTU and suspended solids concentrations <20 

mg/liter are achievable

• Treatment with chlorine dioxide will oxidize iron, sulfides (in any 

form), and kill any bacteria that are present

• Flocculation and sedimentation can remove important scale 

species, such as barite and calcite

 this process can be modified to remove scale-causing compounds 

(e.g., calcium, barium, bicarbonate) that are not present above the 

saturation limit in the raw water
Mobile Unit On-Site Today