A trickling filter removes pollutants from wastewater by filtration, adsorption, and assimilation. To provide time for treatment, wastewater should flow in a thin layer over the medium. The medium acts as a substrate for the growth of a biological film, which is nourished by the nutrients in the wastewater. Biological oxidation reduces the BOD (biochemical oxygen demand) to levels that are no longer harmful. Biologically active particles absorbed on the surface of the medium or trapped within it serve as catalysts for chemical reactions. This type of treatment is commonly used for water pollution control.
Trickling filters consist of large tanks with an even bed of gravel, rock, or other porous material at the bottom. The tank is filled with water up to a certain level. Wastewater flows through the gravel where any impurities are removed by sedimentation before flowing into an underlying body of water. Trickling filters are relatively easy to maintain and inexpensive to operate. They can also treat relatively high volumes of water efficiently.
The treated water flows out of the top of the tank and into a channel leading to the next stage of treatment or disposal. For effective operation, the medium in the tank must be replaced periodically. This prevents clogging of the gravel bed and ensures even distribution of bacteria throughout the unit. A new medium should be added once the original medium is more than half full.
As the medium becomes saturated it needs replacing too.
To remove organic materials from wastewater, trickling filters (TFs) are utilized. The TF is an aerobic treatment system that removes organic materials from wastewater by using microorganisms attached to a medium. Suspended-growth procedures, on the other hand, are systems in which microorganisms are kept alive in a liquid. They require continuous agitation or suspension to remain active. Some examples of suspended-growth procedures include activated sludge systems and fluidized beds.
In a TF, waste water flows through layers of media: one layer of gravel with holes in it for water to pass through (this is called the "media") and another layer of sand or crushed stone. As the water passes through these layers, oxygen from the air helps bacteria grow and decompose any pollutants in the water. Only clean water comes out at the end of the process. Any contaminants such as chemicals, drugs, or people waste that cannot be decomposed by bacteria remain in the TF.
Trickling filters can be built into homes to treat household sewage, or they can be placed in industrial buildings to treat wastewater from factories and businesses.
Household TFs use ceramic plates or baskets filled with gravel or rock as filtering media. These structures allow water to flow through them, while trapping particles larger than 2mm. The key to a successful TF is selecting an appropriate size range of media to optimize treatment efficiency while keeping maintenance costs low.
Modest home septic tank outputs and extremely small rural sewage treatment systems can be treated using single trickling filters. Many trickling filters are often used in tandem in larger centralized sewage treatment plants. They provide most of the treatment required for household recycling.
A trickling filter functions by allowing water to pass through a bed of gravel or other porous material that has been saturated with wastewater. As the water passes through the filter, it flows into an adjacent basin where any particles not removed by the filter will settle out. The filtered water can then be released into your local environment as normal.
Trickling filters were originally developed as a cost-effective method for treating low volumes of wastewater for reuse on agricultural land. However, they have many applications in large-scale sewage treatment facilities as well. These include applications where removing chemicals from the water is important such as for industrial processes or when trying to achieve certain levels of specific pollutants.
Trickling filters are commonly made from polyethylene terephthalate (PET) plastic because this material is resistant to both organic contaminants and high temperatures. It can also be easily cleaned and repaired if needed. However, other materials such as ceramics and wood are also used depending on the application.