Jay Rajapakse

Verification problems in conceptual workflow specifications

Abstract Most of todays business requirements can only be accomplished through integration of various autonomous systems which were initially designed to serve the needs of particular applications. In the literature workflows are proposed to design these kinds of applications. The key tool for designing such applications is a powerful conceptual specification language. Such a language should be capable of capturing interactions and cooperation between component tasks of workflows among others. These include sequential execution, iteration, choice, parallelism and synchronisation. The central focus of this paper is the verification of such process control aspects in conceptual workflow specifications. As is generally agreed upon, that the later in the software development process an error is detected, the more it will cost to correct it; it is thus of vital importance to detect errors as early as possible in the systems-development process. In this paper some typical verification problems in workflow specifications are identified and their complexity is addressed. It will be proven that some fundamental problems are not tractable and we will show what restriction is needed to allow termination problems to be recognized in polynomial time.

Evaluation of Alternative Media for Pebble Matrix Filtration Using Clay Balls and Recycled Crushed Glass

Protecting slow sand filters (SSFs) from high-turbidity waters by pretreatment using pebble matrix filtration (PMF) has previously been studied in the laboratory at University College London, followed by pilot field trials in Papua New Guinea and Serbia. The first full-scale PMF plant was completed at a water-treatment plant in Sri Lanka in 2008, and during its construction, problems were encountered in sourcing the required size of pebbles and sand as filter media. Because sourcing of uniform-sized pebbles may be problematic in many countries, the performance of alternative media has been investigated for the sustainability of the PMF system. Hand-formed clay balls made at a 100-yearold brick factory in the United Kingdom appear to have satisfied the role of pebbles, and a laboratory filter column was operated by using these clay balls together with recycled crushed glass as an alternative to sand media in the PMF. Results showed that in countries where uniform-sized pebbles are difficult to obtain, clay balls are an effective and feasible alternative to natural pebbles. Also, recycled crushed glass performed as well as or better than silica sand as an alternative fine media in the clarification process, although cleaning by drainage was more effective with sand media. In the tested filtration velocity range of ð0:72–1:33Þ m=h and inlet turbidity range of (78–589) NTU, both sand and glass produced above 95% removal efficiencies. The head loss development during clogging was about 30% higher in sand than in glass media.

Applicability of pebble matrix filtration for the pre-treatment of surface waters containing high turbidity and NOM

AbstractPurification of drinking water is routinely achieved by use of conventional coagulants and disinfection procedures. However, there are instances such as flood events when the level of turbidity reaches extreme levels while natural organic matter (NOM) may be an issue throughout the year. Consequently, there is a need to develop technologies which can effectively treat water of high turbidity during flood events and NOM content year round. It was our hypothesis that pebble matrix filtration potentially offered a relatively cheap, simple and reliable means to clarify such challenging water samples. Therefore, a laboratory scale pebble matrix filter (PMF) column was used to evaluate the turbidity and NOM pre-treatment performance in relation to 2013 Brisbane River flood water. Since the high turbidity was only a seasonal and short-term problem, the general applicability of PMFs for NOM removal was also investigated. A 1.0-m-deep bed of pebbles (the matrix) partly infilled with either sand or crushed ...

Significance of Drying Periods on Nitrate Removal in Experimental Biofilters

Nitrogen is an important nutrient that can impact the quality of aquatic environments when present in high concentration. Even though low concentration levels of ammonium-nitrogen have been observed in laboratory studies in bioretention basins, poor removal or even the production of nitrate-nitrogen within the filter is often recorded in such studies. Ten Perspex biofilter columns of 94 mm (internal diameter) were packed with a filter layer, transition layer and a gravel layer. While the filter layer was packed to a height of 800 mm, transition and gravel layers were packed to a composite height of 220 mm and operated with simulated stormwater in the laboratory. The filter layer contained 8% organic material by weight. A free board of 350 mm provided detention storage and head to facilitate infiltration. The columns were operated with different antecedent dry days (0 d to 21 d) and constant inflow concentration at a feed rate of 100 mL/min. Samples were collected from the outflow at different time intervals, between 2 min and 150 min from the start of outflow, and were tested for nitrate-nitrogen and total organic carbon. Washoff of organic carbon from the filter layer was observed to occur for 30 min of outflow. This indicated washoff of organic carbon from the filter itself. At the same time, a very low concentration of nitrate-nitrogen was recorded at the beginning of the outflow, indicating the effective removal of nitrate-nitrogen. We conclude that the removal of nitrate-nitrogen is insignificant during the wetting phase of a rainfall event and the process of denitrification is more pronounced during the drying phase of a rainfall event. Thus intermittent wetting and drying is crucial for the removal of nitrate-nitrogen in bioretention basins.

Unsafe drinking water quality in remote Western Australian Aboriginal communities: Chronic kidney disease and water quality

Chronic kidney disease (CKD) is important in the fields of public health and health geography because of its heavy burden on the health system and high cost of treatment in its advanced stages. The causes of CKD are associated with diabetes and hypertension, but in some parts of the world, the disease occurs in the absence of these factors. Researchers identify this condition as CKD of “unknown” causes (CKDu). CKDu is a multi‐factored health problem and one suspected causal factor is contaminated drinking water. The disease occurs globally but is found in particularly high concentrations among people of certain ethnic and disadvantaged social groups living in very different locations around the world. CKD has become endemic in Western Australia where hospital admissions for Aboriginal people requiring renal dialysis or treatment for diabetes are much higher than for the general population. The possible proportions of CKDu cases among the CKD patients are unknown. This study examines the drinking water quality among communities such as these. Water chemistry analysis in these areas indicates that the nitrate and uranium content greatly exceed officially recommended levels. Most of these communities rely on raw groundwater to supply their domestic needs, and it is very likely that the people are unwittingly ingesting high levels of nitrates and uranium, probably including uranyl nitrates. Very few such remote communities have access to treated drinking water, and cost‐effective water treatment systems are required to provide potable water at the local scale.

Estimation of Poisson's ratio and variation of tensile yield strength of composite clay balls used in pebble matrix filtration

Clay balls can be used as alternatives to natural pebbles in pebble matrix filtration, a device for drinking water treatment. These clay balls are subjected to stresses due to self-weight and overburden in water saturated conditions. Although there are empirical relationships for evaluating tensile yield strength (Ts) of clay balls using Poisson’s ratio (µ), diameter (d) of clay balls, and failure polar force (Fs), so far for such calculations the value of Poisson’s ratio (µ) was taken from studies based on clay bricks. However, during ball preparation if clay is mixed with other raw materials from industry wastes such as saw dust or alum sludge in order to enhance the pollutant removal properties of the filter media, then the Poisson’s ratio (µ) of composite balls would be quite different to that of clay bricks. This paper describes a novel method for estimating Poisson’s ratio (µ) of composite clay balls by measuring vertical deformation using linear variable displacement transducers (LVDTs) in uniaxial compressive strength (UCS) apparatus and lateral deformation using particle image velocimetry (PIV).

Estimation of Poisson’s Ratio and Variation of Tensile Yield Strength of Composite Clay Balls Used in Pebble Matrix Filtration

AbstractClay balls can be used as an alternative to natural pebbles in pebble matrix filtration, a method for drinking water treatment. These clay balls are subjected to stresses due to self-weight...

Pebble matrix filtration in Papua New Guinea

Slow Sand Filters become inoperative during heavy rains when the raw water supply becomes turbid. A novel pre-treatment method called Pebble Matrix Filtration was tested in the laboratory and then tried out in the field in Papua New Guinea. Pre-treatment was shown to reduce turbidity and faecal coliforms dramatically.