Membrane Aerated Biofilms: Who is There, What are They Doing, and Why are They Beneficial

Transcription

1 Membrane Aerated Biofilms: Who is There, What are They Doing, and Why are They Beneficial Leon Downing, Ph.D. University of Notre Dame Freese and Nichols, Inc.

2 Outline Nitrogen removal in wastewater What is a membrane aerated biofilm (MAB)? Past application research Fundamental research needs Impact of oxygen gradients Impact of BOD concentrations Results Discussion and conclusions

3 Nitrogen Removal in Wastewater Conventional N removal Nitritation a.k.a Shortcut N removal NH 4 + AOB NO 2 - X NOB X 6e NO - - 2e - 3 DB N 2 3e - NO 2 - DB X 2e - AOB - ammonia oxidizing bacteria NOB - nitrite oxidizing bacteria DB - denitrifying bacteria

4 mgod/l Nitrogen Removal in Wastewater Why? Nutrient permits to protect water quality Energy reduction through reduced oxygen demand BOD Ammonium Nitrate Phosphorus removal

5 Membrane aerated biofilms (MABs) Water DO Air Membrane Aeration MBR Heterotrophic Bacteria Nitrifying Bacteria

6 Membrane Aerated Biofilms (MABs) Water Air MAB Advantages Concurrent nitrification and denitrification Biofilm process reduced bulk SRT for nitrifiers Nitrite DO accumulation? Heterotrophic Bacteria Nitrifying Bacteria

7 Past Application Research Membrane aerated biofilm reactors (MABR) Biofilm based process in columns High levels of TN and BOD removal at low loading rates (Semmens et al., Water Research, 2003) Shortcut TN removal suggested (Hibiya et al., Journal of Biotechnology, 2003; Schramm et al., AEM, 2000) Increased BOD loading leads to decreased nitrification (Walter et al., Water Research, 2005)

8 Past Application Research Hybrid Membrane Biofilm Process (HMBP) Relies on attached nitrifiers and suspended heterotrophs (similar to IFAS) Achieves TN removal with a low bulk liquid SRT and limited heterotrophic biofilm (Downing and Nerenberg (2007) WS&T) Less susceptible to BOD loadings; BOD concentration controls nitrification and impacts heterotrophic content of biofilm (Downing and Nerenberg (2008) Water Research) Pilot scale testing indicated low level TN removal (effluent <6 mgn/l) was possible with a real wastewater (Downing et al. (accepted) WER)

9 Research Needs Impact of constituent gradients on MABs Oxygen gradients and BOD gradients Who is there What are they doing How does this impact the beneficial aspects of MAB systems

10 Methods Column reactors with a single membrane Two sets of experiments, with a new membrane for each condition Varied intra-membrane pressure, constant ammonium and no BOD Varied BOD, constant intramembrane pressure and ammonium

11 Microsensor Studies 200μm HFM biofilm Measure gradients through the biofilm microsensor Small spatial resolution Determine flux into or out of the biofilm Net production of nitrite and nitrate

12 Methods Fluorescence in situ hybridization (FISH) DNA tagging technique Identify: Nitrosomonas spp. (AOB) Nitrobacter spp. (NOB) Nitrospira spp. (NOB) heterotrophs

13 Methods *Note: From Schramm, 1996

14 Density (10 9 cells cm -3 ) Density (10 9 cells cm -3 ) Results Impact of Oxygen Gradients Who s There? Lower DO Fewer NOB; Nitrospira spp. more prevalent Higher DO Nitrobacter spp. more prevalent kpa 35 kpa 70 kpa 70 kpa, Aerobic bulk kpa 35 kpa 70 kpa 70 kpa, Aerobic bulk Distance from Membrane ( m) Distance from Membrane ( m) Nitrobacter spp. Nitrospira spp. Downing and Nerenberg (2008) Biotechnology and Bioengineering

15 Flux (gn m -2 day -1 ) Results Impact of Oxygen Gradients What are they doing? Ammonium flux Nitrite flux Nitrate flux (aerobic bulk) Intra-membrane pressure (kpa) Downing and Nerenberg (2008) Biotechnology and Bioengineering

16 Nitrogen Flux (gn m -2 day -1 ) Results Impact of Oxygen Gradients What are they doing? Parameter Value Nitrobacter spp. μ 0.33 gn gx -1 day -1 K O2, Nit 0.51 gn m -3 K s, Nit 0.39 gn m -3 Nitrospira spp. μ 0.26 gn gx -1 day -1 K O2, Nsr 0.4 gn m -3 K s, Nsr 0.27 gn m Oxygen Concentration (g m -3 ) Nitrite Nitrate Ammonia Downing and Nerenberg (2008) Biotechnology and Bioengineering

17 Results Impact of Oxygen Gradients Why is this beneficial? Adjust MAB operation to your conditions Low carbon more nitrite accumulation Excess carbon higher nitrification rates Kinetics for NOB in biofilm systems Nitrospira spp. have a higher tolerance to low DO conditions Nitrospira spp. have a lower nitrite oxidation and SOUR that Nitrobacter spp. (Blackburne et al. (2008) Water Research)

18 Cell density (10 9 cells cm -3 ) Cell density (10 9 cells cm -3 ) Cell density (10 9 cells cm -3 ) Results Impact of BOD Concentration Who is there? Distance from Membrane ( m) Heterotrophs AOB Nitrospira spp. Nitrobacter spp Distance from Membrane ( m) Heterotrophs AOB 250 Nitrospira spp. Nitrobacter spp Downing and Nerenberg (2008) Applied Microbiology and Biotechnology Distance from Membrane ( m) Heterotroph AOB Nitrospira spp. Nitrobacter spp.

19 Flux (gn m -2 day -1 ) % Denitrification Results Impact of BOD Concentration What are they doing? Ammonium Flux Nitrite Flux Nitrate Flux % Denitrification Bulk Liquid BOD Concentrations (g m -3 ) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Downing and Nerenberg (2008) Applied Microbiology and Biotechnology

20 Rate (gn m -2 day -1 ) Results Impact of BOD Concentration What are they doing? CB Nitrification CB Denitrification MAB Nitrification MAB Denitrification BOD Concentration (g m -3 ) CB-Conventional Biofilm Downing and Nerenberg (2008) Applied Microbiology and Biotechnology

21 Results Impact of Oxygen Gradients Why is this beneficial? Bulk liquid BOD concentration controls nitrification Hybrid system lowers the bulk liquid concentration with decreased heterotrophic biofilm thickness Conventional biofilm vs. MAB MAB sustains nitrification at much higher BOD concentrations than a CB Downing and Nerenberg (2008) Applied Microbiology and Biotechnology

22 Conclusions/Discussion Fundamentals of MABs Oxygen concentration can be controlled within a biofilm The resulting oxygen gradients can be used to control shortcut nitrification BOD concentration is the controlling parameter for nitrification in MABs Nitrification in MABs is less sensitive to BOD concentration than nitrification in conventional biofilms

23 Conclusions/Discussion Application of nitrification dynamics Nitrospira spp. are selected for in low DO conditions Nitrospira spp. have lower nitrite oxidation kinetics, and their presence as the dominant NOB can lead to more nitrite accumulation Nitrification in a biofilm is dependent on the bulk liquid BOD concentration IFAS and MBBRs

24 Acknowledgements Advisor: Rob Nerenberg Nerenberg Research Group Funding agencies CICEET (Cooperative Institute for Coastal and Estuarine Environmental Technology) NSF GRFP (National Science Foundation Graduate Research Fellowship Program)

25 Questions?

26 Past Application Research DB NB DB NB BOD NB BOD NO 3 - DO Biofilm MABR NO - 3 DO BOD HMBP Biofilm