Exploring a multifunctional geoengineering material for eutrophication remediation: simultaneously control internal nutrient load and tackle hypoxia

An effective approach for control of internal nutrient loading and sediment hypoxia remains a longstanding challenge to the restoration of aquatic ecosystems. In order to simultaneously tackle these issues, a MultiFunction Geoengineering material (MFG) was developed for sediment remediation through the synergistic functions of physical capping, nutrient adsorption and delivery of O2 nanobubbles. The MFG, derived from natural zeolite, exhibited superior (1.5-4 times higher) adsorption capabilities for both phosphate (PO43--P) and ammonium (NH4+-N), than pristine zeolite. The O2 adsorption capacity was also enhanced from 46, observed in the natural zeolite, to 121 mg O2/g for the MFG. An in-situ sediment capping experiment in a eutrophic lake demonstrated that the application of MFG dramatically reversed sediment hypoxia (ORP -200 mV) to an aerobic status (ORP 175 mV) and, furthermore, stimulated sediment microbial activity, particularly nitrifying bacteria. The MFG treatment resulted the sediment changing from a nutrient source to a sink through decreasing the cumulative PO43--P and NH4+-N fluxes from the sediment by 124.6% and 131.1%, respectively. Moreover, the comprehensive functionalities of the material have been, for the first time, quantified, from which data O2 nanobubble delivery was determined to be the largest contributor, reducing the fluxes of PO43--P and NH4+-N by 57.3% and 56.1% of, respectively. Our findings highlight the viability of such multifunctional material for the remediation of internal nutrient loads in lacustrine environments, towards sustainable eutrophication control.