COMPOUND FLOCCULANT AND SLUDGE TREATMENT METHOD USING THE SAME

PROBLEM TO BE SOLVED: To provide a compound flocculant produced from biomass raw materials, which is safe for animals and plants and does not cause environmental pollution, and to provide a sludge treatment method using the flocculant without using an aluminum salt which is a substance causing Alzheimer's disease nor an acrylamide polymer from which a carcinogenic substance is derived as a flocculant in the treatment of sludge from municipal wastewater and industrial wastewater. SOLUTION: Two types of substances derived from natural biomass raw materials; an alginic acid salt derived from Cryptophyceae and chitin-chitosan derived from shells of crab and shrimp; are used as a flocculant to be added to object water to be treated. A first combination of ammonium alginate with chitin-chitosan, which may be a fertilizer for soil, and a second combination of sodium alginate with chitin- chitosan are suggested as the compound flocculant. In order to heighten the flocculation efficiency, the deacetylation ratio of chitin-chitosan is controlled to be 80% or higher and the pH of alginic acid is controlled to be within 5-7 and then both flocculants are added as an aqueous weakly acidic solution to object water containing sludge. As a result, the flocculants are evenly dispersed in the object water and accelerate flocculation of the sludge.