Example of Project Competition of Ammonia- Oxidizing and Nitrite-Oxidizing Bacteria CE Environmental Biotechnology University of Notre Dame

Problem: Eutrophication

Major Cases of Eutrophication Long Island Sound Chesapeake Bay Gulf of Mexico

Biological Nitrogen Removal 1) Nitrification Ammonia oxidizing bacteria (AOB) (Nitrosomonas) NH O 2  NO 2 - Nitrite oxidizing bacteria (NOB) (Nitrobacter, Nitrospira) NO O 2  NO 3 -

Biological Nitrogen Removal 2) Denitrification Heterotrophic denitrifying bacteria (DB) NO BOD  NO 2 - NO BOD  N 2

N2N2 3e - 2e - DB NO 2 - Nitrogen Removal NO 2 - NO 3 - AOB NOB Conventional N removal Shortcut N removal NH 4 + 6e - 2e - SHORTCUT:  25% reduction in oxygen  40% reduction in BOD

Nitrification Under ambient conditions and DO over 2 mg/L, growth kinetics are similar for AOB and NOB High temperatures: AOB significantly faster than NOB Low DO: AOB outcompete NOB for oxygen

Hollow-Fiber Membrane-Supported Biofilms 281  m 1  m Water O2O2 O2O2 BOD  Hydrophobic polymers  High specific surface area  Variable driving force  J=K(C L -C)  Low energy consumption

Hollow-Fiber Membranes for Gas Transfer 1 mm 2  m

Membrane Aerated Biofilm Reactor (MABR) Biofilm liquid (aerobic) Solid attachment surface DO BOD NB LDL HB Biofilm Membrane attachment Liquid (anoxic) BOD DO O2O2 LDL NB Alternative approach HB

Research Needs Under conditions observed in the HMBP process: How does bulk liquid DO impact stratification and activity of AOB and NOB? How does membrane gas pressure impact stratification and activity of AOB and NOB?

Reactor Conditions Anticipated effluent ammonia will vary between 2 and 3 mgN/L Expose pressurized single membrane in a column to 3 mgN/L ammonia at a very high loading rate Small decrease in ammonia will be observed due to high loading

Reactor Conditions What does bulk liquid concentration matter? Monod kinetics Concentration observed by the biofilm controls growth of bacteria Therefore, the effluent concentration expected in the HMBP will control the ecology of the biofilm

Modeling Aquasim 2.0 software Biofilm compartment and membrane compartment Simulates impact of bulk liquid DO and membrane pressure on biofilm Same modeling concepts as used for HMBP (Downing and Nerenberg, 2007b)

Modeling Conditions modeled 50 day simulation Steady-state conditions Experiment Ammonia Concentration Intra- Membrane Pressure Bulk Liquid Oxygen (mgN/L)(psi)(mg/L)

Modeling Results - Activity 10 psi, 2 mg/L DO 10 psi, 0 mg/L DO 5 psi, 0 mg/L DO Ammonia (♦), nitrite (■), and nitrate (□).

Modeling Results - Ecology 10 psi, 2 mg/L DO 10 psi, 0 mg/L DO 5 psi, 0 mg/L DO AOB (♦) and NOB (◊)

Modeling Results - Ecology NOB biomass with 10 psi and 2 mg/L DO ( ▲), 10 psi and 0 mg/L DO (■), and 5 psi and 0 mg/L DO (♦) NOB yield: mgVSS/mgNO 2 - AOB yield: 0.34 mgVSS/mgNH 4 +

Discussion Oxygen gradients select for AOB over NOB Higher DO provides an advantage to NOB Oxidation to nitrite rather than nitrate saves energy and addition of exogenous donor