Paper Mill Process Waters Research Articles

Recycled paper mill process water pre-treatment using ultrafiltration for water system closure

The use of membranes in integrated water systems has garnered increasing attention in paper mills operating with virgin fibres, with documented closed water loops in industry. However, limited research exists on the performance of ultrafiltration (UF) in mills operating with 100% recycled fibres (RCF) and closed water systems, as these result in the introduction and accumulation of insoluble contaminants in the effluent. This study investigated the effect of transmembrane pressure (TMP) and feed organic load on the flux, types of fouling, and organic separation with UF membranes in a recycled paper mill using 100% RCF. The high feed organic load caused inevitable fouling, limiting the highest achievable flux. However, the TMP could be manipulated to improve on or exacerbate the process performance, within the range that was set as a result of the feed's characteristics. Low TMP (1.35 bar) generated the highest permeability and chemical oxygen demand removal, while higher TMPs produced higher fluxes and recoveries. The process was characterised by high initial fluxes, followed by cake formation, which dominated, and pore blockage. The excess cake formation induced cake filtration. This study shows the potential of UF membranes to be used as pre-treatment in filtering the process water in a recycled paper mill operating with 100% RCF, a critical step forward in implementing an integrated water system, and eventually closing the water loop.

Treatment of a Mixture of Chloromethoxyphenols in Hypochlorite Medium by Electrochemical AOPs as an Alternative for the Remediation of Pulp and Paper Mill Process Waters

Here, 100 mg L−1 of dissolved organic carbon of aromatics including chloromethoxyphenols were prepared by exposition of a mixture of guaiacol, syringol, and vanillin in 200 mM NaClO at pH 3.0 and 25 °C for 14 h and further degraded by electrochemical advanced oxidation processes (EAOPs) like anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF), and photoelectro-Fenton (PEF). Electrolyses were performed with a cell containing either a Pt or boron-doped diamond (BDD) anode and an air-diffusion cathode at constant current density. Oxidants were hydroxyl radicals (•OH) formed at the anode surface from water oxidation and in the bulk from Fenton’s reaction between added Fe2+ and H2O2 generated at the cathode, as well as active chlorine species produced from the anodic oxidation of HClO. Oxychlorine ions like ClO3 − using Pt and ClO3 − + ClO4 − using BDD were detected in the electrolyzed solutions. A poor mineralization was found using the Pt/air-diffusion cell, with increasing relative oxidation ability in the sequence AO-H2O2 < EF < PEF. In contrast, overall mineralization was achieved in all EAOPs using the BDD/air-diffusion cell due to the larger amounts of highly oxidizing •OH generated at BDD. For this latter system, the effect of UVA light, current density, and NaClO and/or Fe2+ concentration on the mineralization rate was examined. Up to 11 chloroderivatives of the parent molecules including four chlorophenols, six chloromethoxyphenols, and one chloromethoxynaphthalene were identified by GC–MS. The removal of these aromatics in AO-H2O2 with Pt or BDD was monitored by UV–vis spectrophotometry, HPLC, and GC–MS.

Influence of Pitch Composition and Wood Substances on the Phase Distribution of Resin and Fatty Acids at Different pH Levels

Pitch emulsions were prepared to mimic the colloidal wood resin system in paper mill process waters. The phase distribution of resin and fatty acids (RFAs) between the colloidal lipophilic droplets (l) and the water phase (w) were determined as pKlw values. The effect of triglyceride to RFA ratio on pKlw values was studied, to determine if seasonal variations in wood extractives influence their phase distribution. The effect of water-soluble hemicelluloses on pKlw values was also determined. The pKlw values of the RFAs were lower in emulsions with a low triglyceride to RFA ratio. Addition of water-soluble galactoglucomannans also lowered the pKlw values of the RFAs.

Evaluation of behavior and fouling potential of wood extractives in ultrafiltration of pulp and paper mill process water

Colloidal extractives particles are potential foulants in pulp and paper mill applications. Characterization of them as foulants is a challenging task because of the complexity of these mill waters. In this study one regenerated cellulose (RC) membrane and two polyethersulphone (PES) membranes were used to study the fouling of extractives in ultrafiltration (UF) of two chemithermomechanical (CTMP) pulp mill process waters. The process waters originated from a pulping process using softwood and a mixture of hardwood and softwood. Extractives were analyzed by extracting them from the membranes and further analyzing them with gas chromatography and by measuring Fourier Transform Infrared (FTIR) spectra for the pure, fouled, and extracted membrane samples. In this study retention of extractives was over 90% even though their molar masses are less than 1kgmol−1. Both dissolved and colloidal extractives fouled the membranes. The fouling behavior was different for the process waters used and it seems that the individual extractive groups had different fouling mechanisms. Mostly fatty and resin acids fouled the membranes, but sterols contributed to the fouling of RC membrane remarkably even though their amount in the process waters used was low.

Membrane evaluation for the treatment of acidic clear filtrate

The total effluent load of a paper mill can be significantly decreased by recycling of purified clear filtrate (CF) back to paper-making process. The CF treated with membranes can be reused, for instance, as wire section shower water and in the dilution of chemicals. The main requirements for a membrane in CF treatment are high filtration capacity, high retention of turbidity and low fouling tendency. Previous studies have shown that the regenerated cellulose (RC) ultrafiltration (UF) membrane C30F (current trade name UC030T) is especially suitable for the treatment of paper mill process waters. Every paper-making process is, however, different. Thus, filtration experiments are required in order to find the most optimal membrane for the treatment of a certain process water. In this study the best membrane for the treatment of acidic clear filtrate (ACF) was searched. The performance of the C30F membrane was compared with five UF and three microfiltration (MF) membranes. The results revealed that in addition to the C30F membrane, also some other membranes produced high filtration capacity with ACF (approximately 200 L/(m 2h bar)). All the tested membranes also retained over 90% of turbidity. The extremely hydrophilic C30F membrane had, however, lower fouling tendency compared to the other tested membranes. Therefore, it was concluded that the C30F membranes were the best possible membrane for the ACF treatment.

The Influence of Modified Starch on the Process Water Quality in Papermaking and the Paper Properties

AbstractThe influence of modified (cationic) starch on the process water quality in papermaking and paper properties has been investigated. The experiments were conducted on sulfate hardwood pulp by applying both tap and paper mill process water. When process water is used, the retained amount of starch on fibers decreases, which most probably results from a partial neutralization of the cationic charge on modified starch, thereby reducing its attraction to the anionic groups on a fiber. By adding the modified starch, the turbidity of process water is to some extent reduced, indicating that the suspended organic substances are removed from process water. Due to starch accumulation, the load of process water by organic substances (determined via the TOC analysis) is not reduced, but is rather increased when the modified starch is added. In most cases, the addition of modified starch improved the investigated paper properties. However, these properties varied in correlation with the quality of the used water, despite the fact that the dosage of modified starch remained constant. This demonstrates the influence of process water quality, not only on the paper properties, but also on the efficiency of process chemicals, such as the modified starch, in the papermaking process.

Determination of aluminium using high performance chelation ion chromatography

The suitability of high performance chelation ion chromatography (HPCIC) using postcolumn reaction for the separation and determination of dissolved aluminium in complex samples was investigated. Use of a chelating ion-exchanger allowed for differentiation between kinetically labile and kinetically stable species of aluminium. Separation through a combination of chelation and cation-exchange was achieved using a 200 x 4.0 mm id column packed with particles of silica functionalised with iminodiacetic acid, with nitric acid-potassium chloride eluents. A temperature anomaly causing a five-fold increase in column efficiency for aluminium is believed to be a result of localised temperature effects in the particular type of instrument used. Postcolumn reagents investigated for the photometric detection included Tiron, Pyrocatechol Violet, Chrome Azurol S, and Eriochrome Cyanine R. The lowest detection limit (2.7 microg/L for a 100 microL sample volume) was achieved using 0.25 mM Eriochrome Cyanine R in 0.2 M hexamine (pH 6.1) with 1 mM cetyltrimethylpyridium bromide (CTAB). The optimised HPCIC system was applied successfully to the quantification of labile aluminium in paper mill process water.

Organic compounds in paper-mill process waters and effluents

Paper-mill effluents are characterized by the presence of color and suspended solids, bad smell, high concentration of nutrients that cause eutrophication of receiving waters, and high toxicity overall. This study attempts to give an overview of organic compounds that contribute to the toxicity of paper-mill waters and effluents, their levels, toxicological characterization and the methodologies used for their analysis. Families included are natural products, such as resin and fatty acids (wood extractives), additives used during paper-making, such as biocides, surfactants and phenolic compounds and by-products generated during bleaching, such as dioxins and furans. Several extraction methods, such as liquid-liquid extraction (LLE) or solid phase extraction (SPE) followed by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI) or electrospray (ESP) are described and method performance is discussed for each family of compounds. This study contributes to the characterization of the organic fraction of paper-mill effluents and highlights elimination strategies.

Comparison of gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry for the determination of fatty and resin acids in paper mill process waters

A comparative study of the performance of liquid chromatography (LC)–atmospheric pressure chemical ionisation (APCI)–mass spectrometry (MS) and gas chromatography (GC)–mass spectrometry techniques for the determination of resin and fatty acids from paper mill process waters was carried out. These compounds are responsible for the high toxicity of paper mill effluents and little research has been carried out regarding their analysis using mass spectrometric techniques. To prove the usability of GC and LC–MS, 16 treated and untreated water samples of recycle, kraft and pulp paper mills were analysed and good agreement was observed as regards to compounds detected and corresponding concentrations. This paper also reports the limits of detection, recoveries, reproducibility, linearity and precision using the two methods. GC–MS presented better selectivity and lower detection limits (below 0.2 μg/l), but derivatization of the extracts and the short life of derivatives (12–24 h) made the technique tedious and prone to high variations. Although LC–APCI–MS presented coelution of the non-aromatic resin acids, it also showed good sensitivity (limits of detection <3 μg/l) and permitted the detection of resin and fatty acids at μg/l level. In addition, since samples could be directly injected to the chromatographic system, LC–APCI–MS was proven as a powerful technique for quick and unequivocal quality control during papermaking.

Closing pulp and paper mill water circuits with membrane filtration.

In this study membrane filtration, ultrafiltration, and nanofiltration alone and as part of hybrid processes are considered as means to purify pulp and paper mill process waters suitable for reuse. Thermophilic aerobic biological treatment, pH adjustment, flocculation, and ozonation were tested as pretreatment methods on pilot or on laboratory scale. The aim was to increase flux and reduce fouling by various pretreatment steps and, thus, increase the competitiveness of the membrane process. The results were also evaluated by comparing the benefits obtained against the costs. It was discovered that benefits could be obtained with all the pretreatments tried. Thermophilic aerobic biology assisted in the removal of organic material and increased flux significantly, but the costs were the highest. The most cost-effective processes, however, seem to be pH-adjusted nanofiltration and flocculation nanofiltration hybrid processes, which is understandable because of their significantly lower investment costs compared to, for example, those of biological process. The pH adjustment increased the electrostatic repulsion between negatively charged solutes and membrane, thereby increasing the flux. Flocculation removed the foulants effectively from the feed and it both increased flux and reduced fouling. Yet, many noteworthy benefits were obtained also with ultrafiltration and ozonation. All of the hybrid processes tested could be applied at various points of the water circuit of an integrated pulp and paper mill for purification purposes. The eventual superiority and cost-effectiveness of the applied process remains to be determined case by case.

Comparison of nanofiltration and tight ultrafiltration membranes in the filtration of paper mill process water

Several nanofiltration and tight ultrafiltration membranes were tested by mill-site filtrations using a DSS-Labstak M20-filter. Retention, flux and fouling were analysed. Membranes were also characterised by measuring contact angles and pure water permeability. These data were used to explain the experimental results with effluents and to choose the possible membranes for the paper mill process waters. Comparison of different membranes in the constant pressure filtrations showed that usually the membranes with high pure water permeability or contact angle had worse fouling (fouling that had to be removed by alkaline cleaning). In addition, the fouling was stronger in filtrations made at acidic pH than at neutral conditions. The organic substances were retained significantly better at neutral pH than at acidic pH. Generally, when the hydrophilicity of the membrane increased the effect of pH on the retention properties increased as well. However, an individual membrane may deviate remarkably from the general trends. The results showed that some commercially available membranes have both high permeability and good retention properties at the same time.

Mesophilic and thermophilic activated sludge post-treatment of paper mill process water

Increasing system closure in paper mills and higher process water temperatures make the applicability of thermophilic treatment systems increasingly important. The use of activated sludge as a suitable thermophilic post-treatment system for anaerobically pre-treated paper process water from a paper mill using recycled wastepaper was studied. Two lab-scale plug flow activated sludge reactors were run in parallel for 6 months; a thermophilic reactor at 55°C and a reference reactor at 30°C. Both reactors were operated simultaneously at 20, 15 and 10 days SRT. The effects of temperature and SRT on sludge settleability and chemical oxygen demand (COD) removal efficiencies of different fractions were studied. Total COD removal percentages over the whole experimental period were 58±5% at 30°C and 48±10% at 55°C. The effect of the SRT on the total COD removal was negligible. Differences in total COD removal between both systems were due to a lesser removal of soluble and colloidal COD at 55°C compared to the reference system. At 30°C, colloidal COD removal percentages were 65±25%, 75±17% and 86±22% at 20, 15 and 10 days SRT, respectively. At 55°C, these percentages were 48±34%, 40±28% and 70±25%, respectively. The effluent concentrations of colloidal COD in both systems were related to the influent concentration of colloidal material. The thermophilic sludge was not able to retain influent colloidal material as well as the mesophilic sludge causing a higher thermophilic effluent turbidity. Sludge settling properties were excellent in both reactor systems. These were neither temperature nor SRT dependent but were rather caused by extensive calcium precipitation in the aeration tanks creating a very dense sludge. For application in the board industry, a thermophilic in line treatment system seems feasible. The higher effluent turbidity is most likely offset by the energy gains of treatment under thermophilic conditions.

Monitoring of biofouling in papermill process waters

Slime or biofilm formation on paper machine equipment requires costly countermeasures. To provide early detection and efficacy control of countermeasures, deposit formation should be monitored. In this study, a monitoring method was developed based on differential turbidity measurement (DTM). Measurement was performed continuously, on-line, non-destructively, and in real time. As reference techniques, automatic pressure drop (PD) measurement and accumulation of biomass on slime boards were used. Both DTM and PD proved to be useful for the measurement of deposit formation on line in the side stream of a paper machine whitewater circuit. With these methods, the efficacy of chemical cleaning procedures and bacteriostatic compounds could be demonstrated, whereas enzymes and nontoxic dispersants turned out to be less effective. The effect of toxic substances confirms the role of vital microbial cells in the formation of the deposits. The use of such substances, which represent a potential hazard to the environment, can be optimized by automated monitoring systems as presented in this study.

Further evaporation and final treatment of process-water concentrates

The study is part of a longer-term effort aimed at developing a separate treatment process for evaporation-concentrates of paper-mill process waters. This article deals with research on the two key processing steps; namely, the further evaporation and the final treatment of the concentrates. In laboratory experiments, various feed waters, including several different TMP filtrates, were evaporated to high dry-solids contents. The condensates recovered in most experiments contained relatively small amounts of organic matter. The extent of vapourisation of organic acids, relative to water, increased somewhat with increase in dry-solids content. Two TMP concentrates from large-scale evaporation plants were further concentrated in a pilot-scale forced-circulation evaporator. Viscosity was the factor limiting the extent of concentration. Using an evaporation temperature of about 80°C, the maximum dry-solids contents achieved with the two different concentrates were about 45 wt% and about 60 wt%, respectively. Fouling of heat-transfer surfaces was observed with both concentrates. A techno-economic evaluation of final-treatment options for alkali-rich concentrates is under way. According to intermediate results, molten-phase combustion processes would not require support fuel once the dry-solids content of TMP concentrate exceeds about 50 wt%. The aim of future work is to optimise the overall treatment process.

Nitrogen Fixation in a Biotype of Erwinia herbicola Resembling Escherichia coli

Two nitrogen‐fixing members of the Enterobacteriaceae have been isolated from paper mill process water and compost. Although they closely resembled Escherichia coli, detailed biochemical characterization of these and 7 other isolates established that they should be assigned to a biotype of Erwinia herbicola. They may be distinguished from E. coli by their lack of amino acid decarboxylase activity, their ability to utilize cellobiose and malonate and to ferment cellobiose and amygdalin. In one of them, the capacity to fix nitrogen, ferment cellobiose and utilize malonate was resistant to the effects of ethidium bromide, acridine orange and sodium dodecyl sulphate, and the ability to utilize cellobiose could not be transferred on to E. coli or Salmonella typhi. It is therefore concluded that these characters are not carried on transferable plasmids. Forty‐eight strains of E. coli of varying origin were examined for acetylene reducing activity and all were found to be negative. It is concluded that hitherto no naturally occurring strains of E. coli have been shown to fix nitrogen.

Acetylene Reduction (Nitrogen Fixation) by Enterobacteriaceae Isolated from Paper Mill Process Waters

Using selective media containing galactitol, over 130 Enterobacteriaceae have been isolated from paper mill process waters collected from different localities. These bacteria were extensively characterized and tested for acetylene-reducing (nitrogen-fixing) activity under anaerobic conditions. High activity was found in representatives of Klebsiella pneumoniae, Enterobacter aerogenes, Enterobacter cloacae, Erwinia herbicola, Citrobacter freundii, Citrobacter intermedius, and Escherichia coli. Under argon, nitrogenase synthesis was generally not repressed by 5 mM l-glutamate, l-aspartate, l-leucine or Casamino Acids (0.5 g/liter). In many strains, both the specific activities (nanomoles of C(2)H(4) per minute per milligram of protein) and the activities (nanomoles of C(2)H(4) per minute) had considerably declined after 24 h. In three selected strains, activity in intact cells grown under nitrogen was unaffected by the presence during assay of 10 mM l-amino acids or ammonium acetate. All of the strains examined were tolerant towards inactivation of nitrogen-fixing activity by 1.8% (vol/vol) oxygen during assay, and inactivation by up to 10% oxygen was partly reversible. Representatives of the six taxa synthesized nitrogenase in stirred aerobic cultures, though the protein concentrations attained were lower than under anaerobic conditions. It seems reasonable to suggest that under natural conditions, nitrogen fixation is able to contribute significantly to the nitrogen economy of the cells.

Effect of various chemical agents for the inhibition of Sphaerotilus natans in paper mill process water

In order to effectively control slime production in paper plants and other major water consuming industries, the efficacy of selected chemical compounds as inhibitors of growth of Sphaerotilus natans was investigated. It was determined that a few products were effective against Sp. natans in paper mill process water (80°F). These are listed in the following order of decreasing effectiveness: chlorine, Busan 90, chlorine dioxide and Slimacide V-10. In vitro studies can suggest those chemicals which may be useful; however, the choice of inhibitors depends largely on the individual plant, i.e., the mill processes' capacity to tolerate the concentration, contact time or cost of the specific chemical.