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Valorisation of nutrients in wastewaters using reactive inorganic sorbents

Abstract:

The recovery and removal of nutrients from the main anthropogenic flows (e.g. urban/industrial wastewater and animal manure) could be crucial to maintain the ecosystems and to secure a renewable source of nutrients. Technology options for recovering phosphorus (P) from wastewater have often been limited by the need to treat large volume of diluted waste streams. The solid-liquid technology, which uses an adsorbent in conventional sorption-regeneration processes, is one of the most realistic solutions for P recovery from wastewater. In particular, the approaches based on a low-cost inorganic adsorbent have attracted increasing attention for recovering P from wastewater treatment plants. This chapter describes the use of coal combustion fly ash and its derivative zeolites as low-cost inorganic adsorbents for P recovery from wastewater. Laboratory experiments showed that the presence of aluminium and iron oxides as well as calcium (Ca)-based minerals was critical to promote the complexation with phosphate (P i ) on the solid structure, thereby forming brushite (CaHPO 4 ·2H 2 O) deposits. Bioavailability assays have demonstrated that the P i -loaded inorganic sorbents could serve as a slow-release P i fertiliser in both basic and acidic soils. Furthermore, the use of synthetic zeolite mixtures has demonstrated their ability to simultaneously remove P i and ammonium from wastewater. The recovered products could be used not only as mineral fertiliser but also as soil amendment, since the zeolite-based particles have a structure capable of improving the water retention capacity of soil. The potential implementation of the zeolite-based sorbents as P i recovery technology has also been evaluated using a hybrid process consisting of P i sorption and membrane ultrafiltration.