Centrifugal Sludge Thickening Process

Sludge that comes out from clarifier or sedimentation tanks can have varying solid contents depending on efficiency and control of the whole wastewater operation. Generally the higher the liquid percentage, the less desirable it is because wet sludge is harder to handle and when it comes to subsequent wastewater processes like drying and digestion, it will mean more energy consumption.

In other words, higher energy is required for heating to bring up to certain temperature during digestion process, longer time needed to dry the sludge and further to that, it will also incur additional cost factor when it comes to transportation to move the sludge for disposal and further processing. Dry sludge with lower volume will definitely save the number of trips required to move it between one location to another. Other than that, it will also mean less tank space required for holding and storage. Therefore, Sludge Thickening Process is always looked upon as a cost effective related method that is used to remove more liquid content in order to increase the solid fraction.

Sludge thickening using centrifugal force is one of the common processes that can be applied to reduce the water content and thus thickens the sludge. There are basically two different types of centrifuge designed for the application and both methods rely on the same principal to separate out the liquid and solid content. First is the "solid bowl centrifuge", which is placed horizontally and during the operation, wastewater wet sludge will be continuously fed into the unit. The moving shaft actually has a set of helical scrolls, which will act to push the solid waste towards the other end, far away from the liquid moving towards another direction. As solid content starts to collect and buildup, soon enough the accumulated sludge will become just too heavy and then drops down to a collection bin.

Unlike the solid bowl centrifuge, which is based on continuous operation, the "imperforate basket" is a batch process, which will need operators' intervention to handle and remove accumulated sludge. Compared to solid bowl which has a helical scroll that automatically push and separate out the sludge, solid buildup that accumulates on the vertical surface of the imperforate basket will accumulate there until it reaches a certain holding capacity before the bowl decelerates. During this, a scraper can be used to remove out the sludge inside it before everything goes back to normal operation. For both methods, in order to achieve good separation, usually polymers can be mixed into the wet sludge prior to feeding into the centrifugal sludge thickening unit.

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