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Biological fluidized bed treatment of ethylene and propylene glycols
8)
Pergamon
Wal. Sci. Tecla. Vol. 38. No.
PH:S0273-1223(98)OO523-X
4-,. pp. 14'-"3. 1998.
1AWQ C 1998 Published byElsevier Science Ltd. Printedin Great Britain.All righlareserved 0273-1223/98 S19'00 + 0'00
BIOLOGICAL FLUIDIZED BED TREATMENT OF ETHYLENE AND PROPYLENE GLYCOLS Wen K. Shieh, John A. Lepore and Iraj Zandi Department ofSystems Engineering, University ofPennsylvania Philadelphia, Pennsylvania 19104-6315. USA
ABSTRACf The bioremediation of ethylene and propylene glycols using the aerobic biological fluidized bed (BFB)
technology is evaluated. Under the steady-state conditions tested,the BFB reactors are capable of achieving good TOe removal(i.e.•>96%) at empty bed HRTsas short as 1.7 hrs and at TOe loadingsas high as 0.88 g/L-day.In addition. the BFB reactors are also capableof sustaining good TOe removal (i.e.• >87%) during single-pulse loadings with a IQ-fold increasein pulse magnitude and pulse durations as long as 7 hrs. The observed BFB processefficiency and stabilityare attributable to the high immobilized biomass inventories attainedin reactors by using porousmedia panicles for cell immobilization and retention. C 1998 Published by ElsevierScience Ltd. All rightsreserved
KEYWORDS Deicing; fluidized bed; glycols; immobilized cells;transient-state. INTRODUcnON Glycol-based fluids are commonly used to remove ice, snow, and frost from aircraft, and to curtail their accumulation in order to insure air transport safety in cold weather (MacDonald et al., 1992; Mayer et al., 1986). Ethylene glycol (EG)-based fluids are the most common deicing/anti-icing fluids used in North America(MacDonald et al., 1992). An alternative is propylene glycol (PG)-based fluids which are less toxic (e.g., LDso in laboratory rats: 8.54 g/kg for EO and 30.0 g/kg for PG) and have lower freeZing points (MacDonald et al., 1992; Majewski et al., 1978). Under most environmental conditions glycols are not volatile because of their low vapor pressures (Verschueren, 1985). In addition, partition of glycols into the biotic and solid phases are unlikely because of their low Kow values (Miller, 1979; Rai and Franklin, 1978). On the other hand, glycols are susceptible to biodegradation (Haines and Alexander, 1975; Jerger and Flatman, 1990; MacDonald et al., 1992; Schink and Stieb, 1983), and the long- term biochemical oxygen demand(BOD)exertions of thesefluidsobserved in this studyare rapidand substantial (Figure 1). It has been estimated that up to 80% of the glycol-based fluids applied are left on tarmacs and runways which may be washed away by airport storm runoff (MacDonald et al., 1992; Mayer et al., 1986; Schultz and Comerton, 1974). As a result, large quantities of spentfluids could be spilled into receiving waters over short periodsof time. The primaryimpacts of glycol spills are on the oxygeninventories of receivingwaters 145
146
W. K.SHIEH et aI.
as well as on aquatic organisms (MacDonald, et al., 1992). The spent fluids may also be collected, stored, and treated on-site and then released into municipal wastewater treatment plants for further treatment, or discharged directly into receiving waters. 1200 ...----------~~"'" 00 000 0 0 00 0 1100
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Figure I. Long-term BODcurvesof ethylene and propylene glycols.
The treatability of EO and PG using the biological fluidized bed (BFB) technology was evaluated in this study. The primary goal was to provide an effective on-sitetreatment of spent glycol-based fluids to reduce their pollution loads. MATERIALS ANDMETHODS
Reactor Design. Two identical glass reactors wereoperated concurrently (Figure 2). Each reactorconsisted of a glasscolumn (I.D.: 4.8 em, length: 64 cm) withbottom cone and a I-L, enlargedtop compartment. The top compartment was used to: (I) receive the feed, (2) withdraw the recycle flow, and (3) house a dissolved oxygen (DO) probe, a pH probe. and a thermometer. The oxygen was transferred into the reactor using an aquarium air pump and an air diffuser, which was placed directly above the expanded media bed. This oxygenation design, in conjunction with the adjustment of the recycle rate, controlled the expansion of the media bed and the mean cell residence time (MCRT) by continuously removing the excessive biomass produced in the reactor. The reactors were located in the laboratory where the ambienttemperature was at 23±loC.
Experimental Design. 300 g Manville R-633 beadstaken from an aerobic BFB reactortreating a mixture of phenol and amines were evenly distributed between two reactors. Sitlce the particles were already coated with biofilms, they were directly fed with glycol solutions without furtherinoculation. Each reactorwas fed with a specificglycol solution but otherwise was operated under identical conditions. The expanded media bed volume was maintained at 1 L. Pure EO and PO liquids dilutedwith the mineral solution wereused to feed the reactors. The resulting mean feed total organic carbon (TOC)concentration was 65 mgIL (56-73 mgIL). The mineral solution contained excess nitrogen, phosphorus, and alkalinity (NaHCOy to insure healthy bacterial growth. In addition, trace elements such as calcium. cobalt, copper, iron, magnesium. and yeast extract were also provided in the mineral solution (Nguyen and Shieh, 1995). The experimental work was divided into two phases: steady-and transient-state phases which are described as follows.
Biologicall1uidized bed ueatment
147
• Steady-State Phase. The volumetric TOC loading. based on the expanded media bed. was used as the prime experimental variable. The loadings ranging from 0.15 to 0.88 g /L-day were used by varying the feed rate. As a result of this experimental design. the empty bed hydraulic retention time (HRT) varied from 1.7 to 10.0 hrs. The reactors were operated under given conditions until stable TOC removal was observed. Then daily samples were taken and analyzed for substrate utilization. biomass production. and biomass inventories following the procedures described in Standard Methods (1989) and elsewhere (Nguyen and Shieh. 1995). • Transient-State Phase. Single-pulse loadings were tested and the baseline loading was set at 0.15 gIL-day. The pulse magnitude was 10 times of the normal feed concentration. whereas two pulse durations were tested: 3 and 7 hrs. A number of samples were taken during and after a transient-state experiment and analyzed for TOC to permit detailed assessments of reactor responses. At the end of a transient-state experiment. the reactors were switched back to normal feed solutions for at least two weeks to restore their steady- state performance.
Figure2. Reactor flow scheme (not prepared to the exact scale).
RESULTS AND DISCUSSION
Steady.State Pluue. The addition of ISO g biofilm-coated media particles yielded approximately 12 g AVS (AVS: attached volatile solids) or 80 mg AVS/g media in each BFB reactor. As a result of these high immob ilized biomass inventories. the BFB reactors were acclimatized directly with glycol solutions at 0.15 g TOC/L-day without further inoculation. In spite of the different substrates utilized. the BFB reactors were capable of achieving >90% TOC removal within 10 days after reactor startup. and steady-state BFB effluent TOC concentrations were achieved shortly afterwards. Stable TOC removal was also achieved rapidly at higher TOC loadings with no noticeable delays. Figure 3 presents steady-state TOC utilization rates as a function of TOC loading rates. It is seen that >96% Toe removal could be sustained in aerobic BFB reactors at empty bed HRTs as short as 1.7 hrs. Therefore. the effectiveness of the aerobic BFB technology for the bioremediation of ethylene and propylene glycols was clearly demonstrated .
148
W. K. SHIEHet al,
The oxygenation in BFB reactors was effective under the loading conditions tested. The bulk- liquid DO concentrations were consistently >3.0 mgIL, indicating that DO was apparently not a limiting factor in the biodegradation of ethylene and propylene glycolsat TOC loadings as high as 0.88 g /L-day. 1.0 ~-----------~
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Figure3. Steady.slate TOe utilization ratesas a function ofTOC loadingrates.
The immobilized biomass inventories in BFB reactors were substantial and they increased with increasing TOe loadings (Figure 4). In contrast, the suspended biomass inventories in BFB reactors remained low withoutnoticeable increasesin spite of a 5-fold increase in TOC loadings. These observations confirmedthe ability of the porous media particles to retain the additional bacterial cells synthesized. As in the cases reported elsewhere(El-Farhan, 1994; Shieh and Hsu, 1996), >94%of total reactorbiomass inventories were immobilized. The variations of MCRTs with TOC loadings (Figure 4) also followed similar patterns reported elsewhere for BFB reactors (Chen et al., 1988; Li and Shieh, 1989). In this case, effective bioremediation of ethylene and propyleneglycolscould be achieved at MCRTsas low as 8 days. The MCRT is definedas:
where ec is the MCRT, days; X is the immobilized (attached) biomassconcentration in the expandedmedia bed, mg AVS (attachedvolatile solids)/L; V is the expandedmediabed volume, L; Q is the feed rate, Uday; and Xc is the suspendedbiomassconcentration in the reactor,mg MLVSS (mixed liquor volatile suspended solids)/L. Transient-State Phase. The responses of BFB reactorssubjectedto sin·gle-pulse loadingswere evaluated by comparing the measured effluent TOC concentrations with those predicted by CFSTR (continuous-flow, stirred-tank reactor) dilution curves. The CFSTR dilution curves were prepared by assuming that the additional TOC added in a single-pulse loading is not utilized, and that the aqueous phase is completely mixed. Therefore,
where C(t) is the effluent TOC concentration, mg/L; Co is the TOC pulse magnitude, mg/L; t is the time, min; e is the empty bed HRT, min; and t. is the TOC pulse duration, min. C(t,> in Eq, (3) is calculatedby substituting t by Is in Eq. (2). Figure 5 presentsthe transient-state data.
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Figure4. Biomass inventories and MCRTs as a functionof TOe loadingrates.
In spite of a pulse magnitude which was 10 times the normal feed TOe concentration. no discernible adverse effects on BFB reactors could be observed when the pulse duration was 3 hrs. The effluent TOe concentrations increased to slightly >30 mgIL when the pulse loading was terminated, and the BFB reactors fuIly recovered within 4 hrs. Approximately 94% of the additional TOe added was removed (PO-fed BFB reactor: 209 mg added vs. 194 mg removed; EO-fed BFB reactor: 186 mg added vs. 176 mg removed). indicating that the immobilized cells in BFB reactors were highly active to facilitate rapid biodegradation of the extra amounts of glycols added. Moreover. the completely mixed conditions attained in BFB reactors by means of effluent recirculation at high rates also helped to mitigate the negative impacts of a pulse loading. By comparison. according to predictions by CFSTR dilution curves. the effluent TOC concentrations should have increased to >150 mgIL when the pulse loading was terminated, and it would have taken >36 hrs for BFB reactors to fully recover. The oxygenation design of the BFB reactors was sufficiently effective to meet the extra oxygen demands brought about by greater bacterial activities during the 3-hr pulse duration. The bulk- liquid DO concentrations in BFB reactors during the pulse duration remained stable at 6.8-7.3 mgIL which were virtually identical to their steady-state values.
150
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As would be expected. the increases in BFB effluent TOe concentrations were more noticeable when the pulse duration was increased to 7 hrs, However, the magnitudes of these increases were <50% of those predicted by CFSTR dilution curves, indicating that glycol utilization still proceeded at discernible rates in BFB reactors. Moreover, it took <9 hrs for BFB reactors to fully recover from this 7-hr pulse loading,
W. K. SHIEH et al,
152
whereas the predicted recovery time would have exceeded 40 hrs. The PG-fed BFB reactor achieved 87% removal of the additional TOC added whereas the corresponding TOC removal for the EG-fedBFB reactor was 90%. The lower removal efficiency observed in the PG-fedBFB reactorcould be the result of a greater pulsemagnitude imposed(i.e.•a 12·foldincrease instead of a planned Io-fold increase). The oxygenation design of the BFB reactors was apparently less satisfactory for the 7-hr pulse loading and the bulk-liquid DO concentrations dropped to slightly above 3 mgIL during the pulse duration. Once the pulse loading was removed. however. the bulk-liquid DO concentrations increased and back to their respective steady-state valueswithin6 hrs. In summary. the added BFB processstabilityshown during pulse loadings could be attributable to the high immobilized biomass inventories and the long MCRTs attained in reactors. The high recycle rates used also helpedto mitigatethe negative impacts of pulse loadings. CONCLUSIONS The aerobic BFB reactors using porous media particles were demonstrated to be highly effective for the bioremediation of ethylene and propylene glycols. Under the steady- state conditions tested. the BFB reactors were capable of achieving 96% TOC removal at empty bed HRTs as short as 1.7 hrs and at TOC loadings as high as 0.88 gIL-day. Morethan 94% of total reactorbiomass inventories were immobilized. indicating that porousmedia particles werecapableof retaining the additional bacterial cells synthesized. The aerobic BFB reactors were demonstrated to be capableof sustaining good TOC removal during singlepulse loadings with a pulse magnitude of 10 times of the normal feed concentration and pulse durations as long as 7 hrs. No discernible adverseeffectscould be observed and >&7% of the additional TOC added was removed. The recovery of BFB reactors from single-pulse loadings wasprompt. The addedBFB process stability shownduring pulse loadings could be attributable to the high immobilized biomass inventories and the long MCRTs attained in reactors. The high recycle rates used also helped to mitigate the negativeimpactsof pulse loadings. ACKNOWLEDGMENT This project was supported by the U.s. Air Force (F336I6-94-C-S800) and the U.S. Army (CREUCRDAlCPAR). The paper has not been reviewed by the funding agencies and the views expressed are solely those of the authors. No officialendorsements shouldbe inferred. REFERENCES Chen. S. J.• Li, C. T. and Shieh, W. K. (\988). Anaerobic fluidized bed treatment of an industrial wastewater. J. Wat. Poitut. Control Fed.. 60.1826-1832. EI-Farhan. M. H. (1994). Perfonnance and kinetics of anaerobic reactors duringsteady state and transient stale operation. Ph.D. Dissertation. Universityof Pennsylvania, Philadelphia, Pennsylvania. Haines. J. R. andAlexander. M. (1975). Microbial degradation of polyethylene glycols. App~ Microbiol••29, 621-6~ . Jerger. D. E. and Flatman, P. E. (1990). In situ biological lrcatment of ethylene glycol-conteminated ground water and soil at Naval Air Engineering Center. Lakehurst, New Jersey. Presented at the 83rd Annual Meeting of the Air and Waste Management Association. Pittsburgh. Pennsylvania. U. C. T. and Shieh. W. K. (1989). Perfonnance and kinetics of aerated fluidized bed biofilm reactor. J. Env. Eng. Div., ASCE. 114.639-654. MacDonald. D. D.• Cuthbert, I. D. and Outridge. P. M. (1992). Canadian environmental quality guidelines for three glycols used in aircraft de-icingtanti-icing fluids: ethylene glycol; diethylene glycol; and propylene glycol. Report prepared for Environmenl Canadaand Transpon Canada.
Biological fluidized bed treatment
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Majewski. H. S.• Klaverkamp, J. F. and Scott, D. P. (1978). Acute lethality. and sub-lethal effects of acetone. ethanol. and propyleneglycol on the cardiovascular and respiratory systemsof rainbow trout (Salmo gairdnen). Wat. Res., 13, 217221. Mayer.D.• MichitschJ. and Yu, R. (1986). Groundaircraftdeicingtechnology review. ReportDOTIFAAICT-85-21. Department of Transport. FederalAviation Administration Technology Center.Atlantic City. New Jersey, Miller. L. M. (1979). Investigation of selected potential environmental contaminants: ethylene glycol. propylene glycols and butyleneglycols.NTISReportPB80-109119. FranklinResearch Center.Pennsylvania. Nguyen. V. T. and Shieh. W. K. (1975). Evaluation of intrinsic and inhibition kinetics in biological flautist bed reactors. Wat. Res., 29. 2520-2524. Rai, D. and Franklin. W. T. (1978).Effectof moisturecontenton ethyleneglycolretentionby clay minerals. Goederma, 21. 7579. Schink, B. and Stieb, M. (1983). Fermentation degradation of propylene glycol by a strictly anaerobic. gram-negative. nonsporeforming bacterium. Pelobacter venetianus sp. nov. AppL Environ. Microbiol••45. 1905-1913. Schultz, M. and Comerton, L. T. (1974). Effect of aircraftdeicer on airport storm runoff. J. Wat. Pollut. Control Fed., 46. 173180. Shieh.W. K. and Hsu, Y. (1996).Biomassloss from an anaerobic fluidized bed reactor. Wat. Res.• 30. 1253-1257 Standard Methods for the Exmnination of Water and Wastewater. 17th Edition. APHA- AWWA-WPCF. Washington. D.C. (1989). Verschueren, K. (1985). Handbook of Environmental Data on Organic Chemicals. Second. Edition. Van Nostrand Reinhold Company. New York, NewYork(1985).
Pergamon
Wal. Sci. Tecla. Vol. 38. No.
PH:S0273-1223(98)OO523-X
4-,. pp. 14'-"3. 1998.
1AWQ C 1998 Published byElsevier Science Ltd. Printedin Great Britain.All righlareserved 0273-1223/98 S19'00 + 0'00
BIOLOGICAL FLUIDIZED BED TREATMENT OF ETHYLENE AND PROPYLENE GLYCOLS Wen K. Shieh, John A. Lepore and Iraj Zandi Department ofSystems Engineering, University ofPennsylvania Philadelphia, Pennsylvania 19104-6315. USA
ABSTRACf The bioremediation of ethylene and propylene glycols using the aerobic biological fluidized bed (BFB)
technology is evaluated. Under the steady-state conditions tested,the BFB reactors are capable of achieving good TOe removal(i.e.•>96%) at empty bed HRTsas short as 1.7 hrs and at TOe loadingsas high as 0.88 g/L-day.In addition. the BFB reactors are also capableof sustaining good TOe removal (i.e.• >87%) during single-pulse loadings with a IQ-fold increasein pulse magnitude and pulse durations as long as 7 hrs. The observed BFB processefficiency and stabilityare attributable to the high immobilized biomass inventories attainedin reactors by using porousmedia panicles for cell immobilization and retention. C 1998 Published by ElsevierScience Ltd. All rightsreserved
KEYWORDS Deicing; fluidized bed; glycols; immobilized cells;transient-state. INTRODUcnON Glycol-based fluids are commonly used to remove ice, snow, and frost from aircraft, and to curtail their accumulation in order to insure air transport safety in cold weather (MacDonald et al., 1992; Mayer et al., 1986). Ethylene glycol (EG)-based fluids are the most common deicing/anti-icing fluids used in North America(MacDonald et al., 1992). An alternative is propylene glycol (PG)-based fluids which are less toxic (e.g., LDso in laboratory rats: 8.54 g/kg for EO and 30.0 g/kg for PG) and have lower freeZing points (MacDonald et al., 1992; Majewski et al., 1978). Under most environmental conditions glycols are not volatile because of their low vapor pressures (Verschueren, 1985). In addition, partition of glycols into the biotic and solid phases are unlikely because of their low Kow values (Miller, 1979; Rai and Franklin, 1978). On the other hand, glycols are susceptible to biodegradation (Haines and Alexander, 1975; Jerger and Flatman, 1990; MacDonald et al., 1992; Schink and Stieb, 1983), and the long- term biochemical oxygen demand(BOD)exertions of thesefluidsobserved in this studyare rapidand substantial (Figure 1). It has been estimated that up to 80% of the glycol-based fluids applied are left on tarmacs and runways which may be washed away by airport storm runoff (MacDonald et al., 1992; Mayer et al., 1986; Schultz and Comerton, 1974). As a result, large quantities of spentfluids could be spilled into receiving waters over short periodsof time. The primaryimpacts of glycol spills are on the oxygeninventories of receivingwaters 145
146
W. K.SHIEH et aI.
as well as on aquatic organisms (MacDonald, et al., 1992). The spent fluids may also be collected, stored, and treated on-site and then released into municipal wastewater treatment plants for further treatment, or discharged directly into receiving waters. 1200 ...----------~~"'" 00 000 0 0 00 0 1100
o
1000
o
IlOO
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0
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PropyleneGlycol Elhylene Glycol
I
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200
100
00---.--.-..--.---.--.-..--.---.--1 o
2
4
e
e
10
12
14
1& Ie
20
Time (deya)
Figure I. Long-term BODcurvesof ethylene and propylene glycols.
The treatability of EO and PG using the biological fluidized bed (BFB) technology was evaluated in this study. The primary goal was to provide an effective on-sitetreatment of spent glycol-based fluids to reduce their pollution loads. MATERIALS ANDMETHODS
Reactor Design. Two identical glass reactors wereoperated concurrently (Figure 2). Each reactorconsisted of a glasscolumn (I.D.: 4.8 em, length: 64 cm) withbottom cone and a I-L, enlargedtop compartment. The top compartment was used to: (I) receive the feed, (2) withdraw the recycle flow, and (3) house a dissolved oxygen (DO) probe, a pH probe. and a thermometer. The oxygen was transferred into the reactor using an aquarium air pump and an air diffuser, which was placed directly above the expanded media bed. This oxygenation design, in conjunction with the adjustment of the recycle rate, controlled the expansion of the media bed and the mean cell residence time (MCRT) by continuously removing the excessive biomass produced in the reactor. The reactors were located in the laboratory where the ambienttemperature was at 23±loC.
Experimental Design. 300 g Manville R-633 beadstaken from an aerobic BFB reactortreating a mixture of phenol and amines were evenly distributed between two reactors. Sitlce the particles were already coated with biofilms, they were directly fed with glycol solutions without furtherinoculation. Each reactorwas fed with a specificglycol solution but otherwise was operated under identical conditions. The expanded media bed volume was maintained at 1 L. Pure EO and PO liquids dilutedwith the mineral solution wereused to feed the reactors. The resulting mean feed total organic carbon (TOC)concentration was 65 mgIL (56-73 mgIL). The mineral solution contained excess nitrogen, phosphorus, and alkalinity (NaHCOy to insure healthy bacterial growth. In addition, trace elements such as calcium. cobalt, copper, iron, magnesium. and yeast extract were also provided in the mineral solution (Nguyen and Shieh, 1995). The experimental work was divided into two phases: steady-and transient-state phases which are described as follows.
Biologicall1uidized bed ueatment
147
• Steady-State Phase. The volumetric TOC loading. based on the expanded media bed. was used as the prime experimental variable. The loadings ranging from 0.15 to 0.88 g /L-day were used by varying the feed rate. As a result of this experimental design. the empty bed hydraulic retention time (HRT) varied from 1.7 to 10.0 hrs. The reactors were operated under given conditions until stable TOC removal was observed. Then daily samples were taken and analyzed for substrate utilization. biomass production. and biomass inventories following the procedures described in Standard Methods (1989) and elsewhere (Nguyen and Shieh. 1995). • Transient-State Phase. Single-pulse loadings were tested and the baseline loading was set at 0.15 gIL-day. The pulse magnitude was 10 times of the normal feed concentration. whereas two pulse durations were tested: 3 and 7 hrs. A number of samples were taken during and after a transient-state experiment and analyzed for TOC to permit detailed assessments of reactor responses. At the end of a transient-state experiment. the reactors were switched back to normal feed solutions for at least two weeks to restore their steady- state performance.
Figure2. Reactor flow scheme (not prepared to the exact scale).
RESULTS AND DISCUSSION
Steady.State Pluue. The addition of ISO g biofilm-coated media particles yielded approximately 12 g AVS (AVS: attached volatile solids) or 80 mg AVS/g media in each BFB reactor. As a result of these high immob ilized biomass inventories. the BFB reactors were acclimatized directly with glycol solutions at 0.15 g TOC/L-day without further inoculation. In spite of the different substrates utilized. the BFB reactors were capable of achieving >90% TOC removal within 10 days after reactor startup. and steady-state BFB effluent TOC concentrations were achieved shortly afterwards. Stable TOC removal was also achieved rapidly at higher TOC loadings with no noticeable delays. Figure 3 presents steady-state TOC utilization rates as a function of TOC loading rates. It is seen that >96% Toe removal could be sustained in aerobic BFB reactors at empty bed HRTs as short as 1.7 hrs. Therefore. the effectiveness of the aerobic BFB technology for the bioremediation of ethylene and propylene glycols was clearly demonstrated .
148
W. K. SHIEHet al,
The oxygenation in BFB reactors was effective under the loading conditions tested. The bulk- liquid DO concentrations were consistently >3.0 mgIL, indicating that DO was apparently not a limiting factor in the biodegradation of ethylene and propylene glycolsat TOC loadings as high as 0.88 g /L-day. 1.0 ~-----------~
01
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02 0.1
01
0.2 0.3
0.4 05
05
0.7 0.5
0.'
10
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Figure3. Steady.slate TOe utilization ratesas a function ofTOC loadingrates.
The immobilized biomass inventories in BFB reactors were substantial and they increased with increasing TOe loadings (Figure 4). In contrast, the suspended biomass inventories in BFB reactors remained low withoutnoticeable increasesin spite of a 5-fold increase in TOC loadings. These observations confirmedthe ability of the porous media particles to retain the additional bacterial cells synthesized. As in the cases reported elsewhere(El-Farhan, 1994; Shieh and Hsu, 1996), >94%of total reactorbiomass inventories were immobilized. The variations of MCRTs with TOC loadings (Figure 4) also followed similar patterns reported elsewhere for BFB reactors (Chen et al., 1988; Li and Shieh, 1989). In this case, effective bioremediation of ethylene and propyleneglycolscould be achieved at MCRTsas low as 8 days. The MCRT is definedas:
where ec is the MCRT, days; X is the immobilized (attached) biomassconcentration in the expandedmedia bed, mg AVS (attachedvolatile solids)/L; V is the expandedmediabed volume, L; Q is the feed rate, Uday; and Xc is the suspendedbiomassconcentration in the reactor,mg MLVSS (mixed liquor volatile suspended solids)/L. Transient-State Phase. The responses of BFB reactorssubjectedto sin·gle-pulse loadingswere evaluated by comparing the measured effluent TOC concentrations with those predicted by CFSTR (continuous-flow, stirred-tank reactor) dilution curves. The CFSTR dilution curves were prepared by assuming that the additional TOC added in a single-pulse loading is not utilized, and that the aqueous phase is completely mixed. Therefore,
where C(t) is the effluent TOC concentration, mg/L; Co is the TOC pulse magnitude, mg/L; t is the time, min; e is the empty bed HRT, min; and t. is the TOC pulse duration, min. C(t,> in Eq, (3) is calculatedby substituting t by Is in Eq. (2). Figure 5 presentsthe transient-state data.
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Figure4. Biomass inventories and MCRTs as a functionof TOe loadingrates.
In spite of a pulse magnitude which was 10 times the normal feed TOe concentration. no discernible adverse effects on BFB reactors could be observed when the pulse duration was 3 hrs. The effluent TOe concentrations increased to slightly >30 mgIL when the pulse loading was terminated, and the BFB reactors fuIly recovered within 4 hrs. Approximately 94% of the additional TOe added was removed (PO-fed BFB reactor: 209 mg added vs. 194 mg removed; EO-fed BFB reactor: 186 mg added vs. 176 mg removed). indicating that the immobilized cells in BFB reactors were highly active to facilitate rapid biodegradation of the extra amounts of glycols added. Moreover. the completely mixed conditions attained in BFB reactors by means of effluent recirculation at high rates also helped to mitigate the negative impacts of a pulse loading. By comparison. according to predictions by CFSTR dilution curves. the effluent TOC concentrations should have increased to >150 mgIL when the pulse loading was terminated, and it would have taken >36 hrs for BFB reactors to fully recover. The oxygenation design of the BFB reactors was sufficiently effective to meet the extra oxygen demands brought about by greater bacterial activities during the 3-hr pulse duration. The bulk- liquid DO concentrations in BFB reactors during the pulse duration remained stable at 6.8-7.3 mgIL which were virtually identical to their steady-state values.
150
W. K. SHIEH et al.
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Biological fluidized bed treatment
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As would be expected. the increases in BFB effluent TOe concentrations were more noticeable when the pulse duration was increased to 7 hrs, However, the magnitudes of these increases were <50% of those predicted by CFSTR dilution curves, indicating that glycol utilization still proceeded at discernible rates in BFB reactors. Moreover, it took <9 hrs for BFB reactors to fully recover from this 7-hr pulse loading,
W. K. SHIEH et al,
152
whereas the predicted recovery time would have exceeded 40 hrs. The PG-fed BFB reactor achieved 87% removal of the additional TOC added whereas the corresponding TOC removal for the EG-fedBFB reactor was 90%. The lower removal efficiency observed in the PG-fedBFB reactorcould be the result of a greater pulsemagnitude imposed(i.e.•a 12·foldincrease instead of a planned Io-fold increase). The oxygenation design of the BFB reactors was apparently less satisfactory for the 7-hr pulse loading and the bulk-liquid DO concentrations dropped to slightly above 3 mgIL during the pulse duration. Once the pulse loading was removed. however. the bulk-liquid DO concentrations increased and back to their respective steady-state valueswithin6 hrs. In summary. the added BFB processstabilityshown during pulse loadings could be attributable to the high immobilized biomass inventories and the long MCRTs attained in reactors. The high recycle rates used also helpedto mitigatethe negative impacts of pulse loadings. CONCLUSIONS The aerobic BFB reactors using porous media particles were demonstrated to be highly effective for the bioremediation of ethylene and propylene glycols. Under the steady- state conditions tested. the BFB reactors were capable of achieving 96% TOC removal at empty bed HRTs as short as 1.7 hrs and at TOC loadings as high as 0.88 gIL-day. Morethan 94% of total reactorbiomass inventories were immobilized. indicating that porousmedia particles werecapableof retaining the additional bacterial cells synthesized. The aerobic BFB reactors were demonstrated to be capableof sustaining good TOC removal during singlepulse loadings with a pulse magnitude of 10 times of the normal feed concentration and pulse durations as long as 7 hrs. No discernible adverseeffectscould be observed and >&7% of the additional TOC added was removed. The recovery of BFB reactors from single-pulse loadings wasprompt. The addedBFB process stability shownduring pulse loadings could be attributable to the high immobilized biomass inventories and the long MCRTs attained in reactors. The high recycle rates used also helped to mitigate the negativeimpactsof pulse loadings. ACKNOWLEDGMENT This project was supported by the U.s. Air Force (F336I6-94-C-S800) and the U.S. Army (CREUCRDAlCPAR). The paper has not been reviewed by the funding agencies and the views expressed are solely those of the authors. No officialendorsements shouldbe inferred. REFERENCES Chen. S. J.• Li, C. T. and Shieh, W. K. (\988). Anaerobic fluidized bed treatment of an industrial wastewater. J. Wat. Poitut. Control Fed.. 60.1826-1832. EI-Farhan. M. H. (1994). Perfonnance and kinetics of anaerobic reactors duringsteady state and transient stale operation. Ph.D. Dissertation. Universityof Pennsylvania, Philadelphia, Pennsylvania. Haines. J. R. andAlexander. M. (1975). Microbial degradation of polyethylene glycols. App~ Microbiol••29, 621-6~ . Jerger. D. E. and Flatman, P. E. (1990). In situ biological lrcatment of ethylene glycol-conteminated ground water and soil at Naval Air Engineering Center. Lakehurst, New Jersey. Presented at the 83rd Annual Meeting of the Air and Waste Management Association. Pittsburgh. Pennsylvania. U. C. T. and Shieh. W. K. (1989). Perfonnance and kinetics of aerated fluidized bed biofilm reactor. J. Env. Eng. Div., ASCE. 114.639-654. MacDonald. D. D.• Cuthbert, I. D. and Outridge. P. M. (1992). Canadian environmental quality guidelines for three glycols used in aircraft de-icingtanti-icing fluids: ethylene glycol; diethylene glycol; and propylene glycol. Report prepared for Environmenl Canadaand Transpon Canada.
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Majewski. H. S.• Klaverkamp, J. F. and Scott, D. P. (1978). Acute lethality. and sub-lethal effects of acetone. ethanol. and propyleneglycol on the cardiovascular and respiratory systemsof rainbow trout (Salmo gairdnen). Wat. Res., 13, 217221. Mayer.D.• MichitschJ. and Yu, R. (1986). Groundaircraftdeicingtechnology review. ReportDOTIFAAICT-85-21. Department of Transport. FederalAviation Administration Technology Center.Atlantic City. New Jersey, Miller. L. M. (1979). Investigation of selected potential environmental contaminants: ethylene glycol. propylene glycols and butyleneglycols.NTISReportPB80-109119. FranklinResearch Center.Pennsylvania. Nguyen. V. T. and Shieh. W. K. (1975). Evaluation of intrinsic and inhibition kinetics in biological flautist bed reactors. Wat. Res., 29. 2520-2524. Rai, D. and Franklin. W. T. (1978).Effectof moisturecontenton ethyleneglycolretentionby clay minerals. Goederma, 21. 7579. Schink, B. and Stieb, M. (1983). Fermentation degradation of propylene glycol by a strictly anaerobic. gram-negative. nonsporeforming bacterium. Pelobacter venetianus sp. nov. AppL Environ. Microbiol••45. 1905-1913. Schultz, M. and Comerton, L. T. (1974). Effect of aircraftdeicer on airport storm runoff. J. Wat. Pollut. Control Fed., 46. 173180. Shieh.W. K. and Hsu, Y. (1996).Biomassloss from an anaerobic fluidized bed reactor. Wat. Res.• 30. 1253-1257 Standard Methods for the Exmnination of Water and Wastewater. 17th Edition. APHA- AWWA-WPCF. Washington. D.C. (1989). Verschueren, K. (1985). Handbook of Environmental Data on Organic Chemicals. Second. Edition. Van Nostrand Reinhold Company. New York, NewYork(1985).