Energy Recovery in Wastewater Treatment More than Biogas!

Transcription

1 Energy Recovery in Wastewater Treatment More than Biogas! Hugh Monteith, M.Sc., P.Eng. Hydromantis ESS, Inc. Hamilton, ON Energy Efficient Wastewater Treatment and Solid Waste Management Seminar Edmonton, AB, April 19, 2011

2 Biogas Presentation Outline What it is Where it comes from Why it is valuable How energy is recovered Other types of energy recovery in WW treatment Heat recovery from sewers and wastewater Potential energy from falling WW or effluent Biofuels and Microbial Fuel Cells

3 What Is the Source of Biogas? Anaerobic fermentation (digestion) of organic wastes (e.g. wastewater sludges) Could also be high organic strength wastewater On a simple basis, it is a 2-step 2 process Acidogenic bacteria convert complex organics to short chain volatile acids: Methanogenic bacteria convert volatile acids to methane and carbon dioxide Methanogens are slow-growing and control the digestion process

4 Why is Biogas Valuable? 60-80% methane by volume BTU/ft 3 Can be used on-site in a multitude of recovery units for: Heat Electricity Mechanical energy Can be purified (upgraded) for off-site vehicle use or natural gas substitute

5 Why is Biogas Use Green? Unused digester biogas is typically flared A waste of an energy source Release of 5-10% 5 methane in uncombusted biogas at flare [CH 4 GWP = 25 (over 100 years)] Electricity must be purchased for operations Use of biogas Reduces need for purchased electricity and related emissions by generation Reduces emissions from combustion of hydrocarbon fuels (CO, NO x, PM, NMVOCs,, etc.)

6 Emissions from Vehicles Fuel CO Emission Rate (g/km) Total HCs NO x CO 2 Partic- ulates Diesel , Nat l gas Biogas * Source: Trend-Setter. Biogas as a Vehicle Fuel: A European Overview, Oct. 2003

7 Before Biogas is Used Removal of Contaminants Moisture and particulates in all recovery processes Inefficient combustion, blocked nozzles Reduced by condensers, filters Hydrogen sulfide in most recovery processes In presence of moisture, forms sulfuric acid, which causes corrosion Reduced by iron salts, iron sponge,, scrubbers Volatile methyl siloxanes in most processes Leave highly abrasive silica on combustion surfaces Causes very high maintenance costs

8 More about Siloxanes Present in many personal care products Shampoos, body wash, deodorants Partition to biogas from sludge (volatile) During biogas combustion, carbon is burned away leaving silica (same as sand!) deposits on surfaces Very difficult to remove Treated by granular activated carbon (some patented) and condensers

9 Siloxane Deposits, Lewiston NY Photos courtesy Tim Lockwood Lewiston PCC

10 Siloxane Removal Granular activated carbon pellets Photos courtesy Tim Lockwood Lewiston PCC

11 Thermal Energy Recovery Boilers the simplest technology Most common process for biogas energy recovery Heat recovery only Heating of digester feed sludge and tank Space heating

12 Boiler, Terminal Island, CA Hot water Biogas Line

13 Energy Recovery Processes Sludge Combined Heat & Power (CHP) Digester Solids residual Biogas Gas treatment Energy Conversion Technology Thermal Energy Electrical Energy

14 Electricity from Biogas Assume Biogas is 65% methane by volume Methane heat value = 1000 BTU/ft 3 Electrical conversion efficiency = 33% Electricity produced kwh/ft 3 of biogas 2.24 kwh/m 3 of biogas

15 Gas Engine, Lewiston, NY Engine Generator Photo courtesy Tim Lockwood

16 Microturbines, San Elijo,, CA Microturbine Heat exchanger

17 Fuel Cell - Terminal Island, CA

18 Energy Recovery Processes Sludge Direct Drive Engine Digester Solids residual Biogas Gas treatment Energy Conversion Technology Thermal Energy Electrical Energy Mechanical Energy

19 Direct Drive Blower, Madison, WI Air to aeration DD Engine Blower Biogas Line

20 Off-Site Biogas Use Need to clean to pipeline natural gas quality Removal of moisture, H 2 S, siloxanes Also remove CO 2 to obtain required heat value Uses (almost all European) Vehicle fuel Natural gas pipeline supplement

21 Biogas as Vehicle Fuel Europe leads the way in biogas vehicle fleets (as of 2003) Sweden: 1500 vehicles and 22 re-fuelling stations Switzerland: 600 vehicles (biogas/ng blend) France (Lille): 124 vehicles (buses) Iceland (Reykjavik): 44 vehicles Italy (Rome): 12 vehicles Source: Trend-Setter. Biogas as a Vehicle Fuel: A European Overview, Oct. 2003

22 Biogas as Vehicle Fuel Sweden is a global leader Biogas-fueled buses Biogas-fueled garbage trucks Pictures: europe.org

23 How Does Sweden Do It? Dual biogas/natural gas compression to overcome fluctuations in biogas production Costs relative to fossil fuel use are approx. equal there, and higher maintenance costs are acceptable Longer term contracts signed with transport operators A determination to adopt more sustainable and environmentally friendly technology In 2003, 12% of Stockholm s s 85 waste collection trucks were biogas powered Half of Stockholm s s city center buses are to operate on biogas in 2008

24 Natural Gas Supplementation Most European countries have developed standards for biogas supplementation to a natural gas grid E.g., minimum energy value, and limits on moisture, dust, CO/CO 2 and total sulfur A Swedish study confirmed the risk of pathogen transmission from biogas was the same as for natural gas

25 Biogas: a Chemical Feedstock? Methane is used as a chemical precursor Production of hydrogen, methanol, acetic acid and acetic anhydride Steam reforming process produces CO and H 2 This is the basis for fuel cells operating on biogas The Int l l Energy Agency report suggests that the EU will be a net importer of natural gas by 2010

26 Producing More Biogas Technologies that make secondary sludge more digestible by cell lysis Mechanical processes such as sonification and pulsed electric fields Heat and pressure (CAMBI) Heat and chemicals (Micro-Sludge) Others Co-digestion of organic waste Kitchen wastes, fats, oils, and greases e.g., EBMUD and others

27 Innovative Energy Recovery Heat recovery from wastewater Potential energy recovery Biofuels Microbial Fuel Cells

28 Recovery of Heat from WW Whistler, BC Winter Olympics Village

29 Recovery of Heat from WW Whistler, BC Winter Olympics Village Up to 9 o F of heat extracted from Whistler s treatment plant effluent Closed loop pipe of heated water runs 0.3 mi to Athletes Village (over 65 buildings) for space and hot water heating Two 800 gpm heat exchangers extract 3 MBTU/hr each from the effluent 2 back-up gas-fired boilers are available Estimated payback of years Source: AWWA,

30 Recovery of Heat from WW Saanich Peninsula (Vancouver Island, BC) Heated recovered from the SP WWTP will be used to heat the swimming pool of the local recreation center and potentially other adjacent buildings and homes Expected completion date: summer 2010 Zurich, Switzerland Heat recovered by an energy utility from the Werdhölzli wastewater treatment plant effluent will save 5 million litres of heating oil a year

31 Recovery of Heat from WW Swiss sewer pipe technology from Rabtherm Used at 2010 Winter Olympics Typical heat extraction rate is 2-99 kw/m 2 of heat exchanger area Note embedded thermal fluid exchange lines Investment cost is $ /kW 1960/kW of connected heating power for complete heating system Payback period ranges from 2 to 7 years Source: Water 21, June, Picture: Rabtherm Energy Systems

32 Energy Recovery from Effluent Drops Vienna, Austria AWTP discharges 560,000 m3/d (148 MGD) to Danube River Drop to Danube River from plant outfall 5 m (16.5 ft drop) between headworks and Danube River Electricity requirements for operation = 175,000 kwh/d (63.8 Million kwh per year) Vertical axis turbine produces 1.5 Million kwh per year used on-site in treatment plant s s grid (2.6% of plant use) Source: AquaTreat,

33 Energy Recovery from Effluent Drops Clark County, NV 150 MGD treated effluent to Lake Mead (2007) 400 MGD effluent by 2050 Systems Conveyance & Operations Program Approx. 400 ft drop over conveyance length of 72,000 ft (overall slope = 0.56%) Source: Karafa et al., WEFTEC07

34 SCOP Hydraulic Profile City of Las Vegas Diversion Structure Elev ft Hydroelectric Powerhouse Elev ft ~400 Lake Mead Source: Karafa et al., 2007

35 SCOP Projection 16 MW hydroelectric generating station Two 8.25 MW Francis type turbines 85 Million kwh/yr generated per year Annual pumping energy required = 4 Million kwh Connects to grid by switchyard 0.5 mile away from powerhouse Net present value of electricity generated = $60/MWh ($0.06/kWh) Power generation startup slated for 2012

36 Northern Cal. Power Agency Innovative use of POTW effluent for injection to geothermal field Lake County Sanitation District effluent pumped at 6,000 gpm through 26 mile Southeast Geysers Effluent Pipeline Injected effluent is turned into steam for electricity generation In operation since 1990s, by 2007 generated 100 MW of electricity from effluent But, even better

37 NCPA Geothermal Project Effluent drops 100 ft in injection wells to 1700 ft of water column (water head of hydro system) Small water turbines installed in the bottom of each injection well Currently 250 kw/yr capacity added to grid Plans to expand to 500 kw/yr capacity by late 2010 Source: Environmental Council of Sacramento,

38 Biofuels from Algae? LCA assessment of algae for biofuels Not sustainable compared to biofuels from land-based crops without ready source of nutrients large land footprint Can be feasible using treated WW effluents CAS effluent better than BNR effluent because of higher remaining nutrient levels Source-separated urine has highest potential Source: Clarens et al., Environ. Sci. Technol. 2010, 44,

39 Biofuels from Algae? Dr. Robert Ruan,, University of Minnesota working Metro. Council Environmental Services (Twin Cities) Settling pond sludge centrate is nutrient-rich rich feedstock One acre of algae, even in an inefficient open pond, can produce 5,000 gallons of biodiesel per year (100x more than soybeans) Cultured algae yield 30 percent of their mass as oil, and grow fast enough to be harvested daily Oil recovery from the algae is a major economic hurdle Source: G. Breining, Environment

40 Biofuels Using Bacteria? Production of ethanol from sewage sludge a special bacterium converts cellulosic fraction of wastewater sludge MIT Technology Review, Oct. 13/09

41 WW Microbial Fuel Cells A little known fact The chemical energy in raw wastewater is approximately 9x that needed to operate the whole POTW (Shizas( and Bagley, 2004) Microbial fuel cells (MFCs( MFCs) ) can extract this chemical energy MFCs are still in early development stages, but efficiencies are improving rapidly Bruce Logan, Penn State U Nancy Love, U Michigan Baikun Li, U Connecticut

42 How a Microbial Fuel Cell Works Microbes convert organics (COD) in the anode, producing protons and electrons H 2 O --> > 12CO H e - C 12 H 22 O 11 Electrons travel to the cathode via the external electric circuit, creating a current Anode Cathode Photo of MFC from Dr. B. Li Protons travel to the cathode though a membrane In the cathodic compartment, protons and electrons combine with oxygen to form water

43 Resources for Biogas Energy Global Bioenergy Partnership: International Energy Association: European Union s TrendSetter program: europe.org/index.php?id=953

44 Recap Energy from WWT Digester biogas has been main form of recovered energy More plants are using CHP New technologies enhance biogas production Wastewater (raw or treated) has Thermal energy value Potential energy Chemical energy (raw WW) WW effluent and sludge can be a substrate for biofuel production Biogas could be a potential chemical feedstock

45 The Message Wastewater and sludge are not waste materials, but resources to be exploited

46 The End! Any Questions Hugh Monteith software.com Mobile: