Native microorganisms for sustainable dye biodegradation in wastewaters from jeans finishing

The textile mill is one of the most water-consuming industries. Wastewater production is very high, and among the main generated pollutants are dyes. In particular, jeans finishing, which is performed all over the world, generates wastewater with indigo dye that has to be eliminated before discharge. This work studies the biological treatment of this type of wastewater using native microorganisms, i.e., without the need for external seed sludge to start-up the process. Two strategies for starting up the biological treatment using laboratory sequencing batch reactors have been compared: the addition of seed sludge from a biological reactor of a wastewater treatment plant and the non-addition of seed sludge, which means that native microorganisms (those in wastewater coming from the industry facilities) are responsible for COD and color degradation. Special attention is paid to biomass shift in both reactors, analyzing both bacterial and fungal populations. Results yielded more than 90% of COD and color removal after 25 days in both reactors. MLSS increased in both reactors during the operation, reaching very similar values (around 1840 mg/L). Rozellomycota was the predominant phylum in the reactors. Concerning bacteria, Planctomycetota abundance increased considerably in both reactors, which shows the important role of these bacteria in the treatment. It can be concluded that the lower bacterial diversity in the native population in comparison with the seeded sludge was shifting to a higher microbial diversity during the process, achieving a similar microbial population in reactors. It implies that it is not necessary to either work with isolated cultures or seeded sludge, which leads to a simpler and more sustainable solution for textile wastewater treatment in areas all over the world.