The innovative moving bed biofilm reactor/solids contact reaeration process for secondary treatment of municipal wastewater

Abstract

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 (BOD 5 ) of less than 10 mg/L was achieved at an organic load on the MBBR of 15 g BOD 5 /m 2 ·d (5.0 kg BOD 5 /m 3 ·d). With the same MCRT, a final effluent of less than 15 mg BOD 5 /L was achieved at an organic load on the MBBR of 20 g BOD 5 /m 2 ·d (6.7 kg BOD 5 /m 3 ·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 BOD 5 /m 2 ·d (13.3 kg BOD 5 /m 3 ·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.