Chemical-mineralogical characterisation of coarse recycled concrete aggregate

The construction industry is now putting greater emphasis than ever before on increasing recycling and promoting more sustainable waste management practices. In keeping with this approach, many sectors of the industry have actively sought to encourage the use of recycled concrete aggregate (RCA) as an alternative to primary aggregates in concrete production. The results of a laboratory experimental programme aimed at establishing chemical and mineralogical characteristics of coarse RCA and its likely influence on concrete performance are reported in this paper. Commercially produced coarse RCA and natural aggregates (16-4 mm size fraction) were tested. Results of X-ray fluorescence (XRF) analyses showed that original source of RCA had a negligible effect on the major elements and a comparable chemical composition between recycled and natural aggregates. X-ray diffraction (XRD) analyses results indicated the presence of calcite, portlandite and minor peaks of muscovite/illite in recycled aggregates, although they were directly proportioned to their original composition. The influence of 30%, 50%, and 100% coarse RCA on the chemical composition of equal design strength concrete has been established, and its suitability for use in a concrete application has been assessed. In this work, coarse RCA was used as a direct replacement for natural gravel in concrete production. Test results indicated that up to 30% coarse RCA had no effect on the main three oxides (SiO2, Al2O3 and CaO) of concrete, but thereafter there was a marginal decrease in SiO2 and increase in Al2O3 and CaO contents with increase in RCA content in the mix, reflecting the original constituent's composition.     

Vanadium recovery from oil fly ash by leaching, precipitation and solvent extraction processes

In order to reduce the environmental impact due to land disposal of oil fly ash from power plants and to valorize this waste material, the removal of vanadium was investigated using leaching processes (acidic and alkaline treatments), followed by a second step of metal recovery from leachates involving either solvent extraction or selective precipitation. Despite a lower leaching efficiency (compared to sulfuric acid), sodium hydroxide was selected for vanadium leaching since it is more selective for vanadium (versus other transition metals). Precipitation was preferred to solvent extraction for the second step in the treatment since: (a) it is more selective; enabling complete recovery of vanadate from the leachate in the form of pure ammonium vanadate; and (b) stripping of the loaded organic phase (in the solvent extraction process) was not efficient. Precipitation was performed in a two-step procedure: (a) aluminum was first precipitated at pH 8; (b) then ammonium chloride was added at pH 5 to bring about vanadium precipitation.     

Passive drainage and biofiltration of landfill gas: Australian field trial

In Australia a significant number of landfill waste disposal sites do not incorporate measures for the collection and treatment of landfill gas. This includes many old/former landfill sites, rural landfill sites, non-putrescible solid waste and inert waste landfill sites, where landfill gas generation is low and it is not commercially viable to extract and beneficially utilize the landfill gas. Previous research has demonstrated that biofiltration has the potential to degrade methane in landfill gas, however, the microbial processes can be affected by many local conditions and factors including moisture content, temperature, nutrient supply, including the availability of oxygen and methane, and the movement of gas (oxygen and methane) to/from the micro-organisms. A field scale trial is being undertaken at a landfill site in Sydney, Australia, to investigate passive drainage and biofiltration of landfill gas as a means of managing landfill gas emissions at low to moderate gas generation landfill sites. The design and construction of the trial is described and the experimental results will provide in-depth knowledge on the application of passive gas drainage and landfill gas biofiltration under Sydney (Australian) conditions, including the performance of recycled materials for the management of landfill gas emissions.     

Adsorption of natural organic matter from waters by iron coated pumice

Natural pumice particles were used as granular support media and coated with iron oxides to investigate their adsorptive natural organic matter (NOM) removal from waters. The impacts of natural pumice source, particle size fraction, pumice dose, pumice surface chemistry and specific surface area, and NOM source on the ultimate extent and rate of NOM removal were studied. All adsorption isotherm experiments were conducted employing the variable-dose completely mixed batch reactor bottle-point method. Iron oxide coating overwhelmed the surface electrical properties of the underlying pumice particles. Surface areas as high as 20.6m(2)g(-1) were achieved after iron coating of pumice samples, which are above than those of iron coated sand samples reported in the literature. For all particle size fractions, iron coating of natural pumices significantly increased their NOM uptakes both on an adsorbent mass- and surface area-basis. The smallest size fractions (<63 microm) of coated pumices generally exhibited the highest NOM uptakes. A strong linear correlation between the iron contents of coated pumices and their Freundlich affinity parameters (K(F)) indicated that the enhanced NOM uptake is due to iron oxides bound on pumice surfaces. Iron oxide coated pumice surfaces preferentially removed high UV-absorbing fractions of NOM, with UV absorbance reductions up to 90%. Control experiments indicated that iron oxide species bound on pumice surfaces are stable, and potential iron release to the solution is not a concern at pH values of typical natural waters. Based on high NOM adsorption capacities, iron oxide coated pumice may be a promising novel adsorbent in removing NOM from waters. Furthermore, due to preferential removal of high UV-absorbing NOM fractions, iron oxide coated pumice may also be effective in controlling the formation of disinfection by-products in drinking water treatment.     

Seasonal variations of selected herbicides and related metabolites in water, sediment, seaweed and clams in the Sacca di Goro coastal lagoon (Northern Adriatic)

This study assesses the status of Sacca di Goro coastal lagoon (Northern Adriatic, Italy) with respect to watershed pollution. Because 80% of its watershed is devoted to agriculture, plant protection products and their metabolites were found in the water column, sediments (the upper 0-15 cm layer), macroalgae (Ulva rigida) and clams (Tapes philippinarum). Five seasonal sampling campaigns were performed from May 2004 to April 2005 and concentrations measured in five stations in the lagoon and six in the watershed. Relatively high concentrations of the s-triazine - terbuthylazine -, urea herbicides - diuron - and alachlor were detected through the year mainly at stations directly influenced by the Po di Volano inflow. The concentrations of products in use follow a clear seasonal pattern with spring peaks. This pattern is also visible in the sediments as well as in biota. Among metabolites, hydroxylated compounds prevailed, often with concentrations greater than those of the parent compounds. For the most part of the year, the concentrations in biota were close to detection limits, with concentration peaks in spring.     

Bioaccumulation of anthropogenic contaminants by detritivorous fish in the Río de la Plata estuary: 2-Polychlorinated biphenyls

The temporal variability and bioaccumulation dynamics of individual PCBs were studied in a detritivorous fish (Sábalo: Prochilodus lineatus) collected from 1999 to 2005 in the polluted Buenos Aires coastal area. Fish muscles contain high concentrations of total PCBs (11+/-7.2, 4.6+/-3.4 or 19+/-13 microg g(-1), dry, fresh and lipid weight, respectively) reflecting chronic bioaccumulation from sewage-industrial particulates. On a temporal basis, lipid normalized PCBs concentrations peaked by the end of 2001-2002 coincident with the rainiest period over the last four decades and shortly after PCB prohibition in the country, reflecting massive discharges to the coastal ecosystem. PCB composition in fish muscles show a prevailing contribution of hexachlorobiphenyls (35+/-4.2%), followed by hepta (23+/-3.0%), penta (20+/-3.6%), tri-tetra (16+/-4.8%) and minor proportions of octa-decachlorobiphenyls (5.7+/-3.1%) similar to an Aroclor 1242-1254-1260 1:2:4 mixture. During 2001-2002 maxima fish showed an enrichment in tri-tetrachlorobiphenyls ( approximately 1242-1254-1260 1:1:1 mixture) denoting a fresher signature. Fish/settling material lipid-organic carbon accumulation factors (BSAFs: 2.4-46, average: 21+/-10) plotted against kow showed a parabolic trend (BSAFs=-0.38 log kow2 + 5.16 log kow -15.85; R2=0.46) maximizing at hexa, hepta and octachlorobiphenyl 203 with reduced bioaccumulation of a few hepta (170, 191) and most octa-decachlorobihenyls suggesting limited intestinal absorption.     

Evaluation of natural and anthropogenic influences on the Guadalquivir River (Spain) by dissolved heavy metals and nutrients

To evaluate both the natural and anthropogenic influences on surface waters of Guadalquivir River (SW-Spain), concentrations of dissolved trace metals (Mn, Co, Ni, Cu, Cd, Zn, and Pb), inorganic nutrients (N-NH(4)(+), N-NO(3)(-), N-NO(2)(-), and P-PO(4)(3-)) and other variables as conductivity, pH, dissolved oxygen (DO) and suspended solids (SS) were measured during a three-years period (2001-2003). Samples were taken at 26 stations twice a year, during rain and dry periods. The analysis of variance (ANOVA) suggested that temporal variations within the period of study were statistically negligible. Spatial distributions identified three different zones, mainly influenced by sewage (Eastern Zone), agriculture runoffs (Central Zone), and estuarine processes (Western Zone), respectively. Principal Component and Cluster Analysis allowed to identify the variables controlling the water quality of each zone as: N-NH(4)(+), N-NO(2)(-), Mn, and Co, (Eastern Zone), SS, and P-PO(4)(3-) (Central Zone), and Cd, pH and conductivity (Western Zone). Other variables such as Ni, Cu, Zn or N-NO(3)(-), influenced two different zones, while Pb presented a singular behavior.     

Accumulation and partitioning of heavy metals in mangroves: a synthesis of field-based studies

We report the findings of a comparative analysis examining patterns of accumulation and partitioning of the heavy metals copper (Cu), lead (Pb) and zinc (Zn) in mangroves from available field-based studies to date, employing both species level analyses and a phylogenetic approach. Despite mangroves being a taxonomically diverse group, metal accumulation and partitioning for all metals examined were broadly similar across genera and families. Patterns of metal accumulation were also similar regardless of whether species were classified as salt secreting or non-secreting. Metals were accumulated in roots to concentrations similar to those of adjacent sediments with root bio-concentration factors (BCF; ratio of root metal to sediment metal concentration) of 1< or =. Root BCFs were constant across the exposure range for all metals. Metal concentrations in leaves were half that of roots or lower. Essential metals (Cu and Zn; translocation factors (TF; ratio of leaf metal to root metal concentration) of 0.52 and 0.53, and leaf BCFs of 0.47 and 0.51, respectively) showed greater mobility than non-essential metals (Pb; TF of 0.31 and leaf BCF of 0.11). Leaf BCFs for the essential metals Cu and Zn decreased as environmental concentrations increased. The non-essential metal Pb was excluded from leaf tissue regardless of environmental concentrations. Thus mangroves as a group tend to operate as excluder species for non-essential metals and regulators of essential metals. For phytoremediation initiatives, mangrove ecosystems are perhaps best employed as phytostabilisers, potentially aiding in the retention of toxic metals and thereby reducing transport to adjacent estuarine and marine systems.     

Biodegradability and ecotoxicity of amine oxide based surfactants

The aerobic and anaerobic biodegradability as well as the aquatic toxicity of two fatty amine oxides and one fatty amido amine oxide were investigated. Aerobic biodegradation was evaluated using the CO(2) headspace test (ISO 14593) and biodegradation under anaerobic conditions was assessed employing a standardised batch test. The three amine oxide based surfactants tested were readily biodegradable under aerobic conditions but only the alkyl amido amine oxide was found to be easily biodegradable under anaerobic conditions. Toxicity to Photobacterium phosphoreum and Daphnia magna was evaluated. Bacteria (EC(50) from 0.11 to 11 mg l(-1)) proved to be more sensitive to the toxic effects of the amine oxide based surfactants than crustacea (IC(50) from 6.8 to 45 mg l(-1)). The fatty amido amine oxide showed the lowest aquatic toxicity.     

How Plants Cope with Foreign Compounds. Translocation of xenobiotic glutathione conjugates in roots of barley (Hordeum vulgare) (9 pp)

Background, Aim and Scope Numerous herbicides and xenobiotic organic pollutants are detoxified in plants to glutathione conjugates. Following this enzyme catalyzed reaction, xenobiotic GS-conjugates are thought to be compartmentalized in the vacuole of plant cells. In the present study, evidence is presented for long range transport of these conjugates in plants, rather than storage in the vacuole. To our knowledge this is the first report about the unidirectional long range transport of xenobiotic conjugates in plants and the exudation of a glutathione conjugate from the root tips. This could mean that plants possess an excretion system for unwanted compounds which give them similar advantages as animals. Materials and Methods: Barley plants (Hordeum vulgare L. cv. Cherie) were grown in Petri dishes soaked with tap water in the greenhouse. - Fluorescence Microscopy. Monobromo- and Monochlorobimane, two model xenobiotics that are conjugated rapidly in plant cells with glutathione, hereby forming fluorescent metabolites, were used as markers for our experiments. Their transport in the root could be followed sensitively with very good temporal and spatial resolution. Roots of barley seedlings were cut under water and the end at which xenobiotics were applied was fixed in an aperture with a thin latex foil and transferred into a drop of water on a cover slide. The cover slide was fixed in a measuring chamber on the stage of an inverse fluorescence microscope (Zeiss Axiovert 100). - Spectrometric enzyme assay. Glutathione S-transferase (GST) activity was determined in the protein extracts following established methods. Aliquots of the enzyme extract were incubated with 1-chloro-2,4-dinitrobenzene (CDNB), or monochlorobimane. Controls lacking enzyme or GSH were measured. - Pitman chamber experiments. Ten days old barley plants or detached roots were inserted into special incubation chambers, either complete with tips or decapitated, as well as 10 days old barley plants without root tips. Compartment A was filled with a transport medium and GSH conjugate or L-cysteine conjugate. Compartments B and C contained sugar free media. Samples were taken from the root tip containing compartment C and the amount of conjugate transported was determined spectro-photometrically. Results: The transport in roots is unidirectional towards the root tips and leads to exsudation of the conjugates at rates between 20 and 200 nmol min-1. The microscopic studies have been complemented by transport studies in small root chambers and spectroscopic quantification of dinitrobenzene-conjugates. The latter experiments confirm the microscopic studies. Furthermore it was shown that glutathione conjugates are transported at higher rates than cysteine conjugates, despite of their higher molecular weights. This observation points to the existence of glutathione specific carriers and a specific role of glutathione in the root. Discussion: It can be assumed that long distance transport of glutathione conjugates within the plant proceeds like GSH or amino acid transport in both, phloem and xylem. The high velocity of this translocation of the GS-X is indicative of an active transport. For free glutathione, a rapid transport-system is essential because an accumulation of GSH in the root tip inhibits further uptake of sulfur. Taking into account that all described MRP transporters and also the GSH plasmalemma ATPases have side activities for glutathione derivatives and conjugates, co-transport of these xenobiotic metabolites seems credible. - On the other hand, when GS-B was applied to the root tips from the outside, no significant uptake was observed. Thus it can be concluded that only those conjugates can be transported in the xylem which are formed inside the root apex. Having left the root once, there seems to be no return into the root vessels, probably because of a lack of inward directed transporters. Conclusions: Plants seem to possess the capability to store glutathione conjugates in the vacuole, but under certain conditions, these metabolites might also undergo long range transport, predominantly into the plant root. The transport seems dependent on specific carriers and is unidirectional, this means that xenobiotic conjugates from the rhizosphere are not taken up again. The exudation of xenobiotic metabolites offers an opportunity to avoid the accumulation of such compounds in the plant. Recommendations and Perspectives: The role of glutathione and glutathione related metabolites in the rhizosphere has not been studied in any detail, and only scattered data are available on interactions between the plant root and rhizosphere bacteria that encounter such conjugates. The final fate of these compounds in the root zone has also not been addressed so far. It will be interesting to study effects of the exuded metabolites on the biology of rhizosphere bacteria and fungi.