Japanese Sewage Sludge Treatment, Utilization and Disposal – Report on IWEM/JSWA Technology Exchange Programme, November 1991

The report describes visits made as part of a mission to Japan which included, under the IWEM/JSWA Technology Exchange Programme, a Technical Workshop on sewage sludge technology held in Tokyo on 11–18 November 1991.     

Diffuse Sources of Pollution by Heavy Metals

Significant reductions in the amount of heavy metals released to the aquatic environment have been achieved by applying strict controls on point source industrial discharges. Because of these tight controls, diffuse pollution sources have increased in importance as a contribution to the total load. Diffuse inputs originate mainly from the use of chemical products. Thus control of these inputs can be achieved by refraining from or limiting the use of these products or by restricting the amount of heavy metals permitted in such products. Control of diffuse sources of heavy metals could be based on a 'positive approval'system, permitting only those uses which do not lead to environmental harm and which could not be replaced by less harmful alternatives. Assessing the environmental impact of the alternatives will require the introduction of a 'cradle to grave'approach.     

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.     

COMPARISON OF THE LONG-TERM SECURITY OF SEWAGE-SLUDGE TREATMENT AND DISPOSAL OPTIONS

A comparative 'best practicable environmental option' assessment of fourteen potential sewage-sludge treatment processes and disposal options was undertaken to support the development of Thames Water's sewage-sludge strategy. The assessment was generic in nature and designed to provide comparative performance data on a range of potential process options forming the basis for subsequent site-specific assessments. The study assessed: the relative technical practicability of each process option; the discounted costs of each option (including necessary environmental-mitigation measures); environmental sustainability; and environmental nuisance. The assessment was quantitative wherever possible.
The paper (a) describes the evaluation process. (b) highlights some weaknesses and strengths of the technique, and (c) demonstrates that the technique should form an essential first step in the development of any sludge treatment and disposal strategy.     

The Effectiveness of the Land-Drainage Consent System

ABSTRACT This paper presents the results of a study into the effectiveness of the land-drainage consents system. The investigation studied eighteen main river reaches, each 2 km in length, in the north-east Thames region. All works within the main channel and the 8 m margin, subject to the regulations in the Water Resources Act 1991, were recorded. The impact that each of these works might have had upon the environment, including the ability of the river to pass the peak flow and the potential for an increase in pollution, has been assessed and an overall impact rating for each reach has been determined. Each of the works identified on the reaches has been cross-referenced with consent records held by the National Rivers Authority. Results that indicate that a high proportion (92%) of works do not have consent under the present system.     

EFFECT ON ESTUARINE FINE-SEDIMENT TRANSPORT OF INTERMITTENT PUMP DISCHARGE AT PAGHAM HARBOUR, WEST SUSSEX

Field investigations were undertaken to identify the mechanisms of fine-sediment transport at a landward limit of Pagham Harbour. Which is a semi-enclosed natural harbour in West Sussex, UK. Measurements of water level, velocity, salinity and turbidity were made during three tidal cycles between June and August 2002. Near-bed measurements revealed that, for spring tides, the most significant transport occurs during the flood tide, with smaller turbidity peaks recorded at times of intermittent pumped discharges at low water. Vertical profiling revealed that the timing of these discharges acts as a control on the landward transport of fine sediment by increasing salinity stratification. The resulting graphs show that, while increased near-bed velocity leads to increased turbidity and sediment transport, the degree of vertical salinity gradient is also linked with landward transport of fine sediment. These results help to explain the role of tides and fresh-water flow in controlling the transport of fine sediment in natural harbours, emphasising the importance of taking stratification into account when using 2-D depth-averaged predictive numerical models.     

Flow Estimation from Flap-Gate Monitoring

The measurement of flows and recording of storm events at combined sewer overflows are a key requirement in effective urban pollution management. Staff of Thames Water Utilities have developed a low-cost system based on monitoring the behaviour of flap valves on numerous major river outfalls. The paper presents the development of a modelling approach based on the principle of conservation of angular momentum and its application to experimental data for circular gates. Flow-prediction accuracies, based on the measurement of gate inclination and water depths, in the range ± 20–30%, are found to be achievable for wider gate openings (<20°) – the recommended calibration offering conservative flow predictions at lower angles.     

KNOWLEDGE-BASED SYSTEM ON WATER-RESOURCE MANAGEMENT IN COASTAL WATERS

Computers which are used conventionally in numerical models for problem-solving and fast number-crunching are not user-friendly and lack knowledge transfer in model interpretation. Recent advances in artificial intelligence make it possible to systemise the experience and decision-making procedures of human experts. This paper describes the development of a prototype knowledge-based system (an advanced technique of artificial intelligence) as a knowledge-transfer tool for water-resource planning and management in coastal waters. The system can (a) run on a desktop computer and (b) act as a design aid, to assist in numerical modelling to simulate flow and/or water quality. Using the application in Hong Kong coastal waters, it was verified that the prototype system had the capability to undertake the reasoning process to select the model and associated parameters, equivalent to a human expert.     

Groundwater Investigations in the Lower Spey Valley, near Fochabers

A Series of : comprehensive studies have been carried out to identify potential water abstraction sources to meet future demands throughout the Grampian area, in Scotland. In the Moray and Banff coastal areas a new supply is to be developed to meet future increases in demand which have been predicted to be about 9 MVd by the year 2001, increasing to about 18.5 Ml/d by the year 2011. Grampian Regional Council has engaged Sir M. MacDonald & Partners, consulting engineers, to examine various options within the area and the consultant has concluded that the development of the alluvial gravels on the west bank of the river Spey immediately upstream of Fochabers would provide the Council with the best solution. The paper describes the various investigations undertaken. The main conclusions and results of the studies are briefly outlined in the following paragraphs. The alluvium was shown to have good water-transmitting properties. The seismic refraction and borehole investigations confirmed the superficial deposits to be about 10 to 15 m. Test pumping of wells with associated piezometers proved the transmissivity values and storage coefficients of the aquifer and hence a suitable wellfield. The wellfield so identified extends some 2.8 km upstream on the west bank from the bridge across the river Spey at Fochabers, with an estimated reliable yield of 20 MVd. The water abstracted from the test wells was shown to be about 80 per cent river water which had been drawn into the aquifer. The contribution from the landward side could result in a reduction of the watertable affecting the yield of deep rooted crops (cereals and grass) over about one-half the area one year in three. Examination of the water drawn from the wells confirmed it to be low in colour, iron, and manganese. The results were consistent and were of drinking quality. The mechanism causing the dramatic change in the water from river to well was thoroughly explored and found to be a biological process so ensuring that water qualities would be sustained. In conclusion, the various studies undertaken have shown that a consistent high quality water can be produced from the alluvial gravels of the river Spey near Fochabers in sufficient quantity to meet the needs of the lower Moray and Banff coastal areas of Grampian Region to the year 2011.