08/20/10 Feasibility Study - Border Environment Portalserver.cocef.org/Final_Reports_B2012/20109/20109_Final_Report_EN.pdf · According to 2009 projections from the population council

CESPT Food Waste Digester Feasibility DWW 08/20-10 Page 1

08/20/10

FFeeaassiibbiilliittyy SSttuuddyy

Biodiesel Production, using Biogas from the Digestion of Glycerin,

and Grease Traps’ Food Waste and Wastewater.

CESPT’s Atrapa la Grasa Programme, Baja, Mexico. Project Entity: BioTonalli S.A.P.I. de C.V.

Attention: Arturo Viniegra Cortes Berlin 345, Ampliacion Moderna Ensenada, Baja California. Mexico. Cell: (52) 1 55 55 04 70 28 Email: [email protected]

Location: Comision Estatal de Servivios Publicos de Tijuana (CESPT). Tijuana, BC, Mexico.

Contact: Ing. Hernando Duran Cabrera, General Director, CESPT

Engineer: Douglas W. Williams

Williams Engineering Associates 18039 Blue Winged Court Woodland, CA 95695

530-669-7236(Office) 805-459-2985 (Cell) [email protected] This document and its contents are CONFIDENTIAL AND PROPRIETARY information and the property of BioTonalli S.A.P.I. de C.V. This document should not be disclosed without the written consent of BioTonalli S.A.P.I. de C.V.


INTRODUCTION Purpose: to determine the Feasibility of an anaerobic digester and biodiesel processor to be located at Tijuana, BC, Mexico. This study includes the following components: I. Description of the existing site at CESPT. II. Characterization and Analysis of the Proposed Waste Stream

A. Wastewater from restaurant grease traps and other food waste B. Glycerin from Biodiesel production

III. Feasibility of anaerobic digestion

A. Collection and separation of wastewater from grease B. Mix tank for wastewater and glycerin C. Design parameters of an unheated, unmixed covered lagoon digester D. Design parameters of complete mix, heated digester E. Mixing and heating systems F. Piping into and out of digester G. Digester cover and liner specifications. H. Gas handling including blower, H2S filter, moisture removal, flare and piping I. Biogas engine, electrical generation, heat recovery and heat exchange with

digester contents J. Biodiesel plant specifications

IV. Cost Analysis

A. Phase 1: unheated unmixed covered lagoon digester costs and benefits. B. Phase 2: biodiesel production C. Phase 3: heated, mixed digester with electrical production.


Generation of Gas from the Digestion of Glycerin and Food Wastewater from Grease Traps

I. Description of the existing site at CESPT CESPT manages the San Antonio de los Buenos Waste Water Treatment Plant (WWTP) serving Tijuana, BC, and located near the Pacific Ocean. The project is located in the municipality of Tijuana in the northwestern side of the State of Baja California, Mexico. Tijuana borders the United States–San Diego, California Metropolitan Area– to the north, the municipality of Playas de Rosarito to the south, the Pacific Ocean to the west, and the municipality of Tecate to the east, (Figure 1- Location Map). According to 2009 projections from the population council of Baja California (CONEPO, by its initials in Spanish), the municipality of Tijuana has an estimated population of 1,590,420 residents.1. At present the WWTP processes 1,100 liters per second and uses aerated lagoons as the treatment process. Figure 2 shows an aerial view of the CESPT WWTP, with the potential digester site indicated by the yellow marker, “Punta Bandera”

Figure 1. Location map for CESPT sewage treatment plant 1. http://www.epa.gov/usmexicoborder/infrastructure/tijuana-unserved/pdfs/tijuana-expansion-ea.pdf


Figure 2. Aerial View of the CESPT WWT, with digester site, ”Punta Bandera”


II. Characterization and Analysis of the Proposed Waste Stream Flows

A. Wastewater from restaurant grease traps and other food waste: The anticipated loading of the digester will be a mixture of a)restaurant grease trap liquids, which are separated from the grease using a settling tank next to the digester and b) vegetable food wastes from the restaurants. The estimated initial volume of these wastes is estimated to be 10 cubic meters or 10,000 liters/day. The COD of this material, based on samples that were taken from a typical truck load, and sent to Dellavalle laboratory in Fresno, CA. These results, shown in Table 1 showed that the COD was 6,580 mg/l, with a total solids(TS) content of 20,500 mg/l(2.05%), and a volatile solids(VS) content of 16,500 mg/l(1.65%).

Total Total Nitrogen Total

pH NO3-N TKN TN COD TDS TSS TS VS unit mg/L mg/L mg/L mg/L mg/L mg/L mg/L mg/L

4.7 <0.1 379 379 6050 1300 17500 20500 16500 Table 1. Results of Laboratory Testing of Food Wastewater

The potential methane conversion rate from this material was found to be 0.53 cubic meters per kg VS in tests performed by the East Bay Municipal Utility District at their digesters2. At a methane % of 65%, this corresponds to a biogas production of .81 cubic meters of biogas per kg of VS. The assumptions and calculation for this biogas yield is as follows:

• 10,000 l wastewater/day X .0165 kg VS/l = 165 kg VS/day • 165 kg VS/day X .81 cu m biogas/kg VS = 134 cu. m.biogas/day

2.”Anaerobic Digestion of Food Waste” prepared for EPA by East Bay MUD, 2008. http://www.epa.gov/region9/waste/organics/ad/EBMUDFinalReport.pdf Table 2 lists the characteristics of the influent for the unheated, covered lagoon digester

Influent component

Total waste Daily input

Volatile solids content

Volatile solids input per day

Biogas Potential per day

(kg) % (kg) Cubic meters

Kg

Food wastewater

10,000 1.65% 165 134 162

Table 2: Biogas potential from only food wastewater


B. Glycerin from Biodiesel production A biodiesel facility will be located next to the proposed digester at the CESPT site, and will process yellow and brown grease collected from various restaurants and other processing facilities. Initially the volumes of grease collected will be 15,000 liters/month(~4000 gallons), to be increased to 60,000 liters/month (~16,000 gallons). The volume of glycerin produced as a byproduct during biodiesel production is one kg for every 10 kg of biodiesel. This form of glycerin is usually called crude glycerin and contains 80% glycerin by volume. The volatile solids content of this glycerin has been tested at 81% volatile solids(VS), and anaerobic digestion tests showed that the biogas yield was 0.72 liters/gr VS The reference for this number the ASABE paper cited below in footnote number 3. The assumptions and calculation for this biogas yield is as follows:

• 60,000 liters grease will produce 60,000 liters of biodiesel • 1 liter of biodiesel weighs .84 kg; • 60,000 l biodiesel X .84 kg/liter biodieselX1 kg glycerin /10 kg biodiesel =

5040 kg glycerin/month • 5040 kg glycerin/month/30 days/month = 168 kg glycerin/day • 168 kg raw glycerin/day X .8 kg pure glycerin/kg raw = 134 kg pure • 134 kg pure glycerin/day X .81 kg VS/kg glycerin = 109 kg VS/day • 109 kg VS/day X 1000 gr/kg X .72 liters biogas/gr VS = 78,000 liters • 78,000 liters biogas /1000 liters/cu. m = 78 cu. m biogas/day

3. Anaerobic Co-Digestion of Dairy Manure and Glycerin, by Xiguang Chen, et al, ASABE Paper Number: 084496, St. Joseph, MI. 2008. http://asae.frymulti.com/azdez.asp?JID=5&AID=25099&CID=prov2008&v=&i=&T=2&refer=7&access= Table 3 lists the glycerin available per day along with the food wastes and their respective VS contents, and the biogas potential from each influent component.

Influent component


Volatile solids content

Volatile solids input per day

Biogas Potential per day

(kg) % (kg) Cubic meters

Kg

Food wastewater

30,000 1.65% 495 400 484

Glycerin 168 65% 109 78 94 Table 3: Biogas potential from Food wastewater and Glycerin


Table 4. Influent C/N ratios

Table 4 shows the C and N contents for each substrate, and the resulting C/N ratio. For food waste, the laboratory results, listed in Table 1, showed that the nitrogen content was 379 mg/l, the volatile solids was 1.65% and according to the compost literature(Reference 4) the carbon content is 58% of VS. Reference 2 reported that for glycerin, on a VS basis, there amounted to 0.475 g C per g VS and 0.0017 g N per g VS, thus the C/N of glycerin was calculated to be 274. The combined C/N ratio was calculated to be 30, which is almost ideal for anaerobic digestion. 4. Carbon to Nitrogen Ratios of Various Waste Materials. http://www.norganics.com/applications/cnratio.pdf

Influent component


Volatile solids

Carbon, % of VS

Carbon Content

Nitrogen Content

C/N Ratio

(kg) % % Kg Kg Food wastewater

30,000 1.65 58 288 11.37 25

Glycerin 168 65 47.5 63 .23 274 Mixture 10,168 351 11.6 30


III. Feasibility of anaerobic digestion

A. Collection and separation of wastewater from grease Wastewater from restaurant grease traps will be trucked to the site and place in a sedimentation tank located next to the proposed digester, which is shown in Figure 4. Sedimentation is a treatment process in which the velocity of the water is lowered below the suspension velocity and the suspended particles settle out of the water due to gravity. The process is also known as settling or clarification. Settled solids are removed as sludge, and floating solids are removed as scum, which for this grease trap material, will be primarily fats, oils and grease(FOG). Wastewater leaves the sedimentation tank over an effluent weir to the next step of treatment. The efficiency or performance of the process is controlled by: detention time, temperature, tank design, and condition of the equipment.

Rectangular basins are the simplest design, allowing water to flow horizontally through a long tank. This type of basin is usually found in large-scale water treatment plants. Rectangular basins have a variety of advantages - predictability, cost-effectiveness, and low maintenance. In addition, rectangular basins are the least likely to short-circuit, especially if the length is at least twice the width. See Figure correct for a sketch of the settling/clarification basin. In S Out to Mix tank: Waste water and settleable solids Figure 3. Sedimentation tank This settling tank needs to have a volume such that it holds at least the volume of one of the tank trucks bringing the wastewater/grease mixture to the digester site. This volume is 5000 liters. Therefore the settling tank must be at least this volume, 0.5 cubic meters. A bar screen should be installed at the entrance to the settling tank, such that large particles, say 8 cm and larger, are prevented from entering the settling chamber. If possible, this settling tank should be heated to about 40 degrees C and gentling agitated by hand to break up the large particles of grease. In order to keep heavy non-organic particles from entering the mix tank, the outlet pipe should be located approximately 30 cm above the floor of the settling basin. After 1 to 3 hours of settling time, the wastewater is drained off the middle portion into the mix tank, and the grease is skimmed off the top to be taken to the biodiesel production unit.

Settleable solids

Floatable grease skimmed off to biodiesel production

Baffle to separate grease


. Figure 4. Existing 500-cubic meter concrete tank with proposed influent pipe and

location of gravity settling tank for grease trap wastewater

B. Mix tank for wastewater and glycerin The mix tank should hold at least one-day's wastewater and glycerin volume, or approximately 10,000 liters(2,500 gallons). The existing two polyethylene tanks of 5 cubic meters each will be satisfactory. These tanks should have a combination agitation/comminuting pump, that both mixes the wastewater and the glycerin, and also pumps the influent into the digester, through a new influent pipe that exits near the floor of the digester as shown in Figure 4. The agitation pump should be 5 horsepower with a voltage of 220 volts..

Proposed Gravity settling tank for food and grease trap wastewater

Biodiesel Processing, grease input from settling tank

Mix tank(s) for food waste, glycerin and grease trap wastewater, with agitation/comminuting pump

New Influent pipe to bottom of


Figure 5. Proposed digester using 500 cubic meter concrete tank at CESPT

C. Design parameters of an unheated, unmixed covered lagoon digester Figure 5 shows the 500-cubic meter tank with existing outlet structures(not functional) and the concrete walkway, which may be retained for support of digester mixers which may be used in the future. The initial digester should, however, be configured as an unmixed, unheated covered lagoon-type digester. In this first-step situation, the input will be only the 10,000 liters per day of food wastewater containing 1.65% volatile solids and producing 134 cubic meters of biogas per day as shown in Table 2. This is equivalent to over 4700 cubic feet of biogas per day which at 65% methane would have an energy content of 3 million Btu/day. This could fuel a large water heater/industrial boiler with from 100,000 to 200,000 Btu/hour capacity for 15 to 24 hours per day. This water heater could produce almost 200 gallons per hour or 4500 gallons per day of water with a temperature of 150 degrees F (65 degrees C). This would be hot enough to warm up the incoming wastewater to liquefy the grease. The value of this biogas, in terms of propane would be the equivalent of 30 gallons (113 liters) per day, which at $1.50/gallon would return over $15,000 per year. The capital cost of this system would be much less than that of an electrical generation system, and these details are listed in the Cost Analysis section of this report. Table 5 lists the parameters of this unheated, unmixed covered lagoon digester.

Overflow Pipe

Digester Mixer shaft to within 1m of floor


Digester Parameters and units Unmixed covered lagoon

digester@ 10 cu m

added/day Length (meters) 14

Width (m) 12

Average Depth (m), liquid 4.5

Freeboard, m 0.5

Side Slope, Vertical:Horizontal 4:1

Loading Rate (kg VS/cubic m/day) .33

Hydraulic Retention Time (days) 50

Digester Liquid Volume, cubic meters 500

Surface Area (square m) 168

Biogas Production, cubic m/day 134

Methane Content of Biogas, % 65

Biogas Energy @ 24 MJ/cubic meter, MJ/day

3216

Equivalent Liters of propane equivalent for water heater, l/day

113

Table 5. Parameters of an unmixed, unheated covered lagoon digester

The liquid influent, approximately 10,000 liters per day is loaded into the digester with dimensions given above. A cover is placed over 100% of this system. The effluent, also 10,000 liters per day overflows from the digester through a new effluent pipe, which is connected to a transfer pipe of approximately 250 meter length that exits at the adjacent CESPT Waste water treatment plant. Based on the assumptions given above, a preliminary mass and energy flow diagram of the digestion system is shown in Figure 6.


Total grease trap and food waste hauled in by truck, ~10 cubic meters/day Separated grease from settling tank Hauled to another site . Wastewater and food waste 10, 000 liters/day @ 1.65% VS ~ Digester Influent Liquids 10,000 liters/day @ 1.65 % VS, 165 kg VS/day @ .81 cu. m./kg VS, 134 cu. m./day - Biogas produced from digester@ 24 MJ/cu. meter 162 kg of biogas Heat exchanger

Digested Liquids ~ 10,000 liters /day @V.S. <0 .1 %

Hot water For heating influent and liquefying grease Figure 6. Flow Diagram Unheated, Unmixed, Covered Lagoon Digester Mass and Energy Flow diagram

Unheated, unmixed covered lagoon Digester 12m X 14m X 5m overall depth, 4.5m liquid depth, 500 cubic meters @ 50 –day Hydraulic Retention Time (HRT)

Overflow pipe, approximately 250 meters

Gravity settling tank

Hot Water Boiler/Heater with 100,000 to 200,000 Btu/hr , 100 to 200 MJ/hr

New Mix Tank and Pump

Wastewater treatment plant lagoons

Flare for waste gas


D. Design parameters of complete mix, heated digester If glycerin is included and the capacity of the digester is increased to 30,000 liters per day the digester could be converted to a complete mixed, heated reactor. This will require mechanical mixers mounted on the concrete walkway, and hot water coils in the digester to maintain the temperature at 35C. These mechanical mixers should be approximately 7.5 to15 horsepower each (6 to 12 KW), and the exact power requirements will be determined during the full scale design. The heating coils would be connected to a biogas-fueled internal combustion engine-cogenerator, which could also supply hot water for the heating requirements for the biodiesel production facility to be built next to the digester. The digester heating system will consist of HDPE pipe approximately 3” in diameter with warm water from the engine-water jacket pumped through them using a circulation pump. The approximate heat capacity of this heating system should be approximately 50,000 to 100,000 Btu/hour, and the capacity of the circulation pump to be determined during full scale design. This biodiesel facility will use yellow grease collected from various restaurants and other processing facilities, initially the volumes will be 500 liters/day (4000 gallons per month), to be increased to 2500 liters/day (20,000 gallons per month). The anticipated loading of the digester will be a mixture of: a) restaurant grease trap liquids, which are separated from the grease using a settling tank next to the digester, b) Food waste solids from the grease traps that may have separated at the sedimentation tank and previous screening c) Glycerin which is a byproduct of the biodiesel operation. This heated, mixed digester has the capability of handling up to 30 cubic meters of influent per day, corresponding to an HRT of 16 days, which would optimize the operation of this digester size and the parameters are shown in Table 6.


Digester Parameters and units Heated Mixed digester @ 30 cu m added

per day Length (meters) 14

Width (m) 12

Average Depth (m), liquid 4.5

Freeboard, m 0.5

Side Slope, Vertical:Horizontal 4:1

Loading Rate (kg VS/cubic m/day) 1.19

Hydraulic Retention Time (days) 16

Digester Liquid Volume, cubic meters 500

Surface Area (square m) 168

Biogas Production, cubic m/day 478

Methane Content of Biogas, % 65

Biogas Energy @ 24 MJ/cubic meter, MJ/day

11,472

Kwhrs/day @ 25% engine-generator efficiency

800

Hours of operation per day of the engine-generator, assuming 50 KW

16

Table 6: Complete/y Mixed and Heated Digester Parameters

The liquid influent, approximately 30,000 liters per day including the wastewater and the glycerin from the biodiesel plant is loaded into the digester with dimensions given above. A cover is placed over 100% of this system. The effluent, also 30,000 liters per day overflows from the digester through a new effluent pipe, which is connected to a transfer pipe of approximately 250 meter length that exits at the adjacent CESPT Waste water treatment plant. Based on the assumptions given above, a preliminary mass and energy flow diagram of the digestion system is shown in Figure 7.


Total grease trap and food waste hauled in by truck, ~30 cubic meters/day Separated grease from settling tank Other Yellow Grease

~ ~60 cu m /day . Glycerin 168 Kg/day Wastewater and food waste Biodiesel Production @ 65% VS 30, 000 liters/day @ 1.65% VS ~ 2000 liters/day Digester influent Liquids = 30,151 liters/day @ 2 % VS, 593 kg VS/day 478 cu. m./day - Biogas produced from digester@ 24 MJ/cu. meter 478 cubic meters Biogas/day End use is fuel @ 16 hrs/day 7 days/week, Heat exchanger 30 cu.m/hr(720 MJ/hr) Circulate hot water in heating pipe 11,472 MJ/day Loop in digester for new engine-gen

Digested Liquids ~ 30,000 liters /day @V.S. <0.1%

800 kwhrs/day 7 days/week Figure 7. Flow Diagram Complete Mixed and Heated Digester Mass and Energy Flow diagram The complete mixed and heated digester is estimated to produce biogas at an average rate of 478 cubic meters/day. The biogas will be transported by pipeline to a new engine-generator at the rate of 11,472 MJ/day, or approximately 720 MJ/hour assuming 15 hours per day, 7 days per week run time. This generator will produce 50 KW of electrical power at an efficiency of 25%, and 200 to 300 MJ /hr of thermal energy to heat lagoon. The gas produced during the hours that the engine is not running will be stored under the flexible digester cover.

Complete mix, heated Digester 12m X 14m X 5m overall depth, 4.5m liquid depth, 500 cubic meters @ 50 to 20 –day Hydraulic Retention Time (HRT)

Overflow pipe, approximately 250 meters

Biodiesel Plant

Gravity settling tank

50 KW engine generator @ 25% efficiency

New Mix Tank and Pump

Wastewater treatment plant lagoons

Heat Exchanger Thermal energy from: engine to heat digester, 200 to 300 MJ//hr


D. Mixing and heating systems 1. Use 1 or 2 mixers as shown in Figure 5, submerged chopper type pumps

with motor mounted on top of the existing concrete walkway. Horsepower and other specifications to be determined, estimated to be approximately 7.5 to 15 hp(6 to 12 KW)

2. Use submerged 3” diameter, coiled HDPE pipe connected to heat exchanger on engine-generator set, length to be determined

E. Piping into and out of digester

1. Sludge Removal, Length, to be determined, 4” diameter PVC, 2 sludge removal pipes mounted under the cover and near the bottom (approximately 12” off bottom, on concrete blocks), with perforations in portion of pipe mounted at bottom of digester.

2. Influent, use new 4” diameter PVC pipe from mix tank, through the cover and Length of piping to be determined.

3. Effluent, use new 4” diameter PVC pipe installed through digester wall approximately 0.5 meter below the top of digester. Connect this to new 250-meter pipe to wastewater treatment plant.

F. Digester cover and liner specifications.

The existing concrete tank will be utilized first as an unheated, unmixed digester with the influent being 10,000 liters per day food wastewater, no glycerin. The biogas will be utilized in a hot water boiler and/or waste gas flare. Later the digester will be converted to a mixed and heated digester, with dimensions of 14 meters long by 12 meters wide by 4 meters total depth and 4.5 meters liquid depth. The cover design is one that stores the gas for up to one-half day at 468 cubic meters per day, and then utilizes the gas in an electrical generation unit of 50 KW that consumes the biogas at the rate of 30 cubic meters per hour, 7 days per week and 15 hours per day. This cover design should include a relief vent system that allow excess and emergency biogas releases to escape through a pipe that is elevated high enough to provide adequate dispersion that ensures safety for all personnel. The cover design should include the perimeter biogas collection system, a rainfall removal system and a sludge removal system that includes two sludge pipes along the bottom of the digester, installed below the cover with the outlet end of the sludge pipes accessible above the cover.

G. Gas handling including blower, H2S filter, moisture removal, metering, flare and piping, for engine-generator operation.

1. Blower specification, 30 cu m/hr(16 scfm) (7 days/week, 15 hrs/day), @ 5 psi pressure, The blower is to be located at the generator / gas handling area.

2. H2S filter specification, 30 cu m/hr(16 scfm) (7 days/week, 15 hrs/day) ppmv input and 50 ppmv output of H2S. Iron sponge H2S filter, operating cost is approximately $.01/kwhr of electricity produced. The cost of H2S scrubbing will be $1000 for the Phase 1 digester and approximately $3,000 for Phase 3.


3. Moisture removal is by gravity condensing separator installed in the gas piping between the digester and the generator set.

4. Gas meter specification, pressure in and out, scfm, data storage capability. 5. Gas piping type: size and length. HDPE material is favored (probably most

cost effective. 6. System will be include an emergency flare to combust gas during generator

maintenance.

H. Biogas engine, electrical generation, heat recovery and heat exchange with digester contents

1. Engine-generator: 50KW, 250 Volts, 200 amps, 13,500 Btu/kwhr Heat rate, high heating value, and emissions

2. 750 Kwh generation per day, 7 days per week 3. Heat recovery specification, water jacket to effluent, 200 to 300 MJ/hr

(200,000 Btu/hr) I. Biodiesel plant specifications 1. Biodiesel production unit with capacity for 60,000 liters per month of biodiesel: 2. Process is as follows, assuming 20 days per month( See Reference 5 below) a) Day 1: Fill biodiesel processing tank with one-day’s production of waste oil, 3000 liters and warm to 40 degrees C, and settle out water and heavy residue. b. Day 2: Drain off water which has settled, and warm contents to 55 degrees C. Calculate sodium hydroxide to raise pH of oil to 8.0, approximately 3 to 5 gr per liter, or 10 kg to 15 kg NaOH. Measure the required methanol, approximately 20% of the oil volume, or 600 liters. This should be a 1000 liter tank Add the NaOH to the methanol, mix and then add this mixture (sodium methoxide) to the tank containing the waste oil, and agitate for at least an hour until completely mixed. The resultant mixture is biodiesel and glycerol and will settle into two distinct layers. Glycerol is more dense and will settle to the bottom of the tank. Leave to settle. c. Day 3: Pour off the glycerol which is noticeably darker and more viscous than biodiesel. The biodiesel can now be purified and filtered to use as fuel. d. Since this is a three-day process, the there needs to be 3 complete batch units available for meeting the daily requirement of 2000 liters per day. The tankage requirements are as follows: 1) 3- 4000 liter biodiesel processing tanks with agitators and heating system 2) 3- 1000-liter methanol tanks with agitators 3) 1- 10,000-liter biodiesel storage tank. 5.http://www.ag.ndsu.edu/pubs/ageng/machine/ae1344.htm


IV. Cost Analysis This cost analysis is presented in three phases: A. In the Phase 1 the grease and oils are separated so that the food wastewater goes to the covered lagoon digester described earlier where it is anaerobically treated such that the resulting effluent has less than 75 ppm grease and can be safely discharged to the WWTP. In this first phase BioRegeneradora sells all the grease to a third party for biodiesel conversion. Table 7 summarizes the costs and benefits of this digester. Table 7: Preliminary Cost and Benefit Analysis, Phase 1-Unheated unmixed covered lagoon digester, biogas used for water heating

COSTS: Phase 1: Unheated, unmixed covered lagoon digester for food wastewater only,

10 cu m/day

influent $

Grease separation tank, 5000 liters 5,000 Mix tank, 10,000 liters, one-day capacity 5 Hp influent and mixing pump

8,000 7,000

Digester Modifications: influent pipe(5 meters), effluent overflow pipe, 5 meters and sludge pipes, 20 meters

5,000

Digester liner and Cover 22,000 Effluent pipe connecting to WWTP, 250 meters 8,000 Gas Handling: Piping, H2S removal, blower Biogas Water Heater

15,000 5,000

Subtotal Equipment costs 75,000 Engineering @ 20% of Equipment 15,000 Contingency @ 13.3 % of Equipment 10,000 TOTAL CAPITAL COSTS 100,000 BENEFITS Estimated Annual Value of Biogas, equivalent to 10,000 gallons per year Propane Savings @ $1.50/gallon,

15,000

OPERATING COSTS: Annual Maintenance Costs @ 2% of Capital costs (2,000) Cost of Scrubbing H2S (1,000) Net Benefits 12,000 Simple Payback, years 8


B. Phase 2 will add the biodiesel production unit which was described in section I above and the costs and benefits are listed below in Table 8. Table 8: Preliminary Cost and Benefit Analysis, Phase 2 – Biodiesel production from waste oil/grease

COSTS: Phase 2: Biodiesel production unit, based on maximum of 3000 liters per day of waste oil/grease, 250 days per year operation Annual production 750,000 liters (200,000 gallons) biodiesel

US $

Grease separation tank, 5000 liters, included in Phase 1

Biodiesel processing tank, 4000 liters, with heating and agitation, 3 required Methanol Tank, 1000 liters, with NaOH addition, three required. Biodiesel storage tank, 10,000 liters, one required Other tanks, valves, pumps and controls Subtotal Equipment costs, based on $1/gallon of annual biodiesel

200,000

Engineering @ 15% of Equipment 30,000 Contingency @ 10 % of Equipment 20,000 TOTAL CAPITAL COSTS 250,000 BENEFITS Estimated Annual Value of Biodiesel, estimated at 200,000 gallons per year @ $1.50/gallon,

300,000

ANNUAL OPERATING COSTS: Methanol @ $.52/gallon 104,000 Sodium Hydroxide(NaOH) @ $.07/gallon 14,000 Electricity @ $0.05/gallon 12,500 Maintenance and Supplies @ $.05/gallon 12,500 Labor @ $.24/gallon 48,000 TOTAL ANNAUL OPERATING COSTS 191,000 Net Benefits 109,000 Simple Payback, years 2.3


C. Phase 3 is the heated mixed digestion of the food wastewater and the use of the biogas for cogeneration of electricity to be placed into the electrical grid at the WWTP, and residual heat. The residual heat available from the 50 KW generator is 200 to 300 MJ/hr, or an average of 250 MJ/hr( 237,000 Btu/hr). The biodiesel heating requirement is primarily that required to heat the grease from ambient temperatures, say 20 degrees C( 68 degrees F) to a maximum of 55 degrees C(131 degrees F). The actual heat requirement to heat 3600 liters of grease and methanol from 20 to 55 C would be 527 MJ or 500,000 Btu, assuming 50 % efficiency of heating, the actual heat required would be approximately 1 million Btu. The total daily heat available from the generator is 4,000 MJ (3.8 million Btu), so the estimated 3000 liters per day of biodiesel can be processed with 25% of the residual heat from the generator. The digester heating will require approximately 2000 to 3000 MJ (1.9 million to 2.8 million Btu) per day. Therefore the residual heat (4000 MJ) from the 50 KW generator can both heat the digester(3000 MJ) and provide process heat for biodiesel production(1000 MJ). The biogas can be used to power an engine generator with a rating of 50 kW. At a rate of 30 cubic meters per day of wastewater, this generator will produce approximately 274,000 kwhrs of electricity for export into the electrical grid at the WWTP. This would be worth approximately $27,400 in displaced electrical costs, with an additional 250 MJ/hr (237,000 Btu/hr), the equivalent of approximately 2 gallons of propane per hour, or $3/hour at present propane costs of $1.50/gallon, for a total of $16,000 per year in displaced propane costs. A summary of the estimated costs and benefits are detailed in Table 9. Shown here is the cost analysis if more wastewater can be obtained, up to 30 cubic meters per day, which is the maximum capacity of this digester. As shown, the capital cost is higher than the unmixed, unheated covered lagoon digester, $237,000, because of the need for larger grease separation and mixing tanks, a digester heating system and the engine-generator. The biogas production and thus electrical and heat production are higher, $42,000 per year and thus the simple payback is 7.5 years. It must be understood that this analysis does not include the potential returns from the tipping fees received from the restaurants for the disposal of their grease trap wastes. If this income were to be included, the simple payback on the investment would be fewer years.


Table 9: Preliminary Cost and Benefit Analysis, Phase 3- Complete Mix Digester System

Shown below is a site plan for the digester system with the location of the various components placed on an aerial view of the site, Figure 8.

COSTS 30 cu m/day

influent $

Grease separation Tank, 3-hour capacity 10,000 Mix tank, one-day capacity and influent pump Please breakdown

20,000

Digester Modifications: influent, effluent and sludge pipes, heating pipes, and mixer

20,000

Digester liner and Cover 22,000 Effluent pipe connecting to WWTP, 250 meters 8,000 Engine-Generator , 50 KW @ $1400/kw 70,000 Gas Handling, piping, H2S removal, blower 20,000 Electrical Interconnection 20,000 Subtotal Equipment costs 190,000 Engineering @ 15% of Equipment 28,000 Contingency @ 10 % of Equipment 19,000 TOTAL COSTS 237,000 BENEFITS Annual Electrical Savings @ $.10/kwh 27,000 Propane Savings @ $1.20/gallon 15,000 TOTAL BENEFITS 42,000 1.Annual Operating Costs @ $.023/kwhr, includes H2S scrubbing

(6600)

2. Annual Maintenance Costs @ 2% of Capital costs (2600) Net Benefits 31,800 Simple Payback, years 7.5


Figure 8. Site map and layout of digester components, not to scale

Digester

Settling Tank

Mix tank

Engine-Generator Pad and enclosure

Biodiesel processing area

Documents

08/20/10 Feasibility Study - Border Environment Portalserver.cocef.org/Final_Reports_B2012/20109/20109_Final_Report_EN.pdf · According to 2009 projections from the population council