Commonly used treatment methods are biological and physicalchemical methods. In both cases, biological methods are morecommon and more efficient.
Flocculants can be used in various stages of biologicaltreatment,such as in primary and secondary settling tanks and concentrators.However, the most important application area forflocculants is to help and promote sludge dewatering.
When the sludge is dewatered,the flocculant causes the sludgeto produce large and dense flocs which can be separated fromthe clear liquid by a centrifuge,belt or plate and frame filterpress.
The selection of flocculants is one of the keys to success, When choosing a type of flocculant, consider the followingfactors:
1. Know to the user the source, nature, composition (such as theratio of organic/inorganic matter) and solid content of the sludgeGenerally speaking, cationic flocculant is used to treat organicsludge, while anionic flocculant is used to treat inorganic sludge, cationic flocculant should not be used when the alkali is strong.and anionic flocculant should not be used when the acidity isstrong, the solid content is high. The sludge usually has a largeamount of flocculant.
2. the size of the floc: the floc is too small will affect the drainagespeed, too large will make the floc bind more water and reduce the degree of mud biscuits. The floc size can be adjusted by selecting the molecular weight of the flocculant.
3. lonicity of flocculant: For the sludge to be dehydrated, the flocculant with different ionicity is used for screening in the laboratory, and the most suitable one is selected. This wilachieve the best flocculation effect and minimize the amount ofdosing.
4. Floc strength: The floc should be stable and not broken undershearing action. Increase the molecular weight of the flocculantor choose the appropriate molecular structureHelps improve the stability of the floc.
5. Mixing of flocculant and sludge: The flocculant must react fully with the sludge at a certain position of the dewatering equipment to cause flocculation. For this reason, the viscosity of the flocculant solution must be appropriate to allow uniform mixing with the sludge under existing equipment conditions. The uniformity of the two is another key factor for success. The viscosity of the flocculant solution is related to its molecular weight and formulation concentration.
6. Dissolution of flocculant: good dissolution can fully exertflocculation. Sometimes it is necessary to speed up the dissolution rate. In this case, it is considered to increase the concentration of the flocculant solution (the higher the concentration, the faster the dissolution rate), the use of anemulsion flocculant, or an appropriate increase in watert emperature.
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BIOLOGICAL METHOD
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PHYSICAL CHEMISTRY
