PURPOSE: To flocculate the protein existing in a dissolved or suspended state effectively by controlling the pH of the liquid wherein the protein exists, the adding carragenein mixed with sodium salts, etc. to this.

CONSTITUTION: Waste liquid which is discharged from processing stages for cattle meat, fish meat, viscera, etc. and in which protein exists in a soln. state or suspended state is controlled to (4.0W5.0)pH by an acid addition or CO2 blowing method. Carrageenin or a mixture of carrageenin and sodium aluginate which is mixed with ≥1 kind of sodium salts such as sodium chloride and calcium salts such as calcium primary phosphate is added as a flocculating agent to this liquid. The protein existing the dissolved or suspended state in the liquid is flocculated by this, and the flocs settle down. The flocculating agent is used at about (0.1W1.0) part based on 100pts.wt. the luquid.