Abstract
In this study, two modes of hybrid anaerobic digestion (AD) bioreactor with built-in BESs (electrodes installed in liquid phase (R1) and sludge phase (R2)) were tested for identifying the effect of electrodes position on azo dye wastewater treatment. Alizarin yellow R (AYR) was used as a model dye. Decolorization efficiency of R1 was 90.41 ± 6.20% at influent loading rate of 800 g-AYR/ m3·d, which was 39% higher than that of R2. The contribution of bioelectrochemical reduction to AYR decolorization (16.23 ± 1.86% for R1 versus 22.24 ± 2.14% for R2) implied that although azo dye was mainly removed in sludge zone, BES further improved the effluent quality, especially for R1 where electrodes were installed in liquid phase. The microbial communities in the electrode biofilms (dominant by Enterobacter) and sludge (dominant by Enterococcus) were well distinguished in R1, but they were similar in R2. These results suggest that electrodes installed in liquid phase in the anaerobic hybrid system are more efficient than that in sludge phase for azo dye removal, which give great inspirations for the application of AD-BES hybrid process for various refractory wastewaters treatment.
Highlights
In this study, an up-flow hybrid anaerobic digestion reactor with built-in Bioelectrochemical system (BES) was developed for azo dye wastewater treatment
To evaluate the effect of electrode positions on azo dye removal in the hybrid anaerobic reactors with built-in BES, three reactors equipped with different electrode positions and configurations were compared
The second reactor (R2 in Fig. 1B) was filled with anaerobic sludge to a half of the reactor, and electrodes were placed in sludge zone
Summary
DE was improved for all three reactors at ALR < 400 g AYR/m3·d (Fig. 2B). DE in R1 showed over 90% even at higher ALR (800 g AYR/ m3·d), while DE significantly decreased in R2 and R3 at the higher ALR This result indicates that electrodes immersing in supernatant (liquid phase) is better than that in sludge zone. At 100 g-AYR /m3 d, R1 showed the COD removal efficiencies of 82.76 and 81.60% at open and closed circuit, respectively, which were nearly 15–37% higher than those in the other two reactors (Fig. 4A). The lower VFAs accumulation and better COD removal in R1 support the higher metabolic activity of anode-respiring microorganisms when electrodes are placed in the liquid phase. The effects of segregation on azo dye decolorization as well as the current generation are still unclear and warrant further study
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