Developing low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L−1 showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

The physiological adaptation of the phosphate uptake behaviour of the cyanobacterium Anacystis nidulans (Synechococcus leopoliensis) has been studied under phosphate-deficient conditions. We show that, during additions of pulses of phosphate, the individual cells of a population potentially develop a coherent behaviour with respect to the kinetic and energetic properties of the high-affinity phosphate uptake system. These adaptive responses are independent of the amount of stored phosphate and the absolute external phosphate concentration, but depend on the exposure time to elevated phosphate concentrations. We demonstrate that the response to additions of pulses of phosphate triggers further metabolic alterations to CO2 fixation, and the flow of fixed carbon into the pool of low-molecular weight-compounds or glycogen. These alterations may also affect subsequent growth. The ecological relevance of the adaptive phosphate uptake behaviour is discussed with respect to the establishment and stability of natural communities.