Use of P-rich materials produced from municipal wastewater treatment as waste-derived fertilizers

Nutrient recovery from wastewater treatment plants (WWTP) is an emerging strategy to tackle global challenges, including resource depletion and sustainable fertilizer production. This study aims to close the global P-cycle, by recovering P from wastewater at the WWTP and reintroducing it into the value chain, following our previous investigation on P recovery from WWTP using two distinct processes: (1) two-step chemical precipitation, and (2) adsorption with calcined eggshell (CES). These approaches produced two waste-derived fertilizers, struvite (103 mg P/g) and P-loaded CES (0.61 mg P/g). Dried and grounded sewage sludge ( Escherichia coli <1.0 × 10 1 CFU/g and absence of Salmonella spp.) from WWTP was combined with these waste-derived fertilizers, primarily serving as an organic soil amendment (12 t db /ha). Fertilizers were applied at 32 mg P/kg soil in a greenhouse experiment, with lettuce, using a P-deficient soil. Soil analysis showed that over 60 % and 80 % of applied P became soluble for P-loaded CES and struvite, respectively (Egner-Riehm extraction). Struvite enhanced plant physiological status and photosynthetic capacity, while P content in lettuce leaves remained significantly lower (2.3 g/kg) than in the mineral control (3.8 g/kg). Sewage sludge application led to a small increment in soil organic matter content but increased macro- and micronutrient content in soil and plants. The results indicate that struvite, recovered through a two-step process, holds strong potential as a substitute for conventional mineral fertilizers. • Struvite and P-loaded calcined eggshell were applied at 32 mg P/kg soil • Sewage sludge was applied at 12 t db /ha with waste-based fertilizers • Struvite improved plant physiology though leaf P was lower (2.3–3.8 g/kg) • P-loaded CES did not improve plant P nutrition in the soil used in the experiment • Sludge application increased organic matter and micro- and macronutrients in soil