Integrated photocatalytic-biological reactor for accelerated 2,4,6-trichlorophenol degradation and mineralization

An integrated photocatalytic-biological reactor (IPBR) was used for accelerated degradation and mineralization of 2,4,6-trichlorophenol (TCP) through simultaneous, intimate coupling of photocatalysis and biodegradation in one reactor. Intimate coupling was realized by circulating the IPBR’s liquid contents between a TiO₂ film on mat glass illuminated by UV light and honeycomb ceramics as biofilm carriers. Three protocols—photocatalysis alone (P), biodegradation alone (B), and integrated photocatalysis and biodegradation (photobiodegradation, P&B)—were used for degradation of different initial TCP concentrations. Intimately coupled P&B also was compared with sequential P and B. TCP removal by intimately coupled P&B was faster than that by P and B alone or sequentially coupled P and B. Because photocatalysis relieved TCP inhibition to biodegradation by decreasing its concentration, TCP biodegradation could become more important over the full batch P&B experiments. When phenol, an easy biodegradable compounds, was added to TCP in order to promote TCP mineralization by means of secondary utilization, P&B was superior to P and B in terms of mineralization of TCP, giving 95% removal of chemical oxygen demand. Cl⁻ was only partially released during P experiments (24%), and this corresponded to its poor mineralization in P experiments (32%). Thus, intimately coupled P&B in the IPBR made it possible obtain the best features of each: rapid photocatalytic transformation in parallel with mineralization of photocatalytic products.     

Internal loop photobiodegradation reactor (ILPBR) for accelerated degradation of sulfamethoxazole (SMX)

The internal loop photobiodegradation reactor (ILPBR) was evaluated for the degradation of the pharmaceutical sulfamethoxazole (SMX) using batch experiments following three protocols: photolysis alone (P), biodegradation alone (B), and intimately coupled photolysis and biodegradation (P&B). SMX was removed more rapidly by P&B than by either P or B alone, and the corresponding dissolved organic carbon (DOC) removals by P&B also were higher. The faster SMX removal probably was due to a synergy between photolysis and the rapid biodegradation of SMX by the biofilm. The greater DOC removal was brought about by the presence of biofilm bacteria able to biodegrade photolysis products. Ammonium N released during photolysis of SMX gave more evidence for the formation of intermediates and was enough in P&B experiments to support bioactivity when no other N was supplied. Clone libraries performed on the biofilms before and after the P&B experiments showed profound changes in the microbial community. Whereas Rhodopirellula baltica and Methylibium petroleiphilum PM1 dominated the biofilm after the B experiments, they were replaced by Micrococcus luteus, Delftia acidovorans, and Oligotropha carboxidovorans after the P&B experiments. The changes in microbial community structure mirrored the change in function in the P&B experiments: SMX biodegradation (presumably the roles of R. baltica and M. petroleiphilum) was out-competed by SMX photolysis, but biodegradation of photolysis products (most likely by M. luteus and D. acidovorans) became important. The higher removal rates of SMX and DOC, as well as the changes in microbial community structure, confirm the value of intimately coupling photolysis with biodegradation in the ILPBR.     

Biofilm coupled with UV irradiation for phenol degradation and change of its community structure

The extensive use of phenol compounds and the inability to remove these compounds during wastewater treatment have resulted in the widespread occurrence of phenols in the natural environment. Phenols have been linked to serious risks to human and environmental health. Hence, the need to develop technologies that can effectively remove phenols from wastewater and source waters is a pressing challenge. In this study, light ceramic particles were immersed in activated sludge acclimated to degrade phenol, and microorganisms were allowed to attach to the particles surface to form biofilm. Then the ceramic particles with biofilm were moved into the photolytic circulating-bed biofilm reactor made of quartz glass, which was used for the degradation of phenol by three protocols: photolysis with UV light alone (P), biodegradation alone (B), and the two mechanisms operating simultaneously (photobiodegradation, P&B). The experimental results indicated that phenol removal rate was quickest by B experiment. However, P&B experiment gave more complete mineralization of phenol than that by other protocols. During P&B experiment, the microorganisms grown on porous ceramic carrier still kept the bioactivity degrading phenol, even under UV light irradiation. However, the dominant members of the bacterial community changed dramatically after the intimately coupled photobiodegradation, according to molecular biological analysis to the biofilm. Whereas Beijerinckia sp. was the dominant strain in the inoculum, it was replaced by Thauera sp. MZ1T that played a main role on degrading phenol during P&B experiment.     

Integrated photocatalytic-biological reactor for accelerated phenol mineralization

An integrated photocatalytic-biological reactor (IPBR) was developed for accelerated phenol degradation and mineralization. In the IPBR, photodegradation and biodegradation occurred simultaneously, but in two separated zones: a piece of mat-glass plate coated with TiO₂ film and illuminated by UV light was connected by internal circulation to a honeycomb ceramic that was the biofilm carrier for biodegradation. This arrangement was designed to give intimate coupling of photocatalysis and biodegradation. Phenol degradation was investigated by following three protocols: photocatlysis with TiO₂ film under ultraviolet light, but no biofilm (photodegradation); biofilm biodegradation with no UV light (biodegradation); and simultaneous photodegradation and biodegradation (intimately coupled photobiodegradation). Photodegradation alone could partly degrade phenol, but was not able to achieve significant mineralization, even with an HRT of 10 h. Biodegradation alone could completely degrade phenol, but it did not mineralize the COD by more than 74%. Photobiodegradation allowed continuous rapid degradation of phenol, but it also led to more complete mineralization of phenol (up to 92%) than the other protocols. The results demonstrate that intimate coupling was achieved by protecting the biofilm from UV and free-radical inhibition. With phenol as the target compound, the main advantage of intimate coupling in the IPBR was increased mineralization, presumably because photocatalysis made soluble microbial products more rapidly biodegradable.     

Photobiodegradation of phenol with ultraviolet irradiation of new ceramic biofilm carriers

Activated sludge acclimated to biodegrade phenol was allowed to attach on and in light porous ceramic carriers and to function as a biofilm in a photolytic circulating-bed bioreactor (PCBBR). Phenol degradation in the PCBBR was investigated following three protocols: photolysis with ultraviolet light alone (P), biodegradation alone (B), and the two mechanisms operating simultaneously (P/B). Phenol was degraded at approximately equal rates by B and P/B, each of which was much faster than the rate by P. Furthermore, phenol was mineralized to a significantly greater extent with P/B than with either P or B. SEM showed that the biofilm survived well inside macropores that presumably shaded the microorganisms from UV irradiation, even though the UV light greatly reduced biofilm on outer surface of the carriers in the P/B experiments. Rapid biodegradation of phenol, enhanced mineralization, and survival of bacteria inside macropores demonstrated that being in a biofilm inside the porous carriers protected the bacteria from UV-light toxicity, allowing intimate coupling of photolysis and biodegradation.     

UV photolysis for accelerated quinoline biodegradation and mineralization

Sequentially and intimately coupled photolysis with biodegradation were evaluated for their ability to accelerate quinoline-removal and quinoline-mineralization kinetics. UV photolysis sequentially coupled to biodegradation significantly improved biomass-growth kinetics, which could be represented well by the Aiba self-inhibition model: UV photolysis increased the maximum specific growth rate (μ _max) by 15 %, and the inhibition constant (K _SI) doubled. An internal loop photo-biodegradation reactor (ILPBR) was used to realize intimately coupled photolysis with biodegradation. The ILPBR was operated with batch experiments following three protocols: photolysis alone (P), biodegradation alone (B), and intimately coupled photolysis and biodegradation (P&B). For P&B, the maximum quinoline removal rate (r _max) increased by 9 %, K _SI increased by 17 %, and the half-maximum-rate concentration (K _S) decreased by 55 %, compared to B; the composite result was a doubling of the quinoline-biodegradation rate for most of the concentration range tested. The degree of mineralization was increased by both forms of photolysis coupled to biodegradation, and the impact was greater for intimate coupling (18 % increase) than sequential coupling (5 %). The benefits of UV photolysis were greater with intimate coupling than with sequential coupling due to parallel transformation by biodegradation and photolysis.     

Intimate coupling of photocatalysis and biodegradation in a photocatalytic circulating-bed biofilm reactor

Coupling advanced oxidative pretreatment with subsequent biodegradation demonstrates potential for treating wastewaters containing biorecalcitrant and inhibitory organic constituents. However, advanced oxidation is indiscriminate, producing a range of products that can be too oxidized, unavailable for biodegradation, or toxic themselves. This problem could be overcome if advanced oxidation and biodegradation occurred together, an orientation called intimate coupling; then, biodegradable organics are removed as they are formed, focusing the chemical oxidant on the non-biodegradable fraction. Intimate coupling has seemed impossible because the conditions of advanced oxidation, for example, hydroxyl radicals and sometimes UV-light, are severely toxic to microorganisms. Here, we demonstrate that a novel photocatalytic circulating-bed biofilm reactor (PCBBR), which utilizes macro-porous carriers to protect biofilm from toxic reactants and UV light, achieves intimate coupling. We demonstrate the viability of the PCBBR system first with UV only and acetate, where the carriers grew biofilm and sustained acetate biodegradation despite continuous UV irradiation. Images obtained by scanning electron microscopy and confocal laser scanning microscopy show bacteria living behind the exposed surface of the cubes. Second, we used slurry-form Degussa P25 TiO2 to initiate photocatalysis of inhibitory 2,4,5-trichlorophenol (TCP) and acetate. With no bacterial carriers, photocatalysis and physical processes removed TCP and COD to 32% and 26% of their influent levels, but addition of biofilm carriers decreased residuals to 2% and 4%, respectively. Biodegradation alone could not remove TCP. Photomicrographs clearly show that biomass originally on the exterior of the carriers was oxidized (charred), but biofilm a short distance within the carriers was protected. Finally, we coated TiO2 directly onto the carrier surface, producing a hybrid photocatalytic-biological carrier. These carriers likewise demonstrated the concept of photocatalytic degradation of TCP coupled with biodegradation of acetate, but continued TCP degradation required augmentation with slurry-form TiO2.     

Decolourization of olive mill waste-waters by the white-rot fungus Phanerochaete chrysosporium: involvement of the lignin-degrading system

Summary The decolourization of olive mill waste-waters (OMW) by Phanerochaete chrysosporium was investigated. OMW decolourization occurred during the primary phase of growth when glycerol was used as the carbon source, and during secondary metabolism in nitrogen-limited cultures. The decolourization was found to be extensive (74% of colour removal, 80% of chemical oxygen demand removal) when the cultures were supplement d with veratryl alcohol and flushed with O₂. The biodegradation system was repressed with glutamate as a nitrogen source. These results suggest that all or part of the lignin-degrading system of P. chrysosporium played a role in biodegradation of OMW. The decolourization of OMW corresponds to depolymerization of high-molecular-mass aromatics combined with mineralization of a wide range of monoaromatic compounds. Correspondence to: S. Sayadi     

Degradation of reactive dyes in a photocatalytic circulating-bed biofilm reactor

Decolorization and mineralization of reactive dyes by intimately coupled TiO₂‐photocatalysis and biodegradation (ICPB) on a novel TiO₂‐coated biofilm carrier were investigated in a photocatalytic circulating‐bed biofilm reactor (PCBBR). Two typical reactive dyes—Reactive Black 5 (RB5) and Reactive Yellow 86 (RY86)—showed similar first‐order kinetics when being photocatalytically decolorized at low pH (～4–5) in batch experiments. Photocatalytic decolorization was inhibited at neutral pH in the presence of phosphate or carbonate buffer, presumably due to electrostatic repulsion from negatively charged surface sites on TiO₂, radical scavenging by phosphate or carbonate, or both. Therefore, continuous PCBBR experiments were carried out at a low pH (～4.5) to maintain high photocatalytic efficiency. In the PCBBR, photocatalysis alone with TiO₂‐coated carriers could remove target compound RB5 and COD by 97% and 47%, respectively. Addition of biofilm inside macroporous carriers maintained a similar RB5 removal efficiency, but COD removal increased to 65%, which is evidence of ICPB despite the low pH. ICPB was further proven by finding microorganisms inside carriers at the end of the PCBBR experiments. A proposed ICPB pathway for RB5 suggests that a major intermediate, a naphthol derivative, was responsible for most of the residual COD, while most of the nitrogen in the azo‐bonds (? N?N? ) was oxidized to N₂. Biotechnol. Bioeng. 2012; 109:884–893. © 2011 Wiley Periodicals, Inc.     

How UV photolysis accelerates the biodegradation and mineralization of sulfadiazine (SD)

Sulfadiazine (SD), one of broad-spectrum antibiotics, exhibits limited biodegradation in wastewater treatment due to its chemical structure, which requires initial mono-oxygenation reactions to initiate its biodegradation. Intimately coupling UV photolysis with biodegradation, realized with the internal loop photobiodegradation reactor, accelerated SD biodegradation and mineralization by 35 and 71 %, respectively. The main organic products from photolysis were 2-aminopyrimidine (2-AP), p-aminobenzenesulfonic acid (ABS), and aniline (An), and an SD-photolysis pathway could be identified using C, N, and S balances. Adding An or ABS (but not 2-AP) into the SD solution during biodegradation experiments (no UV photolysis) gave SD removal and mineralization rates similar to intimately coupled photolysis and biodegradation. An SD biodegradation pathway, based on a diverse set of the experimental results, explains how the mineralization of ABS and An (but not 2-AP) provided internal electron carriers that accelerated the initial mono-oxygenation reactions of SD biodegradation. Thus, multiple lines of evidence support that the mechanism by which intimately coupled photolysis and biodegradation accelerated SD removal and mineralization was through producing co-substrates whose oxidation produced electron equivalents that stimulated the initial mono-oxygenation reactions for SD biodegradation.     

Biodegradation of chlorophenols by mixed and pure cultures from a fluidized-bed reactor

An aerobic, continuous-flow fluidized-bed reactor was established with inoculum from activated sludge, and fed a mixture of 2,4,6-trichlorophenol (TCP), 2,3,4,6-tetrachlorophenol (TeCP) and pentachlorophenol (PCP) as the sole sources of carbon and energy for 2 years. Experiments with the enrichment were performed with material from the reactor. Later, degradation experiments were completed using pure cultures of bacteria that were isolated from suspended samples of the carrier biofilm. In batch-bottle bioassays, the reactor enrichment degraded PCP, TeCP and TCP both in mineral salts (MS) and tryptone-yeast extract-glucose (TGY) media. ortho-Methoxylated chlorophenols including 4,5-dichloroguaiacol (4,5-DCG), tetrachloroguaiacol (TeCG) and trichlorosyringol (TCS) resisted biodegradation by the enrichment both in MS and TGY media, whereas 5,6-dichlorovanillin (5,6-DCV) was readily transformed to an unidentified metabolite. Experiments with ¹⁴C labeled chlorophenols showed mineralization of 2,4-dichlorophenol (DCP) and 2,3,5-TCP to ¹⁴CO₂ by the enrichment. Material from the suspended biofilm after continuous chlorophenol feeding for 2 years was inoculated onto TGY-agar plates, and showed predominantly two colony, types accounting for over 99% of the total colony counts. The two colony types, were equal in abundance. Six Gram-negative, oxidase- and catalase-positive, non-fermentative small rods were isolated in TGY agar media supplemented with 10 mg/l of TeCP or PCP. All isolates formed colonies in TGY plus 150 mg/l of PCP. The isolates degraded TCP and TeCP but not PCP. In mixtures of isolated bacteria the rates of chlorophenol degradation were similar to those observed with individual isolates. Three isolates were identified as Pseudomonas saccharophila and three were an unidentified species of Pseudomonas.     

Effect of nutrient amendments and sterilization on mineralization and/or biodegradation of 14C-labeled MCPP by soil bacteria under aerobic conditions

Mineralization and/or degradation of the phenoxy herbicide mecoprop (MCPP) by a group of soil bacteria under the effects of nutrient amendments and sterilization were investigated. Five different species of Pseudomonas (P. paucimobilis, P. aeruginosa, P. mallei, P. pseudomallei, and P. pickettii) were isolated from sediments of Lake Mariut, a freshwater lake in south Alexandria, Egypt. MCPP mineralization and/or removal were tested by the selected Pseudomonas species as active and dead masses in minimal and nutrient-rich media supplemented with ¹⁴C-MCPP at a final concentration of 10 μg l⁻¹ for 6 successive weeks. Results revealed significant variations in the removal percentages of MCPP by either mineralization or biodegradation. Pseudomonas spp. exhibited high selectivity toward MCPP. Considering the short duration of the experiment (45 days) Pseudomonas spp. investigated in this study provide an effective and selective potential for MCPP decontamination. As a general trend, all of the investigated species exhibited higher biodegradation and removal efficiency of MCPP (1.3–89.5%) compared to their mineralization abilities (0.10–9.28%) under the experimental conditions. Also the highest MCPP mineralization and degradation by the selected Pseudomonas spp. were achieved by their inactive (dead) followed by active-rich cultures (both were inoculated in nutrient-rich medium), confirming the positive effects of nutrient amendments and sterilization on MCPP decontamination. Efficiency of Pseudomonas spp. was positively correlated with time up to the 3rd week for biodegradation and up to the 6th week for mineralization, indicating high mineralization efficiency provided enough time. Finally, Pseudomonas spp. showed selective preferences among them toward MCPP with the highest mineralization efficiency achieved by P. aeruginosa (1SB) and P. mallei (2SA), while the highest biodegradation efficiency was achieved by P. pickettii (5SB) and P. pseudomallei (3S). They seemed very promising but require longer exposure and higher MCPP concentration to stimulate and enhance their metabolic and mineralization capabilities. Results of this study can be manipulated efficiently to select the most promising Pseudomonas species for decontaminating polluted systems providing the optimum degradation conditions.     

The role of exogenous electron donors for accelerating 2,4,6-trichlorophenol biotransformation and mineralization

2,4,6-Trichlorophenol (TCP) is a biologically recalcitrant compound, but its biodegradation via reductive dechlorination can be accelerated by adding an exogenous electron donor. In this work, acetate and formate were evaluated for their ability to accelerate TCP reductive dechlorination, as well to accelerate mono-oxygenation of TCP’s reduction product, phenol. Acetate and formate accelerated TCP reductive dechlorination, and the impact was proportional to the number of electron equivalents released by oxidation of the donor: 8 e^? equivalents per mol for acetate, compared to 2 e^? eq per mol for formate. The acceleration phenomenon was similar for phenol mono-oxygenation, and this increased the rate of TCP mineralization. Compared to endogenous electron equivalents generated by phenol mineralization, the impact of exogenous electron donor was stronger on a per-equivalent basis.     

Statistical analysis and optimization of nitrogen,phosphorus, and inoculum concentrations for the biodegradation of petroleum hydrocarbons by response surface methodology

In order to optimize and evaluate the influence of nitrogen, phosphorus, and inoculum concentrations on the biodegradation of hydrocarbon contaminated effluents, experiments based on central composite design (CCD) method were carried out for 3 days, employing C1 mixed culture and intermittent aeration. The independent variables were nitrogen concentration (X ₁), phosphorus concentration (X ₂), and inoculum concentration (X ₃) and the removal of total petroleum hydrocarbons (TPH) was the dependent variable. The optimized nutrients ratio (C:N:P = 100:20:2.7) and inoculum concentration (1.32 g/l) provided TPH removal of 71.8% after processing for three days. Analysis using gas chromatography identified five hydrocarbons classes: paraffins, isoparaffins, olefins, naphthenics, and aromatics. The naphthenic compounds did not degrade as readily as the other hydrocarbons that were identified. The following degradation percentages were obtained: 87.1% for the paraffins, 77.7% for the isoparaffins, 78.6% for the olefins, 38.4% for the naphthenics, and 71.7% for the aromatics.     

Intensification of phenol biodegradation by humic substances

Phenol biodegradation was carried out in a batch system by the bacterial strain Cupriavidus metallidurans in the presence of potassium humate that was prepared by alkaline extraction from oxyhumolite. The experiments were focused on the assessment of the humate effect on biodegradation activity of the tested bacterial strain. The achieved results demonstrated that the humate has a positive influence on the biodegradation of phenol and reduces the incubation time necessary for phenol removal. Higher biodegradation rate and more intensive growth were observed during the cultivation in presence of humate in comparison to the cultivation without its addition. Adsorption of the humate on bacterial biomass was observed as well. Subsequently, a phenol biodegradation testing in a continuous-flow system using a biofilm reactor was also carried out. Although the reactor was inoculated by C. metallidurans only, the microbial composition under an aerobic non-aseptic condition during this long-term cultivation changed. The phenol removal efficiency obtained in the biofilm reactor was higher than 92% when phenol concentration in a treated medium was 1200 mg l⁻¹.     

Biodegradation of petroleum industry oily-sludge using Jordanian oil refinery contaminated soil

The main objective of this study was to evaluate the effect of oily sludge concentration on its biodegradability in soil. Oily sludge was collected and applied to microcosms at full-, half-, or quarter-strength concentrations equivalent to 44.2, 22.2, and 11.1 g kg^?1 soil, respectively, of total petroleum hydrocarbons (TPH) contained in oily sludge. The biodegradability of oily sludge was evaluated by measuring CO₂ evolution and by measuring removal of TPH as well as its main composing fractions; namely; alkanes, aromatics, NSO-compounds, and asphaltenes. The collected soil contained 3.63 × 10⁶ cfu g^?1 soil of hydrocarbon-degrading bacteria, which is satisfactory to drive successful biodegradation of hydrocarbons in soil. These numbers increased significantly with oily sludge addition at a rate proportional to the added TPH reaching 3.35 × 10⁷ cfu g^?1 soil in the half-strength treatment. TPH mineralization rate followed the same pattern. However, TPH-mineralization efficiency was the greatest in quarter-strength treatment at 18.3%. TPH-removal efficiency was also highest in quarter-strength treatment at 30.9%. Nutrients addition caused mineralization inhibition. Since nutrients were added as a ratio of the added carbon, inhibition was the greatest with the highest TPH treatment. While alkanes were degraded, aromatics and asphaltenes were not, and NSO-compounds were enriched. Although SDS was completely biodegradable in soil, its addition promoted mineralization and removal of TPH from soil.     

Modeling trichloroethylene degradation by a recombinant pseudomonad expressing toluene ortho-monooxygenase in a fixed-film bioreactor

Burkholderia cepacia PR123(TOM23C), expressing constitutively the TCE-degrading enzyme toluene ortho-monooxygenase (Tom), was immobilized on SIRANtrade mark glass beads in a biofilter for the degradation and mineralization of gas-phase trichloroethylene (TCE). To interpret the experimental results, a mathematical model has been developed which includes axial dispersion, convection, film mass-transfer, and biodegradation coupled with deactivation of the TCE-degrading enzyme. Parameters used for numerical simulation were determined from either independent experiments or values reported in the literature. The model was compared with the experimental data, and there was good agreement between the predicted and measured TCE breakthrough curves. The simulations indicated that TCE degradation in the biofilter was not limited by mass transfer of TCE or oxygen from the gas phase to the liquid/biofilm phase (biodegradation limits), and predicts that improving the specific TCE degradation rates of bacteria will not significantly enhance long-term biofilter performance. The most important factors for prolonging the performance of biofilter are increasing the amount of active biomass and the transformation capacity (enhancing resistance to TCE metabolism). Copyright 1998 John Wiley & Sons, Inc.     

Protection of biofilms against toxic shocks by the adsorption and desorption capacity of carriers in anaerobic fluidized bed reactors

The aim of this study was to select a support medium for an anaerobic biofilm fluidized bed reactor (AFBR) for waste water treatment. Six materials, shale, pumice, porous glass, quartz sand, activated carbon and anthracite were used as carriers for the biofilm. The reactors were operated in parallel for several months with vapour condensate from a sulfite cellulose process as feed. The criteria used for the evaluation were: a) Reproducibility of the reactor performance, b) performance of the different carriers under various loading rates, c) stability against toxic shock loadings using 2,4,6-trichlorophenol (TCP) as toxicant, d) recovery capacity after intoxication and starvation, e) adsorption/desorption behavior of the carriers.A comparison between four runs showed good reproducibility of the steady state removal rates. The performance of the reactors and the stability of the degradation rates were tested for a range of loading conditions. Unbuffered, buffered and pH controlled conditions were compared. The pumice carrier was best with respect to the degradation rate achieved per carrier mass. The response of the reactors to massive TCP step loadings was tested. Loadings less than 1.5 kg TCP/m³d resulted in initially normal gas production rates for all the systems, except the activated carbon, whose gas production was partially inhibited from the start. After increasing the load to 1.5 kg TCP/m³d the gas production rates of all the other reactors fell abruptly to zero. Restarting after 2 months, all reactors showed methanogenic activity without requiring new inoculum.Adsorption and desorption experiments with TCP showed that only the anthracite and activated carbon adsorbed appreciable amounts. The activated carbon had the greatest adsorption capacity but did not release the TCP by desorption, as did the anthracite.A bicomponent (pumice and anthracite) carrier mixture was compared in biological experiments with pumice and anthracite carrier alone, with and without TCP loading. The pumice and the carrier-mix performed equally well under non-toxic-loading conditions. With TCP toxic loading, the performance of the anthracite was superior. The anthracite carrier could be regenerated, owing mainly to its capacity for desorption.     

A constructed microbial consortium for biodegradation of the organophosphorus insecticide parathion

A consortium comprised of two engineered microorganisms was assembled for biodegradation of the organophosphate insecticide parathion. Escherichia coli SD2 harbored two plasmids, one encoding a gene for parathion hydrolase and a second carrying a green fluorescent protein marker. Pseudomonas putida KT2440 pSB337 contained a p-nitrophenol-inducible plasmid-borne operon encoding the genes for p-nitrophenol mineralization. The co-culture effectively hydrolyzed 500 microM parathion (146 mg l(-1)) and prevented the accumulation of p-nitrophenol in suspended culture. Kinetic analyses were conducted to characterize the growth and substrate utilization of the consortium members. Parathion hydrolysis by E. coli SD2 followed Michaelis-Menten kinetics. p-Nitrophenol mineralization by P. putida KT2440 pSB337 exhibited substrate-inhibition kinetics. The growth of both strains was inhibited by increasing concentrations of p-nitrophenol, with E. coli SD2 completely inhibited by 600 microM p-nitrophenol (83 mg l(-1)) and P. putida KT2440 pSB337 inhibited by 1,000 microM p-nitrophenol (139 mg l(-1)). Cultivation of the consortium as a biofilm indicated that the two species could cohabit as a population of attached cells. Analysis by confocal microscopy showed that the biofilm was predominantly comprised of P. putida KT2440 pSB337 and that the distribution of E. coli SD2 within the biofilm was heterogeneous. The use of biofilms for the construction of degradative consortia may prove beneficial.     

2,4-DNT removal in intimately coupled photobiocatalysis: the roles of adsorption, photolysis, photocatalysis, and biotransformation

The removal of 2,4-dinitrotoluene (2,4-DNT) by simultaneous UV-photo(cata)lysis and biodegradation was explored using intimately coupled photolysis/photocatalysis and biodegradation (ICPB) with two novel porous carriers. First, a porous ceramic carrier was used to attach the photocatalyst (TiO?) on its exterior and accumulate biomass in its interior. UV irradiation alone decomposed 71% of the 2,4-DNT in 60 h, and TiO? catalyst improved the photolysis to 77%. Second, a macroporous sponge carrier was used to strongly adsorb 2,4-DNT and protect microorganisms from 2,4-DNT inhibition and UV irradiation. The main photolytic reactions were reduction of the nitryl to amino and hydrolysis of the amino to release NH??. The main biodegradation reactions were oxidative release of NO?? and accelerated reductive release of NH??. ICPB more thoroughly released inorganic N, with nearly equal amounts being oxidized to nitrate and reduced to ammonium. The genera Burkholderia and Bacillus were found inside the sponge carriers, and they are associated with biodegradation of DNT and its photolysis intermediates. Therefore, using an adsorbent and macroporous biofilm carrier enabled the effective removal of 2,4-DNT by ICPB.