Optimizing the Treatment of Produced Water 

and Flowback for Reuse or Disposal 

Brian A. Wrenn 

PureLine
• Chemistry 

– ClO2 is an effective oxidant and biocide 

– treats H2S, iron, FeS, SRB, APB, and other contaminants of 

concern 

– pH independent: effective over a broad range 

– environmentally friendly: EPA and FDA approved 

• Experience

– 134 years collective technical experience 

– scientists, engineers, applications specialists 

• Equipment

– mobile units generate ClO2 on demand for on-the-fly treatment 

• Control

– PureLine ClO2 generators adjust dose automatically...no more 

over treating! 

Why Consider PureLine? 
Mobile Unit On-Site Today 
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 

• 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 
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

ClO2
Oil-Field Implementation of Coagulation-Flocculation-Sedimentation 

14 ft

10 ft

10 ft 40 ft

Floc 1 

Floc 2 

ClO2
Oil-Field Implementation of Coagulation-Flocculation-Sedimentation 

14 ft

10 ft

10 ft 40 ft

Floc 1 

Floc 2 

Sedimentation 

Designed to treat 5,000 bbl/day 

ClO2

oil recovery 
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 

15 
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 
21 

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 
22 

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