Photogranule-Based Sequencing Batch Reactor for Safer Textile Effluent Management: Coupling Pollutant Removal with Detoxification

Abstract

The current study investigates a photosequencing batch reactor (PSBR) operated for 120 days using photogranules (PGs) as a sustainable tertiary treatment alternative for textile effluent. Following an initial adaptation phase of approximately 20 days, the PSBR showed stable phosphate (72.75 ± 9.8%), ammoniacal nitrogen (90.94 ± 5.64%), and COD (76.75 ± 6.4%) removal. Granule size increased from ∼1.5 ± 0.4 mm at day 0 to ∼3.5 ± 0.8 mm at day 120, enhancing settleability, as indicated by a progressive decline in SVI₅ from 55.5 ± 2.5 to 30 ± 2 mL/g. The Chl a/b ratio increased from 3.64 to 7.71, confirming the dominance of cyanobacteria, which played a key role in granule structure, biomass retention, and pollutant removal. MLSS steadily increased, reaching 5.1 ± 0.45 g/L at day 120, demonstrating sustained biomass growth and reactor stability. Furthermore, a comprehensive toxicological assessment using multiple bioassays confirmed significant detoxification in the photogranule-treated effluent (PTE). The PTE demonstrated minimal toxicity across various end points in Artemia salina (immobilization ∼10%), Lemna minor (biomass inhibition ∼4%), Lactuca sativa (seed germination index 93%), and Allium cepa (4% chromosomal aberration rate). Moreover, the low IBR value (1.2) for the PTE in the Allium cepa bioassay indicates substantially reduced toxicity under the tested end points.