2010 TAPPI JOURNAL Titles - By CATEGORY

BIOENERGY

Improving anaerobic conversion of pulp mill secondary sludge to biogas by pretreatment By Nicholas Wood, Honghi Tran, and Emma .Master June, p. 16-21. We examined the effectiveness ofthem1al, caustic, and sonication pretreatment methods in improving anaerobic conversion to biogas of secondary sludge samples obtained from a kraft mill and a sulfite mill. All three methods improved the anaerobic digestion rate and the biogas yield of the sludge samples. Thermal pretreatment was the most effective, followed closely by caustic pretreatment, and sonication the least. The total biogas productions per unit of chemical oxygen demand of sulfite sludge and kraft sludge samples were respectively 1.2 and 3 times higher with pretreatments than without. Also, the biogas production from the untreated sulfite mill sludge was 4 times higher than that from the untreated kraft mill sludge.

Pilot-scale combustion studies with kraft lignin in a powder burner and a CFB boiler By Nildas Berglin, Per romani, Hassan Salman. So/vie Herstad Svard, and Lars-Erik Amand June, p. 24-30. Processes have been developed to produce a solid biofuel with high energy density and low ash content from kraft lignin precipitated from black liquor. Pilot-scale tests of the lignin biofuel were calTied out with alSO kW powder burner and a 12 MW circulating fluidized bed (CFB) boiler. Lignin powder could be fired in a powder burner with good combustion perfOimance after some trimming of the air flows to reduce swirl. Lignin dried to 10% moisture content was easy to feed smoothly and had less bridging tendencies in the feeding s)'stem than did wood/ bark powder. In the CFB boiler, lignin was easily handled and cofired together with bark. Although the filter cake was broken into smaller pieces and fines, the combustion was not disturbed. When cofiring lignin with bark, the sulfur emission increased compared with bark firing only, but most of the sulfur was captured by calcium in the bark ash. Conventional sulfur capture also occurred with addition of limestone to the bed. The sulfur content in the lignin had a significantly positive effect on reducing the alkali chloride content in the deposits, thus reducing the high temperature corrosion risk.

Experiments and mathematical models of black liquor gasification - influence of minor gas components on temperature, gas composition, and fixed carbon conversion By Per Carlsson. Magnus Marklllnd, Erik Furusjo, Henrik Wiinikka. and Rikard Gebart September, p. 15-24. In this work, predictions from a reacting Computational Fluid Dynamics (CFD) model of a gasification reactor are compared to experimentally obtained data from an industrial pressurized black liquor gasification plant. The data consists of gas samples taken from the hot part of the gasification reactor using a water cooled sampling probe. During the considered experimental campaign, the oxygen-to-black liquor equivalence ratio ( ) was varied in three increments, which resulted in a change in reactor temperature and gas composition. The presented numerical study consists of CFD and thennodynamic equilibrium calculations in the considered -range using boundary conditions obtained from the experimental campaign. Specifically, the influence of methane concentration on the gas composition is evaluated using both CFD and thermodynamic equilibrium. The results show that the main gas components (H2, CO, C02) can be predicted within a relative en'or of 5% using CFD if the modeled release of

H2S and CH4 are specified a priori. [n addition, the calculations also show that the methane concentration has large influence on the reactor outlet temperature and final carbon conversion.

Co-tiring black liquor and biomass in a laboratory single droplet reactor ­effects on emissions and combustion characteristics By Nikolai Demartini, Esperanza Monedero, Patrik Yrjas. and Mikko Hupa September, p. 29-34. Mills having recovery boilers with excess capacity can potentially mix other biofuels into the black liquor to produce more electricity from biomass. This work is a laboratory study of the effect on combustion of mixing other biofuels with black liquor. The four fuels mixed with softwood black liquor were bark, wood chips, peat, and bio-sludge (which some mills already bum with black liquor). Droplets of the mixed fuels were burned at 11 OO°C and 3% 02 in a single particle reactor. Video and on-line gas analyzers for CO, C02 and NO were used to measure swelling, combustion times, carbon evolution (CO+C02), and NO formation tendency. We found changes in swelling, char bllllJing, and NO formation, but the results indicate that mixing biofue[s with black liquor may be a reasonable method of producing additional electricity.

BLEACHING

Ozone-enhanced bleaching of softwood kraft pulp B,v Jean-Christophe Hostachy August, p. 16-23. By using ozone in their bleaching processes, many hardwood pulp mills in various parts of the world have improved product quality and their environmental and process performance, and reduced operating costs to increase competitiveness. The challenge for softwood pulp is to rethink the use of ozone according to their specific requirements. This paper summarizes results obtained using ozone bleaching on softwood (Pinus radiata) kraft pulp, for which the brightening ability of limited ozone dosages can enhance the economic benefits without impairing pulp quality. This work evaluated the chemical justification to use ozone at the end of the bleaching sequence and the effect on pulp quality, and considered the practical consequences of this new option. Special attention was given to the economic and technical aspects, including investment cost, variable cost, and process implementation. Ozone was shown to be the ideal complement of chlorine dioxide for final pulp bleaching. Both chemicals can easily be combined at the end of the bleaching sequence. Taking into account pulp mill capacity, capital investment, and total operating cost, the financial savings were calculated to be in the range ofEUR 5 million (USD 6 million) per year, with a payback period of about 1.5 years.

Optimization of elemental chlorine-free bleaching for a softwood kraft pulp ­part 1: impact of oxidative extraction on chlorine dioxide stoichiometry By Brian N. Brogdon August, p. 27-35. The present investigation meticulously analyzes how oxidative alkaline extraction can be augmented through process changes, and how these augmentations can be leveraged to optimize chlorine dioxide usage with elemental chlorine-free (ECF) sequences for a conventional softwood kraft pulp. Bleaching data from Basta and co-workers (1992 TAPPl Pulping Conference) are re-examined and re-interpreted in this study. We determined that -60% to 65% of the overall Cl02 charge should be applied in the DO-stage. Peroxide addition to an (EOP) can replace 0.6 to 2.5 Kg. Cl02 per Kg H202. Boosting the (EO) temperature to 80°C is

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equivalent to a 70°C (EOP) with 0.25% to 0.30% H202,whereas a 90°C (EO) is equivalent to 0.50% - 0.75% H202 in a 700 e (EOP). The stoichiometric bleaching data from this study can guide decision-making for lowering chemical usage and minimize costs to reach target brightness levels with three- and five-stage sequences.

Optimization of elemental chlorine-free bleaching for a softwood kraft pulp - part 2: economic analysis of chemical and steam consumption By Brian N. Brogdon September, p. 47-53. Our previous investigation [I] re-analyzed the data from Basta and co­workers (1992 TAPPI Pulping Conference) to demonstrate how oxidative alkaline extraction can be augmented and how these changes affect chlorine dioxide consumption with elemental chlorine-free (ECF) sequences. The current study manipulates extraction delignification variables to curtail bleaching costs with a conventional U.S. Southern softwood kraft pulp. The economic advantages of ~0.35% to 0.65% H202 peroxide reinforcement in a 70°C (EOP)-stage versus 90°C (EO)-stage are predisposed to the brightness targets, to short or long bleach sequences, and to mill energy costs. Minimized bleaching costs are generally realized when a 900 e (EO) is employed in DO (EO) D I bleaching, whereas a 70°C (EOP) is economically advantageous for DO (EOP) 0 I E2D2 bleaching. The findings we disclose here help to clarify previous ECF optimization studies of conventional softwood kraft pulps.

COATING

Calendering effects on coating pore structure and ink setting behavior By Peter Resch, Wolfgang Bauer, and Ulrich Hirn January, p 27-35. Coating layer pore structure significantly affects surface appearance, optical properties, and print-ability performance of multiply coated papers. Generally, fast ink setting can be realized by use of fine pigments, or pigments with steep particle size distribution. lnk­paper interaction of coated papers also changes significantly in calendering. The objective of this study was to better understand the influence of calendering on the pore structure of multilayered coated papers and to highlight the effect of this pore structure change on ink setting behavior. Laboratory calendering trials demonstrated that the pore structure of calendered paper is reduced with increased calendering temperatures. Mercury porosimetry and image analysis of scanning electron microscope images of calendered papers highlighted the gradual reduction of total pore volume, which, in combination with the reduced surface porosity, resulted in slower ink setting. If ink setting speed is to be preserved, calendering at low surface temperatures and a higher number of nip passes is preferred to reach a desired paper gloss level. Results also were compared to common theoretical models for liquid penetration into porous structures. These models can also be used to describe the influence of calendering-induced pore structure changes on ink setting. This work demonstrates optimization of calendering parameters to reach a balance for paper gloss and ink setting. The optimum depends on the machine equipment available and has to be checked separately for each concept of multiply coated paper and calender conditions.

A new method for quantifying the blocking of coated paperboard By Pauline Skillington, Yolande R. Schoeman, Valeska Cloete, and Patrice C. Hartmann May, p. 29-35. Blocking is undesired adhesion between two surfaces when subjected to pressure and temperature constraints. Blocking between two coated paperboards in contact with each other may be caused by inter-diffusion, adsorption, or electrostatic forces occurring

between the respective coating surfaces. These interactions are influenced by factors such as the temperature, pressure, surface roughness, and surface energy. Blocking potentially can be reduced by adjusting these factors, or by using antiblocking additives such as talc, amorphous silica, fatty acid amides, or polymeric waxes. We developed a method of quantifying blocking using a rheometer. Coated surfaces were put in contact with each other with controlled pressure and temperature for a definite period. We then measured the work necessary to pull the two surfaces apart. This was a reproducible way to accurately quantify blocking. The method was applied to detell11ine the effect external factors have on the blocking tendency of coated paperboards, i.e., antiblocking additive concentration, film thickness, temperature, and humidity.

Changes with aging in the surface hydrophobicity of coated paper By CeciNa Lidenmark, Sven Forsberg, Magnus Norgren. Hakan Edlund. and Ola Karlsson May, p. 40-46. Time-dependent changes in the surface properties of coated papers were studied as the evolution of surface hydrophobicity of laboratory and commercially coated papers. We measured the apparent contact angles on the papers during several weeks post-production. Hydrophobicity upon aging increased for all samples made from traditional coating colors on mechanical base stock and on base stock made from cotton linters. Accelerated aging by heat treatment intensified the increase of the apparent contact angles and accelerated the time­dependent behavior. A key mechanism in these changes may be the spreading of latex particles in a coating.

A novel appl'oach to quantify spatial coating-layer formation By Johannes Kritzinger, Wolfgang Baller, Pekka Salminen, and Janet Preston November, p. 7-13. A straightforward correlation of coating thickness and base sheet surface height (topography) data does not clearly show the expected differences between a contour coat­like structure for curtain coating or a leveling coat-like structure for blade coating. We defined a measure to clearly distinguish between these different kinds of spatial coating-layer formation. Filtering in the frequency domain preserves only the large structures in the coating layer thickness and the base sheet topography data. The coefficient of determination (R2) and the slope ofa linear regression model, between filtered coating thickness and base sheet surface height (topography), are the measures used to describe the leveling behavior of a coating layer. Three application systems-blade, film press, and curtain coating-were compared. Analysis of the original data showed only minor differences in the coating-layer fomlation between the application systems. For the filtered data where large structures are preserved, curtain coating gave an almost ideal contour coat, where coating thickness was hardly influenced by base sheet topography. The coating thickness in blade coating strongly depended on local base sheet surface height variations. A film press application of the coating layer resulted in a coating structure between curtain and blade coating.

Experimental and theoretical study of the manifold flow in a curtain coater By Philippe Martinez, Martine Rue/I David Guerin, and Veroniqlle Morin November, p. 15-21. Curtain coating is a contactless process with the potential for increased quality and productivity for coaters. Nevertheless, this demanding process requires a perfectly stable curtain to obtain good coverage. Problems can originate from the internal flow when the fluid goes through cavities and slots before reaching the inclined plane. Three-dimensional computational fluid dynamics simulations were performed in the manifold of a laboratory curtain coater to analyze the phenomena taking place in the first cavity, determine the causes of defects,

and propose potential solutions. Reynolds number is a relevant parameter for Newtonian and non-Newtonian tluids and increasing it leads to disturbances in the manifold. The power law index also significantly affects t10w uniformity, because its decrease leads to perturbations. Finally, yield shear stress has no effect on vortex formation for coating colors. To maintain vortex-free operation, the Reynolds number at the inlet must remain below a critical value (equal to 20 with the studied geometry), whatever the tluid. Geometrical changes were simulated with a higher radius of the inlet pipe or an end-fed manifold, resulting in improved flow uniformity. Simulation results were validated using flow visualization experiments with tracers using a transparent replica of the coater.

Nanofibrillated cellulose as a coating agent to improve print quality of synthetic fiber sheets By Hi/ami Hamada and Douglas W. Bousfield November, p. 25-29. To determine the potential ofnanofibrillated cellulose (NFC) for use as a coating material, we studied the characteristics of several NFC-coated samples on a synthetic fiber sheet. We used two water-based printing methods to characterize the change in print quality and prepared two types ofNFC by two different physical treatment methods. Various coat weights were applied onto synthetic fiber sheets, and the printability of the coated sheets was evaluated by ink absorption rates and print density. Ink pigment penetration was characterized with a confocal laser scanning microscope and a scanning electron microscope, with chemical analysis of samples using focused ion beam. The contact angle and the ink penetration rates decreased with increased coat weight ofNFC. This result is the opposite of what the Lucas­Washburn equation would predict. For pigment-based flexographic inks, ink pigments were captured at the NFC layer. For dye-based inks, the ink components penetrated and moved through the NFC-coated layer. For ink-jet printing, the print quality improved with the NFC coating.

Superhydrophobic paper coating containing nonconventional clay By Behudin (Beko) Mesic, Chris/ian Kugge, and Lars Jams/rom November, p. 33-40. Hydrophobic clay fillers have not been widely used in dispersion coatings for linerboard because of the difficulty of dispersing them in water. This work investigated whether hydrophobic clay can be used as filler in barrier dispersion coatings. Hydrophobic clay was compared with conventional clay in ten1lS of coating consolidation, structure, wetting, and batTier performance. All coatings were applied to linerboard sheets made using a laboratory dynamic sheet fonner. The coated linerboards were examined using scanning electron microscopy and Raman spectroscopy, and were characterized with respect to water absorption, vapor transmission rate, and contact angles. The results show that a coating containing hydrophobic clay provides a superhydrophobic character to paper; i.e., a high water contact angle (150°) and relatively low water absorption. Raman mapping of cross-sections revealed that the latex distribution is uniform in the presence of either conventional clay or hydrophobic clay, and that the distribution of hydrophobic clay tends to be more uniform than conventional clay, which might reflect good mixing and consolidation of hydrophobic clay.

CORROSION & MATERIALS

Evaluation of a molybdenum sulfide reference electrode in hot alkaline solutions By Outi A. Hyokyvirta and Tom E. Gusrafsson July, p. 35-41. This investigation evaluated the applicability of a molybdenum sulfide reference electrode (MSRE) as an intemal reference electrode for use in alkaline sulfide solutions over a range of pulp digester liquors at 170°C. The electrode remained stable during the exposure period of two weeks. The experimentally determined half cell potential of the MSRE is E = -0.91 VSHE. The surface of the MSRE was examined by scanning electron microscope (SEM) and electron spectroscopy for chemical analysis (ESCA) to verify the chemical composition of the thin surface film. Based on ESCA studies, the surface film contained molybdenum disulfide and sodium disulfide. During storage of the specimens, sulfide was partly oxidized to sodium sulfite in air. Next to the metallic molybdenum, a mixed molybdenum disulfide and molybdenum hydroxide layer was detected.

Smelt spout corrosion in a recovery boiler By Julio Cesar Torres Ribeiro, Marcelo Cardoso, and Honghi Tran August, p. 39-45. Severe cOITosion led to an in-service fai lure of one of the six spouts on a recovery boiler at Cenibra. The failure resulted in a large amount of cooling water entering the boiler and contacting smelt around the spout opening, but fortunately no smelt-water explosion occurred. An extensive investigation was conducted to detelmine the causes of the spout failure. The failure was caused by insufficient cooling water flow to the smelt spout, which, in tum, was caused by a sequence of events that occun'ed after a general blackout of an electrical energy system at the mill. The experience has led to the development and placement of operating and maintenance procedures that ensure adequate cooling water flows to smelt spouts to prevent future failures.

KRAFT PULPING

Characterization of Anthocephalus cadamba and its delignification by kraft pulping By Mohan Lol, Dharm DUff, C. H Tyagi, 1. S. Upadhyay. and Siddharrha Upadhyay March, p. 30-37. Anthocephalus cadamba is a fast-growing deciduous tropical hardwood with anatomical, morphological, and chemical characteristics that make it suitable for pulp production. The fibers are short but fiber width, cell wall thickness, and rigidity coefficient ofA. cadamba are comparable to those of softwoods such as Pinus kesiya and Picea abies. Due to low lignin and high holocellulose contents, A. cadamba produces high pulp yield at milder cooking conditions. We studied the effect of sulfidity, cooking time, and temperature on pulp yield and kappa number during kraft pulping. The effect of ageing on pulp yield, kappa number, and viscosity indicated that 4-year-old A. cadamba is suitable for pulp production and produces optimal strength properties at 44 Schopper-Riegler degree (OSR).

Reappraisal of the role of turpentine vapor in noncondensible gas explosions By Risto Lautkaski April, p. 6-11. Turpentine has been identified as the cause of numerous fires and explosions within the pulp and paper industry. Explosions in the noncondensible gas (NCG) collection systems caused by total reduced sulfur (TRS) compounds have usually been minor and caused

minimal damage, but explosions caused by turpentine could be catastrophic. When flammable conditions have been created by insufficient dilution, air leakage into the system, or accumulation and breakthrough ofTRS gases or turpentine vapor at a chip bin, it is conceivable that turpentine vapor created near-optimum flammable mixtures more often than TRS gases did. In these cases, the burning velocity would have been close to the maximum. On the other hand, when flammable conditions were created due to insufficient dilution of a stream of high volume, low concentration gases (HVLCs) or due to air leakage into a stream of low volume, high concentration gases (LVHCs), then the flammable mixture f0l111ed would be expected to have been off-stoichiometric: lean in the former case and rich in the latter case. In both cases, the bUl11ing velocity could have been much lower than in the near-stoichiometric mixture. The violence of explosions caused by turpentine is attributed to its capability to form near­stoichiometric mixtures more easily than the other components ofNCGs.

Effects of impregnation time on hardwood kraft pulp characteristics and papermaking potential- a mill study By Lasse Tolonen, Eero Hiltllnen, Jukka Helttunen, and Herbert Sixta April, p. 21-27. We conducted a series of trials in a commercial-scale pulp mill producing fully bleached birch hardwood kraft: pulp to study the effects of impregnation time. Retention time in an impregnation vessel was altered between 5 min and 60 min. Cooking kappa number target and brightness targets were held constant and the rest of the fiber line was operated according to n0l111al practices. After analyzing collected pulp samples to monitor changes in characteristics and papel111aking properties, we found that impregnation time has a significant effect on the consumption of effective alkali in the impregnation stage, but the total alkali consumption was not affected when a cooking kappa number was held constant. Reduced impregnation time required higher cooking temperatures to reach the kappa number target. Shorter impregnation times clearly increased the amount of rejects. Viscosity, carbohydrate composition, and fiber saturation point were not significantly influenced by the impregnation time, but some fiber damage occurred with longer impregnation times. The tensile strength and tensile were higher with the shorter impregnation time, whereas tear strength at a given tensile index did not cOtTelate with impregnation time. An obvious reason for the affected papel111aking properties was not found.

Accelerating kraft pulping with hydroxyethylidene diphosphonic acid (HEDP) By Richard Beny, h!/un SlIn, and Corinne Ltlthe June, p. 9-14. Three hardwoods (aspen, maple, and birch) and one softwood (black spruce) were pulped under standard kraft cooking conditions with and without hydroxyethylidene diphosphonic acid (HEDP). The H factor required to give a kappa number of 15 for the aspen furnish was decreased from 1, I00 to 650 by adding 0.1 % HEDP on wood. Significantly smaller rate increases were observed with birch and maple, and no rate increase was observed with the softwood fUl11ish. When aspen and black spruce chips were impregnated with calcium, it was found that aspen delignification was retarded while there was no effect on black spruce. HEDP, therefore, appears to work by removing calcium which, in hardwoods, causes lignin to be strongly bonded to the fiber. Adding carbonate to the pulping liquor showed that carbonate has the same effect as HEDP by removing calcium as insoluble calcium carbonate (CaC03). These observations lead to the conclusion that HEDP is not an effective additive, even for hardwoods, when sufficient carbonate is present.

Comprehensive evaluation of k"aft pulp properties from fast-growing woods By A(vlI QII, Yanhlli Ao, fun Yan. and Guigan Fang June, p. 34-39. To develop new wood cellulose resources and fast-growing pulpwood plantation fiber sources, it is very important to evaluate their pulping properties. A comprehensive multi­index pulping-suitability evaluation model is investigated in this paper by considering four fast­growing wood species. First, a new evaluation-index system for kraft pulp was developed based on traditional evaluation-index systems. Then, the membership degree of every index was analyzed to obtain a fuzzy matrix. The proportional contribution of each parameter to the main pulping properties could then be determined. Finally, a comprehensive evaluation model of kraft pulp properties was developed. The model is reliable compared with traditional assessment methods. The results confirmed the feasibility and rationality of developing new wood cellulose resources and fast-growing pulpwood plantations using fuzzy comprehensive evaluations.

NONWOOD FIBERS

The effect of tlocculants on the filtration of bagasse pulp pads By Thomas 1. Rainey, William o.s. Doherty, D. Mark Martinez, Richard 1. Brmvn. and Alan Dickson May, p. 7-14. This study examined the effect oftlocculants on the filtration parameters of bagasse pulp. In the tirst phase, tlocculants were effective for improving the fiber retention of three different bagasse pulp slun'ies, based on flocculant system studies using a dynamic drainage jar. In the second phase, pulp pads were fonned using these flocculants and the steady­state permeability and compressibility parameters were measured. The results showed that the flocculant system that was effective for a pulp slurry was entirely ineffective in improving pulp pad penneability or compressibility during the second experimental phase for two of the bagasse pulp samples.

Environmentally friendly pulping of rice straw to eliminate black liquor discha"ge By Gllo/in Huang, Xi~hen Liang, Zhongsheng Chen, and Cuizhen Li August, p. 7-12. Rice straw pulping trials were carried out with aqueous ammonia mixed with caustic potash to eliminate problems associated with black liquor in nonwood pulping. This process likely can use the black liquor, which contains nitrogen, potassium, and ammoniacal lignin, as a fertilizer for agricultural production. Excess ammonia in the black liquor was recovered by batch distillation. The black liquor was further treated for reuse by coagulation under alkaline conditions. We studied the effects of flocculating conditions, such as dosage of 10% aluminum polychloride, dosage of 0.1 % polyacrylamide, reaction temperature, and pH of black liquor to obtain suitable technological conditions. Analyses confinned that major quantities of lignin and 23.7% nitrogen (dried basis), 6.2% potassium (dried basis) existed in the flocculating residues, so this is potentially a good solid fertilizer. The amount of delignification and the pulp screen yield for the process remained steady at 83%-85% and 38%-40%, respectively, when reusing the supematant four times.

NONWOVENS

Study on the chemical modification process of jute fiber By Wei-ming Wang. Zai-sheng Cai, and Jian-yong Yu February, p. 23-29. Degumming of pre-chlorite treated jute fiber was studied in this paper. The effects of sodium hydroxide concentration, treatment time, temperature, sodium silicate concentration, fiber-to-liquor ratio, penetrating agent TF-I 078 concentration, and degumming agent TF-125A concentration were the process conditions examined. With respect to gum decomposition, fineness and mechanical properties, sodium hydroxide concentration, sodium silicate concentration, and treatment time were found to be the most important parameters. An orthogonal L9(34) experiment designed to optimize the conditions for degumming resulted in the selection of the following procedure: sodium hydroxide of 12g/L, sodium silicate of3g/L, TF­1078 of2g/L, TF-125A of2g/L, treatment time of lOS min, temperature of 100°C and fiber to liquor ratio of I :20. The effect of the above degumming process on the removal of impurities was also examined and the results showed that degumming was an effective method for removing impurities, especially hemicelluloses.

A computational fluid dynamics modeling and experimental study of the mixing process for dispersion of synthetic fibers in wet-lay forming By Melur K. Ramasubramanian, Donald A. Shiffler, and Am it Jayachandran March, p. 6-13. In this paper, we present results from a computational fluid dynamics (CF D) model for the mixing process used to disperse synthetic fibers in wet-lay process. We used CF D software, FLUENT, together with the MIXSI M user interface to accurately model the impeller geometry. A multiple reference frame (MRF ) model and standard k-e turbulence model were used to model the problem. After obtaining a converged solution for the mixing tank with water, a discrete phase model was constructed by injecting spherical particles into the flow. A mixing tank with baffles and a centrally located impeller was used in experiments. PET fibers (1.5 denier, 6.35 mm, 12.7 mm, and 38.7 mm) at a concentration of 0.01% were mixed in water for the study. In regions behind the baffles, where the model predicted higher concentration of particles, experimental results showed a 34% higher concentration relative to the region in the high turbulence zone near the center. Instantaneous sheets were formed by rapidly dipping and removing a flat wire mesh strainer into the tank at two different locations to assess the state of dispersion in the tank. The sheets were transferred onto a blotting paper and examined under a microscope to count defects. Results show that the number of rope defects was 43% higher in sheets drawn from the region behind the baffles than in the sheets drawn from regions near the center of the tank. Changing baffles from a rectangular to a triangular cross section decreased the number of rope defects, but increased the number of log defects in the sample sheets at the same location. The CF 0 model can be used to optimize mixing tank design for wet lay fiber dispersion. The model provides further insight into the mixing process by predicting the effect of changes in design parameters on dispersion quality.

PAPERMAKING

Papermaking potential of novel structuredPCC fillers with enhanced refractive index By Kimmo Koivunen and Hanf1ll Paulapuro January, p. 4-12. While much effort has been focused on optical properties imparted by particle size distribution, shape, and packing of inorganic particles, the refractive index contrasts within the paper matrix have received less attention. PCC fillers can be used as tools for increasing the refractive index contrast, which further improves paper optical properties. We studied the papermaking potential of novel pee fillers with an enhanced refractive index. pee samples were fabricated by conventional carbonation method in the presence of refractive-index enhancing additives. We had previously found that introduction of ZnO as fine spots, including nano-sized structures, on host pee surfaces improved the effective refractive index and optical performance of pee. Now, we have studied the papermaking potential of this approach in experiments with handsheets using moderate Zn modification. In addition to Zn, we studied the effect of Sr as an additive and found that Sr inclusion alters the host particle morphology and crystal structure. We report effects of such modifications on light scattering coefficient, brightness, opacity, tensile strength, bulk. and porosity of paper, both before and after calendering. Our results suggest beneficial optical properties, as well as combination of light scattering with strength properties, especially in the case of Sr modified filler. Zn modified fillers opened the sheet structure, while Sr structuring closed the sheets. Calendering resulted in reduced bulk with all fillers, while optical properties were maintained with the Sr modified pce, but reduced benefit was observed in the combination of light scattering and strength. Calendering conditions should therefore be optimized for these fillers. A higher modification degree of the fillers should also be considered to achieve a more significant refractive index contrast.

Prediction of handsheet tensile strength by computational simulation of structure By Remi Vincent, Martine Rueff; and Christina Voillot January, p. 15-19. To better understand the influence of fiber morphology on paper properties, we developed a novel 3-D computational simulator of paper structure, which was validated through experimental work. This simulator creates virtual pieces of handsheets using the size distributions of the fibers as the main inputs. Once the structure is generated, physical properties can be assessed. The main principles of the simulation and the results for one global texture property, the apparent density, were presented in a previous paper. In this paper, we focus on the prediction of the tensile breaking strength, the most commonly used physical property for paper characterization. The model is based on the model developed by Shallholl1 and Karnis, which was adapted to take into account the fiber morphological distributions. It was successfully applied in the absence of fiber breaks during the test and validated with the 10 pulps used in the first part of the study.

Impact of high-yield pulp substitution on the brightness stability of uncoated wood-free paper By Zhihin He, Lan/eng Hui, Zhong Liu, Yonghao Ni, and Yaiun Zhou March, p. 15-20. Without any fillers and optical brightening agents (OSA s), 15%-20% substitution of high-yield pulps (HYPs) for the hardwood bleached kraft pulp (BKP) in a paper fUl11ish can decrease the brightness stability significantly because HYP contains a large amount of lignin. However, using mineral fillers such as precipitated calcium carbonate (pee) and OBA

in a HYP-containing paper can essentially eliminate the negative effect of HYP substitution on the brightness stability of uncoated wood-free paper. During the commercial production of traditional wood-free paper products, which usually use both pee and OSA , J5%-20% HYP substitution for the hardwood BKP will not have practical impact on the paper brightness stability. Results from commercial printing and writing paper production support the same conclusion.

Starch-modified fillers for linerboard and paper grades: A perspective review By Yulin Deng, Phil Jones. Leslie McLain, and Art J. Ragauskas April, p. 31-36. High-filler-content paper is a growing research and development opportunity in papell11aking. These new products must address traditional paper product properties while providing papermakers with distinct product platform benefits. Over the past decade, a research team involving researchers from the Institute of Paper Science and Technology at Georgia Institute of Technology and from lmerys have significantly advanced the application of starch­encapsulated papelmaking fillers. This review summarizes these accomplishments from initial laboratory studies to mill trials. Laboratory results have illustrated that starch-encapsulated fillers can facilitate a near-doubling of filler content over conventional levels at equal tensile and z­direction tensile (lOT) values. Equally important is that the use of starch-encapsulated kaolin (SEK) filler has been shown to facilitate a doubling of filler addition rate without any detrimental impact on ring crush compared with control studies with tiller. Pilot-plant and mill trials have shown that SEK can function as a fiber extender, reduce steam demand for drying by 10%, and increase papennaking speeds and production rates.

Influence of machine-side filaments and jet-to-wire speed ratio on the flow through of a forming fabric By Ali Vakil. Arash Olyaei, and Sheldon I. Green July, p. 25-31. In the f0ll11ing section of a paper machine, pulp is spread over a moving fabric and water is drained through the fabric. The tibers left behind form a wet sheet. The mechanical dewatering that begins in the forming section is important to the final paper quality because any non-unifOlmities arising in this section cannot be cOlTected later in the paper machine. Therefore, understanding the flow field through the forming section provides insight into the finished paper. We analyzed the effect of the machine-side filaments of the fabric on the flow field upstream of the paper-side filaments. The resistance of a multilayer fabric was found to be nearly equal to the sum of the resistances of each layer considered in isolation. For the particular fabric, the machine-side layer produced up to a 10% effect on the velocity above the paper-side layer. For the effect of jet-to-wire speed ratio on the flow, an angled approach flow to the fabric produced very little change in the average flow perpendicular to the fabric (i.e., little change in fabric penneability). However, it has a marked effect on the machine-direction shear stress in the vicinity of the paper-side filaments. This shear stress drives the fiber orientation characteristics of so-called rush or drag jet impingement.

Z-direction fiber orientation in paperboard By John M. Considine. David W. Vahey, Roland Gleisner, Alan Rudie, Sabine Rolland Du Roscoat. and Jean-Francis Bloch October, p. 25-32. This work evaluated the use of conventional tests to show beneficial attributes of z-direction tiber orientation (lOFO) for structural paperboards. A survey of commercial linerboards indicated the presence of lDFO in one material that had higher Taber

stiffness, out-of-plane shear strength, directional dependence of Scott internal bond strength and directional brightness. Laboratory handsheets were made with a specialized procedure to produce ZDFO. Handsheets with ZDFO had higher out-of-plane shear strength than handsheets formed conventionally. Materials with high out-of-plane shear strength had greater bending stiffness and compressive strength because of their abi lity to resist shear defomlations.

PRINTING

Comparison of ultraviolet inkjet printing on different synthetic fib.·ous papers By Mirica Debeljak, Sabina BraCko, Ale.5 Hladnik, and Diana Cregor-Sl'etec May, p. 17-25. We investigated the printability of fibrous synthetic papers with ultraviolet (UY) inkjet technology. Cyan, magenta, yellow, and black (CMYK) color fields were printed on two types of fibrous synthetic papers using two different wide-fonnat UY inkjet printers. Spectrophotometric and densitometric measurements were perfotll1ed on CMYK color fields with different ink coverages, along with a microscopic analysis of unprinted paper, black prints with 100% ink coverage, and a print mottle of magenta and black prints. Colorimetry and optical densities of the CMYK prints were qualitatively and quantitatively compared. Color deviations in CMYK prints were affected by paper type and were dependent on the UV inkjet printer used.

Use of confocal laser scanning microscopy and a computer model to understand ink cavitation and filamentation B.v Hanna Koivula. DOl/glas Bow·field. and Mariti Toivakka October, p. 7-15. In the offset printing process, ink film splitting has an important impact on formation of ink filaments. The filament size and its distribution influence the leveling of ink and hence affect ink setting and the print quality. However, ink filaments are difficult to image due to their short lifetime and fine length scale. Due to this difficulty, limited work has been reported on the parameters that influence filament size and methods to characterize it. We imaged ink filament remains and quantified some of their characteristics by changing printing speed, ink amount, and fountain solution type. Printed samples were prepared using a laboratory printability tester with varying ink levels and operating settings. Rhodamine B dye was incorporated into fountain solutions to aid in the detection of the filaments. The prints were then imaged with a confocal laser scanning microscope (CLSM) and images were further analyzed for their surface topography. Modeling of the pressure pulses in the printing nip was included to better understand the mechanism of filament formation and the origin of fi lament length scale. Printing speed and ink amount changed the size distribution of the observed filament remains. There was no significant difference between fountain solutions with or without isopropyl alcohol on the observed patterns of the filament remains.

PROCESS CONTROL

Applications of tension and nip load profile measurement using a novel roll mounted electret film sensor By TalLl Pitkiinen and Bob BetlendOlf April, p. 13-19. An intelligent roll is a mechatronic system consisting of a roll in a web handling machine that also is used as a transducer for sensing cross-machine tension or linear

load. The intelligent roll has electret film force sensors mounted on it in a helical arrangement. The sensors measure the force applied by the material being produced, such as a paper web, and thus provide information about the behavior and quality of the product. In addition to the force sensors, the intelligent roll system has an electronic signal processing module on the roll end and a digital radio link to transmit the data from the rotating roll. The receiver is connected to an automation network. An intelligent roll can be used to measure the tension profile online without separate scanning devices. An intelligent roll used as a reel or winder drum enables online measurement of linear load profiles during reeling and winding. Intelligent roll technology also enables temporary process and runnability analysis measurements by using tapemounted sensors. Problems such as loose web edges, off-machine coater web shifting, winding problems, and reeling defects have been solved with these measurements. This paper describes the technology and presents three examples of its application to improve process runnabi Iity.

Online monitoring of inorganic cooking chemicals in white liquor by pulse voltammetry By Robert B. Bjorklund, Dan LOllthander, Per Miirtensson, SlafJan Andersson, Erland Kvist, Margareta Ohrn, and Christina Krantz-Riilcker August, p. 49-53. White liquor parameters in the recovery area of a kraft pulp mill were monitored for a I-year period using rhodium as an electrode material in a sensor system based on pulse voltammetry. Shift personnel perfonned offline titration analysis of the liquor every 4 hours. The results for effective alkali, sulfidity, and total titratable alkali were used to train and validate the sensor for online monitoring. Partial least square regression models developed from 150 reference titration results for each parameter from the first month of the study predicted concentrations for the following II months. Validation of the models using titration results indicated that overall relative root mean squared enol'S for prediction of the parameters were 3.7% for effective alkali, 3.4% for sulfidity, and 5.1 % for total titratable alkali. Process stops that exposed the sensor to temperature excursions or acid washings resulted in temporary periods of poor prediction.

RECOVERY BOILER

CFD-based modeling of kraft char beds - part 1: char bed burning model By Nici Bergroth, Markus Engblom, Christian Mueller, and Mikko Hupa February, p. 6-13. Understanding the physical and chemical phenomena governing char bed burning is important for stable and efficient operation of the recovery boiler. Stand-alone char bed models have been developed and evaluated to increase knowledge of the complex char bed conversion processes. Available computational f1uid dynamics (CFD)-based recovery furnace models previously have been applied to evaluate lower and upper furnace processes rather than to investigate the behavior of the char bed. In this first of two papers, a stand-alone char bed model for predicting the chemical processes of char bed burning was modified and implemented into a CFD-based furnace model. The char bed model, which is fully coupled with the gas phase and a simplified black liquor droplet model, solves equations describing the mass and energy balance on the surface of the char bed and includes carbon conversion via direct oxidation, gasification reactions, and sulfate reduction. The model was tested by simulating a 3150 tons dry solids/day recovery boiler. Simulations for two different primary air distributions and lIsing two sulfate reduction degrees in droplets alTiving to the bed were performed to evaluate the char bed

model. The effects on bed conversion processes were clearly revealed by the new char bed model. The model gives a reasonable description of the chemical processes occurring on the char bed in steady state. In the second part of this work, the model is applied to study the effects of droplet size and bed shape.

CFD-based modeling of kraft char beds - part 2: a study on the effects of droplet size and bed shape on bed processes By Markus Engblom, Nici Bergroth, Christian Muefler. Andrew Jones, Anders Brink. and Mikkv Hupa February, p. t 5-20. This is the second of two papers. The first paper presented the char bed burning model used in this work. In this paper, the effects of liquor droplet size and bed shape on kraft char bed processes and lower furnace combustion are studied using a computational fluid dynamics (CFD)-based furnace model. The simulations show that droplet size affects not only the amount of in-flight conversion and the amount of combustible material reaching the bed, but also to what degree char carbon conversion in the char bed is due to direct oxidation or gasification. Droplet size also affects char bed burning indirectly through bed shape. Char bed shape affects the degree to which combustion air jets impinge on the bed surface, increasing carbon conversion by direct oxidation. Tn addition, changes in bed shape over time affect char bed processes. The results suggest that when a char bed starts to grow, the local carbon input to the bed could increase with bed height. Tn addition, carbon conversion decreases in locations of air jet impingement if the bed shape is not maintained.

Nonp."ocess-element control in the liquor cycle using an ash leaching system By Peter W. Hart, Mathias E. Lind'Strom. GGly W. Col.wn. and George M. Wiley July, p. 7-13. To lengthen run time between washes and reduce thernlal cycling of the recovery boiler, the Evadale, Texas, mill has been attempting to reduce the levels of nonprocess elements (NPEs) in the liquor cycle. The mill has periodically purged electrostatic precipitator ash in an effort to reduce and control potassium (K) and chloride (CI) concentrations. Additional efforts to lower chloride concentrations involved changing the makeup chemical from diaphragm- to membrane-grade caustic and improving the operation of the chlorine dioxide generator spent acid salt filter. The change in makeup chemical NPE content successfully reduced the amount of boiler plugging due to sticky ash fornlation, but did not provide the desired amount of time between boiler washes. In an effort to further reduce the amounts of potassium and chloride in the liquor cycle, an ash leaching system was installed. The leaching system partially dissolves precipitator ash in hot water. The potassium and chloride are selectively leached into the liquid phase and remain in solution. Sodium sulfate crystals are separated from the leaching SllllTy using a decanting centrifuge and returned to the liquor cycle via a mix tank. The potassium- and chloride- rich liquid is sewered. Since the implementation of these nonprocess-element reduction methods, the chloride content of the incoming electrostatic precipitator ash has been reduced by roughly 55% and the potassium content by approximately 50%. Approximately 80% of the soda entering the ash leaching process is recovered into the liquor cycle.

In-furnace temperature and heat flux mapping in a kraft recovery boiler By Anders Brink, Tor Lauren, Mikko Hupa, RalfKoschack, and Christian Mueller September, p. 7-11. Gas temperatures, incident heat flux, and sUlface temperatures were measured in a large kraft recovery boiler. The measurements were a part of an extensive campaign planned and carried out to support validation of models based on computational fluid

dynamics. The gas temperatures were measured with three different techniques: infrared (lR) pyrometer, suction pyrometer, and unshielded thermocouples. In addition to the temperature measurements, the radiative heat flux was measured in a number of locations in the boiler using a portable heat flux probe, and the surface temperatures inside the boiler were measured using a p011able single-band lR camera.

Optimizing operation to increase recovery boiler throughput By F. Donald McCabe, David Savoy, Chris Halcrmv, and Honghi Tran September, p. 39-44. The recovery boiler at the Trving Pulp and Paper Saint John, NB, mill has been through several major retrofits to increase its original firing capacity of 1100 metric tons/day of black liquor dry solids to the present level of 1680 metric tons/day. Many problems have been encountered over the years, including tube cOlTosion and cracking, as well as plugging of flue gas passages, but they all have been overcome through operational changes and process optimization. The latest challenge is to increase throughput without experiencing high total reduced sulfur (TRS) levels that would impact the environment and jeopardize compliance. An optimization program has been in place at the mill since December 2008 to further increase boiler production while maintaining environmental perfonnance. The program, which automates liquor addition at full capacity according to targeted stack gas 02 and TRS levels, enables the boiler to operate at lower stack gas 02 targets and to achieve a 2%-3% increase in liquor throughput, while keeping TRS emissions under compliance.

RECYCLING

Understanding the role of surface active substances in flotation deinking mills by coupling surfactant and ink balance with process simulation By Davide Beneventi, Elisa Zenob, Bruno Can'rib, Jriremy Allixb, Patrice Nortiera, and Marie Christine Angelierb February, p. 31-39. Surfactants are largely present in pape1l11akiog/recycling processes. They are added intentionally or come with raw materials or process/functional additives. Once they have reached the process, they build-up in the circuits and, depending on their surface activity and concentration, they can have adverse effects 00 deinking and on the whole papermaking process, such as excessive frothing, depression of ink floatability, and paper sizing/retention difficulties. In this paper, the removal of apparent surface active chemicals (ASA C) is first evaluated io different flotation deinking mi lis through mass balances using surface tension measurements and a specific methodology. Mill data show that, in two-stage deinking lines, ASA C are slightly concentrated io the second stage, contributing to an increase in pulp frothing behavior, in flotation loss, and in some cases to a low ink removal efficiency. Trends observed in deinking mills are then interpreted using experimental data obtained at the laboratory scale in the presence of a model surfactant, and by process simulation. The effect of ASA C concentration on the efficiency of the flotation deinking process is explained in tenns of their effect on particle and water transport sub processes, namely, flotation, entrainment, frothing, and drainage.

Determination of aluminum soaps in pitch deposits by gas chromatography By Bruce Sithole and Paul Abb.vad October, p. 19-22. Aluminum soaps can be detennined by formation of aluminum­acetylacetonate chelates that are volatile enough to be analyzed by gas chromatography.

Application of the technique to pitch deposits containing aluminum soaps entails acid hydrolysis to break down the aluminum soaps, chelation of the aluminum with acetylacetonate at pH >6, and analysis of the aluminum chelates by gas chromatography. The technique offers results that are comparable to those obtained by a traditional, much longer method that requires acid digestion of aluminum soaps and analysis of aluminum content by inductively coupled plasma spectroscopy.

THERMOMECHANICAL PULPING

Water-uptake studies of dry, mountain pine beetle-infested, grey-stage lodgepole pine sapwood chips By Thomas Q. HlI, Michelle Zhao, James Drummond, and Palll Watsoll March, p. 22-28. Water-uptake studies of dry, mountain pine beetle-infested, grey-stage lodgepole pine (LPP) sapwood chips showed that it was possible to increase the moisture content of these chips significantly (e.g., from 20.5% to 37.0% for early-grey chips) by soaking the chips for 8 min-IO min at optimal conductivity (-200 /lS/cm) and pH (-6.0). The environmental scanning electron microscopy (ESEM)-energy-dispersive spectroscopy chemical-tracer technique provided qualitative infol1nation on water movement within 10 min of water soaking of both the green and the beetle-infested, late-grey LPP blocks. ESEM studies also showed the presence of fissures, fungal hyphae, and incipient decay in the late-grey blocks.

Influence of oxidation and cationization on the properties of thermomechanical pulp fibers By Pli Ma, Hllamin Zhai. Kvvei-Nam Len-v, alld Claude Danealiit October, p. 36-43. Thel1110mechanical pulp (TMP) fibers were separately oxidized using 4­acetamido-2,2,6,6- tetramethylpiperidyl- L-oxyl (4-acetamido TEMPO) and cationized by 2,3­epoxy-propyl-tri-methyl ammonium chloride. The goal was to evaluate the influences of the interaction of oxidized, cationized, and untreated fiber components on paper properties. TEMPO­mediated oxidation can enhance interfiber bonding potential of mechanical long fibers. Cationization can improve the interfiber bonding only when the cationic charge density is lower than 400 mmol/kg; the bonding capacity drops off with increasing cationic charge density. However, as these modified long fibers were mixed with untreated long fibers and short fibers, the interaction between these fibers affected the paper sheet strength. The addition of oxidized fibers improved the sheet density remarkably, but it only had apparent effort on tensile strength when the carboxyl group content was less than 500 mmol/kg; higher carboxyl content did not enhance the sheet properties. The addition of cationized fibers had no positive effort on sheet density, and when they were mixed with other fiber fractions the interaction between positively charged and negatively charged fibers resulted in poor paper structure with rough surface and decreased tensile strength. Both oxidation and cationization had adverse influence on intrinsic fiber strength and tear index; either high carboxyl content or high cationic charge density could lead to remarkable decrease in these two properties. The side reactions, such as p-elimination and alkoxy fragmentation during TEMPO-mediated oxidation and alkaline degradation during cationization, which degraded the cellulose, were responsible for the drastic decrease in zero span tensile strength and tear strength.

Characterization of spruce thermomechanical pulps at the fiber cell wall level: a method for quantitatively assessing pulp fiber development using Simons' stain By Dinesh Fernando and Geoffrey Daniel October, p. 47-55. Fiber development of mechanical pulps is nomlally assessed by a combination of conventional numerical analyses of fiber features using FiberMaster, PulpEye, and Kajaani instruments. When observed, changes in fiber morphology are nomlally subjective with use of light- and electron microscopy observations of representative fibers. Thus, visualization and quantification of changes in the fiber cell wall, like delaminatonlintemal fibrillation (D/IF) induced during processing, would offer a great advantage. Here, we developed a method using Simons' stain (SS) that allows quantification of pulp fiber development in temlS of fiber wallO/IF during different process conditions, as well as statistical analysis of whole pulp fiber populations of different thermomechanical pulp (TMP) types for the degree of D/IF developed in pulp fibers. The attributes of SS for producing different colored reactions (blue, green, orange, etc.) in pulp fibers through cell wall modification during processing were used in correlation with light microscopy. The method readily measured the degree of cell wall D/IF of pulp fibers from different double-disc refined TMPs produced using varying levels of specific energy and refining pressures. The SS method revealed the presence oftive sub-fiber populations in a whole pulp of a given TMP type representing different categories of fibers that possessed varying degrees of cell wall D/IF as a result of process conditions/treatments. Results of statistical analysis indicated that, while D/IF was significantly induced by both the applied refining pressure and specific energy, the effect of energy had the greatest influence. Based on statistical analysis for Bauer McNett fractions of 10,30, and 50 mesh, we suggest that fraction 30 is the most suitable fiber fraction for the analysis ofTMPs using fiber characterization procedures, as this fraction possesses the most treated fibers. The method provided useful information regarding pulp fiber development at the cell wall level that has the potential to explain pulp and paper properties developed in furnishes. The present SS method represents a valuable tool for assessing fiber development at the cell wall level in mechanical pulping.

Use of thermomechanical pulp fibers from waste woods for making eco-friendly cushioning material By Ji-Young Lee. Chul-Hwan Kim, Jeong-Min Seo, Ho-KYllng Chung, Kyung-Kil Back, Sung-Ho Kim, and Hye-Jeong Gvvak July, p.15-21. Eco-friendly cushioning materials were made with thermomechanical pulps (TMPs) from waste woods collected from local mountains in Korea, using a suction-forming method without physical pressing. The TMP cushions had superior shock-absorbing performance, with lower elastic moduli than expanded polystyrene (EPS) or molded pulp. Even though the TMP cushions made using various suction times had many voids in their inner fiber structure, their apparent densities were a little higher than that of EPS and much lower than that of molded pulp. The addition of cationic starch contributed to an increase in the elastic modulus of the TMP cushions without increasing the apparent density, an effect which was different from that of surface sizing with starch. In the impact test, the TMP cushions showed a more ductile pattem than the brittle EPS. The porosity of the TMP cushion was a little less than that of EPS and much greater than that of molded pulp. The porous structure of the TM P cushions contributed to their excellent thermal insulating capacity, which was equivalent to that of EPS. In summary, the TMP packing cushions showed great potential for surviving extemal impacts during product distribution.

WASTEWATER TREATMENT

Cha.oacterizing carbonaceous biochemical oxygen demand load reductions from pulp and paper mills for activities related to total maximum daily loads By James E. Paillmbo al1d Linjfeld C. Brown January, p. 20-26. Characterizing the effect of organic materials on receiving water-dissolved oxygen levels is important in water quality assessment studies involving pulp and paper facilities. Long-term biochemical oxygen demand (LTBOD) tests of pulp and paper effluents can be used to estimate many important characteristics such as ultimate BOD, rate coefficients, ultimate to 5-day BOD ratios (f-ratios), and reactivity. However, many of these characteristics are difficult to forecast as a function of future efforts to improve wastewater treatment, which is precisely what is needed for typical water quality assessments such as total maximum daily loads (TMDL ). We provide a conceptual framework using simulation to predict effluent BOD characteristics as a function of improved wastewater treatment. The simulations use equations that describe BOD kinetics and are able to reproduce trends in f-ratio observed at various pulp and paper facilities and predict BOD reactivity as a function of treatment.