Evaluation of a new approach for swine wastewater valorisation and treatment: A combined system of ammonium recovery and aerated constructed wetland

Abstract

Nitrate Vulnerable Zones (NVZs) are faced with a surplus of animal manure due to intensive livestock production, and the high use of mineral nitrogen (N) fertilisers in crop production. Recovery of N from animal manure to replace synthetic mineral fertilisers is considered a key strategy to close the N loop for more sustainable agriculture and to meet strict legal frameworks. In this study, N recovery from swine wastewater by an ammonia (NH3) stripping process followed by purification via an aerated constructed wetland (ACW) was proposed as an alternative approach to conventional systems based on biological nitrification-denitrification (NDN) treatment. The performance of the NH3 stripping pilot as well as the ACW was monitored in 2019–2020 over three periods, to evaluate the quality of recovered ammonium nitrate (AN) solution and the effluent of the ACW. Results showed that the NH3 stripping unit recovered 21% of total-N (32% of mineral-N) in the form of AN solution. This could be used as a mineral fertiliser according to the criteria of the European Fertilising Products Regulation 2019/1009 and the technical proposal of manure-derived RENURE (REcovered Nitrogen from manURE) products by the European Joint Research Centre. As a RENURE product, AN solution would reach an end-of-manure status and could be used as a synthetic N fertiliser replacement. The tested ACW achieved a high removal efficiency with respect to suspended solids (96%), biological oxygen demand (96%), chemical oxygen demand (90%), total-N (80%), and total phosphorus (97%). The quality of ACW effluent was comparable to that of NDN treatment. Though the overall cost of the proposed pilot-scale process consisting of NH3 stripping (5.1 € t−1) and ACW (12 € t−1) was calculated slightly higher than conventional NDN treatment (16 € t−1), it is foreseen to outcompete at a higher loading rate (over 45 m3 ha−1 d−1). Furthermore, post-purification will be needed for the ACW effluent to meet the requirements for discharge to surface water.