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.