Living membrane bioreactor for highly effective and eco-friendly treatment of textile wastewater

The treatability of synthetic textile wastewater containing model dyes, such as reactive black and direct black dye (25.0 ± 2.6 mg_dye/L), with chemical oxygen demand (COD, 1000 ± 113 mg/L), ammonia‑nitrogen (NH₃-N, 140 ± 97 mg/L) and sulphate ions (SO₄^2-, 1357 ± 10.86 mg/L) was investigated in this study using an innovative living membrane bioreactor (LMBR) using an encapsulated self-forming dynamic membrane (ESFDM). The key advantage of ESFDMBR is the self-forming of the biological filtering layer protected between two meshes of inert robust and inexpensive material. A laboratory scale bioreactor (BR) equipped with a filtering unit mounting polyester meshes with a pore size of 30 μm, operated at an influent flux of 30 LMH was thus used. After the formation of the biological living membrane (LM), the treatment significantly reduced COD and DOC concentrations to the average values of 34 ± 10 mg/L and 32 ± 7 mg/L, corresponding to reduction efficiencies of 96.0 ± 1.1 % and 94 ± 1.05 %, respectively. Throughout the LMBR operation, the colours were successfully removed from synthetic textile wastewater with an overall removal efficiency of about 85.0 ± 1.8 and 86.0 ± 1.9 % for direct and reactive dyes, respectively. In addition, the proposed system was also found effective in affording removal efficiency of ammonia (NH₃) of 97 ± 0.5 %. Finally, this treatment afforded circa 40.7 ± 5.8 % sulphate removal, with a final concentration value of 805 ± 78.61 mg/L. The innovative living membrane, based on an encapsulated self-forming dynamic membrane allows a prolonged containment of the membrane fouling, confirmed by investigating the concentration of membrane fouling precursors and the time-course variations of turbidity and transmembrane pressure (TMP). Those final concentrations of wastewater pollutants were found to be below the limits for admission of the effluents in public sanitation networks in Italy and Tunisia, as representative countries for the regulation in force in Europe and North Africa. In conclusion, due to the low costs of plant and maintenance, the simple applicability, the rapid online implementation, the application of LMBR results in a promising method for the treatment of textile wastewater.