INTEGRATING RISK ANALYSIS IN THE DESIGN/SIMULATION OF ACTIVATED SLUDGE SYSTEMS

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.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 paper provides a description of the approach, a useful demonstration of the general adequacy of the method and clarifies areas of strength and weakness.The methodology has been used as a support of decision making in an upgrade of a conventional WWTP towards strict nutrient removal consents. The analysis led to reducing the capital investment by 43%, producing savings of more than 1,000,000 .The results suggest that the proposed methodology can enhance the likelihood of meeting effluent standards not entailing above-normal capital investment in a transparent, robust and tailor-made way.