DDGS Sulfur Content. Sources And Possible Ways To Maintain Lower Levels Distillers Grain Technology Council Symposium

Transcription

1 DDGS Sulfur Content Sources And Possible Ways To Maintain Lower Levels 2008 Distillers Grain Technology Council Symposium Kansas City, MO, USA May 22, 2008 Dr. Dennis Bayrock

2 Seminar outline Sulfur containing compounds at an ethanol plant Exploration of types and amounts added to a plant Locations where sulfur is added Fermenter example Possible ways to reduce sulfur at an ethanol plant Alternative processing chemicals Changing processing conditions

3 Sulfur in DDGS The Problem? Toxicity of high sulfur in cattle diets can lead to polioencephalmalacia (PEM) can be lethal in as little as 48h (Crawford, G. 2007)

4 Sulfur addition at an ethanol plant Sulfur containing chemicals (added to the process): Sodium Sulfite/Bisulfite Na2SO3/NaHSO3 - mw g/mol / g/mol (anhydrous) - Antimicrobial (Not selective - kills both yeasts and bacteria) - Used in the wine industry - Releases sulfur dioxide when added to water - Reacts with acetaldehyde to form ethanol Sulfamic acid H3NSO3 - mw g/mol - Weak acid - Descaling agent - Contains an amino moiety (H3N) Sulfuric acid - mw g/mol - Strong acid H2SO4

5 Sulfur addition at an ethanol plant Sulfur containing chemicals (added to the process): Magnesium/Zinc sulfate MgSO4/ZnSO4 - mw g/mol / g/mol (anhydrous) - Added to Anaerobic Digestor (Methanator) as a nutrient for bacteria.

6 Sulfur addition at an ethanol plant Sulfur containing materials (inherent to the process): Yeast (Maloney, 1998; Reed and Nagodawithana, 1991; Ingledew et al, 1977; Patel and Ingledew, 1973; Peppler, 1970)

7 Sulfur addition at an ethanol plant Sulfur containing materials (inherent to the process): Yeast Sulfur (dry weight) Total: 3.9 g/kg dry = 1.77 g/lb dry (Maloney, 1998; Reed and Nagodawithana, 1991; Ingledew et al, 1977; Patel and Ingledew, 1973; Peppler, 1970)

8 Sulfur addition at an ethanol plant Sulfur containing materials (inherent to the process): Corn 2 (Lorenz and Kulp, Handbook of Cereal Science and Technology)

9 Sulfur addition at an ethanol plant Sulfur containing materials (inherent to the process): Corn 2 (Lorenz and Kulp, Handbook of Cereal Science and Technology) Sulfur (dry weights) Total (mineral): Protein (amino acid): Nutrient (vitamin): (Lorenz and Kulp, Handbook of Cereal Science and Technology) 0.12% w/w 0.44% w/w (0.107% w/w as S) % w/w ( % as S)

10 Sulfur addition at an ethanol plant Sulfur containing materials (inherent to the process): Water - Sulfate concentration varies greatly in aquifers at different plant locations - Ethanol plants recycle water within the plant not all process water is from well (USGS,USDOI, 2001)

11 Where are the chemicals primarily added? (Adapted from Madson and Monseaux,1990)

12 Where are the chemicals primarily added? Yeast Water Corn (Adapted from Madson and Monseaux,1990)

13 Where are the chemicals primarily added? Sulfuric acid - ph control - Continuous addition - Compatible with yeast Sulfamic acid Yeast - CIP/Descaling - Intermittent addition Water Sodium sulfite/ Sodium bisulfite - Removal of acetaldehyde - Continuous addition Corn (Adapted from Madson and Monseaux,1990)

14 Where are the chemicals primarily added? Zn/Mg sulfate -Nutrients for anaerobic bacteria -Continuous addition (Ingledew 2006)

15 Where are the chemicals primarily added? Sulfuric acid - Defouling/CIP - Intermittent use Sulfamic acid - Descaling/CIP - Intermittent use (Madson and Monseaux,1990)

16 How much is added? Nearly impossible to model S content in the plant or in the DDG based on inputs of S at the plant since: - Ethanol plants utilize water recycling - Feedback loops occur and at different levels. - Process conditions can change on a daily basis. - Changes in S content in DDG may take time to materialize. - Sulfur containing chemicals are added continuously or intermittently - Addition location and timing, amounts, and process flows

17 An example from a dry grind batch ethanol plant A Fermenter example (no recycle) ph 5.7 (Liq) ----> ph 5.2 (Ferm set) Corn Fermentor volume Dry solids Amount of corn in fermentor Amount of yeast added to prop = 750,000 gal (2,839,058L) = 33% = 2,021,247 lbs (916,822 kg) = 5x 22lbs = 110 lbs (49.8 kg) Sulfuric acid (99%) to Liq Mash GPM to Ferm = 0.56 GPM = 1508 GPM As S Total mineral: 2425 lb Protein (amino acid): Nutrient (vitamin): Yeast Sulfuric acid Water (n/a) % of Total 2163 lb 0.9 lb 0.4 lb 1401 lb Total 3827 lb 57% 37%

18 An example from a dry grind batch ethanol plant A Fermenter example (no recycle) ph 5.7 (Liq) ----> ph 4.5 (Ferm set) Corn Fermentor volume Dry solids Amount of corn in fermentor Amount of yeast added to prop = 750,000 gal (2,839,058L) = 33% = 2,021,247 lbs (916,822 kg) = 5x 22lbs = 110 lbs (49.8 kg) Sulfuric acid (99%) to Liq Mash GPM to Ferm = 1.12 GPM (extrapolated) = 1508 GPM As S Total mineral: 2425 lb Protein (amino acid): Nutrient (vitamin): Yeast Sulfuric acid Water (n/a) % of Total 2163 lb 0.9 lb 0.4 lb 2803 lb Total 5229 lb 41% 54%

19 How much is added? Average S containing chemical addition at an ethanol plant Chemical lbs/month lbs/year % of Total Sodium bisulfite (38%) Sulfamic acid Sulfuric acid (99%) MgSO4 70,824 20, ,570 2, , ,700 6,774,840 30, Total 7,897,668 Strategy for reducing S in DDGS? - Cannot easily change composition of corn and yeast - Can we reduce the use of S-containing chemicals?

20 1. Reduce Sulfuric acid use - Many ethanol plants poise their fermenter ph <5.0 (4.5, 4.0, 3.7) - Prevailing thought: A lower ph will inhibit bacterial growth. Lactic Acid Bacteria (LAB) family * Lactobacillus sp paracasei, plantarum, casei, brevis, fermentum, rhamnosus, delbrueckii, buchneri, pentosus, acidophilus, gasseri, jenserii, amylovorus, reuteri, cornyeformis, divergens, carnis, piscicola, sake, sharpeae, bavaricus, curvatus, hamsteri, amylophilus, agilis, homohiochii Weisellia sp paramesenteroides, confusa, viridescens Lactococcus lactis, raffinolactus, plantarium Nearly all of the bacteria that typically infect an ethanol plant (and in PhibroChem's library of over 500 bacteria) are inhibited in growth and metabolic activity when the ph is less than 4.5. * Approx 70% of infections at an ethanol plant are due to LAB (Skinner and Leathers, 2003; Bayrock, unpublished results)

21 1. Reduce Sulfuric acid use (cont) - Problems with lowering the ph below Additional sulfate added to process

22 1. Reduce Sulfuric acid use (cont) ph 5.7 (Liq) ----> ph? (Ferm set) Corn Fermentor volume Dry solids Amount of corn in fermentor Amount of yeast added to prop = 750,000 gal (2,839,058L) = 33% = 2,021,247 lbs (916,822 kg) = 5x 22lbs = 110 lbs (49.8 kg) Sulfuric acid (99%) to Liq Mash GPM to Ferm = 0.56 GPM (5.2), 1.12 GPM (4.5)* = 1508 GPM Total mineral: Protein (amino acid): Nutrient (vitamin): Yeast Sulfuric acid ph 5.2 ph 4.5* 2425 lb 2425 lb 2163 lb (57%) 0.9 lb 2163 lb (41%) 0.9 lb 0.4 lb 1401 lb (37%) 0.4 lb 2803 lb (54%) Total 3827 lb * Extrapolated data 5229 lb

23 1. Reduce Sulfuric acid use (cont) - Problems with lowering the ph below Additional sulfate added to process 2. Less ph room for yeasts. Optimal growth range for typical yeast: Yeasts naturally reduce the ph to ~4.0 in corn fermentations. Most yeasts have a lower growth ph of 3.8 Yeasts require a ph delta (above 3.8) in order to properly grow and ferment. Losses in ethanol yield increase as this low ph is approached (Ingledew, 1991)

24 1. Reduce Sulfuric acid use (cont) - Problems with lowering the ph below Additional sulfate added to process 2. Less ph room for yeasts. 3. Non-optimal ph for glucoamylase. - Traditional glucoamylase activity is best between a ph 4.5 and Newer glycoamylase products have extended ph activity

25 2. Control bacterial contamination - Yeasts do not manufacture proteases to break down mash proteins X Proteases Methionine Cysteine X Metabolism H2S, SO4 (Patel and Ingledew, 1973)

26 2. Control bacterial contamination (cont) Metabolism H2S, SO4 Proteases Protein Methionine Metabolism Cysteine

27 2. Control bacterial contamination (cont) - Proteolytic bacteria that have infected ethanol plants Lactic Acid Bacteria (LAB) family * Lactobacillus sp paracasei, plantarum, casei, brevis, fermentum, rhamnosus, delbrueckii, buchneri, pentosus, acidophilus, gasseri, jenserii, amylovorus, reuteri, cornyeformis, divergens, carnis, piscicola, sake, sharpeae, bavaricus, curvatus, hamsteri, amylophilus, agilis, homohiochii Weisellia sp paramesenteroides, confusa, viridescens Lactococcus lactis, raffinolactus, plantarium - In general, a bacterial contamination level of 1x105 CFU/ml begins to be inhibitory for yeast (lactic/acetic acids), and competes nutritionally with the yeast. - In plants where contamination was controlled, SO4 and H2S levels decreased in the system. * Approx 70% of infections at an ethanol plant are due to LAB (Skinner and Leathers, 2003; Bayrock, unpublished results)

28 3. Use different liquefaction enzyme Corn slurry ph ~4.5 α-amylase glucoamylase Liquefaction ph ~ Saccharification ph ~ ph increase ph decrease (sulfuric acid)

29 3. Use different liquefaction enzyme (cont) Corn slurry ph ~4.5 α-amylase glucoamylase Liquefaction ph ~ Saccharification ph ~ ph increase ph decrease (sulfuric acid) - Research into new enzymes for liquefaction that operate at potentially lower ph's Corn slurry ph ~4.5 α-amylase glucoamylase Liquefaction ph? Saccharification ph ~ ph increase ph decrease (sulfuric acid)

30 4. Remove solids prior to fermentation Removal of solids prior to distillation

31 4. Remove solids prior to fermentation (cont) Removal of solids - The removal of solids prior to fermentation has been proposed for many years as a part of VHG technology developed by Dr. Mike Ingledew at the University of Saskatchewan.

32 4. Remove solids prior to fermentation (cont) Advantages of VHG technology in fuel ethanol production Increased plant capacity or reduction in capital costs - Increase in alcohol concentration to >18% v/v - Increase in fermentor space due to removal of insolubles Increased plant efficiency - Reduction in labor costs/litre ethanol - Reduction in energy costs/litre ethanol - No cooling of insolubles in fermentor - No heating of insolubles in the still - Less water to process in the still - Optimum ethanol concentration for efficient distillation - Lower solids in the still (liquid-liquid extraction) - Reduction in inputs/litre ethanol - Decreased water usage - Reduction in fermentor downtime - Reduction in cleaners and sanitizers Other advantages - Opportunity for food quality co-products or distillers grains - Opportunity for harvest of high protein spent yeast - Reduction in abrasion in pipes/vessels. (Adapted from Thomas et al, 1996)

33 4. Remove solids prior to fermentation (cont) Advantages of VHG technology in fuel ethanol production Increased plant capacity or reduction in capital costs - Increase in alcohol concentration to >18% v/v - Increase in fermentor space due to removal of insolubles Increased plant efficiency - Reduction in labor costs/litre ethanol - Reduction in energy costs/litre ethanol - No cooling of insolubles in fermentor - No heating of insolubles in the still - Less water to process in the still - Optimum ethanol concentration for efficient distillation - Lower solids in the still (liquid-liquid extraction) - Reduction in inputs/litre ethanol - Decreased water usage - Reduction in fermentor downtime - Reduction in cleaners and sanitizers Other advantages - Opportunity for food quality co-products or distillers grains - Opportunity for harvest of high protein spent yeast - Reduction in abrasion in pipes/vessels. (Adapted from Thomas et al, 1996)

34 5. Reduce sulfite/bisulfite use in CO2 scrubber CH3CHO + NaHSO3 + H2O --> C2H5OH + NaHSO4 Sodium bisulfite Na2SO3 Sodium sulfite Sodium bisulfate Na2SO4 Sodium sulfate - Added to CO2 scrubbers to convert acetaldehyde (produced by yeasts and bacteria) to ethanol - Sulfites are very antimicrobial both to yeast and bacteria

35 5. Reduce sulfite/bisulfite use in CO2 scrubber (cont) CH3CHO + NaHSO3 + H2O --> C2H5OH + NaHSO4 Sodium bisulfite Sodium bisulfate Na2SO3 Sodium sulfite Concentration of Sodium bisulfite Sodium bisulfite GPM to scrubbers Mash GPM to Ferm Fermenter volume Na2SO4 Sodium sulfate = 38% = 0.14 GPM = 1508 GPM = 750,000 gal

36 5. Reduce sulfite/bisulfite use in CO2 scrubber (cont) CH3CHO + NaHSO3 + H2O --> C2H5OH + NaHSO4 Sodium bisulfite Sodium bisulfate Na2SO3 Sodium sulfite Concentration of Sodium bisulfite Sodium bisulfite GPM to scrubbers Mash GPM to Ferm Fermenter volume Na2SO4 Sodium sulfate = 38% = 0.14 GPM = 1508 GPM = 750,000 gal Sodium bisulfite concentration in fermenter = 0.35%

37 5. Reduce sulfite/bisulfite use in CO2 scrubber (cont) % Sodium bisulfite is enough to negatively affect yeast Fermenting yeast (Ingledew, 1991)

38 5. Reduce sulfite/bisulfite use in CO2 scrubber (cont) % Sodium bisulfite is enough to negatively affect yeast Fermenting yeast with sulfite (Ingledew, 1991)

39 5. Reduce sulfite/bisulfite use in CO2 scrubber (cont) % Sodium bisulfite is enough to negatively affect yeast Fermenting yeast with sulfite Glycerol (Ingledew, 1991)

40 5. Reduce sulfite/bisulfite use in CO2 scrubber (cont) - Bisulfite/Sulfite presence: Decreases ethanol yield Increases yeast stress (includes production of acetaldehyde) Increases glycerol production Creating a feedback loop with yeast!

41 6. Reduce yeast stress (Be good to your yeast!) Non-Microbial factors Sugar content Sulfite (38% w/v max) Temperature (35ºC = 95ºF) (100 ppm) Sodium (500 ppm) CIP Chemicals (varies) Nutritional factors (media formulation) Lack of: Sterols, Nitrogen, Oxygen, UFA, Minerals/Vitamins Microbial factors Chemical Acetic acid (0.05% w/v) Ethanol (23% v/v max) Lactic acid (0.8% w/v max) Mycotoxins ( ) ( ppm) Competition Nutrient depletion (trace nutrients) ph

42 Thank you for your time!