1. ISHAK at al: REFINERY WASTEWATER BIOLOGICAL TREATMENT: A SHORT REVIEW
Journal of Scientific & Industrial Research 251
Vol. 71, April 2012, pp. 251-256
Refinery wastewater biological treatment: A short review
S Ishak*, A Malakahmad and M H Isa
Civil Engineering Department, Faculty of Engineering, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia
Received 29 November 2010; revised 02 February 2012; accepted 09 February 2012
This review presents biological treatment methods for petroleum refinery wastewater, their applications, advantages and
disadvantages. It covers refinery wastewater characteristics, different categories of biological treatment systems (suspended,
attached and hybrid growths) and comparison between each system with conventional activated sludge process.
Keywords: Biological treatment, Refinery wastewater
Introduction 94% and 72-92.5% respectively) 14 ]. However, physical
Petroleum refining utilize large quantities of water and chemical methods are costly due to high price of
for desalting, distillation, thermal cracking, catalytic and chemicals and equipments, and excessive amounts of
treatment processes to produce useful products [liquefied sludge production. Thus, biological methods are preferred
petroleum gas (LPG), gasoline, jet fuel, diesel, asphalt due to simple, cheap and environmentally friendly
and petrochemical feedstock] 1-3. Refining process operations 3,15. This review presents characteristics of
generates wastewater (0.4-1.6 times the volume of crude PRW and biological treatment technologies.
oil processed) 4. Discharge of untreated petroleum refining
wastewater (PRW) into water bodies results in Characteristics of Petroleum Refinery Wastewater
environmental and human health effects due to release (PRW)
of toxic contaminants (hydrocarbons, phenol and Crude oil contains various organic and inorganic
dissolved minerals)5,6 . Hydrocarbons [benzene, toluene, compounds including salts, suspended solids and water-
ethyl benzene and xylenes (BTEX)] are of serious soluble metals. It undergoes desalting process as a first
concern due to their toxicity and as carcinogenic step to remove contaminants using large quantities of
compounds 3,7,8 . High exposure for long periods to these water; the process causes corrosion, plugging and fouling
compounds can cause leukemia and tumors in multiple of equipment 16 . Composition of PRW depends on
organs 3 . Phenol and dissolved minerals are also toxic to complexity of refining process 17 but in general,
aquatic life and lead to liver, lung, kidney and vascular compounds in PRW include dissolved and dispersed oil
system infection 9,10 . Therefore, according to and dissolved formation minerals 18 . Oil (Table 1) 4,19-21 is
Environmental Protection Agency (USEPA), PRW have a mixture of hydrocarbons [benzene, toluene,
to be sufficiently treated for quality to meet the established ethylbenzene, xylenes, polyaromatic hydrocarbons
regulations 11 . Physical and chemical treatments of PRW (PAHs) and phenol]. While, dissolved formation minerals
have been carried out using different methods are inorganic compounds, which include anions and
[electrocoagulation (93% of sulfate and 63% of COD cations including heavy metals 18 .
removal) 12 , electrochemical oxidation (92.8% for COD
removal and low salinity of 84µScm-13 and dissolved air Biological Treatment
flotation (BOD and COD removal efficiencies of 76- Biological processes utilize microorganisms
(naturally-occurring, commercial, specific groups and
acclimatized sewage sludge) to oxidize organic matter
*Author for correspondence into simple products (CO2 , H 2 O and CH4 ) under aerobic,
E-mail: syukaz83@yahoo.com.sg anaerobic or semi aerobic conditions 18,20. A C: N: P ratio

2. 252 J SCI IND RES VOL 71 APRIL 2012
Table 1—Characteristics of petroleum refinery wastewater (PRW)
Parameter Coelho et al4 Dold19 M a et al20 Khaing et al21
BOD5 , mg/l 570 150 - 350 150 - 350 -
COD, mg/l 850 -1020 300 - 800 300 - 600 330 - 556
Phenol, mg/l 98 - 128 20 - 200 - -
Oil, mg/l 12.7 3000 50 40 - 91
TSS, mg/l - 100 150 130 - 250
BTEX, mg/l 23.9 1 - 100 - -
Heavy metals, mg/l - 0.1 - 100 - -
Chrome, mg/l - 0.2 - 10 - -
Ammonia, mg/l 5.1 - 2.1 - 10 - 30 4.1 - 33.4
pH 8.0 - 8.2 - 7-9 7.5 - 10.3
Turbidity, NTU 22 - 52 - - 10.5 - 159.4
(100:5:1) is adequate for microorganisms to grow 1,22. A might affect activity and biological performance in
study on biodegradation of petroleum oil by nematodes treatment plant that leads to constant drop in bacterial
has identified Bacillus sp. as a primary degrader and count during acclimatization period28-30. SBR [hydraulic
cooperation with nematodes for degradation of retention time (HRT), 1 d; and a solid retention time,
pollutants23 . In a study using bioaugmentation, activated 14 d] using toxicants loading (phenol, 0.1 - 0.8 kg /m3 .d;
sludge system (ASS) took only 20 days to achieve COD and o-cresol, 0.1 - 0.6 kg /m3 .d) showed removal of phenol
below 80 mg/l (84.2% COD removal efficiency) and (99%) and o-cresol (94%), while biodegradability
NH4 +-N concentration of 10 mg/l compared to non- (BOD5 /COD) of samples were not affected by toxicants
bioaugmented system, which needed an extra 10 days to loading by showing consistent values of BOD 5
reach similar effluent quality20 . Biological processes are (< 5 mg/l), total soluble solids (TSS) (12 mg/l) and sludge
classified as suspended-growth, attached-growth or volume index (SVI) (80 ml/g) 31 . Another study32 using
hybrid processes. toxicants (Hg2+, 9.03 ± 0.02 mg/l; and Cd2+, 15.52 ± 0.02
mg/l) have shown removal efficiencies of Hg (II) (88%)
Suspended Growth and Cd (II) (97.4%), which indicates the ability of SBR
In suspended-growth processes, microorganisms are system in noxious environment. During acclimatization
maintained in suspension mode within the liquid in batch phase, mixed liquor suspended solid (MLSS) and mixed
reactor, which is allowed to operate with mixing under liquor volatile suspended solid (MLVSS) rise steadily,
aerobic or anaerobic conditions. One of the common reflecting active growth of bacteria and started to
suspended-growth processes is ASS. Typical ASSs used decrease rapidly with addition of Hg(II) and Cd (II)32 as
in wastewater treatment are plug-flow, complete mix and bacteria transform Hg into methylated Hg and becomes
sequencing batch reactor (SBR)1 . While plug-flow and extremely toxic to biological systems 33 .
complete mix activated sludge require return activated- Other suspended-growth methods are continuous
sludge (RAS) system and clarifiers, SBR operates without stirred tank reactor (CSTR) and membrane bioreactor.
a clarifier. A study34 of CSTR using bioaugmented microbial
SBR is based on fill-and-draw batch system24 and consortium [Aeromonas punctata (A. caviae),
has been applied for industrial and municipal wastewater B. cereus, Ochrobactrum intermedium, Steno
treatments due to high removal efficiency of BOD, COD trophomonas maltophilia and Rhodococcus sp.]
and suspended solid (SS)25-27. Study using SBR with showed removal up to 95% of COD and 97.5% of total
12 h cycle indicated almost complete phenol removal petroleum hydrocarbon (TPH). Aerobic degrading
with sufficient long react step and sludge morphology bacteria in organo-polluted site belong to Pseudomonas
did not affect phenol removal efficiency with increased sp., Acinetobacter sp., Alcaligenes sp.,
phenol influent28 . However, poor settleability of sludge Flavobacterium/Cytophaga group, Xanthomonas sp.,
was observed at 400 mg/l of influent phenol concentration Nocardia sp., Mycobacterium sp., Corynebacterium
due to floc had been inactivated and disintegrated to sp., Arthrobacter sp., Comamonas sp., and Bacillus
microfloc 28 . Moreover, toxic compounds like phenol sp. 35 .

3. ISHAK at al: REFINERY WASTEWATER BIOLOGICAL TREATMENT: A SHORT REVIEW 253
Table 2—Application of suspended-growth in noxious refinery wastewater treatment
Parameters Nakla et al31 Malakahmad et al32 Gargouri et al34 Yaopo et al36 Wiszniowski et al37
System SBR SBR CSTR Membrane Plug flow
bioreactor membrane
Cycle, h 12 8 - - -
HRT, d 1 15 - - -
SRT, d 14 - - - -
BOD5 removal, % 99 - - 96 - 99 99
COD removal, % 94 80 Up to 95 78 - 98 93
Type of Phenol and o-cresol Hg2+ and Cd2+ TPH - TPH
contaminants
Influent 0.1 - 0.8 and 0.1 - 9.03 ± 0.02 and 320 mg TPH-1 - 50 – 100 µL/l
contaminants 0.6 (kg/m3 .d) 15.52 ± 0.02 (mg/L)
Contaminants - 88.3 and 97.4 97.5 - Almost 100
removal, %
Effluent TSS, mg/l 12 - - - -
SVI, ml/g 80 58 - - -
A membrane bioreactor 36 showed removal efficiency and air velocities (u , LT-1) = 0.029 m/s42 . A pilot internal
of COD (78-98%), BOD5 (96-99%), SS (74-99%) and circulating three-phase FBB (ICTFBB) was found more
turbidity (99-100%). Another study37 using plug flow resistance to COD and phenol shock loading. Its operation
membrane bioreactor showed removal of COD (93%), was more stable compared to activated sludge reactor
BOD (99%) and TOC (96%), and bacterial community and average removal efficiencies were found as
was affected at high petroleum pollutants concentration follows43 : COD, 75.9; oil, 75.3; phenol, 92.8; ammonia
(1000 µl/l). Bacterial population started to diverge at this nitrogen, 40.0; and phosphorus, 87.2%. RBC reactor
dosage 37 (Table 2). consists of series of disc, on which biofilm grows, mounted
on a horizontal shaft, positioned above the liquid level
Attached Growth that rotates at right angles to the flow of wastewater.
In attached-growth process, microorganisms are Discs are partially submerged and exposed both to the
attached to an inert material (rocks, slag or plastic), which atmosphere where oxygen is absorbed and to the liquid
enables to generate biofilm38 containing extracellular phase, where soluble organic matter is utilized1 . A study
polymeric substances produced by microorganisms 1 . on treatment of hydrocarbon-rich wastewater using RBC
Bioreactors with adhered biofilm have greater (HRT, 21 h; OLR, 27.33 g TPH/m2 d) showed that system
concentration of biomass retained in the system with is able to remove 41 TPH (99%) and COD (97%).
greater metabolic activities3 . A study on PRW treatment
using fixed-film bioreactor showed COD removal rates Hybrid System
of 80-90% at HRT of 8 h39 . Study40 on anaerobic upflow This process is a combination of suspended and
fixed-film reactor operated at 37°C showed 0.33 m3 kg-1 attached-growth process in the same reactor like the
COD d-1 methane production at an organic loading rate combination of activated sludge and submerged biofilters
(OLR) of 6 kg COD m-3 d-1. Fixed-film processes, which (fixed bed biofilters). A carrier material in reactor is
are attached growth biological treatment systems, can maintained in suspension by aeration or mechanical
be divided into trickling filter, fluidized bed bioreactor mixing (moving bed reactor)1 . Tyagi et al44 studied
(FBB) and rotating biological contactor (RBC)1,41. An performance of RBC-polyurethane foam (PUF) to
FBB involves solid particles denser than water, which biodegrade PRW, achieved COD removal efficiency of
are suspended in column by an upflow stream of liquid 42 . 87%, and found PUF advantageous as a structure for
It has been found that largest COD reduction was microorganism to attach, grow and protect from high
achieved at various ratio of bed (settled) volume external shear. A study45 using hybrid system showed
(Vb, L3 ) to bioreactor volume (VR, L3 ), (Vb/VR) = 0.55 over 90% of 2,4,6-trichlorophenol (TCP), COD and

4. 254 J SCI IND RES VOL 71 APRIL 2012
Table 3—Comparison between developed methods and conventional activated sludge process
Method Operation Cost Toxic removal Sludge
` settleability
Sequencing Batch Reactor (SBR) A1 B2 A C3
Continuously Stirred Tank Bioreactor (CSTB) A B B B
Membrane bioreactor A B A B
Fluidized Bed Bioreactor (FBB) B B A B
Rotating Biological Contactor (RBC) B B B B
1
A, very good; 2 B, good; 3 C, normal
toxicity removal efficiencies. Application of submerged particles that has large specific area for bacterial growth.
membrane bioreactor (SMBR) showed increase in Stability of bacterial growth is very important in order to
removal efficiencies for COD (17%) and TOC (20%) achieve optimum degradation of organic matter. CSTR
compared to the system without membrane 46 . A and RBC also considered good in toxicity removal. Main
crossflow membrane bioreactor showed 93% of COD problem in SBR is the possibility of SS to be discharged
removal efficiency. HRT does not significantly affect during draw step due to less sludge settleability24 .
performance of this system47 . However, CSTR, membrane, FBB and RBC have been
characterized with good sludge settleability based on
Comparison of Biological Treatment Systems reactor design. Bioparticles are retaining in the reactor
In conventional ASS, settleable solid is separated by and there is less possibility of SS to be discharged due to
gravity settling in sedimentation tank followed by physical good sludge settleability49 .
and chemical processes. ASS is affected by wastewater
flow and quality, wastewater aeration time, volume and Conclusions
sludge loading, SVI, MLSS, dissolved oxygen (DO) and PRW is an indisputable pollution source for
aeration requirements, sludge age, wastewater watercourses. Many different bioreactor designs have
temperature and concentration of wastewater1,48. Over been used in treatment of refinery wastewater including
the years, ASS has improved to comply with high-quality batch reactors, standard activated sludge systems and
effluent of wastewater treatment plant. New wastewater their variations, fluidized beds and membrane systems.
treatment systems (SBR, CSTR, FBB, RBC, airlift Selection among alternative processes is based on capital
bioreactor and membrane bioreactor) were developed and operating cost, land availability, operational complexity
to overcome lack of ASS. and standard discharge limits.
Comparison between developed processes
(Table 3) with conventional ASS indicates that operation Acknowledgement
of SBR, CSTR and membrane bioreactor is very good Authors thank Universiti Teknologi PETRONAS
based on simplicity and flexibility of operation. However, Research and Innovation Office (UTPRIO) for funding
FBB and RBC require more complicated operations and (Project code: STIRF No. 07/09.10) this study.
process design compared to ASS49 . SBR, CSTR and
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