Biological sulfamethoxazole degradation along with anaerobically digested centrate treatment by immobilized microalgal-bacterial consortium: Performance, mechanism and shifts in bacterial and microalgal communities

Though microalgal-bacterial consortium in photobioreactor (PBR) has been investigated to the anaerobically digested centrate (ADC) treatment, the impact and degradation of micropollutant sulfamethoxazole (SMX) in this system has never been reported. In this research, three microalgal-bacterial consortiums were parallel operated with suspended Chlorella vulgaris (C. vulgaris), immobilized C. vulgaris and immobilized C. vulgaris-powdered activated carbon (PAC), namely PBR (SCV), PBR (ICV) and PBR (ICV + PAC), respectively. The impact of SMX on the ADC treatment performance, C. vulgaris growth and microbial community shifts were investigated. The performance of SMX removal and potential SMX degradation mechanism by the microalgal-bacterial consortium were explored. The results showed that SMX significantly inhibited PBR (SCV) with unsatisfactory C. vulgaris growth, ADC treatment and SMX removal. Comparatively, immobilized microalgae beads protected microalgae in PBR (ICV) and PBR (ICV + PAC) obtaining higher proportion of living C. vulgaris of 85.1% and 86.2%, respectively, comparing to that of 74.6% in PBR (SCV) (p < 0.05). Moreover, microalgae immobilization coupled with PAC adsorption mitigated toxicity of SMX and accelerated the formation of stable microalgal-bacterial consortium. Thus, PBR (ICV + PAC) obtained the maximum SMX removal (99.0 ± 0.2%) and the highest ADC treatment performance (COD, TN and TP removal of 72.12 ± 1.34%, 98.47 ± 0.69% and 98.49 ± 0.73%, respectively). Bacterial diversity was dramatically reduced by SMX in the PBR (SCV), which was significantly mitigated by microalgae immobilization in PBR (ICV) and PBR (ICV + PAC). The enrichment of functional genera Pseudomonas, Brevundimonas and Hydrogenophaga were conducive to SMX degradation; while the dominant microalgae of specie of C. vulgaris was not perturbed by SMX. The pathways of SMX degradation involved oxazole ring fracture, mononitration effect, S-N bond and C-N bond broken. This research revealed the inhibition of SMX on PBR (SCV) and demonstrated the potential of PBR (ICV + PAC) on SMX degradation with simultaneous ADC treatment.