Mutual treatment of algae organic matters and heavy metal ions using a coagulation process: Processes and mechanisms

The eutrophication of water bodies and rapid industrial development have generated large amounts of algae-laden water and heavy metal wastewater. Herein, algal organic matters (AOMS), a traditional pollutant, was extracted from algae-laden water and used as a flocculant to remove heavy metal ions (HMs), achieving the mutual treatment of two pollutants. Furthermore, the coagulation kinetics was studied via online monitoring of floc size, and the mutual removal mechanism of AOMS and HMs was explored using density functional theory (DFT) calculations. Results show that the main components of AOMS in this study are polysaccharides, proteins, and humic acids, which contain functional groups such as –OH, –COOH, and –NH 2 that can coordinate and complex with HMs to form micro-flocs. At the same time, due to the bridging effect of the AOMS molecular skeleton, flocs can grow rapidly. With the rise of AOMS dosages, the removal efficiency of HMs gradually increases, ultimately reaching 86.7 % (Cu 2+ ), 81.6 % (Zn 2+ ), and 77.2 % (Cd 2+ ), respectively. Furthermore, higher pH values can cause deprotonation on AOMS surface, which enhances the conjugated coordination effect, further improving the coagulation efficiency. DFT calculations indicate that the adsorption binding energies between each point on AOMS and HMs are considerably different, and the strongest binding ability is observed between Cu 2+ and AOMS in mixed-HMs solutions, followed by Zn 2+ and Cd 2+ . In summary, the synchronous coagulation process of AOMS and HMs realizes the rational reuse of algae-laden water and meanwhile provides a feasible solution for the efficient, low-carbon, and low-cost treatment of heavy metal wastewater.