Optimization of greywater reuse systems: integration of economic and environmental objectives in real case scenarios

Abstract

Greywater reuse is presented as a key strategy to face the growing water shortage, especially in decentralized contexts. This study develops and applies an optimization model adapted to the Chilean regulatory framework, with the aim of minimizing both operational costs and the environmental impact associated with greywater treatment and reuse. The model considers different water sources, two reuse destinations (toilet and irrigation), and two treatment technologies (microfiltration and biological treatment RBC type). It was applied to three representative cases: a rural housing, a tourist accommodation and a public school, using real data obtained in the field. The results show that, without regulatory restrictions, the model chooses not to reuse, given the low cost of drinking water in formal systems. However, by incorporating normative restrictions and environmental objectives, the model identifies viable and cost-efficient configurations, with preference for biological treatment due to its greater efficiency of removal. The sensitivity analysis confirms that the most decisive parameters are the price of drinking water and the factors associated with the cost and scalability exponent of the treatment. This approach allows exploring implementation strategies adapted to different contexts and scales, becoming an approximation to a useful tool for sustainable water planning.