The formation and stabilization of aerobic granular sludge in a sequencing batch airlift reactor for treating tapioca-processing wastewater

Abstract

This study evaluated performance and granule features of a sequencing batch airlift reactor (SBAR) to treat tapioca-processing wastewater. The effect of organic loading rate (OLR) on the stabilization of aerobic granules was also investigated by increasing the OLR gradually from 2.5 kgCOD/m3.day to 10 kgCOD/m3.day. The results indicated that clear boundary granules were formed after a two-week cultivation period. The aerobic granules’ average diameter increased according to rise in OLR and got a stable value of 2.5 mm at an OLR of 7.5 kgCOD/m3.day. The mature granules consisted of a dark core (anoxic) and yellow sludge surroundings (aerobic). The higher OLR led to forming granules of diameter 3-4 mm which were then broken due to substrate diffusion limitation. Aerobic granules could successfully treat organic substances, NH4+-N, and phosphorus with high removal efficiencies of 93.9-96.3%, 79.7-82.6%, and 80-95%, respectively. We observed that the aerobic granular sludge has good settling ability with a sludge volume index (SVI) lower than 50 mL/g, and is able to withstand high OLR. The experimental findings created a new prospect for granulation and employment of aerobic granules to treat industrial wastewater.