From harmful Microcystis blooms to multi-functional core-double-shell microsphere bio-hydrochar materials.

Harmful algal blooms (HABs) induced by eutrophication is becoming a serious global environmental problem affecting public health and aquatic ecological sustainability. A novel strategy for the utilization of biomass from HABs was developed by converting the algae cells into hollow mesoporous bio-hydrochar microspheres via hydrothermal carbonization method. The hollow microspheres were used as microreactors and carriers for constructing CaO core-mesoporous shell-CaO shell microspheres (OCRMs). The CaO shells could quickly increase dissolved oxygen to extremely anaerobic water in the initial 40 min until the CaO shells were consumed. The mesoporous shells continued to act as regulators restricting the release of oxygen from CaO cores. The oxygen-release time using OCRMs was 7 times longer than when directly using CaO. More interestingly, OCRMs presented a high phosphate removal efficiency (95.6%) and prevented the pH of the solution from rising to high levels in comparison with directly adding CaO due to the OH controlled-release effect of OCRMs. The distinct core-double-shell micro/nanostructure endowed the OCRMs with triple functions for oxygen controlled-release, phosphorus removal and less impact on water pH. The study is to explore the possibility to prepare smarter bio-hydrochar materials by utilizing algal blooms.