Removal of organic pollutants and analysis of MLSS-COD removal relationship at different HRTs in a submerged membrane bioreactor

In order to investigate the influence of hydraulic retention time (HRT) on organic pollutant removal in a submerged membrane bioreactor (SMBR), a laboratory-scale experiment was conducted using domestic sewage as influent. The dissolved oxygen (DO) concentration was controlled at 2.0-3.0mgL-1 during the experimental period. The experiments demonstrated that when HRT was 3, 2 and 1 h, the reduction of chemical oxygen demand (COD) was 89.3-97.2, 88.5-97.3 and 80-91.1%, and the effluent COD was 38.9-11.2, 41.6-10.8 and 63.4-35.8mgL-1, respectively. It is suggested that an HRT of 1 h could meet the normal standard of discharged domestic sewage, and an HRT of 2 h could meet that of water reclamation. In addition, we use mathematical software MATLAB to analyse the relation of mixed liquor suspended solids (MLSS) and COD removal. The results showed that the optimum MLSS concentration should be maintained at around 6000mgL-1 in the SMBR. The results also showed that the COD removal was related to HRT (τ), influent concentration (S0) and sludge loading rate for COD removal (NS). Moreover, the high COD removal could be achieved through adjusting τ, S0 and NS.