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.     

Performance of the Burwarton Estate Waste Stabilization Ponds

The Burwarton Estate waste stabilization ponds, near Bridgnorth, Shropshire, serve a population of 150. There are three ponds in series: a facultative pond, and two equal maturation ponds, followed by two parallel and alternately used constructed wetland ditches. This paper describes the design of the ponds and reports upon their performance during the first two years of operation.     

NATURAL SEWAGE TREATMENT IN THE UK: SELECTION GUIDELINES

The design of septic tanks, constructed wetlands, waste-stabilisation ponds and rock filters is detailed, and their applicability in the UK is discussed. Septic tanks are a suitable primary treatment system for villages with a population of less than 500. Constructed wetlands, which are secondary or tertiary treatment units, have the disadvantage that their plants do not play any significant role in their performance, except for nitrogen removal. Secondary facultative waste-stabilisation ponds, with pre-treatment in septic tanks and post-treatment in rock filters, provide primary, secondary and tertiary treatment and can produce high-quality effluents. The costs of these processes for small rural communities in the UK are compared.     

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.     

Oestrogenicity and Wastewater Recycling: Experience from Essex and Suffolk Water

Research into possible endocrine disrupters and their effects, which is necessary to prove the safety of recycling schemes, is described. The research concentrated on the analysis of three steroid oestrogens and on trout bioassay (vitellogenin). The work was carried out in (a) experimental fish tanks using various mixtures of river water and treated wastewater, (b) pilot plants for wastewater and potable water treatment, and (c) monitoring the oestrogenic effects of discharging disinfected treated wastewater into Hanningfield reservoir during the 1995–98 drought. The overall conclusion is that the presence of minute traces of oestrogens in wastewater is not an insurmountable problem because they can be removed by dilution and self-purification in rivers and reservoirs, by activated carbon and ultraviolet radiation in the recycling plant, and by ozone and activated carbon in water-treatment plants.     

The Prevention of Oil and Chemical Pollution: Proactive Approaches in the UK and Canada

In the UK, various initiatives have been launched in an attempt to provide guidance on the occurrence and avoidance of oil and chemical pollution. Despite these efforts, oil and chemicals remain a major cause of pollution. In Canada, similar initiatives have been more successful due to a participative approach to campaign development and implementation. This paper compares UK and Canadian initiatives and identifies factors which led to the success of the Canadian campaigns.     

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.