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Biofiltration is a pollution control technique using a bioreactor containing living material to capture and biologically degrade pollutants. Common uses include processing waste water, capturing harmful chemicals or silt from surface runoff, and microbiotic oxidation of contaminants in air. Industrial biofiltration can be classified as the process of utilizing biological oxidation to remove volatile organic compounds, odors, and hydrocarbons.

A biofilter is a bed of media on which microorganisms attach and grow to form a biological layer called biofilm. Biofiltration is thus usually referred to as a fixed–film process. Generally, the biofilm is formed by a community of different microorganisms (bacteria, fungi, yeast, etc.), macro-organisms (protozoa, worms, insect's larvae, etc.) and extracellular polymeric substances (EPS) (Flemming and Wingender, 2010). Air or water flows through a media bed and any suspended compounds are transferred into a surface biofilm where microorganisms are held to degrade pollutants. The aspect of the biofilm is usually slimy and muddy.

Microorganisms' activity is a key-factor of the process performance. The main influencing factors are the water composition, the biofilter hydraulic loading, the type of media, the feeding strategy (percolation or submerged media), the age of the biofilm, temperature, aeration, etc. Microbial activities in biofiltration are challenging to generalize since the influent characteristics and filtration rates can change target pollutant removal efficiency.

The mechanisms by which certain microorganisms can attach and colonize on the surface of filter media of a biofilter can be via transportation, initial adhesion, firm attachment, and colonization [Van Loosdrecht et al., 1990]. The transportation of microorganisms to the surface of the filter media is further controlled by four main processes of diffusion (Brownian motion), convection, sedimentation, and active mobility of the microorganisms. The overall filtration process consists of microorganism attachment, substrate utilization which causes biomass growth, to biomass detachment [Chaudhary, 2003]

Typically in drinking water treatment; granular activated carbon or sand filters are used to prevent re-growth of microorganisms in water distribution pipes by reducing levels of iron and nitrate that act as a microbial nutrient. GAC also reduces chlorine demand and other disinfection by-product accumulation by acting as a first line of disinfection. Bacteria attached to filter media as a biofilm oxidize organic material as both an energy and carbon source, this prevents undesired bacteria from using these sources which can reduce water odors and tastes [Bouwer, 1998]. These biological treatment systems effectively reduce water-borne diseases, dissolved organic carbon, turbidity and color in surface water, thus improving overall water quality.

In anaerobic wastewater treatment facilities, biogas is fed through a bio-scrubber and “scrubbed” with activated sludge liquid from an aeration tank. [Removal of hydrogen sulfide from an anaerobic biogas using a bio-scrubber - ScienceDirect] Most commonly found in wastewater treatment is the trickling filter process (TFs) [Chaudhary, 2003]. Trickling filters are an aerobic treatment that uses microorganisms on attached medium to remove organic matter from wastewater.

In primary wastewater treatment, biofiltration is used to control levels of biochemical oxygen, demand, chemical oxygen demand, and suspended solids. In tertiary treatment processes, biofiltration is used to control levels of organic carbon [ Carlson, 1998].

Bibliography:

Biofilter Bags SE-14. (2012). California Stormwater BMP Handbook, 1–3. Retrieved from https://www.cityofventura.ca.gov/DocumentCenter/View/13163/CASQA-Guidance-SE-14-Biofilter-Bags.

Bouwer, E. J. and Crowe, P. B., “Biological Processes in Drinking Water Treatment,” J. AWWA, 80(9), 82 (1988).

Chaudhary, D. S., Vigneswaran, S., Ngo, H.-H., Shim, W. G., & Moon, H. (n.d.). Biofilter in water and wastewater treatment - korean journal of chemical engineering. SpringerLink. Retrieved from https://link.springer.com/article/10.1007/BF02706936

Carlson, K. H. and Amy, G. L., “BOM Removal during Biofiltraiton,” J. AWWA, 90(12), 42 (1998)

la Pagans, E., Font, X., & Sánchez, A. (2005). Biofiltration for ammonia removal from composting exhaust gases. Chemical Engineering Journal, 113(2-3), 105-110.

Nishimura, S., & Yoda, M. (1998, July 24). Removal of hydrogen sulfide from an anaerobic biogas using a bio-scrubber. Water Science and Technology. Retrieved from https://www.sciencedirect.com/science/article/abs/pii/S0273122397005428

van Loosdrecht MC, Lyklema J, Norde W, Zehnder AJ. Influence of interfaces on microbial activity. Microbiol Rev. 1990 Mar;54(1):75-87. doi: 10.1128/mr.54.1.75-87.1990. PMID: 2181260; PMCID: PMC372760.