World Oil paper

Produced water RePORT
For engineers and industry professionals
by Produced Water Society +1 (281) 480-3087 www.producedwatersociety.com
World Oil AUGUST 2009 1
An aerobic, submerged-filter membrane bioreactor was used
to treat produced water from offshore oil reservoirs at up to 4.7
bpd. Despite the high salinity (2–5% total dissolved solids) and
chemical oxygen demand (up to 50,000 mg/L), the produced
water was effectively treated, with reductions of greater than
97% in COD, and greater than 99% for specific organic com-
ponents such as aliphatic hydrocarbons, monoaromatic hy-
drocarbons, aliphatic acids, aromatic acids and Polycyclic Aro-
matic Hydrocarbons (PAHs). In general, metal removal during
treatment was limited. Exceptions were iron, manganese and
barium, of which more than 90% was removed.
Reversible fouling of the membrane filter was observed in
response to changes in flux rates and mode of operation. Per-
meability was restored by in situ cleaning at pH 2–2.5, fol-
lowed by an oxidative treatment using sodium hypochlorite.
The Membrane BioReactor (MBR) appeared to be well suited
to produced water duty. Despite a very high degree of removal
of organics, the effluent COD was greater than the target 250-
mg/L discharge specification.
INTRODUCTION
The Sangachal Terminal, located 55 km south of Baku,
Azerbaijan, sits at the head of the Baku-Tiblisi-Ceyhan (BTC)
oil export line. The 1,768-km BTC pipeline is the second-
longest oil pipeline in the world, crossing Azerbaijan, Georgia
and Turkey, terminating at the Ceyhan Marine Terminal on
the southeastern Mediterranean coast of Turkey. The pipeline
has a capacity of 1 million bopd. The Sangachal Terminal
receives production from the Azeri-Chirag-Guneshli (ACG)
and Shah Deniz offshore production facilities. The first pro-
duction from an early oil project reached the terminal in De-
cember 1997, and in February 2002 the Sangachal Terminal
Expansion Project was initiated.
Initially, produced water at the terminal was utilized as
process water in a nearby cement production facility, but as
produced water volumes increased, alternative treatment and
disposal schemes were evaluated, including treatment by a
membrane bioreactor. This technology combines a membrane
process such as microfiltration or ultrafiltration with a sus-
pended growth bioreactor, and is widely used for municipal
and industrial wastewater treatment. The MBR option was
assessed over 4 months to evaluate the impact of anticipated
fluctuations in produced water composition.
Biological treatment had previously been shown to be effec-
tive on produced water. For example, a pilot-scale (up to 11 bpd)
plant demonstrated more than 99% removal of total petroleum
hydrocarbons from produced water with aTotal Dissolved Solids
(TDS) concentration up to 57,000 mg/L.1 The full-scale treat-
ment of produced water in Sumatra (with a predicted peak flow
of 25,000 bpd), using activated sludge technology, reduced Bio-
chemical Oxygen Demand (BOD) and COD concentrations
by 90%.2 Biological treatment in the form of a wetland system
treating 35,000 bpd of produced water in the United States has
been shown to meet all discharge limits.3 In some cases, where
the produced water’s Total Organic Carbon (TOC) is relatively
low (32.7 mg/L), biological treatment and discharge has been
shown to be a cheaper option than disposal by re-injection.3
Although some produced waters are amenable to biologi-
cal treatment, it was anticipated that produced water with a
high salinity and high TOC would be difficult to treat in a
conventional biological process plant. An MBR appeared to be
suitable, because high sludge densities could be achieved and
separation difficulties associated with highly saline water could
be avoided by membrane filtration of the effluent. MBRs have
successfully treated a range of industrial wastewaters such as
those from textile, paper and dye industries4 and automotive
and tank cleaning.5 MBRs have been shown to reduce the con-
centration of oil and surfactants in non-saline wastewater by
99%.6 Experience with highly saline effluents from the tanning
industry suggests that MBRs would be particularly suitable for
treating saline produced water.7 The potential of MBR technol-
ogy for treating produced water was assessed in fouling studies
using a synthetic mixture as an influent. This study reported
95% reduction in COD; however, a 50% decrease in mem-
brane permeability was noted when compared with treating
municipal wastewater.8 We are unaware of any published field
experience in treating oilfield produced water in an MBR.
MATERIALS AND METHODS
Produced water from offshore oil production platforms was
piped onshore in pipelines containing the produced water, oil
and gas. Onshore, gravity separation of the water phase was
Pilot-scale membrane bioreactor
treats produced water
Located at the Sangachal Terminal in Azerbaijan, the plant removed over 97%
of chemical oxygen demand and over 99% of several organic contaminants.
Arnold Zilverentant and Adriaan van Nieuwkerk, DHV BV; Ian Vance, Centromere Limited;
Annette Watlow, BP Exploration; and Matthew Rees, Azerbaijan International Operating Company
PROOF

2 AUGUST 2009 World Oil
Produced Water Report for Engineers and Industry Professionals
achieved in heater-treaters, and the separated water was stored
in tanks prior to disposal. Sub-samples of stored produced wa-
ter (about 6 bbl) were transferred as required to a day tank
holding the influent for the MBR.
MBR pilot plant. The MBR pilot plant built by DHV
had a 35-bbl capacity and operated with a recycle feed rate of
5 bpd, Fig. 1. An oily-water interceptor was placed upstream
of the MBR unit to remove free oil from the influent. The
produced water was aerated in the anti-bulking reactor up-
stream of the MBR to improve the MBR’s operability.
The submerged filter was a full-scale, low-pressure mem-
brane module comprised of reinforced hollow-fiber, ultra-
filtration membranes arranged in a cassette of three elements
with a total surface area of 495 sq ft.
Membrane permeate was returned to the bioreactor system
from the permeate tank if the tank level was low, or was dis-
charged when the tank level reached its high-level set point.
Under these conditions, the system throughput was controlled
by the feed pump speed and bioreactor level, rather than the
clarification throughput.
Commissioning and startup. Because of produced water’s
high salinity and COD, steps were taken to acclimate the bio-
mass to the imposed operating conditions. The plant was ini-
tially filled with water from the Caspian Sea (12.8 g/kg TDS)
and seeded with 10 L of biomass from a laboratory reactor that
had shown successful biological treatment of the produced wa-
ter. The laboratory reactor was originally seeded with sludge
from a municipal wastewater treatment plant that had been
slowly adapted to the high salinity of the produced water over
a period of 2 months. Once the MBR plant was operational, it
was fed produced water at a low rate (1.3–3.1 bpd). A relatively
high residence time (11 days) was used to facilitate a gradual
adaptation to the produced water, while still maintaining an
acceptable Food-to-Microorganism (F/M) ratio.
Steady-state operation. The plant was fed with a num-
ber of batches of produced water. The COD concentration
of each batch was measured and the feed flow was adjusted to
maintain the required F/M ratio. As a result, the feed flowrate
varied between 10 and 30 L/hr. The permeate flux was nor-
mally 600 L/hr. Accordingly, at least 95% of the permeate was
recycled through the unit. This very high recycle ratio resulted
from the unexpectedly high influent COD concentration.
The dissolved oxygen concentration was controlled at a val-
ue between 1.5 and 2.5 mg/L by using fine bubble aeration.
The pH and temperature inside the MBR were monitored,
but not controlled. Urea and phosphoric acid were added as
necessary to balance the nutrient status of the influent.
Membrane cleaning. When membrane cleaning was re-
quired, appropriate chemicals were added to the permeate tank,
to allow in situ cleaning. Cleaning in air was also performed at
irregular intervals. After initial trials with hydrogen peroxide
(H2O2), all further cleaning was carried out at pH 2–2.5, fol-
lowed by an oxidative cleaning regime using sodium hypochlo-
rite (NaOCl), at a range of concentrations and durations. At
the end of the 5-month test period, an extensive cleaning re-
gime was performed to evaluate any irreversible fouling.
Production chemicals. Since the produced water came from
a fully operational process, it contained the water-soluble por-
tion of the production chemicals in current use. In order to as-
sess the possible impact of future changes in production chemi-
cal use, the day tank was amended with additional production
chemicals at concentrations predicted to be the maximum dose
at any point in field life. Hydrate inhibitor (methanol, 500
ppm), demulsifier (86 ppm), antifoam (43 ppm), corrosion in-
hibitor (170 ppm), wax inhibitor (270 ppm) and scale inhibitor
(9 ppm) were added to the day tank, and the effects on plant
performance were recorded. The chemical spiking contributed
about 3,000 mg/L to the total COD of the wastewater.
RESULTS AND DISCUSSION
At the time of the pilot trail, the development of the oil
fields was at a very early stage. The produced water flow at
that time was only a fraction of the volume anticipated in
the future. As a result of the relatively long storage time, the
produced water cooled down to about ambient temperature.
During the pilot plant startup under winter conditions, and
with limited biological heat production, the temperature
in the pilot plant was relatively low (average 15°C). Three
months later, the average temperature had increased to 27°C
(Fig. 2), owing to rising ambient temperatures and increased
heat generation from biological activity. Once the fields are in
full production, the temperature of the produced water in the
storage tank will be higher than ambient, and cooling prior to
biological treatment will become necessary.
The increase in the influent salinity from
about 2% TDS to 4–5% corresponded with
the observed temperature increase, Fig. 2. This
is considered to be coincidental and is an exam-
ple of the variability expected in the composi-
tion of produced water. This is particularly true
where the water is produced from multiple sub-
surface horizons from multiple wells that pro-
duce fluids at different rates depending upon
reservoir management requirements.
Sludge concentration and F/M ratio.
Upon startup, the aim was to reach a Mixed
Liquor Suspended Solids (MLSS) value in
the bioreactor of at least 10,000 mg/L in 4–6
weeks. This was achieved, and the MLSS
was allowed to increase over the following 3
months and was maintained at 20,000 mg/L.
Toward the end of the trial, MLSS peaked at
25,000 mg/L, but this was not found to be
detrimental to overall plant performance.
MBR feed
pump Anti-Bulking
Reactor (ABR)
ABR aeration
Membrane
aeration
Membrane
cassette
Membrane
circulation pump
Foam-breaking
pump
Acid
Alkali
Clean-in-place
system
Permeate
pump
Permeate
discharge
Pre-DN
Aerobic
carbon and nitrogen
removal
Biological
aeration
Nozzles
Antifoam oil
Excess
wastewater
to drain
Skimmed
oil
Reﬁnery
wastewater
Fig. 1. Schematic diagram of the pilot plant.
PROOF

World Oil AUGUST 2009 3
After measuring the COD concentration of each batch of
produced water added to the MBR, the influent flow was ad-
justed to maintain an F/M ratio of 0.2 (measured as influent
COD divided by MLSS). Figure 3 shows how the F/M ratio
varied with time. At the beginning and middle of the trial,
the plant was operating at higher values of F/M ratio than the
target. This substantial increase appeared to have little or no
effect on the effluent quality.
Removal of COD. The influent COD concentration (up
to 50,000 mg/L) is unusually high for produced water, which
according to a 1992 study typically has values up to 2,070
mg/L.9 Total COD and soluble COD values were very close
throughout the trial, indicating that little of the COD exists
as suspended solids.
The influent COD also proved to be highly variable, rang-
ing from 4,000 to 50,000 mg/L, but biological treatment at
high salinity did not pose insurmountable problems. Under
steady-state conditions, the COD removal efficiency was, in
general, greater than 97%. This is similar to the performance
reported for a synthetic produced water that had methanol
as a major component.8 However, despite the high removal
efficiency, the high COD of the influent resulted in an ef-
fluent COD typically between 1,000 and 2,000 mg/L. The
treated effluent did not meet the World Bank industry sector
guidelines for petroleum refining of 150 mg/L or the general
environmental guidelines of 250 mg/L.
Removal of organics. The produced water contained a
complex mixture of organics, and all of those analyzed showed
some degree of removal during treatment in the MBR,Table 1.
In general, the removal of organic compounds was high (great-
er than 94%). The produced water contained a relatively high
concentration of aliphatic aids, the most abundant of which
was 3-methylbutanoic acid (2,200 mg/L). The concentration
of naphthenic acids was also high, with cyclopentane carboxy-
lic acid and cyclohexane carboxylic acid both being present at
1,000 mg/L. All of the acids were effectively removed during
treatment by greater than 99%. Out of the aromatic compo-
nents (27 mg/L), only a very low concentration of benzene
(0.0019 mg/L) was analyzed in the effluent. The removal of
BTEX (99.9%) was the same as that reported for a synthetic
produced water containing 33 mg/L of BTEX.8
Removal of metals. Heavy metals were in general only pres-
ent at very low concentrations, mostly even below the detection
limit, Table 1. Removal of metals was limited. A notable excep-
tion was iron, of which 99.8% was removed during treatment.
Over 70% of the total iron was present in particulate form, so
removal by the membrane filter would be expected to be high.
Similarly, removal of over 90% of barium and manganese was
achieved; these were also present mainly in the insoluble state
(96% and 93%, respectively). The limited removal of calcium
and magnesium was probably due to precipitation as carbonate,
produced through the biological conversion of organics.
Membrane performance. The performance of the hollow-
fiber membranes was measured and assessed during three dif-
ferent operating conditions summarized in Table 2. Predict-
ably, fouling of the membrane was observed during the trial,
but this did not result in permanent damage. The effect of
fouling was reversed by routine cleaning. Generally, the per-
meability of the membranes declined with time, Fig. 4. A
steady decline of up to 80% permeability was observed over
25 days for Period 1. The loss of permeability was less appar-
ent (only 20% over 15 days) for Periods 2 and 3.
Permeability was enhanced by operating with a reduced
flux rate, achievable by a lower feed rate or introduction of a
membrane relaxation period. The permeability of the mem-
brane at equivalent flux rates was generally lower than that
described for a system treating synthetic produced water.8 The
pilot plant, however, was treating real produced water with a
COD over 50 times higher than the synthetic mixture and
was operating with an MLSS concentration up to 3.3 times
5
10
15
20
25
30
35
2-20-05 3-22-05 4-21-05 5-21-05 6-20-05
Temperature,°C
0
1
2
3
4
5
6
Salinity,%
Temperature
Salinity
Fig. 2. Operating temperature and influent salinity.
0
7-09-05 7-13-05
Spill simulation
7-17-05 7-21-05 7-25-05
2
4
6
8
10
Oxygenuptakerate,mg/(ghr)
0.00
0.05
0.10
0.15
0.20
0.25
F/Mratio
Respiration rate (OUR)
F/M ratio
Fig. 3. Specific oxygen uptake rate and F/M ratio during
production chemical amendment.
Component Concentration, mg/L % removed
Influent Effluent
Monoaromatic hydrocarbons 27 0.0019 99.9
Benzene, Toluene, Ethylbenzene
and Xylenes (BTEX) 12 0.0019 99.9
C9–C40 aliphatic hydrocarbons 36 0.046 99.9
Aliphatic acids 5,000 0.34 99.9
Aromatic acids 580 1.8 99.7
C5–C9 naphthenic acids 3,900 4.3 99.9
Total Polycyclic Aromatic
Hydrocarbons (PAH) 0.21 0.00021 99.9
C2–C7 volatile fatty acids 1,707 10 98.0
Barium 3.12 0.01 99.7
Boron 93.5 87.6 6.3
Calcium 59.2 23 60.7
Chromium 0.01 0.01 0.0
Copper 0.32 0.29 9.4
Iron 19.3 0.03 99.8
Magnesium 59.5 28.7 51.8
Manganese 0.15 0.01 93.3
Potassium 296 271 8.4
Table 1. Major organics and metals
in produced water and their removal efficiency
in the MBR
PROOF

4 AUGUST 2009 World Oil
Produced Water Report for Engineers and Industry Professionals
higher.The results from the pilot plant are encouraging, show-
ing that effective membrane operation can be maintained un-
der realistic operating conditions, tending toward the worst
case, using routine cleaning to restore membrane permeability.
Membrane lifetimes are expected to be at least 2–3 years.
Effect of production chemicals. Some production chemi-
cals have biocidal or biostatic properties, so an evaluation of
possible deleterious effects upon plant operation was carried
out by dosing the proposed production chemicals at their
maximum predicted concentration at any point in field life.
This was deemed a worst-case scenario since maximum dosing
of all production chemicals would not necessarily coincide.
The amendment with production chemicals appeared to
initially depress the Specific Oxygen Uptake Rate (SOUR), as
shown in Fig. 3. The SOUR then remained about 40% lower
than the rate prior to amendment. The amendment with pro-
duction chemicals, however, coincided with a substantial de-
crease in the F/M-loading rate (Fig. 3), which normally also
results in a drop in the SOUR. With increasing F/M ratio, the
SOUR also increased. The impact of the production chemi-
cals on the MBR performance is therefore considered to be
limited. Any seriously negative effects of deliberately added
process chemicals could be minimized by careful selection and
testing programs prior to their deployment for routine use.
Potential for reuse. In terms of high salinity and COD,
the composition of the produced water is viewed as a worst
case. Even after successful treatment, the salinity remained
high, which precluded options for reuse in the absence of a
suitable diluent. The treated effluent COD was also too high
for uses such as irrigation.
In addition, the concentration of boron was high enough
that it alone would preclude use for irrigation. Additional
treatment, such as reverse osmosis, would be required in order
to comply with water quality specifications for irrigation. In
fact, further treatment would be required to meet a 250-mg/L
COD standard for discharged water if applied at the end of the
pipe. Initial testing using nanofiltration showed a substantial
additional COD removal at a recovery of more than 90%.
CONCLUSIONS
Despite the high and fluctuating values of COD and salin-
ity in the produced water influent (up to 50,000 mg/L), suc-
cessful treatment was carried with the MBR. Removal rates of
more than 97% for COD and more than 99% for aliphatic
hydrocarbons, monoaromatic hydrocarbons, aliphatic acids,
aromatic acids, naphthenic acids and PAH were achieved.
Despite the high removal rates, the high COD concen-
tration of the influent resulted in an effluent COD that was
higher than the 250-mg/L discharge standard. WO
ACKNOWLEDGEMENTS
The authors thank the Azerbaijan International Operating Company and part-
ners in Azeri, Chirag and Guneshli Fields for permission to publish this work.
LITERATURE CITED
1 Tellez, G. and N. Khandan, N., “Biological treatment processes for removing petroleum hydrocarbons
from oilfield produced waters,” in Reed, M. and S. Johnson, eds., Produced Water 2: Environmental Issues
and Mitigation Technologies. Environmental Science Research, Volume 52, Plenum Press, New York, 1996,
pp. 499–597.
2 Madian, E.S ., Moelyodihardjo, T., Snavely, E. S. and R. J. Jan, “Treating of produced water for surface
discharge at the Arun gas condensate field,” SPE 28946 presented at the SPE International Symposium on
Oilfield Chemistry, San Antonio, Texas, Feb. 14–17, 1995.
3 Myers, J. E., Jackson, L. M., Bernier, R. F. and D. A. Miles, “An evaluation of the Department of Energy
Naval Petroleum Reserve No. 3 produced water bio-treatment facility,” SPE 66522 presented at the SPE/
EPA/DOE Exploration and Production Environmental Conference, San Antonio, Texas, Feb. 26–28,
2001.
4 Marrot, B., Barrios-Martinez, A., Moulin, P. and N. Roche, “Industrial wastewater treatment in a mem-
brane bioreactor: A review,” Environmental Progress, 23, No. 1, 2004, pp. 59–68.
5 Lawrence, D., Van Gool, H. and A. Zilverentant, “Potentials for MBR in industry,” H2O, MBR Special II,
2003, pp. 13–15.
6 Scholz, W. and W. Fuchs, “Treatment of oil contaminated wastewater in a membrane bioreactor,” Water
Research, 34, No. 14, 1999, pp. 3621–3629.
7 Scholz, W. G., Rouge, P., Bodalo, A. and U. Leitz, “Desalination of mixed tannery effluent with mem-
brane bioreactor and reverse osmosis treatment,” Environmental Science Technology, 39, No. 21, 2005,
pp. 8505–8511.
8 Brookes, A., Jefferson, B., Le Clech, P. and S. J. Judd, “Fouling of membrane bioreactors during treatment
of produced water,” paper 074 presented at the International Membrane Science and Technology Confer-
ence, Sydney, Australia, Nov. 10–14, 2003.
9 Tibbets, P. J. C., Buchanan, I. T., Gawel, L. J. and R. Large, “A comprehensive determination of produced
water composition,” in Ray, J. P. and F. R. Engelhardt, eds., Produced Water Technological/Environmental Is-
sues and Solutions. Environmental Science Research, Volume 46, Plenum Press, New York, 1992, pp. 97–112.
The authors
Arnold Zilverentant is a Senior Specialist at DHV on water and waste-
water treatment, with involvement in process design, engineering and
research projects. With almost 30 years of experience as a wastewater
treatment and process engineer, he has carried out numerous projects in
Europe and overseas. He has an MSc degree in chemical engineering.
Adriaan van Nieuwkerk has MSc degrees in chemical engineering and
management science. He has more than 30 years of experience with
industrial water treatment projects in various countries. As an Account/
Project Manager of DHV Water, Mr. van Nieuwkerk is responsible for the
realization of industrial water treatment projects.
Ian Vance has a BSc degree in biological sciences and a PhD degree in
marine microbial ecology. After three years as a research fellow working
in fermentation technology, he joined the New Technology division of
BP, specializing in the microbiological conversion of cellulose to ethanol.
He then worked on many diverse projects for BP. He now operates an
independent consultancy specializing in microbiological water treatment
and environmental issues.
Annette Watlow is an Environmental Engineer with BP, working to in-
crease energy efficiency and reduce environmental impact of company
projects in the early design stages. She has an engineering degree and
an MBA and has 29 years experience in the oil and gas industry.
Mathew Rees has an engineering degree and holds an MA from Cam-
bridge University. He has 20 years of experience working in the oil and
gas industry. He has worked for BP as a Project Manager since 2001 on
various projects related to ACG Field in Azerbaijan. He currently over-
sees brownfield modification and upgrade work on the six offshore facili-
ties operated by BP in the Caspian Sea.
0
20
40
60
80
100
120
140
0 5 10 15 20 25 30
Run time, days
Permeability,L/(m2hrbar)
Period 1
Period 2
Period 3
Fig. 4. Membrane permeability decline under different
operating conditions.
Period Feed flow, Relaxation, Gross flux, Net flux,
L/hr s L/m2hr L/m2hr
1 600 0 13 11
2 600 400 13 4
3 385 0 8.5 7
Table 2. Operating conditions during
membrane fouling assessment periods
PROOF

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