A review of the importance of hydraulic residence time on improved design of mine water treatment systems.

Hydraulic residence time is an important parameter for the design of mine water treatment systems, in particular for wetland system and settlement lagoon. Despite much investigations have been done on system hydraulic residence time, little is still known about how the residence time may relate to treatment system performance. Such an understanding will be useful for improvement of existing treatment system performance and in the design of future systems. Thus, this review attempts to explore this issue on how the assessment of system hydraulic behaviour (of which the residence time), coupled with the assessment of geochemical factors may be incorporated in future design of mine water treatment systems. Review of current design practice for mine water treatment systems in UK applications of passive treatment is also presented. Recommendation for design guidance is discussed to provide some insights into new approach for improved design of such systems

Coupled hydraulic and geochemical performance assessment of passive mine water treatments in the UK

PhD ThesisCurrent design practice for aerobic wetlands treating net-alkaline mine water in UK applications of passive treatment is based on zero-order kinetics for pollutant removal; the commonly used area-adjusted removal formula. Lagoons are designed to allow 48 hours of estimated retention time. However, there is significant variation in performance between systems. Neither of these approaches takes account of the hydraulic factors that may influence treatment performance. Therefore, this study aimed to improve understanding of both hydraulic and geochemical factors that govern contaminant behaviour, such that future design of treatment systems is able to optimise treatment efficiency and make performance more predictable, and improve performance over the long-term. Assessment of the hydraulic behaviour (flow pattern) of the treatment systems was accomplished by means of tracer tests. The tracer tests and simultaneous sampling of mine water were undertaken at eight UK Coal Authority mine water treatment systems (lagoons and wetlands) within Northern England (main study areas) and part of southern Scotland. Analyses of mine water samples were also undertaken in the laboratory alongside the field tests for assessment of geochemical processes controlling iron removal in the lagoons and wetlands studied. Analyses of the tracer test results were performed using a residence time distribution (RTD) analysis to account for the different shapes of tracer breakthrough curves observed. There appear to be multiple influences that possibly affect the RTDs in lagoons and wetlands e.g. vegetation and seasonal variation (growing or non-growing season), system age, flow and geometry (length-to-width ratio and depth). The RTD analysis shows that lagoons generally have a more dispersed flow pattern, associated with a more pronounced short-circuiting effects and a long tail compared to wetlands. A modelling approach using a tanks- in-series (TIS) model was adopted to precisely analyse and characterise the RTDs, in an effort to account for the different flow patterns across the treatment systems. Generally, lagoon RTDs are characterised by a greater flow dispersion compared to wetlands (i.e. higher dispersion number, D and lower number of TIS, n). Consequently, the hydraulic efficiency, e for lagoons is much lower than wetlands (mean of 0.20 for lagoons compared to 0.66 for wetlands). This is attributed primarily to a much lower volumetric efficiency, ev in lagoons, meaning that a greater proportion of the total volume of the lagoon system is not being involved in the flow of water through them, with implications for design to optimise performance. In contrast, in wetlands a greater volumetric efficiency is evident, and there is therefore a longer relative mean residence time for retention and attenuation of iron. On the evidence of field data, in lagoon systems the iron removal processes are primarily controlled by ferrous iron oxidation, whilst in wetlands the removal is controlled by iron settlement. The time- and concentration-dependence of iron removal (oxidation and / or settlement rate) has also been investigated in the laboratory alongside the field data. The rates are faster in lagoons compared to wetlands due to higher concentration of iron available for the processes. General trends showed that efficient treatment performance for iron removal corresponds with greater system hydraulic efficiency in wetlands compared to lagoon systems. The greater hydraulic efficiency in wetlands was mainly attributed to a grea ter volumetric efficiency in the wetland systems. In contrast, shorter relative mean residence time was found in lagoons, thus a lower retention time for iron attenuation and lower removal efficiency as a consequence. For lagoon systems, performance can be optimised by ensuring greater volumetric efficiency (hence residence time), which can be achieved with a large length-to-width ratio system (up to a ratio of 4.7), but also a greater depth (up to 3.0 m), though only if systems are regularly maintained (dredged). For wetlands, the use of the area-adjusted removal rate formula appears to work well for the design of aerobic wetlands, despite the observed concentration-dependence of iron removal processes. However, use of first-order removal formula (TIS basis) would be a more appropriate approach to the design of mine water treatment systems since it takes account of the flow pattern effect on pollutant removal processes, in addition to the first-order kinetics (concentration-dependence) for iron removal. Regular sludge removal (yearly) is recommended in lagoons to provide longer residence time because lagoon depth and volume tends to rapidly decrease over time due to build up of ochre and debris (7- 49% depth reduction per year). Thinning of reeds is recommended whenever apparent channelisation would otherwise dominate the flow pattern, and therefore limit the capacity for adsorption and settlement of precipitated iron hydroxide.Ministry of Higher Education Malaysia, Universiti Putra Malaysi

Anoxic limestone drain for treatment of highly acidic water

Limestone has been widely used in the treatment of acidic water due to its capability of neutralizing acid and removing metals in water. This study investigated the efficiency of limestone treatment in treating acidic water in anoxic limestone drain at a laboratory scale. The anoxic limestone drain was basically designed to enhance limestone dissolution and alkalinity generation thus minimizing the potential of armouring, which may decrease the rate of acid neutralization. Actual raw water samples from two different locations within Sg. Bekok catchment which were highly acidic with low pH values were used in the experiment treated by 30 mm diameter of 112 kg of limestone. The conditions under which the pH increases, acidity decreases, alkalinity produced and metals were removed in the anoxic limestone drain have been determined. pH was significantly increased from initially 3.27–4.09 to 6.49–6.67 after flowing through the anoxic drain in 10 min of contact with the limestone. Acidity was reduced from 73–99 mg/L as CaCO3 to 17–19 mg/L as CaCO3 as pH were raised to reach near neutral levels. Iron and aluminium were also being removed in the anoxic limestone drain

Coupled physicochemical and bacterial reduction mechanisms for passive remediation of sulfate- and metal-rich acid mine drainage

Treatment of acid mine drainage (AMD) highly rich in sulfate and multiple metal elements has been investigated in a continuous flow column experiment using organic and inorganic reactive media. Treatment substrates that composed of spent mushroom compost (SMC), limestone, activated sludge and woodchips were incorporated into bacterial sulfate reduction (BSR) treatment for AMD. SMC greatly assisted the removals of sulfate and metals and acted as essential carbon source for sulfate-reducing bacteria (SRB). Alkalinity produced by dissolution of limestone and metabolism of SRB has provided acidity neutralization capacity for AMD where pH was maintained at neutral state, thus aiding the removal of sulfate. Fe, Pb, Cu, Zn and Al were effectively removed (87–100%); however, Mn was not successfully removed despite initial Mn reduction during early phase due to interference with Fe. The first half of the treatment was an essential phase for removal of most metals where contaminants were primarily removed by the BSR in addition to carbonate dissolution function. The importance of BSR in the presence of organic materials was also supported by metal fraction analysis that primary metal accumulation occurs mainly through metal adsorption onto the organic matter, e.g., as sulfides and onto Fe/Mn oxides surfaces

A comparative study of anoxic limestone drain and open limestone channel for acidic raw water treatment.

This study presents the performance of an anoxic limestone drain in comparison to an open limestone channel for treating acidic water. The anoxic limestone drain was designed to enhance limestone dissolution and alkalinity generation thus minimizing the potential of armouring which may decrease the rate of acid neutralization. Actual raw water from two different locations within Sg. Bekok catchment that is highly acidic with low pH value (~ pH 2.5) was used in the experiment. The anoxic limestone drain was found to perform better than the open limestone channel with respect to pH increase, acidicy decrease and alkality production. Iron was removed at relatively higher rate in open limestone channel but resulted in the armouring of limestone surfaces thus limiting further generation of alkalinity

A review of applied GIS based in sustainable water resources management in Malacca River case study: an observation perspective

Water resources have become an issue in supplying freshwater for human to carry out daily activities. The reasons for this problem water pollution occurring in rivers. Among the methods to overcome this problem is the adoption of the concept of sustainability in water resources management in Malacca River. Practicing this concept will require a technology to help in planning as a whole, namely Geographical Information System or GIS. GIS is a tool widely used in determining the quality and quantity of water resources, especially at the river basin scale, to manage water resources. The site selection for observation in this review paper is Malacca River, which have a wide river basin and suitable for study. As a result, GIS has the ability to combine various data and provide an answer for decision making in sustainable water resources management in Malacca River, such as physical perspective data (elevation and slope boundary, landuse data, meteorological data, hydrological data, etc.) and human perspective data (demographic and population data, stakeholders and businesses data, etc.). GIS helps users to develop a new model (for example water quality model) which become a main point in saving and protecting the environment and the human society

Applied GIS in assessment water quality modeling in the Malacca River. Case study: introduction to research study

A research study documents the process of examination, using experimentation or investigation to discover and interpret on certain topic for the purpose of increasing the understanding of an issue. The main purposes of research study are to help people to understand and solve problems, communicate ideas and information to the public, help researchers to make decisions through data collection, and develop new knowledge for humankind. Research may be divided into the first stage (problem statement, research questions, hypothesis or objectives), second stage (literature review, research design, instrumentation, preliminary study), and third stage (data collection, data analysis or research findings, preparation of reports). The problem statement of this study involves river water pollution, while the objective of the study is to assess river water quality in the Malacca River, to determine major source and the factors contributing to river pollution, and to determine a spatial decision support system (SDSS) for minimizing water pollution in the Malacca River. The research design involves a quantitative approach (experimental methods), which collects primary data (water sample from Malacca River and GPS data information) and secondary data (water sample from government, GIS map-based data, and RS data). This data will be grouped together and undergo the analysis process of GIS and RS to develop SDSS. Information and results provided will become answers to the objective and determination of achievement of the research study. Therefore, this study provides new information for other researchers to perform more in depth research according to their field of study

Hydraulic residence time and iron removal in a wetland receiving ferruginous mine water over a 4 year period from commissioning.

Analysis of residence time distribution (RTD) has been conducted for the UK Coal Authority's mine water treatment wetland at Lambley, Northumberland, to determine the hydraulic performance of the wetland over a period of approximately 4 years since site commissioning. The wetland RTD was evaluated in accordance with moment analysis and modelled based on a tanks-in-series (TIS) model to yield the hydraulic characteristics of system performance. Greater hydraulic performance was seen during the second site monitoring after 21 months of site operation i.e. longer hydraulic residence time to reflect overall system hydraulic efficiency, compared to wetland performance during its early operation. Further monitoring of residence time during the third year of wetland operation indicated a slight reduction in hydraulic residence time, thus a lower system hydraulic efficiency. In contrast, performance during the fourth year of wetland operation exhibited an improved overall system hydraulic efficiency, suggesting the influence of reed growth over the lifetime of such systems on hydraulic performance. Interestingly, the same pattern was found for iron (which is the primary pollutant of concern in ferruginous mine waters) removal efficiency of the wetland system from the second to fourth year of wetland operation. This may therefore, reflect the maturity of reeds for maintaining efficient flow distribution across the wetland to retain a longer residence time and significant fractions of water involved to enhance the extent of treatment received for iron attenuation. Further monitoring will be conducted to establish whether such performance is maintained, or whether efficiency decreases over time due to accumulation of dead plant material within the wetland cells

Hydraulic performance and iron removal in wetlands and lagoons treating ferruginous coal mine waters

A study of hydraulic residence time has been conducted for several UK Coal Authority mine water treatment systems to evaluate the impact of residence time on the overall hydraulic performance and iron removal within the systems. A series of tracer tests were conducted within the Coal Authority mine water treatment wetlands and lagoons to measure actual hydraulic residence time. The tracer residence time distributions (RTDs) were analysed based on a tanks-in-series (TIS) model to yield the mean residence time and corresponding hydraulic characteristics of the systems. The relationship between iron retention and residence time was tested against a first-order removal model. The mean hydraulic efficiency is 69 % for the wetlands compared to 24 % for the lagoons, mainly attributable to comparatively greater volumetric efficiency within the wetland systems. The mean number of TIS, n, is 3.9 for the wetlands and 2.1 for the lagoons, illustrating considerably different flow patterns between wetlands and lagoons. There is also a notable difference of treatment efficiency for iron; mean of 81 % and 47 % for wetlands and lagoons, respectively. Generally, it appears that system hydraulic efficiency (derived from the principle of TIS model) corresponds with iron retention in the treatment systems

Performance assessment of centrifuge dewatering unit using multivariate statistical approach: a case study of a centralized sludge treatment facility (CSTF) in Malacca, Malaysia

The performance of the centrifuge dewatering unit in Sungai Udang centralized sludge treatment facility has been studied using multivariate statistical approach. The relationships between bio-solids production and 14 parameters were analyzed using principle component analysis (PCA) and multiple linear regression (MLR) analysis. PCA was used to simplify the complexity among variables affecting the production of bio-solids in the treatment facility. All varimax factor (VF) values obtained from the PCA were used as independent variables in MLR analysis. It was found that VF1 (wet sludge and mixed liquor suspended solids) and VF4 (polymer dosage) had significant linear relationships with bio-solids production, which accounted for 74.32% of variations in the bio-solids production. This approach could be used to precisely estimate the amount of sludge produced by the centrifuge dewatering unit and for better evaluation of system performance that meets the design criteria and future requirements for sludge disposal