Media Filtrasi : Sand Filter, Carbon Filter dan Iron Filter

The process of reducing the Total Suspended Solids (TSS) content in water by coagulation-flocculation-sedimentation is often not enough.

Especially when the desired outlet TSS content is less than 10 mg/l, while there are still TSS particles that are not deposited in the clarifier so that the TSS is still high. Then further treatment is needed, namely Filtration. There are 2 types of filtration, namely media filters that use media beds in the vessel and ultrafiltration which uses a membrane.

What is Filter Media

In this article, we will discuss about Media Filters. Media filters in general can filter particles measuring 5-10 microns (visible particle size > 40 microns). The water flow in the filter media is from top to bottom (downflow) through the inlet flow distributor so that it is evenly distributed to the surface of the media. At the bottom of the media there is a strainer with a certain slot size that is installed evenly so that clean water that has passed through the media can flow out.

Flow Drivers

Based on the flow driver, there are filter media that use gravity and some are pressurized. Gravity media filters are usually used for water treatment plants with very large capacities such as in communal IPAs and using civil / concrete buildings. While pressurized media filters are commonly used for industrial and household scales using pressure vessels made of FRP or steel material.

Types of Media

Based on the type of media, media filters are divided into sand filters, activated carbon filters and iron filters. Sand filter (SF) uses silica sand and gravel media, aiming to capture TSS and turbidity. Activated carbon filter (ACF) uses activated carbon media, aiming to capture organic substances, colors and odors. Iron filter (IF) uses Manganese Greensand media to capture iron and / or manganese content.

Then how to determine the size of the Filter Media? In general, the hydraulic loading rate (HLR) or linear velocity (LV) of filter media is 10-25 m³ / (m².hour) or 10-25 m / hour. For example, for a river water flowrate of 100 m³/h and LV of 18 m/h, the required filter area = 100/18 = 5.55m², since the filter is cylindrical, the filter diameter = 2700 mm.

But of course HLR or LV is not the only determinant of filter size. For activated carbon filters we must consider the empty bed contact time (EBCT) first. EBCT is the minimum contact time required for water in activated carbon media so that the process of adsorption of impurities into carbon pores can take place optimally. Usually the EBCT range is 6 - 20 minutes. So for a flowrate of 100 m3 / h, EBCT 6 minutes, the required carbon volume = (100 / 60) x 6 = 10m³. If the maximum bed depth of the media is 1.5m, then the diameter of the ACF = 2900 mm.

Conclusion

Can the filter media be used continuously? When impurities have accumulated in the filter media marked by a pressure drop of almost 1 bar, it is time to backwash, which is by flowing water from bottom to top and sometimes must be assisted by scouring with air, especially for sand filters because this media is quite heavy. In order not to backwash too often, try to limit the water entering the filter to a maximum load of 50 mg/l TSS content. More than that, it is certain that the filter media will often 'block'. If you have any questions about Filter Media, please contact our engineering team. Hopefully useful, see you in our next article.