What are two types of aids used for filter backwashing?

The correct answer is based on the primary methods used to facilitate effective filter backwashing, which is essential in maintaining the efficiency and longevity of water treatment filters.

Air wash is one of the methods where air is introduced into the filter media. This process helps to loosen and remove trapped particulates, thus aiding in the backwashing by elevating any accumulated debris that needs to be expelled. Air washing is particularly beneficial because it can be performed quickly and does not require the use of chemicals or extensive manual labor.

Surface wash, on the other hand, involves using water sprays to clean the surface of the filter media. This is vital in removing any small particles that may clog the surface and inhibit the flow of water through the filter. Surface washing helps maintain the integrity of the filtration and ensures that the water treatment process remains efficient.

Together, these methods improve the overall performance of the filtration system by ensuring that the filter media is kept clean and effective in removing contaminants from the water. Other methods mentioned in the distractor options, like manual wash or chemical wash, may not be as widely recognized or integrated as common practices in filter backwashing compared to air wash and surface wash. This further supports the reason why the combination of air wash and surface wash is considered the best