The wastewater treatment method is to obtain demanganized wastewater, through a step wherein an acid or an alkali is added to sulfuric acid acidified wastewater to adjust pH to not less than 4.0 and not more than 6.0, whereby the sulfuric acid acidified wastewater is separated into a dealuminized solution and an aluminum precipitate; a step wherein a slurrying solution is added to the aluminum precipitate to form a slurry, then an alkali is added to adjust pH to not less than 9.0 and not more than 9.5, whereby an pH-adjusted aluminum precipitate slurry is formed; a step wherein an alkali is added to the dealuminized solution to adjust pH to not less than 8.0 and not more than 9.0; and others.