Abstract
Microorganisms in aerobic granules formed in sequencing batch reactors (SBR) remove contaminants, such as xenobiotics or dyes, from wastewater. The granules, however, are not stable over time, decreasing the removal of the pollutant. A better understanding of the granule formation and the dynamics of the microorganisms involved will help to optimize the removal of contaminants from wastewater in a SBR. Sequencing the 16S rRNA gene and internal transcribed spacer PCR amplicons revealed that during the acclimation phase the relative abundance of Acinetobacter reached 70.8%. At the start of the granulation phase the relative abundance of Agrobacterium reached 35.9% and that of Dipodascus 89.7% during the mature granule phase. Fluffy granules were detected on day 43. The granules with filamentous overgrowth were not stable and they lysed on day 46 resulting in biomass wash-out. It was found that the reactor operation strategy resulted in stable aerobic granules for 46 days. As the reactor operations remained the same from the mature granule phase to the end of the experiment, the disintegration of the granules after day 46 was due to changes in the microbial community structure and not by the reactor operation.
Highlights
The formation of aerobic granules in sequencing batch reactors (SBR) has been used as a technique to remove specific contaminants, such as xenobiotics or dyes, from wastewater (Coma et al, 2012)
On day 15, at phase II, start of granulation, Agrobacterium reached its maximum relative abundance indicating its participation in cell aggregation
The relative abundance of Xanthobacter reached a maximum between days 29 and 32 and its members might have had a positive effect on nitrogen removal
Summary
The formation of aerobic granules in sequencing batch reactors (SBR) has been used as a technique to remove specific contaminants, such as xenobiotics or dyes, from wastewater (Coma et al, 2012). The functioning of the SBR and granule formation is controlled by the operation parameters (Weissbrodt, Shani & Holliger, 2014). A cycle of 1.5 h generated the largest granules whereas 4 h resulted in the most condense ones (Liu & Tay, 2007). An OLR with a value of chemical oxygen demand (COD) of 2.52 kg/m3 per day was adequate for granule formation (Kim, Kim & Jang, 2008). Aerobic granules formation from wastewater at an OLR of 1.05–1.68 kg COD/m3/day was possible, 9 months were needed to form mature granules (Wang et al, 2009)
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