Decolorization of acid orange 7 in moving bed biofilm reactor packed with polyhydroxyalkanoate/activated carbon

Abstract

Moving bed biofilm reactor (MBBR) using various carrier medium has been widely employed in wastewater treatment. This study aimed to investigate the feasibility of polyhydroxyalkanoate (PHA) and activated carbon (AC) composite (PHA/AC) as biofilm carrier to enhance MBBR treatment of azo dye acid orange 7 (AO7). Each PHA/AC carrier had a height of 0.40 cm and a cylindrical diameter of 1.25 cm. The biofilm on PHA/AC carrier was characterized using microscopic and chemical analysis. AO7 decolorization efficiency and kinetics were evaluated. The incorporation of AC in PHA was found to promote biofilm growth. Mature biofilm of 2075 ± 79.30 μm was successfully formed on PHA/AC carrier. Compared to a control reactor, the MBBR with 5 % (v/v) PHA/AC exhibited improved decolorization, with decolorization efficiency and first-order rate constant, kAO7, increasing from 78.2 % and 9.90 × 10−4 min−1 to 95.0 % and 1.70 × 10−3 min−1, respectively. The enhancement of decolorization in MBBR was attributed to the presence of anoxic zone within the biofilm that favored the azo bond cleavage. Batch studies on the effects of suspended activated sludge (AS) and biofilm amounts showed an additive effect on decolorization efficiency when combined. The combined suspended AS and biofilm also resulted a 3–4 folds increase in kAO7 value compared to AS alone. The results indicate that PHA/AC was an effective carrier and its biofilm exhibited high decolorizing ability for AO7. The enhancement provided by the PHA/AC biofilm makes it advantageous for developing efficient and environmentally-friendly wastewater treatment systems with compact design and minimal sludge production.