Roland Leduc

Conjugation of laccase from the white rot fungus Trametes versicolor to chitosan and its utilization for the elimination of triclosan

A commercial laccase from Trametes versicolor was conjugated with biopolymer chitosan using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) as the cross-linking agent. Laccase-chitosan conjugation strategies were tested using different molar ratios of glucosamine monomer/protein with different molar excess ratios of EDC relative to laccase. Immobilization techniques were developed to improve the stability against thermal and chemical denaturation, storage and reusability of this biocatalyst. The conjugation resulted in a solid biocatalyst with an apparent laccase activity of ±626 U/g, 12 and 60 folds higher in the conjugation efficiency of biocatalyst relative to the immobilized and free laccase activity respectively when compared with zero EDC/laccase ratio used in conjugation solution. The conjugated laccases formed successfully eliminated the emerging pollutant triclosan (TCS) from aqueous solutions, having a higher potential to transform TCS than free laccase. UPLC-QTOF results indicate the formation of TCS oligomers. Furthermore, they are the first evidence of direct dechlorination of TCS mediated by the oxidative action of laccases.

Influence of the starting microbial nucleus type on the anaerobic granulation dynamics

Abstract The influence of four different granulation precursors, syntroph-enriched methanogenic consortia, Methanosaeta-enriched, Methanosarcina-enriched nuclei and acidogenic flocs, on the time course of complex granule development and the lag time for start-up was investigated in four upflow anaerobic sludge-bed and filter reactors. Although the operational conditions allowed the maintenance of the same specific growth rate of biomass in the four reactors, granulation proceeded rapidly with syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei. However, granulation was significantly retarded when acidogenic flocs were used as precursors. The granule mean Sauter diameter increased rapidly in the reactor inoculated with syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei and reached, at the end of the experiment, 3.1, 2.7 and 2.4 mm compared to 1.1 mm in that inoculated with acidogenic flocs. This corresponded to a rate of granule size increase of 31, 21, 18 μm/day in syntroph/methanogenic consortia, Methanosaeta and Methanosarcina nuclei, respectively, compared to 7 μm/day in acidogenic flocs. Biomass specific activities (i.e. acidogenic, syntrophic and methanogenic activities) increased stepwise in all reactors with time, especially in those inoculated with syntroph/methanogenic consortia and Methanosaeta nuclei. From these results it appears that syntrophs and Methanosaeta spp. play an important role in the anaerobic granulation process.

Characterization of different microbial nuclei as potential precursors of anaerobic granulation

Anaerobic granule nuclei enriched in either acidogens, syntrophic consortia, Methanosaeta spp. or Methanosarcina spp. were developed in four upflow bed filter reactors fed with sucrose, an ethanol/acetate mixture, acetate and methanol, respectively. The enrichment process was evaluated by scanning electron microscopy and by the change in trophic specific activities. The four developed granule nuclei presented different settling velocities: 3.2, 8.7, 10.5 and 11.3 m h−1 for the acidogenic floes, the Methanosarcina-, the syntrophic consortia and the Methanosaeta-enriched nuclei, respectively. These velocities were related to the size and the ash content of the various aggregates. Acidogenic floes were relatively small in size ( < 0.6 mm in diameter), compared to the other granule nuclei (up to 1.2 mm in diameter). The ash content represented 60%, 40%, 30% and 16% for Methanosaeta-, Methanosarcina-enriched nuclei, syntrophic consortia and acidogenic floes, respectively. Methanosaeta-enriched nuclei contained high amounts of Ca2+ (140 mg per g SS) compared to the other ones (1–8 mg per g SS). Acidogenic floes contained high amount of extracellular polymeric substances compared to the other types of nuclei.

Behavior of nitrogen-substituted naphthalenes in flooded soil—Part II. Effect of bioavailability on biodegration kinetics

Abstract Mineralization of 1-aminonaphthalene, 2-aminonaphthalene and 1-amino-2-methyl-naphthalene under aerobic conditions in flooded soil was found to proceed with a biphasic pattern, an initial fast phase followed by a slower second one. Also the sorption isotherms of these substrates were found to be hyperbolic and were best described by the Langmuir model. When initial mineralization rates were expressed in terms of initial aqueous-phase concentrations, they gave rise to simple hyperbolic kinetics that obeyed Michaelis-Menten model for enzyme-catalysed reactions. These initial mineralization rates were found to be directly proportional to the substrate aqueous concentration reaching their maxima at about 100 μg g −1 (aminonaphthalene/soil slurry). Whereas the second phase mineralization rates were found to be first order with respect to the adsorbed fraction of the substrate and showed no sign of saturation, thus indicating that biodegradation is controlled by the rate of desorption.

Behavior of nitrogen-substituted naphthalenes in flooded soil—Part I. sorption/desorption and biodegradation

The sorption and aerobic biodegradation of 1-NH2 naphthalene (I), 2-NH2-naphthalene- (II), 1-NH2-2-CH3-naphthalene (III), 1-NO2 naphthalene (IV), 2-NO2 naphthalene (V) and 1-NO2-2-CH3-naphthalene (VI) were investigated in flooded soil under different pH conditions. Compounds (I–VI) showed curvilinear adsorption patterns. The observed enhancement in the adsorption of the ionizable aminonaphthalenes (I–III) under acidic conditions suggests that, in addition to the hydrophobic interactions and hydrogen bonding, cation exchange of the protonated compounds is an important adsorption mechanism. The adsorption of the nonionizable nitronaphthalenes (IV and VI) showed no variation with pH and their partition coefficients correlated well with solubility suggesting the predominance of hydrophobic interactions. The aerobic mineralization pattern of compounds I–VI were biphasic giving an initial fast phase followed by a slow phase controlled by the substrate bioavailability. The initial mineralization rates of the nitro-compounds IV and V were higher than those of the corresponding amines I and II. Methyl substitution at the ortho-position, i.e. compounds (III) and (VI), increased Freundlich adsorption constant, (KF), despite its steric effect on H-bonding, and interestingly reduced the initial and second phase mineralization rates. All compounds I–VI showed recalcitrance under anoxic denitrifying, sulfate reducing and methanogenic conditions.

Phosphate Adsorption onto Chitosan-Based Hydrogel Microspheres

Phosphate discharges are closely linked to eutrophication, algal and cyanobacterial blooms in natural water bodies. Chitosan hydrogel microspheres (CHMs) were used as an adsorbent to remove phosphate (PO43–) from aqueous solution. The CHMs were prepared by a sequential methodology consisting of spraying and gelation processes. The physicochemical properties of the hydrogel microspheres were determined by size and zeta-potential analysis. Batch experiments, to investigate the kinetics of phosphate adsorption onto CHMs, show that equilibrum was reached within 30 minutes. The kinetic model was pseudo-second-order (R2 > 0.999). The effect of varying operating conditions (initial anions concentration, adsorbent loading, pH and temperature) on the experiments were also studied. According to the Boyd model, the rate of adsorption is controlled by the diffusion in the boundary layer. The Langmuir, Freundlich and Dubinin–Radushkhevic (D–R) adsorption models were applied to describe the equilibrium isotherms, and the data correlated better with the Freundlich model (R2 = 0.975). The mean free-energy values (obtained from the D–R model) indicate that the adsorption was physical in nature. The values of ΔG and ΔH demonstrated the spontaneous and exothermic nature of the reaction and the negative value of ΔS indicates a decrease in entropy.

Cactus juice as bioflocculant in the coagulation–flocculation process for industrial wastewater treatment: a comparative study with polyacrylamide

Most industries in the world treat their wastewaters with a conventional coagulation-flocculation process using alum as coagulant, polyacrylamide (PAM) as flocculant and lime as coagulant aid. To reduce the use of chemical products in the process, experiments were conducted to substitute the PAM with cactus juice (CJ) as flocculant. From the obtained data, it was concluded that the substitution of PAM with CJ in the coagulation-flocculation process was very effective, compared with PAM. Depending on the wastewaters origin, the bioflocculant showed removal efficiencies of 83.3-88.7% for suspended solids (SS) and 59.1-69.1% for chemical oxygen demand (COD). Lime addition enhanced the coagulation-flocculation process in the presence of CJ similarly to the PAM with efficiencies greater than 90% for both SS and COD. The CJ powders infrared (IR) spectrum showed the main functional groups present in PAM. It was concluded that CJ as a flocculant fits well with the definition of sustainability and it is appropriate for countries that have regions where cactuses grow naturally.

Removal of phosphorus and residual aluminium with the simultaneous use of chitosan and alum on the effluent of an MBBR biological system during start–up

Physico–chemical treatment with aluminium salts is a common practice to remove total phosphorus (TP) from wastewaters. However, the use of alum can increase the residual aluminium concentration both in the effluent and biosolids. Chitosan, an alternative coagulant, does not allow for the removal of TP below the requirement level when lower than the soluble phosphorus fraction of the water. Hence, simultaneous dosage of alum and chitosan solutions was evaluated on the effluent of a newly installed MBBR (moving bed biofilm reactor) system for residual TP and aluminium removal. At alum optimal dosage, the most effective chitosan solution generated: 1) an optimal dosage zone for which residual TP and aluminium concentrations were minimal; 2) maximal abatements for TP and aluminium that reached 35 and 85%, respectively, the concentrations observed with alum only. Also, the fraction of residual aluminium in the biosolids was increased, particularly from 84 to 98% at optimal chitosan dosage.

Fungal pretreatment by Phanerochaete chrysosporium to reduce the inhibition of methanogenesis by dehydroabietic acid

Abstract The white-rot basidiomycete Phanerochaete chrysosporium BKM-F-1767 was tested for its capacity to degrade dehydroabietic acid (DHA). In anaerobic treatment, this molecule is the most recalcitrant member of the resin acid group, which is known to cause operational problems to anaerobic reactors treating pulp and paper industry wastewaters. In this study the effect of DHA on different parameters, such as growth, ligninolytic enzyme activity, extracellular protein production as well as both glycerol and ammonium consumption by the fungus, was determined. Although the above parameters were affected by the addition of DHA, the results show that the fungus could still produce significant titres of ligninolytic enzymes. The fungus removed 47% of the DHA initially present in the static culture, after 10 days of incubation. Anaerobic toxicity assays showed that the treatment of DHA with P. chrysosporium reduced the methanogenesis and acetogenesis inhibition caused by DHA and allowed improved methane production by the anaerobic bacteria.

Optimizing rotating biological contactor disc area

Abstract A method of minimizing the total active disc area required for soluble biochemical oxygen demand (SBOD) removal by a multi-stage rotating biological contactor (RBC) in which the substrate removal rate is not oxygen limited, is applied to two generalized steady-state SBOD removal models. The active disc area of each stage is optimized according to an analytically determined optimal relationship between SBOD concentrations of adjacent stages.