Development and Application of Models and Guidelines to Facilitate Decision making in the Extension of Wastewater Treatment Plants (WWTPs) and to Increase Operational Efficiency of Existing WWTPs
in Croatia

In Croatia, two national strategic projects are being implemented in the field of water pollution control, namely the Coastal Cities Pollution Control Project (The Adriatic Project) in the Adriatic Basin, and the Inland Waters Project in the Black Sea Basin. The objective of the Inland Waters Project is to improve water pollution control, flood protection and public water supply in the Sava and Drava and Danube river basin districts.

 The project entitled Development and Application of Models and Guidelines to Facilitate Decision making in the Extension of Wastewater Treatment Plants (WWTPs) and to Increase Operational Efficiency of Existing WWTPs has been initiated under the Technical Assistance component of the Inland Water Project - Loan 7453/HR.


The Contract for Consultant’s Services HV/TA–A1.2.2 for this project was signed in Zagreb on 24th August 2010 by Hrvatske vode (the Client), and Croatian-Dutch consortium consisting of PRONING DHI d.o.o., Croatia  (Lead Partner), UNESCO-IHE Institute for Water Education, Netherlands (Partner), and ASM DESIGN, Netherlands (Partner). The project duration was fifteen months. The project consists of four distinctive but inter-related steps.

Why modelling?
Application of mathematical modelling to wastewater sector started in early 80’s. Several models surfaced and each model was using different nomenclature and different approach. In that time, the former International Water Quality Association (IAWQ), originally formed as the International Association for Water Pollution Research (IAWPRC) in 1965, and in 1999 became the International Water Association (IWA), played a pivotal role for the development of wastewater modelling by establishing the “IAWPRC Task Group on Mathematical Modelling for Design and Operation of Biological Wastewater Treatment” in 1986. A year later, this group produced the Activated Sludge Model nr 1 (ASM1) and this year (1987), is considered the “year zero” for wastewater modelling. ASM1 is in essence a consensus model – compromising result of discussions at the time between different modelling groups, most prominently from South Africa, U.S.A., Switzerland, Japan and Denmark. Many of the basic concepts of ASM1 were adapted from the activated sludge model defined in 1980 by the group from University of Cape Town, S.A. In 90’s we witnessed sudden burst and gradual increase in use of mathematical models. Nowadays there is an array of models from the ASM family that evolved over last two decades such as ASM2, ASM2d, ASM3, ASM3+ etc. This evolution was undoubtedly supported by the availability of more powerful computers and fast expansion of knowledge on metabolism of the concerned bacteria or bacterial groups (transition from the black box to opaque box knowledge). Nowadays models are regularly used in almost every plant in the US, Australia, Canada, Japan and many EU countries. In the Netherlands for example, in 1994 the Dutch practitioners started to feel that models can be useful. Soon after (1995): STOWA advised to use SIMBA simulator as a national standard. In 1996 the STOWA modelling and characterization protocol was published. By 1997 approximately half of all WWTPs in the Netherlands were modelled. In 1999 the new protocol for model calibration was introduced. Nowadays more than 90% of the new WTTPs in the Netherlands are modelled. At the moment, looking from the practical perspective, models are considered sufficiently developed and reliable for most of the purposes for which they are used for. Modelers became a standard asset of any serious consulting company in the country and even specialist modelling companies emerged in the sector. This was accompanied with the global developments such as establishment of IWA Specialist Group on Good Modeling Practice and biannual specialist IWA conference on mathematical modelling that started in 1995 in Denmark. Latest encouraging developments demonstrate that modelling is not anymore a privilege of developed world only, as the applications in developing countries (e.g. India) and countries in transition (Korea, Bosnia and Herzegovina) are increasing.