DESIGN AND DESIGN EVALUATION OF BIOLOGICAL WASTE-WATER TREATMENT PLANTS

We are facing a rapid development of more stringent effluent standards and new biological treatment processes during the last decade. At the same time we recognise strong differences between the actual water pr otection situation in different countries of the world, e.g. between t he western and the eastern European or northern and southern American states. We are also aware of a trend towards privatisation of the wate r industry, resulting in turnkey bids including even operation of the treatment plants. This development results in a new challenge for a sc ientific based process selection and comparison. One of the basic ques tions to be answered by international co-operation is: What informatio n is necessary for the characterisation of the specific local problem to be solved, and how can the results of different design solutions be compared in regard to reliability and treatment efficiency? Reliabili ty and even treatment efficiency up to now have not been defined exact ly enough for a sound comparison of different treatment processes or s equences of processes. If this problem cannot be solved on an internat ional basis it will be very difficult to base such comparisons on a co st benefit (= water protection) calculation. As a consequence less imp ortant and inadequate criteria will pig the decisive role. One of the methods to evaluate design procedures and process selections is a scie ntifically based evaluation of the results from full scale treatment p lants. The actual standard of reports in literature on full scale expe rience is not sufficient to reach this goal in most of the cases. Two schemes try to show the complexity of the design procedure and the eva luation of full scale experience for design evaluation and could be us ed as a starting point of an international co-operation.