Environmental comparison of N and P removal technologies for the treatment of anaerobic digestion supernatant

Anaerobic digestion is one of the commonest treatments for the sludge produced in wastewater treatment plants (WWTP). The supernatant resulting from this process presents high concentrations of both N and P but low amounts of organic matter. Although this flow is usually sent back to the biological treatment of the water line, in recent years several processes have been designed and optimized for the treatment of anaerobic supernatant. Anammox and nitrification-denitrification through the nitrite short-cut (NSC) processes require less oxygen than the conventional nitrogen removal process, leading to either in a reduction in aeration costs or an effluent of a better quality (Joss, et al., 2009; Peng and Zhu, 2006). Struvite crystallization process (SPC) presents the advantage of reducing N and P producing a mineral fertilizer, struvite, with virtually no-heavy metals (Ueno and Fujii, 2001). Life Cycle Assessment (LCA) is a technique which quantifies the potential environmental impact of a product, service or process through all its stages from cradle to grave (ISO, 2006). It has been widely used within the field of WWTP and anaerobic digestion (Corominas et al., 2011; Peters and Rowley, 2009); however, to the best of our knowledge, this is the first LCA focused on the treatment of anaerobic supernatant.