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Immobilized marine algal biomass for multiple cycles of copper adsorption and desorption
Separation and Purification Technology 19 (2000) 39 – 42 www.elsevier.com/locate/seppur
Immobilized marine algal biomass for multiple cycles of copper adsorption and desorption M.A. Hashim *, H.N. Tan, K.H. Chu Institute of Postgraduate Studies and Research, Uni6ersity of Malaya, 50603 Kuala Lumpur, Malaysia Received 24 September 1999; accepted 15 November 1999
Abstract The biomass of a marine alga, Sargassum baccularia, was immobilized by using polyvinyl alcohol as the polymeric matrix. The reusability of the immobilized biomass was studied by using copper as the model metal ion in five consecutive cycles of adsorption–desorption. Hydrochloric acid at pH 1.0 and ethylenediaminetetraacetic acid (EDTA) solution at 2 mM were used as the desorbing agents. Both desorbents were effective in stripping the adsorbed copper from the immobilized biomass over the five cycles. However, copper uptake in Cycles 2 – 5 was lower than that in Cycle 1, indicating that the two desorbing agents limited the reuse potential of the immobilized biomass in multiple cycles of adsorption–desorption. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Immobilized; Algal; Copper; Adsorption; Desorption
1. Introduction Marine algae have shown impressive binding capacities for a wide range of heavy metals [1]. However, the fragile biomass of the marine algae is not suitable for robust wastewater treatment operations [2]. As a result, immobilization methods have been developed to incorporate the fragile biomass into porous beads which are more suitable to be operated in a fixed-bed reactor or to facilitate separation of the biomass from solution in a batch reactor. * Corresponding author. Tel.: +60-3-7594617; fax: +60-37568940. E-mail address: [email protected] (M.A. Hashim)
Natural and synthetic polymers such as Ca alginate [3,4] and polyacrylamide [5,6] have been used widely as the matrix in some immobilization techniques. It has been reported that the immobilized biomass showed comparable heavy metal uptake to the free, non-immobilized biomass [7]. In this work, the biomass of a marine alga, Sargassum baccularia, was immobilized using polyvinyl alcohol as the polymeric matrix [8]. The reusability of the immobilized biomass was assessed in multiple cycles of copper adsorption– desorption in a batch system. The effectiveness of two desorbing agents, hydrochloric acid and ethylenediaminetetraacetic acid (EDTA) in stripping adsorbed copper from the immobilized biomass was investigated in detail.
1383-5866/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 9 9 ) 0 0 0 7 6 - 3
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M.A. Hashim et al. / Separation/Purification Technology 19 (2000) 39–42
2. Materials and methods The immobilization procedures of Chen and Lin [8] were adopted in this work. Dried biomass of S. baccularia in the particle size range of 250 – 500 mm was mixed with a 15% polyvinyl alcohol (PVA) aqueous solution to a solid – liquid ratio of approximately 150 mg/ml. The mixture was dropped into a gently stirred saturated boric acid solution to form spherical gel beads. The gel beads formed were then transferred to a sodium phosphate solution, adjusted to pH 5.5, for hardening. Finally, the beads were washed with distilled water to remove any chemical residue. Copper solution (100 mg/l) was prepared by dissolving an appropriate amount of copper nitrate salt in distilled deionized water. The pH of the solution was adjusted to 6.0. The adsorption – desorption experiments were carried out in a batch manner. Approximately 80 beads, comprising about 0.1 g of biomass, were added to each capped-flask containing 0.1 l of copper solution. The flasks were incubated for 24 h in a shaker at 25°C and 200 rev./min. Upon equilibrium, the immobilized biomass beads were separated from the solution and the residual copper in the solution was determined by an inductively couple plasma spectrometer. The amount of copper adsorbed by the biomass was calculated from a mass balance. The copper-laden immobilized biomass was washed repeatedly with distilled deionized water to remove any residual copper solution. The beads were then placed in a flask containing 0.1 l of hydrochloric acid (HCl) at pH 1.0 or 2 mM solution of disodium salt of ethylenediaminetetraacetic acid (EDTA). The flasks were incubated at 25°C and 200 rev./min for a period of 24 h, ample time for the system to reach equilibrium. Following equilibrium of the desorption step, the solution was filtered and the copper concentration of the filtrate determined. The eluted beads were washed with distilled deionized water to remove any residual desorbing solution. The experimental procedures described above constitute one single cycle of adsorption – desorption. The procedures were conducted for a total of five consecutive cycles to evaluate the effect of the
two desorbing agents on the copper reloading capacity of the immobilized biomass. 3. Results and discussion The reusability of the immobilized algal biomass was tested in five consecutive cycles of copper adsorption and desorption by using two desorbing agents, hydrochloric acid (HCl) at pH 1.0 and aqueous solution containing 2 mM ethylenediaminetetraacetic acid (EDTA). Preliminary studies have shown that HCl at pH 1.0 and 2 mM EDTA solution could easily desorb more than 90% of the adsorbed copper in a single cycle of adsorption–desorption. For a desorbing agent to be considered efficient it must fulfil two major criteria: (1) complete desorption in each cycle and (2) metal uptake capacity of the adsorbent remains unchanged in successive cycles. Desorption efficiency as defined in Eq. (1) can be used as a parameter to assess whether a desorbing agent is able to meet the first criterion: Desorption efficiency =
Amount of metal desorbed in one cycle Amount of metal loaded in one cycle
× 100% (1) The ability of a desorbing agent to meet the second criterion in multiple cycles of adsorption– desorption can be assessed by defining a parameter called ‘reloading efficiency’: Reloading efficiency =
Amount of metal loaded in higher cycle Amount of metal loaded in first cycle
× 100% (2) Eq. (2) allows one to assess the reusability of an adsorbent by comparing metal uptake in subsequent cycles to metal uptake by the virgin adsorbent in the first cycle. Figs. 1 and 2 show the experimental results obtained from five consecutive cycles of copper adsorption–desorption using HCl at pH 1.0 and 2 mM EDTA solution as the desorbing agent. The open bars depict the amount of copper adsorbed while the solid bars represent the amount of cop-
M.A. Hashim et al. / Separation/Purification Technology 19 (2000) 39–42
per desorbed in each cycle. Figs. 1 and 2 clearly show a noticeable decrease in copper uptake after the first cycle of adsorption – desorption. Calculated values of the desorption and reloading efficiencies of the five cycles according to Eqs. (1) and (2) are tabulated in Tables 1 and 2. Tables 1 and 2 show that the desorption efficiency ranged from 89 to 104% with HCl as the desorbing agent and from 89 to 100% with EDTA
41
Table 1 Desorption efficiency and reloading efficiency in five consecutive cycles of copper adsorption and desorption using HCl at pH 1.0 as desorbing agent Cycle
1 2 3 4 5
Desorbing efficiency (%) Reloading efficiency (%) 91 91 96 104 89
– 56 55 52 59
Table 2 Desorption efficiency and reloading efficiency in five consecutive cycles of copper adsorption–desorption using 2 mM EDTA solution as desorbing agent Cycle
1 2 3 4 5
Fig. 1. Five consecutive cycles of copper adsorption–desorption using HCl at pH 1.0 as desorbing agent ( , amount adsorbed; , amount desorbed).
Fig. 2. Five consecutive cycles of copper adsorption–desorption using 2 mM EDTA solution as desorbing agent ( , amount adsorbed; , amount desorbed).
Desorption efficiency (%) 94 100 97 94 89
Reloading efficiency (%)
– 71 69 68 66
Table 3 Total amounts of copper adsorbed and desorbed over five cycles of adsorption–desorption Desorbing agent
Copper loaded (mg)
Copper desorbed (mg)
HCl EDTA
16.3 20.0
15.2 18.9
as the desorbing agent, indicating that both desorbing agents were effective in stripping adsorbed copper from the immobilized biomass over five consecutive cycles of adsorption–desorption. A desorption efficiency greater than 100% indicates that the excess copper must have come from the copper that was not desorbed in the preceding cycles. Table 3 shows the cumulative amounts of copper adsorbed and desorbed over the entire five cycles. In both cases the quantity of copper desorbed was very close to the quantity loaded, indicating that almost complete desorption was
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M.A. Hashim et al. / Separation/Purification Technology 19 (2000) 39–42
eventually achieved. It is clear that copper uptake by the immobilized biomass is reversible with very little accumulation of irreversibly bound copper on the biomass. This observation indicates that the two desorbing agents had successfully fulfilled the first criterion stated earlier, i.e. complete desorption of adsorbed metal. Tables 1 and 2 show that while the two desorbing agents were efficient in releasing the adsorbed copper into solution in each cycle, their application negatively affected subsequent copper uptake (reloading). After the first cycle, copper uptake by the immobilized biomass in Cycles 2 – 5 with HCl as the desorbing agent was reduced to 52 – 59% of the original copper uptake observed in the first cycle. A similar reduction was observed with EDTA as the desorbing agent, yielding adsorption efficiencies ranging from 66 to 71% in Cycles 2–5. The results presented above therefore suggest that the two desorbing agents had failed to meet the second criterion which requires a desorbing agent to cause little reduction in the metal uptake capacity of an adsorbent in multiple cycles of adsorption–desorption. The reduction in the copper reloading capacity of the immobilized biomass may be attributed to the release of residual desorbing agent during the copper uptake step in Cycles 2 – 5. Following the stripping of adsorbed copper in each cycle, the polymeric beads were repeatedly washed with distilled deionized water to remove any residual desorbing agent adhered to the structure of the beads. The beads were then reloaded with copper. If the desorbing agent was not completely removed, the release of the residual desorbing solution during the copper reloading step would hinder copper uptake by the immobilized biomass. Another possible cause of the observed reduction in the copper reloading capacity of the immobilized biomass may be attributed to the adverse effect of the desorbing agents on the binding sites of the biomass. A portion of the functional groups on the surface of the biomass responsible for copper binding could have been destroyed by the two desorbing agents following the stripping of the adsorbed copper in the first cycle. Consequently, the number of copper binding sites on the surface
of the biomass was reduced, limiting copper uptake in Cycles 2–5. 4. Conclusions Two desorbing agents, HCl at pH 1.0 and 2 mM EDTA solution, were found to be effective in stripping adsorbed copper from the biomass of S. baccularia immobilized in polyvinyl alcohol beads over five consecutive cycles of adsorption– desorption. The quantity of copper desorbed over the five cycles corresponded well to the quantity loaded, indicating that almost complete recovery of the adsorbed copper was readily achieved. Unfortunately, following the completion of the first cycle, the copper uptake capacity of the immobilized biomass deteriorated in subsequent cycles. It can therefore be concluded that neither HCl nor EDTA appear to be attractive as a desorbing agent although both possess excellent desorption efficiency. References [1] B. Volesky, Advances in biosorption of metals: Selection of biomass types, FEMS Microbiol. Rev. 14 (1994) 291. [2] K.H. Chu, M.A. Hashim, S.M. Phang, V.B. Samuel, Biosorption of cadmium by algal biomass: Adsorption and desorption characteristics, Water Sci. Technol. 35 (7) (1997) 115. [3] Y. Sag, M. Nourbakhsh, Z. Aksu, T. Kutsal, Comparison of Ca-alginate and immobilized Z. ramigera as sorbents for copper(II) removal, Proc. Biochem. 30 (2) (1995) 175. [4] G.M. Garnham, G.A. Codd, G.M. Gadd, Accumulation of cobalt, zinc, and manganese by the estuarine green microalgal Chlorella salina immobilized in alginate microbeads, Environ. Sci. Technol. 26 (9) (1992) 1764. [5] P.K. Wong, K.C. Lam, C.M. So, Removal and recovery of Cu(II) from industrial effluent by immobilized cells of Pseudomonas putida II-11, Appl. Microbiol. Biotechnol. 39 (1993) 127. [6] A. Nakajima, T. Horikoshi, T. Sakaguchi, Recovery of uranium by immobilized microorganisms, Eur. J. Appl. Microbiol. Biotechnol. 16 (1982) 88. [7] L.C. Rai, N. Mallick, Removal and assessment of toxicity of Cu and Fe to Anabaena dollolum and Chlorella 6ulgaris using free and immobilized cells, World J. Microbiol. Biotechnol. 8 (1992) 110. [8] K.C. Chen, Y.F. Lin, Immobilization of microorganisms with phosphorylated polyvinyl alcohol (PVA) gel, Enzyme Microb. Technol. 16 (1994) 79.
Immobilized marine algal biomass for multiple cycles of copper adsorption and desorption M.A. Hashim *, H.N. Tan, K.H. Chu Institute of Postgraduate Studies and Research, Uni6ersity of Malaya, 50603 Kuala Lumpur, Malaysia Received 24 September 1999; accepted 15 November 1999
Abstract The biomass of a marine alga, Sargassum baccularia, was immobilized by using polyvinyl alcohol as the polymeric matrix. The reusability of the immobilized biomass was studied by using copper as the model metal ion in five consecutive cycles of adsorption–desorption. Hydrochloric acid at pH 1.0 and ethylenediaminetetraacetic acid (EDTA) solution at 2 mM were used as the desorbing agents. Both desorbents were effective in stripping the adsorbed copper from the immobilized biomass over the five cycles. However, copper uptake in Cycles 2 – 5 was lower than that in Cycle 1, indicating that the two desorbing agents limited the reuse potential of the immobilized biomass in multiple cycles of adsorption–desorption. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Immobilized; Algal; Copper; Adsorption; Desorption
1. Introduction Marine algae have shown impressive binding capacities for a wide range of heavy metals [1]. However, the fragile biomass of the marine algae is not suitable for robust wastewater treatment operations [2]. As a result, immobilization methods have been developed to incorporate the fragile biomass into porous beads which are more suitable to be operated in a fixed-bed reactor or to facilitate separation of the biomass from solution in a batch reactor. * Corresponding author. Tel.: +60-3-7594617; fax: +60-37568940. E-mail address: [email protected] (M.A. Hashim)
Natural and synthetic polymers such as Ca alginate [3,4] and polyacrylamide [5,6] have been used widely as the matrix in some immobilization techniques. It has been reported that the immobilized biomass showed comparable heavy metal uptake to the free, non-immobilized biomass [7]. In this work, the biomass of a marine alga, Sargassum baccularia, was immobilized using polyvinyl alcohol as the polymeric matrix [8]. The reusability of the immobilized biomass was assessed in multiple cycles of copper adsorption– desorption in a batch system. The effectiveness of two desorbing agents, hydrochloric acid and ethylenediaminetetraacetic acid (EDTA) in stripping adsorbed copper from the immobilized biomass was investigated in detail.
1383-5866/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 9 9 ) 0 0 0 7 6 - 3
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M.A. Hashim et al. / Separation/Purification Technology 19 (2000) 39–42
2. Materials and methods The immobilization procedures of Chen and Lin [8] were adopted in this work. Dried biomass of S. baccularia in the particle size range of 250 – 500 mm was mixed with a 15% polyvinyl alcohol (PVA) aqueous solution to a solid – liquid ratio of approximately 150 mg/ml. The mixture was dropped into a gently stirred saturated boric acid solution to form spherical gel beads. The gel beads formed were then transferred to a sodium phosphate solution, adjusted to pH 5.5, for hardening. Finally, the beads were washed with distilled water to remove any chemical residue. Copper solution (100 mg/l) was prepared by dissolving an appropriate amount of copper nitrate salt in distilled deionized water. The pH of the solution was adjusted to 6.0. The adsorption – desorption experiments were carried out in a batch manner. Approximately 80 beads, comprising about 0.1 g of biomass, were added to each capped-flask containing 0.1 l of copper solution. The flasks were incubated for 24 h in a shaker at 25°C and 200 rev./min. Upon equilibrium, the immobilized biomass beads were separated from the solution and the residual copper in the solution was determined by an inductively couple plasma spectrometer. The amount of copper adsorbed by the biomass was calculated from a mass balance. The copper-laden immobilized biomass was washed repeatedly with distilled deionized water to remove any residual copper solution. The beads were then placed in a flask containing 0.1 l of hydrochloric acid (HCl) at pH 1.0 or 2 mM solution of disodium salt of ethylenediaminetetraacetic acid (EDTA). The flasks were incubated at 25°C and 200 rev./min for a period of 24 h, ample time for the system to reach equilibrium. Following equilibrium of the desorption step, the solution was filtered and the copper concentration of the filtrate determined. The eluted beads were washed with distilled deionized water to remove any residual desorbing solution. The experimental procedures described above constitute one single cycle of adsorption – desorption. The procedures were conducted for a total of five consecutive cycles to evaluate the effect of the
two desorbing agents on the copper reloading capacity of the immobilized biomass. 3. Results and discussion The reusability of the immobilized algal biomass was tested in five consecutive cycles of copper adsorption and desorption by using two desorbing agents, hydrochloric acid (HCl) at pH 1.0 and aqueous solution containing 2 mM ethylenediaminetetraacetic acid (EDTA). Preliminary studies have shown that HCl at pH 1.0 and 2 mM EDTA solution could easily desorb more than 90% of the adsorbed copper in a single cycle of adsorption–desorption. For a desorbing agent to be considered efficient it must fulfil two major criteria: (1) complete desorption in each cycle and (2) metal uptake capacity of the adsorbent remains unchanged in successive cycles. Desorption efficiency as defined in Eq. (1) can be used as a parameter to assess whether a desorbing agent is able to meet the first criterion: Desorption efficiency =
Amount of metal desorbed in one cycle Amount of metal loaded in one cycle
× 100% (1) The ability of a desorbing agent to meet the second criterion in multiple cycles of adsorption– desorption can be assessed by defining a parameter called ‘reloading efficiency’: Reloading efficiency =
Amount of metal loaded in higher cycle Amount of metal loaded in first cycle
× 100% (2) Eq. (2) allows one to assess the reusability of an adsorbent by comparing metal uptake in subsequent cycles to metal uptake by the virgin adsorbent in the first cycle. Figs. 1 and 2 show the experimental results obtained from five consecutive cycles of copper adsorption–desorption using HCl at pH 1.0 and 2 mM EDTA solution as the desorbing agent. The open bars depict the amount of copper adsorbed while the solid bars represent the amount of cop-
M.A. Hashim et al. / Separation/Purification Technology 19 (2000) 39–42
per desorbed in each cycle. Figs. 1 and 2 clearly show a noticeable decrease in copper uptake after the first cycle of adsorption – desorption. Calculated values of the desorption and reloading efficiencies of the five cycles according to Eqs. (1) and (2) are tabulated in Tables 1 and 2. Tables 1 and 2 show that the desorption efficiency ranged from 89 to 104% with HCl as the desorbing agent and from 89 to 100% with EDTA
41
Table 1 Desorption efficiency and reloading efficiency in five consecutive cycles of copper adsorption and desorption using HCl at pH 1.0 as desorbing agent Cycle
1 2 3 4 5
Desorbing efficiency (%) Reloading efficiency (%) 91 91 96 104 89
– 56 55 52 59
Table 2 Desorption efficiency and reloading efficiency in five consecutive cycles of copper adsorption–desorption using 2 mM EDTA solution as desorbing agent Cycle
1 2 3 4 5
Fig. 1. Five consecutive cycles of copper adsorption–desorption using HCl at pH 1.0 as desorbing agent ( , amount adsorbed; , amount desorbed).
Fig. 2. Five consecutive cycles of copper adsorption–desorption using 2 mM EDTA solution as desorbing agent ( , amount adsorbed; , amount desorbed).
Desorption efficiency (%) 94 100 97 94 89
Reloading efficiency (%)
– 71 69 68 66
Table 3 Total amounts of copper adsorbed and desorbed over five cycles of adsorption–desorption Desorbing agent
Copper loaded (mg)
Copper desorbed (mg)
HCl EDTA
16.3 20.0
15.2 18.9
as the desorbing agent, indicating that both desorbing agents were effective in stripping adsorbed copper from the immobilized biomass over five consecutive cycles of adsorption–desorption. A desorption efficiency greater than 100% indicates that the excess copper must have come from the copper that was not desorbed in the preceding cycles. Table 3 shows the cumulative amounts of copper adsorbed and desorbed over the entire five cycles. In both cases the quantity of copper desorbed was very close to the quantity loaded, indicating that almost complete desorption was
42
M.A. Hashim et al. / Separation/Purification Technology 19 (2000) 39–42
eventually achieved. It is clear that copper uptake by the immobilized biomass is reversible with very little accumulation of irreversibly bound copper on the biomass. This observation indicates that the two desorbing agents had successfully fulfilled the first criterion stated earlier, i.e. complete desorption of adsorbed metal. Tables 1 and 2 show that while the two desorbing agents were efficient in releasing the adsorbed copper into solution in each cycle, their application negatively affected subsequent copper uptake (reloading). After the first cycle, copper uptake by the immobilized biomass in Cycles 2 – 5 with HCl as the desorbing agent was reduced to 52 – 59% of the original copper uptake observed in the first cycle. A similar reduction was observed with EDTA as the desorbing agent, yielding adsorption efficiencies ranging from 66 to 71% in Cycles 2–5. The results presented above therefore suggest that the two desorbing agents had failed to meet the second criterion which requires a desorbing agent to cause little reduction in the metal uptake capacity of an adsorbent in multiple cycles of adsorption–desorption. The reduction in the copper reloading capacity of the immobilized biomass may be attributed to the release of residual desorbing agent during the copper uptake step in Cycles 2 – 5. Following the stripping of adsorbed copper in each cycle, the polymeric beads were repeatedly washed with distilled deionized water to remove any residual desorbing agent adhered to the structure of the beads. The beads were then reloaded with copper. If the desorbing agent was not completely removed, the release of the residual desorbing solution during the copper reloading step would hinder copper uptake by the immobilized biomass. Another possible cause of the observed reduction in the copper reloading capacity of the immobilized biomass may be attributed to the adverse effect of the desorbing agents on the binding sites of the biomass. A portion of the functional groups on the surface of the biomass responsible for copper binding could have been destroyed by the two desorbing agents following the stripping of the adsorbed copper in the first cycle. Consequently, the number of copper binding sites on the surface
of the biomass was reduced, limiting copper uptake in Cycles 2–5. 4. Conclusions Two desorbing agents, HCl at pH 1.0 and 2 mM EDTA solution, were found to be effective in stripping adsorbed copper from the biomass of S. baccularia immobilized in polyvinyl alcohol beads over five consecutive cycles of adsorption– desorption. The quantity of copper desorbed over the five cycles corresponded well to the quantity loaded, indicating that almost complete recovery of the adsorbed copper was readily achieved. Unfortunately, following the completion of the first cycle, the copper uptake capacity of the immobilized biomass deteriorated in subsequent cycles. It can therefore be concluded that neither HCl nor EDTA appear to be attractive as a desorbing agent although both possess excellent desorption efficiency. References [1] B. Volesky, Advances in biosorption of metals: Selection of biomass types, FEMS Microbiol. Rev. 14 (1994) 291. [2] K.H. Chu, M.A. Hashim, S.M. Phang, V.B. Samuel, Biosorption of cadmium by algal biomass: Adsorption and desorption characteristics, Water Sci. Technol. 35 (7) (1997) 115. [3] Y. Sag, M. Nourbakhsh, Z. Aksu, T. Kutsal, Comparison of Ca-alginate and immobilized Z. ramigera as sorbents for copper(II) removal, Proc. Biochem. 30 (2) (1995) 175. [4] G.M. Garnham, G.A. Codd, G.M. Gadd, Accumulation of cobalt, zinc, and manganese by the estuarine green microalgal Chlorella salina immobilized in alginate microbeads, Environ. Sci. Technol. 26 (9) (1992) 1764. [5] P.K. Wong, K.C. Lam, C.M. So, Removal and recovery of Cu(II) from industrial effluent by immobilized cells of Pseudomonas putida II-11, Appl. Microbiol. Biotechnol. 39 (1993) 127. [6] A. Nakajima, T. Horikoshi, T. Sakaguchi, Recovery of uranium by immobilized microorganisms, Eur. J. Appl. Microbiol. Biotechnol. 16 (1982) 88. [7] L.C. Rai, N. Mallick, Removal and assessment of toxicity of Cu and Fe to Anabaena dollolum and Chlorella 6ulgaris using free and immobilized cells, World J. Microbiol. Biotechnol. 8 (1992) 110. [8] K.C. Chen, Y.F. Lin, Immobilization of microorganisms with phosphorylated polyvinyl alcohol (PVA) gel, Enzyme Microb. Technol. 16 (1994) 79.