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Manure represents an exquisite mining opportunity for nutrient recovery (nitrogen and phosphorus), and for their reuse as renewable fertilisers. The ManureEcoMine proposes an integrated approach of technologies, operated in a pilot-scale installation treating swine manure (83.7%) and Ecofrit (16.3%), a mix of vegetable residues. Thermophilic anaerobic digestion was performed for 150 days, the final organic loading rate was 4.6 kgCOD m d, with a biogas production rate of 1.4 Nm m d. The digester was coupled to an ammonia side-stream stripping column and a scrubbing unit for free ammonia inhibition reduction in the digester, and nitrogen recovery as ammonium sulphate. The stripped digestate was recirculated daily in the digester for 15 days (68% of the digester volume), increasing the gas production rate by 27%. Following a decanter centrifuge, the digestate liquid fraction was treated with an ultrafiltration membrane. The filtrate was fed into a struvite reactor, with a phosphorus recovery efficiency of 83% (as orthophosphate). Acidification of digestate could increment the soluble orthophosphate concentration up to four times, enhancing phosphorus enrichment in the liquid fraction and its recovery via struvite. A synergistic combination of manure processing steps was demonstrated to be technologically feasible to upgrade livestock waste into refined, concentrated fertilisers.

BACKGROUND This study provides a methodology for recovering two essential macronutrients (potassium and phosphorus) from the liquid fraction of manure. This methodology paves the way for K‐struvite recovery from manure by determining the suitable operational conditions (pH and temperature). RESULTS The theoretical operational conditions were established by modelling and experimentally adjusted with manure, achieving the highest recoveries (80% of P‐recovery) at pH 10 and 38 °C when using a 10% manure solution. Then, the suitable operational conditions were evaluated using 0–10–50–100% manure solutions. The lowest percentages of manure (0–10%) favoured the co‐precipitation of other products besides K‐struvite (magnesium phosphate and magnesium hydroxide); and at the highest percentages of manure (50–100%), all the phosphate was recovered as K‐struvite, but also the co‐precipitation of magnesium hydroxide due to the Mg/P molar ratio applied (Mg/P = 2). Suspended particles acted as nuclei for heterogeneous nucleation and favoured the aggregation of crystals resulting in a star‐asterisk form. CONCLUSION The viability of the process was demonstrated, this study being the first proof‐of‐concept of K‐struvite recovery from complex waste streams. © 2017 Society of Chemical Industry

BACKGROUND Phosphorus (P) resources are limited, and to assure its supply, efforts must be focused on P‐recovery rather than its removal. In this sense, manure is a mining opportunity for nutrient recovery, for example, when recovered as struvite. However, manure treatment is challenging due to its characteristics, such as the solids content, one of the main hindrances to struvite formation. Many researchers have setablished a limit value of 1 g of total suspended solids (TSS)·L−1 to avoid interferences with struvite precipitation. Despite this, few studies have focused on the effect of solids on struvite formation. RESULTS This study identified the role of solids in struvite nucleation and growth, and its interaction. The viability of struvite recovery from digested manure is ensured, even at high concentrations of solids (from 1 to 3 g TSS L−1), recovering more than 95% of the phosphorus as struvite. The results showed that solids not only did not interfere on struvite formation, but also played an important role during struvite crystallization, acting as nuclei favoring heterogeneous nucleation. CONCLUSIONS Suspended particles favored the aggregation and/or agglomeration of struvite crystals, forming crystal nets and recovering bigger crystalline structures. The presence of solids on the recovered product might be beneficial for meeting crop demands and maintaining or restoring soil fertility, while applying an excellent slow‐release fertilizer. © 2018 Society of Chemical Industry