BIOMAT

(1) (Hydraulics) A term used in subsoil hydraulics to describe a clogging layer of typically densely packed decaying organic matter which impedes the downward flow of water. (2) (Water Quality) A restrictive layer that develops beneath the distribution lines of the Soil Absorption System (SAS) of Septic Tanks at the gravel-soil or bed-soil interface. As the Septic Tank Effluent (STE) is not suitable for direct discharge into surface waters or onto land surfaces because of the presence of biodegradable organics and high bacterial content that may include Pathogens, the effluent typically undergoes further purification by three processes: absorption, filtration, and microbiological decomposition. The biomat constitutes a clogging mat, Anaerobic in nature, characterized as a black slimy layer, and composed of accumulated suspended solids, minerals, bacterial cells, microorganism fragments, polysaccharides, and polyuronides. The biomat is extremely active biologically and helps ensure the conditions for optimal treatment of the effluent by restricting the infiltration rate into the soil, inducing unsaturated soil conditions and reducing the chances of high dispersion below the system. Biomats are also highly effective in removing bacterial and pathogens from the STE and can also detain viruses that can be present in the effluent. Also referred to as Biocrust, Clogging Mat, and Clogging Zone.