Burnley Sewage-Treatment Works: Design and Operation of a High-Rate Nitrifying Filter

The paper deals with the planning, construction, operation and performance of the purpose-built nitrifying filter from its commissioning in August 1986 to the present day. Burnley sewage-treatment works consists of inlet screens, Dorr detritors, primary sedimentation tanks, surface-aeration activated sludge units, and final settlement; sludge is digested and tankered to farmland.
The filter was designed and built following the closure of several local works and subsequent diversion of flows to Burnley. It was realized that the increased volume from the extended Burnley works would reduce the dilution of the effluent by the River Calder. This would result in a deterioration in the quality of the river. As a consequence an ammonia standard of 14 mg/l was imposed on the works following the completion of the nitrifying filter.     

Groundwater Model of Conditions in Liverpool Sandstone Aquifer

T his study considers the groundwater conditions for the period 1948–82 in the Permo-Triassic Sandstone aquifer of the Liverpool area. During this period, significant changes have occurred in the abstraction patterns and a new railway tunnel has been constructed below sea level in Central Liverpool. To understand the flow conditions within the aquifer, detailed studies have been carried out into the aquifer properties, the influence of rivers and tunnels, and the estimation of recharge. It is found that conventional rainfall recharge accounts for only one-third of the total recharge.
Numerical model solutions were used to check the adequacy of the understanding of the flow processes and the solutions have confirmed that the rising water levels in Central Liverpool result from high recharge and a reduction in abstraction. Having validated the model by comparisons with field data, the model was then used to predict the probable future water level changes.     

PLANNING FOR FLOOD RISK IN THE FENS

The fens of eastern England rely on flood defences for their existence, and planning for flood risk has always had a high priority. A new focus was given with the issue of Planning Policy Guidance 25, and this paper presents experience from a Strategic Flood Risk Assessment of South Holland District, in Lincolnshire. The assessment pioneered the examination of fenland flood risk in terms of risk zones related to flood hazard and standard of protection. Methods for evaluating the risk zones are described; they consider flooding from embanked rivers which are subject to tide locking, internal drainage systems, tide level and wave action. The methods would be appropriate for many lowland areas of the UK where conventional flood analysis cannot be used.     

Ultra-Violet Disinfection of Sewage Effluents: A Pilot Study at Bellozanne, Jersey

In March 1990 a pilot ultra-violet disinfection plant was installed at the sewage-treatment works in Bellozanne, Jersey. The pilot plant was set up to test the ability of the process to meet certain defined objectives and, ultimately, to enable the island authorities to satisfy stringent water quality objectives in the receiving waters of St Aubins Bay.
The pilot study simulated an open channel installation using medium pressure ultra-violet lamps parallel to the direction of flow. The pilot plant was supplied by Trojan Technologies Inc.
The pilot study met its objectives and confirmed the design parameters for a full-scale plant installation to follow.     

Environmental Implications of Treatment of Coastal Sewage Discharges

The environmental implications of implementing the requirement for treatment of coastal sewage prior to discharge, which were put forward in an EC draft Directive on municipal waste-water treatment, are examined. In order to establish the current situation, the results of a national survey of coastal and estuarine sewage discharges are presented. A review of the impact of sewage discharges on the marine environment is presented in conjunction with an assessment of the impact of sewage-treatment processes on the land and in the air. These aspects are integrated into overall conclusions about net environmental impact. Finally, a decision-tree approach to the assignment of priority to additional action required at individual locations is developed.     

Impacts of Sewers on Groundwater Quality

This paper summarizes the findings of a recent research project on groundwater contamination from leaking sewers, which was completed for the Construction Industry Research and Information Association. Fifty-four incidents were identified in England and Wales from a combined questionnaire survey and literature review. In addition to recorded incidents, the poor quality of many urban groundwaters suggests some effects from leaking sewers. Age is considered to be the most significant characteristic governing leakage from sewers; ground conditions (predominantly aquifer vulnerability) and usage (private versus public ownership) are also important factors relating to the likelihood of groundwater pollution from leaking sewers. Recommended strategies for reducing groundwater contamination include (a) modification of existing criteria for the service performance grading of existing sewers, (b) improved construction of new sewers in appropriate areas, (c) increased groundwater monitoring, and (d) risk assessments for new groundwater sources.     

An Independent Perception of Regulation in Practice

The paper reviews the regulation of water companies in England and Wales since 1989 by reference to the historical regulation of utilities in these countries. It considers how comparative competition, service standards and charging arrangements are developing. Particular mention is made of the debates over rates of return and household metering. The conclusion is that regulation, to be effective and appropriate, must be capable of evolution.     

Water and Sewerage Charges in Scotland

The paper outlines the statutory arrangements governing water and sewerage charges in Scotland, and comments on the factors affecting the levels of charges. Trends in revenue expenditure over the period 1989–90 to 1992–93 are considered in relation to increases in personal community water charge levels, metered water rates, and costs per household. Non-domestic sewerage rates and industrial effluent charges are also discussed. Some comparisons are made with England and Wales and with other countries. The funding arrangements for capital expenditure and their effect on the levels of charges are described, with particular reference to debt levels and rising expenditure to meet UK and EC standards. Factors affecting future charge levels are also identified.     

HYDRAULICS, WATER QUALITY AND VEGETATION CHARACTERISTICS OF GROUNDWATER-FED OPEN DITCHES

A novel peatland management strategy to utilise the high nutrient-retention potential of degenerated peatlands has been implemented in Northern Germany. The effect of raised water levels and extensive land-use management on hydraulic properties, water quality and vegetation characteristics of heavily vegetated and groundwater-fed open ditches, was investigated at the River Elder Valley - a nationally important wetland case study. A better understanding of the effect of vegetation on the temporal flow patterns and the hydraulic retention times is of high scientific interest, especially for improving nutrient standards in lowland rivers. Within-ditch vegetation and other hydraulic obstructions, including accumulated silt and organic debris, increase the hydraulic retention time and lead to an improvement of the water quality along the open ditch. Lower parts of the open ditches were flooded by the River Elder, due to the absence of a mowing scheme during late summer     

ESTIMATING RECHARGE FOR BRITISH AQUIFERS

This paper reviews methods of estimating recharge for a wide variety of aquifers in Britain. A soil moisture balance technique is used with direct representation of relevant soil and crop properties. Recharge contributions due to rainfall, runoff from impervious areas and leaking water mains and sewers are considered. In many field situations low permeability strata, which overlie the main aquifer, modify the timing and magnitude of the actual recharge. Runoff from less permeable strata can become runoff-recharge at the aquifer outcrop. Reference is made to several case studies.