Polymerized Titanium Salts for Algae-Laden Surface Water Treatment and the Algae-Rich Sludge Recycle toward Chromium and Phenol Degradation from Aqueous Solution

The emerging titanium coagulants are increasingly utilized for water purification due to their strong coagulation capability. Coagulated sludge recovery is one of the most serious environmental challenges. This study proposed polytitanium coagulation for algae-laden surface water treatment, followed by the algae-rich coagulated sludge recovery and reuse. Polytitanium coagulation had advantages over conventional Al- and Fe-coagulation in terms of synergetic removal of algae and organics. Polytitanium tetrachloride (PTC) could achieve efficient algae removal (∼95%), accompanied by ∼62% organics removal. Anatase nano-TiO2 spheres were produced from PTC coagulated sludge under high-temperature incineration. Compared with commercially available TiO2, the nano-TiO2 was more capable for both Cr(VI) reduction and phenol oxidation in aqueous solutions. Impurities, i.e., carbon, Mg, Al, Fe, on the surface of nano-TiO2, were speculated to accelerate the separation of hole–electron pairs and the transportation rate of ecb–, and therefore improved the photocatalytic activity of nano-TiO2. Moreover, compound contamination caused by chromium and phenol could be degraded by the nano-TiO2, as indicated by synergetic removal of Cr(VI) and phenol up to 99% when they coexisted. This study utilizes polytitanium coagulation as an alternative to conventional Al and Fe coagulation, which has practical value for both algae-laden water purification and resource recycling.