The advent of plastic media has made trickling filters up to three times more effective for treating sewage or waste water that has high content of pollutants. These pollutants are usually organic matter, Suspended Solids (SS), and Biochemical Oxygen Demand (BOD).
The treatment aims to alleviate the BOD and SS levels such that the resultant levels become acceptable. Reductions of over 95% in BOD ammonia are now possible via trickling filters due to which it has become a viable solution in several situations.
A primary advantage of this old and well established solution, as compared to other treatment solutions, is its quite low power requirements. According to the 2011’s Global Water Research Coalition, trickling filters consume the lowest energy as compared to any secondary processes in the pyramid of wastewater treatment procedure.
This power pack benefit with the simplicity of operation as well as the strength to handle variable loadings make trickling filters more effective than other treatment technologies.
A Trickling Filter (TF) is also known by other names: Trickling bio-filter, biological filter, bio-filter, intermittent filter, percolating filter, alternative septic system, roughing filter, and attached growth processes.
Technically, it is a wastewater treatment technique that works by biodegrading organic matter and also aims to achieve nitrification. In this process, the microorganisms that are in charge of digestion are added to an inert filter material.
This material is a fixed bed of rock, slag, plastic filter media, polyurethane foam, sand, gravel, and/or a variety of plastic and other synthetic materials. Over this material, wastewater flows downward to form a microbial slime layer, covering the media bed.
In simply words, the pollutant removal process here involves both absorption &exclusion of organic materials via a microbial bio-film layer. The packing media is usually the one that offers a high surface area to volume.
A trickling filter holds a cylindrical tank and a high surface area material. The high specific surface offers a big region for creating a biofilm. Organisms growing in this slim biofilm over the media surface oxidize the organic content in the wastewater.
This chemical reaction emits carbon dioxide and water, and also forms new biomass at the same time. It occurs chiefly in the external region of the slime layer having a thickness of usually 0.1 to 0.2 mm.
The incoming pre-processed wastewater trickles via the bed or over the filter by using a rotating sprinkler. It is continuously distributed from above the media bed via a rotating sprinkler.
In the waste water, the microorganisms attach themselves to the filter media or bed, which is enclosed with bacteria. The bacteria oxidize the organic waste and emit pollutants out of it.
Proper aerobicconditions are sustained by splattering, diffusing, and either by natural air convection in case of porous filter medium or forced air via the bed. Diffusion of wastewater over the media supplies oxygen for oxidation of the organic compounds by the slime layer and emits carbon dioxide, water, and some more end products.
With the thickening of the slime layer, it becomes tougher for the air to enter into the layer. This results in an internal anaerobic layer. This slime layer keeps on developing until it sloughs off to form theprocessed effluent as a sludge requiring successive removal and disposal.
Usually, a sedimentation tank or clarifier trails a trickling filter for separating and removing the muddling/sloughing. Unlike the tricking filters, other filters implementing higher-density media such as peat moss, foam, and sand do not result in a removal sludge but need forced air blowers and a walled anaerobic environment.
When too many nutrients became an issue, it became essential to adapt to the traditional sewage treatment techniques for fulfilling the increased demand for oxygen for waste water effluents having high ammonia nitrogen quantities. TFsproved themselves efficient by oxidizing the quantities into nitrate nitrogen (nitrification).
This technology aims at removing dissolved organic solids, suspended solids, suspended organic solids, and nutrients. Keeping this in mind, the technology is considered feasible for upgrading sewage for vital tasks such as irrigation usage and upgrading sewage to approximatefiltered standards so that it can be made available for human consumption.
Trickling filters are split into different types, depending upon the various criteria listed below.
These trickling filters are used to treat small individual, rural, or residential sewage, industrial waste, and even municipal sewage by using them in large centralized systems.
A low-rate trickling filter is simple and generates effluent discharge with a stable quality. There is no recirculation of wastewater and only the top filter media portion are filled with the biological slime. The lower region is filled with the nitrifying bacteria for oxidizing ammonia to nitrite and then nitrate.
With proper loadings, a low-rate filter removesup to 85% of the applied organic matter. On the other hand, high-rate filters have higher organic loadings.
Recirculation is required for boosting the filter’s efficiency, wherein the filter effluent is reapplied onto the filter. This ensures more contact of the waste with the microorganisms in terms of time and aids to “seed” the lower filter portionwith active organisms.
Below are some really admirable advantages of using TFs.