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Phosphorus (P) is limiting nutrient in soil system. The P availability in soil strongly depend on Iron (Fe) speciation. Colloidal iron phosphate (FePO4coll) is an important phosphorus (P) fraction in soil solution that carry P from soil to water bodies. This study tested the hypothesis that phytate exudation by Pteris vittata (P. vittata) can dissolve FePO4coll that leads to release of P and Fe. The phytate exudation in P. vittata increased from 434−2136 mg kg−1 as the FePO4coll concentration increased from 0−300 mM. The total P in P. vittata tissue increased from 2.88 to 8.28 g kg−1, the trichloroacetic acid P fractions (TCA fractions) were: inorganic P (0.86–5.10 mg g−1), soluble organic P (0.25–0.87 mg g−1), and insoluble organic P (0.16–2.03 mg g−1) which leads to higher biomass as FePO4coll increased from 0−300 mM. The linear regression analysis showed that FePO4 solubilizing activity has a positive correlation with TP, TCA P fractions in P. vittata, TP in growth media, and root exudates. This study shows that phytate exudation dissolved the FePO4coll due to the chelation effect of phytic acid on Fe, and due to the high Fe–P solubilizing activity in root exudates of P. vittata.

Background Trace amounts of nitrogen and phosphorus can easily trigger eutrophication damage in surface water, while cost-effective adsorption treatment is in prospect for clearing these pollutants simultaneously and efficiently. In this study, engineered adsorbents decorated with ZnFe-LDH by alkaline coprecipitation (3-6 mm, with modified ceramsite as CZF and modified volcanic rock as VZF) were prepared for NH 4 + and H 2 PO 4 - co-adsorption from aqueous solutions.Results Coexisting ions showed great effects on phosphate adsorption, especially Ca 2+ and CO 3 2- , and humic acid exhibited only a limited shielding impact on co-adsorption properties. Though comprehensive tests presented that the maximum captured amount of ammonium and phosphate occurred at pH 7, the isotherm and kinetic results suggest that two adsorbents preferentially adsorbed each pollutant. Specifically, the maximum uptake quantity of NH 4 + (15.55 mg-N g -1 ) and H 2 PO 4 - (11.21 mg-P g -1 ) were achieved by VZF and CZF, respectively, and controlled by physisorption and chemisorption distinctively, revealing that contaminants were cleared in disparate ways. Performances of seven consecutive adsorption/desorption cycles using 5% NaOH regenerant suggested that CZF retained 71.9% of PO 4 - removal efficiency, and VZF retained 47.9% of the NH 4 + adsorption rate, implying the strong reusability of ZnFe-LDH-modified adsorbents. A dynamic study has assessed that with 1 kg of combined modified adsorbents, approximately 527 L of polluted runoff flow could be continuously treated to below the National limits within one adsorption cycle.Conclusion Comparing with other parallel adsorbents, ZnFe-LDH-modified adsorbent is promising in eliminating eutrophication due to their superior capacity, stability, renewability, and non-toxicity.

Ammonium is strongly related to eutrophication and a key control of eutrophication in aquatic systems, especially in agricultural runoff. In this study, a novel Fe-Mn binary oxide-modified lava (FMML) granular adsorbent was synthesized for ammonium removal from aqueous solutions by co-precipitation method. The kinetic data were described by pseudo-second-order kinetic model well and intraparticle diffusion had effects on ammonium adsorption. For pH between 4.0 and 10.0, the adsorption efficiency was >80%, and its optimum was recorded at pH 7.0. FMML exhibited strong ammonium adsorption selectivity under the single presence of cations like Na+ , K+ , Ca2+ , and Mg2+ . The optimum adsorbent dose and particle size were 4 g/L and 3-5 mm, respectively, for an aqueous solution containing 10 mg/L of ammonium under normal conditions (298 K and pH 7.0). Furthermore, the adsorption process was endothermic, following both the Langmuir (R2 > 0.98) and Freundlich (R2 > 0.96) models. Compared with other adsorbents, the FMML can be prepared following a simpler protocol. After 30 times of adsorption-regeneration cycle, the FMML also had a relatively high ammonium adsorption capacity; hence, we see it as a prospective adsorbent for ammonium adsorption from aqueous solutions. PRACTITIONER POINTS: Fe-Mn binary oxide-modified lava with Fe/Mn ratio 3:1 was prepared using co-precipitation method. Adsorption maximum of modified lava was 20.8 mg/g (298 K and pH 7.0). Adsorption was sensitive to changes in adsorbent dose, particle size, and pH. Inorganic cations decreased ammonium adsorption in order of Na+ > K+ > Ca2+ > Mg2+ . Mechanisms for ammonium removal by FMML include diffusion, electrostatic attraction, oxidation, and complexation reaction.

Modified ceramsite has been widely reported as a P adsorbent in wastewater treatments; however, its performance in removing P from agricultural runoff is unclear. A new low-cost ceramsite is modified in this study applying Zn/Fe-layered double hydroxides (LDHs; CZF) to investigate its practicality in treating P-polluted agricultural runoff. The results revealed that the CZF has a theoretical maximum P-adsorption capacity of 11.2 mg-P g−1. Various factors in P-adsorption performance followed the order of pH value (−22.6) > Ca2+ (21.5) > Mg2+ (19.9) > CO32− (−14.5) > SO42− (−13.3) > humic acid (−10.7) > NO3− (−5.57) > Cl− (−2.93) > Na+ (0.32) > NH4+ (0.19). Through iterant adsorption/regeneration, CZF cyclically reduced P concentration in agricultural runoff from 0.58 mg-P L−1 to below 0.1 mg-P L−1 under the preferred parameters of 20 g L−1 dosage, 2 h adsorption time at pH 7.2, and 1 h desorption time at pH 13.0. The treated water has low luminescence toxicity as well as low leaching risks of embedded Zn and adsorbed P in the spent CZF. Additionally, the CZF packing module significantly decreased P in agricultural runoff within four weeks. The CZF dosage and hydraulic retention time (HRT) prolonged the effective operating time (EOT) for P removal, whereas the total organic carbon (TOC) concentration had a negative impact. The cost of CZF for removing P from agricultural runoff was as low as 0.45 ¥ m−3. Overall, this research indicates that using CZF as the adsorption substrate in a ditch purification system is an effective approach for mitigating P pollution in agricultural runoff.