Environmental Technology

Williams, P. T.; Williams, E. A.

doi: 10.1080/09593332008616908pmid: N/A

Polystyrene has been pyrolysed in a fluidised bed pyrolysis reactor and the influence of pyrolysis temperature from 500 to 700°C on the yield and composition of the derived products has been determined. The main products from pyrolysis of polystyrene were a wax/oil product collected, as a condensed wax fraction and a separate oil fraction, using an industrial demister system. The oils and waxes were analysed by size exclusion chromatography to determine their molecular weight distribution, by Fourier transform infra-red spectrometry to determine their functional group composition and by gas chromatography to determine their detailed composition. The derived oils had a molecular weight distribution from 60 to 200 Da, with higher molecular weight material occurring in the wax fraction with a distribution of 60 to over 1000. Detailed analysis of the oils showed that the pyrolysis of polystyrene gave a mainly aromatic composition dominated by styrene and styrene oligomers. The oils also contained polycyclic aromatic hydrocarbons which increased in concentration as the pyrolysis temperature was increased to 700°C. Low concentrations of hydrogen, methane, ethane, ethene, propane, propene, butane and butene were also formed. There was an increase in gas yield with increasing temperature of pyrolysis.

Ghestem, J. P.; Bermond, A.

doi: 10.1080/09593332008616909pmid: N/A

The hazard due to the presence of large amounts of trace metals in some soils is related strongly to the speciation of these metals. The aim of this work was to study the feasibility of an operationally defined fractionation based on kinetics which could distinguish ‘labile’ (quickly extracted) and ‘non-labile’ or ‘slowly labile’ i.e. slowly extracted) cations, using the extraction kinetics of trace metals by EDTA.. The chosen reagent was EDTA because of its strong ability to extract cations from the main compartments of the soil and the fit of experimental curves with a sum of two first-order kinetics showed this to be possible and led to the definition of ‘labile’ or ‘non-labile’ cations. Some statistical parameters of the proposed method were estimated. The interest of the speciation was briefly outlined; its application to various soil samples indicates that amounts of ‘labile’ cations may be useful to evaluate the environmental risk due to trace metals.

Cousin, C. P.; Ganczarczyk, J. J.

doi: 10.1080/09593332008616910pmid: N/A

The effect of increased calcium ion concentrations up to 10 meq l−1, in the presence of a fixed sodium ion concentration of 4 meq l−1, on the physical structure of activated sludge flocs was studied. Samples of activated sludge were exposed for 15 minutes to solutions with increasing calcium ion concentrations and then the physical structure of the individual flocs was investigated. It was observed that a minimum mean floc size (floc area, equivalent diameter, longest dimension, and perimeter) was achieved at a calcium ion concentration of 4.0 meq l−1 and that the flocs' shape was not correlated with their size. The flocs' porosity decreased with increasing ion concentration until an equilibrium value was achieved. As previously observed, the floc surface profile was found to be more rugged with an increased floc size and smoother with a decreased floc size. Examination of all size distributions revealed that the data were best fitted by a log normal distribution.

Neralla, S.; Weaver, R. W.; Varvel, T. W.; Lesikar, B. J.

doi: 10.1080/09593332008616911pmid: N/A

Phytoremediation may be one of the mechanisms leading to improvement of water quality in sub-surface flow constructed wetlands. Experiments were undertaken in a glasshouse by growing plants in microcosms, and at a sub-surface flow constructed wetland to evaluate the importance of phytoremediation in improving water quality and the adaptability of different aquatic plants to grow in domestic wastewater from septic tanks. Wastewater was provided every two days to microcosms to simulate detention time in a constructed wetland. An initial screening of 20 plant species resulted in selection of Cyperus alternifolius, C. isocladus, Sagittaria lancifolia, Canna flacccida, Iris sp., Typha latifolia and T. angustifolia, based on their ability to grow well in the wastewater, for experimentation on phytoremediation. Phytoremediation generally reduced biological oxygen demand, NH4 +-N, P, turbidity, and volatile suspended solids. Populations of fecal coliforms were consistently reduced by 90 to 99% by 2-d detention in microcosms with and without plants. Overall it appears that for improvement of water quality, largest water loss by evapotranspiration, vigor of plant growth and ease of maintenance, Typha and Cyperus were the best performers. Cyperus alternifolius seemed highly desirable because of its high water requirement, resistance to insects, ability to grow throughout the year, winter hardiness, absence of a period of dormancy and rapid recovery from frost damage. Phytoremediation in sub-surface flow constructed wetlands has potential for improvement of water quality and reducing the quantity of water to be disposed.

Dinçer, A. R.; Kargi, F.

doi: 10.1080/09593332008616912pmid: N/A

Biological processes used for nitrification and denitrification of saline wastewater results in low treatment efficiencies because of plasmolysis or loss of activity of organisms in the presence of salt. However, adverse effects of salt on performance of nitrification/denitrification processes has not been systematically investigated and mathematically formulated. Biological nitrification and denitrification of synthetic wastewater containing different concentrations of salt were investigated in this study. Effect of salt concentration on the system performance was investigated. Salt concentrations above 2% resulted in significant reductions in performances of both nitrification and denitrification. Denitrification was more sensitive to salt compared to nitrification. A mathematical model was developed and the salt inhibition constants were determined using the experimental data.

Quarmby, J.; Scott, J. R.; Mason, A. K.; Davies, G.; Parsons, S. A.

doi: 10.1080/09593332008616913pmid: N/A

The sonication of sewage sludge can be used as a pre-treatment to anaerobic digestion. The anaerobic digestion process has the potential to become more efficient through the break-up and solubilisation of solid sludge particles. Here, the performance of anaerobic digestion was compared when fed with unsonicated sludge and sludges sonicated at two different intensities. The tests were run as a series of batch flasks and three 100 litre anaerobic digesters. The data from the batch tests clearly indicated the positive effect on anaerobic digestion through gas production (increase by 15%) and volatile fatty acid production. The data from the anaerobic digesters was less distinct. Little difference was observed between the volumes of gas produced, however there was an increase in methane production, volatile solids reduction and the soluble COD by up to 6%, 5.5% and 15% respectively when a comparison was made between sonicated and unsonicated sludges. However, sonication was observed to have a detrimental effect on the sludge dewaterability. This effect was more acute when a higher sonication intensity was used, however anaerobic digestion did reduce this effect. Therefore, while sonication can enhance anaerobic digestion, the negative effect on the sludge properties must be considered before applying this technique to any site where dewatering processes are used. The two different sonication intensities indicated that there was a minimal difference in performance. Therefore, the application of low intensity sonication can allow both process and economic benefits.

Vela, F. J.; Gianotti, E. P.; Foresti, E.; Zaiat, M.

doi: 10.1080/09593332008616914pmid: N/A

A simple and rapid method to estimate effective diffusivities (De) of substrates in bioparticles containing anaerobic sludge is proposed. The method is based on substrate mass balances under unsteady-state conditions utilizing data obtained from ‘finite-bath’ assays performed in an incubator shaker. The experiments were carried out under conditions of negligible liquid-phase mass transfer resistance and absence of biochemical reactions. The first condition was obtained by the application of high agitation speeds. The biomass was inactivated with ethanol solution 50% (v/v) to reach the second condition. Values of the effective diffusivity (De) of glucose, sucrose and acetate were obtained from the temporal variation of substrate concentration in the bulk liquid in assays utilizing alginate gel and polyurethane foam bioparticles. Additionally, the specific methanogenic activity technique was used to evaluate the effectiveness of the method proposed for biomass inactivation. The method used to estimate the substrate diffusivity coefficient was found to provide suitable values of De for substrates at very low concentrations. Values of De for glucose, sucrose and acetate in alginate gel bioparticles were estimated as 0.58 × 10−5, 1.06 × 10−5 and 1.49 × 10−5 cm2 s−1, respectively. The value of De for glucose in polyurethane foam particles was found to correspond to the value of glucose diffusion in water at infinite dilution. The method applied for cell inactivation was found to be adequate for intraparticle mass transfer experiments, making the temporary sludge inactivity long enough to avoid interference due to biochemical reactions.

Lin, K.-S.; Wang, H. P.; Kuo, C.-W.; Jou, C.-J. G.; Chien, Y.-C.

doi: 10.1080/09593332008616915pmid: N/A

Liquefaction of auto crusher residue (ACR) in hot motor oil with product oils recycling was investigated. Approximately 86% of oils, 10% of noncondensible gases and 4% of metal-rich residues were recovered from liquefaction of ACR at 643 K. The cuts of the product light oil weighted into boiling fraction are primarily naphtha (30.2%) and gas oil (68.6%). The product heavy oils recovered from liquefaction of ACR contain noticeable amounts of gas oil (95.4%). Proton NMR and FTIR data reveal that the condensation reaction may be involved in the ACR liquefaction process. However, the undesired condensation reaction is decreased significantly in the liquefaction of ACR effected by Fe2O3, FeO or CaO.

Bassi, R.; Prasher, S. O.; Simpson, B. K.

doi: 10.1080/09593332008616916pmid: N/A

The objective of this study was to study, under various physicochemical conditions, the ability of chitosan to trap heavy metals leached during remedial washing of contaminated soils with organic extractants. The contaminated soil was washed with 0.1M citric acid, pH 5.5, for 24 h, producing a metal-rich leachate containing 0.06, 0.02, 0.003, and 5.87 μmoles ml−1 of Zn, Cu, Cd, and Pb, respectively. Equilibrium and kinetic sorption studies revealed that chitosan significantly reduced the levels of these metal ions in the leachate. A 12 h mixing of the leachate with chitosan flakes resulted in about 50% reduction in metal ion contents of the leachate. However, the adsorption of metal ions by the chitosan was found to depend on the relative concentrations of metal ions present in the leachate. The mass of chitosan required for achieving adsorption equilibrium was consequently dependent on the initial concentrations of metal ions. Reduction in metal ion contents of the leachate by chitosan flakes did not appear to be significantly improved by agitation. In addition, heavy metal removal by chitosan was found to be highest at pH 6.0. Results from the experiments involving replacement of metal-laden chitosan with fresh chitosan suggested that at least four replacements of chitosan would be required for absolute remediation of the leachate.

Bourg, A.C. M.; Kedziorek, M. A. M.

doi: 10.1080/09593332008616917pmid: N/A

Aquifer sediments are known to have a large potential for filtering heavy metal cations from percolating groundwater. To investigate the role of riverine alluvions from the Seine River in filtering heavy metals, we collected three calcareous alluvion profiles (5 m in depth), one taken from an island and two from adjacent river banks. The major element content (Si, Al and Ca) is independent of the profile and of depth. In the river bank profiles heavy metals and organic C (Corg) are also rather constant. In the island profile peak concentrations of heavy metals and Corg are found at a depth of between 1 to 3 m (3.2 ppm Ag, 5 ppm Cd, 47 ppm Cr, 93 ppm, Cu 235 ppm Pb, 260 ppm Zn and 1.8 % Corg). Enrichment in these heavy metals demonstrates the strong potential of island alluvions for natural geochemical filtering.