Simultaneous in situ nutrient recovery and sustainable wastewater purification based on metal anion- and cation-targeted selective adsorbents

The recovery of nitrogen (N) and phosphorus (P) from wastewater is of great importance in addressing the global nutrient crisis. The limitations of existing methods require the development of effective technology. Here, two different hydrogel adsorbents were fabricated with good separation ability for metal cation (M+) and metal anion (M-) but showed little removal of nutrients. Based on the materials, a novel three-stage operation system combining adsorption and capacitive deionization (CDI) technology was presented for nutrient recovery and wastewater treatment. In the first two stages, mixed metals in wastewater were successfully separated (Cu2+: 144.6 mg/g; Cr2O72-: 167.0 mg/g), and nutrients were retained (N and P < 1 mg/g). In the third stage, the residual trace metal ions in the solution were removed (2.0 mg/L to N/A), and the nutrients were enriched through electroadsorption and desorption processes by CDI. Plants using recovered liquid fertilizers revealed similar values for height, root length, and chlorophyll compared with those obtained using actual fertilizers. The results indicated that this novel three-stage operation system (3S A-C system) combining adsorption and CDI is efficient in recovering liquid fertilizers from wastewater and is a promising technology for simultaneously addressing nutrient crises and environmental pollution.