As an important part of urban domestic sewage, restaurant sewage has high oil content. Combined with the use of detergent, it makes the oil suspended in the wastewater, not easy to settle, but also makes the amount of COD in the water increase, which makes the treatment more difficult.

Chemical oxygen demand (COD) is an important index to measure the content of organic matter in water, and also an important index to measure whether the organic pollution and water discharge are up to the standard. At present, the methods of COD reduction include flocculation, electrolytic oxidation and so on.

The combination of inorganic flocculant polyferric sulfate and organic flocculant polyacrylamide can reduce the COD value to 73 mg / L and the COD removal rate to more than 90%. The operation conditions of the method are as follows: 500 ml water sample with pH = 9, 0.5 g PFS, 0.4 g polyacrylamide and 30 min sedimentation. The inorganic organic flocculant composed of poly ferric sulfate and polyacrylamide can reduce the dosage of flocculant, save the cost, and has good flocculation effect. The composite flocculant gives full play to the electric neutralization function of inorganic flocculant and the bridging function of organic polymer flocculant, so that its advantages can be brought into play together, and the formed flocs are large and dense. The addition of organic flocculant can improve the shear resistance, sedimentation rate and flocculation efficiency of flocs.