How to choose a flocculant in wastewater treatment should be selected according to the characteristics of the wastewater in a specific industry, and at the same time, it also depends on where the flocculant is added and what purpose it is used for. Generally, when selecting inorganic flocculants, the composition and pH of wastewater should be considered, and then the most suitable one (iron salt, aluminum salt or iron aluminum salt, silicon aluminum salt, silicon iron salt, etc.) should be selected.
When choosing an organic flocculant (for example: polyacrylamide PAM), it mainly depends on whether to use anionic polyacrylamide, cationic polyacrylamide or non-ionic polyacrylamide. Anionic polyacrylamide is generally divided into weak anion, middle anion, and strong anion according to the degree of hydrolysis.
The selection of cations is generally used in sludge dewatering. The selection of cationic polyacrylamide is very important. Medium-strong cationic polyacrylamide is generally used in urban sewage treatment plants. Weak cations are generally used for sludge dewatering in paper and printing and dyeing plants, and medical wastewater is generally used. Choose strong cations and so on.
Each type of wastewater has its own unique characteristics. Non-ionic polyacrylamide is mainly used under weakly acidic conditions. Printing and dyeing plants use non-ionic PAM more.
The selection of all these flocculants must be determined based on experiments. In the experiment, first determine the approximate dosage, observe the flocculation sedimentation speed, calculate the treatment cost, and select economical and applicable flocculants.
Analyze the classification of flocculants from the charged type, charge density, molecular weight and molecular structure of flocculants, understand their general situation, understand the application of various flocculants more clearly, and have a clearer understanding of the selection of sewage flocculants ,
1. Charge type of flocculant
The electrification of the flocculant is selected according to the type of particles in the sewage. Generally speaking, the electrification of the flocculant should be selected as follows
in principle;
Use negatively charged flocculants to capture inorganic particles
Use positively charged flocculants to capture organic particles
Usually the method of experimentation can be used to accurately determine the charging type of the flocculant.
2. Flocculant charged charge distribution density (ion degree)
The density of the charged charge distribution of the flocculant represents the number of positive or negative charges that the flocculant needs to obtain the best flocculation effect when the amount of flocculant used is the least. The charge distribution density is related to the sludge type. The charge distribution density of municipal sludge is usually a function of the organic content in the sludge, and the organic content is usually related to the volatile content. The higher the volatile content, the higher the charge required. The flocculant.
3. Molecular weight
The choice of molecular weight depends on the type of equipment used in the dehydration treatment, and the molecular weight also indicates the length of the polymer chain. For centrifuge-type dehydration treatment equipment: the higher the molecular weight of the polymer, the better, because in the process of centrifugal dehydration treatment, the flocs will be subjected to a large shear force. For filter-type dehydration treatment equipment: choosing a flocculant with a low molecular weight to a medium molecular weight can meet the requirements, and at the same time, it can get a good water filter function.
4. Molecular structure
The choice of the molecular structure of the flocculant depends on the required dehydration performance. The molecular structure of cationic flocculant is divided into: linear structure, branched structure, cross-linked network structure
From the above aspects, it is not difficult to find that the choice of flocculant has a great regularity. As long as we carefully observe the regularity and summarize it in daily application, we find that each type of wastewater has its specific one. One or more flocculants can meet the flocculation or dehydration conditions of sewage treatment.