At the bench scale, the performance of the HMBP was assessed for a variety of nitrogen and BOD loading rates. The nitrification rate increased from 0.8 to 1.7 gN m-2 d-1 in response to ammonium loadings increasing from 0.8 to 2.2 gN m-2 d-1. The nitrification rate remained at approximately 1.2 gN m-2 d-1 over BOD loadings of 4 to 17 gBOD m-2 d-1 at a nitrogen loading of 1.7 gN m-2 day-1.
Liquid ion exchange microsensors were used to measure ammonium, nitrite, and nitrate gradients through the HMBP biofilm. Nitrite was shown to be the dominant form of oxidized nitrogen produced by the biofilm. This is a major benefit, as the reduction of nitrite rather than nitrate during denitrification reduces organic carbon demand by 40%. 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. Results suggest the process may be suitable for muncipal and industrial wastewater treatment.