Jian Lin Chen

Instant curing adhesives typically fall within three categories, being activated by either light (photocuring), heat (thermocuring) or chemical means. These curing strategies limit applications to specific substrates and can only be activated under certain conditions. Here we present the development of an instant curing adhesive through low-voltage activation. The electrocuring adhesive is synthesized by grafting carbene precursors on polyamidoamine dendrimers and dissolving in aqueous solvents to form viscous gels. The electrocuring adhesives are activated at −2 V versus Ag/AgCl, allowing tunable crosslinking within the dendrimer matrix and on both electrode surfaces. As the applied voltage discontinued, crosslinking immediately terminated. Thus, crosslinking initiation and propagation are observed to be voltage and time dependent, enabling tuning of both material properties and adhesive strength. The electrocuring adhesive has immediate implications in manufacturing and development of implantable bioadhesives.

Critical review of anaerobic toxicity focusing on fundamental mechanismsLooks at specific organics — chlorophenols, halogenated aliphatics, and long fatty acidsLooks at specific inorganics — ammonia, sulfide and heavy metalsLooks at novel nanomaterials and how they inhibit anaerobesNeed to develop toxicity sensors with rapid response timesAnaerobic digestion is increasingly being used to treat wastes from many sources because of its manifold advantages over aerobic treatment, e.g. low sludge production and low energy requirements. However, anaerobic digestion is sensitive to toxicants, and a wide range of compounds can inhibit the process and cause upset or failure. Substantial research has been carried out over the years to identify specific inhibitors/toxicants, and their mechanism of toxicity in anaerobic digestion. In this review we present a detailed and critical summary of research on the inhibition of anaerobic processes by specific organic toxicants (e.g., chlorophenols, halogenated aliphatics and long chain fatty acids), inorganic toxicants (e.g., ammonia, sulfide and heavy metals) and in particular, nanomaterials, focusing on the mechanism of their inhibition/toxicity. A better understanding of the fundamental mechanisms behind inhibition/toxicity will enhance the wider application of anaerobic digestion.

Studies the effect of PCP on pure anaerobe and anaerobic sludge by resazurin assay.Provides a rapid optical measurement of solute toxicity for anaerobic digestion.Gives information about biogas production rate by this “indirect” measurement.Potential application of the assay in a biosensor for advanced warning of toxicity.A rapid fluorescence measurement based on resazurin reduction was developed and applied for the detection of toxicants/inhibitors to anaerobic digestion metabolism. By initially using a pure facultative anaerobic strain, Enterococcus faecalis as a model organism, this technique proved to be fast and sensitive when detecting the model toxicant, pentachlorophenol (PCP). The technique revealed significant metabolic changes in Enterococcus faecalis with a PCP spike ranging from 0.05 to 100 mg/L, and could detect PCP's toxicity to E. faecalis at a concentration of only 0.05 mg/L in 8 min. Furthermore, by extending this technique to a mixed anaerobic sludge, not only could the effect of 0.05–100 mg/L PCP be determined on anaerobic digestion metabolism within 10 min, but also its rate of biogas production. These results suggest that a resazurin-based fluorescence measurement can potentially be incorporated into a microfluidic system to develop a biosensor for the real-time monitoring, control and early warning of toxicant/inhibitor loads in the influent to an anaerobic digestion system.

A mathematical model, combining both sorption and biodegradation process, was developed to predict the biodegradation of phenanthrene by Sphingomonas sp. in different sediment slurries. The model includes two sorption parameters, α (the partition coefficient) and 1/K (the diffusion resistance); a kinetic parameter k (the first order rate constant); and a sediment parameter, AV (the specific sediment surface area in unit volume of slurry). These parameters were evaluated and verified in three types of sediment slurry systems (namely sandy clay loam Ho Chung sediment with fastest degradation, sandy Kei Ling Ha sediment with medium degradation, and clay Mai Po sediment with slowest degradation) at different initial phenanthrene concentrations. High R2 values, ranging from 0.935 to 0.969, were obtained. Based on this integrated sorption–biodegradation model, the phenanthrene biodegradation in any sediment slurry could be predicted as long as the parameters of the specific sediment surface area in unit volume of slurry, total organic carbon and clay content were measured.

The static and dynamic sorption of phenanthrene (Phe) in three types of mangrove sediment slurries (sandy, silty and muddy) were described by three models, namely linear model, Freundlich adsorption isotherm model and Langmuir adsorption isotherm model. The Freundlich adsorption isotherm was the best model to describe the static sorption behavior of Phe in mangrove sediment slurry with the regression coefficients ranging from 0.96 to 0.99. In static sorption, the sorption capacity and sorption intensity were reduced with the inoculation of Sphingomonas, a PAH-degrading bacterial isolate, suggesting that the inoculum even though inactive and/or dead would enhance bioavailability of Phe. On the other hand, the static sorption of Phe was significantly enhanced at high salinity (20 ppt) while no difference was found at low salinities ranging from 5 to 15 ppt. During the dynamic sorption process, i.e. with biodegradation by indigenous microorganisms and the inoculation of Sphingomonas, linear regression was the most suitable model to describe Phe sorption behavior. The partition coefficient α was the highest in silty sediment, followed by sandy sediment and the muddy sediment had the lowest value. These results indicated that the sorption behavior of Phe changed from non-linear to linear when biodegradation took place and the silty mangrove sediment slurry had the highest sorption affinity.

In the present paper, the effects of four factors, each at three levels, on biodegradation of phenanthrene, a 3-ring PAH, in contaminated mangrove sediment slurry were investigated using the orthogonal experimental design. The factors and levels were (i) sediment types (clay loam, clayey and sandy); (ii) different inoculums (Sphingomonas sp., a mixture of Sphingomonas sp. and Mycobacterium sp., and without inoculum); (iii) presence of other PAHs (fluorene, pyrene, and none); and (iv) different salinities (5, 15 and 25 ppt). Variance analysis based on the percentages of Phe biodegradation showed that the presence of other PAHs had little effect on phenanthrene biodegradation. The kinetics of phenanthrene biodegradation in all experiments was best fitted by the first order rate model. The highest first order rate constant, k value was 0.1172 h−1 with 97% Phe degradation; while the lowest k value was 0.0004 and phenanthrene was not degraded throughout the 7-d experiment. The p values of k for the four factors followed the same trend as that for the biodegradation percentage. Difference analysis revealed that optimal phenanthrene biodegradation would take place in clay loam sediment slurry at low salinity (5 to 15 ppt) with the inoculation of both Sphingomonas sp. and Mycobacterium sp.

Biodegradation of polycyclic aromatic hydrocarbons (PAHs) in contaminated sediment is an attractive remediation technique and its success depends on biodegradation kinetics, and the optimal condition for the PAH-degrading isolates; however, information on this aspect is still scarce. The effects of multi-factors on biodegradation of phenanthrene, a 3-ring model PAH, in contaminated sediment slurry by Sphingomonas sp. a bacterial strain isolated from surface mangrove sediment, were investigated using the orthogonal experimental design (form L16(45)). The most significant factors were salinity and inoculum size, while the effects of phenanthrene concentrations, nutrient addition and temperatures were insignificant. The optimal biodegradation condition in contaminated mangrove sediment slurry was 30 °C, 15 ppt salinity, a carbon/nitrogen ratio of 100:1 (the background ratio in sediment) and an inoculum size of 106 most probable number g−1 sediment. The phenanthrene biodegradation could be best described by the first order rate model, C = C0e−kt, where k (the rate constant) is equaled to 0.1185, under the optimal condition. The kinetic model was verified and its validity in predicting biodegradation by Sphingomonas sp. at various phenanthrene concentrations was proved by experimental data.

A rigid spherical biporous matrix was prepared by radical suspension polymerization. Functionalized with diethylamine, a biporous ion-exchange resin (IER-B) was obtained. The properties of IER-B were compared with the microporous ion exchange resin (IER-M) in pore size distributions and specific surface areas. Batch adsorption showed that IER-B and IER-M had comparable static adsorption capacities for BSA, i.e., 55.6 and 63.8 mg · g-1 wet resin, respectively. The dynamic capacity of IER-B column decreased slightly with increasing the flow rate, which maintained at 38 mg · mL-1 bed at a flow rate of 30 cm · min-1. In contrast, the dynamic capacity of IER-M column decreased drastically to a value of only 13 mg · mL-1 bed at a flow rate of 24 cm · min-1. Then, the IER-B column was used for the purification of molecular chaperonins GroEL and GroES. At elevated flow rates from 2.55 to 10.1 cm · min-1, the resolution and capacity of the column for GroEL and GroES purification was not affected by increasing flow rate. The results indicate that the biporous resin was promising for high-speed chromatographic purification of proteins.