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Process and Utility Water Requirements for Cellulosic

Ethanol Production Processes via Fermentation Pathway

Journal: Energy & Fuels

Manuscript ID: Draft

Manuscript Type: Article

Date Submitted by theAuthor:

n/a

Complete List of Authors: Lee, Joo-Youp; University of Cincinnati, Chemical & MaterialsEngineeringLingaraju, Bala; Universityof Cincinnati, Chemical EngineeringProgramYang, Jeffrey; EPA, Office of Research and Development, NationalRisk Management Research LaboratoryKeener, Tim; University of Cincinnati, College of Engineering andApplied Science

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Process and Utility Water Requirements for Cellulosic Ethanol Production Processes via3

Fermentation Pathway4

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Submitted to6

Energy and Fuels7

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By9

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Bala P. Lingaraju, Joo-Youp Lee

,*, Y. Jeffery Yang

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Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical14

Engineering, University of Cincinnati, Cincinnati, OH 45221-001215

National Risk Management Research Laboratory, U.S. Environmental Protection Agency,16MS 690, 26 W. Martin Luther King Drive, Cincinnati, OH 4526817

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Page 1 of 33 Submitted to Energy & Fuels

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Process and Utility Water Requirements for20

Cellulosic Ethanol Production Processes via21

Fermentation Pathway22

Bala P. Lingaraju, Joo-Youp Lee,*, Y. Jeffery Yang23

Chemical Engineering Program, School of Energy, Environmental, Biological, and Medical24

Engineering, University of Cincinnati, Cincinnati, OH 45221-001225

National Risk Management Research Laboratory, U.S. Environmental Protection Agency, MS26

690, 26 W. Martin Luther King Drive, Cincinnati, OH 4526827

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ABSTRACT29

The increasing need of additional water resources for energy production is a growing30

concern for future economic development. For developing technologies such as ethanol31

production from cellulosic feedstocks, a more detailed assessment of the quantity and quality of32

water required, and the critical factors over water consumption which can be controlled in these33

technologies need to be identified for maximum water conservation. In this paper, the water34

requirement for fermentation process in cellulosic ethanol production is assessed on a volume-to-35

volume basis (gallons of water per gallon of ethanol produced). This process-based unit36

Page 2 of 33Submitted to Energy & Fuels

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of recycled water used, for which three feedstocks (i.e. hardwood, corn stover, and switchgrass)41

and two pretreatment processes (i.e. dilute acid and AFEX - Ammonia Fiber Expansion) were42

examined as an illustration. The results indicate that the pretreatment process and feedstock43

most significantly influence the degree of process water requirement, while the effectiveness of44

cooling tower design and operation offers the most likely opportunity for water saving. Water45

loss in evaporation reaches to ~75% of water input in ethanol fermentation. Use of recycled46

water reduces the water requirement by 50% compared to once through operation. However,47

water reuse in cooling water and to a lesser degree, pretreatment water, require intensive process48

operation for scale build-up and a high level of wastewater treatment because of the high49

chemical oxygen demand (COD) levels in the wastewater stream. In these aspects, further50

research and technology developments are necessary.51

KEYWORDS52

Cellulosic ethanol, water quantity and quality, wastewater treatment from cellulosic ethanol53

production.54

55

1. INTRODUCTION56

Finite petroleum resources along with the increasing demand for petroleum by emerging57

and developing economies have made industrial nations to search for new types of transportation58

fuels. The Energy Independence and Security Act (Energy Bill) of 2007 calls for a fourfold59

increase in the amount of biofuels, such as ethanol, currently produced in the U.S. by 2022. This60


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and 4 billion gallons from any source) respectively (1). The U.S. currently consumes ~14064

billion gallons of gasoline a year (2), and produces ~8.8 billion gallons of ethanol from corn65

kernels (3).66

Although there is only one biorefinery plant for the demonstration of cellulosic ethanol67

production with a capacity of 1.4 Million gallons per year (Mgy) (4) at Jennings, LA in the U.S.,68

there are many corn-derived fuel ethanol plants available in the country. There are currently69

~201 crop-based ethanol plants in the U.S. with a total name plate capacity of 13,063 Million70

gallons per year (Mgy) (5). Most of these ethanol plants use corn kernel as the feedstock along71

with other cellulosic and starch-based feedstocks. Other feedstocks such as corn stover,72

sorghum, sugar cane bagasse, beverage waste, wood waste, and cheese whey are part of the73

small percentages of feedstocks used (6). The operating capacity of the biorefineries is 11,53274

Mgy. There are also 16 plants under construction for the production of corn and cellulosic75

ethanol with a potential capacity of 1,472 Mgy (5), and these plants are being scaled up from76

pilot to commercial scale.77

Freshwater demand for energy production is a growing concern in the U.S. Increased use78

of biofuels is expected to offer benefits such as decreased dependence on foreign oil, but also to79

present challenges such as the depletion of domestic agricultural resources, air quality, surface80

and ground water (7). A National Research Council (NRC)s report also indicates that the81

current estimates of consumptive water use by ethanol biorefineries are 4 and 9.5 gallons of82

water per gallon of ethanol produced from corn kernels and cellulosic feedstocks, respectively83


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unsustainable sources. For example, current withdrawals in the High Plains Aquifer (more than87

1.5 billion gallons per day) are greater than the aquifers recharge rate (approximately 0.02~0.0588

ft/year in south central Nebraska) and the loss of this resource would be irreversible if the current89

withdrawal rate is not reduced (9).90

Cellulosic ethanol has received much attention in recent years as it does not compete with91

the food production by the use of by-products and energy crops which can grow in arid regions92

for ethanol production (10-13). It was reported that the water quantity requirement for irrigation93

significantly varies in terms of region (14). Yet, agricultural residues comprised of more than94

70% of biomass resources (3) for cellulosic ethanol production are by-products, and the water95

consumption in irrigation is directed at cultivating crops. Hence, in this study, the process and96

utility water requirement for cellulosic ethanol production is quantitatively evaluated. There are97

very few studies available about the water quality and quantity required for cellulosic ethanol98

production in the literature, and the quantity estimates available are summarized in Table 1.99

Among these, the two reportspublished by National Renewable Energy Laboratory (NREL) (15,100

20) have been widely used as a basis. The NREL developed a pilot plant for converting101

lignocellulosic feedstock to ethanol. Hardwood chips were used as the feedstock in the report102

published in 1999, and corn stover was used as the feedstock in the report published in 2002.103

For water quantity estimation, different authors have used various units of measurements to meet104

their respective objectives. The unit, gallon of water per gallon of ethanol production, is selected105

for this study so that the water requirement of future ethanol plants can be estimated by the106


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Expansion (AFEX)], and use of recycled water. The result shows a strong dependency of110

process water requirement on the choice of the pretreatment process for a specific feedstock. It111

highlights the importance of using recycled water to reduce fresh water make-up requirement112

and identifies the most important factor affecting water reuse.113

114

2. ANALYSIS PROCEDURE115

2.1. Case Selection116

The feedstock for cellulosic ethanol production can be classified into three following117

categories: forest residues, crop residues, perennial crops (3). Three representative feedstocks118

(i.e. hardwood, corn stover, and switchgrass) and two representative pretreatment technologies119

[i.e. dilute acid and Ammonia Fiber Expansion (AFEX)] are selected for this investigation.120

Detailed descriptions about the pretreatment technologies are present elsewhere (25, 26).121

Combinations of feedstocks and pretreatment technologies are summarized in Table 2, for which122

the water requirement is compared between different feedstock, pretreatment technologies, and123

the use of recycled water. Water in the process was classified into the following three124

categories: (i) fresh water is make-up water from an external source such as river and water well;125

(ii) recycled water can be either treated or non-treated process water. Treated water is the water126

to the wastewater treatment unit, subjected to aerobic and anaerobic treatment, and then recycled.127

Non-treated water refers to a direct evaporator condensate captured from the cooling process,128

which requires no further treatment; and (iii) Carried-over process water is the water in the129


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All the four Cases share a common process layout with minor variations on the132

distribution of freshwater and recycled water among the various units. The common process133

layout in Figure 1 is a schematic representation of the detailed flow diagram summarized from134

the NREL reports (15, 21) and other publications (24, 25). The individual process layout of each135

Case is shown in the Figures (3-6), among which water flow is the primary difference between136

individual layouts.137

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2.2 Water Quantity139

The water requirement analysis was based on overall water balance in the entire process,140

as well as for water balance in each unit operation. Water input into the entire ethanol plant141

(Figure 2) consists of (i) moisture in feedstock, (ii) moisture in the air, chemicals and nutrients;142

and (iii) make-up water. The overall water output from the entire ethanol plant includes water143

loss from the following: (i) windage and evaporation loss; (ii) vent to atmosphere; (iii) moisture144

included in solid waste; and (iv) other handling losses. The cellulosic ethanol production process145

typically has the following unit operations on the process side: pretreatment, fermentation, and146

product recovery. The utility section of the cellulosic ethanol plant consists of cooling tower,147

residue processing, steam generation, and wastewater treatment. The purpose and water148

consumption of each unit operation are as follows:149

Pretreatment: The pretreatment physicochemically changes the structure of cellulosic150

biomass to make the cellulose easily accessible to the enzymes in the conversion of cellulose and151


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the hydrolyzate before being sent to the fermentation unit in order to maintain a required solid-155

to-liquid ratio in the saccharification and fermentation tank.156

Saccharification & Fermentation:In this unit operation, the cellulose and hemicellulose157

are converted into sugars by the action of cellulase followed by fermentation by microorganisms.158

Water is required for the activity of microorganisms in the broth.159

Product Recovery: The product recovery section primarily constitutes the distillation160

section, where ethanol and water mixture is separated to produce ethanol. Along with the161

ethanol-water mixture, the product recovery section also receives a stream of carbon dioxide162

produced during fermentation. Water is required for scrubbing carbon dioxide from the vent163

stream and also for pre-heating the feed to the distillation column and for the reboiler.164

Cooling Tower: Cooling water is required throughout the process as utility water. For165

the NREL process (6), the following sections require cooling water: (i) cooling of pretreated166

hydrolyzate; (ii) cooling of the flash vent from the pretreatment unit and pneumapress air vent167

before being sent to wastewater treatment unit; (iii) maintaining the temperature in the168

fermentation tank at 41 C; (iv) cooling of rectification column reflux; (v) cooling of the waste169

water streams before entering anaerobic digestion; and (vi) cooling of the evaporator liquid into170

condensate for recycling water. Then heated water is cooled down by free or forced convection171

with make-up water acting as a heat sink in heat transfer. In this process, a significant amount of172

water is evaporated from the cooling tower and is counted as evaporation and windage loss. A173

typical cooling tower operation can consume 75% of the water sent to the cooling tower by174


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Steam Generation: Steam is required in the pretreatment section as process water and in177

the product recovery section as utility water for the preheater and reboiler of the distillation178

column. Fresh water is subjected to boiler feed water treatment before steam generation inside179

the boiler requiring the highest quality water.180

The individual cases for analysis are summarized in Table 2. The volumetric water flow181

rate in gallons per hour was divided by ethanol produced in gallons per hour in order to obtain182

water quantity consumption rate. In the calculation, the accuracy of the data is the same as that183

in the references, which are the sources of the data.184

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2.3 Water Quality186

Soluble solids, insoluble solids, and Chemical Oxygen Demand (COD) are the primary187

indicators of water quality affecting the cellulose ethanol production process. In this analysis,188

their concentrations were calculated for the streams sent to wastewater treatment, treated water,189

and water recycled without treatment. Then the COD of each stream was calculated by190

multiplying the mass flow rate of each component by a COD factor reported in a previous191

Merrick and Companys study (27).192

Recycled water: Water recycling is a supplement for make-upwater.. The high-strength193

wastewater treatment process consists of aerobic oxidation followed by anaerobic digestion for a194

typical COD reduction rate of 95%. A treatment feasibility study by DOE NREL (27) suggests it195

economical for a cellulosic ethanol plant to treat wastewater on-site instead of discharge to the196


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labeled as recycled water in the analysis. Separately, a series of centrifuges and evaporators are200

installed in series in distillation column to remove the solids and recycle water through a three-201

stage evaporation process (27). The evaporator condensate is referred as non-treated recycle202

water. In the NREL process design (20), the size of the wastewater treatment unit is reduced for203

treatment economics by routing the water containing high levels of suspended solids (SS) to the204

centrifuge-evaporator system. Water containing high levels of dissolved solids (DS) mostly of205

high COD content is routed to the wastewater treatment unit instead of the evaporator system. In206

this analysis, a small process variation in the water network was made to the individual cases207

leading to difference in the recycled water quantity in each Case. The differences in water208

network design are shown in the Figures 3-6.209

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3. RESULTS AND DISCUSSION211

Four Cases of cellulose ethanol production were analyzed for water consumption. In the212

overall water balance (Table 3), fresh water make-up is a single and the most important water213

input into the system. Other minor water flow components include feedstock moisture and214

moisture in chemicals and nutrients (i.e. 0-0.2 gal/gal). Fresh water make-up ranges 9-15 gal of215

water per gal of ethanol. Relatively, Cases 2, 3, and 4 require a greater amount of fresh water216

than Case 1 because of a smaller quantity of water recycled. Among windage and evaporation217

loss, the water loss from the cooling tower takes about 7580% of the make-up water supplied to218

the cooling tower. The loss from cooling tower windage and evaporation for Case 4 is largest219


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Table 4 shows the water quantity requirements for individual unit operations. Details are222

described below. Large potential exists to 1) recycle and reuse most of the wastewater; and 2)223

avoid the windage and evaporation water loss for significantly reduced fresh water make-ups.224

Pretreatment and Detoxification: In the water requirement estimation, the dilute acid225

pretreatment in Cases 1, 2, and 3 requires 1718 gallons of water in producing one gallon of226

ethanol irrespective of the feedstock, while the AFEX pretreatment (Case 4) consumes 13227

gallons of water for the production of a gallon ethanol. The process steam directly injected into228

the pretreatment reactor, accounts for 23 gallons of water per gallon of ethanol for Cases 1, 2,229

and 3 and for one gallon of water per gallon of ethanol in Case 4. In total, the water and steam230

usage differs among the four Cases (Table 4). Dilute acid pretreatment for switchgrass231

consumes the most water. On the other side, a combination of switchgrass and AFEX232

pretreatment in Case 4 yields almost three times as much ethanol than Case 3. This is largely233

related to the solids allowed in the pretreatment reactor. The solid to water ratio in the reactor is234

typically 30% to 70% for dilute acid pretreatment, and 50% for AFEX pretreatment (23-24).235

Furthermore, operating conditions differ among the four Cases. Typical operating236

temperature and pressure of the dilute acid pretreatment are 12.1 atm and 190 C, while AFEX237

pretreatment is typically operated at 21 atm and 90 C (24). For no stringent water quality238

requirement for the slurry dilution in the pretreatment reactor, recycle water can be used as the239

freshwater make-up for the slurry dilution. In Case 2 for example, the condensate from the240

evaporator was directly used without routing it through the wastewater treatment unit (Figure 2)241


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5 gal/gal to the waste water treatment, and 12 gal/gal as carried over to fermentation as the245

process water.246

Fermentation: Water consumption in fermentation is minimum as the hydrolyzate carried247

over from the pretreatment and detoxification unit is already water-diluted. Approximately 1248

gal/gal is added into the process to maintain the micro-organism growth in fermentation.249

Product Recovery: Fermented beer is distilled to separate ethanol from water in product250

recovery operations. Cooling water is continuously recirculated in the condenser of a distillation251

column with no addition of water. The vent scrubber for scrubbing CO2 before releasing252

consumes water at ~1 gal/gal rate. In order to minimize steam usage from this section,253

distillation column bottoms are concentrated using waste heat. The steam requirement as utility254

water for the reboiler and preheater of the feed stream is less than 0.5 gal/gal of ethanol for all255

Cases. This utility steam consumption is smaller than the process steam consumption for the256

pretreatment section in all Cases.257

Waste Water Treatment: The aerobic and anaerobic waste water treatment unit originally258

designed by Merrick and Company (28) was used in all the four Cases. High COD streams are259

sent to the waste water treatment unit, and a 95% decrease in the COD value was assumed to be260

achieved in the treated water streams. The input streams of the waste water treatment unit come261

from all unit operations. Those streams originate from the following unit operations: (1)262

Pretreatment: waste as flash vents and waste from ion-exchange unit (2) Product recovery: Part263

of the evaporator condensate is treated in the waste water treatment unit, and is routed back to264


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The quality of the water streams used in the cellulosic ethanol plant is summarized in268

Table 5. The COD level of the influent wastewater streams is in the range of 20,000

50,000 mg269

COD/L. After waste water treatment, a reduction of 95% or higher is expected, and the COD270

level will decrease to the range of 7002,500 mg COD/L. The COD level of influent wastewater271

depends on the streams that are chosen to be treated in the wastewater treatment. Hence the272

COD level of influent wastewater streams is different among Cases 14.273

Cooling Tower: The primary water consumption in the cellulosic ethanol production274

process stems from evaporation loss. Evaporation and windage loss accounts for 7080% of275

freshwater make-up. The loss can be avoided by switching to advanced cooling technologies,276

and some of the water saving options and alternatives under consideration and development are277

summarized in Table 6. From the water requirement analysis of the current cellulosic ethanol278

plant and the literature survey of water requirement for thermoelectric power plants, it is279

understood that a major share of make-up water withdrawal is used as cooling water. Hence, the280

development of advanced cooling technologies that can reduce cooling water consumption and281

utilize unconventional water resources will be critical to reducing water requirements for energy282

production (33-35).283

Steam Generation: Steam is required for direct injection into the pretreatment reactor as284

process water and for the preheater and reboiler in the product recovery section as utility water.285

The steam requirement for the preheater and reboiler in the distillation column is approximately286

less than 0 5 gal per gal of ethanol production and is much less than that for the pretreatment287


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alumina (15). The water quality of the boiler feed water in all the four cases is total suspended291

solids of less than 1% (15, 20). Because of these stringent water quality requirements, the292

wastewater treatment effluent (Table 5) is unlikely suited for stream generations.293

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4. CONCLUSIONS295

This paper describes an assessment of the process and utility water requirements for296

cellulosic ethanol production based on published literatures and unit process analysis (See297

Figures 1-6). The study is not intended for a life-cycle analysis of water usage from biomass298

production to waste disposal. Instead it is focused on detailed engineering examination of water299

usage and potentials for conservation in unit operations of a cellulosic ethanol plant.300

Overall, 1217 gallon water input used for one gallon ethanol production is derived in a301

mass balance analysis for four combination cases of feedstocks and pretreatment technologies.302

A comparison of the water quantity from the literature summarized in Table 1 for corn ethanol303

with that obtained from the current study for cellulosic ethanol shows that cellulosic ethanol304

production requires approximately twice as much water as for the corn ethanol. More305

specifically, our assessment results indicate that the pretreatment unit process primarily defines306

water consumption for both the process and utility water sides. Among the four Cases of307

cellulosic ethanol production pathways, AFEX pretreatment technology requires less process308

water than all three dilute acid pretreatment technologies. The water consumption rate is 13309

gal/gal ethanol compared to 1718 gal/gal ethanol in the diluted acid pretreatment. It also has a310

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higher (i.e. 14 gal/gal ethanol for Case 4, and 8 gal/gal ethanol for Cases 13) because of the314

chilled water requirement for the ammonia recovery. As a result, the total process and utility315

water consumption is indifferent for all Cases (i.e. 2829 gal/gal ethanol). In this study, the net316

water consumption (i.e. make-up water) listed in Table 3 is estimated based on the process317

configurations reported in the literature, and could be substantially different for different ethanol318

production processes. Nonetheless for the 4 Cases analyzed, the use of recycled as a substitution319

of make-up freshwater depends on process economics, and this in turn is a function of the make-320

up freshwater availability, and the capital and operating costs of an onsite wastewater treatment321

system to produce the required quality of recycled water. Overall, alternative water saving322

options and advanced cooling technologies are critically important to minimize freshwater323

consumption and reduce the large volumetric ratio of freshwater usage per gallons of cellulosic324

ethanol produced. Combined with effective water-resource planning, the water reuse and325

conservation in production process help mitigate the stresses of freshwater resources from a326

rapid growth of the ethanol industry.327

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6. ACKNOWLEDGEMENT329

The U.S. Environmental Protection Agency, through its Office of Research and330

Development, funded and managed, or partially funded and collaborated in, the research331

described herein. It has been subjected to the Agencys peer and administrative review and has332

been approved for external publication. Conclusions presented in this paper are those of the333

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purpose of the paper, and shall not be interpreted as endorsement of the products or services by336

the Agency.337

338

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LIST OF FIGURES AND TABLES437

FIGURES438

FIGURE 1. Process Schematic for Cellulosic Ethanol Production.439

FIGURE 2. Overall Water Balance of Ethanol Plant.440

FIGURE 3. Process Layout of Case 1 (Hardwood + Dilute Acid Pretreatment)441

FIGURE 4. Process Layout of Case 2 (Corn stover + Dilute Acid Pretreatment)442

FIGURE 5. Process Layout of Case 3 (Switchgrass + Dilute Acid Pretreatment)443

FIGURE 6. Process Layout of Case 4 (Switchgrass + AFEX)444

TABLES445

TABLE 1. Literature Review of Water Requirement for Ethanol Production.446

TABLE 2. Four Cases Analyzed for Water Quality and Quantity Requirement.447

TABLE 3.Overall Water Balance.448

TABLE 4. Water Balance by Each Individual Unit Operation for Four Cases.449

TABLE 5. Water Quality Used for the Four Cases.450

TABLE 6. Review of Water-Saving Options451

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TABLE 1. Literature Review of Water Requirement for Ethanol Production

Water Requirement Quantity Units of Water

Requirement

Feedstock Refere

nce

4.5 gal of water / gal of ethanol Corn Kernel (8)

Fresh water make-up* 9 gal of water / gal of ethanol Cellulosic (8)

Fresh water make-up* 3.5-6 gal of water / gal of ethanol Corn Kernel (13)

Fresh water make-up* 2.85 gal of water / gal of ethanol Dry Distillers

Grain

(16)

Fresh water make-up* 4.7 gal of water / gal of ethanol Dry Distillers

Grain

(17)

Fresh water make-up* < 3 gal of water / gal of ethanol Corn Kernel (18)

Fresh water make-up* 6 gal of water / gal of ethanol Corn Stover (20,21)

Water Re-circulated 2.6-46 gallons of water per each

mile travelled by a vehicle

with ethanol

Corn Stover (22)

Once-Through Water 5.6-63 gallons of water per eachmile travelled by a vehicle

with ethanol

Corn Stover (22)

Fresh water make-up* 5.79-16.681.5-4.3

liters of water per liter ofgasoline equivalent of

ethanol

Gallons of water per gallon

of ethanol

Switchgrass (23,24)

Note: * make-up = net = input - output455

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TABLE 2. Four Cases Analyzed for Water Quality and Quantity Requirements

Feedstock Basis(dry tonne/day )

Pretreatment Reference

Case 1 Hardwood 2,000 Dilute Acid (14)

Case 2 Corn Stover 2,000 Dilute Acid (20)

Case 3 Switchgrass 4,535 Dilute Acid (23)

Case 4 Switchgrass 4,535 AFEX (23)

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TABLE 3. Overall Water Balance*

Case 1(Dilute acid + Hardwood)

Case 2(Dilute acid + Corn stover)

Case 3(Dilute acid + Switchgrass)

Case 4(AFEX + Switchgrass)

Input (gallons of water per gallon of ethanol)

Feedstock Moisture 3 1 2 1

Air, Chemicals,Nutrients 0 0 Negligible Negligible

Make-up water 9 12 15 12

Inlet Total 12 13 17 13

Output (gallons of water per gallon of ethanol)

Evaporation Loss 7 7 7 10Vent to Atmosphere 2 2 3 2

Moisture in Residues

for Landfill 2 3 5 1

Handling Loss 1 1 2 0

Outlet Total 12 13 17 13

Note: * This water balance does not include carried-over and recycled water used inside the process.

ACS Paragon Plus Environment

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TABLE 4. Water Balance in Individual Unit Operations

Case 1

(Dilute acid +

Hardwood)

Case 2

(Dilute acid + Corn

stover)

Case 3

(Dilute acid +

Switchgrass)

Case 4

(AFEX +

Switchgrass)

Biomass capacity (Dry tonnes per day) 2,000 2,000 4,535 4,535

Ethanol capacity (Gallons of ethanol/hr) 6,181 8,219 7,018 21,888

Process Water (gallons of water per gallon of ethanol)

Input Output Input Output Input Output Input Output

Pretreatment Total water 17 17 17 17 18 18 13 13

Raw materials 3 (18%) 1 (6%) 2 (12%) 1 (8%)

Recycled water 9 (53%) 9 (53 %) 8 (47%) 7 (54%)Make-up water 2 (12%) 5 (29 %) 6 (29%) 4 (30%)

Process steam** 3 (18%) 2 (12%) 2 (12%) 1 (8%)

Fermentation Total water 13 13 13 13 13 13 13 13

Carried over water 12 (92%) 12 (92%) 12 (92%) 12 (92%)

Recycled water 1 (8%) 1 (8%) 1 (8%) 0 (0%)

Make-up water 0 (0%) 0 (0%) 1 (0%) 1 (8%)

Product Recovery Total water 13 13 13 13 14 14 14 14Carried over water 12 (92%) 12 (92%) 13 (93%) 13 (93%)

Recycled water 0 (0%) 0 (0%) 0 (0%) 1 (7%)

Make-up water 1 (8%) 1 (8%) 1 (7%) 0 (0%)

Utility Water (gallons of water per gallon of ethanol)

Cooling Tower Total water 8 1 8 1 8 1 14 4

Recycled water 5 (65%) 5 (60%) 3 (35%) 9 (64%)

Make-up water 3 (35%) 3 (40%) 5 (65%) 5 (36%)

Steam Generation Total water 3 3 3 3 2 2 2 2

Recycled water 0 (0%) 0 (0%) 0 (0%) 0 (0%)

Make-up water* 3 (100%) 3 (100%) 2 (100%) 2 (100%)

Note: Make-up water for steam generation* is used for process steam directly injected into the pretreatment reactor** andutility steam for the preheater and reboiler for the distillation column. The utility steam used for the distillation is not shown because

its consumption is relatively small.


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TABLE 5. Water Quality Used for Four Cases

Case 1(Dilute acid +

Hardwood)


Corn stover)


Switchgrass)

Case 4(AFEX +

Switchgrass)

Biomass capacity (Dry tonne/day) 2,000 2,000 4,535 4,535

Ethanol capacity (Gallons of ethanol/day) 148,344 197,256 168,432 525,312

Quality of Influent Wastewater to Wastewater Treatment

Total input mass flow rate (kg/hr)* 179,283 97,265 187,603 1,323,100

COD (mg COD/L)* 29,164 14,575 49,283 22,333

COD (kg/hr)* 5,511 1,446 4,833 29,917

% Soluble Solids < 0.1 < 0.1


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TABLE 6. Review of Water-Saving Options

Water Reduction Technology Water Reduction Claimed Reference

Hardness and silica removal process 20% (30)Dry cooling technology 20% (31)

Closed loop wet surface air coolers 50% (32)

Desalination of brackish waters to fresh water Not Available (33)


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FIGURE 1. Process Schematic for Cellulosic Ethanol Production


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Corresponding Author: E-mail: [email protected]. FAX: 413-556-0018.

123

4FIGURE 2. Overall Water Balance of Cellulosic Ethanol Plant.5

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WaterfromWWT

(7gal/gal)RW

CoolingTo

wer

Blowdow

n

(1gal/gal)WW

Hydroly

zate

(12gal/gal)

Produ

ct

(12gal/gal)

WasteW

ater

(1gal/gal)

7Figure 3. Process Layout Based on Case 1 (Hardwood + Dilute Acid Pretreatment8


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Waterfro

mWWT

(7gal/g

al)RW

Wat

erforCellulase

Production

(1gal/gal)RW

Cooling

Tower

Blowdown

(1gal/gal)WW

Hydrolyzate

(12gal/gal)

Produ

ct

(12gal/gal)

Waste

Water

(1ga

l/gal)

9Figure 4. Process Layout Based on Case 2 (Corn stover + Dilute Acid Pretreatment).10


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CoolingTower

Blow

down

(1gal/gal)WW

Hydro

lyzate

(12gal/gal)

Pro

duct

(13g

al/gal)

Was

tewater

(1g

al/gal)

TreatedWater

(7gal/gal)

11Figure 5. Process Layout Based on Case 3 (Switchgrass + Dilute Acid Pretreatment).12

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AFEX

Pretreatment

Fermentation

and

Cellulase

Production

Product Recovery

Waste Water

Treatment

Plant WaterDistribution

Fresh Make-up Water(12 gal/gal)

Feedstock

Moisture

(1 gal/gal)

Air, Chemicals,

Nutrients

(0 gal/gal)

Evaporator and

Windage Loss(10 gal/gal)

Scrubber Vent toAtmosphere

(2 gal/gal)

Solids to Landfill

(1 gal/gal)

Water for Vent Scrubber

(1 gal/gal) MW

Water for Vent

Scrubber

(1 gal/gal)

Boiler Water

(1 gal/gal) MW

Water for

Pretreatment

(4 gal/gal) MW

(7 gal/gal) RW

Boiler Water

(1 gal/gal) MW

Water for Cellulase

Production(1 gal/gal) MW

Steam

(1 gal/gal)

Steam

(1 gal/gal)

CoolingTower

Blowdown

(4gal/gal)WW

Hydrolyzate

(13g

al/gal)

Product

(12

gal/gal)

Ethanol

WasteWater

(10gal/gal)

Make-up Water(5 gal/gal) MW

(9 gal/gal) RW

TreatedWater

(16gal/gal)RW

Boiler Blowdown

(2 gal/gal) WW

Boiler

Cooling

Tower

Process Water Section

Note: MW : Make-up Water; RW: Recycled Water; WW: Waste Water.

Unit Operation Gallons of Water per Gallon of Ethanol

Pretreatment

Process Water

Total Water Input

Raw Material Moisture

Steam

Fermentation Total Water Input

Carried Over Water

Product

RecoveryTotal Water Input

Carried Over Water

Utility Water

Cooling Tower

SteamGeneration

Total Water Input

Make-up Water

Total Water Input

Make-up Water

13

1

Make-up Water

Recycled Water 7

4

Recycled Water 0

Make-up Water 113

12

14

1

13

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Recycled Water

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Recycled Water

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Recycled Water

Make-up Water

Carried Over Water

Waste Water

14Figure 6. Process Layout Based on Case 4 (Switchgrass + AFEX Pretreatment).15

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