'Green' treatment of acid mine drainage - a step towards sustainability

Sustainability is becoming increasingly important in the mining and mineral processing industries and must incorporate the associated waste products. Acid mine drainage (AMD) is one such by-product and is one of the most serious environmental problems facing the minerals industry today. The oxidation of sulphidic mine wastes often continues for a substantial period of time after mine closure, resulting in difficult and costly remediation and rehabilitation works. Mining companies are often reluctant to spend increasing amounts of money on waste treatment when the mine life is limited or even finished. Hence a simple, low maintenance and low-cost method of treating AMD is required. Whilst this paper does not address the issue of AMD, it does propose methods for removal of individual species from AMD with potential benefits, including raising AMD pH.

A novel concept of using biosolids as a biological adsorbent, or ‘biosorbent’, of metals from AMD is being investigated at a laboratory/pilot scale level. Biosolids are a by-product resulting from the biological treatment of wastewater, and have been previously shown to adsorb metals from aqueous solutions. This could lead to an environmentally sustainable or ‘green’ method for treating both AMD discharges and disposing/reusing the biosolids.

The result of a laboratory-scale study of the biosorption of Zn(II) is presented in this paper. Physical parameters including reaction kinetics, mixing speed and solution pH were investigated. Solution pH also rose an average of 2 pH units over the 24 hour equilibrium time – a valuable side effect when treating acid mine drainage. The outcome of the study highlights the usefulness of biosolids as a biosorbent for the removal/recovery of metal ions from acid mine drainage. A simple, low-cost treatment technology requiring low maintenance would be beneficial to the mining industry to address some issues relating to AMD and would help integrate environmental and economic considerations into sustainable environmental management.

The normative distribution of chest tube drainage volume after coronary artery bypass grafting

Background
Little evidence exists to describe expected volumes of chest tube (CT) drainage after coronary artery bypass grafting (CABG).

Objectives
The study objective was to map the trajectory of CT drainage volumes from insertion to removal after CABG.

Design

This was a retrospective, descriptive study.
Patients
The study included 239 patients who underwent CABG at a single metropolitan hospital in Melbourne, Australia.

Results
The sample (N = 234), aged 68.7 years (standard deviation [SD] 9.9), was predominantly male (N = 185, 79.1%). The mean duration of CT insertion was 45.2 hours (SD 26.7), and total drainage volume was 1300.6 mL (SD 763.8). Drainage volumes plateau to 31 mL per hour, 8 hours after surgery. From 24 to 48 hours, the mean drainage was 21 mL per hour. Drainage volumes varied between genders.

Conclusions
Evidence of similar drainage patterns in other populations is difficult to locate. If the pattern of drainage shown in this study is consistent, experimental intervention studies comparing standard removal time and earlier removal are recommended. If not, prospective collection of relevant preoperative, intraoperative, and postoperative factors across multiple sites is necessary to determine which patient or practice variations influence CT drainage patterns after CABG.

Sudden drawdown and drainage of a horizontal aquifer

Drainage of a saturated horizontal aquifer following a sudden drawdown is reanalyzed using the Boussinesq equation. The effect of the finite length of the aquifer is considered in detail. An analytical approximation based on a superposition principle yields a very good estimate of the outflow when compared to accurate numerical solutions. An illustration of the new analytical approach to analyze basin-scale field data is used to demonstrate possible field applications of the new solution.

Acid drainage, limnology and bioremediation of western Victorian coal mine lakes

Rehabilitation of Alcoa's Anglesea open cut brown coal mine to a healthy lake has many environmental challenges. The study of regional acid drainage, limnology of Wenslydale Coal Mine Lake and passive bioremediation of acid mine water has shown that a healthy lake can be created.

The drainage of thin liquid films between solid surfaces

We present measurements of the thickness as a function of time of liquid films as they are squeezed between molecularly smooth mica surfaces. Three Newtonian, nonpolar liquids have been studied: octamethylcyclotetrasiloxane, n-tetradecane, and n-hexadecane. The film thicknesses are determined with an accuracy of 0.2 nm as they drain from ∼1 μm to a few molecular layers. Results are in excellent agreement with the Reynolds theory of lubrication for film thicknesses above 50 nm. For thinner films the drainage is slower than the theoretical prediction, which can be accounted for by assuming that the liquid within about two molecular layers of each solid surface does not undergo shear. In very thin films the continuum Reynolds theory breaks down, as drainage occurs in a series of abrupt steps whose size matches the thickness of molecular layers in the liquid. The presence of trace amounts of water has a dramatic effect on the drainage of a nonpolar liquid between hydrophilic surfaces, causing film rupture which is not observed in the dry liquids.

The 'wimple' : rippled deformation of a fluid drop caused by hydrodynamic and surface forces during thin film drainage

It is well-known that hydrodynamic pressures in a thin draining liquid film can cause inversion of the curvature of a drop or bubble surface as it approaches another surface, creating a so-called “dimple”. Here it is shown that a more complicated rippled shape, dubbed a “wimple”, can be formed if a fluid drop that is already close to a solid wall is abruptly pushed further toward it. The wimple includes a central region in which the film remains thin, surrounded by a ring of greater film thickness that is bounded at the outer edge by a barrier rim where the film is thin. This shape later evolves into a conventional dimple bounded by the barrier rim, which then drains in the normal way. During the evolution from wimple to dimple, some of the fluid in the thicker part of the film ring flows toward the central region before eventually draining in the opposite direction. Although the drop is pressed toward the wall, the central part of the drop moves away from the wall before approaching it again. This is observed even when the inward push is too small to create a wimple.

The influence of surface forces on thin film drainage between a fluid drop and a flat solid

An experiment is described in which a mica surface is driven towards a mercury drop immersed in aqueous electrolyte. Under appropriate conditions, hydrodynamic pressure in the aqueous film creates a classical dimple in the mercury drop. The use of optical interferometry and video recording to monitor the shape of the drop and the thickness of the aqueous film with sub-nanometre resolution yields a high density of precise data showing the formation and evolution of the dimple as the film drains. Variation of electrical potential applied to the mercury phase allows control of the surface forces acting between the drop and the mica surface, so that the effect of surface forces on the film drainage process is highlighted. It is found that the film thickness at the centre of the dimple and the lateral extent of the dimple are not significantly affected by surface forces. On the other hand, the minimum film thickness at the edge of the dimple is sensitive even to weak surface forces. Since this minimum film thickness is a major determinant of the film drainage rate, it is shown that surface forces have an important effect on the overall drainage process.

Thin film drainage : hydrodynamic and disjoining pressures determined from experimental measurements of the shape of a fluid drop approaching a solid wall

Accurate measurements of the shape of a mercury drop separated from a smooth flat solid surface by a thin aqueous film reported recently by Connor and Horn (Faraday Discuss. 2003, 123, 193-206) have been analyzed to calculate the excess pressure in the film. The analysis is based on calculating the local curvature of the mercury/aqueous interface, and relating it via the Young-Laplace equation to the pressure drop across the interface, which is the difference between the aqueous film pressure and the known internal pressure of the mercury drop. For drop shapes measured under quiescent conditions, the only contribution to film pressure is the disjoining pressure arising from double-layer forces acting between the mercury and mica surfaces. Under dynamic conditions, hydrodynamic pressure is also present, and this is calculated by subtracting the disjoining pressure from the total film pressure. The data, which were measured to investigate the thin film drainage during approach of a fluid drop to a solid wall, show a classical dimpling of the mercury drop when it approaches the mica surface. Four data sets are available, corresponding to different magnitudes and signs of disjoining pressure, obtained by controlling the surface potential of the mercury. The analysis shows that total film pressure does not vary greatly during the evolution of the dimple formed during the thin film drainage process, nor between the different data sets. The hydrodynamic pressure appears to adjust to the different disjoining pressures in such a way that the total film pressure is maintained approximately constant within the dimpled region.

Nurses’ advice regarding sterile or clean urinary drainage bags for individuals with a long-term Indwelling urinary catheter

PURPOSE: The purpose of this study was to identify, compare, and explore advice nurses give to community-dwelling long-term indwelling catheter users on the use of sterile or clean urinary drainage bags, and to obtain information that would inform the design of a larger-scale international survey.


SUBJECTS AND SETTINGS: A survey was targeted to nurse members of the International Continence Society (n = 130). Respondents (n = 28; 21.5%) included nurses from Australia, Canada, Belgium, Switzerland, the United Kingdom, and the United States, who specialized in managing incontinence.


METHODS: The project was conducted as a descriptive, exploratory pilot study. Respondents completed an online anonymous survey that was distributed by the International Continence Society. The survey instrument was designed by the investigators and comprised 14 questions with both fixed and open-ended response options.


RESULTS: Most respondents in this survey advised indwelling catheter users to reuse their catheter bags (n = 15; 68%). Factors that influenced advice included concerns about the cost of catheter bags, an evaluation of the individual's infection risk, local and national policies, evidence-based guidelines, users' living arrangements, and their ability to clean the bags. Advice on decontamination methods varied; however, the most commonly recommended cleaning agent was water and vinegar, followed by a sterilizing or bleach solution or dishwashing detergent.


CONCLUSION: Nurses play a key role in educating and supporting indwelling catheter users. Results of this study highlight variability in the advice nurses give to community-dwelling long-term indwelling catheter users about sterile or clean urinary drainage bags. This variability requires further investigation and affirms the need for a larger-scale study that draws on a broader sample of nurses.

The four national taps of Singapore: a holistic approach to water resources management from drainage to drinking water

 Water resources in Singapore are managed following the principles of a closed loop hydrologic cycle by one agency, the Public Utility Board (PUB), which promotes its management philosophy through the Four National Taps of Singapore program. The four national taps are: water from local catchment areas; imported water (from Malaysia); reused water (known as NEWater); and desalinated water. Given the uncertainty of water imports, the remaining three national taps have become increasingly important and this paper begins with a general overview of the innovative programs implemented by PUB in support of these three taps. Stormwater runoff is captured from two-thirds of Singapore’s land area and stored in reservoirs for subsequent use. Stormwater management is an important component of the catchment area tap and extensive low impact development (LID) implementation has become a priority through the ABC (Active, Beautiful, Clean) Waters Program. Examples of several ABC Waters projects are discussed. NEWater currently supplies 30% of the country’s demand and this is projected to increase to 50% by 2060. NEWater plants take treated wastewater through the additional steps of microfiltration, reverse osmosis and ultraviolet treatment for use primarily in industry, although a portion also is blended into the municipal reservoirs. Singapore’s single desalination plant currently meets 10% of its demand, with a second plant to be completed in 2013 that will more than double production. Also discussed are the results of recently completed pilot projects related to stormwater management including testing of E. coli in runoff from high density residential areas, a blind taste test and survey on acceptance of NEWater, and a survey of Singaporean understanding about stormwater management issues.Water resources in Singapore are managed following the principles of a closed loop hydrologic cycle by one agency, the Public Utility Board (PUB), which promotes its management philosophy through the Four National Taps of Singapore program. The four national taps are: water from local catchment areas; imported water (from Malaysia); reused water (known as NEWater); and desalinated water. Given the uncertainty of water imports, the remaining three national taps have become increasingly important and this paper begins with a general overview of the innovative programs implemented by PUB in support of these three taps. Stormwater runoff is captured from two-thirds of Singapore’s land area and stored in reservoirs for subsequent use. Stormwater management is an important component of the catchment area tap and extensive low impact development (LID) implementation has become a priority through the ABC (Active, Beautiful, Clean) Waters Program. Examples of several ABC Waters projects are discussed. NEWater currently supplies 30% of the country’s demand and this is projected to increase to 50% by 2060. NEWater plants take treated wastewater through the additional steps of microfiltration, reverse osmosis and ultraviolet treatment for use primarily in industry, although a portion also is blended into the municipal reservoirs. Singapore’s single desalination plant currently meets 10% of its demand, with a second plant to be completed in 2013 that will more than double production. Also discussed are the results of recently completed pilot projects related to stormwater management including testing of E. coli in runoff from high density residential areas, a blind taste test and survey on acceptance of NEWater, and a survey of Singaporean understanding about stormwater management issues.