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'''A Trickling Filter is a fixed bed, biological filter that operates under (mostly) aerobic conditions. Pre-settled wastewater is ‘trickled’ or sprayed over the filter. As the water migrates through the pores of the filter, organics are degraded by the biomass covering the filter material.'''
With time, the biomass will grow thick and the attached layer will be deprived of oxygen; it will enter an endogenous state, will lose its ability to stay attached and will slough off. High-rate loading conditions will also cause sloughing. The collected effluent should be clarified in a settling tank to remove any biomass that may have dislodged from the filter. The hydraulic and nutrient loading rate (i.e. how much wastewater can be applied to the filter) is determined based on the characteristics of the wastewater, the type of filter media, the ambient temperature, and the discharge requirements.
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{{procontable | pro=
- Can be operated at a range of organic and hydraulic loading rates. <br> - Small land area required compared to Constructed Wetlands. | con=
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<br>===Adequacy===
This technology can only be used following primary clarification since high solids loading will cause the filter to clog. A skilled operator is required to monitor and repair the filter and the pump in case of problems. A low-energy (gravity) trickling system can be designed, but in general, a continuous supply of power and wastewater is required.
Compared to other technologies (e.g. [[Waste Stabilization Pond|WSPs]]), trickling filters are compact, although they are still are best suited for peri-urban or large, rural settlements. Trickling Filters can be built in almost all environments, although special adaptations for cold climates are required.
===Health Aspects/Acceptance===
The odour and fly problems require that the filter be built away from homes and businesses. There must be appropriate measures taken for pre-treatment, effluent discharge and solids treatment, all of which can still pose health risks.
===Maintenance===
The sludge that accumulates on the filter must be periodically washed away to prevent clogging. High hydraulic loading rates can be used to flush the filter. The packing must be kept moist. This may be problematic at night when the water flow is reduced or when there are power failures.
===References===
* U.S. EPA (2000). [http://water.epa.gov/scitech/wastetech/upload/2002_06_28_mtb_trickling_filter.pdf Wastewater Technology Fact Sheet- Trickling Filters, 832-F-00-014]. US [http://www.epa.gov Environmental Protection Agency], Washington. Design summary including tips for trouble shooting.
* Tchobanoglous, G., Burton, FL. and Stensel, HD. (2003). [http://books.google.com/books/about/Wastewater_Engineering_Treatment_and_Reu.html?id=L1MAXTAkL-QC Wastewater Engineering: Treatment and Reuse, 4th Edition]. Metcalf & Eddy, New York. pp 890–930 . Detailed description and example calculations.
===Acknowledgements===
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