2PAD™ Anaerobic Digestion System

Source: SUEZ

ID 2PADâ„¢ Two-phase Anaerobic Digestion System

Whether you are retrofitting an existing plant or building a new one, the 2PAD System is ready to take your sludge to a new class - Class A Biosolids.

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This unique two-phase anaerobic digestion system produces Class A Biosolids, which can be land - applied without restrictions in accordance with the EPA’s 40 CFR Part 503 regulations. Our innovative process separates the acid - and methane - forming digestion phases (acidogenesis and methanogenesis), increasing the efficiency of both and, combined with the high temperature, destroys the pathogens to below detectable limits. A two - year pilot study confirmed the effectiveness of the 2PAD System to meet EPA requirements for Class A Biosolids. In fact, the 2PAD System has been granted “PFRP Conditional National Equivalency” by the Environmental Protection Agency, as recommended by the Pathogen Equivalency Committee.


  • Raw sludge is heated as it passes through a heat recovery exchanger and then enters a thermophilic digester where it is held for two days and reaches a temperature of 55ºC, maximizing pathogen destruction.
  • The discharge goes through the heat recovery exchanger to cool the sludge, recover the heat, and partially heat the raw sludge.
  • The cooled sludge is pumped into a mesophilic digester for ten days, where volatile solids are destroyed and gas is produced.
  • The result is Class A Biosolids, which can be land - applied without restrictions.