Aerobic granular sludge to treat paper mill effluent: selection of ideal strains that contribute to the formation of strong aggregates

The formation of aerobic granules after the treatment of paper mill effluents was feasible. Granular sludge presented a lower fouling potential than flocculent sludge, allowing a higher flux through the membranes in a membrane bioreactor (MBR). However, it was observed that after filtration many of the biogranules disrupted, which increased the membrane fouling. Therefore, the formation of aggregates that are physically and mechanically more resistant to decomposition would be beneficial to an MBR process. This work determines which of the microorganisms found in the aerobic granular sludge contribute to microbial aggregation, thereby increasing the mechanical resistance of aggregates. Nineteen strains were isolated from granular aerobic sludge. Tests for coaggregation showed that some isolates (E2, E7, E9, E13, and E25) were able to improve the formation of granules, while others (E10, E14, E18, and E26) inhibited the aggregation. The extracellular polymeric substances analyses indicated which substances contributed to the granule formation. The mechanical resistance of the aggregates was determined and the results showed that isolate E19 substantially improved the resistance of the aggregates to disruption.