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In this study, three different biological methods—a conventional activated sludge (CAS) system, membrane bioreactor (MBR), and moving bed biofilm reactor (MBBR)—were investigated to treat textile wastewater from a local industry. The results showed that technically, MBR was the most efficient technology, of which the chemical oxygen demand (COD), total suspended solids (TSS), and color removal efficiency were 91%, 99.4%, and 80%, respectively, with a hydraulic retention time (HRT) of 1.3 days. MBBR, on the other hand, had a similar COD removal performance compared with CAS (82% vs. 83%) with halved HRT (1 day vs. 2 days) and 73% of TSS removed, while CAS had 66%. Economically, MBBR was a more attractive option for an industrial-scale plant since it saved 68.4% of the capital expenditures (CAPEX) and had the same operational expenditures (OPEX) as MBR. The MBBR system also had lower environmental impacts compared with CAS and MBR processes in the life cycle assessment (LCA) study, since it reduced the consumption of electricity and decolorizing agent with respect to CAS. According to the results of economic and LCA analyses, the water treated by the MBBR system was reused to make new dyeings because water reuse in the textile industry, which is a large water consumer, could achieve environmental and economic benefits. The quality of new dyed fabrics was within the acceptable limits of the textile industry.

Optical brighteners (OBs) are colorless fluorescent dyes, widely used in industry to improve whiteness in materials. Nearly 80% of all OBs in the market are derivatives of stilbene. They absorb the near-ultraviolet light and re-emit most of it in the blue range as visible fluorescence. OBs are commonly applied on textiles, detergents, paper and plastic products, among others. OBs have a low degradation ratio. In biological plants, they can only be partially removed by adsorption into the sludge and a tertiary treatment could be required to fully remove them. Part of them may persist and can be found in river and lake waters. The current work aims to evaluate the effect of the OBs in the bacterial activity of biological wastewater treatment plants. The influence of two commercial OBs (Goldblanc BHA and Leucophor PC) on respiration rate was monitored by means of a semi-continuous electrolytic respirometer, in order to obtain information related to the growth of the biomass and the degradation of the substrate. Their acute toxicity was also determined. It was concluded that the OB effect on bacteria population is variable depending on its chemical structure. Unlike the former, the Leucophor-PC brightener had an impact on the respirometric rate.