Risk Assessment Procedure for design of WWTP

Modeling uncertainty in the risk of exceeding effluentlimits of a WWTP


What is the probability of exceeding an effluent standard of a wastewater treatment plant? This is the central question in this project on a risk assessment procedure for the design and retrofitting of wastewater treatment plants.

Up to now, within the design/retrofit of wastewater treatment plants (WWTPs), deterministic models were used to evaluate different scenarios on their merits in terms of effluent compliance. To obviate this problem, an alternative design approach explicitly incorporating uncertainty is herein proposed. A probabilistic Monte Carlo engine is coupled to deterministic wastewater treatment plant (WWTP) models.The risk interpretation is done in two forms:

  • Concentration duration frequency (cdf) curves of norm exceedance
  • and effleunt distributions.

    The combination of probabilistic modelling techniques with the currently available deterministic models allows to determine the probability of exceeding the effluent limits of a WWTP. This percentage of exceedance is accompanied by confidence intervals resulting from the inherent uncertainty of influent characteristics and model parameters.

    Uncertainty is a central concept in the decision making process, especially when dealing with biological systems subject to large natural variations. In the design of activated sludge systems, a conventional approach in dealing with uncertainty is implicitly translating it in above-normal safety factors, which in some cases may even increase the capital investments by an order of magnitude.

    1. Development of the RAP add-in to WEST (sep 1999 - aug 2000)

    In this first part, sponsored by Aquafin, Biomath developed the software (modelling, Monte Carlo, other statistical tools,...).

    2. Probabilistic Risk Assessment of CDF-curves: a case study for WWTP Hove (feb 2002 - sep 2002)


    Bixio D., Rousseau D., Verdonck F., Thoeye C., Meirlaen J., Peter A. Vanrolleghem. (2001). A quantitative risk analysis tool for design/simulation of waste water treatment plants. IWA 2nd World Water Congress, Berlin, Germany, 15-18 October 2001.

    Bixio D., Parmentier G., Rousseau D., Verdonck F., Meirlaen J., Vanrolleghem P.A. and Thoeye C. (2001). Intergrating risk analysis in the design/simulation of activated sludge systems. Proceedings 74th Annual Conference and Exposition of Water Environment Federation (WEFTEC). Atlanta, USA, October 14-18 2001.

    Rousseau, D., Verdonck, F., Moerman, O., Carrette, R., Thoeye,C., Meirlaen, J., Vanrolleghem, P.A. (2000). Development of a risk assessment based technique for design/retrofitting of WWTPs.

  • Water Science & Technology, 43 (7), 287-294.
  • Preprints on the 5th International Symposium on Systems Analysis and Computing in Water Quality Management, 5.17-5.24.Oral presentation on the WATERMATEX 2000 Symposium, September 18-20, 2000, Gent.

    Rousseau, D., Verdonck, F., Moerman, O., Carrette, R., Thoeye,C., Meirlaen, J., Vanrolleghem, P.A. (2000). Risk assessment tool for the design of wastewater treatment plants. Med. Fac. Landbouw. Univ. Gent. 65/4, 2000, 219-223. Presented as a poster on the PhD-Symposium, October, 11, 2000, Gent, Belgium.

    Project duration: 1999-09-01 - 0000-00-00

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    Frederik Verdonck
    Department of Applied Mathematics, Biometrics and Process Control
    Coupure Links 653
    9000 Gent
    Tel: +32 (0)9 246.59.37
    Fax: +32 (0)9 246.62.20
    Email: RAP@biomath.rug.ac.be

    Last update: 01 december 2008, webmaster@biomath.ugent.be

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