Greywater treatment in SBR-SND reactor - optimization of hydraulic retention time, volumetric exchange ratio and sludge retention time

In this study, simultaneous nitrification and denitrification-sequencing batch reactor (SND-SBR) process was investigated to treat greywater. The effect of three process parameters, including hydraulic retention time (HRT), volumetric exchange ratio (VER) and sludge retention time (SRT), was optimised using a 23 full factorial design. The statistic model was developed for two response variables, i.e. chemical oxygen demand (COD) and ammonia (NH3-N) removal. The optimum conditions were 6.8 h HRT (anaerobic/aerobic/anoxic: 1.77 h/2.77 h/2.27 h), 0.7 VER and 7.94 d SRT, which resulted in 93.9% COD and 84.6% NH3-N removal efficiency. SRT was the most significant factor, followed by HRT and VER for COD and NH3-N removal. The interaction effect of VER and SRT was significant in COD removal. On the other hand, the interaction effects of HRT-VER and HRT-SRT were significant in NH3-N removal. The removal efficiencies of 89.6 ± 1.1% and 83.7 ± 2.3% were observed for TKN and TN, respectively, in the optimised SND-SBR system. NH3-N removal was obtained via nitrate pathway in the SND-SBR system. The PO43--P removal of 74.2 ± 3.4% was obtained via aerobic phosphorus uptake and post anoxic denitrification at the optimal condition. To enhance PO43--P removal, adsorption (using corn cob adsorbent) was integrated with SBR by adding the optimum adsorbent dose (0.5 g/L). The PO43--P removal efficiency in the SBR-adsorption system was found to be 80 ± 1.5%. The biodegradation of emerging contaminants (ECs) was also carried out in the SND-SBR system, and the results showed removal rate of 58.9 ± 2.3% benzophenone-3 (BP) and 80.1 ± 2.2% anionic surfactant (AS).