Performance of a sequential anaerobic baffled reactor (ABR)/membrane bioreactor (MBR) system treating caffeine wastewater

Treatment of caffeine wastewater with high COD, high nitrogen content and poor biodegradability was investigated with a sequential anaerobic baffled reactor (ABR)/membrane bioreactor (MBR) system. The effect of organic loading rate (OLR) and temperature on the performance of the system was examined. The experimental results show that the COD removal efficiency decreases with the increasing OLR for ABR, the ammonia nitrogen levels raise greatly after the ABR process and decrease to desired levels after the MBR process. Fed at an OLR of 2.23 kgCOD/m³d, the system works efficiently with an HRT of 27.5 h at 37°C, and the COD removal of 71.3% and 92.7% are achieved for ABR and MBR, respectively, and the removal of ammonia nitrogen is 91.7% in MBR with the effluent level of 11.49 mg/L. The optimum temperature for the ABR is 37°C, close to the mesophilic temperature, however, the MBR performs well in a wider temperature range of 19-37°C. The nitrogen compounds are converted to ammonia nitrogen in ABR and to nitrite and nitrate in MBR, thus accomplishing the removal. Therefore, the sequential ABR/MBR system may be regarded as a promising alternative for the treatment of caffeine wastewater.