A single strain capable of efficient S2−-oxidizing was isolated from a black-odor river in Beijing. The single strain was identified as Stenotrophomonas through the physiology and biochemical characteristics as well as the 16S rRNA sequencing experiment. This strain was named as Stenotrophomonas sp.sp3 (strain sp3). The experimental results showed that for the strain sp3 growth and S2− oxidization, the optimal conditions were as follows: 25 °C of temperature, initial pH 7, 2.5 g/L of initial glucose concentration and 1.00 g/L of initial cell concentration. It was found that there were 31 kinds of sulfur oxidation related genes in the strain sp3 through the whole genomic analysis. The results of the transcriptome analysis suggested that the main metabolic pathway of S2− to SO42− was the paracoccus sulfur oxidation process. The bioconversion processes of S2− to S0, S2− to SO32−, S2O32− to S0 and SO32−, and SO32− to SO42− were controlled by hdrA, cysIJ, tst and sox gene, respectively.

The redox balance of inorganic sulfur in heavily polluted rivers might be disrupted, making sulfur reduction a major metabolic pathway of sulfate-reducing bacteria (SRB), leading to a massive accumulation of S2− and blackening the water bodies. A mixed culture microbial consortium (MCMC) of Citrobacter sp.sp1, Ochrobactrum sp.sp2, and Stenotrophomonas sp.sp3 was used to activate native sulfate-oxidizing bacteria (SOB) to augment the S2− oxidizing process. The results demonstrated that MCMC had a significant sulfur oxidation effect, with 98% S2− removal efficiency within 50 h. The sulfide species varied greatly and were all finally oxidized to SO42−. The mechanism of bio-augmentation was revealed through high throughput sequencing analysis. The MCMC could stimulate and simplify the community structure to cope with the sulfide change. The microorganisms (family level) including Enterococcaceae, Flavobacteriaceae, Comamonadaceae, Methylophilaceae, Caulobacteraceae, Rhodobacteraceae, and Burkholderiaceae were thought to be associated with sulfide metabolism through the significant microbial abundance difference in the bio-treatment group and control group. Further Pearson correlation analysis inferred the functions of different microorganisms: Comamonadaceae, Burkholderiaceae, Alcaligenaceae, Methylophilaceae, and Caulobacteraceae played important roles in S2− oxidization and SO42− accumulation; and Comamonadaceae, Burkholderiaceae, Alcaligenaceae, Methylophilaceae, Caulobacteraceae, Campylobacteraceae, Bacteriovoracaceae, and Rhodobacteraceae promoted the sulfur oxidation during the whole process.

S2− is one of the common pollutants in heavily polluted rivers. A pump-and-treat ex-situ process with enriched consortium (PEPEC) was used to remove S2− in this study. The kinetic model of S2− removal was developed, and the inflow ratio of the PEPEC was analyzed according to the results of the kinetic models. The results showed that the S2− removal ratio could reach 97.5% 5 0.5%, when the inflow ratio was controlled at 2% for the PEPEC operation. Meanwhile, the removal efficiency and operation performance were assessed for both the simulating ex-situ and in-situ bench-scale tests. Compared with the in-situ processes, the PEPEC showed a stable operation performance during 120 h of bio-treatment, and the concentrations of S2−, COD, NH3-N and TP in the effluent reached approximately 0.5, 20, 0.5 and 0.5 mg/L, respectively. The time consumption (8 h for one batch) and consortium dosage (3 g for the whole operation) in the PEPEC were significantly less than those in the in-situ processes. The PEPEC presented some potential advantages for the bio-treatment of a heavily polluted river.

The balance of inorganic sulfur redox in heavily polluted rivers could be disrupted, making sulfur reduction a major metabolic pathway regulated by sulfate reducing bacterium (SRB), leading to massive accumulation of S2- and blackening of water bodies. In order to promote S2- oxidation, mixed culture with Citrobacter sp., Ochrobactrum sp. and Stenotrophomonas sp. was used to active native sulfur oxidizing bacterium (SOB) to augment S2- oxidizing process. The results demonstrated that mixed culture microbial consortium had significant sulfur oxidation effect, with 98% of S2- removal efficiency within 50 h. The sulfur chemical forms varied greatly with mixed culture bio-augmentation, and all the sulfides’ species were finally oxidized to SO42-. The mechanism involved was revealed using high throughput sequencing analysis. The microbial diversity indicated that mixed culture could stimulate and simplify the community structure, enabling native microorganisms cope with the sulfides change. Some microorganisms (family level) including Flavobacteriaceae, Enterococcaceae, Sphingomonadaceae, Cryomorphaceae, Rhodobacteraceae, Campylobacteraceae, Burkholderiaceae, Comamonadaceae, Alcaligenaceae, Methylophilaceae, Bacteriovoracaceae and Caulobacteraceae were thought to be associated with sulfides metabolism and their abundance appeared significant difference in two treatments. Further pearson correlation analysis was performed to determine the role played by different strains at different times. This work demonstrated that the mixed culture might have the potential to be used to promote S2- oxidation and clarify water in the heavily polluted rivers.

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