It is a challenge for developing countries to realize socio-economical development without impairing water resources in an unacceptable way. A possible means for controlling water pollution is through defining, applying and enforcing effluent standards for wastewater discharges. However, in many developing countries the definition of effluent standards is still poor. They are either too stringent because they are based on standards from developed countries, or too relaxed and therefore they do not guarantee the safe intended uses of water. In order to define an approach for setting effluent standards that suits the needs and means of developing counties, water quality management practices in the USA, the EU, the New Independent States (NIS) and the Philippines were analyzed and compared. Four criteria (protection of the environment, technical viability, economic feasibility and institutional capacity requirements) were used to assess the suitability of these practices for developing countries. It is concluded that a combined approach that is based on best available technology not entailing excessive costs and environmental quality standards is the best way to define effluent standards that restrict water pollution against affordable costs.

/ To guarantee protection from storm floods in the southwestern part of the Netherlands, the length of exposed coastline is being greatly reduced by the construction of dams and a storm surge barrier. As part of the Delta Project, the mouth of the Grevelingen estuary was closed in 1971. Due to the closure, tidal movement was eliminated, which resulted in changes in environmental factors such as transparency and chloride and phosphate concentration. The number of plant and animal groups decreased. Large areas of sand flats and salt marshes, which were formerly exposed to the tides, were left "high and dry." This resulted in enormous changes for the communities living in these areas. The development of a new ecological system and the changed potential afforded by the water and land areas for human use, emphasized the need for physical planning. The potential uses (functions) of the new system are discussed in this article. Special attention is given to the demand for recreational facilities and nature conservation and to the balanced realization of these main functions. The methods applied in choosing between alternatives in physical planning are explained. Water quality and ecosystem management are discussed, One of the main management objectives is the prevention of a further decrease in the chloride concentration and the number of species. A sluice was, therefore, put into operation in 1978, by means of which water was exchanged between the North Sea and Lake Grevelingen. The responses observed are discussed here. In the near future, a crucial decision will have to be made: Will Lake Grevelingen remain a salt-water lake or will it become a fresh-water lake?

The disappearance of several polychlorinated biphenyls (PCBs) was observed in the deeper anaerobic sediment layers of Lake Ketelmeer, a sedimentation area of the Rhine River. Laboratory studies with an anaerobic consortium from this area demonstrated the capabilities for transforming PCBs. The field and laboratory observations indicate that disappearances of PCBs in the sediment might be caused by in situ microbial dechlorination. These processes appear to have lowered the PCB toxicity of four reactive congeners by 75% during the last two decades. In addition, dechlorination reactions are the essential first steps in the only natural pathway that eventually may lead to a complete elimination of PCBs from the aquatic environment. This can only be achieved if the dechlorination products are subsequently mineralized under aerobic conditions. Several implications for environmental policies with regard to contaminated sediments are discussed. Long-term prognoses on sediment quality generated with mathematical models that include these reactions may lead to a distinct, probably less costly, sediment policy.

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