Chapter 9 mainly introduces the selection and preparation methods of coagulants or flocculants. First, explain the purpose and content of chemical treatment, covering aspects such as alkalinity, pH value, turbidity, color, temperature, hardness, as well as taste and odor. Next, let’s discuss the issue of residual aluminum in water bodies. Then, the beaker coagulation experiment will be explained, including the selection of beaker experimental instruments, the determination of the beaker coagulation test, the selection of the final treatment process, and the evaluation of coagulants. Finally, explain the preparation, measurement and addition of the liquid medicine, as well as the relevant content of the liquid medicine preparation.