FeCa-based layered double hydroxide, a high-performance phosphorus adsorbent in constructed wetlands and ecological dams - A pilot scale study.

Research studies have modified traditional substances to seek fast-acting removal of phosphorus in constructed wetlands (CWs) and ecological dams, rather than develop a brand-new nano-adsorbent. This work synthesized FeCa-based layered double hydroxide (FeCa-LDH) with a chemical co-precipitation method, and the performance, mechanism and factors of phosphorus removal were investigated. FeCa-LDH showed a marked ability to adsorb phosphorus from waste water, with a removal efficiency of 94.4% and 98.2% in CWs and ecological dams, respectively. Both FTIR and XPS spectrum evidenced that FeCa-LDH removed phosphorus via electrostatic and hydrogen-bonding adsorption, as well as a coordination reaction and interlayer anion exchange. FeCa-LDH showed a higher capacity to remove phosphorus in alkaline and neutral waste water than in acid conditions. Co-occurrence anions, which influenced the efficiency of the phosphorus removal capacity are considered in the sequence below: CO32- ≈ HCO3- > SO42- > NO3-. Innovatively, FeCa-LDH was not affected by the low-temperature limitation for CWs, and phosphorus removal efficiency at 5 °C was almost equal to that at 25 °C. These results cast a new idea on the construction, application and phosphorus removal performance of CWs and ecological dams.

Layered double hydroxides, an effective nanomaterial to remove phosphorus from wastewater: Performance, mechanism, factors and reusability.

Systematic understanding of phosphorus adsorption performance, mechanism, factors and reusability of layered double hydroxides (LDH) remains limited. Thus, iron (Fe), calcium (Ca) and magnesium (Mg)-based LDH (FeCa-LDH and FeMg-LDH), were synthesized with a co-precipitation method to improve phosphorus removal efficiency during the wastewater treatment process. Both FeCa-LDH and FeMg-LDH showed a considerable ability to remove phosphorus in wastewater. When the phosphorus concentration was 10 mg/L, the removal efficiency reached 99 % (FeCa-LDH: 1 min) and 82 % (FeMg-LDH: 10 min), respectively. The phosphorus removal mechanism was observed to be electrostatic adsorption, coordination reaction and anionic exchange, which was more evident at pH = 10 for FeCa-LDH. Co-occurrence anions that affected phosphorus removal efficiency, were observed in the following order: HCO3- > CO32- ≈ NO3- > SO42-. After five adsorption-desorption cycles, phosphorus removal efficiency was still up to 85 % (FeCa-LDH) and 42 % (FeMg-LDH), respectively. Together, the present findings suggest that LDHs were high-performance, strongly-stable and reusable phosphorus adsorbents.