Bioregeneration of granular activated carbon in simultaneous adsorption and biodegradation of chlorophenols

The objectives of this study are to obtain the time courses of the amount of chlorophenol adsorbed onto granular activated carbon (GAC) in the simultaneous adsorption and biodegradation processes involving 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP), respectively, and to quantify the bioregeneration efficiency of GAC loaded with 4-CP and 2,4-DCP by direct measurement of the amount of chlorophenol adsorbed onto GAC. Under abiotic and biotic conditions, the time courses of the amount of chlorophenol adsorbed onto GAC at various GAC dosages for the initial 4-CP and 2,4-DCP concentrations below and above the biomass acclimated concentrations of 300 and 150 mg/L, respectively, were determined. The results show that the highest bioregeneration efficiency was achieved provided that the initial adsorbate concentration was lower than the acclimated concentration. When the initial adsorbate concentration was higher than the acclimated concentration, the highest bioregeneration efficiency was achieved if excess adsorbent was used.     

Adsorption of fluorobenzene onto granular activated carbon: isotherm and bioavailability studies

The adsorption of a recalcitrant fluoroaromatic compound, fluorobenzene (FB), onto granular activated carbon (GAC) was evaluated. The respective isotherm was obtained and the Langmuir, Freundlich and Redlich-Peterson models were fitted to the experimental data, with the Redlich-Peterson model giving the best fitting. Freundlich model also provided a good fit but the Langmuir model could not adequately fit the experimental data, especially at high FB concentrations. Maximal adsorption capacity of FB onto GAC was found to be 388mg of FB per gram of GAC. The reversibility of the adsorption of FB onto GAC was investigated, both in the absence and presence of microorganisms. Abiotic desorption of FB occurred to a small extent (between 3% and 22%, for amounts of FB initially adsorbed to the GAC between 37 and 388mgg(-1)), and bioregeneration of GAC was shown to occur when the matrix was exposed to a FB degrading culture, with 58-80% of the adsorbed FB being biodegraded. A residual amount of FB showed not to be bioavailable, suggesting that part of the adsorbed FB may be irreversibly bound. The fraction of the non-bioavailable FB increased at higher amounts of adsorbed FB, from 19% to 33%. The results indicate that the GAC employed in this study has a good capacity to adsorb FB and that bioregeneration of this matrix is a feasible process.     

Biodegradation of mixed phenolic compounds by Aspergillus awamori NRRL 3112

The ability of the fungus Aspergillus awamori NRRL 3112 to degrade mixtures of some common phenolic compounds, namely phenol, catechol, 2,4-dichlorphenol and 2,6-dimethoxyphenol was investigated in the present study. For all combinations in which dichlorophenol was incorporated, it took equal time for the nearly complete degradation of the compound—4 days. Phenol was decomposed almost completely (99.5%) in a combination with dimethoxyphenol, to a lesser extent (88%) in a combination with catechol and to the least degree (25%) in the presence of 2,4-dichlorophenol. Catechol experienced a more substantial biotransformation (64%) when mixed with phenol and weaker (45%)—in a combination with dichlorophenol. 2,6-Dimethoxyphenol was better decomposed (69%) in mixtures containing phenol, while its biodegradation in a combination with 2,4-dichlorophenol was considerably poor (only 5%).     

Phenol biodegradation in hybrid hollow-fiber membrane bioreactors

Hollow-fiber membrane bioreactors were developed with granular activated carbon (GAC) for the biodegradation of phenol using Pseudomonas putida. Hollow fibers showed similar structure with/without GAC incorporated; while GAC hollow fiber had a stronger phenol adsorption capacity. In batch biotransformation experiments, complete depletion of 1000 mg phenol l⁻¹ (at which concentration free cells cannot grow) was accomplished in the reactor within 18 h in the hybrid bioreactor, comparing with 23 h in the GAC free bioreactor. Desorption and bioregeneration of the hollow-fiber membrane were believed to be the key for the enhancement of bioreactor performance. At continuous running, the GAC bioreactor showed its superiority over the GAC free bioreactor during start-up and elevated loading phase. More than 90% of the phenol was transformed in the GAC bioreactor when the phenol loading was <24 mg h⁻¹. The better bioreactor performance may be due to the enhanced mass transportation and adsorption capacity with the incorporation of GAC.     

Incorporation of granular activated carbon in an immobilized membrane bioreactor for the biodegradation of phenol by <Emphasis Type="Italic">Pseudomonas putida</Emphasis>

Granular activated carbon (GAC) was incorporated into hollow fiber membrane bioreactors for the biodegradation of 1,000 mg phenol l⁻¹ through immobilization of Pseudomonas putida. The phenol was removed within 25 h in the hybrid bioreactor, comparing with 31 h for a GAC-free bioreactor. Sorption, biodegradation, desorption, and bioregeneration were four steps for the phenol removal during batch operation.     

Biodegradation of 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid by dichlorophenol-adapted microorganisms from freshwater,anaerobic sediments

Reductive dechlorination of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) was investigated in anaerobic sediments by non-adapted microorganisms and by microorganisms adapted to either 2,4- or 3,4-dichlorophenol (DCP). The rate of dechlorination of 2,4-D was increased by adaptation of sediment microorganisms to 2,4-DCP while dechlorination by sediment microorganisms adapted to 3,4-DCP displayed a lag phase similar to non-adapted sediment slurries. Both 2,4- and 3,4-DCP-adapted microorganisms produced 4-chlorophenoxyacetic acid by ortho-chlorine removal. Lag phases prior to dechlorination of the initial addition of 2,4,5-T by DCP-adapted sediment microorganisms were comparable to those from non-adapted sediment slurries. However, the rates of dechlorination increased upon subsequent additions of 2,4,5-T. Biodegradation of 2,4,5-T by sediment microorganisms adapted to 2,4- and/ or 3,4-DCP produced 2,5-D as the initial intermediate followed by 3-chlorophenol and phenol indicating a para > ortho > meta order of dechlorination. Dechlorination of 2,4,5-T, by either adapted or non-adapted sediment microorganisms, progressed without detection of 2,4,5-trichlorophenol as an intermediate.     

Possibility of Using Phenol- and 2,4-Dichlorophenol-Degrading Strain, <Emphasis Type="Italic">Rhodococcus erythropolis</Emphasis> 17S,for Treatment of Industrial Wastewater

A new phenol- and 2,4-dichlorophenol (2,4-DCP)-degrading strain Rhodococcus erythropolis 17S isolated from the soil contaminated with phenol and its derivatives for a long time was characterized. The strain was identified based on phenotypic, physiological, and biochemical features as well as on the results of 16S rRNA gene sequencing. The growth of R. erythropolis 17S in batch culture using phenol and 2,4-DCP as sources of carbon and energy has been studied. The concentration of phenol and 2,4-DCP in culture medium decreased by 55% (on the fourth day) and 47% (on the 22nd day) in comparison to the control, respectively. It is concluded that R. erythropolis 17S can be used for phenol removal from industrial wastewaters of petrochemical and tanning extract production plants.     

Induction of enzymes of 2,4-dichlorophenoxyacetate degradation in Burkholderia cepacia 2a and toxicity of metabolic intermediates

Burkholderia cepacia 2a inducibly degraded 2,4-dichlorophenoxyacetate (2,4-D) sequentially via 2,4-dichlorophenol, 3,5-dichlorocatechol, 2,4-dichloromuconate, 2-chloromuconolactone and 2-chloromaleylacetate. Cells grown on nutrient agar or broth grew on 2,4-D-salts only if first passaged on 4-hydroxybenzoate- or succinate-salts agar. Buffered suspensions of 4-hydroxybenzoate-grown cells did not adapt to 2,4-D or 3,5-dichlorocatechol, but responded to 2,4-dichlorophenol at concentrations <0.4 mM. Uptake of 2,4-dichlorophenol by non-induced cells displayed a type S (cooperative uptake) uptake isotherm in which the accelerated uptake of the phenol began before the equivalent of a surface monolayer had been adsorbed, and growth inhibition corresponded with the acquisition of 2.2-fold excess of phenol required for the establishment of the monolayer. No evidence of saturation was seen even at 2 mM 2,4-dichlorophenol, possibly due to absorption by intracellular poly-beta-hydroxybutyrate inclusions. With increasing concentration, 2,4-dichlorophenol caused progressive cell membrane damage and, sequentially, leakage of intracellular K(+), P(i), ribose and material absorbing light at 260 nm (presumed nucleotide cofactors), until at 0.4 mM, protein synthesis and enzyme induction were forestalled. Growth of non-adapted cells was inhibited by 0.35 mM 2,4-dichlorophenol and 0.25 mM 3,5-dichlorocatechol; the corresponding minimum bacteriocidal concentrations were 0.45 and 0.35 mM. Strain 2a grew in chemostat culture on carbon-limited media containing 2,4-D, with an apparent growth yield coefficient of 0.23, and on 2,4-dichlorophenol. Growth on 3,5-dichlorocatechol did not occur without a supplement of succinate, probably due to accumulation of toxic quantities of quinonoid and polymerisation products. Cells grown on these compounds were active towards all three, but not when grown on other substrates. The enzymes of the pathway therefore appeared to be induced by 3,5-dichlorocatechol or some later metabolite. A possible reason is offered for the environmental persistence of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).     

Analysis of oxygenation reactions in a multi-substrate system-A new approach for estimating substrate-specific true yields

A series of experiments was performed in an aerobic chemostat reactor using a multi-substrate system consisting of acetate, phenol, and 2,4-dichlorophenol (DCP). The phenolic compounds require initial oxygenation reactions, while acetate is oxidized without oxygenations. The biomass completely dechlorinated DCP and utilized all of the substrates simultaneously as electron donors and carbon sources. However, DCP removal was less than for phenol and depended on the solids retention time. A novel substrate-specific yield analysis indicated that true yield values were approximated well by the number of electrons removed in non-oxygenation reactions. Experiments for estimating the kinetic parameters for utilization of the phenolic compounds were designed to eliminate the effects of the key cosubstrates of oxygenation reactions, O2, and the reduced intracellular electron carrier, NADH + H+. The maximum specific rate of substrate utilization, qmax, and the half-maximum rate concentration, K, for phenol and DCP were estimated. The kinetics for DCP were much slower than those for phenol, and the largest effect was a half-maximum rate concentration, which was 19 times larger for DCP. The larger K for DCP explains why DCP removal was low and sensitive to the solids retention time.     

Biodegradation of mixed phenolic compounds by Aspergillus awamori NRRL 3112

The ability of the fungus Aspergillus awamori NRRL 3112 to degrade mixtures of some common phenolic compounds, namely phenol, catechol, 2,4-dichlorphenol and 2,6-dimethoxyphenol was investigated in the present study. For all combinations in which dichlorophenol was incorporated, it took equal time for the nearly complete degradation of the compound—4 days. Phenol was decomposed almost completely (99.5%) in a combination with dimethoxyphenol, to a lesser extent (88%) in a combination with catechol and to the least degree (25%) in the presence of 2,4-dichlorophenol. Catechol experienced a more substantial biotransformation (64%) when mixed with phenol and weaker (45%)—in a combination with dichlorophenol. 2,6-Dimethoxyphenol was better decomposed (69%) in mixtures containing phenol, while its biodegradation in a combination with 2,4-dichlorophenol was considerably poor (only 5%).     

Gaseous TCE and PCE removal by an activated carbon biofilter

Gaseous trichloroethylene (TCE) and tetrachloroethylene (PCE) are emitted in the treatment of contaminated groundwaters with air stripping and/or the remediation of contaminated soils using vapor extraction techniques. This study investigated the application of biofiltration using cometabolic process to remediate gaseous TCE and PCE that are highly recalcitrant to biodegradation. The investigation was conducted using two specially built stainless steel columns, one for TCE and the other for PCE, packed with granular activated carbon (GAC) coated with phenol-oxidizing microorganisms at residence times of 1.5–7 min. Two activated carbon biofilters were fed with phenol at a specific concentration along with a nutrient solution to optimize the various catalyzed biochemical reactions. The removal efficiency of gaseous TCE was 100% at a residence time of 7 min and average inlet concentration of 85 ppm. For gaseous PCE, 100% removal efficiency was obtained at residence times of 4–7 min and average concentrations of 47–84 ppm. It was found that phenol fed to the biofilters was completely utilized by the phenol-oxidizing microorganisms, as an indirect indicator of the microorganisms growth in the biofilters, throughout the period of the biofilter operation. Transformation yields of gaseous TCE and PCE were about 8–48 g of TCE/g of phenol and 6–25 g of PCE/g of phenol, depending on different residence times. It was found that adsorption by GAC and absorption by the influent nutrient solution were a minor negligible mechanism for TCE and PCE removal in the activated carbon biofilters.     

Microbial removal of chlorinated phenols during aerobic treatment of effluents from radiata pine kraft pulps bleached with chlorine-based chemicals,with or without hemicellulases

  The removal of chlorophenolic compounds from kraft mill effluents bleached with chlorine (cBKME) or chlorine plus hemicellulases (bBKME) was studied in reactors of aerobic treatment lagoons. In these laboratory models, a stable microbial population removed biochemical oxygen demand at similar rates of the mill lagoon. Complete removal of nine chlorophenols and chloroguaiacols during microbial treatment of these effluents was detected by gas chromatography. Abiotic removal was only observed with 2,4-dichlorophenol and 2,4,5-trichlorophenol. There were no significant differences in degradative ability between microorganisms acclimated to grow in reactors fed with cBKME or bBKME. The latter had a lower content of adsorbable organic halogen and chlorophenols than cBKME. Microorganisms acclimated to cBKME or bBKME were only able to grow on phenol or guaiacol as sole carbon source. However, these microorganisms removed (0.1–0.5 mM) 4-chlorophenol, 2,4-dichlorophenol and 2,4-dichlorophenoxyacetate with BKME as primary carbon source. Under these conditions, 2,4,6- and 2,4,5-trichlorophenol, 4,5-dichloroguaiacol, 4,5,6-trichloroguaiacol and tetrachloroguaiacol were not removed. These results suggest that the microbial removal of bleaching chlorophenols and chloroguaiacols during aerobic treatment, probably takes place only because of their very low concentration (1–200 ppb) in BKME. Received: 12 February 1996 / Received revision: 10 June 1996 / Accepted: 22 June 1996     

Reducing effect of aerobic selector on the toxicity of synthetic organic compounds in activated sludge process

The effects of phenol, 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 1,2,4-trichlorobenzene (1,2,4-TCB) on the biodegradation kinetics of the conventional activated sludge system (CASS) and the selector activated sludge system (SASS) were investigated. Experiments were carried out using a respirometric method on unacclimated biomass from two lab-scale systems that were operated with the sludge age of 8 days. Toxicity of the test compounds for both reactors were arranged according to EC₅₀ (effective concentration) values in order as: 1,2,4-TCB > 2,4-DCP > 2-CP > phenol. All selected test compounds induced higher inhibition effect in the CASS. The SASS appeared to reduce inhibition effect in comparison to the CASS, by 21.36%, 66.95%, 64.37% and 33.33% for phenol, 2-CP, 2,4-DCP and 1,2,4-TCB, respectively. Consequently, the SASS may be recommended as a promising configuration alternative for the waste streams containing toxic compounds.     

Chlorophenol degradation coupled to sulfate reduction.

We studied chlorophenol degradation under sulfate-reducing conditions with an estuarine sediment inoculum. These cultures degraded 0.1 mM 2-, 3-, and 4-chlorophenol and 2,4-dichlorophenol within 120 to 220 days, but after refeeding with chlorophenols degradation took place in 40 days or less. Further refeeding greatly enhanced the rate of degradation. Sulfate consumption by the cultures corresponded to the stoichiometric values expected for complete oxidation of the chlorophenol to CO2. Formation of sulfide from sulfate was confirmed with a radiotracer technique. No methane was formed, verifying that sulfate reduction was the electron sink. Addition of molybdate, a specific inhibitor of sulfate reduction, inhibited chlorophenol degradation completely. These results indicate that the chlorophenols were mineralized under sulfidogenic conditions and that substrate oxidation was coupled to sulfate reduction. In acclimated cultures the three monochlorophenol isomers and 2,4-dichlorophenol were degraded at rates of 8 to 37 mumol liter-1 day-1. The relative rates of degradation were 4-chlorophenol greater than 3-chlorophenol greater than 2-chlorophenol, 2,4-dichlorophenol. Sulfidogenic cultures initiated with biomass from an anaerobic bioreactor used in treatment of pulp-bleaching effluents dechlorinated 2,4-dichlorophenol to 4-chlorophenol, which persisted, whereas 2,6-dichlorophenol was sequentially dechlorinated first to 2-chlorophenol and then to phenol.     

Chlorophenol degradation coupled to sulfate reduction

We studied chlorophenol degradation under sulfate-reducing conditions with an estuarine sediment inoculum. These cultures degraded 0.1 mM 2-, 3-, and 4-chlorophenol and 2,4-dichlorophenol within 120 to 220 days, but after refeeding with chlorophenols degradation took place in 40 days or less. Further refeeding greatly enhanced the rate of degradation. Sulfate consumption by the cultures corresponded to the stoichiometric values expected for complete oxidation of the chlorophenol to CO2. Formation of sulfide from sulfate was confirmed with a radiotracer technique. No methane was formed, verifying that sulfate reduction was the electron sink. Addition of molybdate, a specific inhibitor of sulfate reduction, inhibited chlorophenol degradation completely. These results indicate that the chlorophenols were mineralized under sulfidogenic conditions and that substrate oxidation was coupled to sulfate reduction. In acclimated cultures the three monochlorophenol isomers and 2,4-dichlorophenol were degraded at rates of 8 to 37 mumol liter-1 day-1. The relative rates of degradation were 4-chlorophenol greater than 3-chlorophenol greater than 2-chlorophenol, 2,4-dichlorophenol. Sulfidogenic cultures initiated with biomass from an anaerobic bioreactor used in treatment of pulp-bleaching effluents dechlorinated 2,4-dichlorophenol to 4-chlorophenol, which persisted, whereas 2,6-dichlorophenol was sequentially dechlorinated first to 2-chlorophenol and then to phenol.     

Degradation ofortho-chlorophenol,para-chlorophenol, and 2,4-dichlorophenoxyacetic acid by the bacterial community of anaerobic sludge

The bacterial community of anaerobic sludge could degradeo-chlorophenol,p-chlorophenol, and 2,4-dichlorophenoxyacetic acid at concentrations as high as 100 mg/l. The time needed for the degradation of a given chlorinated phenol derivative increased 1.5- to 2-fold upon a twofold increase in its concentration (from 50 to 100 mg/l). The duration of the adaptation period depended on the compound studied and on its concentration. The degradation of 2,4-dichlorophenoxyacetic acid proceeded via 2,4-dichlorophenol andp-chlorophenol as intermediates; the degradation ofo-chlorophenol occurred with the formation of phenol. The dynamics ofp-chlorophenol degradation and chloride ion accumulation were studied.     

Degradation of the phenoxy acid herbicide diclofop-methyl by Sphingomonas paucimobilis isolated from a Canadian prairie soil

Sphingomonas paucimobilis , isolated from a soil in Manitoba, Canada, was able to utilize diclofop-methyl, (R,S)-methyl-2-[4-(2,4-dichlorophenoxy)phenoxy]propionate, as the sole source of carbon and energy. An actively growing aerobic culture completely degraded 1.5 μg diclofop-methyl ml⁻¹ to diclofop acid within 54 h, at 25°C. A biphasic growth pattern indicated that this organism was capable of degrading diclofop acid to 4-(2,4-dichlorophenoxy)phenol and 2,4-dichlorophenol and/or phenol. The accumulation of 2,4-dichlorophenol in the growth medium, however, suggested that Sphingomonas paucimobilis was unable to utilize this compound as a source of carbon and energy. Received 26 April 1999/ Accepted in revised form 30 July 1999     

Studies on composition and stability of a large membered bacterial consortium degrading phenol

A ten member microbial consortium (AS) consisting of eight phenol-degrading and two non-phenol-degrading strains of bacteria was developed and maintained in a fed-batch reactor by feeding 500 mg l⁻¹ phenol for four years at 28 ± 3 °C. The consortium could degrade 99% of 500 mg l⁻¹ phenol after 24 hours incubation with a biomass increase of 2.6 × 10⁷ to 4 × 10¹² CFU ml⁻¹. Characterization of the members revealed that it consisted of 4 principal genera, Bacillus, Pseudomonas, Rhodococcus, Streptomyces and an unidentified bacterium. Phenol degradation by the mixed culture and Bacillus subtilis, an isolate from the consortium was compared using a range of phenol concentrations (400 to 700 mg l⁻¹) and by mixing with either 160 mg l⁻¹ glucose or 50 mg l⁻¹ of 2,4-dichlorophenol in the medium. Simultaneous utilization of unrelated mixed substrates (glucose/2,4-dichlorophenol) by the consortium and Bacillus subtilis, indicated the diauxic growth pattern of the organisms. A unique characteristic of the members of the consortia was their ability to oxidize chloro aromatic compounds via meta pathway and methyl aromatic compounds via ortho cleavage pathway. The ability of a large membered microbial consortia to maintain its stability with respect to its composition and effectiveness in phenol degradation indicated its suitability for bioremediation applications.     

Isolation and partial characterization of aClostridium species transforming para-hydroxybenzoate and 3,4-dihydroxybenzoate and producing phenols as the final transformation products

Organisms present in methanogenic freshwater lake sediments from the vicinity of Athens, Georgia, were adapted to mineralize 2,4-dichlorophenol. Repeated addition of 0.5 to 2.7 mmol/liter of phenol, and later of 0.5–6.2 mmol/liter p-hydroxybenzoate (p-OHB), to such enrichments led to the conversion of p-OHB to phenol at a rate of up to 100 mmol p-OHB per liter per day. Subsequently, a spore-forming, obligately anaerobic bacterium, strain JW/Z-1, was isolated which transformed p-OHB to phenol and 3,4-dihydroxybenzoate (3,4-OHB) to catechol (1,2-dihydroxybenzene) stoichiometrically without further metabolism of the phenols. The strain did not transform benzoate, 4-chlorophenol, 2,4-dichlorophenol, 4-chlorobenzoate, o- and m-hydroxybenzoate, 2,4- and 3,5-dihydroxybenzoate, 2,3,4- and 3,4,5-trihydroxybenzoate, or 4-aminobenzoate. Yeast extract was required for growth of strain JW/Z-1 and only high concentrations of casein hydrolysate or tryptone could substitute it, to some extent. Except for sodium acetate, and some amino acids together with a 20-fold increased concentration of vitamins, no single carbohydrate or defined organic compound has been found to support growth of this strain in the presence (or in the absence) of 0.2 to 0.5% (w/v) yeast extract. The fermentation products during growth on yeast extract indicated that the metabolism of amino acid degradation was the major source for growth. The decarboxylating activity was inducible by p-OHB for the decarboxylation of p-OHB, and at a lower rate for 3,4-OHB, and by 3,4-OHB only for 3,4-OHB, suggesting that two different enzyme systems exist. The addition of the aromatic amino acids phenol or benzoate did not induce the decarboxylation activity in cultures growing with yeast extract. Growth was observed at temperatures ranging from 12–41°C (T_opt, 33–34°C) and at pH-values ranging from 6.0–10.0 (pH_opt, 7.2–8.2). The shortest doubling time observed for strain JW/Z-1 was 3.2 hours.     

Anaerobic degradation of chlorophenol by an enrichment culture

Summary An anaerobic mixed culture from sewage sludge was enriched in a yeast extract and peptone-containing medium; it was able to degrade 2-cholorophenol completely to methane and CO₂. Degradation rates of 2-chlorophenol of up to 0.18 g/l per day were observed in suspended cultures without biomass retention and of 0.375 g/l per day in cultures immobilized on Liapor clay beads. Attempts to isolate the dechlorinating organism failed. The mixed culture was reduced to three morphologically distinctive microorganisms using a medium with limited amounts of yeast extract and peptone and n-butyrate as a co-substrate. Under these conditions the phenol-degrading bacterium was lost and phenol accumulated in the medium. No growth and no dehalogenation of 2-chlorophenol was obtained when yeast extract and peptone were omitted completely. Besides serving as a source of supplementary components, yeast extract and peptone were apparently required as the main source of carbon, wereas reducing equivalents for reductive dehalogenation were obtained by oxidation of n-butyrate. A spirochaete-like organism was presumably the dechlorinating bacterium. The mixed culture lost its dehalogenation capability if this organism was lost. n-Butyrate could be replaced by n-valerate, hexanoate, heptanoate, octanoate, pelargonic acid, n-decanoic acid or palmitate as co-substrates for dehalogenation of either 2-chlorophenol, 2-bromophenol or complete dechlorination of 2,6-dichlorophenol, whereas from 2,4-dichlorophenol only the substituent in the ortho-position could be eliminated.Dedicated to Professor O. Kandler on the occassion of his 70th birthdayOffprint requests to: J. Winter