ENZYMATIC DEINKING OF SORTED Researchers at the Forest Products Laboratory have demon­ MIXED OFFICE WASTE: strated that cellulases used in combination with surfactants RECOMMENDATIONS FOR SCALE-UP and the mechanical action of medium consistency repulping effectively remove toners from laser and xerographic paper Marguerite Sykes John Klungness (2,3). Preliminary work on sorted MOW indicated that Forest Products Technologist Chemical Engineer enzyme deinking is also economically and technically Thomas Jeffries Kathleen Cropsey feasible on heterogeneous paper furnishes. Some benefits of Supv. Microbiologist Forest Products Technologist enzyme-enhanced deinking may be in its secondary effects. Said Abubakr USDA Forest Service For example, in addition to removing toners, enzymes have Supv. Chemical Engineer Forest Products Laboratory been shown to improve pulp drainage, disperse stickies, and USDA Forest Service Madison, WI 53705-2398 produce a less deleterious effluent (3-5). Forest Products Laboratory1 Madison, WI 53705-2398 The study reported here summarizes results of experiments statistically designed to optimize controllable process variables that affect ink removal. We used conditions and ABSTRACT equipment similar to those available in deinking mills. Several enzyme sources, levels of enzyme addition, pulping consistency, pH, surfactant brand and addition level, and process conditions were investigated. We modified our Researchers at the Forest Products Laboratory have demon­ laboratory procedure to accommodate mill process times and strated that cellulases used in combination with surfactants examined the possible effects of these changes on pulp and the mechanical action of medium consistency pulping properties. These findings formed the basis for recommenda­ effectively remove toners from laser-printed and xerographic tions for industrial-scale deinking. paper. Preliminary work on sorted mixed office waste indicated that enzyme deinking is also economically and Industrial-scale deinking trials on sorted office wastepaper are technically feasible on heterogeneous paper furnishes. Here scheduled for early December 1994. During these trials, we we summarize results of experiments designed to optimize will examine the benefits of enzyme-enhanced deinking on controllable process variables that influence ink removal 10-ton batches of office wastepaper with a high percentage of using conditions and equipment similar to those available in laser-printed paper. The ability of enzyme-deinked pulp to be deinking mills. Study parameters included the level of processed through paper machines will be compared with that enzyme addition, pulping consistency and pH, and brand and of pulp produced by conventional deinking methods. We will addition level of surfactant for various process conditions. We also evaluate the bleachability of the deinked pulps with both present recommendations for pulp consistency and enzyme oxidative and reductive bleach chemicals. In addition to level for industrial-scale trials. conducting conventional paper testing and dirt count, we will monitor effluent quality throughout the deinking trials. Results will be presented at the Recycling Symposium in INTRODUCTION February. Mixed office waste (MOW) paper is a potentially valuable resource. Unsorted MOW consists of approximately 72% DISCUSSION uncoated free sheet; the fiber content is 88% chemical fiber (1). Less than half the wastepaper generated is recycled, Pulping mostly into lower grades of paper. Xerographic and laser- An early premise in our work (2,3) was that medium consis­ printed papers create a major barrier to recycling MOW tency (12%) pulping is advantageous for removing toner because they contain nondispersible synthetic polymers. through the combined effect of enzyme and mechanical Thermosetting toners fuse to paper during noncontact attrition. We have subsequently found that increasing the printing. This physical attachment to the paper fibers as well consistency to as high as 16% increases deinking efficiency as their nondispersible properties make toners difficult and (Table I). However, at higher pulping consistencies and expensive to remove by existing technologies. Therefore, extended pulping times, the effect of mechanical action much of this prime fiber is currently recycled into a lower predominates and we have observed little additional benefit value paper product or it is landfilled. from the enzyme. Because enzyme activity is site-specific, 1The Forest Products Laboratory is maintained in cooperation distribution of the enzyme throughout the pulper is essential. with the University of Wisconsin. This article was written and We have found that fiberizing at 16% and pulping at 14% prepared by U.S. Government employees on official time, and consistency, consistencies compatible with mill pulpers, it is therefore in the public domain and not subject to copyright. assure adequate enzyme distribution. Under these conditions, 1995 Recycling Symposium / 61 Table I. Effect of Pulping Consistency on Ink Removala Table II. Effect of Adding Surfactant via Flotation Cell or Pulpera Residual ink at various levels of consistency (ppm) Residual ink (ppm) Specimen 12% 16% Specimen Flotation cell Pulper Control 681 343 Control 326 231 Enzyme-treated 329 220 Enzyme-treated 278 168 aResidual ink on handsheets counted in 10-2000µ range. Table III. Enzyme/Surfactant Synergy the benefit from using enzymes for reducing dirt count is clear. We recommend these pulping consistencies for the Variable Residual ink (ppm) industrial-scaletrials. Control 368 Surfactant Enzyme A, surfactant A 242 Surfactants, which are essential for separating ink from pulp Enzyme A, surfactant B 303 fibers during flotation (5), play an additional role when enzymes are used in the deinking process. At 16% consis­ Enzyme B, surfactant A 278 tency, distribution of the enzyme during limited pulper residence time is critical. Surfactants make cellulose more Enzyme B, surfactant B 214 accessible to cellulosic enzymes and facilitate enzyme desorption, thus making the enzyme available to reattach to Table IV. Effect of pH on Ink Removal other cellulose sites. Under appropriate conditions, surfac­ tants increase cellulase effectiveness (6,7). Surfactants Specimen pH Residual ink (ppm) stabilize enzymes and may be instrumental in preventing their deactivation under the shear forces present in the pulper Control – 139 during high consistency mixing (8). Enzyme-treated 8.6 64 In the study reported here, we added a nonionic surfactant to Enzyme-treated 7 47 the pulper prior to adding the enzyme. The favorable results (Table 11) led us to include surfactants in the pulper prior to adding enzymes in all subsequent experiments. We then compared the effectiveness of several brands of nonionic ambient pulp pH and with adjustment to pH 7 (Table IV). A surfactants in combination with two different cellulase considerable amount of sulfuric acid was required to neutral­ preparations and found synergy with specific enzyme­ ize the pulp. Adjustment for pH is costly and difficult to surfactant mixtures (Table III). Our studies demonstrated that control when using a variable paper stock. Therefore, we will 0.05% surfactant (based on oven-dry [OD] pulp) was the run one industrial trial with enzyme addition using ambient appropriate addition level with the enzyme and equipment pH; additional trials will use either adjusted pH or more used in our laboratory and pilot plant experiments. Less enzyme to compensate for the less-than-optimum pH. surfactant is required to form a stable foam when paper ash is high and enzyme is present. However, we intend to use Enzyme 0.125% surfactant in the industrial trials, based on recommen­ dations by mill personnel for the process and equipment that Access to cellulose is essential for cellulase activity. Mixing will be used. the pulp at medium consistency (11%-16%) dislodges toner particles from fibers, and the presence of a surfactant in the pH pulper helps the enzyme penetrate through paper additives. This increases cellulose availability for cellulase attachment. The commercial cellulase preparation selected for the mill Research has indicated that cellulase adsorbs onto the fibers trials is most active at pH 6.5 and 50°C. Office wastepaper and severs fibrils attached to toner particles (3,4). Released contains many paper additives that influence pH; most toner particles subsequently can be removed by flotation. batches have a repulped pH of approximately 8.5-8.8, Removal of fibrils and the resultant smoothing of fibers primarily as a result of the use of calcium carbonate in increase pulp freeness, which prevents toner particles from alkaline papermaking. We examined deinking efficiency at becoming trapped in the repulped fiber network (3,9). 62 / TAPPI Proceedings The enzyme preparation selected for the industrial trials is a Table V. Effect of Holding Time on Strength of Enzyme- mixture of cellulase and hemicellulase. We previously Treated Pulp established that a very low level of this enzyme is required for optimum ink removal under controlled laboratory condi­ tions. When pH is adjusted to a neutral range and reverse Pulp Vis- Tensile Burst consistency cosity osmosis water is used for repulping, we have found that 0.2 Specimen index index (%) (CPS) mL enzyme per kilogram of OD pulp is the optimum enzyme dosage. However, when the conditions for enzyme activity Control 0.0444 2.85 – 12.5 are less than optimum, as will be the case for the industrial a trials, we