THE INNOVATIVE MOVING-BED BIOFILM REACTOR SOLIDS CONTACT REAERATION PROCESS FOR SECONDARY-TREATMENT OF MUNICIPAL WASTE-WATER

The innovative moving bed biofilm reactor/solids contact reaeration (M BBR/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 w ide range of organic loads under both steady and transient-flow condit ions demonstrated that the MBBR/SCR process produced the required effl uent quality at loads higher than used in the original design. At 3 da ys mean cell residence time (MCRT) in the SCR stage, a final effluent with a 5-day biochemical oxygen demand (BOD5) of less than 10 mg/L was achieved at an organic load on the MBBR of 15 g BOD5/ m(2).d (5.0 kg BOD5/m(3).d). With the same MCRT, a final effluent of less than 15 mg BOD5/L was achieved at an organic load on the MBBR of 20 g BOD5/m(2).d (6.7 kg BOD5/m(3).d). Dynamic loading tests demonstrated that a good- quality effluent was produced with a diurnal peak-hour load on the MBB R of more than 40 g BOD5/m(2).d (13.3 kg BOD5/ m(3).d). The MBBR/SCR p rocess was more compact and significantly cheaper than a conventional trickling filter/solids contact or activated-sludge process at the Moa Point site.