IC (Internal Circulation) anaerobic reactor can, through its internal circulation, use the produced gas to agitate the sludge blanket. Therefore, the reactor can prolong sludge retention time to hundreds of days while at the same time shorten hydraulic retention time to a few hours. IC anaerobic reactors must be used with caution when dealing with wastewater that cannot form granular sludge because of calcification and high salinity.
Water is pumped into the bottom of the reactor where it enters an efficient water distribution system and is then mixed with anaerobic granular sludge in the reactor. In the lower part of the reactor, namely the main processing zone, most organics are converted to methane and carbon dioxide. Biogas is collected by the lower part of the three-phase separator, producing gas lift power to push water through up-flow column into gas-liquid separator on the top of the reactor. Biogas is separated in the separator while water flows back to the bottom of the reactor. Hence the name Internal Circulation reactor. In the second section of the reactor, namely the upper part, wastewater is further treated. In this part, the produced biogas is collected by the three-phase separator and clean water is discharged from the top of the reactor. An IC reactor is a vertical tank with a height ranging from 16 meters to 28 meters and a diameter ranging from 2.2 meters to 20 meters.