1. ISHAK at al: REFINERY WASTEWATER BIOLOGICAL TREATMENT: A SHORT REVIEWJournal of Scientific & Industrial Research 251Vol. 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 wastewaterIntroduction 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 offor desalting, distillation, thermal cracking, catalytic and chemicals and equipments, and excessive amounts oftreatment processes to produce useful products [liquefied sludge production. Thus, biological methods are preferredpetroleum gas (LPG), gasoline, jet fuel, diesel, asphalt due to simple, cheap and environmentally friendlyand petrochemical feedstock] 1-3. Refining process operations 3,15. This review presents characteristics ofgenerates wastewater (0.4-1.6 times the volume of crude PRW and biological treatment technologies.oil processed) 4. Discharge of untreated petroleum refiningwastewater (PRW) into water bodies results in Characteristics of Petroleum Refinery Wastewaterenvironmental and human health effects due to release (PRW)of toxic contaminants (hydrocarbons, phenol and Crude oil contains various organic and inorganicdissolved 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 firstconcern due to their toxicity and as carcinogenic step to remove contaminants using large quantities ofcompounds 3,7,8 . High exposure for long periods to these water; the process causes corrosion, plugging and foulingcompounds can cause leukemia and tumors in multiple of equipment 16 . Composition of PRW depends onorgans 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 oilsystem infection 9,10 . Therefore, according to and dissolved formation minerals 18 . Oil (Table 1) 4,19-21 isEnvironmental Protection Agency (USEPA), PRW have a mixture of hydrocarbons [benzene, toluene,to be sufficiently treated for quality to meet the established ethylbenzene, xylenes, polyaromatic hydrocarbonsregulations 11 . Physical and chemical treatments of PRW (PAHs) and phenol]. While, dissolved formation mineralshave 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 CODremoval and low salinity of 84µScm-13 and dissolved air Biological Treatmentflotation (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: firstname.lastname@example.org 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 instudy on biodegradation of petroleum oil by nematodes treatment plant that leads to constant drop in bacterialhas identified Bacillus sp. as a primary degrader and count during acclimatization period28-30. SBR [hydrauliccooperation 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 phenolbelow 80 mg/l (84.2% COD removal efficiency) and (99%) and o-cresol (94%), while biodegradabilityNH4 +-N concentration of 10 mg/l compared to non- (BOD5 /COD) of samples were not affected by toxicantsbioaugmented system, which needed an extra 10 days to loading by showing consistent values of BOD 5reach similar effluent quality20 . Biological processes are (< 5 mg/l), total soluble solids (TSS) (12 mg/l) and sludgeclassified as suspended-growth, attached-growth or volume index (SVI) (80 ml/g) 31 . Another study32 usinghybrid 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 acclimatizationmaintained in suspension mode within the liquid in batch phase, mixed liquor suspended solid (MLSS) and mixedreactor, 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 tosuspended-growth processes is ASS. Typical ASSs used decrease rapidly with addition of Hg(II) and Cd (II)32 asin wastewater treatment are plug-flow, complete mix and bacteria transform Hg into methylated Hg and becomessequencing 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 continuoussludge (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, Stenotreatments 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 total12 h cycle indicated almost complete phenol removal petroleum hydrocarbon (TPH). Aerobic degradingwith sufficient long react step and sludge morphology bacteria in organo-polluted site belong to Pseudomonasdid 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., Corynebacteriumdue to floc had been inactivated and disintegrated to sp., Arthrobacter sp., Comamonas sp., and Bacillusmicrofloc 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 treatmentParameters Nakla et al31 Malakahmad et al32 Gargouri et al34 Yaopo et al36 Wiszniowski et al37System SBR SBR CSTR Membrane Plug flow bioreactor membraneCycle, h 12 8 - - -HRT, d 1 15 - - -SRT, d 14 - - - -BOD5 removal, % 99 - - 96 - 99 99COD removal, % 94 80 Up to 95 78 - 98 93Type of Phenol and o-cresol Hg2+ and Cd2+ TPH - TPHcontaminantsInfluent 0.1 - 0.8 and 0.1 - 9.03 ± 0.02 and 320 mg TPH-1 - 50 – 100 µL/lcontaminants 0.6 (kg/m3 .d) 15.52 ± 0.02 (mg/L)Contaminants - 88.3 and 97.4 97.5 - Almost 100removal, %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 internalof COD (78-98%), BOD5 (96-99%), SS (74-99%) and circulating three-phase FBB (ICTFBB) was found moreturbidity (99-100%). Another study37 using plug flow resistance to COD and phenol shock loading. Its operationmembrane bioreactor showed removal of COD (93%), was more stable compared to activated sludge reactorBOD (99%) and TOC (96%), and bacterial community and average removal efficiencies were found aswas 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 reactordosage 37 (Table 2). consists of series of disc, on which biofilm grows, mounted on a horizontal shaft, positioned above the liquid levelAttached 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 theattached to an inert material (rocks, slag or plastic), which atmosphere where oxygen is absorbed and to the liquidenables to generate biofilm38 containing extracellular phase, where soluble organic matter is utilized1 . A studypolymeric substances produced by microorganisms 1 . on treatment of hydrocarbon-rich wastewater using RBCBioreactors with adhered biofilm have greater (HRT, 21 h; OLR, 27.33 g TPH/m2 d) showed that systemconcentration of biomass retained in the system with is able to remove 41 TPH (99%) and COD (97%).greater metabolic activities3 . A study on PRW treatmentusing fixed-film bioreactor showed COD removal rates Hybrid Systemof 80-90% at HRT of 8 h39 . Study40 on anaerobic upflow This process is a combination of suspended andfixed-film reactor operated at 37°C showed 0.33 m3 kg-1 attached-growth process in the same reactor like theCOD 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 isare attached growth biological treatment systems, can maintained in suspension by aeration or mechanicalbe 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) toFBB involves solid particles denser than water, which biodegrade PRW, achieved COD removal efficiency ofare suspended in column by an upflow stream of liquid 42 . 87%, and found PUF advantageous as a structure forIt has been found that largest COD reduction was microorganism to attach, grow and protect from highachieved 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 processMethod Operation Cost Toxic removal Sludge ` settleabilitySequencing Batch Reactor (SBR) A1 B2 A C3Continuously Stirred Tank Bioreactor (CSTB) A B B BMembrane bioreactor A B A BFluidized Bed Bioreactor (FBB) B B A BRotating Biological Contactor (RBC) B B B B1 A, very good; 2 B, good; 3 C, normaltoxicity 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 toremoval efficiencies for COD (17%) and TOC (20%) achieve optimum degradation of organic matter. CSTRcompared to the system without membrane 46 . A and RBC also considered good in toxicity removal. Maincrossflow membrane bioreactor showed 93% of COD problem in SBR is the possibility of SS to be dischargedremoval 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 onComparison 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 togravity settling in sedimentation tank followed by physical good sludge settleability49 .and chemical processes. ASS is affected by wastewaterflow and quality, wastewater aeration time, volume and Conclusionssludge loading, SVI, MLSS, dissolved oxygen (DO) and PRW is an indisputable pollution source foraeration requirements, sludge age, wastewater watercourses. Many different bioreactor designs havetemperature and concentration of wastewater1,48. Over been used in treatment of refinery wastewater includingthe years, ASS has improved to comply with high-quality batch reactors, standard activated sludge systems andeffluent 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 capitalbioreactor and membrane bioreactor) were developed and operating cost, land availability, operational complexityto overcome lack of ASS. and standard discharge limits. Comparison between developed processes(Table 3) with conventional ASS indicates that operation Acknowledgementof SBR, CSTR and membrane bioreactor is very good Authors thank Universiti Teknologi PETRONASbased on simplicity and flexibility of operation. However, Research and Innovation Office (UTPRIO) for fundingFBB and RBC require more complicated operations and (Project code: STIRF No. 07/09.10) this study.process design compared to ASS49 . SBR, CSTR andFBB are more economical due to elimination of clarifiers Referencesand less required of equipments and civil works. However, 1 Metcalf & Eddy, Wastewater Engineering: Treatment andwell trained personnel are required to monitor the reactor Reuse, (McGraw-Hill Inc., New York) 2003.process. Membrane and RBC obviously require higher 2 Bagajewicz M, A review of recent design procedures for water networks in refineries and process plants, J Com Chem Eng, 24cost for reactor setup and maintence50 . SBR showed (2000) 2093-2113.very good performance in toxicity removal. Membrane 3 Muneron de Mello J M, Heloisa de lima B, Antonio A & Debioreactor also has a great potential in toxic removal Saouza U, Biodegradation of BTEX compounds in a biofilmcompared to conventional ASS due to the use of low reactor – modelling and simulation, J Petrol Sci Eng, 70 (2000) 131-139.sludge load and high sludge age. High sludge age helps 4 Coelho A, Castro V A, Dezotti M & Sant’ Anna Jr G L,the bacteria to adapt with pollutants51 . FBB offers very Treatment of petroleum refinery wastewater by advancedgood toxic removal due to the use of small size carrier oxidation processes, J Haz Mat, B137 (2006) 178-184.
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