Anaerobic/aerobic conditions and biostimulation for enhanced chlorophenols degradation in biocathode microbial fuel cells

Anaerobic/aerobic conditions affected bacterial community composition and the subsequent chlorophenols (CPs) degradation in biocathode microbial fuel cells (MFCs). Bacterial communities acclimated with either 4-chlorophenol (4-CP) or 2,4-dichlorophenol (2,4-DCP) under anaerobiosis can degrade the respective substrates more efficiently than the facultative aerobic bacterial communities. The anaerobic bacterial communities well developed with 2,4-DCP were then adapted to 2,4,6-trichlorophenol (2,4,6-TCP) and successfully stimulated for enhanced 2,4,6-TCP degradation and power generation. A 2,4,6-TCP degradation rate of 0.10 mol/m³/d and a maximum power density of 2.6 W/m³ (11.7 A/m³) were achieved, 138 and 13 % improvements, respectively compared to the controls with no stimulation. Bacterial communities developed with the specific CPs under anaerobic/aerobic conditions as well as the stimulated biofilm shared some dominant genera and also exhibited great differences. These results provide the most convincing evidence to date that anaerobic/aerobic conditions affected CPs degradation with power generation from the biocathode systems, and using deliberate substrates can stimulate the microbial consortia and be potentially feasible for the selection of an appropriate microbial community for the target substrate (e.g. 2,4,6-TCP) degradation in the biocathode MFCs.     

Degradation of 2,4,6-trichlorophenol (2,4,6-TCP) by co-immobilization of anaerobic and aerobic microbial communities in an upflow reactor under air-limited conditions

The co-immobilization and the culture of anaerobic and aerobic communities was tested for the mineralization of 2,4,6-trichlorophenol (2,4,6-TCP). At first, the anaerobic microorganisms (aggregated into granules) were cultivated in an upflow anaerobic sludge blanket (UASB) reactor, in a continuous mode, with glucose, propionate, acetate (COD loading rate = 0.5-2.0 g COD/l per day, ratio 1:1:1) and 2,4,6-TCP (2,4,6-TCP loading rate = 25-278 micromol/l per day) as substrates. 2,4,6-TCP was degraded into 2,4-DCP and 4-CP, but it was not mineralized because of the low degradation rates of 4-CP. Furthermore, the highest loading rates of 2,4,6-TCP (>126 micromol/l per day) caused the inhibition of the strains degrading the propionate. The granules were therefore tested in association with the aerobic community. They were immobilized in kappa-carrageenan/gelatin [2% (w/w) of each polymer] gel beads and cultivated in a reactor, on their own (to test the influence of the gel), and then with the aerobic community, under anaerobic and air-limited conditions, respectively. The results showed that (1) the gel did not influence the activity of the granules, (2) the anaerobic and aerobic communities could be easily co-immobilized in gel beads and cultivated in a reactor, (3) the mineralization of 2,4,6-TCP (2,4,6-TCP loading rate = 10-506 micromol/l per day), its intermediates of degradation and the other substrates [glucose + acetate + propionate (ratio 1:1:1) = COD loading rate = 500 mg COD/l per day] could be obtained under air-limited conditions if the culture parameters were strictly controlled [airflow = 36-48 vvd (volume of air/volume of liquid in the reactor per day), pH value at around 7.5]. Finally, the gel did not retain its structure during the whole culture (263 days) in the air-limited reactor, but the anaerobic and aerobic communities retained their activities and worked together for the mineralization.     

厌氧微生物菌群XH-1对2,4,6-三氯苯酚的降解特性

有机污染物2,4,6-三氯苯酚(2,4,6-TCP)普遍存在于地下水和河流底泥等厌氧环境中。为了探究厌氧微生物菌群XH-1对2,4,6-TCP的降解能力,本研究以2,4,6-TCP为底物,接种XH-1建立微宇宙培养体系,并以中间产物4-氯苯酚(4-CP)和苯酚为底物分别进行分段富集培养,利用高效液相色谱分析底物的降解转化,同时基于16S rRNA基因高通量测序分析微生物群落结构变化。结果表明: 2,4,6-TCP(122 μmol·L^-1)以0.15 μmol·d^-1的速率在80 d内被完全降解转化,降解中间产物分别为2,4-二氯苯酚(2,4-DCP)、4-氯苯酚和苯酚,所有中间产物最终在325 d被完全降解。高通量测序结果表明,脱卤杆菌和脱卤球菌可能驱动2,4,6-TCP还原脱氯,其中,脱卤球菌可能在4-CP的脱氯转化中发挥重要作用,并与丁酸互营菌和产甲烷菌联合作用彻底降解2,4,6-TCP。     

Removal of chlorophenols in sequential anaerobic-aerobic reactors

Combination of upflow anaerobic sludge blanket (UASB) and aerobic rotating biological contactor (RBC) reactors having higher biomass concentration and higher sludge retention time (SRT) was applied for the sequential treatment of priority pollutant chlorophenol containing wastewater. Target compounds 2-chlorophenol (2-CP) and 2,4-dichlorophenol (2,4-DCP) present in two simulated wastewaters at a concentration of 30 mg/l each individually were sequentially treated in continuous mode by combined UASB-I, RBC-I and combined UASB-II, RBC-II reactors, respectively after the acclimation of their biomass with the corresponding chlorophenol. Reactor combinations took 190 and 215 days for acclimation with 30 mg/l of 2-CP and 2,4-DCP respectively. Hydraulic retention time (HRT) studies showed that 12h HRT of UASB-I and 23 h HRT of RBC-I as well as 12h HRT of UASB-II and 28.8h HRT of RBC-II were the optimum combinations for the treatment of simulated wastewater containing 2-CP and 2,4-DCP respectively. Optimum HRT combinations produced 2-CP and 2,4-DCP effluent having corresponding chlorophenol concentration of below detectable limit (BDL) and 0.1 mg/l respectively. Half velocity coefficients (Ks) for 2-CP and 2,4-DCP biodegradation in UASB reactors were determined to be 5.07 mg 2-CP/l and 6.49 mg 2,4-DCP/l. Optimum ratio of substrate (chlorophenol): co-substrate (sodium acetate) was 1:100.     

Effect of carbon sources and shock loading on the removal of chlorophenols in sequential anaerobic-aerobic reactors

The effect of carbon sources and shock loadings have been studied using two sets of sequential upflow anaerobic sludge blanket (UASB) and rotating biological contactor (RBC) reactors viz., UASB-I followed by RBC-I and UASB-II followed by RBC-II for the removal of two different priority pollutants, 2-CP and 2,4-DCP present in simulated wastewaters. Sodium formate, sodium propionate, glucose and methanol were used separately as four different carbon sources in the feed as co-substrate. Methanol was found to be the best carbon source for UASB reactors showing 95% 2-CP and 81.1% 2,4-DCP removals. The carbon sources formate and propionate were not found suitable in UASB reactors as only 22.6-46.8% 2-CP and 41.9-42.8% 2,4-DCP removals were observed. With glucose as carbon source 93.7% 2-CP and 79.6% 2,4-DCP removals were observed in UASB reactors. For all the four carbon sources more than 97.6% 2-CP and 99.7% 2,4-DCP removals were observed in sequential reactors. Although all the four carbon sources could not serve as good carbon source for UASB reactor alone but could be successfully used by the sequential reactors for the removal of chlorophenols. The Performance of sequential reactors was also evaluated at five different chlorophenolic shock loadings. During shock loading study the concentration of chlorophenols in the wastewaters was increased to 45, 60, 75, 90 and 105 mg/l as compared to the normal feed containing 30 mg/l 2-CP or 2,4-DCP. During shock loading study complete removal of 2-CP and more than 99.6% removal of 2,4-DCP was observed in sequential reactors. Sequential reactors successfully withstood all the shock loadings and produced high quality effluents.     

Biodegradation kinetics of 2,4-dichlorophenol by acclimated mixed cultures

The biodegradation kinetics of 2,4-dichlorophenol (2,4-DCP) by culture (Culture M) acclimated to mixture of 4-chlorophenol (4-CP) and 2,4-DCP and the culture (Culture 4) acclimated to 4-CP only were investigated in aerobic batch reactors. Also, pure strains isolated from mixed cultures were searched for their ability towards the biodegradation of 2,4-DCP. Culture 4 was able to completely degrade 2,4-DCP up to 80 mg/L within 30 h and removal efficiency dropped to 21% upon increasing initial concentration to 108.8 mg/L. When the Culture M was used, complete degradation of 2,4-DCP in the range of 12.5-104.4 mg/L was attained. A linear relationship between time required for complete degradation and initial 2,4-DCP concentrations was observed for both mixed cultures. It was observed that the Haldane equation can be used to predict specific degradation rate (SDR) (R(2)>0.99) as a function of initial 2,4-DCP concentrations and it adequately describes 2,4-DCP concentration profiles. Both of the mixed cultures settled well, which is important to maintain good removal efficiency for longer periods of time for real full-scale applications. Although the pure strains isolated from mixed cultures were found to have higher SDR of 2,4-DCP compared to mixed cultures, they did not settle well under quiescent conditions.     

Sequential anaerobic degradation of 2,4-dichlorophenol in freshwater sediments.

2,4-Dichlorophenol (2,4-DCP) was anaerobically degraded in freshwater lake sediments. From observed intermediates in incubated sediment samples and from enrichment cultures, the following sequence of transformations was postulated. 2,4-DCP is dechlorinated to 4-chlorophenol (4-CP), 4-CP is dechlorinated to phenol, phenol is carboxylated to benzoate, and benzoate is degraded via acetate to methane and CO2; at least five different organisms are involved sequentially. The rate-limiting step was the transformation of 4-CP to phenol. Sediment-free enrichment cultures were obtained which catalyzed only the dechlorination of 2,4-DCP, the carboxylation of phenol, and the degradation of benzoate, respectively. Whereas the dechlorination of 2,4-DCP was not inhibited by H2, the dechlorination of 4-CP, and the transformation of phenol and benzoate were. Low concentrations of 4-CP inhibited phenol and benzoate degradation. Transformation rates and maximum concentrations allowing degradation were determined in both freshly collected sediments and in adapted samples: at 31 degrees C, which was the optimal temperature for the dechlorination, the average adaptation time for 2,4-DCP, 4-CP, phenol, and benzoate transformations were 7, 37, 11 and 2 days, respectively. The maximal observed transformation rates for these compounds in acclimated sediments were 300, 78, 2, 130, and 2,080 micromol/liter(-1)/day(-1), respectively. The highest concentrations which still allowed the transformation of the compound in acclimated sediments were 3.1 m/M 2,4-DCP, 3.1 mM 4-CP, 13 mM phenol, and greater than 52 mM benzoate. The corresponding values were lower for sediments which had not been adapted for the transformation steps.     

Aerobic degradation of 2,4-dichlorophenoxyacetic acid and other chlorophenols by <Emphasis Type="Italic">Pseudomonas</Emphasis> strains indigenous to contaminated soil in South Africa: Growth kinetics and degradation pathway

Three indigenous pseudomonads, Pseudomonas putida DLL-E4, Pseudomonas reactans and Pseudomonas fluorescens, were isolated from chlorophenol-contaminated soil samples collected from a sawmill located in Durban (South Africa). The obtained isolates were tested for their ability to degrade chlorophenolic compounds: 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) in batch cultures. The isolates were found to effectively degrade up to 99.5, 98.4 and 94.0% with a degradation rate in the range of 0.67–0.99 (2,4-D), 0.57–0.93 (2,4-DCP) and 0.30–0.39 (2,4,6-TCP) mgL^–1 day^–1 for 2,4-D; 2,4-DCP and 2,4,6-TCP, respectively. The degradation kinetics model revealed that these organisms could tolerate up to 600 mg/L of 2,4-DCP. Catechol 2,3-dioxygenase activity detected in the crude cell lysates of P. putida DLL-E4 and P. reactans was 21.9- and 37.6-fold higher than catechol 1,2-dioxygenase activity assayed, suggesting a meta-pathway for chlorophenol degradation by these organisms. This is also supported by the generally high expression of C23O gene (involved in meta-pathway) relative to tfdC gene (involved in ortho-pathway) expression. Results of this study will be helpful in the exploitation of these organisms and/or their enzymes in bioremediation strategies for chlorophenol-polluted environment.     

Sequential anaerobic degradation of 2,4-dichlorophenol in freshwater sediments

2,4-Dichlorophenol (2,4-DCP) was anaerobically degraded in freshwater lake sediments. From observed intermediates in incubated sediment samples and from enrichment cultures, the following sequence of transformations was postulated. 2,4-DCP is dechlorinated to 4-chlorophenol (4-CP), 4-CP is dechlorinated to phenol, phenol is carboxylated to benzoate, and benzoate is degraded via acetate to methane and CO2; at least five different organisms are involved sequentially. The rate-limiting step was the transformation of 4-CP to phenol. Sediment-free enrichment cultures were obtained which catalyzed only the dechlorination of 2,4-DCP, the carboxylation of phenol, and the degradation of benzoate, respectively. Whereas the dechlorination of 2,4-DCP was not inhibited by H2, the dechlorination of 4-CP, and the transformation of phenol and benzoate were. Low concentrations of 4-CP inhibited phenol and benzoate degradation. Transformation rates and maximum concentrations allowing degradation were determined in both freshly collected sediments and in adapted samples: at 31 degrees C, which was the optimal temperature for the dechlorination, the average adaptation time for 2,4-DCP, 4-CP, phenol, and benzoate transformations were 7, 37, 11 and 2 days, respectively. The maximal observed transformation rates for these compounds in acclimated sediments were 300, 78, 2, 130, and 2,080 micromol/liter(-1)/day(-1), respectively. The highest concentrations which still allowed the transformation of the compound in acclimated sediments were 3.1 m/M 2,4-DCP, 3.1 mM 4-CP, 13 mM phenol, and greater than 52 mM benzoate. The corresponding values were lower for sediments which had not been adapted for the transformation steps.     

Effect of influent pH and alkalinity on the removal of chlorophenols in sequential anaerobic–aerobic reactors

This study was carried out to determine the effect of influent pH and alkalinity on the performance of sequential UASB and RBC reactors for the removal of 2-CP and 2,4-DCP from two different simulated wastewaters. The performance of methanogens at low (<6.0) to high (>8.0) pH values and at sufficiently high alkalinity (1500–3500 mg/l as CaCO₃) is described in this paper. Sequential reactors were capable of handling wastewaters with influent pH, 5.5–8.5. However, with influent pH 7.0 ± 0.1 UASB reactor showed best performance for 2-CP (99%) and 2,4-DCP (88%) removals. Increase in alkalinity/COD ratio in the influent (>1.1) caused gradual decrease in the chlorophenol removal in UASB reactors. The UASB reactors could not tolerate wastewater with higher alkalinity/COD ratio (2.6) and showed significant deterioration of its performance in terms of chlorophenols removal achieving only 74.7% 2-CP and 60% 2,4-DCP removals, respectively.     

Evaluation of toxicity and degradation of a chlorophenol mixture by the laccase produced by Trametes pubescens

In this study, the biodegradation of a mixture of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP) using the laccase produced by the white-rot fungus Trametes pubescens CBS 696.94 was evaluated. Two laccase isoenzymes with molecular weights of about 60 and 120 kDa were identified in the enzymatic crude extract. The highest laccase activity with syringaldazine was observed with pH 6.0 and 60°C, while with 2,2-azino-bis(3-ethylbenzothiazoline-6) sulphonic acid the highest activity was observed between 50 and 60°C and 3.0-4.0 pH. A biodegradation of 100%, 99%, 82.1% and 41.1% for 2-CP, 2,4-DCP, 2,4,6-TCP and PCP, respectively, was observed after 4h of reaction. The reduction in chlorophenols concentration allowed 90% reduction in mixture toxicity. In summary, these results show the feasibility of a laccase enzymatic crude extract from T. pubescens for the reduction of concentration and toxicity of chlorophenols.     

Effect of pH on the anaerobic dechlorination of chlorophenols in a defined medium

Anaerobic dehalogenation of aromatic compounds is a well-documented phenomenon. However, the effects of operating parameters such as pH have received little attention despite their potential impact on treatment processes using dehalogenating organisms. In this work the effect of pH on the dehalogenation of 2,4,6-trichlorophenol (2,4,6-TCP) was studied using defined media containing one of several non-fermentable buffering agents (MOPS, TRICINE, BICINE, CHES), and no chloride ions. The dechlorination process was followed by monitoring the disappearance of 2,4,6-TCP, as well as the appearance of its dehalogenation products, i.e., 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP), and chloride ions. The results indicate that dechlorination occurs only if the pH is within the range 8.0–8.8. The newly formed 2,4-DCP was also dehalogenated in the process. However, even within this pH range dechlorination ceased when all 2,4,6-TCP and 2,4-DCP was converted to 4-CP. Stoichiometric amounts of all dehalogenation products (including chloride) could be recovered at any stage during the process. In addition, the biomass concentration was measured. After an initial lag phase, it appeared that the rate of dechlorination per unit biomass (proportional to the Cl^– concentration divided by the biomass concentration) went through a rapid increase and then remained constant throughout the process. This indicates that the dechlorinating organism(s) either make up the entire population or constitute a stable fraction of it. Correspondence to: P. M. Armenante     

Evaluation of an integrated anaerobic/aerobic SBR system for the treatment of wool dyeing effluents

This work examined the performance of a sequencing batch reactor treating dyeing effluents from a factory that processes mainly wool and wool/polyester blends. Different operational conditions were evaluated, namely the influence of the anaerobic and the subsequent aerobic phase on the organic load removal, as well as the effect of the length of the aeration period (from 8 to 12h) on process efficiency. A comparison between a fill stage in fast and slow modes was carried out. Results indicate that the cycle 2 conditions (fast fill and 12h aeration time) improved the overall efficiency (85±6% soluble COD and 95±4% BOD₅ removal yields) with a predominant COD uptake occurring in the aerobic stage. Slow, linear COD removal was observed in the anaerobic phase, in contrast with an exponential COD decrease in the oxic phase. For SS a level under 100mg/l was general achieved in the exit of the reactor. With respect to dye degradation, a noticeable decrease of the absorbance measured in the UV–visible range was observed. This could be explained by the reduction of the azo bonds of some of the present dyes in the anaerobic step, in which ORP values lower than –400mV were attained. Some oxidation of anthraquinone sulphonate dyes and of the aromatic amines resulting from azo bond cleavage could also have been taken place, as well as bioelimination mechanisms such as dye sorption.     

Degradation of 2,4,5-trichlorophenol and 2,3,5,6-tetrachlorophenol by combining pulse electric discharge with bioremediation

Degradation of 2,4,5-trichlorophenol (2,4,5-TCP) and 2,3,5,6-tetrachlorophenol (TeCP) was studied using a two-stage approach that utilized efficient pulse electric discharge (PED) followed by biological degradation with a consortium from acclimated return activated sludge. The chlorinated phenols were treated in the PED reactor as an aerosol at a voltage of 55–60 kV, a frequency of 385 Hz, a current of 50–60, and with a 200-ns pulse. As determined by gas chromatography and mass spectrometry (GC/MS), the first stage converted 500 ppm 2,4,5-TCP to 163 ppm 2,4,5-TCP and dimethyldecene, dichloronaphthalenol, octyl acetate, and silyl esters. The total carbon content of 2,4,5-TCP after PED treatment was determined to be 228 ± 35 ppm. The remaining 2,4,5-TCP and the products formed were then mineralized by the acclimated activated sludge in shake flasks; the initial rate of degradation of 2,4,5-TCP was calculated to be 5 nmol min⁻¹ mg protein⁻¹ at 163 ppm initial concentration (three orders of magnitude higher than the only rate found in the literature). By combining the two techniques, a synergistic effect (2.3-fold increase in the concentration of 2,4,5-TCP degraded and 3.3-fold increase in total carbon degraded) was observed, in that bacteria without any treatment degraded a maximum of 70 ppm 2,4,5-TCP but after PED treatment 163 ppm 2,4,5-TCP was degraded. TeCP was also mineralized by the acclimated activated sludge after treatment with PED. This two-stage approach was also evaluated using a continuous 1-l fluidized-bed reactor. Received: 3 November 1998 / Received revision: 28 February 1999 / Accepted: 14 March 1999     

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.     

Anaerobic biodegradation of 2,4-dichlorophenol in freshwater lake sediments at different temperatures

Anaerobic degradation of 2,4-dichlorophenol (2,4-DCP) between 5 and 72 degrees C was investigated. Anaerobic sediment slurries prepared from local freshwater pond sediments were partitioned into anaerobic tubes or serum vials, which then were incubated separately at the various temperatures. Reductive 2,4-DCP dechlorination occurred only in the temperature range between 5 and 50 degrees C, although methane was formed up to 60 degrees C. In sediment samples from two sites and at all tested temperatures from 5 to 50 degrees C, 2,4-DCP was transformed to 4-chlorophenol (4-CP). The 4-CP intermediate was subsequently degraded after an extended lag period in the temperature range from 15 to 40 degrees C. Adaptation periods for 2,4-DCP transformation decreased between 5 and 25 degrees C, were essentially constant between 25 and 35 degrees C, and increased in the tubes incubated at temperatures between 35 and 40 degrees C. The degradation rates increased exponentially between 15 and 30 degrees C, had a second peak at 35 degrees C, and decreased to about 5% of the peak activity by 40 degrees C. In tubes from one sediment sample, incubated at temperatures above 40 degrees C, an increase in the degradation rate was observed following the minimum at 40 degrees C. This suggests that at least two different organisms were involved in the transformation of 2,4-DCP to 4-CP. Storage of the original sediment slurries for 2 months at 12 degrees C resulted in increased adaptation times, but did not affect the degradation rates.     

Anaerobic biodegradation of 2,4-dichlorophenol in freshwater lake sediments at different temperatures.

Anaerobic degradation of 2,4-dichlorophenol (2,4-DCP) between 5 and 72 degrees C was investigated. Anaerobic sediment slurries prepared from local freshwater pond sediments were partitioned into anaerobic tubes or serum vials, which then were incubated separately at the various temperatures. Reductive 2,4-DCP dechlorination occurred only in the temperature range between 5 and 50 degrees C, although methane was formed up to 60 degrees C. In sediment samples from two sites and at all tested temperatures from 5 to 50 degrees C, 2,4-DCP was transformed to 4-chlorophenol (4-CP). The 4-CP intermediate was subsequently degraded after an extended lag period in the temperature range from 15 to 40 degrees C. Adaptation periods for 2,4-DCP transformation decreased between 5 and 25 degrees C, were essentially constant between 25 and 35 degrees C, and increased in the tubes incubated at temperatures between 35 and 40 degrees C. The degradation rates increased exponentially between 15 and 30 degrees C, had a second peak at 35 degrees C, and decreased to about 5% of the peak activity by 40 degrees C. In tubes from one sediment sample, incubated at temperatures above 40 degrees C, an increase in the degradation rate was observed following the minimum at 40 degrees C. This suggests that at least two different organisms were involved in the transformation of 2,4-DCP to 4-CP. Storage of the original sediment slurries for 2 months at 12 degrees C resulted in increased adaptation times, but did not affect the degradation rates.     

Biodegradation kinetics of 2,4,6-Trichlorophenol by an acclimated mixed microbial culture under aerobic conditions

The objective of this study was to achieve a better quantitative understanding of the kinetics of 2,4,6-trichlorophenol (TCP) biodegradation by an acclimated mixed microbial culture. An aerobic mixed microbial culture, obtained from the aeration basin of the wastewater treatment plant, was acclimated in shake flasks utilizing various combinations of 2,4,6-TCP (25–100 mg l⁻¹), phenol (300 mg l⁻¹) and glycerol (2.5 mg l⁻¹) as substrates. Complete primary TCP degradation and a corresponding stoichiometric release of chloride ion were observed by HPLC and IEC analytical techniques, respectively. The acclimated cultures were then used as an inoculum for bench scale experiments in a 4 l stirred-tank reactor (STR) with 2,4,6-TCP as the sole carbon/energy (C/E) source. The phenol acclimated mixed microbial culture consisted of primarily Gram positive and negative rods and was capable of degrading 2,4,6-TCP completely. None of the predicted intermediate compounds were detected by gas chromatography in the cell cytoplasm or supernatant. Based on the disappearance of 2,4,6-TCP, degradation was well modelled by zero-order kinetics which was also consistent with the observed oxygen consumption. Biodegradation rates were compared for four operating conditions including two different initial 2,4,6-TCP concentrations and two different initial biomass concentrations. While the specific rate constant was not dependent on the initial 2,4,6-TCP concentration, it did depend on the initial biomass concentration (X _init). A lower biomass concentration gave a much higher zero-order specific degradation rate. This behaviour was attributed to a lower average biomass age or cell retention time (θ_x) for these cultures. The implications of this investigation are important for determining and predicting the potential risks associated with TCP, its degradation in the natural environment or the engineering implications for ex situ treatment of contaminated ground water or soil.     

Degradation of dissolved and sorbed 2,4-dichlorophenol in soil columns by suspended and sorbed bacteria

The influence of sorption of bacteria, as well as 2,4-dichlorophenol (2,4-DCP), on themineralization of 100 g l^-1 of the organic compound was examined in an aquifer material under advective flow conditions (column displacement technique). The study was designed to distinguish the rates and extent of biodegradation of the sorbed and the dissolved trace organic and the contribution of sorbed and suspended bacteria to the degradation. The degradation of dissolved 2,4-DCP was significantly faster thanthe degradation of the same compound sorbed to the solids, and suspended bacteriadegraded the dissolved compound at a higher rate than sorbed bacteria, also on a percell basis. The suspended bacteria degraded 8–12% of the added dissolved 2,4-DCP, while sorbed bacteria made a smaller contribution by degrading about 5% of sorbed 2,4-DCP. No degradation was seen with sorbed 2,4-DCP and suspended bacteria, and a marginal contribution was made by sorbed bacteria on the degradation of dissolved 2,4-DCP (<0.4%).     

Degradation of chlorophenols catalyzed by laccase

The degradations of 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 2-chlorophenol (2-CP) catalyzed by laccase were carried out. The optimal condition regarding degradation efficiency was also discussed, which included reaction time, pH value, temperature, concentration series of chlorophenols and laccase. Results showed that the capability of laccase was the best, while to oxidize 2,4-DCP among the above-mentioned chlorophenols. Within 10 h, the removal efficiency of 2,4-DCP, 2-CP and 4-CP could reach 94%, 75% and 69%, respectively. The optimal pH for laccase to degrade chlorophenols was around 5.5. The increase of laccase concentration or temperature might result in the degradation promotion. The trends of degradation percentage were various among these three chlorophenols with the concentration increase of chlorophenols. Degradation of 2,4-DCP is a first-order reaction and the reaction activation energy is about 44.8 kJ mol⁻¹. When laccase was immobilized on chitosan, crosslinked with glutaraldehyde, the activity of immobilized laccase was lower than that of free laccase, but the stability improved significantly. The removal efficiency of immobilized laccase to 2,4-DCP still remained over 65% after six cycles of operation.