Granulation strategies applied to industrial wastewater treatment: from lab to full-scale

About one third of the industrial activated sludge (AS) plants worldwide suffer from bad settling sludge, often caused by filamentous bulking phenomena. The present study investigated the effectiveness of a sludge granulation/densification strategy, based only on a metabolic selection mechanism, to eliminate sludge bulking in a sequencing batch reactor (SBR) treating real industrial wastewater. The wastewater originated from a tank truck cleaning company transporting chocolate and beer. The proposed strategy involved the introduction of a slow unaerated/anaerobic feeding step in the SBR operation. On lab-scale, the new feeding strategy resulted in (1) excellent settling with a sludge volume index (SVI) decreasing from more than 300 mL·g^-1 to 100 mL·g^-1 and lower, (2) the elimination of sludge bulking genera and (3) the significant enrichment of glycogen-accumulating organisms (GAO), mainly Defluviicoccus and Candidatus Competibacter, and this in less than 80 days. The feeding strategy was then applied to the full-scale installation, yielding similar results: a stable average SVI of 37 mL·g^-1 was reached after approximately 150 days. Full granulation was however not reached, which warrants further optimization. The present study shows that the proposed strategy can easily be applied in existing SBR systems to solve the problem of sludge bulking.