The Innovative Moving Bed Biofilm Reactor/Solids Contact Reaeration Process for Secondary Treatment of Municipal Wastewater

The innovative moving bed biofilm reactor/solids contact reaeration (MBBR/SCR) process has been chosen for a new wastewater treatment plant serving a population of 200 000 at Moa Point, Wellington, New Zealand. Because the MBBR/SCR combination was new, a pilot-scale demonstration project was made part of the contract. Thorough pilot tests using a wide range of organic loads under both steady and transient-flow conditions demonstrated that the MBBR/SCR process produced the required effluent quality at loads higher than used in the original design. At 3 days mean cell residence time (MCRT) in the SCR stage, a final effluent with a 5-day biochemical oxygen demand$({\rm BOD}_{5})$of less than 10 mg/L was achieved at an organic load on the MBBR of 15 g${\rm BOD}_{5}/{\rm m}^{2}\cdot {\rm d}$(5.0 kg${\rm BOD}_{5}/{\rm m}^{3}\cdot {\rm d}$). With the same MCRT, a final effluent of less than 15 mg${\rm BOD}_{5}/{\rm L}$was achieved at an organic load on the MBBR of 20 g${\rm BOD}_{5}/{\rm m}^{2}\cdot {\rm d}$(6.7 kg${\rm BOD}_{5}/{\rm m}^{3}\cdot {\rm d}$). Dynamic loading tests demonstrated that a good-quality effluent was produced with a diurnal peak-hour load on the MBBR of more than 40 g${\rm BOD}_{5}/{\rm m}^{2}\cdot {\rm d}$(13.3 kg${\rm BOD}_{5}/{\rm m}^{3}\cdot {\rm d}$). The MBBR/SCR process was more compact and significantly cheaper than a conventional trickling filter/solids contact or activated-sludge process at the Moa Point site.