Wastewater treatment plants began to be built near large cities to collect and

Wastewater treatment plants began to be built near

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Wastewater treatment plants began to be built near large cities to collect and treat polluted water and control the pollution of urban surface waters. In the Netherlands, in 1970, the Surface Water Pollution Act (Wet Verontreiniging Opper- vlaktewateren, WVO) was adopted, aiming at the reduction and prevention of polluted overflows to surface water. It enforced treatment of polluted overflows to surface waters based on a system of pollution permits. This Act has been replaced by the Dutch Water Law (Waterwet) in December 2009. In the Netherlands, in 1970, the Surface Water Pollution Act (Wet Verontreiniging Opper- vlaktewateren, WVO) was adopted, aiming at the reduction and prevention of polluted overflows to surface water. It enforced treatment of polluted overflows to surface waters based on a system of pollution permits. This Act has been replaced by the Dutch Water Law (Waterwet) in December 2009. In 1986 a fire at the Santoz chemical plant in Switzerland had disastrous consequences for the Rhine. Thousands of gallons of toxic chemicals were washed into the river and millions of fish and other wildlife were killed. There was a public outcry and politicians from all the Rhine countries agreed that action had to be taken. The result was the Rhine Action Programme of 1987. The Rhine Action Programme stated that by 1995: Discharge of the most important noxious substances should be cut by 50% compared with 1985. Safety norms in industrial plants should be tightened. Weirs must be fitted with fish passages to allow the fish to travel upstream and spawning grounds must be restored in the upper tributaries. The riverside environment should be restored to allow the return of plants and animals typical of the Rhine. The first point has been an important trigger for reduction of (combined) overflows from urban drainage systems. Still there are approximately 13,000 overflow structures of (improved) combined sewer systems in the Netherlands. During heavy rainfall, sewage water diluted with stormwater is discharged, together with disturbed sewage sludge, from the combined Figure 4.1 - Polluted spills to surface waters
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21 SANITARY ENGINEERING - CT 3420 URBAN DRAINAGE sewer systems via the overflow structures into the surface water. In separate systems, collected stormwater is discharged to surface water together with pollutions washed down from impervious surfaces. Many overflow structures are situated on small(semi-)stagnant watercourses. As a result, the influence of discharges from overflow structures on surface water quality, sediments and the aquatic ecosystem is considerable. Initially, requirements for granting discharge permits based on the Surface Water Pollution Act, mainly concerned the average frequency at which overflows from combined sewer systems can occur. No permit was necessary for stormwater outlets of separate systems. Meanwhile research has shown that the overflow frequency is representative to a limited extent only for the pollution load and the effects on surface water.
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  • Fall '13
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  • Sewage treatment, Sanitary sewer, Sewage, sewer systems

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