Developing Scientific Aspects of Water Treatment

Severn Trent Water is currently undertaking an extensive capital programme to enhance water-treatment facilities at many of its major plants, and this work is underpinned by the need to apply robust, cost-effective solutions utilizing modern treatment technology.
The paper describes various aspects in the development of these functional designs in relation to treatment objectives, technical innovation and value engineering, drawing examples from Severn Trent schemes and particularly from the redevelopment of the Birmingham water-treatment plant.     

A Joint US and UK Approach to Water Supply and Distribution Modelling

Network analysis has been practised in the water industry for many years, both in the UK and US, especially for capital investment planning and operational strategies. Driven now by the need to improve and maintain customer service levels, the management of water distribution is beginning to rely more on network analysis techniques. The combination of large, detailed models and easy-to-use software is moving network analysis into new areas of benefits in Severn Trent Water using the Stoner workstation service. By providing a simple, geographic interface with the user, the use of network simulation facilities has been increased tenfold in the company. In addition to the hydraulic benefits, Severn Trent Water has followed a lead from the US with water quality modelling, including nitrate blending, source water mixing and chlorine residual analysis.     

Quality Control of Water-Treatment Chemicals

Quality control measures for regionally purchased treatment chemicals in Severn Trent Water Ltd apply from the point of manufacture through to their arrival and acceptance on a water-treatment works. This approach involves a formalized examination of the control systems of treatment chemical suppliers and the introduction of standard documented acceptance procedures at each treatment works. These measures are intended to not only provide a high degree of reassurance to customers, but to ensure that staff of Severn Trent Water are purchasing and receiving cost-effective materials which are of an acceptable quality in terms of active constituents and background contaminants, before use in the treatment of water     

The Application of a Computer-Based System in the Development of Objective River Maintenance

During recent years the need for more objective ways of planning river maintenance work has been highlighted by (a) a greater emphasis on justifying budgets, (b) the requirement to provide 'levels of service' indicators, and (c) the growing concern from conservationists. This has prompted the development of a computer system within the Severn Trent Authority, known as the Rivers Information and Maintenance System (RIMS), which is described in this paper. This system allows engineers who are responsible for the maintenance of about 3500 km of main river in the STWA area to assess the costs, benefits, and ultimately the environmental impact, of carrying out such works as dredging, tree work and weed control.     

Denitrification of Wastewater: Operating Experiences in the US and Pilot-Plant Studies in the UK

Due to the EC urban wastewater treatment Directive, considerable attention has been focused on nitrogen removal, particularly from biological filter nitrified effluents. The paper presents a reliable and proven full-scale fixed-film denitrification system installed in the US and evaluated on pilot scale by Severn Trent Water. Methanol has been used as a carbon source dosed prior to the deep-bed sand filter. The filter removes considerable suspended solids as well as providing the hydraulic retention and surface area for the growth of the biological denitrifying bacteria. Flow sheets of typical US installations are given and operational data with costs are presented for the pilot-plant evaluation.     

Oestrogens and oestrogenic activity in raw and treated water in Severn Trent Water

Sewage effluent discharged to surface water has been shown to contain human hormones, particularly oestrogens, and synthetic chemicals which may be able to disrupt the endocrine system. Since many surface waters which receive sewage effluent are subsequently used as drinking water sources, it is important to demonstrate that treated drinking water is not contaminated. Oestrogenic activity in rivers and drinking water in the region of Severn Trent Water was studied using a combination of bioassay, to integrate exposure over time, and advanced chemical analysis. There was little or no evidence of substances that were oestrogenic, even in waters receiving significant amounts of sewage effluent. Oestrogenic activity, as measured in the rainbow trout vitellogenin assay, was seen at the Tame/Trent confluence but this activity was relatively weak. There was no activity detected at raw water intakes and no hormones or substances that are oestrogenic were detected in the final drinking water.     

Wastewater Rapid-Gravity Filtration in Severn Trent Water

In Severn Trent Water, rapid-gravity filtration is used as a tertiary treatment process on a number of large sewage-treatment works, and is likely to find further use in meeting more stringent discharge quality limits in the future. Design maximum hydraulic loadings and average suspended-solids loadings are identified, and average hydraulic and solids loadings for 1989–91 are presented. Established filters are hydraulically underloaded, but on average suspended-solids loadings they are mostly overloaded due to relatively poor quality influents. High mean solids and BOD removals are achieved. Reduced medium relative density has been found to vary with the degree of fouling and causes over-expansion of the bed and medium loss. A correlation has been demonstrated between relative density and percentage dry matter, which could be used to assess the degree of medium fouling.     

Sewage Treatment for Small Communities: the Severn Trent Approach

When faced with the requirement to refurbish or upgrade a large number of small sewage-treatment works, Severn Trent Water standardized process selection on rotating biological contactors and, where higher standards of effluent were demanded, constructed reed beds. These systems are described and costs are presented and discussed.
Performance data from rotary biological contactors and reed-bed sites are used to illustrate the additional security provided by the reed beds. Results from a survey of a reed bed treating a storm-sewage overflow are shown for a storm event.     

Pumps as Turbines and Induction Motors as Generators for Energy Recovery in Water Supply Systems

Pressure-reducing valves, which dissipate energy, are often used in water supply systems to regulate the downstream pressure levels. If a reverse running pumpset is installed alongside such a valve, most of the dissipated energy can be recovered.
This paper describes a system of this type which has recently been installed by North West Water, with advice and specialized equipment supplied by the Nottingham Trent University Micro-Hydro Group. The power produced by the energy-recovery system is used to run and monitor a remote potable-water dosing plant.     

EC and UK Legislation on Environmental Assessment and its Effect on the UK Water Industry

The development of the practice and purpose of environmental assessment (EA) both in the UK and overseas is reviewed, and the implementation of European Commission EA legislation into the UK planning system is examined, together with its relevance to the water industry. The effects and obligations on the industry are discussed with reference to practice prior to and since the introduction of EA legislation. The process of EA is illustrated by reference to the River Avon Sluices Scheme being undertaken by NRA (Severn Trent), and the environmental statements being prepared in accordance with SI 1217. Likely future developments in EA are suggested.     

Book Reviews

Chemical Safety Matters, by the International Union of Pure and Applied Chemistry and the International Programme on Chemical Safety. Published by Cambridge University Press, The Pitt Building, Trumpington Street, Cambridge CB2 1RP
Remediation Manual for Petroleum Contaminated Sites, by David L. Russell. Published by Technomic Publishing AG, Missionstrasse 44, CH-4055 Basel, Switzerland
Land, Water and Development. River Basin Systems and their Sustainable Management, by Malcolm Newson. Published by Routledge, 11 New Fetter Lane, London EC4P 4EE
Overland Flow-Hydraulics and Erosion Mechanics. Edited by A. J. Parsons and A. D. Abrahams. Published by UCL Press Ltd, University College London, Gower Street, London WC1E 6BT
Urban Waste Waters – Treatment for Use in Steam and Power Generation, by K. Abdullaev, I. Malakhov, L. Poletaev and A. Sobol. Published by Ellis Horwood Ltd, Market Cross House, Cooper Street, Chichester, West Sussex PO19 1EB
Water Quality Assessments – A Guide to the Use of Biota, Sediments and Water in Environmental Monitoring. Edited by D. Chapman. Published by Chapman & Hall Ltd, 2–6 Boundary Row, London SE1 8HN
National Vocational Qualifications in Water Treatment. Written and produced by Severn Trent Water Ltd. Special Projects Unit, Finham Sewage Treatment Works, St Martins Road, Coventry CV3 6PR     

Evaluation of Lake Vyrnwy within the Integrated Water Supply Systems of North West Water

ABSTRACT In 1992, the National Rivers Authority published a discussion document on the National Water Resource Strategy which highlighted the future probability of a water-supply deficit in the south-east and a surplus in the north and west of England and Wales. One suggestion for rectifying this imbalance was to divert Lake Vyrnwy water which, at present, supplies Liverpool. This would allow further regulation of the River Severn, and subsequent transfer to the River Thames. Joint investigations by the National Rivers Authority and North West Water have established the implications of this diversion on the existing water resources and supply systems of North West Water.
The studies considered (a) the relationship between increased regulation releases, and reduced direct supply rates from Lake Vyrnwy, (b) the investment and operating cost implications of replacing Lake Vyrnwy supplies from sources within the southern command zone or by transfer from the northern command zone, and (c) the potential operational difficulties.
The paper describes how each of these aspects has been addressed. The results demonstrate the necessity of evaluating Lake Vyrnwy as a component of the integrated water supply systems of North West Water, and of other parts of the country.     

The Use of Membranes for Salt Reduction in the UK

Reverse-osmosis membranes, which have been used for reducing the salt content of water since the late 1960s, are available for a variety of desalination applications, ranging from seawater to brackish water and specific species removal, including hardness and organics. In recent years, major advancements have been made in the salt-rejection capabilities and in pressure requirements, which have made the use of membrane technology in water treatment an attractive proposition.
The paper focuses on (i) seawater desalination, reviewing the present study which is being carried out by Anglian Water; (ii) brackish water desalination, in particular a project which is being undertaken by Essex and Suffolk Water, and (iii) well-water desalination, describing a project which is being executed by Anglian Water.     

The Seaton Carew Sewerage Scheme: Design Features and Contractual Arrangements

Northumbrian Water Limited has thirty-four bathing waters and a substantial investment programme to ensure that these waters meet EC standards by 1995. One project within this overall programme is the Seaton Carew Sewerage Scheme. Seaton Carew lies on the southern edge of Hartlepool which has a population of 95000. The scheme will combine existing flows into new foul and storm-sewage outfalls. The headworks will incorporate screening, grit removal and pumping stations with substantial measures for odour control. Hydraulic operating regimes using active pump control and passive flume control have been investigated to ensure efficient treatment for a wide range of flows. The onerous design, manufacture and construction programme has required the development of new approaches to procuring the work, whilst maintaining a substantial element of competition. The various programmes have been substantially overlapped to ensure that the scheme is completed by April 1993.     

Lincolnshire’s middle trent valley: the building stock before enclosure. The case of manor farm house,thorpe-on-the-hill

Based on research undertaken by RUBL, a new building-recording group in Lincolnshire, this contribution originates in the observation that there are a very few standing timber-framed buildings in the county’s Middle Trent Valley. The paper is the first from a larger project exploring this absence. It addresses the suggestion that, although there were once similar numbers of vernacular buildings of this type as elsewhere in the north-east Midlands, this part of Lincolnshire was so greatly affected by a great rebuilding following enclosure between c. 1750 and c. 1850 that virtually all earlier box-framed structures were replaced in brick. Preliminary survey by the group suggests that this may be true, but it also reveals that some members of this earlier generation of box-framed buildings may survive disarticulated, as re-used timbers in those enclosure-period farmsteads that replaced them. Consequently, the group has undertaken a detailed analysis of the timbers re-used in the enclosure-period farmhouse at Thorpe-on-the-Hill in order to assess techniques for reconstructing the frames of predecessor buildings. Following extensive recording work, the outlines of two closely connected predecessor structures have been reconstructed and dated - through techniques including dendrochronology - to the mid-fifteenth and early sixteenth centuries. It is suggested that they were both ranges from the previous Manor Farm House, which occupied the same footprint as that still standing.     

Fluvial Redistribution of Chernobyl Fallout: Reservoir Evidence in the Severn Basin

Sediments in the Chelmarsh pump-storage reservoir have provided a valuable record of the ¹³⁷Cs levels associated with suspended particulates transported by the River Severn since 1965. The presence of Chernobyl-derived ¹³⁷Cs and ¹³⁴Cs within the sedimentary record of the site, despite the absence of any direct fallout on the local area, confirmed that radiocaesium from the Ukrainian reactor accident has been mobilized from the upper reaches of the Severn basin where atmospheric deposition was relatively high. The incorporation of Chernobyl radiocaesium within these sediments can be used to date the 1986 fallout episode, and the established geochronology indicated variable rates of post-1986 sediment accumulation. As radiocaesium is strongly bound to fluvial particulates, this mechanism of redistribution has not adversely affected the quality of the drinking-water source at the site which was studied.     

Drinking Water Directive and Proposed Water Supply (Water Quality) Regulations for Scotland

Taken in conjunction with the clauses added to the Water (Scotland) Act 1980 by the Water Act 1989 in respect of quality, as opposed to organizational terms, the introduction of the EC drinking water Directive¹ and the proposed water quality Regulations² represents the most fundamental change to Scottish water supply legislation since the Water (Scotland) Act 1946.
The drinking water Directive¹ was passed by the European Council on 15 July 1980, with the requirement for full compliance by Member States by 18 July 1985.
Water Supply (Water Quality) Regulations for Scotland were circulated in draft form by the Scottish Development Department for informal consultation during September 1989. This had been preceded by informal consultation through the Convention of Scottish local authorities during the discussion stage of the UK Advisory Group on Drinking Water Regulations.
This paper attempts to provide a simplified interpretation of the proposed Scottish Regulations on drinking water quality. It comments briefly on those requirements likely to have a significant impact on Scottish water authorities, including public communications, laboratory facilities, water treatment operational practices, and capital funding.     

The Reservoir Safety Programme in Northern Ireland

F ollowing P ublication of early proposals for the Reservoirs Act 1975, a systematic programme of reservoir investigation and repair work was carried out by the Department of the Environment for Northern Ireland, Water Service.
The paper describes the full procedure followed for data collection, inspections, risk classification and stability and hydraulic investigations of 60 'large raised reservoirs' impounded by dams up to 42 m high and up to 148 years old. Also described are examples of some unusual repair works carried out, and the implementation of a recording, monitoring, and inspection system which now continually oversees all of the reservoirs involved.     

Conservation in a Privatized Water Industry: The Anglian Water Experience

Anglian Water has adopted a positive approach to conservation. This forms an integral part of the Company's environmental policy which includes a commitment to full compliance with the Code of Practice on Conservation, Access and Recreation and acknowledges the Company's statutory responsibilities towards conservation.
The Company is actively incorporating conservation considerations into routine environmental assessment of a growing capital programme. The implementation of nature conservation and landscaping initiatives is making an important contribution to the wildlife and visual amenity of the Company's sites. Management plans and nature reserve agreements have been prepared for operational sites including the 10% of the Company's land which has been designated by English Nature as of Site of Special Scientific Interest status. Buildings and objects of cultural heritage interest are being restored and displayed, and the Company supports archaeological investigations around the Anglian region.
Anglian is promoting awareness of conservation issues, and of its work, through support for environmental projects within the community. Regular dialogue with conservation organizations forms an important component of the Company's conservation work.     

Use of the Streaming Current Detector at Langsett Water-Treatment Works

A major capital programme is being undertaken by Yorkshire Water to rebuild its water-treatment plants.
Despite good process design, more stringent standards mean that process control, in particular chemical dosing, has become increasingly important.
This paper describes the investigation of chemical dosing control using streaming current detection, which was initially applied at Langsett water-treatment works as a means of controlling the ferric sulphate dose in the clarification process.
Following this successful application, further evaluation was carried out using streaming current detection to control the polyelectrolyte dose in the sludge thickening process.