Abstract
This work explores the possibilities of improving the eco-efficiency of Wastewater Treatment Plants (WWTPs) introducing a plant-wide perspective in the formulation of the control strategy. Eco-efficiency goals are contemplated in the analysis of the appropriateness of control actions, considering the seasonal effects of temperature into the decision-making process. Plant-wide control strategy handles are the operation variables of the activated sludge process, the volume of the primary clarifier, and the temperature of the anaerobic digester. Performance is evaluated in terms of energy use, biogas production, effluent quality, emissions to air and soil, considering annual and bimestrial average values of indicators to capture seasonal effect of temperature. The result is a set of possible solutions, obtained from a multi-objective decision-making procedure, consisting on a sequence of control actions applied at different temporal windows that improve the eco-efficiency indicators of the plant. The results obtained when applying the different solutions make evident how the application of plant-wide control strategies is useful to improve performance indicators that represent individual goals, leading to trade-off solutions that describe WWTPs’ eco-efficiency.
Highlights
The eco-efficiency concept is proposed as a new paradigm within an industrial framework as defined by the World Business Council for Sustainable Development (WBCSD):“eco-efficiency is achieved by the delivery of competitively priced goods and services that satisfy human needs and bring quality of life, while progressively reducing ecological impacts and resource intensity throughout the life-cycle to a level at least in line with the Earth’s estimated carrying capacity” [1]
Annual average values of indicators are computed to measure the performance in the full operation period, and bimestrial variations are considered to capture relevant and beneficial seasonal effects associated with temperature variation
Except for biogas flow (Qgas/Qin), a positive deviation implies that the evaluated control action produces an improvement on energy consumption, effluent quality or sludge for disposal reducing the magnitude of the performance indicator
Summary
The eco-efficiency concept is proposed as a new paradigm within an industrial framework as defined by the World Business Council for Sustainable Development (WBCSD):“eco-efficiency is achieved by the delivery of competitively priced goods and services that satisfy human needs and bring quality of life, while progressively reducing ecological impacts and resource intensity throughout the life-cycle to a level at least in line with the Earth’s estimated carrying capacity” [1]. Eco-efficiency is a management philosophy that encourages business to search for environmental improvements that yield parallel economic benefits. It focuses on business opportunities and allows companies to become more environmentally responsible and profitable. Wastewater Treatment Plants (WWTPs) are crucial to mitigate the impact of pollutants on water bodies. The urban wastewater treatment plants (WWTPs) comprise a water line, where pollutants are removed from wastewater, a sludge line, where sludge is stabilized while biogas is obtained as by-product, and a gas line for biogas conditioning [2]. Energy consumption and energy recovery from biogas are important issues to be considered in processes oriented to produce environmental benefits, since the use of energy from external sources to treat wastewater involve additional environmental impacts (i.e., emissions of greenhouse gasses, GHG). The use of chemicals agents for nutrient removal and sludge conditioning affect toxicity, but it involves environmental impacts associated with the production and transportation of chemicals [4]
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