World
Journal
of Microbiology
Bamboo reactors W.P. Tritt,*
and Biotechnology,
9. 229432
as a support
F. Zadrazil,
U. Menge-Hartmann
material
and S. Schwarz
The changes in 2.5~an thick bamboo rings during their use as a that the wash out and degradation processes are largely completed the bamboo used decreased more quickly in the first half of the year approached a loss limit of approximately 15% (w/w). The decrease the t-year experimental period led to reductions in wall thickness pressure of 21%. Bamboo thus appears to be suitable for long-term Key words: Anaerobic,
bamboo,
support
material, wastewater
While synthetic filling materials in fixed-bed reactors have very positive properties in terms of purification output and reliability, these properties have to be seen in relation to the high costs of such materials. The use of synthetic fillers in countries of the Third World can be expected to be even more expensive due to the transport costs involved. The idea that bamboo, if suitable, might be an alternative material because of its wide distribution (tropics and subtropics), its rapid growth rates and its cheapness in the Third World compared with synthetic materials (the bamboo/synthetic material price-ratio is about I : 10 to I: 15, without transport), led to research on the long-term behaviour of bamboo in anaerobic reactors. The suitability of bamboo, principally as a support material in anaerobic fixed-bed reactors, was successfully demonstrated, in terms of running-in, biomass fixation or biomass retention, and blockage-free running, with laboratory-scale (Tritt 1992) and pilot-scale (TriH & Meyer-Jacob 1992) reactors. The residence time of a support material consisting mainly of organic components is of crucial importance to operational reliability; it must be able to compete with synthetic material specifically on this point. The aims of the present study were to get information about the behaviour of bamboo in reactors and the W.P. Tritt and S Schwarz are with the Institute of Technology, F. Zadrazll IS with the Institute of Soil Biology and U. Menge-Hartmann is with the Institute of Crop Science and Plant Breeding, all of the Federal Research Centre of Agriculture, Bundesallee 50. D-W-3300 Braunschweig, Germany; fax: (+49) 531 596363. *Corresponding author. @ 1993 Rapid
Communications
of Oxford
in anaerobic
support material in an anaerobic reactor show within 6 months to a year. The dry mass of than during the second half and asymptotically in substances contained in the bamboo during of the rings of 0.8 mm and in the absorbable use in an anaerobic reactor.
treatment.
residence times which chemical and biological
Material
could be expected, methods.
using physical,
and Methods
Bamboo rings Commercially-available bamboo stems (3 m long x 60 to 100 mm) from Taiwan were used. Before transport, the stems were fumigated with a pesticide (bromomethane). (Exact data on the species, age, felling date, drying process and storage time of the bamboo were not available). The bamboo stems were sawn with a band saw into 2.5-cm thick rings and inserted at the head of the 2.8-m’ reactor. The characteristics and sizes of the rings of stems are given in Table 1. The reactor was charged with slaughterhouse wastewater, pH 7.4 to 7.9, and run in both an upflow and a downflow process with loading rates of I to 4 kg/m3.d. The temperature of substrate was constant (37’C). To determine the compressive strength of the bamboo, parallel
to the fibres, pairs of adjoining rings were each divided radially into 155 during the sawing of the stems. The first batch was pressed immediately. The second batch was used in the reactor and then pressed at the end of the experimental period under the same external conditions (temperature, moisture content) as the first batch, after determining the wall thickness at four points per ring. In order to document the change in the weight of rings in the reactor, 30 were weighed both before and after use in the reactor, after drying af 105°C. The used rings were manually cleaned of their covering of anaerobic sludge before they were dried. Light microscope studies were carried out after staining microtomed sections with lignin-specific colorant (phloroglucinol).
Lfd World ]ournai of Microbiology and Biotechnology, Vol 9, 1993
229
W.P. Tritt et al. Table
1. initial
characteristics
of the bamboo
rings
used
Dimension Surface area Porosity Dry mass as proportion of total mass in rings immediately after cutting After 5 days in waterbath Volume increase
in maximum
At the start of the experiment After 2 years in the reactor l
Two random samples fibre and the resulting gold and subsequently at an angle of 10”.
60 to 100 mm diam 88 m21m3 89% 88.5 48% 1%
t0
absorbable
5 SD. points on each
Calculated
of the rings were also broken parallel to the breakage points were sputter-coated with examined in a scanning electron microscope
Chemical Analysis. The proportion of soluble substances was determined after extraction of 1 g of milled sample (3 h, 80°C) in 100 ml of water, 0.1 M NaOH (Zadrazil et al. 1982) or 0.1 M H,SO,. Lignin was determined as the solid residue after hydrolysis with concentrated HCI and H,SO, (Halse 1926; Zadrazil 8s Brunnert 1980) carbon content was determined with an automatic carbon analyser (model IR 12, Leco Corporation, St. Joseph, MI, USA), and nitrogen with an analyser (Heraeus Macro N) which works on the Dumas method.
89% after 5 days in water vertical and parallel fibre
pressure
and
stem
wail
thickness
Wail
bath to the
of the
thickness* (mm)
6.86 f 0.05 (N = 620) 6.06 &- 0.10 (N= 316)
subject to change. As there was an overall decrease in wall thickness, the area of the bamboo rings exposed to pressure also decreased; the results of the pressure experiment, therefore, can only be given as maximum absorbable pressures, not as the usual, surface-related, comprehensive stress (N/mm’). Compared with the values at the beginning of the experiment, the average compressive strength at the end of the experiments was 21% lower. The changes in the dry mass are shown in Figure 1. During the first 6 months, II% of dry mass was lost but the rate of dry mass loss fell sharply during the rest of the period and only 15% of the initial dry mass had been lost after 2 years.
Analyses. The in vitro digestibility was determined after (48 h) of the sample with lumen liquor and a further (24 h) with pepsin/HCl (Tilley & Terry 1963).
and Discussion 0
As Table 2 shows, within the experimental period of 2 years, both the wall thickness of the bamboo rings and the maximum pressure they could take parallel to the fibres were
230
arithmetically
ring.
thawed and milled.
Results
x 25 mm
81,470 +_ 1267 (IV= 155) 64,485 k 4542 (A’ = 79)
Chemical and Biological Analyses Periodically, single segments were removed from each of 20 rings, pooled and stored at -20°C. Prior to analysis the samples were
Biological incubation incubation
Remarks
Maximum absorbable pressure parallel to the fibres (N)
Time
Values are means t Measured at four
material.
Value
Parameter
Table 2. Changes bamboo.*
as support
World Joumuf
of
Mtcrobiology and Biotechnology, Vol 9, 1993
0.5
1
1.5
Time (years)
Figure 1. Loss in dry-mass material in an anaerobic
of bamboo reactor.
during
its use as a support
2
Bamboo: a support material
(A)
(B)
Figure 2. Parenchyma cells in a bamboo segment (parallel to the fibre) (A) before and (B) after two years use in an anaerobic reactor (bar--f0 pm; arrow---cell wall; arrow head--pit).
Microscopical Examination The thick-walled fibre cells and sclereids under the outer and inner epidermis and the sclerenchyma fibres of the vascular bundle were intensely stained with phloroglucinol. The parenchyma cell walls reacted weakly, their intercellular spaces and middle lamellae most intensively. At the end of the experimental period, the staining of the parenchyma cell walls from the ring surface inwards to a depth of some 5 ram, was less than that seen initially, whereas there were no changes apparent in the deeper layers. Scanning electron microscopical examination showed a decrease in the parenchyma cell wall layers close to the surface of the rings (Figure 2). While many parenchyma cell wall layers and the relatively smooth surface of the inner wall layers can be clearly seen in the material not used in the anaerobic reactor (Figure 2A), Figure 2B shows the reduced number of celt wall layers, the degradation of the inner cell walls and the apparent enlargement of the pits in
the cell walls of material used in the reactor for 2 years. The expectation that the intensity of these degradative processes would decrease from the outside towards the inside of the material was confirmed. Destruction of the vascular tissue (vascular bundles) could only be established _
Journal
of Microbiology
Bamboo reactors W.P. Tritt,*
and Biotechnology,
9. 229432
as a support
F. Zadrazil,
U. Menge-Hartmann
material
and S. Schwarz
The changes in 2.5~an thick bamboo rings during their use as a that the wash out and degradation processes are largely completed the bamboo used decreased more quickly in the first half of the year approached a loss limit of approximately 15% (w/w). The decrease the t-year experimental period led to reductions in wall thickness pressure of 21%. Bamboo thus appears to be suitable for long-term Key words: Anaerobic,
bamboo,
support
material, wastewater
While synthetic filling materials in fixed-bed reactors have very positive properties in terms of purification output and reliability, these properties have to be seen in relation to the high costs of such materials. The use of synthetic fillers in countries of the Third World can be expected to be even more expensive due to the transport costs involved. The idea that bamboo, if suitable, might be an alternative material because of its wide distribution (tropics and subtropics), its rapid growth rates and its cheapness in the Third World compared with synthetic materials (the bamboo/synthetic material price-ratio is about I : 10 to I: 15, without transport), led to research on the long-term behaviour of bamboo in anaerobic reactors. The suitability of bamboo, principally as a support material in anaerobic fixed-bed reactors, was successfully demonstrated, in terms of running-in, biomass fixation or biomass retention, and blockage-free running, with laboratory-scale (Tritt 1992) and pilot-scale (TriH & Meyer-Jacob 1992) reactors. The residence time of a support material consisting mainly of organic components is of crucial importance to operational reliability; it must be able to compete with synthetic material specifically on this point. The aims of the present study were to get information about the behaviour of bamboo in reactors and the W.P. Tritt and S Schwarz are with the Institute of Technology, F. Zadrazll IS with the Institute of Soil Biology and U. Menge-Hartmann is with the Institute of Crop Science and Plant Breeding, all of the Federal Research Centre of Agriculture, Bundesallee 50. D-W-3300 Braunschweig, Germany; fax: (+49) 531 596363. *Corresponding author. @ 1993 Rapid
Communications
of Oxford
in anaerobic
support material in an anaerobic reactor show within 6 months to a year. The dry mass of than during the second half and asymptotically in substances contained in the bamboo during of the rings of 0.8 mm and in the absorbable use in an anaerobic reactor.
treatment.
residence times which chemical and biological
Material
could be expected, methods.
using physical,
and Methods
Bamboo rings Commercially-available bamboo stems (3 m long x 60 to 100 mm) from Taiwan were used. Before transport, the stems were fumigated with a pesticide (bromomethane). (Exact data on the species, age, felling date, drying process and storage time of the bamboo were not available). The bamboo stems were sawn with a band saw into 2.5-cm thick rings and inserted at the head of the 2.8-m’ reactor. The characteristics and sizes of the rings of stems are given in Table 1. The reactor was charged with slaughterhouse wastewater, pH 7.4 to 7.9, and run in both an upflow and a downflow process with loading rates of I to 4 kg/m3.d. The temperature of substrate was constant (37’C). To determine the compressive strength of the bamboo, parallel
to the fibres, pairs of adjoining rings were each divided radially into 155 during the sawing of the stems. The first batch was pressed immediately. The second batch was used in the reactor and then pressed at the end of the experimental period under the same external conditions (temperature, moisture content) as the first batch, after determining the wall thickness at four points per ring. In order to document the change in the weight of rings in the reactor, 30 were weighed both before and after use in the reactor, after drying af 105°C. The used rings were manually cleaned of their covering of anaerobic sludge before they were dried. Light microscope studies were carried out after staining microtomed sections with lignin-specific colorant (phloroglucinol).
Lfd World ]ournai of Microbiology and Biotechnology, Vol 9, 1993
229
W.P. Tritt et al. Table
1. initial
characteristics
of the bamboo
rings
used
Dimension Surface area Porosity Dry mass as proportion of total mass in rings immediately after cutting After 5 days in waterbath Volume increase
in maximum
At the start of the experiment After 2 years in the reactor l
Two random samples fibre and the resulting gold and subsequently at an angle of 10”.
60 to 100 mm diam 88 m21m3 89% 88.5 48% 1%
t0
absorbable
5 SD. points on each
Calculated
of the rings were also broken parallel to the breakage points were sputter-coated with examined in a scanning electron microscope
Chemical Analysis. The proportion of soluble substances was determined after extraction of 1 g of milled sample (3 h, 80°C) in 100 ml of water, 0.1 M NaOH (Zadrazil et al. 1982) or 0.1 M H,SO,. Lignin was determined as the solid residue after hydrolysis with concentrated HCI and H,SO, (Halse 1926; Zadrazil 8s Brunnert 1980) carbon content was determined with an automatic carbon analyser (model IR 12, Leco Corporation, St. Joseph, MI, USA), and nitrogen with an analyser (Heraeus Macro N) which works on the Dumas method.
89% after 5 days in water vertical and parallel fibre
pressure
and
stem
wail
thickness
Wail
bath to the
of the
thickness* (mm)
6.86 f 0.05 (N = 620) 6.06 &- 0.10 (N= 316)
subject to change. As there was an overall decrease in wall thickness, the area of the bamboo rings exposed to pressure also decreased; the results of the pressure experiment, therefore, can only be given as maximum absorbable pressures, not as the usual, surface-related, comprehensive stress (N/mm’). Compared with the values at the beginning of the experiment, the average compressive strength at the end of the experiments was 21% lower. The changes in the dry mass are shown in Figure 1. During the first 6 months, II% of dry mass was lost but the rate of dry mass loss fell sharply during the rest of the period and only 15% of the initial dry mass had been lost after 2 years.
Analyses. The in vitro digestibility was determined after (48 h) of the sample with lumen liquor and a further (24 h) with pepsin/HCl (Tilley & Terry 1963).
and Discussion 0
As Table 2 shows, within the experimental period of 2 years, both the wall thickness of the bamboo rings and the maximum pressure they could take parallel to the fibres were
230
arithmetically
ring.
thawed and milled.
Results
x 25 mm
81,470 +_ 1267 (IV= 155) 64,485 k 4542 (A’ = 79)
Chemical and Biological Analyses Periodically, single segments were removed from each of 20 rings, pooled and stored at -20°C. Prior to analysis the samples were
Biological incubation incubation
Remarks
Maximum absorbable pressure parallel to the fibres (N)
Time
Values are means t Measured at four
material.
Value
Parameter
Table 2. Changes bamboo.*
as support
World Joumuf
of
Mtcrobiology and Biotechnology, Vol 9, 1993
0.5
1
1.5
Time (years)
Figure 1. Loss in dry-mass material in an anaerobic
of bamboo reactor.
during
its use as a support
2
Bamboo: a support material
(A)
(B)
Figure 2. Parenchyma cells in a bamboo segment (parallel to the fibre) (A) before and (B) after two years use in an anaerobic reactor (bar--f0 pm; arrow---cell wall; arrow head--pit).
Microscopical Examination The thick-walled fibre cells and sclereids under the outer and inner epidermis and the sclerenchyma fibres of the vascular bundle were intensely stained with phloroglucinol. The parenchyma cell walls reacted weakly, their intercellular spaces and middle lamellae most intensively. At the end of the experimental period, the staining of the parenchyma cell walls from the ring surface inwards to a depth of some 5 ram, was less than that seen initially, whereas there were no changes apparent in the deeper layers. Scanning electron microscopical examination showed a decrease in the parenchyma cell wall layers close to the surface of the rings (Figure 2). While many parenchyma cell wall layers and the relatively smooth surface of the inner wall layers can be clearly seen in the material not used in the anaerobic reactor (Figure 2A), Figure 2B shows the reduced number of celt wall layers, the degradation of the inner cell walls and the apparent enlargement of the pits in
the cell walls of material used in the reactor for 2 years. The expectation that the intensity of these degradative processes would decrease from the outside towards the inside of the material was confirmed. Destruction of the vascular tissue (vascular bundles) could only be established _
