Upflow Anaerobic Sludge Blanket Reactor

The upflow anaerobic sludge blanket reactor, which was developed by Lettinga, van Velsen, and Hobma in 1979, is most commonly used among anaerobic bioreactors with over 500 installations

Upflow Biogas Reactors
Figure 3 Schematic diagram of various anaerobic wastewater treatment reactors. AR: anaerobic reactor; B/MS: biofilm/media separator; CZ: clarification zone; E: effluent; G: biogas; G/LS: gas-liquid separator; I: influent; RS: return sludge; SC: secondary clarifier; SZ: sludge zone; WS: waste slude.

treating a wide range of industrial wastewaters [4], The UASB is essentially a suspended-growth reactor with the fixed biomass process incorporated. Wastewater is directed to the bottom of the reactor where it is in contact with the active anaerobic sludge solids distributed over the sludge blanket. Conversion of organics into methane and carbon dioxide gas takes place in the sludge blanket. The sludge solids concentration in the sludge bed can be as high as 100,000 mg/L. A gas-liquid separator is usually incorporated to separate biogas, sludge, and liquid. The success of UASB is dependent on the ability of the gas-liquid separator to retain sludge solids in the system. Bad effluent quality occurs when the sludge flocs do not form granules or form granules that float.

The UASB can be used solely or as part of the soft drink wastewater treatment process. Soft drink wastewater containing COD of 1.1-30.7 g/L, TSS of 0.8-23.1 g/L, alkalinity of

Table 4 Operating Conditions of Common Anaerobic Reactors

Reactor type





Organic loading (kg COD/ m3-day)





COD removal (%)





HRT (hour)





Optimal temperature (°C)

30-35 (mesophilic)

49-55 (thermophilic)

Optimal pH


Optimal total alkalinity (mgCaCO3/L)


Optimal volatile acids (mg/L as acetic



AC, anaerobic contactor; UASB, upflow anaerobic sludge bed; AF, anaerobic filter; AFBR, anaerobic fluidized bed reactor. Source: Ref. 7.

AC, anaerobic contactor; UASB, upflow anaerobic sludge bed; AF, anaerobic filter; AFBR, anaerobic fluidized bed reactor. Source: Ref. 7.

1.25-1.93 g CaCO3/L, nitrogen of 0-0.05 gN/L and phosphate of 0.01-0.07 gP/L was treated by a 1.8 L UASB reactor [8]. The pH of wastewater was 4.3-13.0 and temperature was between 20 and 32°C. The highest organic loading reported was 16.5 kg COD m-3 day-1. A treatment efficiency of 82% was achieved.

The "Biothane" reactor is a patented UASB system developed by the Bioethane Corporation in the United States. Its industrial application in wastewater treatment systems was described by Zoutberg and Housley [9]. The wastewater mainly consists of waste sugar solution, product spillage, and wastewater from the production lines. The flow rate averages about 900 m /day with an average BOD and COD load of 2340 and 3510 kg/day, respectively. The soft drink factory was then producing 650x106 L of product annually, with three canning lines each capable of producing 2000 cans/min and three bottling lines each capable of filling 300 bottles/min. A flow diagram of the "Biothane" wastewater treatment plant is shown in Fig. 4. Monitoring of the plant could be performed on or off site. A supervisory control and data acquisition system (SCADA) was responsible for providing continuous monitoring of the process and onsite equipment. In normal operation, COD removal of 75-85% was reported with 0.35 m3 of biogas produced per kg COD.

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