A pilot- scale(10 m3/d) anoxic/oxic membrane bioreactor(A/O MBR) was tested for dyeing wastewater treatment of woolen mill without wasting sludge in 125 days operation. Results showed that the effluent quality was excellent, i. e. effluent COD less than 25 mg/L, BOD5 under 5 mg/L, turbidity lower than 0.65 NIU, and colour less than 30 DT, and met with the reuse water standard of China. The removal rates of COD, BOD5, colour, and turbidity were 92.4%, 98.4%, 74% and 98.9%, respectively. Constant- flux operation mode was carried out in this study, and backwash was effective for reducing membrane fouling and maintaining constant flux. Membrane fouling had heavy impact on energy consumption. More attention should be paid on pipe selection and design for the sidestream MBR system, too.

A laboratory- scale membrane bioreactor(MBR) with a gravity drain was tested for dyeing and printing wastewater treatment from a wool mill. The MBR was operated with continuous permeate by gravity and without chemical cleaning for 135 days. Results showed that excellent effluent quality could meet the reuse water standard in China. The average concentrations of COD, BOD5, turbidity and color in the effluent were 36.9 mg l-1, 3.7 mg l-1, 0.2 NTU and 21 dilution times(DT), respectively. The average removal rates of COD, BOD5, turbidity and color were 80.3%, 95.0%, 99.3% and 58.7%, respectively. The membrane flux increased with increasing of aeration intensity, and its increasing rate was related to pressure- heads. The higher the pressure- head, the greater the impact of aeration intensity on membrane flux. Statistical analysis also showed that both the pressure- head and aeration intensity significantly affected membrane flux. Due to its compact design, simple operation and easy maintenance, MBR with a gravitational filtration system hs low energy consumption and is cost- effective to build and operate. If the life expectancy of the membrane is set for 3- 4 years and the membrane flux is set at 15 l/m2h, such a MBR would be very competitive.