Dr Vasiliki Ioannidou

Passive Mine Water Treatment Schemes (MWTS) have been developed to remove iron from coal mine drainage before discharge into the environment to prevent potential ecological environmental problems caused by coal mine drainage. The performance of these MWTS vary across distinct climatic conditions, based on variations in temperature and rainfall patterns. Therefore, this study analysed monthly iron concentrations of 10 settlement lagoons and 5 constructed wetlands (CWs) in 5 full-scale MWTS to assess the influence of varying seasons on the MWTS lagoons and CWs treatment performance using removal efficiency (R.E.). The comparative performance of monthly records of Ferric Iron (Fe3+), Ferrous Iron (Fe2+) and pH over a period of 12 years were conducted using comprehensive statistical analysis of Fe3+ R.E. Fe3+ R.E. obtained for the 5 MWTS ranged from 50.97 to 98.98% and is in the order Site A > Site C > Site B > Site E > Site D. pH increased from slightly acidic to neutral while Fe3+ and Fe2+ concentrations decreased. The MWTS achieved an average Fe2+ R.E. of 46.66–98.16%. Seasonal variation affected iron removal from the schemes, i.e., Fe3+ R.E. in the lagoons and wetlands was in the order summer > spring > autumn > winter. Due to increased rates of sedimentation, filtration and absorption in warmer seasons, treatment performance of the schemes was better compared to colder seasons. The experimental results obtained provide a scientific basis for MWTS operators, research scientists, policy makers to improve R.E. and ensure consistent treatment performance in different seasons throughout the year.

In response to the potential ecological problems caused by coal mine drainage, passive Mine Water Treatment Schemes (MWTS), consisting of settlement lagoons and aerobic wetlands, are developed to remove iron and other contaminants prior to discharge into the environment. Existing research has examined individual design aspects separately, addressing the effect of lagoons' design on treatment performance. However, long-term research lacks data on the design aspects of full-scale mine drainage lagoons, to ensure consistent iron removal and optimal treatment of the mine drainage. This study analysed and assessed the design aspects of five full-scale lagoons, alongside monthly iron concentrations spanning over a period of twelve years, aiming to evaluate lagoon treatment performance based on different design aspects. Correlation and regression analyses were conducted to offer a better understanding of the potential relationships between iron removal efficiencies and the various design aspects of lagoons. Results indicated that the mean iron removal efficiencies of the lagoons studied, ranged from 25.12% to 92.85%, being impacted by the different design features. The correlation and multiple regression analysis results suggest that operational Water Levels, Surface Area, Aspect Ratio, layout and number of inlets and outlets, as well as shape of the lagoons affected iron removal (R2 0.78, p-value <0.05). Lagoons with larger aspect ratio were observed to have performed better in removing iron. In addition, a reduction in operational water level was observed to lead to increased iron removal. Furthermore, the result of the regression analysis demonstrated that the age of the lagoon significantly affects its treatment performance. Overall, lagoons with mid-mid configuration, multiple inlets and outlets and aspect ratio of 4 are found to allow for better flow and contaminant spread within the system, ensuring better adsorption and optimal removal of iron, although subject to regular ochre removal. This study offers valuable insights to lagoons design engineers, research scientists, policy makers and MWTS operators to optimize treatment performance.

The efficiency of pond and constructed wetland (CW) treatment systems is influenced by the internal hydrodynamics and mixing interactions between water and aquatic vegetation. In order to contribute to current knowledge of how emergent real vegetation affects solute mixing, and on what the shape and size effects are on the mixing characteristics, an understanding and quantification of those physical processes and interactions were made. This paper presents results from tracer tests conducted during 2015–2016 in six full-scale systems in the UK under different flow regimes, operational depths, shapes and sizes, and inlet/outlet configurations. The aim was to quantify the hydraulic performance and mixing characteristics of the treatment units, and to investigate the effect of size and shape on the mixing processes. Relative comparison of outlet configuration, inflow conditions, and internal features between the six different treatment units showed variations in residence times of up to a factor of 3. A key outcome of this study was that the width is a more important dimension for the efficiency of the unit compared to the depth. Results underlined the importance of investigating hydrodynamics and physics of flow in full-size units to enhance treatment efficiency and predictions of water quality models.