Membrane Biofilm Reactor (MBfR): A New Approach to Denitrification in Wastewater Setting

Transcription

1 Membrane Biofilm Reactor (MBfR): A New Approach to Denitrification in Wastewater Setting Ramesh Sharma, Ph.D. Shane Trussell, Ph.D., P.E. Trussell Technologies, Inc. Pasadena, CA April 2007

2 Outline Understanding of the problem Regulatory aspect Autotrophs vs. Heterotrophs MBfR technology overview State of Art Previous work Piloting effort

3 Understanding of the Problem The Basics Regulatory aspects

4 Drivers for nitrogen removal Important component of water reclamation and reuse Stricter regulations with some locales having 6 mg/l N Some are talking about 2 mg/l N Difficult to go below 10 mg/l N Enlarging anoxic tanks Additional electron donor Both increases cost

5 Conventional MLE process Nitrate feed mg/l BOD mg N/L Anoxic Aerobic/ nitrification mg N/L 20 mg/l BOD Return activated sludge Sludge

6 Conventional Tertiary Treatment mg/l BOD mg N/L Anoxic Nitrate feed Aerobic/ nitrification Return activated sludge mg N/L 20 mg/l BOD Sludge Methanol Post denitrification Sludge Dosing Issues?

7 Conventional Tertiary Treatment mg/l BOD mg N/L Anoxic Nitrate feed Aerobic/ nitrification Return activated sludge mg N/L 20 mg/l BOD Methanol Post denitrification Sludge Dosing Issues? Sludge Can we use another approach?

8 Autotrophs vs. Heterotrophs Autotrophic bacteria Inorganic electron donor Hydrogen gas is electron donor Inorganic carbon source (CO 2 or HCO3 - No H 2 overdosing issue Low sludge yield (40% less) Heterotrophic bacteria Organic electron donor Methanol, acetate etc. Electron donor for nitrate reduction Carbon source for cell synthesis Methanol is toxic to humans

9 Why so much interest in H 2 now? Efficient delivery system was not available Low solubility Flammable (cannot be bubbled) MBfR overcomes the limitations of H 2 delivery Diffusion of H 2 Bubbleless delivery possible Hollow fibers

10 MBfR Technology Overview State-of-the-Art

11 MBfRs are not MBRs MBR = Biological reactor +filter Provides secondary treatment and Membrane separates biomass from the effluent water

12 MBfRs are not MBRs MBR = Biological reactor +filter Membrane separates biomass from the effluent water MBfR = bubbless hydrogen gas + biofilm and hence the name Membrane biofilm recator (MBfR) H 2 NO 3 - NO 3 - Biofilm H 2

13 Hollow-fibers a key player Can be operated at high pressure without bubbling H 2 Higher gas pressure inside the tubes improves H 2 availability for the biofilm Higher packing of fibers is possible Smaller foot-print Single fiber Open end for H 2 gas Sealed end

14 Counter-diffusion in MBfR: Membrane-Biofilm Partnership H 2 H 2

15 Counter-diffusion in MBfR: Membrane-Biofilm Partnership H 2 H 2

16 MBfR opens the door for Hydrogen All the advantages with hydrogen fueled autotrophic denitrifies can be exploited No overdosing issue Low solubility, ~1.2 mg/l at 1 atm Amount of electron donor needed is less Low sludge yield (40% less) H 2 gas is low-cost and non-toxic

17 MBfR Features H 2 gas diffuses through the walls across bubbleless hollow-fiber membranes Membrane is the meeting point for the nitrate and H 2, biofilm grows on the interface Nitrate is reduced to harmless N 2 gas Biofilm H 2 H 2 NO 3 - NO 3 -

18 Current status of the research Dr. Rittman and his group invented the technology Most of the work is in drinking water setting Partial or full removal of nitrate was possible (Lee and Rittman 2000, 2002, 2003) Removal of perchlorate, arsenate, chromate, selenate, bromate (Nereneberg and Rittman 2002, 2004) Pilot study for perchlorate and nitrate (Adham et al., 2003) Wastewater application is new Stricter regulation ( 1-2 mgn/l vs. 10 mgn/l) High solids

19 Piloting effort Grass Valley WWTP Lake Arrowhead, CA ~14,000 people 5,106 feet elevation

20 Treatment Train at GVWWTP Primary settling tank Trickling Filters Secondary settling tank 2.3 MGD WWTP BOD ~ 20 mg/l Nitrate 8-14 mgn/l Methanol Chlorine Denitrification tank Provides unique opportunity to compare MBfR and methanol fed denitrification

21 MBfR Module 330 micron o.d. 40,000 fibers Membrane area 42.3 m 2 Reactor Volume = 10.5 gal

22 MBfR Process Schematics Q R = 20 gpm

23 Two Pilot Units (long-term and short-term testing) Long-term O&M issues Short-term Loading rates HRT recycle rate Membrane flux

24 Pilot start-up Continuous mode 0.15 gpm flow rate (HRT = 70 min) 20 gpm recycle rate 15 psi hydrogen gas No inoculum was added Clean fibers at start

25 Pilot start-up At start After 10 days

26 Pilot start-up (autotrophs accumulate quickly) Influent NO 3 -N Effluent NO 2 -N Effluent NO 3 -N 0.0 3/9/07 3/14/07 3/19/07 3/24/07 3/29/07 Time, days

27 Current Efforts Evaluate hydraulic limitation of the system Recycle rate, HRT, loading rates, hydrogen pressure O&M issues and long-term performance evaluation Optimization of the MBfR configuration Membrane material Fiber diameter Packing density Bulk liquid mixing strategy Compare cost and performance with methanolfed denitrification

28 Conclusion MBfR combines biofilm and H 2 gas Eliminates need for organic C Over and under-dosing issues are irrelevant Less sludge yield Emerging contaminants removal Shows promise for low N Improved water quality decreased cost O&M issues remain

29 Acknowledgements Lake Arrowhead Community Services District Ken Nelson, Ryan Gross, Bob Bobik, and other LACSD staff members WateReuse Foundation Applied Process Technology, Inc.

30 Questions? Tel #