Wastewater Management: Problem or Opportunity? CEE357 Seminar November 29, 2012 H. David Stensel, PhD, PE University of Washington
Overview of Presentation Traditional Wastewater Treatment Activities Sustainable technology in wastewater treatment Energy production and utilization in wastewater treatment Codigestion for increased methane production Phosphorus recovery
Domestic Wastewater Management in U.S. About 22,000 publically owned wastewater treatment systems for 75% of the United States population treat about ~30 billion gallons of wastewater per day ~60 million lbs/day of organic substances ~11 million lbs/day of nitrogen ~2.5 million lbs per day of phosphorus.
Conventional Pollutants in Wastewater Constituent Unit Value (typical) Solids, total (TS) mg/l 390-1230 (720) Dissolved, total (TDS) mg/l 270 860 (500) Suspended solids, total (TSS) mg/l 120 400 (210) Biochemical oxygen demand mg/l 110 350 (200) (BOD) 5-d, 20 C Total organic carbon (TOC) mg/l 80 260 (140) Chemical oxygen demand mg/l 250 800 (450) (COD) Oil and grease mg/l 30 90 (60) Total Nitrogen (TKN) mg/l 25-75 (40) Total Phosphorus (TP) mg/l 4 9 (6)
Elements of Conventional Wastewater Treatment Energy Hog Biomethane
Looks like a work of art!
Water and Wastewater Utilities and Municipal Energy Uses At CDM, We Don t Make the Energy Savings. We Make the Energy Savings Better. J. Peters, P.E. 1*, BCEE, Chris Varnon, P.E. 1, Dean Towery2, WEFTEC, 2008
Traditional Goals for Wastewater Treatment Protect public Health Minimize discharge of pathogens Protect environmental health Minimize oxygen deficit in surface waters Organic loads Eutrophication due to nutrient enrichment Recreational and beneficial uses of water
Cuyahoga River, (Cleveland, Ohio) Convenient disposal for industrial and municipal ii wastes Famous for river on fire 1969 Helped pass the 1972 Clean Water Act
Fish Kill in China due to Oxygen Depletion
What are the effects of excess nutrients? Low oxygen levels in water. photo of dead fish (webpage electronic photo image, EPA; 35 mm slide, Kent Mountford, CBPO) Not to be outdone CHESAPEAKE BAY FISH KILL
Algae Biomass Production ALGAE COMPOSITION: C 106 H 263 O 110 N 16 P C:N:P Ratio = 106:16:1 1 Lb of P can produce 106 Lbs of Algae Biomass & 1 Lb of N can produce 16 Lbs of Algae Biomass 1 Lb of Algae Biomass = 1.24 Lbs of COD (BOD u ) Therefore: 1 Lb P can generate 131 Lbs of COD, 5 mg/l effluent P can generate 655 mg/l COD, and 1 Lb N can generate 19.8 Lbs of COD, 1 Lb N can generate 19.8 Lbs of COD, 20 mg/l effluent N can generate 397 mg/l of COD.
These focused on effluent goals Increasing interest on other issues Energy needs and carbon footprint Greenhouse gas emissions Sustainable technology
What is Sustainability? Preserving Resources for future generations Energy Social Environmental Stewardship Greenhouse Gas
Evolving Urban Water and Residual Management Paradigms: Water Reclamation and Reuse, Decentralization, Resource Recovery by Dr. Daigger with CH2M HILL at WEFTEC, 2008 Sustainability Criteria for Wastewater Treatment 1. Water reclamation and reuse 2. Reduce process energy demands 3. Recover energy 4. Reduce release of greenhouse gases (CH 4 and CO 2 ) at WWTP or off-site 5. Recover nutrients; nitrogen, phosphorus
Technology Exist and demonstrated for reclaimed water, ~2.5% currently used Potable Water Reuse 16
Reduce Process Energy Demands
Port Orchard Karcher Creek WWTP Reducing Energy Demand and Energy Recovery HYDROVOLT SYSTEM
Energy is available from Wastewater is available as heat or by conversion of organic material (COD) Constituent Unit Value Wastewater, heat MJ/ 0 C-1000 m 3 4,200 basis Wastewater, COD MJ/kg COD 12-15 basis Conversion of COD to energy Thermal oxidation- need to reduce water content Anaerobic degradation water not a problem Biomethane
Methane Use Generally needs cleaning CH 4, CO 2, H 2 S, siloxanes Canbeusedtomakeelectricityon electricity on site Some used to heat digesters to 35 0 C Used in city vehicles Added to natural gas pipeline King County South Plant Renton. WA
Municipal Anaerobic Digestion Biomethane Production Bacteria digest solids to produce methane and carbon dioxid Typically ~ 20 ft 3 methane gas Per ft 3 of feed! About 65% methane CODIGESTION Can add other community Wastes to increase biomethane Output i.e. food wastes, restaurant oils and grease Waste solids flow in Corona, California
m 3 J/1000 m M 50,000 40,000 30,000 20,000 Wastewater Energy Available biodegradable COD = 320 mg/l Effluent delta T = 10 0 C WWT bcod 75% E for heat pump WWT Heat 31,500 MJ 42,000 MJ 10,000 0 4,160 MJ Energy Source
Evaluation of wastewater biodegradable COD to energy - Assumptions 35% removal of bcod in primary treatment 50% of influent bcod oxidized in activated sludge 85% of bcod fed to digesters converted to CH 4 100 Hp/Million Gallon-d of wastewater treated 30% efficiency from methane to electricity 50.1 kj/g CH 4
5,000 About 33% of wastewater plant energy need can be provided by biomethane to electricity m 3 MJ J/1000 m 4,000 3,000 2,000 4160 4,160 1,700 WWT bcod Energy Need Biomethane Electrical 2,160 1,000 650 0 Energy Need and Sources
Opportunities for and Benefits of Combined Heat and Power (CHP) at Wastewater Treatment Facilities U.S. EPA (April 2007) ~1,000 facilities have influent flow >19,000 m 3 /d (~5.0 Mgal/d) 544 use anaerobic digestion 106 use methane for heating or electricity (76 use CHP) Note that t with heat recovery from electric generators about 80% of heat value is used.
How can more methane be produced? d? Increase bcod removal in primary treatment About 25% of waste organics are not converted technology to convert this carbon. Find other waste sources to add to the anaerobic digester Co-Digestion
Codigestion Add other local wastes to municipal anaerobic digesters Fats, oils, grease (FOG), food processing, distillery, beverage, biodiesel, food wastes etc High concentration, small volume, 50 200 g COD/L
UW Activities Codigestion of biodiesel wastes Control Digester Biodiesel Waste Co-Digester SRT (days) 15 15 WPS + WAS 4,600 4,600 Avg. Daily Load mg bcod / L Reactor / Day mg bcod / L Reactor / Day Biodiesel Waste Avg. Daily Load - 1,840 mg bcod/l/day (29% of total bcod load)
Co-Digester: 15-day SRT with daily biodiesel waste additions
Example of Questions with Codigestion Methane production efficiency of waste? How is waste feed collected, stored, fed to digester? Inhibition Is acetoclastic methanogenesis (V max ) inhibited by glycerol? a No inhibition by glycerol at 11,200 mg scod / L and below Acclimation Is glycerol readily degradable in sludge digestion? Glycerol degradability improves with acclimation time Degradability Is biodiesel waste fully degradable in anaerobic digestion? Biodiesel waste is 100% biodegradable in acclimated sludge
Examples of codigest substrates UW lab study (Heidi and John) Table 1: Description of Co-digestion Substrates Parameter Description Substrate A scum material collected from CTP s primary clarifiers flower and vegetable wastes collect from a pilot Substrate B source separation program Substrate C blood product from the processing of animals dissolved air floatation sludge from the rendering Substrate D process Substrate E grease trap material (brown grease) liquor from a tallow separation tank of a chili, soup Substrate F and salad ad dressing manufacturing ac u plant dissolved air floatation sludge from a chili, soup and Substrate G salad dressing manufacturing process confectionary waste, sugar, caramel, nuts, butter and Substrate H chocolate Substrate I bear, wine, soda and juice waste products
Waste Characteristics affect methane production. Fats, oil and grease (FOG) have high energy output Theoretical Gas Production from Different Organic Waste Components (Li et. al. (2002)) Gas Compon Production CH 4 % Reaction of Methane Fermentation in ent m 3 - Biogas biogas/kg Lipids (Fats) C 15 H 90 O 6 + 24.5 H 2 O 34.75 CH 4 + 15.25 CO 2 22.9 69.5 Carbohy drates (C 6 H 10 O 5 ) + nh H2 O 3n CH 4 + 3nCO 2 13.3 3 50 Proteins C 11 H 24 O 5 N 4 + 14.5 H 2 O 8.25 CH 4 + 3.75 CO 2 + 4 NH 4+ + 4HCO 3 14.8 68.8
Another exciting resource recovery topic Phosphorus h Recovery
(MODIFIED) BARDENPHO PROCESS Another problem turned into an opportunity ANAEROBIC INFL. AEROBIC ANOXIC ANOXIC WAS Gravity Thickener Centrate / Filtrate Anaerobic Digestion Dewatering RAS Biosolids Anaerobic contact selects for bacteria that store large amounts of P and thus P removal without chemicals BUT -anaerobic digestion P released, struvite can form scaling gp problems, need to deal with P in recycle add chemicals 47
Phosphorus Recovery Need enhanced biological phosphorus removal process Solids digestion releases phosphorus Controlled formation and removal of struvite in digester solids dewatering liquid (MgNH4PO4) control ph and add Mg Portland, Oregon has first U.S. facility Ostara Process Biological phosphorus removal process on liquid stream Excellent fertilizer, also high in nitrogen 60% of domestic waste phosphorus recovered
(Mg 2+ ) P Recovery Reactor Plate Settler Side Stream Treated Side Stream Hydrocyclone P recovery Product Pelletizer Complete Mixed Reactor based Phosphorus Recovery Process (MultiForm)
Wastewater is a resource!! Water reuse Organic material conversion to biomethane Other codigestion wastes can be handled at wastewater treatment facilities Heat recovery from effluent and electricity production Phosphorus recovery is feasible Sustainable technology important to utilities Requires integrated and comprehensive design evaluations