Views:2 Author:Ryde Environment Publish Time: 2019-05-21 Origin:Ryde Environment
Sludge Conditioners, also known as dehydrating agents, can be divided into inorganic conditioners and organic conditioners.
Inorganic conditioners are generally suitable for vacuum filtration and plate-frame filtration of sludge, while organic conditioners are suitable for centrifugal, belt filter press and multi disc screw press.
There are two kinds of inorganic conditioners, iron salt and aluminium salt, which are effective, cheap and commonly used. Ferric salt conditioners mainly include ferric chloride, ferric sulfate, ferrous sulfate and polyferric sulfate. Aluminum salt conditioners mainly include aluminium sulfate, aluminium trichloride, basic aluminium chloride, polyaluminium chloride and so on.
After adding inorganic conditioner, the sludge concentration process can be greatly accelerated and the effect of filtration and dewatering can be improved. Moreover, the combination of iron salt and lime can further improve the conditioning effect. The shortcomings of inorganic conditioning agent are large dosage. Generally speaking, the dosage of inorganic conditioning agent should reach 5%-20% of the dry solid weight of sludge, which leads to the increase of filter cake volume. Secondly, inorganic conditioning agent itself is corrosive (especially iron salt), and the feeding system should have anticorrosive performance. It should be noted that when ferric chloride is used as conditioning agent, it will increase the corrosiveness of metal components of dewatering sludge treatment equipment, so the anti-corrosion grade of equipped dewatering sludge treatment equipment should be improved appropriately.
There are many kinds of organic synthetic macromolecule conditioners, which can be divided into low degree of polymerization (molecular weight is about 10-tens of thousands) and high degree of polymerization (molecular weight is about hundreds of thousands-millions); according to ionic type, they can be divided into cationic type, anionic type, non-ionic type, anionic and cationic type, etc. Compared with inorganic conditioning agent, organic conditioning agent dosage is less, generally 0.1%-0.5% of the dry solid weight of sludge, and there is no corrosiveness.
Organic conditioners used for sludge conditioning are mainly high degree of polymerization of polyacrylamide series of flocculants products, mainly cationic polyacrylamide, anionic polyacrylamide and non-ionic polyacrylamide. Among them, cationic polyacrylamide can neutralize the negative charges on the surface of sludge particles and bridge the particles, which shows strong cohesion and remarkable conditioning effect, but the cost is higher. In order to reduce the cost, the cheaper anionic polyacrylamide-lime combination method can be used. The negative charged flocculant and sludge particles can be adsorbed together by positive charged Ca(OH)2 flocs to form a composite coagulation system.
There is no fixed standard for the consumption of chemicals in sludge conditioning. According to the specific properties of sludge, such as sludge species, digestibility, solid concentration and so on, the dosage will be different. Therefore, the types and dosage of conditioners are mostly determined by laboratory or field direct tests.
Generally speaking, according to the percentage of dry solid weight of sludge, the dosage of ferric chloride is 5%-10%, ferrous sulfate is 10%-15%, lime is 20%-40%, polyaluminium chloride and polyferric sulfate are 1%-3%, cationic polyacrylamide is 0.1%-0.3%. According to relevant information, because the price of commonly used polyacrylamide series organic synthetic polymer conditioners is more expensive (some varieties are more than ten or twenty times of ordinary inorganic conditioners), although their dosage is less, but the cost of using organic synthetic polymer conditioners is still higher when the cost of conditioning per ton of sludge is reduced. It is a common practice to select inorganic conditioning agent. When inorganic conditioning agent has poor effect and is difficult to achieve ideal conditioning effect, the use of organic synthetic polymer conditioning agent or the combination of inorganic and organic conditioning agent should be considered.
Usually, Sludge Conditioner are in a solid state to facilitate transportation and sales. In use, it is necessary to dissolve the solid sludge conditioner into a certain concentration of viscous water solution.
The function of Polymer preparation unit is to make the powder or liquid sludge conditioner dissolve or dilute into sludge conditioner solution. It is usually divided into manual dosing device and the integrated of dosing device. The integrated of dosing device is fully automatic operating including automatic dosing, dissolving and feeding.