Impact of batch seeding on the development of biological activated carbon filter for the simultaneous removal of organics, nitrogen, and emerging contaminants from secondary effluents

Abstract

This study evaluates the batch seeding of granular activated carbon (GAC) with sludge inocula and raw sewage to accelerate its transformation into biological activated carbon (BAC) and achieve rapid steady-state condition, fostering the development of microbial community and simultaneous degradation of residual organics, nitrogen, and emerging contaminants (ECs) from secondary effluents. After 7 days of seeding, pathogens dominated the surface of GAC while heterotrophs, nitrifiers, and denitrifiers were scarce. However, a sustained aerobic condition in the column shifted the community towards these beneficial microbes, enabling rapid biofilm development and attainment of steady-state conditions in the removal of dissolved organic carbon (DOC). Notably, two columns loaded with seeded GAC at food-to-microorganism (F/M) ratios of 0.8 and 0.4 reached steady-state after 4801 (50 days) and 7202 (75 days)-bed volumes (BVs), respectively, while the control required 19 206 (200 days) BVs. The seeded systems showed a higher reduction in the DOC, decreasing from 6.4 to 2 mg L⁻¹ (∼68%), meeting the USEPA DOC recommendation for drinking water. Other studies reported <50% reduction in the DOC after operating for 200 days. Additionally, NH₄-N and NO₃-N were lowered from 1.6 to 0.5 mg L⁻¹ and 5.2 to 2.6 mg L⁻¹, respectively. At a contact time of 15 min, 12 out of 17 ECs showed >70% removal, while the remaining 5 ECs showed >60% removal. A fluorescence–PARAFAC model was used to investigate the DOC removal mechanism by the BAC filters. These filters effectively reduced the total coliforms by >1.5 log₁₀ and strengthened the relationship between the functional enzymes, key metabolic pathways, and contaminant removal. Extracellular polymeric substances (EPS) from BAC were characterized to provide mechanistic insights into the enhanced attenuation of ECs.