Normally, the flocculant can be divided into inorganic and organic flocculant. we should choose the right flocculant according to the characteristics of the wastewater.
Meanwhile, we should know which process the flocculant will be added to and what it is used for.
How to choose flocculant depends on the concentration of the colloid and suspended matter in the water.
If the pollutants show a colloidal state, we should choose an inorganic flocculant to make it destabilization and flocculation, if the floc is small, we need to add a high molecular flocculant or can be used in conjunction with activated silica gel as a coagulant aid.
It can obviously improve the effect of coagulation and expand the application range if the inorganic flocculant is used in concert with the organic flocculant. for high molecular, for the high molecular, the charge on the chain-shaped molecular is greater, the charge is higher and the chain can be extended fully, the effective range of absorption and bridging is also bigger, the flocculent effect is better.
we should consider the composition and PH value of the wastewater when choosing the inorganic flocculant and then choose the optimum model.
We should consider if it is anionic PAM or cationic PAM or nonionic PAM when choosing the organic flocculant. the anionic PAM can be divided into weak, medium, and strong anionic PAM according to the different hydrolysis degrees. the cationic PAM is mainly used for sludge dewatering, the selection test is very important, for municipal sewage treatment, we often use cationic PAM with medium or strong ionicity. the cationic PAM with weak ionicity often is used for the sludge dewatering of papermaking and dyeing plant.
The cationic PAM with strong ionicity often is used for medical wastewater treatment.
Choosing the right flocculant according to the following aspects:
1. The molecular structure
The molecular structure of the flocculant depends on the dewatering performance be required.
The structure of cationic flocculant is as follows:
linear structure: after choosing the right molecular weight, the dosage is small and the dewatering performance is better if we make the dewatering treatment using linear flocculant.
Dendritic structure: medium dosage, can obtain better dewatering performance.
cross-linked structure: big dosage but can get special water filtering and shear resistance performance
2. The molecular weight
The choice of molecular weight depends on the types of dewatering equipment, and the molecular weight has also said the length of the polymer chain.
For centrifuge equipment, the higher the molecular weight the better the application result, because in centrifugal dewatering engineering, floc will be subject to a large shear force.
For the filter type equipment, the lower molecular weight to the medium molecular weight flocculant meets the requirement, meanwhile, we can get a good water filtering performance.
3. Choosing the flocculant charged according to the type of particles in the wastewater.
In general, we will use the flocculant with negatively charged to capture the particle in inorganic sewage, treat organic particles with positively charged flocculant, of course, we have to confirm the best flocculant through simple test and practice on the machine.
4. Flocculant charge density (ionic degree)
That means the quantity that the flocculant will be positive charge or negative charge to get the best flocculent result if the case of minimum quantity. the charge density is related to the type of sludge, municipal sludge is often a function of the content of organic matter in the sludge, the organic content is related to the content of Volatile components. the higher the Volatile content, the higher charge of the flocculant we need.
Each kind of wastewater has its own unique characteristics, nonionic polyacrylamide is mainly used in acidic conditions, printing and dyeing mills often use nonionic PAM. We can only confirm the final model according to the selection test . we can confirm the economic and optimum flocculant according to the dosage, flocculent, and sedimentation result and the cost.
