Sludge is a by-product of urban sewage treatment. With the acceleration of urbanization, the amount of sewage is also increasing, and the output of sludge is also increasing. The sludge has a high moisture content and a large amount of toxic and harmful substances. If it is not handled properly, it will cause secondary pollution.
The traditional disposal methods of sludge include landfill, incineration, land use, etc., but their applications are limited due to the high moisture content of sludge. Therefore, reducing the moisture content of sludge is the key to solving the problem of sludge treatment. At present, in sludge treatment, polymer inorganic flocculant is usually added to flocculate and dewater the sludge, which can not only utilize the bridge flocculation of polymer, but also neutralize the negative charge on the sludge, so as to increase the cohesion of particles and improve the dewatering performance of sludge. In this paper, we will analyze the effect of using polyaluminum chloride (polyaluminum chloride) to improve sludge dewatering performance, and share with you the mechanism of polyaluminum chloride improving sludge dewatering performance.
Effect of polyaluminum chloride on the structure of sludge flocs: EPS, the extracellular polymer of sludge, is an important component of sludge flocs, which has a significant impact on sludge sedimentation, self flocculation, etc. The composition of EPS is very complex, but the protein is the most abundant. It was found that the protein content in the filtrate was increasing with the increase of the dosage of polyaluminum chloride. This may be because the cations generated from the hydrolysis of polyaluminum chloride are adsorbed on the surface of the sludge floc, which makes the EPS on the sludge surface continuously reduce and dissolve in water, thus increasing the protein content in the filtrate. The experimental results show that adding polyaluminum chloride (polyaluminum chloride) in the sludge treatment process can significantly improve the sludge dewatering performance, specifically:
(1) When the dosage of polyaluminum chloride is 0.136s/g, the filtering water content of filter cake is the lowest, which is 72.55%, while when the dosage is 0.149g/g, the turbidity of centrifugal supernatant is the lowest, which is 17NTU.
(2) Adding polyaluminum chloride can change the floc structure of sludge, make EPS on the surface of sludge fall off, and improve its dewatering performance, dewatering speed and settling performance.
(3) Aluminum ions released by polyaluminum chloride can neutralize the negative charge on the sludge particles, and improve the sludge flocculation and sedimentation performance through the macromolecule long chain adsorption bridge. In addition, adding excessive polyaluminum chloride will make the sludge particles positively charged, resulting in repulsion, which will make the sedimentation performance worse.
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