UpFlow Anaerobic Sludge Blanket Reactor

The up-flow anaerobic sludge blanket (UASB) reactor was developed by Lettinga, van Velsen, and Hobma in 1979.27 It is simple in design and is a combination of physical and biological processes.27,28 It can be categorized under suspended growth systems.28 The wastewater flow to be treated is sent upward from the bottom of the reactor. At the bottom of the reactor, wastewater contacts with the active anaerobic sludge solids distributed over the sludge blanket. The sludge blanket contains granules of microorganisms (0.5-2 mm in diameter). If maintained under the proper conditions (e.g., proper mechanical agitation), the good flocculation/settling characteristics of these granules do not allow them to wash out from the reactor.27,28 The sludge solids concentration in the sludge blanket can be as high as 100,000 mg/L. At the sludge blanket, organics convert into methane and carbon dioxide following the steps explained in Section 30.5.1.21 The mixture of the above two gases is separated from the sludge at the "three-phase separator" located at the top of the reactor. The success of the UASB reactor is dependent on the ability of the three-phase separator to retain sludge solids in the system. Bad effluent quality occurs if the sludge flocs do not form granules or form granules that float.21,28 A schematic diagram of the UASB reactor is shown in Figure 30.4.

Effluent

Effluent

Sludge blanket

Sludge blanket

Influent

Influent

FIGURE 30.4 UASB reactor.

Miranda et al.29 reported the performance of a full-scale UASB reactor. Target wastewaters for their work were effluents from a meat packing plant and a pig and cattle slaughterhouse. The volume of the UASB reactor was 800 m3. The high O&G content was reduced using coagulation-flocculation pretreatment and subsequently the wastewater flow was sent through the UASB reactor. This kind of pretreatment reduced sludge washout and the performance of the UASB reactor improved. A COD removal of 70-92% and a maximum organic loading of 2.43 kg COD/(m3 d) were achieved. In another study conducted by El-Gohary et al.,30 the laboratory-scale UASB reactor was studied for the treatment of wastewater from a potato-chips factory. A BOD reduction of 86% and a COD reduction of 82% were reported. The corresponding HRT and organic loading rate were 18 h and 2.9 kg BOD/(m3 d), respectively. Soft drink wastewater containing COD 1.130.7 g/L, TSS 0.8-23.1 g/L, alkalinity 1.25-1.93 g CaCO3/L, nitrogen 0-0.05 g N/L, and phosphate 0.01-0.07 g P/L was treated by a 1.8 L UASB reactor.31 The pH of wastewater was 4.3-13.0 and the temperature was between 20°C and 32°C. The highest organic loading reported was 16.5 kg COD/m3 d. A treatment efficiency of 82% was achieved. Housley et al.32 have reported on the industrial application of the "Biothane" reactor (a patented UASB system) in order to treat wastewater from a soft drink factory. The average flow rate, BOD, and COD of the wastewater were 900 m3/d, 2340 kg/d, and 3510 kg/d, respectively. A supervisory control and data acquisition system (SCADA) was used for continuous monitoring of the process and on-site equipment. Under normal operation, a COD removal of 75-85% and 0.35 m3 of biogas production per kilogram of COD were achieved.

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