To develop a flocculant having a usage smaller than those of commercial available products, producing precipitate consisting of a disposable chemical substance after flocculation, and discharging waste water after treatment in compliance with the environmental standard (BOD and COD).

The flocculant includes a natural organic acid of 1-3 wt%, ammonium aluminum sulfate of 40-55 wt%, sodium aluminum sulfate of 7-10 wt%, an acrylamide polymer, with an average molecular weight of 9 millions-10 millions, of 8-15 wt% and sodium carbonate of 20-25 wt% (set approximately 6.5-7.5 as a pH adjusted value), and the natural organic acid is selected from citric acid, lactic acid and iron lactate.