Biofilters

Biofilters are filtration systems that rely on living microorganisms to remove contaminants from air or water. They use a porous substrate that supports biofilm growth, enabling microbes to biodegrade or transform pollutants. Unlike passive physical filters, biofilters depend on biological activity to reduce substances such as organic matter, odors, ammonia, and certain volatile organic compounds.

In operation, microorganisms colonize the substrate, forming a biofilm where contaminants are metabolized. Aerobic biofilters use oxygen to break down organics into carbon dioxide and water, while specialized communities can perform nitrification and, under appropriate conditions, denitrification. Performance depends on surface area, contact time, moisture, temperature, pH, and oxygen supply.

Applications include wastewater treatment, aquaculture, and air purification. In wastewater systems, trickling filters and moving bed biofilm reactors rely on media that support thick biofilms. In aquariums, biofilters provide surfaces for nitrifying bacteria to oxidize ammonia to nitrite and nitrate. In building ventilation and odor control, biofilters degrade volatile compounds on a bed of organic media.

Advantages include energy efficiency, simplicity, and robustness across a range of pollutants. Limitations involve potential clogging, sensitivity to temperature and moisture, the need for maintenance to sustain the biofilm, and possible emission of odors if the system is poorly managed.

Design and operation vary by application, but core goals are adequate surface area, sufficient residence time, and proper environmental conditions to maintain a stable microbial community.