Performance and Characteristics of Aerobic Granular Sludge Degrading 2,4,6‐Trichlorophenol at Different Volumetric Organic Loading Rates

Abstract

Aerobic granular sludge represents a promising option for the treatment of wastewater contaminated by 2,4,6‐trichlorophenol (2,4,6‐TCP). Nevertheless, the need for high volumetric organic loading rates (vOLR) still constitutes a practical drawback, since the supply of an external carbon source for the treatment of low‐strength industrial wastewater would imply significant costs at full‐scale. This study investigates the possibility to sustain 2,4,6‐TCP degrading aerobic granules with low vOLR, preserving long‐term process performance. Sodium acetate was used as external carbon source for aerobic granules degrading 2,4,6‐TCP (20 mg/L), and its concentration in the influent was progressively reduced from 1000 to 420 mg/L. The effects on process performance, granule properties and microbial population dynamics were investigated: complete 2,4,6‐TCP removal was maintained, specific removal rates increased from 2.2 ± 0.5 to 4.3 ± 0.4 mg 2,4,6‐TCP/g VSS per hour (mg2,4,6‐TCP/gVSS · h) and a shift of granule diameter toward smallest size fractions occurred. Moreover, the qualitative evaluation of polyhydroxyalkanoates (PHA) inclusions in microbial cells suggested their active role in 2,4,6‐TCP degradation. The results showed that for low‐strength wastewater containing toxic substances like 2,4,6‐TCP, high concentrations of the external carbon source are required during the process start‐up, but not in the long‐term operation, thus reducing the operating costs significantly without compromising process performance: this represents an important step toward process scale‐up.