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Sewage treatment works are subject to a range of parameters governing the quality of effluent and sludge produced. An additional product from treatment plants is odorous air. The causes, source, formation and measurement of odour are widely reported and reasonably understood. An important factor in the design and management of works is the prediction of such odours. The importance of this work is explained by the possibility of future legislation controlling odour at wastewaterplants. Odour dispersion modelling involves the on-site measurement or prediction of the emission rate of an odorous compound, oftenhydrogen sulphide, and the subsequent prediction of the atmospheric concentrations of that compound downwind of the source. This paper used theUSEPA models SCREEN3 and ISCST to determine hydrogen sulphide contour concentrations emitted from unit processes at two different sewage treatment works in the United Kingdom. Results indicated that the first site, located in an urban catchment, emitted hydrogen sulphide at varying rates. The predicted downwind concentrations using 'urban' dispersion coefficients correlated well with measured concentrations. At the second site, emission rates were less variable. Results from the second site produced the best correlation using 'rural' dispersion coefficients. Results from both sites suggest that the definition of the surrounding land use is critical in predicting odour dispersion. The problem of determining land use is highlighted and the importanceof correct meteorology is stressed. Both sites were predicted to be capable of producing hydrogen sulphide concentrations at a detectablelevel outside the site boundary. Odour complaints were therefore anticipated. The operational performance of a unit treatment operation is proposed as a major influence on hydrogen sulphide emission. The idea of a large database of expected emission rates from individual unit treatment processes is proposed as an input for dispersion modelling an [ABSTRACT FROM AUTHOR]

The properties of main water ways and infrastructure of rural water systems are often determined by very general design methods. These methods are based on standards that use only little information of the actual water system. Most design methods applied in the Netherlands are based on land use and soil texture. Standards have been developed on the basis of generalized properties of water systems. Details of the actual layout of the water system and the way in which that systemis controlled, are usually not incorporated. Present-day dynamic simulation programs and the computer power currently available enable more detailed modeling and incorporation of location-specific data intomodels. Such models can be used to design the water system and can include real data. A model-based design method is introduced, in whichthe actual situation of the water system is taken into considerationas well as the way in which the water system is controlled. Stochastics concerning the operation and availability of controlling infrastructure are included in the method. Models can be evaluated by including real data. In this way the actual safety of the water system, for example during floods, can be determined. Water-quantity design criteria can be incorporated as well as water-quality criteria. Application of the method makes it possible to design safe water systems in which excess capacities are avoided and in which all requirements of interest are met. The method, called the 'dynamic design procedure', canresult in considerable savings for water authorities when new systems have to be designed or existing designs have to be reconsidered. [ABSTRACT FROM AUTHOR]

This paper describes the development of a strategy to identify the priorities for investment in sewage treatment in the rural areas in Latvia. The strategy is developed from the baseline conditions ascertained for the present quality of the many receiving waters (rivers, lakes, ground water and the Baltic Sea) and from the condition of the 800 Plus sewerage systems which serve all of the small and medium sizedtowns in the country. Technical solutions are developed consistent with Latvian policy goals and the priorities established for improvement to the environment and public health. An investment strategy has been prepared to optimise the use of the available funds, to achieve the best value for money. It has been agreed in consultation with interested parties at national, regional and local levels, to produce a plan with wide acceptance. The strategy is known in Latvia as '800 Plus'. (c) 1998 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]

Three conferences on 'Small Wastewater Treatment Plants' organized by the IAWQ Specialist Group demonstrate worldwide interest and activities in this matter and the need to exchange experience concerning planning, design, construction, operation, maintenance and control of small treatment plants. In near future, the number of small treatment works will increase tremendously and will be accompanied by a strong demand for information on appropriate procedures and technologies. Pollution problems caused by small wastewater flows are usually restricted to small areas, however, in view of the high per capita costs, treatment requirements and alternatives have to be studied carefully. In comparison to larger plants, more pronounced and different boundaryconditions such as load fluctuations, operation and maintenance problems, per capita costs, and a large variety of feasible treatment anddisposal systems ask for experienced engineers with a broad and sound knowledge in rural water quality management. The technical alternatives reaching from mechanical and simple biological low rate systems such as ponds, sand filters and reed beds to complex high rate suspended and fixed biomass reactors have to be evaluated regarding plant size, operation safety, reliability, demand for skilled personnel, investment and operation costs. In this respect, water engineers are increasingly challenged, not only to deal with a broad range of present and future treatment technologies, but also to integrate economical and social aspects into their evaluations. [ABSTRACT FROM AUTHOR]