Biodegradation Of Chlorophenols Research Articles

Enhancement of cometabolic biodegradation of 4-chlorophenol induced with phenol and glucose as carbon sources by Comamonas testosteroni

The biological degradation of phenol and 4-chlorophenol (4-CP) by Comamonas testosteroni CECT 326T has been studied. Phenol and 4-CP were treated alone as a sole carbon and energy source, but only phenol was completely degraded by C. testosteroni. Since the presence of cosubstrates can enhance the toxic compounds removal by pure cultures, phenol and glucose were added as growth substrates for cometabolic transformation of 4-CP. High efficiencies were obtained in all the experiments carried out in presence of both cosubstrates. In spite of the fact that the addition of glucose reduced the lag phase of 4-CP removal, lower phenol concentrations were required to obtain the same degradation efficiencies. The cometabolic transformation of 4-CP was closely related with the extent of phenol removal. The values of the 4-CP/biomass concentration ratio (S/X) obtained for discriminating between complete (S/X ≤ 0.11) and partial 4-CP (S/X ≥ 0.31) transformation showed a narrower range than that reported in the literature. The extent of the cometabolic 4-CP transformation in the presence of phenol could be further enhanced by using glucose as an additional carbon and energy source. However, no significant influence of glucose concentration on 4-CP removal was observed over the concentration range studied.

The characteristics and enzyme activities of 4-chlorophenol biodegradation by Fusarium sp.

The effects of pH, temperature and sucrose addition on biodegradative capacity of Fusarium sp. HJ01 for 4-chlorophenol (4-CP) were examined, the property of dioxygenases produced by Fusarium sp. HJ01 during 4-CP degradation was investigated. The results show that Fusarium sp. HJ01 has a high capacity on degrading 4-CP in solution. The optimum values of pH, sucrose concentration and temperature are pH 7,1 g/L and 30°C, respectively. The strain can produce chlorocatechol 1,2-dioxygenase (CC12O) and chlorocatechol 2,3-dioxygenase (CC23O), which show the highest activities when 4-CP is used as the sole carbon source and energy, and the optimal values of pH and temperature are pH 7 and 50°C for CC12O as well as pH 8 and 60°C for CC23O. The kinetics of enzyme-catalyzed reactions accord with the Michaelis-Menten equation. To our knowledge, this is the first study on biodegradation of 4-CP by Fusarium sp. HJ01.

Biodegradation of 4-chlorophenol by Arthrobacter chlorophenolicus A6: effect of culture conditions and degradation kinetics

Among known microbial species, Arthrobacter chlorophenolicus A6 has shown very good potential to treat phenolic wastewaters. In this study, the levels of various culture conditions, namely initial pH, agitation (rpm), temperature (°C), and inoculum age (h) were optimized to enhance 4-chlorophenol (4-CP) biodegradation and the culture specific growth rate. For optimization, central composite design of experiments followed by response surface methodology (RSM) was applied. Results showed that among the four independent variables, i.e., pH, agitation (rpm), temperature (°C), and inoculum age (h) investigated in this study, interaction effect between agitation and inoculum age as well as that between agitation and temperature were significant on both 4-CP biodegradation efficiency and culture specific growth rate. Also, at the RSM optimized settings of 7.5 pH, 207 rpm, 29.6°C and 39.5 h inoculum age, 100% biodegradation of 4-CP at a high initial concentration of 300 mg l(-1) was achieved within a short span of 18.5 h of culture. The enhancement in the 4-CP biodegradation efficiency was found to be 23% higher than that obtained at the unoptimized settings of the culture conditions. Results of batch growth kinetics of A. chlorophenolicus A6 for various 4-CP initial concentrations revealed that the culture followed substrate inhibition kinetics. Biokinetic constants involved in the process were estimated by fitting the experimental data to several models available from the literature.

Enhancing the biodegradation of 4-chlorophenol by Arthrobacter chlorophenolicus A6 via medium development

This study reports development of a suitable medium for enhancing the 4-chlorophenol (4-CP) biodegradation by Arthrobacter chlorophenolicus A6 employing sequential design of experiments. The media constituents were initially screened using a 2-level factorial design, and the results indicated that dipotassium hydrogen phosphate, ammonium nitrate, magnesium sulfate and calcium chloride significantly influence both 4-CP biodegradation and growth of the culture. Among these significant factors only calcium chloride showed a large positive effect on 4-CP biodegradation by the microorganism. While dipotassium hydrogen phosphate also showed slightly positive effect on the culture specific growth rate, it, however, exhibited some negative effect on 4-CP biodegradation efficiency. Both magnesium sulfate and ammonium nitrate in the media negatively influenced both 4-CP biodegradation as well as the culture specific growth rate. A central composite design of experiments was further used to optimize the levels of the screened media constituents for enhancing the 4-CP biodegradation efficiency. The results revealed 100% 4-CP biodegradation efficiency with a maximum specific growth rate of 0.093 h −1 at an optimum combination of 2.62 g l −1 of dipotassium hydrogen phosphate, 0.58 g l −1 of ammonium nitrate, 0.17 g l −1 of magnesium sulfate and 0.04 g l −1 of calcium chloride in the medium.

Degradation of chlorophenols by sequential biological-advanced oxidative process using Trametes pubescens and TiO 2/UV

The degradation of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) via biological, advanced oxidative process (AOP) and sequential biological-AOP was investigated in this work. The white-rot fungus Trametes pubescens was used for the biodegradation of chlorophenols, while in AOP TiO 2/UV was used. In the biological degradation, the effect of glucose as a cofactor was also evaluated. The highest degradations were obtained when the reaction medium was supplemented with glucose, ranging from 94.6% to 37.8%, with degradation activity for 2-CP > 2,4-DCP > PCP > 2,4,6-TCP. During the AOP the removal initial rate increased in the following order 2-CP > 2,4,6-TCP > 2,4-DCP > PCP, and the obtained degradation range from 82.0% to 24.0%. When biological removal process, supplemented with glucose, was followed for an AOP process, 100% degradation was obtained for all the chlorophenols tested. These results suggest that the white-rot fungi T. pubescens could be used for the degradation of xenobiotic compounds, and its use with an advanced oxidative process, in a sequential mode, may be considered to obtain a complete removal of them.

Cometabolic biodegradation of 4-chlorophenol by sequencing batch reactors at different temperatures

The simultaneous removal of 4-chlorophenol (4-CP) and phenol in lab-scale sequencing batch reactors at different temperatures has been studied. Phenol feed concentration was fixed at 525 mg/L and 4-CP concentration was increased from 105 to 2100 mg/L at a constant hydraulic residence time (HRT) of 10.5 d. Complete phenol and 4-CP biodegradation was achieved during the aerobic stage working with 4-CP concentrations up to 1470 mg/L in the feed. Both 4-CP and phenol specific initial removal rates were strongly affected by 4-CP feed concentration and temperature. Only at the highest temperature tested (35 °C) it was possible to increase the maximum assimilative 4-CP concentration by the biological sludge up to 2100 mg/L, and a significant reduction of the ecotoxicity of the effluents was observed. 4-chlorocatechol (4-CC) was identified as the major intermediate in the aerobic cometabolic 4-CP degradation, being the ecotoxicity of that species substantially lower than that of 4-CP.

Mixed Culture Acclimatization and Biodegradation of Chlorophenols in Shake Flasks: Effect of the Inoculum Source

Shake flask reactors with different inocula were run for the treatment of chlorophenols present in wastewaters. The three different inocula were obtained from—sewage treatment plant, refinery effluent treatment plant (ETP), and paper mill ETP, respectively. The model compounds tested were 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP). The three inocula have different levels of exposure to phenolic compounds. As the paper mill effluent has high level of phenolic compounds, and sewage has no phenolic compound, the inoculum obtained from paper mill ETP would have been acclimatized to some degree to phenolic environment. In our lab, the inocula were acclimatized to synthetic 4-CP and 2,4-DCP for several weeks at 30°C in shake flasks. It was found that each inoculum demonstrated different specific activity in chlorophenols degradation. The inoculum from paper mill ETP yielded highest degradation rate for both 4-CP and 2,4-DCP. The effect of a biogenic substrate (glucose) concentration on the acclimati...

Effect of Starvation and Shock Loads on the Biodegradation of 4-Chlorophenol in a Discontinuous Moving Bed Biofilm Reactor

The influence of starvation (defined as the period without substrate) and shock loads on the performance of a moving bed sequencing batch reactor degrading 4-chlorophenol (4CP) were investigated. The biomass was acclimated to biodegrade 100 mg/L of 4CP, and the colonization of the packing material was followed. Two starvation periods and two shock loads were studied. The degradation capacity of the suspended and the attached biomass present on the moving bed was also evaluated. The experiments showed that, after the starvation period, the specific degradation rate decreased from 30.5 to 28.5 and 20 mg 4CP/gVSS/h, when starvation periods of 24 and 48 h were applied, respectively. When two concentration peaks of 500 and 1,050 mg/L were applied, a loss of 6% and 8% on the specific degradation rate, respectively, was also observed. The moving bed thus showed great robustness against starvation periods and shock loads. Suspended biomass presented higher specific degradation rates, but attached biomass did not generate a metabolite that is inhibitory when it accumulates.

Phenol and 4-chlorophenol biodegradation by yeast Candida tropicalis in a fluidized bed reactor

The objective of this work was to evaluate (i) the hydrodynamics and oxygen transfer characteristics of a fluidized bed reactor (FBR) and (ii) their performance in the continuous biodegradation of a phenol (Phe) and 4-chlorophenol (4-CP)-containing influent when the FBR was loaded with Candida tropicalis yeast immobilized onto granular activated carbon (GAC) particles. The first part was carried out in terms of the behavior of mixing time ( t m95), bubble diameter ( d B), gas hold-up ( ɛ G), gas–liquid interfacial area ( a′) and oxygen transfer coefficient ( k L a) in biphasic (gas–liquid) and triphasic (gas–liquid–carbon) systems, both batch-wise operated in pseudohomogeneous regime at superficial gas flow rates U G below 1.72 cm s −1. Mixing time was determined using a tracer technique, ɛ G was measured by the volume expansion method; ( d B) was determined by the procedure reported by Poulsen and Iversen and k L a was determined by a transient gassing-in technique. It was found that hydrodynamic variables were severely influenced by GAC particles. The d B values were smaller in triphasic than in biphasic system, with the consequent increase in the ɛ G, a′ and k L a values. The removal efficiencies of both Phe and 4-CP in the bioreactor challenged at increasing volumetric loading rate of pollutants were determined in the second part of the study. Phe and 4-CP was determined by HPLC. Immobilized biomass on GAC was estimated from their total nitrogen content. Regarding continuous biodegradation experiments, the FBR was capable of efficiently removing Phe at volumetric loading rates as high as 60 mg Phe L −1 h −1 when it was fed as the sole carbon source. Beyond this point, removal efficiencies drastically decreased. When operated with a feed consisting of a mixture of Phe and 4-CP, the FBR was able to remove more than 98% of 4-CP in the range of volumetric loading rates of 4.1 mg 4-CP L −1 h −1 and 55 mg Phe L −1 h −1 with no apparent deterioration of bioreactor performance.

Environmental significance of O‐demethylation of chloroanisoles by soil bacterial isolates as a mechanism that improves the overall biodegradation of chlorophenols

The biodegradation rate of chlorophenols in the environment seems to be limited by a competitive mechanism of O-methylation which produces chloroanisoles with a high potential of being bioconcentrated in living organisms. In this work we report for the first time the isolation of three soil bacterial strains able to efficiently degrade 2,4,6-trichloroanisole (2,4,6-TCA). These strains were identified as Xanthomonas retroflexus INBB4, Pseudomonas putida INBP1 and Acinetobacter radioresistens INBS1. In these isolates 2,4,6-TCA was efficiently metabolized in a minimal medium containing methanol and 2,4,6-TCA as the only carbon sources, with a concomitant release of 3 mol of chloride ion from 1 mol of 2,4,6-TCA, indicating complete dehalogenation of 2,4,6-TCA. 2,4,6-trichlorophenol (2,4,6-TCP) was identified as a degradative intermediate, indicating that 2,4,6-TCA underwent O-demethylation as the first step in the biodegradation process. 2,4,6-TCP was further transformed into 2,6-dichloro-para-hydroquinone (2,6-DCHQ) and subsequently mineralized. The degradation of chloroanisoles could improve the overall biodegradation of chlorophenols in the environment, because those chlorophenols previously biomethylated might also be later biodegraded. Xanthomonas retroflexus INBB4 has two O-demethylation systems: one is an oxygenase-type demethylase, and the other is a tetrahydrofolate (THF)-dependent O-demethylase. On the contrary O-demethylation of 2,4,6-TCA in P. putida INBP1 is just catalysed by an oxygenase-type NADH/NADPH-dependent O-demethylase, whereas in A. radioresistens INBS1 a THF-dependent O-demethylase activity was detected.

Biodegradation of 4-CP in an activated sludge reactor: Effects of biosurfactant and the sludge age

The biosurfactant's effect on the biodegradation of 4-chlorophenol (4-CP) in the existence of glucose was researched under the circumstances of using unacclimated culture and various sludge ages. The removal efficiencies of chemical oxygen demand (COD) and 4-CP, the growth of biomass and specific substrate removal rates were examined under various operating conditions. When 150 mg/l concentration of 4-CP was applied, glucose and 4-CP degraded in the same period in the unacclimated bioreactors where biosurfactant was added. Nevertheless, the COD removal in the control reactor noticeably decreased and when compared with reactors which biosurfactant was added, a longer period was needed for the degradation of 4-CP in this reactor. While the complete removal of 4-CP in the control reactor eventuated on the 14th day, in the reactor which 2 × critical micelle concentration (CMC) was added the complete removal of 4-CP eventuated on the end of the 1st day. These results showed that addition of biosurfactant reduced the transient time before the steady-state. COD and 4-CP removal performances were improved by increasing the sludge age. No difference in system performance was observed at high sludge ages in the absence and presence of biosurfactant. However, the performance of the system in the presence of biosurfactant was satisfactory even at low sludge ages. That is, the system should be operated either at high sludge ages (>15 days) in the absence of biosurfactant or at low sludge ages (<15 days) in the presence of surfactants.

Biodegradation of 4-Chlorophenol by Candida albicans PDY-07 under Anaerobic Conditions

Candida albicans PDY-07 was isolated from activated sludge under anaerobic conditions and identified as a member belonging to the genus Candida. Pure culture of C. albicans PDY-07, biodegradation of 4-chlorophenol (4-CP) was carried out under anaerobic conditions in Erlenmeyer flasks at 35°C, with an initial pH of 7.0–7.2 and a starting inoculum of 10% (by volume). The results showed that, under the above-mentioned conditions, C. albicans PDY-07 could thoroughly biodegrade 4-CP up to a concentration of 300mg·L −1 within 244h and that it had a high tolerance potential of up to 440mg·L −1 for 4-CP. With the increase in the initial concentrations of 4-CP, substrate inhibition was obviously enhanced. There was increased consumption of 4-CP, which was not assimilated by the cell for growth but was used to counteract the strong substrate inhibition. In addition, the cell growth and substrate-degradation kinetics of 4-CP as the sole source of carbon and energy for the strain in batch cultures were also investigated over a wide range of substrate concentrations (2.2–350mg·L −1), using the proposed cell growth and degradation kinetic models. The results recorded from these experiments showed that the proposed kinetic models adequately described the dynamic behavior of 4-CP biodegradation by C. albicans PDY-07.

Adsorption, desorption and bioregeneration in the treatment of 2-chlorophenol with activated carbon

This study aims to clarify the effect of activated carbon type on the extent of adsorbability, desorbability, and bioregenerability in the treatment of 2-chlorophenol. Four different activated carbon types; thermally activated and chemically activated powdered carbons (PAC), and their granular countertypes (GAC) with similar physical characteristics were used. Thermally activated carbons adsorbed 2-chlorophenol much better than chemically activated ones. However, adsorption was more reversible in the case of chemically activated ones. The use of powdered and granular activated carbon countertypes resulted in comparable adsorption and desorption characteristics. For each activated carbon type, 2-chlorophenol exhibited higher adsorbability and lower desorbability than phenol. Biodegradation of 2-chlorophenol took place very slowly when it was used as the sole carbon source in acclimated and non-acclimated activated sludges. Bioregeneration occurred only via desorption due to an initial concentration gradient and no further desorption took place due to low biodegradability. Bioregeneration of activated carbon loaded with 2-chlorophenol was not a suitable option when 2-chlorophenol was the only carbon source. It is suggested to remove 2-chlorophenol via adsorption onto activated carbon rather than applying biological treatment. Also in such cases, the use of thermally activated carbons with higher adsorption and lower desorption capacities is recommended rather than chemically activated carbons.

The QSPR (quantitative structure–property relationship) study about the anaerobic biodegradation of chlorophenols

In this study, based on quantum chemical and physicochemical descriptors, by the use of partial least squares analysis, a good prediction quantitative structure–property relationship for the disappearance rate constant (log K) of chlorophenols (CPs) in the anaerobic culture was obtained. It was found that the resonance energy of the two-center term ( J), which described the character of the weakest carbon–chlorine bond, played an important role in the reductive chlorine processes, the greater the sizes of CPs molecules, the higher the log K values. Increasing energy of the lowest unoccupied molecular orbital ( E lumo) values of the CPs lead to decreasing log K values, and CPs with large absolute hardness values tended to have big log K values.

Effect of long-term exposure, biogenic substrate presence, and electron acceptor conditions on the biodegradation of multiple substituted benzoates and phenolates

Biodegradation rates of benzoate and related aromatic compounds, 3-nitrobenzoate, 4-chlorobenzoate, 4-chlorophenol, and 2,4-dichlorophenol by unexposed (unacclimated) and long-term exposed (acclimated) biomass were quantified using a modified fed-batch technique. The acclimated biomass was taken after approximately 1-year of operation from three lab-scale sequencing batch reactors (SBR). These reactors were operated under various cycling electron acceptor conditions with a continuous feed of a synthetic wastewater containing biogenic and nonbiogenic chemicals including benzoate, 3-nitrobenzoate, and 4-chlorophenol, but not 4-chlorobenzoate or 2,4-dichlorophenol. The unexposed biomass was taken from a full-scale wastewater treatment plant, which constituted one of the original sources of inoculum for the lab-scale SBRs. The acclimated biomass manifested high removal rates of benzoate and related aromatic compounds with additional removal of structurally similar chemicals (4-chlorobenzoate and 2,4-dichlorophenol). The unacclimated biomass showed no removal of 3-nitrobenzoate, 4-chlorobenzoate or 2,4-dichlorophenol. Addition of biogenic substrates reduced the degradation of most aromatic compounds tested, but it enhanced 2,4-dichlorophenol removal. Biodegradation rates of each aromatic compound with the biomass from the anoxic/aerobic SBR were further determined under anaerobic (absence of aeration and NO 3 −), anoxic (no aeration, but with surplus NO 3 −), standard oxygen (DO>0.2 mg/L), and elevated oxygen (DO>25 mg/L) conditions. The removal rate of both benzoate and 3-nitrobenzoate decreased under anaerobic condition but not under the anoxic condition; 4-chlorophenol biodegradation, on the other hand, was reduced significantly under both anoxic and anaerobic conditions. The removal rates of aromatic compounds, particularly those of 3-nitrobenzoate and 2,4-dichlorophenol, increased significantly under elevated dissolved oxygen conditions. Our results demonstrated that when the biochemical conditions shifted from oxygen-respiration to nitrate respiration, to anaerobiosis, the biodegradation rates of test aromatic compounds decreased or ceased.

Biodegradation of 4-chlorophenol by acclimated and unacclimated activated sludge —Evaluation of biokinetic coefficients

Unacclimated and acclimated activated sludges were examined for their ability to degrade 4-CP (4-chlorophenol) in the presence and absence of a readily growing substrate using aerobic batch reactors. The effects of 4-CP on the μ (specific growth rate), COD removal efficiency, Y (yield coefficient), and q (specific substrate utilization rate) were investigated. It was observed that the toxicity of 4-CP on the culture decreased remarkably after acclimation. For example, the IC 50 value on the basis of μ was found to increase from 130 to 218 mg/L with the acclimation of the culture. Although an increase in 4-CP concentration up to 300 mg/L has no adverse effect on the COD removal efficiency of the acclimated culture, a considerable decrease was observed in the case of an unacclimated culture. Although 4-CP removal was not observed with an unacclimated culture, almost complete removal was achieved with the acclimated culture, up to 300 mg/L. The Haldane kinetic model adequately predicted the biodegradation of 4-CP and the kinetic constants obtained were q m = 41.17 mg / ( g MLVSS h ) , K s = 1.104 mg / L , and K i = 194.4 mg / L . The degradation of 4-CP led to formation of 5-chloro-2-hydroxymuconic semialdehyde, which was further metabolized, indicating complete degradation of 4-CP via a meta-cleavage pathway.

Acclimation of anaerobic sludge degrading chlorophenols and the biodegradation kinetics during acclimation period

The acclimation of sludge from Hangzhou citrate factory and Hangzhou municipal wastewater treatment plant for degradation dechlorination of chlorophenols (CPs) compounds, and its biodegradation kinetics were studied in batch process with or without addition of sucrose. Three monochlorophenols (2-CP; 3-CP; 4-CP) and pentachlorophenol (PCP) were concurrently fed to different bioreactors. The parameters that were monitored included biogas production, biogas composition and chemical oxygen demand (COD). The results showed that acclimation with chlorophenol can increase the degradation activity of anaerobic sludge and degradation rate of chlorophenolic compounds, and reduce the lag time. Degradation dechlorination activity of the acclimated sludge strongly depended on sludge source, microorganism population and chlorophenol congener. 2-CP was more easily acclimated than 3-CP and 4-CP. Among the four tested compounds, 4-CP was the most difficult to be acclimated. The observed degradation rate with presence of sucrose was higher than that with absence of sucrose, suggesting that addition of the external carbon source can stimulate the formation of acclimated sludge which could effectively degrade chlorophenols. Kinetic equations of biodegradation of chlorophenols were also presented in this paper.

Kinetics of biodegradation during remediation of consecutive accidental spills of chlorophenols in a sandy aquifer

Kinetics of biodegradation of chlorophenols were studied in six sandy aquifer columns (0.06 m I.D.; 1.00 m L). Remediation of chlorophenols was enhanced by using a "closed-loop" configuration system, where local groundwater was recirculated through the polluted site in a controlled manner. Consecutive accidental spills of phenol, 2-monochlorophenol (2-MCP) and 2,4,6-trichlorophenol (2,4,6-TCP) as single pollutants were removed following first order kinetics. The removal of chlorophenols increased by one order of magnitude following consecutive accidental spills demonstrating adaptation of the resident micro flora. The biodegradation rate constants in this study were in the same range and agreed with those reported in the literature for biodegradation in aerobic aquifers. Following the fate of the resident micro flora (enhanced by adding NH4Cl and KH2PO4 at a ratio C/N/P equal to 120:10:1), biomass growth was observed in the sandy aquifer columns and particle size analyses of the aqueous phase recirculated through the polluted site experimentally proved aggregation of cells. Aggregation of cells has been hypothesized as one of the causes for low biodegradation rates found in the field compared to those calculated using biodegradation rate constants determined in batch culture.

Biodegradation of chlorophenols using the cell‐free culture broth of Phanerochaete chrysosporium immobilized in polyurethane foam

AbstractA cell‐free culture broth of Phanerochaete chrysosporium immobilized in polyurethane foam has been evaluated for the biodegradation of chlorophenols. Lignin peroxidase, manganese peroxidase, and oxalate concentrations in cell‐free culture broth were measured and compared to find the optimum combination of secondary metabolites for the highest biodegradation of chlorophenols. The isozyme distributions and their expression levels were significantly different and changed with increases in the culture time. The oxalate concentration was also found to vary, depending on culture time. Cell‐free broth containing an optimal combination of secondary metabolites showed the greatest biodegradation of 2,4,5‐chlorophenol in the presence of veratryl alcohol and H2O2. Phenols with greater numbers of chlorines were degraded more efficiently by this cell‐free culture broth according to the results of biodegradation experiments for five chlorophenols, including 2‐, 4‐, 2,4‐, 2,4,5‐, and pentachlorophenol, as well as phenol. This degradation efficiency correlated well with remaining lignin peroxidase activity during degradation. Cell‐free culture broths may readily be used for biodegradation of highly recalcitrant chemicals since the system would not be affected by the toxicity of the chemicals nor would the adsorption characteristics of the cells be of concern.© 2002 Society of Chemical Industry

The Effect of Rhizodeposition from Helophytes on Bacterial Degradation of Phenolic Compounds

The effect of rhizodeposition from helophytes (aquatic plants) on the bacterial degradation of toxic compounds such as phenolic substances was tested. Investigations were carried out as batch experiments with rhizodeposition products obtained from helophytes. DOC concentrations, which were used as points of reference for rhizodeposition, were between 2.5 and 12 mg per litre. Rhizodeposition was found to advance the biodegradation of 4-chlorophenol when using a mixed bacterial culture and pure cultures of bacteria previously isolated from Phalaris arundinacea roots. This stimulation is a result of rhizodeposition products serving as growth substrates for the bacteria. Investigations with Ralstonia eutropha (DSMZ Braunschweig, strain 5536) confirmed the function of rhizodeposition products as growth substrates. Degradation by Acinetobacter baumannii and Ralstonia sp. obtained from Phalaris arundinacea was'accompanied by the dechlorination of 4-chlorophenol. There was no enhancing impact on the degradation of the substances phenol and 2,6-dimethylphenol by rhizodeposition products.