Selection of P-reactive materials for treatment of hypolimnetic water withdrawn from eutrophic lakes

Treatment of Hypolimnion Water on Mineral Aggregates as the Second Step of the Hypolimnetic Withdrawal Method Used for Lake Restoration

“…Two reactive materials were used in the study: LECA and limestone (LS), both having grain sizes of 10-30 mm. As already mentioned, these aggregates were chosen from among four low-cost and easy available materials tested in a previous study for OP removal from hypolimnetic water in static sorption experiments [44]. According to the X-ray diffraction (XRD) analysis, LECA consists mainly of clay minerals (91%), mostly aluminum silicates, including smectite, illite and chlorite, accompanied by quartz, calcite and dolomite.…”

“…Interestingly, at the beginning of experiment, a substantial rise in the pH and concentrations of Mg 2+ and Ca 2+ also took place (Figures 3 and 4), which points at the flushing of calcium and magnesium from the alkaline components of the sorbents. The increase in pH from nearly neutral to slightly alkaline must have reduced, to some extent, the sorption of OP onto LECA, as its adsorption ability decreases with the alkalization of the solution [44,45] due to the change in the ligand type being replaced with OP [45]. In the case of the same LECA as investigated in the current study, a pH rise from 7.0 to 7.5 at the temperature of 10 • C resulted in a 10% lower OP fixation [44].…”

“…The increase in pH from nearly neutral to slightly alkaline must have reduced, to some extent, the sorption of OP onto LECA, as its adsorption ability decreases with the alkalization of the solution [44,45] due to the change in the ligand type being replaced with OP [45]. In the case of the same LECA as investigated in the current study, a pH rise from 7.0 to 7.5 at the temperature of 10 • C resulted in a 10% lower OP fixation [44]. An increase in pH in the range observed after 0.5 h could also affect the performance of LS, as it generally enhances OP sorption onto calcite, most likely by changes in phosphate speciation [46,47].…”

“…The reason for that is the slightly higher adsorption capacity of the LS. Both materials were tested in our previous study [44]. In hypolimnion water, the maximum adsorption capacity of the LS was about 18% higher as compared to the LECA [44].…”

“…The research conducted thus far has focused on the assessment of the sorption capacity of small-grained (<10 mm) mineral aggregates at high-concentration OP solutions, usually found in wastewater (5-200 mg•dm −3 ) [40][41][42][43]. Only a few studies [44,45] have assessed adsorption capacity of mineral aggregates under relatively low OP concentrations typically found in freshwater ecosystems. Therefore, information about the removal of OP under lake-specific OP concentrations and ionic composition is still limited.…”