Sustainability Through Biotechnology TM

Ennix “Fast-Rate" Facultative DigestionTM Process


The aerobic digestion process is a popular method for vector attraction reduction and disinfection of municipal wastewater treatment plant sludges.  The process is inherently stable, easy to operate, and meets EPA 503 Class B standards under ambient conditions provided that sufficient solids residence time is maintained.  A major disadvantage of the process is the large amount of energy needed to provide oxygen for bacteria, which grow on hydrolysis products of the sludge mass.  Energy is also needed for mixing, which is essential for efficient transfer of oxygen to the liquid and for keeping sludge flocs in suspension.


The Ennix “Fast-Rate" Facultative DigestionTM Process provides an alternative means of digester operation without aeration or mixing while achieving or exceeding the same performance goals as those of conventional aerobic digestion. 





Establishing the facultative microbiology requires an initial inoculation of the digester system with a select consortia of specialized bacteria and bio-chemicals necessary to initiate a favorable environment for facultative digestion.  The digester feed continues to be inoculated periodically to maintain the facultative environment.  Since oxygen transfer and mixing is not required for facultative digestion, aeration and mixing is discontinued. Digestion is carried out at ambient temperature. 

Two clearly defined zones are formed and maintained in the facultative digester cell- a sludge blanket and supernatant layer. Without aeration or mixing, the digester is operated in a full-time decant mode with available supernatant returned to the plant to accommodate daily digester feed. Given a normal range of solids concentration in WAS digester feed, 80% or more of WAS gallons wasted to the digester are returned to the plant as decanted supernate. Solids are retained in the digester until dewatering is needed to accommodate digester feed. Decanting of available supernate substaintially increases Sludge Retention Time (SRT) and leads to additional volatile solids reduction. Increased SRT and our consortia of specialized bacteria enhance biodegradation of biomolecules and complete the "Fast-Rate" digestion methodology.

Ennix Service Tech visiting a plant