Development of the Sludge Thermal-Drying Option for South West Water

Sewage-sludge production in South West Water is predicted to more than double, to about 50000 dry tonnes per annum, by the turn of the century. Staff of South West Water Services have carried out a strategic review of sludge utilization and treatment options, and have developed a strategic planning computer model to assist in the financial evaluation of the many options which are available. The strategy allows for the provision of new raw sludge thermal-drying facilities for the anticipated increase in sludge production.
Trials were carried out with an indirect dryer system to develop and investigate the operational issues and use of the dried raw product. The initial trial produced a fluffy, low-density material with poor storage and handling characteristics, apparently associated with the high-fibre content of the sludge. The process has been modified to include pelletization.     

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.     

Trade Effluent Control: Prospects for the 1990s

The proposed privatization of the ten regional water authorities together with the accompanying reorganization of water pollution control responsibilities between the new National Rivers Authority and Her Majesty's Pollution Inspectorate, as well as the ever tightening environmental standards for the aquatic environment emanating from Brussels and from general environmental pressures, means that dischargers of industrial effluents can expect major changes both in the cost of disposing of their effluents and in terms of the legislative controls which will restrict their content.
The paper examines the various factors which will influence the management of trade effluents in the 1990s and endeavours to give some indication of what the future holds both in terms of disposal costs and environmental regulation from the point of view of the discharger.     

Digital Mapping for Watermains in Torbay

T he development of a digital mapping and database system for water supply and distribution is described. The procedures adopted in producing the User Requirement Specification and preparing the existing records for conversion to digital form are outlined, and the manual digitization methods used for data conversion are detailed.     

Radioactivity Monitoring of the Water Cycle following the Chernobyl Accident

D etails are given of the radioactivity monitoring programme following the Chernobyl accident. Measurements of gross beta activity in samples of rainwater, raw water, treated water, waste products from water treatment plants, and sewage sludges, are tabulated.
On a limited sampling regime fallout in the Longdendale water catchment, three months after the accident, was investigated and shown to be mainly absorbed onto grass and soil. Water treatment processes were found to be effective in removing radioactive fallout from raw water, and concentrating it into the waste treatment products. The disposal of these waste products is discussed.     

Automatic Monitoring of Activated Sludge Settling Characteristics and Plant Control Applications

A fully automatic instrument has been developed to allow the on-line measurement of activated sludge settling characteristics. The monitor uses the derived data to calculate final sedimentation tank solids loadings and the required rates of returned activated sludge pumping. The instrument has been developed by Thames Water Utilities Limited and is now manufactured under licence by Phox Systems Ltd. It samples mixed liquor and returned sludge alternately and measures solids concentration, the initial settling rate (or rate of hindered settlement) and the stirred specific volume index. The stirred specific volume index at a standard solids concentration of 3.5 g/l is derived from the data. Actual and maximum final sedimentation tank loadings (kg/m²h) are calculated, and the required returned sludge pumping rate is predicted and may be controlled by the monitor. Tests have been carried out on a number of sewage-treatment works during several years of development, and some of the results are presented and discussed.     

Cyanobacterial (Blue-Green Algal) Toxins and their Significance in UK and European Waters

The cyanobacteria (blue-green algae) which commonly produce mass developments in fresh and saline waters are capable of producing toxins. These compounds have been responsible for the deaths of animals, birds and fish in many countries, and have been linked with several forms of human illness through skin contact and ingestion. Evidence has accumulated over the past decade that cyanobacterial toxins occur commonly in European waters which contain cyanobacterial mass growths. This paper summarizes the recent published occurrence and types of cyanobacterial toxins found in European waters with reference to poisoning incidents.
Cyanobacterial blooms were particularly abundant in the warm dry summer of 1989 in the UK. The deaths of sheep and dogs and the cases of human illness that were ascribed to cyanobacterial toxins were followed by a more intensive and wider investigation into the extent of cyanobacterial toxicity in UK waters than had hitherto been undertaken. Of the cyanobacterial blooms sampled from over 90 freshwaters, approximately two-thirds were toxic (lethal) according to mouse bioassay. Short-term and long-term needs for the recognition, quantification and management of problems which can be caused by potentially toxigenic cyanobacteria in water-bodies used for recreation, aquaculture and potable supply are briefly discussed.     

THE USE OF REED-BEDS FOR SLUDGE DRYING

This paper reviews the design and performance experience with sludge-drying reed-beds over the past fourteen years. Whilst there are very few of these systems in the UK, there is much experience in Europe and particularly in Denmark. The Danish experience is reviewed in some detail. The design of and experience gained from two UK systems is described. The final dry-solids concentration depends upon the concentration in the initial sludge dose. It is possible, when treating anaerobically digested sludges containing 3–4% DS, to achieve about 90% volume reduction and a final dry-solids content of up to 40%. With thinner activated sludges containing 0.3–0.6% DS, a reduction (in volume) of greater than 97% is possible with a final solids concentration in the range 10–20%.     

Results of the First Pilot-Scale Controlled Cohort Epidemiological Investigation into the Possible Health Effects of Bathing in Seawater at Langland Bay, Swansea

A pilot study was conducted to investigate the feasibility of using adult volunteers to examine the possible health effects of bathing in UK seawaters which passed the EC bathing waters Directive. Langland Bay, near Swansea, was chosen for this experiment, which was conducted on 2 September 1989. Adult volunteers were recruited from the City of Swansea and randomly divided into bather and non-bather groups. All volunteers were given medical examinations and medical questionnaire interviews before and after 2 September.
Water quality on the day of the test was relatively unpolluted, as indexed by the commonly-employed bacterial and viral indicator species. The detailed medical questionnaire resulted in higher reported attack rates of perceived illness in both bather and non-bather groups than those published in previous studies, which have commonly employed a single telephone interview to acquire disease perception data. Statistically-significant differences in the bather and non-bather cohorts were found for the following perceived symptoms: sore throat, ear symptom, eye symptom at 3 d after 2 September, and for diarrhoea at three weeks after the experiment. The clinical tests employed failed to confirm these significant perceived symptom attack rate differentials.
The significance of these results is discussed in the context of previous research protocols to demonstrate the feasibility of this novel prospective controlled cohort approach for the acquisition of scientifically robust data on the health effect of recreational water use. If taken to a full-scale study, it is argued that this research protocol could offer considerable advantages over past methods and lead to scientifically valid water-quality standards for recreational waters.     

Survey to Detect Legionella pneumophila in Potable Waters in North West England

L egionella PNEUMOPHILA is a causative agent of respiratory illness in humans. The organism is ubiquitous and commonly frequents aquatic environments. Incidents of legionellosis have been linked with potable water supplies.
An attempt has been made to determine the degree of contamination, if any, by L. pneumophila in samples of potable water treated and distributed to domestic premises in the north west of England. Sampling was initiated in February 1986 and continued throughout the summer months of 1986 and 1987. The majority of sampling sites were chosen at random, but from areas suspected of having dirty water problems or low chlorine residuals. In a few cases samples were taken where there was a known problem, such as a consumer complaint or bacteriological failure.
Results indicate that public potable water supplied in this area does not constitute a significant health risk in the transmission of the disease. Other environmnental factors appear more significant.