สำนักราชบัณฑิตยสภา
215 สมศั กดิ์ ด� ำรงค์เลิ ศ และคณะ วารสารราชบัณฑิตยสถาน ปีที่ ๓๗ ฉบับที่ ๑ ม.ค.-มี.ค. ๒๕๕๕ Kudlich et al. (29) localized a quinoide redox mediator-dependent azo reductase activity in the membrane of a gram-negative bacterium, Sphingomonas sp strain BN6. Therefore, in the present study, the AH 2 QDS is suggested to shuttle reduction equivalents in the cells to extracellular sulfonated azo dye and reduce the azo compound in a purely chemical reaction ((Fig. 5). The anaerobic reduction of AQDS occurred only in the presence of glucose, which seems to be the source of reduction equivalents to reduce the AQDS outside the membrane of strain A5. The proposed mechanism demonstrated in Fig. 5 could be useful in the treatment of sulfonated azo dyes containing wastewaters by strain A5 or other bacteria which able to reduce AQDS. Under anaerobic condi- tions, the chemical reactions of the reduced AQDS (AH 2 QDS) with the sulfonated azo dyes allows for extremely unspecific reduction processes which are mainly governed by the redox potentials of the AH 2 QDS and azo compounds therefore, a wide range of azo dyes can be reduced. The main restriction to this mechanism is that the amines that are formed are usually not further metabolized under anaerobic conditions. Since aromatic amines and also sulfonated aromatics are aerobically degraded by bacteria (8, 20, 37, 35, 36), it has been repeatedly suggested to combined the anaerobic reduction of the azo dyes with an aerobic treatment system for the amines formed (21, 24, 38, 39, 52, 53). The ability of quinone compounds (i.e., AQDS) to convoy electrons between the bacterial membrane and the dye in solution at the same distance from the cell sug- gests that Paenibacillus sp. strain A5-AQDS couple can be used to reduce dye in a separate compartment without direct contact between the sulfonated azo dyes and bacte- rial cell membrane. Since hydroquinones are readily oxidized by sulfonated azo dyes, this hydroquinones only needs to be present at substoichiometric concentrations to be an effective electron carrier as long as these azo dyes are abundant in the wastewaters. Although the effective AQDS dosage levels were low, continuous dosing implies continuous expenses related to procurement of the chemical as well as continuous discharge of this recalcitrant sulfonated azo compounds. Therefore, it is desirable to immobilize the redox mediator in the bioreactor for treatment azo dye-containing wastewater continuously. For this propose, various reactor configurations were em-
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