Gravity Filters:

Gravity filters are a type of water treatment filters that operate under the influence of gravity alone. These filters rely on the force of gravity to allow water to pass through the filter media and remove impurities. Among the given options, both slow sand filters and rapid sand filters are examples of gravity filters.

Slow Sand Filters:

Slow sand filters are a type of gravity filter used for water treatment. They consist of a bed of fine sand through which water is passed at a slow rate. The filter media in slow sand filters is typically 0.15 to 0.35 mm in size and is often layered with different sizes of sand to promote effective filtration. The process of filtration in slow sand filters involves physical straining, biological activity, and adsorption of impurities onto the filter media. Slow sand filters are known for their high efficiency in removing pathogens, turbidity, and organic matter from water.

Rapid Sand Filters:

Rapid sand filters are another type of gravity filter commonly used in water treatment plants. They are designed to remove suspended solids and turbidity from water at a higher flow rate compared to slow sand filters. Rapid sand filters typically consist of a layer of coarse sand, followed by a layer of fine sand, and sometimes an additional layer of anthracite coal or activated carbon. The filter is operated under gravity, allowing water to pass through the filter media and collect in the bottom of the filter bed. Rapid sand filters are efficient in removing particulate matter and improving water clarity.

Pressure Filters:

Unlike slow sand filters and rapid sand filters, pressure filters do not operate under the influence of gravity alone. Pressure filters use pressure to force water through the filter media, rather than relying on the force of gravity. The pressure can be created using a pump or by placing the filter media in a pressurized vessel. Pressure filters are commonly used in applications where a higher flow rate is required or where there is limited space for a gravity filter system.

Conclusion:

In conclusion, both slow sand filters and rapid sand filters are examples of gravity filters. These filters operate under the influence of gravity alone and rely on the force of gravity to allow water to pass through the filter media. Pressure filters, on the other hand, do not operate under gravity and use pressure to force water through the filter media.