Halophilic Martelella sp. AD-3 enhanced phenanthrene degradation in a bioaugmented activated sludge system through syntrophic interaction.

Polycyclic aromatic hydrocarbons (PAHs) are a group of common recalcitrant pollutant in industrial saline wastewater that raised significant concerns, whereas traditional activated sludge (AS) has limited tolerance to high salinity and PAHs toxicity, restricting its capacity to degrade PAHs. It is therefore urgent to develop a bioaugmented sludge (BS) system to aid in the effective degradation of these types of compounds under saline condition. In this study, a novel bioaugmentation strategy was developed by using halophilic Martelella sp. AD-3 for effectively augmented phenanthrene (PHE) degradation under 3% salinity. It was found that a 0.5∼1.5% (w/w) ratio of strain AD-3 to activated sludge was optimal for achieving high PHE degradation activity of the BS system with degradation rates reaching 2.2 mg⋅gVSS⋅h, nearly 25 times that of the AS system. Although 1-hydroxy-2-naphthoic acid (1H2N) was accumulated obviously, the mineralization of PHE was more complete in the BS system. Reads-based metagenomic coupled metatranscriptomic analysis revealed that the expression values of ndoB, encoding a dioxygenase associated with PHE ring-cleavage, was 5600-fold higher in the BS system than in the AS system. Metagenome assembly showed the members of the Corynebacterium and Alcaligenes genera were abundant in the strain AD-3 bioaugmented BS system with expression of 10.3±1.8% and 1.9±0.26%, respectively. Moreover, phdI and nahG accused for metabolism of 1H2N have been annotated in both above two genera. Degradation assays of intermediates of PHE confirmed that the activated sludge actually possessed considerable degradation capacity for downstream intermediates of PHE including 1H2N. The degradation capacity ratio of 1H2N to PHE was 87% in BS system, while it was 26% in strain AD-3. These results indicated that strain AD-3 contributed mainly in transforming PHE to 1H2N in BS system, while species in activated sludge utilized 1H2N as substrate to grow, thus establishing a syntrophic interaction with strain AD-3 and achieving the complete mineralization of PHE. Long-term continuous experiment confirmed a stable PHE removal efficiency of 93% and few 1H2N accumulation in BS SBR system. This study demonstrated an effective bioaugmented strategy for the bioremediation of saline wastewater containing PAHs.