Variability of geotechnical parameters of lateritic gravels overlying contrasted metamorphic rocks in a tropical humid area (Cameroon): implications for road construction

Bulletin of Engineering Geology and the Environment - The variability of the geotechnical properties of lateritic gravels developed on metamorphic rocks from the same clay protolith and of a nearby...     

Biodegradation of organonitriles by adapted activated sludge consortium with acetonitrile-degrading microorganisms

A microbial process for the degradation of three types of structurally distinct organonitriles (i.e., saturated and unsaturated aliphatic nitrile and aromatic nitrile) was studied. Microorganisms were enriched from the activated sludge of a pharmaceutical wastewater treatment plant and adapted through providing acetonitrile as the sole carbon and nitrogen source for their growth. The adapted mixed culture was then examined for their capability of degrading acetonitrile, acrylonitrile and benzonitrile under various operational conditions. The performance of biodegradation and the metabolic intermediate- and end-products in the process were monitored. The results show that an average removal rate of 0.083 g acetonitrile g(-1)-VSS h(-1), 0.0074 g acrylonitrile g(-1)-VSS h(-1) or 0.0029 g benzonitrile g(-1)-VSS h(-1) was achieved in the batch bioreactor under the common operational condition of 25 degrees C and pH 7. The biodegradation of acetonitrile and acrylonitrile showed a two-step pathway, with the generation of acetamide followed by acetic acid and ammonia for acetonitrile or acrylamide followed by acrylic acid and ammonia for acrylonitrile. However, the biodegradation of benzonitrile appeared to have only one step, with the direct production of benzoic acid and ammonia, but without benzamide being detected in the process. The results suggest that, depending on the substrates, the adapted mixed culture can develop very different degradation pathways, such as nitrile hydratase plus amidase for acetonitrile or acrylonitrile and nitrilase for benzonitrile. Therefore, the adapted mixed culture has a great potential and flexibility for actual applications in biodegradation of various organonitrile compounds.     

Development of a membrane‐aerated biofilm reactor to completely mineralise perchloroethylene in wastewaters

The feasibility of perchloroethylene (PCE) biodegradation using hybrid aerobic/anaerobic microcosms was investigated. Four main factors were evaluated in batch studies; the type of the electron donor, the nature of the inoculum, the effect of different concentrations of electron donor, and the effect of addition of different concentrations of oxygen. Results from these studies showed that; glucose was the best electron donor for PCE degradation, serum bottles seeded with acclimated biomass performed better than those seeded with the unacclimated biomass, glucose in excess did not improve PCE degradation, and the addition of pure oxygen significantly enhanced degradation. It was observed that serum bottles with acclimated sludge receiving oxygen achieved complete mineralisation of PCE to ethylene with mineralisation rates of 0.27 mg L^?1 mg cells^?1 h^?1. Following these results a membrane‐aerated biofilm reactor (MABR) was constructed, and the batch degradation of 5.5 mg L^?1 of PCE was followed for 44 days and PCE was completely removed from the system. The appearance of intermediate compounds proved that PCE was degraded, but not completely stripped out from the system. Degradation was not complete as some bio‐products were still found in the effluent, but there was no accumulation of a particular intermediate compound. The PCE removal rate observed in this MABR was 0.24 mg L^?1 h^?1. During the study on the effect of adding different concentrations of oxygen, a mass balance based on chloride in the bottles revealed that, 92–95% of the PCE could be accounted for, while only 60–65% of the PCE fed in the reactor could be accounted for as chloride. The MABR developed here may prove to have considerable potential in treating wastewater containing a variety of refractory organics such as PCE. Copyright © 2006 Society of Chemical Industry     

Effect of perchloroethylene (PCE) and hydraulic shock loads on a membrane‐aerated biofilm reactor (MABR) biodegrading PCE

BACKGROUND: A membrane‐aerated biofilm reactor (MABR) has previously been used to provide both anaerobic and aerobic conditions for mineralisation of perchloroethylene (PCE). However, very little is known about the stability of this reactor under hydraulic and PCE shock loads. An MABR was therefore subjected to sudden hydraulic and PCE shock loads in order to investigate its stability under such conditions. RESULTS: After each shock, the reactor responded with an increase of chemical oxygen demand (COD) and volatile fatty acids (VFA)s, a breakthrough of PCE and its biodegradation intermediates in the effluent, and a decrease in methane production. Although some PCE biodegradation intermediates were found in the effluent during each shock loading, the MABR performance recovered without the accumulation of any particular PCE biodegradation intermediates during PCE shock loads. During the hydraulic shock loads, the MABR was unstable at hydraulic retention times (HRTs) of 6 h with PCE and its biodegradation intermediates detected in the effluent. However, these intermediates were degraded when the HRT was reset to 48 h. CONCLUSIONS: This study suggests that MABRs can withstand fluctuations in influent strength and flows which occur in wastewater treatment works. Copyright © 2009 Society of Chemical Industry     

Estimation of the elastic anisotropy of sisal fibres by an inverse method

This paper is concerned with an inverse method for the characterization of the elastic anisotropy of plant fibres. A good knowledge of the properties of composites reinforced with these fibres is essential for the safe design of the related structures. In this work, experimentation and analytical modelling were thoroughly combined to optimize the determination of plant fibre properties from their related composites. The experimental work focused on the manufacture and characterization of unidirectional (UD) sisal/epoxy composites. Tensile tests were performed to measure the axial and off-axes stiffness of these composites. Tests' data were eventualy used in an optimization process based on a micromechanical model to estimate the fibres’ elastic constants. Sisal fibres used herein exhibited a high degree of elastic anisotropy.     

Biodegradation of PCE in a Hybrid Membrane Aerated Biofilm Reactor

A continuous flow flat sheet hybrid membrane aerated biofilm reactor (MABR) was used to treat a synthetic wastewater containing perchloroethylene (PCE); 1.25–2.5?g chemical oxygen demand (COD)/L of glucose was also added to the synthetic wastewater as a source of COD representative of a real wastewater. The reactor was able to biodegrade 70?mg?L?1 of PCE in 9?h without the accumulation of any intermediate compounds, resulting in a removal rate of 247?mmol of PCE?h?1?m?3 in a reactor with a specific membrane area of 4.048?m2?m?3. MABRs have never been used before for PCE degradation, and this rate is one of the highest volumetric PCE degradation rates reported in the literature. COD removal was also good and varied from 85 to 92%. Since very few volatile fatty acids accumulated in the system, most of the residual COD was attributed to soluble microbial products as reported by previous researchers. A mass balance on chloride during this study showed that only 72–81% of it could be accounted for. It is probable that some of the chlorinated ethenes were adsorbed onto the biofilm or that aerobic intermediates of low-chlorinated compounds such as trichloroethanol, dichloroacetyl, and chloroacetaldehyde were produced in the system. Nevertheless the chloride mass balance in this work compares well with the literature. Due to their high PCE and COD removal rates, hybrid MABRs have the potential to be used for a number of refractory organics which require combined anaerobic/aerobic biological treatment for degradation.