Trickling filter

Trickling Filter is a type of wastewater treatment process, which is used for the removal of organic matter and ammonia from wastewater. It is one of the oldest and most common methods of secondary treatment in sewage treatment plants. The process involves the trickling of wastewater over a bed of media, creating a biofilm that absorbs and metabolizes organic pollutants.

Overview

A trickling filter consists of a fixed bed of rocks, gravel, slag, peat moss, ceramic media, or plastic media, over which sewage or other wastewater flows downward and causes a layer of microbial slime (biofilm) to grow, covering the bed of media. Air passes freely through the bed, promoting aerobic biological processes that decompose the organic load in the wastewater. This method of treatment is known for its simplicity and effectiveness in reducing organic content, suspended solids, and nitrogen compounds.

Components

The main components of a trickling filter include:

• Media: The material that provides a surface upon which biofilms develop. The effectiveness of the filter depends on the surface area, durability, and void space of the media.
• Distributor: A mechanism that evenly distributes the flow of wastewater over the surface of the filter media.
• Underdrain System: Collects the treated effluent from the bottom of the filter and allows air to circulate through the media.
• Recirculation System: In some designs, part of the treated effluent is mixed with incoming wastewater and recirculated over the filter to maintain optimal moisture and nutrient levels for the biofilm.

Process

The trickling filter process involves several steps: 1. Pre-treatment: Removal of large solids and grit from the wastewater before it is distributed over the filter media. 2. Distribution: Wastewater is evenly distributed over the surface of the filter media. 3. Biological Treatment: As the wastewater trickles down the media, microorganisms in the biofilm absorb and metabolize organic matter, converting it into carbon dioxide, water, and biomass. 4. Settling: The treated effluent is collected at the bottom and usually directed to a secondary clarifier where remaining suspended solids and biomass are settled out.

Advantages and Disadvantages

Advantages:

• Cost-effective for small to medium-sized plants.
• Simple to operate and maintain.
• Can handle fluctuating loads and toxic shocks better than some other biological processes.

Disadvantages:

• Requires a large land area for the filter beds.
• Can produce odors if not properly maintained.
• The efficiency can be affected by cold temperatures.

Applications

Trickling filters are used in various applications, including:

• Municipal sewage treatment plants.
• Industrial wastewater treatment, especially for organic-rich effluents.
• Preliminary treatment before more advanced processes.

See Also

• Activated sludge
• Biofilm
• Sewage treatment
• Wastewater treatment plant