Progress towards a more circular phosphorus economy necessitates development of innovative water treatment systems which can reversibly remove inorganic phosphate (P
i
) to ultra-low levels (<100 μg L
−1
), and subsequently recover the P
i
for reuse. In this study, a novel approach using the high-affinity
E. coli
phosphate binding protein (PBP) as a reusable P
i
bio-adsorbent was investigated. PBP was expressed, extracted, purified and immobilized on NHS-activated Sepharose beads. The resultant PBP beads were saturated with P
i
and exposed to varying pH (pH 4.7 to 12.5) and temperatures (25–45 °C) to induce P
i
release. Increase in temperature from 25 to 45 °C and pH conditions between 4.7 and 8.5 released less than 20% of adsorbed P
i
. However, 62% and 86% of the adsorbed P
i
was released at pH 11.4 and 12.5, respectively. Kinetic experiments showed that P
i
desorption occurred nearly instantaneously (<5 min), regardless of pH conditions, which is advantageous for P
i
recovery. Additionally, no loss in P
i
adsorption or desorption capacity was observed when the PBP beads were exposed to 10 repeated cycles of adsorption/desorption using neutral and high pH (≥12.5) washes, respectively. The highest average P
i
adsorption using the PBP beads was 83 ± 5%, with 89 ± 4.1% average desorption using pH 12.5 washes over 10 wash cycles at room temperature. Thermal shift assay of the PBP showed that the protein was structurally stable after 10 cycles, with statistically similar melting temperatures between pH 4 and 12.5. These results indicate that immobilized high-affinity PBP has the potential to be an effective and reversible bio-adsorbent suitable for P
i
recovery from water/wastewater.
A polyurethane (PU) foam nanocomposite impregnated with iron oxide nanoparticles (IONPs) was developed to remove arsenic (As) from drinking water at ppb concentrations. The effect of synthesis and application parameters such as the size of IONPs, pH levels, weight of adsorbents, and arsenic concentrations on the performance of PU-IONP adsorbents in removing arsenic were studied. The prepared adsorbents were characterized by scanning electron microscopy and energy dispersive X-ray microscopy to evaluate the microstructure of PU-IONPs and the surface adsorption of arsenic species, respectively. Atomic absorption spectrometry was conducted to measure the concentration of arsenic in the treated solutions in order to calculate the removal capacity of PU-IONPs. The experimental results revealed that decreasing the size of IONPs from 50–100 nm to 15–20 nm yields a higher removal capacity. Increasing the weight of the used adsorbents and the contact time led to an increase in the removal capacity as well. As the arsenic species (III and V) concentration increased in the solution, the removal capacity of PU-IONPs decreased. In a column study, a long-term cyclic operation mode was found to be very effective in removing arsenic; 100% removal capacity was achieved when 500 ml of As solution (100 ppb) was treated.
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