UTILIZATION OF HIGH-CARBOHYDRATE FOOD WASTES AS THE FEEDSTOCK FOR DEGRADABLE PLASTICS

S. P. Tsai, Ph. D., R. D. Coleman, Ph. D., TenLin S. Tsai, Ph. D., and Patrick. V. Bonsignore, Ph. D. Argonne National Laboratory Energy Systems and Environmental Research Divisions 9700 South Cass Avenue Argonne, Illinois 60439

ABS" ABS"

Wastestreams from food processing industries have become an economic burden a well as a serious environmental problem. In the United States, billions of pounds of potatc -- processed each year is typically discarded or sold as cattle feed at $3-6/ton. For large food processing plants, removal of more than 1 million gallons of waste/day/plant is required As a potential solution to this economic and environmental problem, Argonne National Laboratory is developing technology that (1) bioconverts existing food processing wastestream into lactic acid, and (2) utilizes lactic acid for making environmentally safe, degradable plastics. Although the initial substrate for Argonne's process development is potato waste, the process will be applied to many other high-carbohydrate food wastes. Argonne has developed a process to bioconvert greater than 90% of the fermentable starch in solid potato waste to glucose. Lactic acid is produced from glucose via fermentation and subsequently recovered/purified for plastic synthesis. A continuous lactic acid fermentation and reco~ery process has been designed. Batch fermentation data showed good cell growth and excellent yields (greater than 95%) of lactic acid production from the hydrolyzed potato waste. Three product recovery processes (electrodialysis, liquid-liquid extraction, and esterification) are being evaluated. Plastics containing lactic acid can be designed to have various mechanical properties and degradation rates. Argonne is developing lactic acid plastics that have some novel features. These environmentally-safe,degradable plastics have many attractive applications such as composting bags and agriculture mulch films. Other potential applications of lamc acid polymers include programmable pesticide and fertilizer delivery systems. Such applications are expected to tremendously increase the demand for lactic acid and make the economics of lactic acid production very attractive.

490 ‘.

INTRODUCTION

Wastestreams from food processing industries have become an economic burden as well as a serious environmental problem. In the United States, billions of pounds of potato processed each year is typically discarded or sold as cattle feed at $3-6/ton. For large food processing plants, removal of more than 1 million gallons of waste/day/plant is required. As a potential solution to this economic and environmental problem, Argonne National Laboratory is developing technology that (1) bioconverts existing food processing wastestream into lactic acid, and (2) utilizes lactic acid for making environmentally safe, degradable plastics. Although the initial substrate for Argonne‘s process development is potato waste, the process will be applied to cheese whey permeate and many other high- carbohydrate food wastes. The bioconversion of food wastes into higher-priced products of broader utility is very promising. For example, two (solid potato waste and primary peel effluent) of the three major wastes from french-fry production are highly enriched with carbohydrates, quite clean, and available in large volumes (more than 80,000 gal at 12%starch per day per large processing plants). Other foods that are 70-75% starch (dry weight), such as corn, sorghum, and wheat, also are sources of wastes that are excellent candidates for direct enzymatic or microbial conversions. Argonne has determined that lactic acid has several major advantages over other products that could be made f”such wastes: Made by fermentation with high yields, High current selling price ($l/lb) and, in turn, very attractive revenue, Promising technology being developed is likely to reduce the production cost, and Potential applications of degradable lactic acid polymers.

Although lactic acid has wide utility in industry as an acidulant, flavor ingredient, emulsifier, stabilizer, and antimicrobial agent, its real potential in making plastics is receiving increased attention. Interest in bio- and photodegradable plastics is rapidly expanding. Major environmental concems such as litter, waste materials on beaches and in the ocean, and burgeoning landfills are directly affected by plastics that can remain for hundreds of years. Stimulated by public demand, strong legislative action in state legislatures and the U. S. Congress is forcing industry to explore the development and use of degradable and recyclable plastics. These plastics should degrade to innocuous Compounds, have suitable physical and mechanical properties, and be cost effective. Few, if any, of the degradable plastics currently available, including plastics containing starch, meet these criteria. However, polymers and copolymers with excellent mechanical properties and degradability characteristics can be made from lactic acid [3 1. The availability of a low-cost feedstock (i.e., starch and lactose from potato waste streams and cheese-whey permeate, respectively) and cost-effective bioconversion and recovery processes should greatly stimulate the development of lactic acid as a commodity Compound and its use in making bio- and/or photodegradable plastics. Argonne is developing a proprietary process for the production of degradable lactic acid plastics from potato wastes (Fig. 1). An enzymatic process converts starch contained in the potato waste into dextrose. The dextrose and other products of starch hydrolysis are subsequently fermented by bacteria to produce lactic acid. The lactic acid will be recovered and purified into a polymer-grade product. Novel plastics will then be synthesized from

49 1 Combined Potato Wastestream Processing Step (20 - 30 min)

t I Enzyme Digest (4-8 hrs)

Continuous Fermentation and Recovery of Lactic Acid

Degradable Plastics Polymer Synthesis Using Lactic Acid

Figure 1. The Arqonne ,Process nf IMnradahlo ptsletirrcfmm ~-4-4- QA~--A - - lactic acid. An Argonne process for bioconverting high-carbohydrate food wastes into lactic acid will not only help to solve a waste problem for the food industry, but is likely to be profitable. Technical developments in each step of the overall process will be described in the following sections including further description concerning our work on lactic acid fermentation and recovery. Because of patent considerations, certain proprietary information can't be released in this presentation.

ENZYMATIC HYDROLYSIS

Argonne has developed a proprietary process to bioconvert greater than 90% of the fermentable starch in solid potato waste to glucose. The process involves several substantial improvements over conventional technology (Table 1). In the Argonne process, the processing time has been reduced by 90% (less than 10 hrs vs. more than 100 hrs) while still achieving high yields (greater than 90%) of glucose fiom starch hydrolysis. In addition, two steps of processing have been combined and minimal pH adjustment is necessary. Consequently, both capital and operating costs of hydrolysis will be reduced significantly. Also, because of the process conditions, no microbial contamination is present in the hydrolyzed product which can be fed directly into the fermenter without sterilization or pasteurization.

LACTIC ACID FERMENTATION AND RECOVERY

The dextrose and other products of starch hydrolysis are subsequently fermented by bacteria that produce lactic acid. The lactic acid will be recovered and purified into a polymer-grade product. Lactic acid exists in two optically active isomeric forms (D and L); only the L-form is produced in the human body. But, microorganisms produce both D- and Llactic acid in various proportions. In degradable plastics made from lactic acid, the physical and mechanical properties can be controlled by changing the ratio of D- to L-lactic acids. Consequently, it is important to be able to produce lactic acid in any desirable D/L ratio. Argonne is developing several promising homofermentative strains of lactic acid bacteria that will produce lactic acid with D/L ratios ranging from 100/0 to 10/90. These strains are being acclimated for higher growth temperature and higher lactic acidsodium lactate tolerance level. About 50 percent of all lactic acid production is via fermentation [4 1. The conventional process to make natural lactic acid involves batch fermentation. When dextrose or sucrose is used as the substrate, a batch fermentation normally requires up to 6 days to complete. Several different recovery and purificatisn processes are being used. In general, the conventional lactic acid fermentation and recovery processes have low Productivity and generate large amounts of wastestreams (cell mass and calcium sulfate). These processes are not attractive in the U;.S. and new technology has to be developed. Argonne has determined that the most promising process would be a continuous fermentation system followed by one of several promising product recovery and purification methods.

493 Table 1. Comparison of the Argonne and Conventional Processes of Starch Hydrolysis.

CONVENTIONAL ARGON NE (propri et a ry)

Corn Starch Potato Starch Substrate (from corn wet milling) (Solid Potato Waste)

Jet Cooking Gelatinization (105%, 5 - 10 min) sh (0 Combined P Processing Liquefaction: d- amylase i Step (20 - 30 min) Enzyme (95 - 98"C, 90 min, pH 6) Hydrolysis

Saccharification: glucoamylase Enzyme Enzyme Digest (6OoC, 100 - 120 hrs, pH 4.5) Hydrol ys Is (4-8 hts)

94 - 96% glucose Product > 90% glucose

Bacterial Unknown Contamination None vj av) 0 0 a' L. >a 0 a0 U

c .-0 ca cc LE" 2

.-0 m c -1mo cn 3 0

L3 .-c. sc ,cn a c c

zL

La 3 P) ii

495 In the Argonne process, the fermentation and product recovery steps are to be closely integrated to be an effective system (Figure 2). First, the clarified potato hydrolysate is supplemented with nutrients and fed into the continuous fermenter. Lactic acid bacteria in the fermenter convert glucose into lactic acid, which is, in turn, neutralized by sodium hydroxide to sodium lactate. Cell free fermentation broth containing sodium lactate is continuously withdrawn while cells are retained in the fermenter to maintain the proper cell concentration for high reactor productivity. In the recovery step, the sodium lactate is converted into lactic acid and sodium hydroxide; the latter will be used for pH adjustment of the fermentation, while the lactic acid stream is sent to additional polishing steps, if necessary, to remove any remaining impurities and is then concentrated to the final product. There are a number of advantages in this process. In the conventional lactic acid fermentation and recovery process, calcium sulfate and cell mass are the two major wastestreams. In this process, they are eliminated or greatly reduced. By using the cell- recycle continuous fermenter, the formation of new cell mass is minimized; therefore, the product yield is increased and the addition of nutrient supplement such as yeast extract or corn steep liquor can be minimized. Consequently, product recovery and purification can be simplified. The recovery of sodium hydroxide in this process not only reduces a waste disposal problem but also represent a significant cost saving. Initially, batch fermentation experiments have been carried out to study the feasibility and characteristics of lactic acid fermentation from hydrolyzed potato wastes. We have demonstrated that with supplements of nutrients, lactic acid bacteria grew well in the potato hydrolysate and produced lactic acid with high yields. This showed that the potato wastestream as collected did not contain substances that were toxic to cell growth. In a potato processing plant, it is not unusual to have other waste materials to enter& (contaminate) the potato wastestream. Therefore, the potato waste may not be suitable for certain fermentation processes where the microbial activity is sensitive to the wastestream compositions. Successful results using the potato waste, which was collected from a typical potato processor, suggested that utilization of potato wastes for lactic acid fermentation would not require my special collection system beyond current industrial ~ practices. A typical batch fermentation can be completed in less than 48 hours. At the end * of the fermentation, the residual glucose concentration is less than 0.1 g/L and the lactic acid concentration is 85 g/L. The conversion yield from glucose to lactic acid is greater than 95%. In product recovery, three different methods (liquid-liquid extraction, esterification, and electrodialysis) are being investigated. In the extraction process, an extractant system comprised of a tdary amine as the complexing agent and a water immiscible organic ’ solvent as the diluent has been identified. The process is similar to the extraction process that has been successfully applied in commercial citric acid production. Our laboratory results showed that lactic acid could be recovered by extraction with good yields. However, due to the presence of surface active substances in the potato wastes, phase separation can be a problem if the process is not properly designed. In the esterification process, methyl lactate is made by reacting methanol acid [2 3. Methyl lactate is then hydrolyzed to produce lactic acid, whi distillation. This process is especially promising for facilitating the existing ethanol fermentation plant for lactic acid production. Although cewn are being used for ethanol fermentation, ethanol production is not economically attracu If lactic acid instead of ethanol is produced from the same food wastes, the revenue the sale of the fermentation product can increase 5 to 9 fold. To convert an ethanol ’ fermentation plant for lactic acid production, esterification may be the best product recOvW‘

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496 method, because existing distillation equipment can be used and therefore less capital investment will be required. An electrodialysis process is also being investigated at Argonne. In addition to lactic acid recovery and purification, the process also recovers sodium hydroxide which can be recycled for pH adjustment in the fermenter. The product purity of lactic acid recovered by electrodialysis has been reported to be good [I 1. A major research focus in the development of this process is to reduce the operating energy cost by modifying the operating conditions.

DEGRADABLE LACTIC ACID POLYMERS

Due to their biodegradability, polymers and copolymers containing lactic acid are very promising for certain applications. Two of the most attractive applications are (1) environmentally safe, bio- and photodegradable plastics, and (2) sustained or programmed delivery systems. Although biodegradable plastics made of lactic acid have been used in medical applications, the research focus at Argonne is on lactic acid plastics for non- medical applications. Argonne has designed and is constructing and testing degradable plastics plastics made from lactic acid including bio- and photodegradable plastics. Several monomers as additives (less than 10%)to polylactate are being tested for their ability to effect an increased sensitivity to water hydrolysis and/or photodegradation. Another very attractive area is sustained or programmable delivery systems for pesticides and fertilizers. Approximately 1 billion pounds of pesticides are used every year in the United States, but a high proportion is vastly underutilized and can often contaminate subsurface aquifers. A "time-released" pesticide eluting from a degradable polymer coating or matrix could greatly impmve the efficiency of pesticide use (less wasteful, more cost- effective) and minimize pollution of groundwaters. Argonne is designing and testing polymer formulations for matrices and encapsulations to be implemented for the programmable delivery systems.

CONCLUDING REMARKS

Currently, one of the major constraints for the feasibility of lactic acid production via fermentation of high-carbohydrate wastes is the relative small volume of lactic acid market (about 20 million pounds in 1982 in the United States) [4 3. However, degradable lactic acid polymers could create a huge market for lactic acid. The demand for bio-and photodegradable products such as grocery, trash, and composting bags; beverage O-rings; fast food packings; agricultural mulch films; and diaper backings could produce a large potential need (up to several billion pounds per year in the United States) for new Compounds such as lactic acid. In addition, production costs are likely to be reduced because of the abundant hexpensive carbon sources found in potato waste; cheese whey Permeate etc. and the advance technologies being developed for lactic acid recovery and Purification. The commercial potential of degradable lactic acid plastics from high- carbohydrate food wastes appears to be quite attractive.

497 FUNDING

Work supported (in part) by U. S. Department of Energy, Assistant Secretar Conservation and Renewable Energy, under Contract W-31-109-Eng-38.

REFERENCES CITED

1. Colon, G., "Recovery of Lactic Acid from Fermented Acid Cheese Whe; Electrodialysis", Ph. D. Thesis, University of Massachusetts, Amherst, Massachu (1986). 2. Filachione, E. M. and C. H. Fisher, "Purification of Lactic Acid, Production of M Lactate from Aqueous Solutions of Crude Acid", Industrial and Engine( Chemistry, 38 (1946): 228 - 232. 3. Lipinsky, E. S. and R. G. Sinclair, "Is Lactic Acid a Commodity Chemic; Chemical Engineering Progress, 82(8) (1986): 26 - 32. 4. Vick Roy, T. B., "Lactic Acid", in "Comprehensive Biotechnology", ed. M. I Young, vol. 3 (1985): 761 - 776.