Composite biological flocculant and preparation method thereof

The invention relates to the technical field of sewage treatment, in particular to a composite biological flocculant and a preparation method thereof.The composite biological flocculant is prepared from polyaluminum chloride, CaCl2 and a biopolymer, and the weight ratio of polyaluminum chloride to CaCl2 to biopolymer is (5-15): (15-30): (25-40). The preparation method of the composite biological flocculant comprises the steps that the polyaluminum chloride is added firstly, then the CaCl2 is added, and the biopolymer is added secondly; caCl2 and a biopolymer are sequentially added, and the biopolymer obtained by a biological fermentation method is compounded with a chemically synthesized flocculant/coagulant aid for use, so that the use amount of the chemical flocculant/coagulant aid is effectively reduced, and the harm to the environment and water caused by a large amount of residual chemical flocculant degradation products/monomers is reduced; as the biopolymer is produced by microbial metabolism, the probl