Enrichment, characterization and application of bacterial consortia for degrading 2-mercaptobenzothiazole in rubber processing wastewater

Abstract

Benzothiazoles is widely used as vulcanized accelerator in rubber industry. The high volume of 2-MBT usages resulted in its release into the environment and can cause adverse health impacts. This study aimed to obtain efficient 2-MBT-degrading bacteria for wastewater application. The bacterial consortia were enriched by incubating rubber wastewater sludge in a medium containing 2-MBT for 28 days followed by a stepwise acclimation by gradually increasing 2-MBT concentrations in an NH4Cl-containing medium for 76 days. The process significantly increased the bacterial number and changed the dominant populations and degradative genes. Among these consortia, the EN consortium had the highest specific 2-MBT biodegradation rate of 5.2 ± 0.5 mg L-1 day-1 mg protein-1 and could degrade up to 300 mg L-1 2-MBT. From 16S rRNA gene analysis, Pseudomonas was the dominant genus at approximately 70% of the total population. Stenotrophomonas was the second most abundant populations and have never been reported for 2-MBT biodegradation. The abundance of genes involved in xenobiotic substance biodegradation and tolerance mechanism in the EN consortium were higher than those in original sludge sample. In addition, the EN consortium removed 65-79% and 90-93% of 112 mg L-1 2-MBT and ~4,000 mg L-1 COD in rubber wastewater under batch test, respectively. The values were significantly higher than that of natural attenuation. This research also developed a ready-to-use inoculum by immobilizing the EN consortium in porous carriers. The immobilized cells could retain their activities over 4 cycles of repeated uses. This study further carried out the bioaugmentation of immobilized EN consortium in rubber processing wastewater treatment system. These results suggested that the system not only reduced 2-MBT at approximately 74-76% of its initial concentration, it also exhibited greater than 80% of COD removal at an OLR 3 kg COD m3 day-1. Thus, the bioaugmentation of immobilized EN consortium and activated sludge in the bioreactor at the ratio of 1:2 could enhance wastewater treatment efficiency of rubber processing industry under a continuous operation. Hence, the EN consortium could be an efficient bacterial consortium to remove benzothiazoles by applying it in the post-treatment system of rubber industrial wastewater.