The role of a subsurface lime-fly ash barrier in the mitigation of acid sulphate soils

The effectiveness of using a sub-surface lime-fly ash barrier to reduce the oxidation of a pyritic soil layer and to improve groundwater and surface water quality was investigated for land affected by acid sulphate soils near Berry in southeastern NSW, Australia. Prior to the installation of the lime-fly ash barrier, groundwater and surface water analyses indicated a highly acidic environment. High concentrations of dissolved aluminium, total iron and sulphate in the groundwater were a result of falling groundwater tables and biotic oxidation. Traditional management techniques of ground water manipulation, via floodgates or weirs, would be rendered ineffective in arresting biotic oxidation where the pyrite layer is submerged. The study combined field and laboratory analysis in order to determine the feasibility of the lime-fly ash barrier at the study site. A comprehensive field study incorporated the installation of piezometers and observation wells to determine the level of the phreatic surface along with the monitoring of water quality parameters at the site of the lime-fly ash barrier, and also floodgate sites and the site of the self-regulating tilting weir. The installation of the lime-fly ash barrier was undertaken by the pumping of a slurry through boreholes via pressure pumping. The subsurface lime-fly ash barrier, as an acid sulphate soil remediation technique, was shown to significantly improve groundwater quality. Groundwater pH increased to values between 4.5 and 5.5. The concentration of the pyritic oxidation products, acidic cations Al³+ and Fetotal, basic cations Ca²+ and Mg²+ and anions Cl- and SO4² -, also, on average decreased in the groundwater after the installation of the lime-fly ash barrier. A comparison between the average roundwater table elevations before and after the installation of the barrier also indicated a perched water table, which would reduce the exposure of pyritic soil to oxygen, and in turn reduce pyritic oxidation and the generation of acidic products. The Lime-fly ash barrier is effective in remediating acid sulphate soils in areas in which floodgates and weirs cannot be installed. A comparison of the result shows that the lime-fly ash barrier had greater success in increasing the groundwater pH than the self-regulating tilting weir. The lime-fly ash barrier treats acid sulphate soils and the related environmental problems before they occur, whereas, the floodgates treat the pyrite oxidation products generated after they have been discharged into the flood mitigation drains. Significantly greater concentrations of Al³+, Fetotal and SO4 ²- were found in the groundwater at the floodgate sites

Engaging Citizens and Transforming Designers: Analysis of a Campus- Community Partnership Through the Lens of Children’s Rights to Participate

While an engaged citizenry is often the goal of community service learning, the rights of children to be active agents in this process are largely considered in a separate academic literature. Yet community service learning and children’s participation share much in their goals and approaches to engagement. This paper analyzes a campus-community partnership between undergraduate environmental design and middle school applied science students. The partnership began as a way to promote participatory design processes for the redesign of a middle school and evolved to a proactive co-design program. We describe the goals and approaches to service-learning employed through the partnership, and critique the evolution of the program through the realm of a participation model that has emerged from three decades of children’s participation research. By analyzing a campus-community partnership through this framework, we hope to deepen the discourse on approaches to and evaluation of successful service-learning programs

Engaging Citizens and Transforming Designers: Analysis of a Campus-Community Partnership Through the Lens of Children’s Rights to Participation

While an engaged citizenry is often the goal of community service learning, the rights of children to be active agents in this process are largely considered in a separate academic literature. Yet community service learning and children’s participation share much in their goals and approaches to engagement. This paper analyzes a campus-community partnership between undergraduate environmental design and middle school applied science students. The partnership began as a way to promote participatory design processes for the redesign of a middle school and evolved to a proactive co-design program. We describe the goals and approaches to service-learning employed through the partnership, and critique the evolution of the program through the realm of a participation model that has emerged from three decades of children’s participation research. By analyzing a campus-community partnership through this framework, we hope to deepen the discourse on approaches to and evaluation of successful service-learning programs

Removal of inorganic and trace organic contaminants by electrodialysis

Linkage Project LP0454254With the continual concern over the presence of naturally occurring and anthropogenic inorganic and trace organic contaminants in the aquatic environment there is a growing need for the implementation of innovative treatment processes for the elimination of these contaminants from natural waters and wastewater effluents. While conventional treatment methods are ineffective in the removal of emerging contaminants such as steroidal hormones and pesticides, membrane technology, including electrodialysis (ED), has been highlighted as a potential treatment option. However, the clear lack of fundamental understanding of the behaviour of contaminants in ED is a current limitation for its extensive utilisation and is a critical issue that needs to be addressed. ED processing potentialities have not been fully exploited and more research is needed to account for all the key parameters such as contaminant physicochemical properties, solution chemistry and the presence of organic matter. The purpose of this study was to elucidate the mechanisms of inorganic and trace organic contaminant removal by ED. The inorganic contaminants fluoride, nitrate and boron were selected due to their ubiquitous nature in the environment and public health concerns resulting from longterm exposure. The hydrated radius and strength of hydration shells played a significant role in ionic transport, whereby nitrate with a smaller hydrated radius was removed more effectively (94.1 %) than fluoride (68.3 %) with a larger hydrated radius. While fluoride and nitrate removal was pH independent, the pH dependent speciation of boron enhanced its removal with increasing pH. Territorial binding and/or complexation of the inorganics with organic matter enhanced removal. The removal of a range of trace inorganics (e.g. arsenic, calcium, magnesium, uranium) from a brackish groundwater from a remote Australian community was investigated. Undissociated inorganics were not transported through the membranes, whereas dissociated inorganics were due to electrostatic attraction. At acidic-neutral conditions ionic transport was the dominant removal mechanism. At neutral to alkaline conditions insoluble carbonate species precipitated and deposited as a membrane scaling layer (60 μm). This has serious implications for the long-term practical applicability of ED to treat real waters as scaling increased ED stack resistance (pH 3: 27.5 4, pH 11: 50 4) and decreased total dissolved solids removal (pH 3: 99 %, pH 11: 89.5 %). While the treatment of trace organics by other membrane processes has been widely studied, their fate in ED and interaction with ED membranes is relatively unknown. Trace contaminant-membrane interaction studies were undertaken to quantify the partitioning of trace organics; namely steroidal hormones and the pesticide endosulfan, to ED membranes by measuring membrane-water partition coefficients (log KM). The extremely high sorption capacity of the membranes was attributed to hydrogen bonding between the trace organic and membrane functional groups. Hormone sorption during ED was influenced by solution pH and organic matter. In the case of estrone, membrane sorption decreased at pH 11 (487 μg/cm3) compared to pH 7 (591 μg/cm3) due to dissociation and membrane electrostatic repulsion .At pH 11, repulsion between dissociated estrone and HA coupled with membrane electrostatic attraction resulted in increased sorption. The findings from this study highlight that the transport of trace contaminants will depend largely on the characteristics of the membranes used in the ED process as well as the physicochemical characteristics of the contaminants, their interaction with the ED membranes and the presence of other inorganic and/or organic compounds. The knowledge gained has direct applications to current problems and uncertainties in water and wastewater treatment with regards to the fate and transport of contaminants

Energy Dissipation Efficiency of Geotechnical Seismic Isolation with Gravel-Rubber Mixtures:Insights from FE Non-Linear Numerical Analysis

This paper provides new and useful insights into the performance and efficiency of geotechnical seismic isolation (GSI) systems with gravel-rubber mixtures containing 10%, 25% and 40% volumetric rubber content (VRC). Finite element numerical models were developed in OpenSees and subjected to sinusoidal ground motions with varying input base acceleration and frequency. The best seismic performance was attained for VRC = 40% at a frequency of 8 Hz. Using a newly developed GSI efficiency index, the energy dissipation efficiency of VRC = 40% was found to vary between good to excellent, while that of VRC = 10% and 25% is poor.</p

Sorption of steroidal hormones by electrodialysis membranes

Article in Press (Corrected Proof) - first available online 21 September 2010.The mechanisms of sorption of four steroidal hormones – estradiol, estrone, progesterone and testosterone – to electrodialysis (ED) membranes were investigated as a function of solution pH and presence of humic acid (HA). Hormone-membrane partition coefficients (log KAEM/CEM) determined through sorption isotherm experiments suggested that hormone sorption was due to hydrogen bonding and cation–π interactions between hormone and membrane functional groups. Progesterone sorption at pH 7 (922 μg/cm3) during ED was greater than estrone sorption (591 μg/cm3) due to its greater cation-exchange membrane (CEM) bonding affinity. Estrone sorption at pH 11 (487 μg/cm3) was reduced due to estrone dissociation and electrostatic repulsion with negatively charged CEMs. Permeation of estrone (30–100 ng/cm2 h) through the anion-exchange membranes (AEMs) was observed. At pH 11, charge repulsion between estrone and HA coupled with AEM electrostatic attraction resulted in increased sorption. Partial membrane desorption was noted in isotherm (20–30%) and ED desorption (3.8%) experiments and was dependent on the initial mass sorbed, solution pH and resultant electrostatic interactions

Sorption of pesticide endosulfan by electrodialysis membranes

Endosulfan (ES) is a micropollutant found in reverse osmosis concentrates from water reuse applications. Electrodialysis (ED) can remove and recover charged solutes from such concentrates. While polar compounds cannot normally be removed, their fate in ED is important as they can contribute to membrane fouling/poisoning and be released during cleaning. High adsorption of ES to ED membranes was observed. Consequently, the influence of solution pH and presence of humic acid (HA) on sorption mechanisms of ES to ion-exchange membranes during batch sorption isotherm and ED experiments were investigated systematically. ES-membrane partition coefficients (log KAEM/CEM) quantified through sorption isotherm experiments suggested that ES sorption was resultant of membrane catalysed ES degradation, hydrogen bonding and cation– interactions between ES and membrane functional groups. ES sorption at pH 7 (550 μg/cm3) was greater than sorption at pH 11 (306 μg/cm3) due to alkaline hydrolysed ES and resultant decrease in bonding capacity with the membranes at high pH. The presence of HA reduced sorption at pH 7 (471 μg/cm3) and 11 (307 μg/cm3) due to HA competitive sorption. Partial membrane desorption was noted in isotherm (<20%) desorption experiments and was dependent on the initial mass sorbed, solvent pH and resultant membrane interactions

A novel hydro-geochemical model for treating acidic groundwater utilizing a permeable reactive barrier

Acidic groundwater generation from acid sulfate soil is a severe environmental and socio-economic problem in coastal Australia. A novel permeable reactive barrier (PRB) utilising recycled concrete aggregates as the reactive media was installed in the Shoalhaven Floodplain, south of Wollongong in Australia. The performance of the PRB has been monitored to study the acid neutralisation behaviour of recycled concrete and its potential to remove high concentrations of Al and Fe, which are threatening to living habitat. This study aims to couple geochemistry with geo-hydraulics in the remediation of acidic groundwater generated in acid sulfate soil terrain, which has not been addressed in the past (especially using recycled concrete aggregates), in view of time-dependent modelling and performance verification. Coupling includes complex geochemical reaction kinetics with transient groundwater flows. Moreover, chemical clogging due to mineral precipitates has rarely been quantified. Deposition of precipitated minerals in void spaces within the PRB reduces the porosity and hydraulic conductivity of the reactive medium, which in turn effects the reorientation of flow paths and changes in reaction times. The commercial numerical codes, MODFLOW and RT3D were used to couple the groundwater flow with reaction kinetics. A systematic algorithm was developed for RT3D to simulate geochemical reactions occurring in the PRB. The field results show good agreement with the model predictions. The hydraulic conductivity reductions occur near the entrance of the PRB due to the high amount of mineral precipitation. Compared to the entrance, hydraulic conductivity reductions were negligible midway and at the effluent end of the PRB

Installation of a lime injection barrier for the remediation of acid sulphate soil problems

Oxidation of naturally occurring pyrite (FeS2) in certain low-lying clayey soils generates sulphuric acid, hence the term acid sulphate soils. A horizontal alkaline barrier was installed by radial grouting, for the purpose of remediating leachate from acid sulphate soils and preventing further oxidation. The current research relates to a large-scale field trial of this technique and the effect on the groundwater composition. In coastal Australia, a pyritic layer commonly exists in the soil at shallow depth that is at risk of oxidation, hence the main objective was to inject the barrier above the pyritic layer to (a) stop infiltration of oxygen to the pyritic layer and (b) neutralise any acidity stored in the soil. Two fine-grained alkaline materials, lime and fly ash, were assessed in this study. Lime was selected for its neutralising capacity, while the fly ash was selected to accompany the lime to enhance the pozzolanic reactions. The optimum mix ratio of lime, fly ash and water to form an ideal slurry and the optimum depth and pressure of injection were experimentally determined. For the large-scale field trial, the slurry was injected into a systematic grid of 22 holes to form the reactive barrier. The groundwater composition was monitored in a network of observation holes across the study site to determine the effectiveness of the barrier. The average groundwater pH was 3.25 prior to installation of the barrier, and it rose to 4.6 after the barrier was installed. The influence of the barrier on the groundwater pH was greater in observation holes close to the barrier than those further away. The concentrations of aluminium and iron decreased in the groundwater after the installation of the alkaline barrier. The ratio of Cl/SO4 in the groundwater increased after the barrier was installed which confirmed that the barrier had successfully controlled the subsequent pyrite oxidation in the soil