The Hybrid Membrane Biofilm Process for TN Removal from Wastewater: Bench and Pilot Scale Studies

The hybrid membrane biofilm process (HMBP) is a new approach to achieving total nitrogen removal from wastewater, with great potential for retrofitting into existing plants. It incorporates air-supplying hollow-fiber membranes into a conventional activated sludge tank. The HMBP utilizes both attached and suspended growth to achieve TN removal. At the bench scale, the performance of the HMBP was assessed for a variety of nitrogen and BOD loading rates. The nitrification rate remained at approximately 1.0 gN m^–2 d^–1 despite BOD loadings ranging from 4 to 17 gBOD m^–2 d^–1 at a nitrogen loading of 1.7 gN m^–2 day^–1. Denitrification rates of 100% were achieved when sufficient BOD was available in the influent. Microsensor measurements indicated nitrite was the dominant form of oxidized nitrogen produced by the biofilm, showing that shortcut nitrogen removal was taking place. Fluorescence in-situ hybridization (FISH) tests on the biofilm revealed a unique stratification, with three distinct regions: AOB and NOB near the membrane, strictly AOB at intermediate depths, and AOB and heterotrophs at the outer edge of the biofilm. Pilot scale studies with municipal wastewater primary effluent (PE) indicated a reduced nitrification rate. With an average nitrogen loading rate of 0.6 gN m^–2 day^–1, the average nitrification rate was 0.4 gN m^–2 day^–1, with a maximum of 0.6 gN m^–2 day^–1. These rates are similar to aerobic fixed film systems (i.e., RBCs). However, unlike other fixed-film systems, reduction of nitrate/nitrite to below 1 mgN/L was consistently achieved in the pilot scale HMBP, without the need for an exogenous electron donor.