Design Aspects : Page 3

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A treatment plant consists of different parallel treatment lanes or units to increase reliability . for example a unit is out of operation because of maintenance or cleaning, the other parallel units can take over the flow, avoiding an interruption in drinking water production. The parallel units and the treatment processes in series must be operated in such a way that always, so 24 hours per day, sufficient water can be produced to feed the clear water tank. Therefore sufficient valves and pumps must be available in the treatment plant . However, the installation of too many control devices increases costs and complicates operation . In the process flow diagram the optimal division of control devices is indicated. Finally the treatment plant must be positioned in a building. The building must be compact to diminish investment costs, but the treatment processes pumps and valves must be accessible for
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Better Quality

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In the past the main focus was to remove organic matter from the wastewater, but more recently advanced nutrient removal is applied to avoid eutrophication of the receiving water bodies.Future emphasis will be laid on the removal of Endocrine disrupting compounds such as pesticides and pharmaceuticals to avoid the accumulation of persistent organics in the environment.

With the increased efforts in wastewater treatment, the effluent of the wastewater treatment plant sometimes obtains a better quality than the receiving water bodies. In these cases, the question arises whether the effluent isn't a better source for drinking and industrial water supply than some surface water bodies.

 
Several examples exist. The most famous one is in Windhoek, Namibia, where about 25% of the domestic water supply consists of reclaimed wastewater. The effluent of the wastewater treatment plant is extensively treated with ozone, coagulation, flotation, activated carbon filtration, membrane filtration and chlorination. The product can compete with the water obtained from the original source about 300 km away from the city.

Another example is the water supply for Dow Chemical in Terneuzen, the Netherlands. The industrial water supply is fed by the wastewater treatment plant of the city of Terneuzen. It appears to be more economical to treat the effluent than to desalinate the salt water flowing in front of the industrial area.

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