Most people relate Biofilm bacteria as something nasty and harmful. This is understandable as we normally come across Biofilm bacteria attached to shower heads, pipes, kitchen sinks or chillers at home or public places. Here Biofilm bacteria can cause corrosion, fouling or even lead to legionella growth. In the last few years public media discovered a high public interest for the dangers of biofilm bacteria as the following headlines show.
However for treatment of waste water Biofilm bacteria is very beneficial and essential.
Water contains free floating microorganisms. When the microorganisms attach to a surface the biofilm growth is initiated. Van der Waals forces and hydrophobic characteristics of the bacteria or the media surface can improve the attachment process. After colonization has started the Biofilm bacteria grow through cell division and other free floating microorganisms that anchor to the first bacteria colonists.
Waste water treatment plants use biofilm bacteria to remove BOD and Nitrogen. BOD describes the total amount of dissolved oxygen needed to convert organic waste. Bacteria will decompose the organic waste to solids which can be settled down as sludge. Whereas bacteria for BOD removal are easy to cultivate bacteria for nitrogen removal are more difficult and need certain conditions. Conditions for Nitrifying biofilm bacteria are for example high amounts of dissolved oxygen and nitrogen, a pH value between 7 and 8 as well as a water temperature between 5 and 40 degree Celsius. Nitrifying bacteria have a long life time and double only every 20 hours under good conditions. (As a comparison most bacteria double every 30 minutes) Therefore it takes about 4 weeks until a stable nitrifying biofilm is formed and attached to a surface. As more surface for attached biofilm growth is available as more BOD and nitrogen in waste water can be treated. To significantly increase surface area different types of plastic fill media either fixed or free floating are used in waste water treatment plants. Plastic fill media as provided by AET consists of corrugated foils that are bonded together.
Depending on the application plastic fill media can provide up to 200m2 surface area per one m3 of tank volume!
Organic nitrogen converts into gaseous ammonia (NH3) in waste water. At a Ph value between 7 and 8 – as usual for municipal waste water – almost all gaseous ammonia will be found in the ionic form ammonium (NH4+). In the nitrification process nitrifying bacteria facilitate the oxidation of ammonium (NH4+) first to nitrite (NO2) followed by the oxidation of nitrite to nitrate (NO3).
Nitrate is still toxic and contained in the waste water. Therefore another step has to be taken to convert ammonium into a harmless substrate. Heterotrophic bacteria will denitrify Nitrate (NO3) into Nitrogen Gas (N2). (Click here for more information on Denitrification)
AET can provide Biofilm product systems and engineering support. In case you would like to receive more information on this topic or need support with the design of a plastic fill media application please use the link below to contact us. www.aqua-equip.com