Wastewater management towards a sustainable future. Dairy production: a study case

The increasing demand for heat, electricity, fuels and chemicals is pushing natural resources towards a non-reversible situation. Current solutions have to be adapted, and alternative (desirably sustainable) sources have to be found. With growth assured due to an increasing global population, waste is able to provide a plethora of components in the near future. This work approaches waste management, by using wastewater from a dairy production. The current state-of-the-art which concerns industrial and municipal wastewater treatment focuses on single process design and optimization or, at most, on a set of competing unitary processes. In this study, a superstructure-based model for industrial wastewater integration and valorization is presented. It is formulated as a MILP problem with the objective of minimizing operational costs while constraining investment costs. It comprises traditional waste conversion roots, but more importantly, it proposes greener solutions in order to recover the intrinsic chemical and energetic potential of industrial waste. Starting with a reference scenario of 23.4 MUSD of operating costs and exergy efficiency of 25 %, corresponding to a typical (optimized) wastewater treatment plant, with proper investment, exergy efficiency can go as high as 70 %, which has a direct link to environmental impact. The compromise solution that minimizes total cost, shows external electricity reduction by 70 %, providing an investment of 27 MUSD, recoverable in 12 years. Innovative solutions, like solid oxide co-electrolysis cells and methane synthesis from syngas are, with the present cost assumptions, non-profitable. Nevertheless, with incentives for bio-SNG production, as well as a reduction in electricity prices, an innovative and highly efficient solution is proposed, yielding an exergy efficiency of 86 %. The current work provides operating and investment costs of new technologies, as well as relevant technical data.