Combination of technologies for nutrient recovery from wastewater: A review

The growing human population is increasing the need for crop production, which has resulted in elevated requirements of Nitrogen-Phosphorous-Potassium (NPK) fertilisers. This tremendous demand cannot be sustained on traditional processes, which cause significant resource depletion and unacceptable environmental impacts due to their heavy reliance on fossil fuels. To overcome this, alternative sources to obtain fertilisers have been explored, including the recovery of nutrients from wastewater and waste streams. However, this approach faces several challenges, such as the dilution of the streams, low public acceptance, and lack of support. With the aim of surpassing these barriers, the present study provides a review of existing Research & Development (R&D) projects in the field, comparing the available technologies to identify the optimal train of technologies for nutrient recovery: Anaerobic Digestion followed by the valorisation of the digestate (directly or producing P-based fertilisers such as P salts, CaP, H₃PO₄ and P₂O₅) and the liquid fraction (obtaining struvite, ammonium sulphate/nitrate, and reclaimed water). Moreover, an innovative strategy for nutrient recovery based on the decentralised treatment of separated concentrated streams is proposed as a useful strategy for valorising nutrients, developing a Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis. Finally, non-technological strategies are suggested to mainstream waste valorisation, aimed at overcoming social barriers by promoting stakeholder acceptance and producing recycled fertilisers with low associated rejection. Nutrient valorisation through the decentralised treatment of source separated waste/wastewater using optimised train of technologies seems a sustainable strategy for addressing the current and future massive demand of fertilisers.