Cometabolic Degradation Of Heterocyclic Compounds By Arthrobacter Sp.W1and Its Application In Coking Wastewater Treatment Process

Carbazole (CA), dibenzofuran (DBF) and dibenzothiophene (DBT) are recognized as the predominant nitrogen-, oxygen-, and sulfur-heterocyclic compound and have often been found in coking wastewater, which are known to possess toxic and mutagenic activities and can cause great harm to human health and the environment. Biological treatment is regarded as a feasible and cost-effective method for the removal of these refractory pollutants. The purposess of this study are to invesitigate the cometabolic degradation pathways of CA, DBF, and DBT by Arthrobacter sp. W1using phenol as the primary substrate, and the bioremediation of coking wastewater by bioaugmented zeolite-biological aerated filters (Z-BAFs) with mcrobial community dynamics.The phenol-utilizing bacterium, Arthrobacter sp. W1, was used to cometabolically degrade CA, DBF, and DBT for the first time. Both the growing and washed cells of strain W1were capable of degrading CA, DBF, and DBT. Andrews confirmed that the presence of CA, DBF and DBT in the growing system would inhibit the cells growth and biodegradability of strain W1, and the qmax of CA, DBF and DBT were0.0471,0.0192,0.0184and0.0160h-1, respectively. The relationship between specific degradation rate and CA, DBF and DBT concentration by phenol-grown W1could be described well by Michaelis-Menten kinetics and the Vmax were3.435,3.131and3.102mmol g cell-1h-1, respectively. Real coking wastewater containing high concentration of2mM phenol,0.5mM naphthalene,0.25mM CA,0.25mM DBF,0.25mM DBT and30mg/L NH3-N could be completely degraded by phenol-grown W1coupling with activation zeolite within300min. Toxicity assessment indicated the effluent showed much lower toxicity than the untreated wastewater.A series of newly intermediate metabolites such as1,2-dihydroxycarbazole,3,4-dihydroxycarbazole,2-oxo-4-(3-oxoindolin-2-yl)but-3-enoic acid,3-(1h-indol-2-yl)acrylic acid,2-(1h-indol-2-yl)acetaldehyde, indole-2-acetic acid, isatin, and2-aminophenyl glyoxylic acid derived from CA cometabolic degradation were identified by LC/MS/MS, LC/MS TOF accurate mass and NMR. The structures of these metabolites indicated that a novel cometabolic degradation pathway of CA was possessed by strain W1. Meanwhile, examination of metabolites by LC/MS TOF accurate mass suggested that strain W1was capable of degrading DBF and DBT via a successive hydroxylation and meta-cleavage pathway. These findings provide new insights into the cometabolic degradation process of CA, DBF and DBT and have potential applications in biotechnology and bioremediation.The cometabolic degradation of CA, DBF and DBT by immobilized strain W1was also tested. Gellan gum and magnetic Fe3O4nanoparticle were selected as the optimal immobilization support and most suitable nanoparticle for immobilization, respcectively. The optimal concentration of magnetic Fe3O4nanoparticle was80mg/L. The relationship between specific degradation rate and the initial concentration of CA, DBF and DBT was described well by Michaelis-Menten kinetics and the Vmax were3.534，3.287and3.209mmol g cell-1h-1. The recycling experiments demonstrated that the magnetically immobilized cells coupling with activation zeolite showed highly bioremediation activity on the coking wastewater containing high concentration of phenol, naphthalene, CA, DBF and DBT during ten recycles. In the tenth cycle, magnetically immobilized cells coupling with activation zeolite could completely degrade coking wastewater after240min. Toxicity assessment indicated the treatment of the coking wastewater by magnetically immobilized cells with activation zeolite led to less toxicity than untreated wastewater.Finally, coking wastewater was treated using Z-BAFs bioaugmented by adding free or magnetically immobilized Arthrobacter sp. W1. All treatments were carried out for a period of100days and the data indicated that G3(bioaugmented Z-BAF with magnetically immobilizedstrain W1) was the most efficient for treating coking wastewaters. Coking wastewater containing600mg/L phenol,200mg/L naphthalene,60mg/L CA,90mg/L DBF,90mg/L DBT and30mg/L NH3-N could be completely degraded G3. Illumina sequencing data revealed that the bacterial richness and diversity was recovered by both bioaugmented Z-BAF treatments and that the biodiversity was especially high after phenol, naphthalene, CA, DBF, DBT, and COD loading shocks. Notably, treatment with magnetically immobilized cells showed the highest biodiversity. Furthermore, both bioaugmentation treatments accelerated the shift of the bacterial community structure such that there was a more distinct difference from the structure of the starting bacterial community. Magnetically immobilized cells of strain W1was14%of the total bacterial population in G3on100thday. Thus, the data indicate that both the introduced strain W1and the indigenous degrading bacteria played a significant role in the treatments. These findings were also consistent with the treatment data of G3.