Water Quality Management in the Nitra River Basin

Somlyody, L., Masliev, I., Petrovic, P., & Kularathna, M. (1994). Water Quality Management in the Nitra River Basin. IIASA Collaborative Paper. IIASA, Laxenburg, Austria: CP-94-002

Preview

Text CP-94-002.pdf Download (7MB) | Preview

Abstract

The Nitra River is a tributary of the Vih which enters the Danube downstream of Bratislava. The watershed area is slightly larger than 5000 km2, and more than 650000 inhabitants live there. The quality of the river is one of the poorest in Slovakia due to numerous municipal and industrial discharges and the low level of wastewater treatment. The ongoing economic transition and shortage of financial resources for environmental management call for the development of regional short-run, least-cost policies. The development of such policies was the main objective of this joint study with the participation of IIASA, the Water Research Institute (VUVH, Bratislava) and the Vih River Basin Authority.

The present state of emissions and water quality was evaluated on the basis of available, routine types of information (including observations from the basin-wide water quality monitoring network) and additional data collection. It was found that industrial discharges form problems which can be handled mostly locally with a straight-forward strategy. In contrast, the management of municipal discharges -- representing about 70% of the total BOD5 emission in the catchment -- is a more complex issue requiring the development of a regional policy.

The definition of ambient water quality criteria (or the usage of a combination of ambient and effluent criteria) reflecting water use is a pre-requisite of the establishment of a least-cost policy. Thus, the application of water quality models is necessary to relate emissions to receiving water quality (as well as their changes). Due to the nature of the problem, a number of oxygen and nutrient balance models were used, ranging from the traditional Streeter-Phelps model to the latest version of U.S. EPA's QUAL model family. The models were calibrated and validated on the basis of two comprehensive longitudinal water quality profile observations. These observations were gathered under low-flow conditions to correspond with the design requirements of the strategy development. Due to the presence of uncertainties of different origins, the methodology of Hornberger, Spear, and Young (based on the so-called "behavior definition") was applied for parameter estimation of simpler models which then were directly incorporated into an optimization model. This optimization model was based on dynamic programming, utilizing structural features of river basin water pollution problems.

Elements of the water quality control policy model or decision support system (including the linked hydraulic and water quality model(s), the parameter estimation and uncertainty analysis routines, the dynamic programming, the database, the graphical user-interface, etc.) were developed in a rather generic fashion to allow a transfer from one watershed to another. This philosophy corresponds to the broader goals of IIASA's Water Resources Project dealing with issues of the management of degraded river basins in Central and Eastern Europe and the development of associated methodologies for which the Nitra River served as a case study.

Starting from the existing municipal wastewater treatment facilities, a number of alternatives were developed for each site on the basis of various combinations of well-proven physical, biological, and chemical processes to which different effluent quality (BOD-5, TP, NH4-N, NO3-N, etc.) as well as investment, operation, maintenance, and repair costs belong. The technological alternatives (and their major parameters) serve as input to the management optimization model. A special focus was devoted to phased plant development and innovative, cost-effective upgrading of highly overloaded plants by adding chemicals in low dosage. The issue of upgrading was also experimentally analyzed by jar tests at different treatment plants.

The objectives of the policy model were formulated in terms of minimizing the total annual cost or the investment cost. Constraints might incorporate ambient water quality (characterized by DO, BOD-5 and NH4-N), effluent criteria, and/or minimum level of treatment. The derived least-cost policies were compared to policies based strictly on effluent criteria and to those based on the application of "best available technology." The effluent criteria based policy stems from the new Slovakian legislation if its ambient criteria element was excluded (the legislation defines the simultaneous usage of effluent and ambient criteria and an eleven-year long transition period after which more stringent standards should be met). The role of industrial emissions was demonstrated in a sensitivity fashion, while the influence of parameter uncertainty on the developed policies was analyzed by an a posteriori Monte Carlo simulation and a multi-objective assessment. The study shows that significant cost savings are possible in comparison to uniform, effluent standard policies. They also suggest that a long-term strategy should be realized on the basis of a sequence of properly phased least-cost policies corresponding to ambient (or regionally variable) standards to be tightened gradually as financial resources become available.

Actions (login required)

View Item