Cost-Effective Water-Quality Modelling of Potable Water Distribution Systems

Before privatization of the water authorities in England and Wales in 1989, future water companies were instructed to provide auditable proof of their investment requirements by the production of asset management plans.
With respect to distribution systems for potable water, asset management plan studies have established that unlined ferrous mains are often the main cause of complaints about discoloured water. It has also been found that the investment in water mains rehabilitation, which is driven by water quality problems, overshadows similar investment requirements driven by high burst rates and poor hydraulic performance.
This paper describes how certain techniques of water quality modelling have been developed and refined to provide a rapid, cost-effective method for identifying requirements for water-main rehabilitation.     

Pilot Scale Aerobic Sequencing Batch Reactor for Pig Waste Treatment

A n existing aetated lagoon treating piggery waste was converted into an aerobic sequencing batch reactor (SBR). After the commissioning period, the SBR plant treated piggery wastewater containing BOD and suspended solids (SS) concentrations of 2881 mg/l and 1419 mg/1 respectively, producing an effluent having an average BOD and SS of 18.7 mg/1 and 12.3 mg/1 respectively. The volumetric loadings on the SBR and the process were similar. However, the SBR process operated at a lower mixed liquor suspended solids (MLSS) concentration and shorter sludge retention period. Although the capital and operating costs of the SBR are higher than for the aerated lagoon, the simplicity of operation, the high BOD and SS removal efficiency, and the small land requirement make this type of process an attractive treatment option, particularly in places where land supply is limited and expensive.     

Bacteriological Monitoring of Water with 'Jungle Kits'

A S trict application of recommendations contained in Report 71¹ generates the need for the examination of large numbers of samples with daily analysis being required at certain treatment works. Manpower resources were not available to achieve this, and an alternative procedure for bacteriological monitoring was necessary.
The paper describes a technique for 'on-site' monitoring of the bacteriological quality of a water supply on a daily basis. Based on the multiple tube method, the test provides a qualitative yedno indication of the quality of the water being produced. Experiences in the use of this technique are outlined.     

Health Risks of Chlorination - is there a Problem?

C hlorine is an effective and reliable disinfectant whose use in the treatment of drinking water has ensured water of high microbiological quality. Although the benefits of chlorination are beyond doubt, the fact that chlorine reacts with many of the organic substances in raw waters forming some substances of potential risk to health has led to concern and has stimulated a series of investigations. These investigations have used a variety of approaches and techniques, including advanced organic analysis, epidemiology, and toxicology. The paper reviews this research and discusses some of the factors affecting the risks associated with drinking chlorinated water.     

The Fate of Heavy Metals in Pilot-Plant Scale Upflow Sludge-Blanket Clarifiers

T he R emoval of heavy metals and aluminium residuals during upflow sludge-blanket clarification was investigated using a pilot-plant system. Pilot units treating predosed raw water on site were assessed for sludge-blanket formation and stabilization, and were found to produce clarified water of a comparable quality to the main works units after the start-up and stabilization periods were complete. The heavy metals Cr, Fe, Mn, and Ni were the only heavy metals detectable at the investigation site and these occurred at concentrations well below guidelines values for potable abstraction and supply.
Mean removals of Fe, Mn, Cr, and Ni were about 98, 89, 51, and 30 per cent respectively, during steady-state operation, and Fe, Mn, and Cr all displayed reduced removals during transient changes in surface load, whereas Ni removal appeared to be relatively independent. Aluminium residuals derived from the dosed alum coagulant also showed decreases in removal from about 83 per cent during steady-state operation to between 40 and 50 per cent during transient experiments.     

The Measurement of Plumbosolvency Propensity to Guide the Control of Lead in Tapwaters

A laboratory-scale lead-pipe rig has been developed into an accelerated test for 'plumbosolvency propensity'. High alkalinity water supplies from Anglian Water show either relatively high or low propensity characteristics which appear to be related to the form of the crystal deposit. These have been examined by scanning electron microscopy. The paper describes the uses of the test to (1) supplement random survey data, (2) investigate mixed waters, and (3) optimize orthophosphate dosing.     

Developments in Health-Related Quality Standards for Chemicals in Drinking Water

Small differences in water quality standards can mean huge differences in costs for water treatment; difficulties which are compounded by standards for which the derivation is unclear, such as the EC drinking water Directive. Such situations give no indication of the margin of safety for a parameter or the significance to consumers of exceedances. The WHO Guidelines are being revised and will be presented so that the precise derivation of the numbers is absolutely clear. The scientific and quasi-scientific considerations can be separated and the user given the appropriate information to adapt the guidelines to particular circumstances. In deriving standards for toxicological data the factors incorporated reflect uncertainties in the data and extrapolation from animals to man. Understanding the mechanisms of toxicity or carcinogenicity can reduce the uncertainty and improve the quality of the standard, often allowing higher figures to be used with confidence that public health will not be comprised.     

Aeromonads in Drinking-Water Supplies: Their Occurrence and Significance

Traditionally, bacteriological monitoring of drinking-water supplies has focused on the detection of Escherichia coli and related coliform bacteria. However, attention has recently been given to the occurrence of biofilms and associated organisms which occur in distribution systems. One group of bacteria which have been isolated from water supply systems are the Aeromonads. This group is gaining increased recognition as they have been implicated as causal agents of gastro-enteritis in humans and are indicators of regrowth potential. In order to obtain a better insight into these organisms and their relationship with other parameters, a number of laboratory and field-based studies were undertaken. These included (a) comparison of isolation media, (b) examination of biofilms, (c) temperature growth studies, (d) toxicity testing, and (e) sampling and analysis at treatment works and in distribution systems.     

Integrated Catchment Management Planning

Catchment management plans represent the National Rivers Authority's vision for the water environment. With the National Rivers Authority being organized by hydrological regions, the catchment is seen as the natural management unit, and catchment plans offer the means to integrate the Authority's work programme with those of other agencies. Catchment plans summarize relevant data and include an agreed action programme to optimize catchment uses, produced after wide consultation; they complement local authority statutory plans, are current for five to ten years, and will be reviewed regularly during this period. The catchment planning process is seen by the National Rivers Authority as a medium for promoting discussion, resolving conflict, assigning priorities, and setting targets by which progress on key issues can be monitored.     

Changes in Plant community at Foxcote Reservior Following Use of Ferric Sulphate to Control Nutrient Levels

I n an attempt to control planktonic algal growth in I n an attempt to cosntrol planktonic algal growth in Foxcote water supply reservoir, which is supplied by eutrophic waters from the river Great Ouse, ferric sulphate has been used to reduce ortho-phosphate concentrations in the pumped inlet water. Internal recycling of sediment-bound nutrients retarded the expected algal control for almost three years. During the third year, a marked change in the ecology of the reservoir occurred, and planktonic algae were largely replaced by prolific growths of filamentous species and rooted macrophytes. While the changed flora have caused their own problems, the reservoir is now less prone to closure due to intractable water treatment problems.