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Biodegradation of toluene by an attached biofilm in a rotating biological contactor
Process Biochemistry 36 (2001) 707– 711 www.elsevier.com/locate/procbio
Biodegradation of toluene by an attached biofilm in a rotating biological contactor I. Alemzadeh *, M. Vossoughi Biochemical and Bioen6ironmental Research Center, Sharif Uni6ersity of Technology, 11365 -6891 Tehran, Iran Received 2 February 2000; received in revised form 15 August 2000; accepted 26 August 2000
Abstract A laboratory scale study using a modified rotating biological contactor (RBC) was constructed to assess aerobic treatment of toluene, a typical aromatic hydrocarbon. The RBC consisted of 72 parallel discs rotating in a reservoir and was arranged in three stages, i.e. 24 discs oriented in each stage. An artificial wastewater containing toluene was fed to the RBC, inoculated with an enriched culture from petrochemical sewage. The rotation of the discs and the recycling time ensured good mixing of the bulk liquid and resulted in a regular biofilm thickness. Toluene removal was measured by COD measurement and GC. The effect of initial toluene concentration on toluene biodegradation showed a zero order mechanism. Adaptation of the biofilm to toluene results in higher COD removal at different stages. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Biodegradation; Biofilm; Biomass; RBC
1. Introduction Several kinds of wastewater have been treated or purified by the use of rotating discs contactors. Wastewaters treated with pilot scale or full scale plant originate from dairy, fermentations, poultry, slaughterhouse and meat processing. Available evidence suggests that the biological disc contactor is a promising aerobic process, which will be efficient under tropical conditions. Biological treatment technology for treating waste hydrocarbon is a favourable method and interest has focused on the application of suspended growth biological systems such as activated sludge process [1], but there is also a great potential for the application of attached growth, fixed film biological systems. The other choice for a aerobic fixed film process in wastewater treatment is the trickling filter. The rotating biological contactor (RBC) is efficient [2 – 4] and is attractive for low cost wastewater treatment because of short hydraulic retention times, excellent shock and toxic * Corresponding author.
loading capability, simple process control and low energy requirement. However, the RBC is not so suitable for the treatment of high strength wastewater due to moderate removal efficiencies. Many studies have focused on biodegradation of aromatic compounds under aerobic and anaerobic conditions [5–10]. Aromatic hydrocarbons are among the 50 largest volume industrial chemicals produced at the rate of annual production of million of tons [5,6]. These compounds are widely used as fuels and industrial solvent for painting and degreasing. They are also starting materials for the production of pharmaceutical agrochemicals and polymers. Toluene is a common hydrocarbon pollutant found in wastewater, polluted surface water and soil. The design of RBC for bio-restoration of oil contaminated aquifers is an opportunity to realize the mechanism of toluene degradation. Very little research has been done on the biodegradation of toluene and aromatic hydrocarbons in such systems. Many investigators have studied the kinetic of aromatic hydrocarbons biodegradation in sandy aquifers and fixed films [9,11 –13]. The purpose of this paper is to give an overview of toluene biodegradation in RBC under different conditions.
0032-9592/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 9 5 9 2 ( 0 0 ) 0 0 2 3 2 - 6
708
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711
Fig. 1. Schematic of RBC.
2. Materials and methods
2.1. Rotating biological contactor The schematic of RBC is illustrated in Fig. 1. The laboratory RBC used consisted of three stages each containing 24 parallel discs which were connected to a single stainless steel shaft, supported at both ends and rotated at 15 rpm. The specification of the RBC used is summarized in Table 1. An artificial wastewater consisted of (mg/l): Molasses, 130 –1200; NH4Cl 7 – 69; KH2PO4 3 – 34 as influent. Inoculation was achieved with an enriched culture from petrochemical sewage. The wastewater was fed into the RBC with a peristaltic pump. After 1 week, a thin biofilm was observed on the surface of the discs. After each steady state, wastewater amended with toluene in concentration steps 0 – 40 mg/l, was fed into the RBC. The average hydraulic loading was 0.0087 m3/m2/ day.
Fig. 2. Effect of organic loading on COD removal.
l aliquots taken from the pentane layer was injected into the GC, using heptane (6 mg/l) as an internal standard.
2.3. Biomass dry weight and O2 concentration 2.2. Analytical methods Estimation of toluene was performed with a gas chromatograph (Shimadzu GC.9A) equipped with an OV-1 column, 2 m and 1/8 in. and flame ionization detector, the temperature of injector, column, and detector were: 150, 25 – 30 and 220°C, respectively [5]. Extraction of toluene was carried out in a volumetric flask. The solution containing toluene with pentane as extractant was mixed vigorously for 2 min. A total of 1 Table 1 Summary of RBC
Measurement of the average biofilm thickness at different stages was performed to monitor biofilm growth. A small definite area of biofilm was scraped off from the periphery of the first and the last discs, followed by determination of the biomass dry weight per unit area and the average value was calculated. O2 concentration in wastewater and at different stages of RBC was analyzed, using a Solomet 520°C water quality monitor with DO detector 501 OX
3. Results and discussion
Specification
Value
Number of discs Number of stages Disc diameter (cm) Disc thickness (mm) Disc spacing (cm) Total surface area (cm2) Rotational speed Working volume (cm3) Submergence (%) Temperature (°C)
72 3 21 3 5 712.52 15 8200 40 20–30
3.1. Effect of loading on COD remo6al The effect of different organic loading on COD removal from wastewater without toluene is presented in Fig. 2. Loading from 1.56 to 10.6 g COD/m2/day result in COD removal, however the increase was more significant from 1.56 to 4.05 g COD/m2/day. At lower loading, COD removal was significant at stage 1, however at higher loading, other stages participated in COD reduction.
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711
709
Table 2 Variation of biomass attached on the discs surface under different hydraulic loading Hydraulic loading (m3/m2/day)
Average biomass dry weight (mg/cm2)
0.0020 0.0060 0.0073 0.0076 0.0085 0.0096 0.0098
0.20 0.30 1.40 2.00 2.20 2.40 2.40
Fig. 3. Effect of initial toluene concentration on toluene removal.
3.2. Effect of hydraulic loading on biomass
3.3. Effect of toluene concentration
The average attached biomass on the discs under different hydraulic loading is shown in Table 2. The concentration of attached biomass increased with hydraulic loading, which supplied increased nutrient to the biofilm.
The effect of initial concentration (1 mg/l) of toluene on average biomass dry weight attached on the discs and COD removal is presented in Table 3. Toluene addition loosened the biomass on the discs and initially resulted in a reduction of biomass. After 5 days
Fig. 4. COD removal from wastewater without and with toluene.
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711
710
3.4. Dissol6ed oxygen (DO) Dissolved oxygen in wastewater at different stages in the RBC, were measured by DO electrode in the presence (40 mg/l) and absence of toluene (Fig. 5). DO concentrations were lower than saturation levels, however these concentrations increased in the order of influent, stages 1–3 in the RBC. This result might be caused by inadequate mixing with rotating discs, poor respiration due to decrease of biofilm thickness in the order of stage. Active respiration in the initial stages might result in decrease in DO of the wastewater both with and without toluene.
Fig. 5. Dissolved oxygen in wastewater with and without toluene. Table 3 Effect of toluene concentration (1 mg/l) on biomass dry weight and COD removala Time (days)
Cell dry weight (mg/m2)
COD removal (%)
0 1 2 3 4 5 7 9 10
2.45 2.20 1.27 1.50 1.83 2.29 2.40 2.46 2.50
86.6 84.5 77.0 78.0 77.0 80.8 84.1 87.2 88.3
a
COD was 325 mg/l in the effluent.
when microbial adaptation to toluene was achieved, the COD removal was improved. The change in biofilm dry weight is the result of microbial adaptation to toluene and a stabilization phase, which took 7 days in this system. The effect of toluene concentration on toluene removal is shown in Fig. 3. Toluene measurement for each concentration was effected after stabilization of the system at defined concentration, after 7 – 9 days in this investigation. It is clear that increasing toluene concentrations produced a reduction in % toluene removal. Toluene removal at various toluene concentrations between 1 and 40 mg/l showed zero order reaction kinetics. COD removal from wastewater without toluene and with toluene (40 mg/l) under various COD loading conditions is presented in Fig. 4. In the presence of toluene, COD removal increased 4.5 – 5%, which could be due to biofilm growth under these conditions.
4. Conclusion Toluene biodegradation was studied in RBC system in an aerobic fixed film reactor. The system was first fed by a synthetic medium containing molasses and mineral salts. When the system reached the steady state, toluene addition, 1ppm was effected. Toluene addition resulted in cell loosening from the disc surfaces and decrease in COD removal %, before cell adaption was observed. After a lag period of 5 days, increase in COD removal was observed. Increasing toluene concentration up to 40 mg/l, toluene biodegradation presented a zero order reaction mechanism. Effect of different loading in the presence and absence of toluene, resulted in higher COD removal in the presence of toluene.
References [1] Du YG, Tyagi RD, Bhamidimarri R. Use of fuzzy neutral-net model for rule generation of activated sludge process. Process Biochem 1999;35:77– 83. [2] Clark JA, Moseng EM, Asano T. Performance of a RBC under varying wastewater flow. J Water Pollution Control Fed 1978;50:896– 911. [3] Hamoda MF, Abd-EI-Bary MF. Operating characteristics of aerated submerged fixed film (ASFF) bioreactor. Water Res 1987;21:939– 47. [4] Wu Y, Smith E. Rotating biological contactor system design, J Env Eng Div Am Soc Civ Eng 1982: 578– 588. [5] Acrangeli JP, Arvin E. Toluene biodegradation and biofilm growth in anaerobic fixed film reactor. Appl Microbiol Tech 1992;37:510– 7. [6] Acrangeli JP, Arvin E. Biodegradation rates of aromatic contaminants in biofilm reactor. Water Sci Tech 1995;31:117–28. [7] Acrangeli JP, Arvin E. Kinetics of toluene biodegradation in a biofilm system under denitrifying conditions. Water Sci Tech 1994;29:393– 400. [8] Alvarez PJJ, Vogel TM. Substrate interaction of benzene, toluene and para-xylene during microbial degradation by pure culture and mixed culture. Aquifer slurries. Environ Microbiol 1991;57:2981– 5. [9] Alvarez PJJ, Anid PJ, Vogel TM. Kinetics of aerobic biodegradation of benzene and toluene in sandy aquifer material.
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711 Biodegradation 1991;2:43–51. [10] Clozick R, Irvine RL. Preliminary studies on the granular activated carbon sequencing batch biofilm reactor. Environ Prog 1991;10:282– 9. [11] Tyagi RD. Biological treatment of refinery wastewater, In: Martin AM, editor. London: Elsevier, 1991. p. 323–340.
.
711
[12] Tyagi RD, Tran FT, Chowdhury AKM. Biodegradation of petroleum refinery wastewater in a modified rotating biological contactor with polyurethane foam attached to the discs. Water Res 1993;27:91– 9. [13] Bouwer EJ, Chen CT, Li YH. Transformation of a petroleum mixture in biofilm. Water Sci Tech 1992;26(637):280– 8.
Biodegradation of toluene by an attached biofilm in a rotating biological contactor I. Alemzadeh *, M. Vossoughi Biochemical and Bioen6ironmental Research Center, Sharif Uni6ersity of Technology, 11365 -6891 Tehran, Iran Received 2 February 2000; received in revised form 15 August 2000; accepted 26 August 2000
Abstract A laboratory scale study using a modified rotating biological contactor (RBC) was constructed to assess aerobic treatment of toluene, a typical aromatic hydrocarbon. The RBC consisted of 72 parallel discs rotating in a reservoir and was arranged in three stages, i.e. 24 discs oriented in each stage. An artificial wastewater containing toluene was fed to the RBC, inoculated with an enriched culture from petrochemical sewage. The rotation of the discs and the recycling time ensured good mixing of the bulk liquid and resulted in a regular biofilm thickness. Toluene removal was measured by COD measurement and GC. The effect of initial toluene concentration on toluene biodegradation showed a zero order mechanism. Adaptation of the biofilm to toluene results in higher COD removal at different stages. © 2001 Elsevier Science Ltd. All rights reserved. Keywords: Biodegradation; Biofilm; Biomass; RBC
1. Introduction Several kinds of wastewater have been treated or purified by the use of rotating discs contactors. Wastewaters treated with pilot scale or full scale plant originate from dairy, fermentations, poultry, slaughterhouse and meat processing. Available evidence suggests that the biological disc contactor is a promising aerobic process, which will be efficient under tropical conditions. Biological treatment technology for treating waste hydrocarbon is a favourable method and interest has focused on the application of suspended growth biological systems such as activated sludge process [1], but there is also a great potential for the application of attached growth, fixed film biological systems. The other choice for a aerobic fixed film process in wastewater treatment is the trickling filter. The rotating biological contactor (RBC) is efficient [2 – 4] and is attractive for low cost wastewater treatment because of short hydraulic retention times, excellent shock and toxic * Corresponding author.
loading capability, simple process control and low energy requirement. However, the RBC is not so suitable for the treatment of high strength wastewater due to moderate removal efficiencies. Many studies have focused on biodegradation of aromatic compounds under aerobic and anaerobic conditions [5–10]. Aromatic hydrocarbons are among the 50 largest volume industrial chemicals produced at the rate of annual production of million of tons [5,6]. These compounds are widely used as fuels and industrial solvent for painting and degreasing. They are also starting materials for the production of pharmaceutical agrochemicals and polymers. Toluene is a common hydrocarbon pollutant found in wastewater, polluted surface water and soil. The design of RBC for bio-restoration of oil contaminated aquifers is an opportunity to realize the mechanism of toluene degradation. Very little research has been done on the biodegradation of toluene and aromatic hydrocarbons in such systems. Many investigators have studied the kinetic of aromatic hydrocarbons biodegradation in sandy aquifers and fixed films [9,11 –13]. The purpose of this paper is to give an overview of toluene biodegradation in RBC under different conditions.
0032-9592/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 3 2 - 9 5 9 2 ( 0 0 ) 0 0 2 3 2 - 6
708
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711
Fig. 1. Schematic of RBC.
2. Materials and methods
2.1. Rotating biological contactor The schematic of RBC is illustrated in Fig. 1. The laboratory RBC used consisted of three stages each containing 24 parallel discs which were connected to a single stainless steel shaft, supported at both ends and rotated at 15 rpm. The specification of the RBC used is summarized in Table 1. An artificial wastewater consisted of (mg/l): Molasses, 130 –1200; NH4Cl 7 – 69; KH2PO4 3 – 34 as influent. Inoculation was achieved with an enriched culture from petrochemical sewage. The wastewater was fed into the RBC with a peristaltic pump. After 1 week, a thin biofilm was observed on the surface of the discs. After each steady state, wastewater amended with toluene in concentration steps 0 – 40 mg/l, was fed into the RBC. The average hydraulic loading was 0.0087 m3/m2/ day.
Fig. 2. Effect of organic loading on COD removal.
l aliquots taken from the pentane layer was injected into the GC, using heptane (6 mg/l) as an internal standard.
2.3. Biomass dry weight and O2 concentration 2.2. Analytical methods Estimation of toluene was performed with a gas chromatograph (Shimadzu GC.9A) equipped with an OV-1 column, 2 m and 1/8 in. and flame ionization detector, the temperature of injector, column, and detector were: 150, 25 – 30 and 220°C, respectively [5]. Extraction of toluene was carried out in a volumetric flask. The solution containing toluene with pentane as extractant was mixed vigorously for 2 min. A total of 1 Table 1 Summary of RBC
Measurement of the average biofilm thickness at different stages was performed to monitor biofilm growth. A small definite area of biofilm was scraped off from the periphery of the first and the last discs, followed by determination of the biomass dry weight per unit area and the average value was calculated. O2 concentration in wastewater and at different stages of RBC was analyzed, using a Solomet 520°C water quality monitor with DO detector 501 OX
3. Results and discussion
Specification
Value
Number of discs Number of stages Disc diameter (cm) Disc thickness (mm) Disc spacing (cm) Total surface area (cm2) Rotational speed Working volume (cm3) Submergence (%) Temperature (°C)
72 3 21 3 5 712.52 15 8200 40 20–30
3.1. Effect of loading on COD remo6al The effect of different organic loading on COD removal from wastewater without toluene is presented in Fig. 2. Loading from 1.56 to 10.6 g COD/m2/day result in COD removal, however the increase was more significant from 1.56 to 4.05 g COD/m2/day. At lower loading, COD removal was significant at stage 1, however at higher loading, other stages participated in COD reduction.
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711
709
Table 2 Variation of biomass attached on the discs surface under different hydraulic loading Hydraulic loading (m3/m2/day)
Average biomass dry weight (mg/cm2)
0.0020 0.0060 0.0073 0.0076 0.0085 0.0096 0.0098
0.20 0.30 1.40 2.00 2.20 2.40 2.40
Fig. 3. Effect of initial toluene concentration on toluene removal.
3.2. Effect of hydraulic loading on biomass
3.3. Effect of toluene concentration
The average attached biomass on the discs under different hydraulic loading is shown in Table 2. The concentration of attached biomass increased with hydraulic loading, which supplied increased nutrient to the biofilm.
The effect of initial concentration (1 mg/l) of toluene on average biomass dry weight attached on the discs and COD removal is presented in Table 3. Toluene addition loosened the biomass on the discs and initially resulted in a reduction of biomass. After 5 days
Fig. 4. COD removal from wastewater without and with toluene.
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711
710
3.4. Dissol6ed oxygen (DO) Dissolved oxygen in wastewater at different stages in the RBC, were measured by DO electrode in the presence (40 mg/l) and absence of toluene (Fig. 5). DO concentrations were lower than saturation levels, however these concentrations increased in the order of influent, stages 1–3 in the RBC. This result might be caused by inadequate mixing with rotating discs, poor respiration due to decrease of biofilm thickness in the order of stage. Active respiration in the initial stages might result in decrease in DO of the wastewater both with and without toluene.
Fig. 5. Dissolved oxygen in wastewater with and without toluene. Table 3 Effect of toluene concentration (1 mg/l) on biomass dry weight and COD removala Time (days)
Cell dry weight (mg/m2)
COD removal (%)
0 1 2 3 4 5 7 9 10
2.45 2.20 1.27 1.50 1.83 2.29 2.40 2.46 2.50
86.6 84.5 77.0 78.0 77.0 80.8 84.1 87.2 88.3
a
COD was 325 mg/l in the effluent.
when microbial adaptation to toluene was achieved, the COD removal was improved. The change in biofilm dry weight is the result of microbial adaptation to toluene and a stabilization phase, which took 7 days in this system. The effect of toluene concentration on toluene removal is shown in Fig. 3. Toluene measurement for each concentration was effected after stabilization of the system at defined concentration, after 7 – 9 days in this investigation. It is clear that increasing toluene concentrations produced a reduction in % toluene removal. Toluene removal at various toluene concentrations between 1 and 40 mg/l showed zero order reaction kinetics. COD removal from wastewater without toluene and with toluene (40 mg/l) under various COD loading conditions is presented in Fig. 4. In the presence of toluene, COD removal increased 4.5 – 5%, which could be due to biofilm growth under these conditions.
4. Conclusion Toluene biodegradation was studied in RBC system in an aerobic fixed film reactor. The system was first fed by a synthetic medium containing molasses and mineral salts. When the system reached the steady state, toluene addition, 1ppm was effected. Toluene addition resulted in cell loosening from the disc surfaces and decrease in COD removal %, before cell adaption was observed. After a lag period of 5 days, increase in COD removal was observed. Increasing toluene concentration up to 40 mg/l, toluene biodegradation presented a zero order reaction mechanism. Effect of different loading in the presence and absence of toluene, resulted in higher COD removal in the presence of toluene.
References [1] Du YG, Tyagi RD, Bhamidimarri R. Use of fuzzy neutral-net model for rule generation of activated sludge process. Process Biochem 1999;35:77– 83. [2] Clark JA, Moseng EM, Asano T. Performance of a RBC under varying wastewater flow. J Water Pollution Control Fed 1978;50:896– 911. [3] Hamoda MF, Abd-EI-Bary MF. Operating characteristics of aerated submerged fixed film (ASFF) bioreactor. Water Res 1987;21:939– 47. [4] Wu Y, Smith E. Rotating biological contactor system design, J Env Eng Div Am Soc Civ Eng 1982: 578– 588. [5] Acrangeli JP, Arvin E. Toluene biodegradation and biofilm growth in anaerobic fixed film reactor. Appl Microbiol Tech 1992;37:510– 7. [6] Acrangeli JP, Arvin E. Biodegradation rates of aromatic contaminants in biofilm reactor. Water Sci Tech 1995;31:117–28. [7] Acrangeli JP, Arvin E. Kinetics of toluene biodegradation in a biofilm system under denitrifying conditions. Water Sci Tech 1994;29:393– 400. [8] Alvarez PJJ, Vogel TM. Substrate interaction of benzene, toluene and para-xylene during microbial degradation by pure culture and mixed culture. Aquifer slurries. Environ Microbiol 1991;57:2981– 5. [9] Alvarez PJJ, Anid PJ, Vogel TM. Kinetics of aerobic biodegradation of benzene and toluene in sandy aquifer material.
I. Alemzadeh, M. Vossoughi / Process Biochemistry 36 (2001) 707–711 Biodegradation 1991;2:43–51. [10] Clozick R, Irvine RL. Preliminary studies on the granular activated carbon sequencing batch biofilm reactor. Environ Prog 1991;10:282– 9. [11] Tyagi RD. Biological treatment of refinery wastewater, In: Martin AM, editor. London: Elsevier, 1991. p. 323–340.
.
711
[12] Tyagi RD, Tran FT, Chowdhury AKM. Biodegradation of petroleum refinery wastewater in a modified rotating biological contactor with polyurethane foam attached to the discs. Water Res 1993;27:91– 9. [13] Bouwer EJ, Chen CT, Li YH. Transformation of a petroleum mixture in biofilm. Water Sci Tech 1992;26(637):280– 8.