Metabolic Uncoupling: Biomass Control Strategy in Microbial Processes

Microbial processes have been extensively used in engineered systems, esp. wastewater treatment, in situ bioremediation and most recently for biofuel production. While excess biomass may be desirable in some processes, it is detrimental to other systems including Activated Sludge Process (ASP), biofilters and subsurface bioremediation schemes, where uncontrolled microbial growth leads to increased cost, diminished efficiency and in extreme cases, process failure [1]. It has been reported by several researchers that a certain class of chemicals termed protonophores may be strategically employed to uncouple microbial metabolism. These lipophilic weak acids partially uncouple the catabolism from anabolism which leads to reduced growth yield, while maintaining the substrate utilization rate. This effectively leads to a control on biomass growth without decreasing the substrate consumption. This strategy has been beneficially employed in wastewater treatment to reduce the sludge quantity, without adversely affecting the treatment efficiency and sludge characteristics. Several chemicals have been studied to purposefully induce the uncoupling conditions in ASPs, including antibiotics and aromatic compounds. The more commonly tested uncouplers include 3, 3’, 4’, 5-tetrachlorosalicylanilide (TCS); 2, 4-dinitrophenol (DNP); pentachlorophenol (PCP); carbonyl cyanide m-chlorophenylhydrazone (CCCP); carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP); 2, 4, 6-trichlorophenol (TCP); rotenone; antimycin, etc. [2].