Ceramic-supported graphene oxide membrane bioreactor for the anaerobic decolorization of azo dyes

Abstract

A continuous compact membrane bioreactor consisted of ceramic-supported graphene oxide membrane (CSGoM) was implemented for the first time for anaerobic biodecolorization of monoazo Acid Orange 7 (AO7), diazo Reactive Black 5 (RB5), and triazo Direct Blue 71 (DB71) solutions, showing excellent decolorization potential. The membrane was prepared by vacuum filtration of various graphene oxide solutions using a UF ceramic flat element. The decolorization efficiency of the CSGoM bioreactor, made from 1 mg·mL-1 of GO solution (B-CSGoM-1), was investigated for several structurally distinct azo dyes, initial feed concentrations, and permeate fluxes. Maximum color removal was achieved under low feed concentration (50 mg·L-1) and permeate flux (0.05 L·m-2·h-1), reaching 99% for AO7, 96% RB5, and 92% for DB71. At this low permeate flux, the biodecolorization was stable for all azo dye solutions irrespective of the feed concentration. In a subsequent experiment under higher feed concentration and permeate flux (100 mg·L-1 and 0.10 L·m-2·h-1), the decolorization slightly fell to 93%, 85%, and 81% for monoazo, diazo, and triazo solutions, respectively. The existence of anaerobic bacteria (Geobacter and Pseudomonas guangdongensis) in the B-CSGoM-1 biofilm confirms that they could perform efficient biodegradation of azo dye molecules in association with the graphene oxide membrane.