Performance of a high-rate membrane bioreactor for energy-efficient treatment of textile wastewater.

High-rate membrane bioreactors (MBR), where the wastewater undergoes partial oxidation due to the applied short sludge retention time (SRT) and hydraulic retention time (HRT) values, retain the majority of the organic substances in the sludge through growth and biological flocculation. Thus, a raw material source with a high biomethane production potential is created for the widespread use of circular economy or energy-neutral plants in wastewater treatment. While high-rate MBRs have been successfully employed for energy-efficient treatment of domestic wastewater, there is a lack of research specifically focused on textile wastewater. This study aimed to investigate the textile wastewater treatment and organic matter recovery performances of an aerobic MBR system containing a hollow fiber ultrafiltration membrane with a 0.04 μm pore diameter. The system was initially operated at short SRTs (5 and 3 d) and different SRT/HRT ratios (5, 10, and 20) and subsequently at high-rate conditions (SRT of 0.5-2 d and HRT of 1.2-9.6 h) which are believed to be the most limiting conditions tested for treatment of real textile wastewater. The results showed that chemical oxygen demand (COD) removal averaged 77% even at SRT of 0.5 d and HRT of 1.2 h. Slowly biodegradable substrates and soluble microbial products (SMP) accumulated within the MBR at SRT of 0.5 and 1 d, which resulted in decreased sludge filterability. The observed sludge yield (Yobs ) exhibited a considerable increase when SRT was reduced from 5 to 1 d. On the other hand, the SRT/HRT ratio displayed a decisive effect on the energy requirement for aeration.