Influence of organic loading rates on treatment performance of membrane bioreactor treating tannery wastewater

Abstract

Tannery wastewater contains high pollutants concentrations such as nitrogen, organic matter, salinity, toxic metals, etc. Membrane bioreactor has been widely recognized as potential technology for wastewater treatment and reuse. Finding proper operating conditions and a strategy for fouling mitigation in MBR process is essential to application to tannery wastewater treatment. Herein, this study investigated the effect of organic loading rate (OLR) on the performance and fouling behavior of membrane bioreactor (MBR) treating tannery wastewater during 280 days of operation. The MBR was operated under the low fluxes of 4.2 and 8.3 L m−2 h−1, corresponding to organic loading rates of 1.3 (OLR1) and 2.6 kg COD m−3d−1 (OLR2). The results show that the COD removal was obtained at 78 ± 19% and 89 ± 2% for OLR1 and OLR2, respectively. For the former condition the average removal of total Kjeldahl nitrogen (TKN) and NH4+-N reached 53%–68% and 58%–70%. TKN removal was mainly contributed by cell assimilation. Incomplete nitrification was due to high TDS (11,000–16,790 mg L−1) and the presence of free ammonia ( 6.77–31.11 mg L−1) concentrations under pH 8.7–8.8. Membrane fouling rate was strongly governed by operated flux. At flux of 4.2 LMH the fouling rate was as low as 0.19–0.4 kPa d−1 while the fouling rate accelerated (1.87–1.93 kPa d−1) as increased two times flux . These findings proposed a low flux of 4.2 LMH for MBR operation in treating real tannery wastewater. It was found that influent total suspended solids (TSS) played a crucial factor in spiking mixed liquor suspended solids (MLSS) into MBR. Thus, a pretreatment process is suggested to remove major suspended solids from raw tannery wastewater prior to biological treatment.