Biochemical methane potential of kraft bleaching effluent and codigestion with other in-mill streams

A biochemical methane potential assay was conducted to investigate the anaerobic digestibility of bleaching effluent from hardwood kraft pulping and the potential of codigestion with other effluents from an integrated pulp and paper mill. Four in-mill streams were tested individually and in combination: total bleaching effluent, alkaline bleaching effluent, kraft evaporator condensate, and chemithermomechanical pulping effluent. The total bleaching effluent, consisting of the chlorine dioxide bleaching and alkaline bleaching effluents, exhibited the highest potential for organic matter degradation and methane generation. Chemical oxygen demand (COD) removal ranged from 57%–76%, and methane generation was 220–280 mL/g COD contained in the wastewater, depending on the degree of dilution. When codigestion was tested, the composite consisting of total bleaching effluent, chemithermomechanical pulping effluent, and kraft condensate was most efficient in terms of COD removal (51%) and methane generation (200 mL/g COD contained in the wastewater). The total bleaching effluent is the largest contributor to the overall amount of wastewater at this mill; it contains relatively low concentrations of anaerobic inhibitors such as adsorbable organic halogens (36 mg/L), total sulfur (170 mg/L), and resin and fatty acids (3.2 mg/L). Therefore, the total bleaching effluent from hardwood kraft pulping may be considered for full-scale anaerobic wastewater treatment, either as a singular stream or as part of a composite stream including other in-mill effluents.

Laboratory and mill scale evaluation of biopulping of Eucalyptus grandis Hill ex Maiden with Phanerochaete chrysosporium RP-78 under non-aseptic conditions

Biopulping of Eucalyptus grandis wood chips with Phanerochaete chrysosporium RP-78 was evaluated under non-aseptic conditions in laboratory and mill wood-yard. The ability of P. chrysosporium to compete with indigenous fungi present in fresh wood chips was notorious under controlled laboratory experiments. A subsequent step involved an industrial test performed with 10-ton of fresh wood chips inoculated and maintained at 37±3°C for 39 days in a biopulping pilot plant. Biotreated wood chips were pulped in a chemithermomechanical pulping mill. Net energy consumption during refining was 745 kWh ton-1 and 610 kWh ton-1 of processed pulp for control and biotreated wood chips, respectively. Accordingly, 18.5% net energy saving could be achieved. Biopulps contained lower shive content and had improved strength properties compared to control pulps. Tensile index improved from 25±1 N m g-1 to 33.6±0.5 N m g-1 and delamination strength from 217±19 kPa to 295±30 kPa.

Alkaline-sulfite chemithermomechanical pulping of Eucalyptus grandis biotreated by Ceriporiopsis subvermispora under varied culture conditions

The effect of different culture conditions have been evaluated concerning the extracellular enzyme activities of the white-rot fungus Ceriporiopsis subvermispora growing on Eucalyptus grandis wood. The consequence of the varied fungal pretreatment on a subsequent chemithermomechanical pulping (CTMP) was addressed. In all cultures, manganese peroxidase (MnP) and xylanase were the predominant extracellular enzymes. The biopulping efficiency was evaluated based on the amount of fiber bundles obtained after the first fiberizing step and the fibrillation levels of refined pulps. It was found that the MnP levels in the cultures correlated positively with the biopulping benefits. On the other hand, xylanase and total oxalate levels did not vary significantly. Accordingly, it was not possible to determine whether MnP accomplishes the effect alone or depends on synergic action of other extracellular agents. Pulp strength and fiber size distribution were also evaluated. The average fiber length of CTMP pulps prepared from untreated wood chips was 623 μm. Analogous values were observed for most of the biopulps; however, significant amounts of shorter fibers were found in the biopulp prepared from wood chips biotreated in cultures supplemented with glucose plus corn-steep liquor. Despite evidence of reduced average fiber length, biopulps prepared from these wood chips presented the highest improvement in tensile indexes (+28% at 23° Schopper-Riegler).

De-esterification and sulfonation in spruce CTMP: Effects on pulp and paper properties

De-esterification and sulfonation reactions, which create new anionic groups in the middle lamella and primary wall layers, are the key chemical reactions in chemithermomechanical pulping. The effects of these reactions on the resulting fibre dimensions, refining energy demand, hand-sheet bulk and strength properties were assessed by laboratory-scale chemical pre-treatments and refining of Norway spruce chips. After pre-treatments with alkaline, sulfite, alkaline sulfite and alkaline peroxide liquors, a Wing defibrator-type batch refiner was used. The refining energy was measured. The degree of alkaline hydrolysis of acetyl and methyl ester groups in galactoglucomannans (GGMs) and pectins, and the degree of lignin sulfonation were determined. Hand-sheets were prepared and their physical properties were tested. The data were subjected to multivariate analysis and the order of significance of the chemical reactions towards pulp and paper properties was estimated. Chemical pre-treatments were found to increase the fibre length and the energy demand considerably. The fibre length and width after refining were strongly influenced by lignin sulfonation and pectin demethylation. GGM deacetylation had little influence on preserving the fibre dimensions in CTMP refining. The bulk, on the other hand, was highly influenced by GGM deacetylation. Peroxide reactions in alkaline peroxide treatments had no effect on the pulp and paper properties.

Dissolution of fibre material in alkaline pre-treatment and refining of spruce CTMP

The chemistry of chemithermomechanical pulping (CTMP) was assessed by chemical pre-treatment of spruce chips, followed by laboratory-scale refining. Pre-treatments with alkali, sulfite, alkaline sulfite and alkaline peroxide liquors were carried out at 40°C, 60°C and 80°C. The sodium hydroxide dosages were 1% and 2% and the sodium sulfite and hydrogen peroxide dosages were 2%, 4% and 6% on a dry wood basis. Process water samples were taken before and after refining. Alkali consumption in the pre-treatments and the amount and composition of released wood components were determined. A major part of the alkali was consumed in the alkaline and alkaline sulfite pre-treatments. In the alkaline peroxide pre-treatments, however, alkali consumption was considerably lower. Acetic acid was the main wood component released to the process waters in alkaline pre-treatments. Pectins, determined as galacturonic acid and rhamnose by acid methanolysis, were also released to some extent, as well as easily soluble polysaccharides. After fibre separation in refining, more hemicelluloses and pectins were released. There was a significant difference between the degree of demethylation for pectins and the degree of deacetylation for galactoglucomannans after the pre-treatments. The diffusion of chemicals into the secondary wall layers seemed to be slower than the liquor penetration into the porous middle lamella through the pit pores. Up to 10% of the pectins were dissolved in the process waters as a result of depolymerisation and extensive demethylation. The residual amount of pectins in the fibres, however, was determined to be as low as 65–70% of the initial pectin content.

Characterization of Treated Effluent from a Chemithermomechanical Pulping Process Using Macroporous Resins

This study developed a characterization of the organic matter remaining in a chemithermomechanical pulping (CTMP) effluent after biological treatment and evaluated the potential impact of this effluent when discharged into the receiving environment. The methodology employed involved fractionation with macroporous resins to allow for the isolation of hydrophobic and hydro-philic organic materials. The study also examined the treated effluent’s reactivity with chlorine, a typical drinking water disinfectant, in order to assess the formation potential of chlorinated by-products and the chlorine demand in a downstream drinking water treatment plant. Results showed that the dissolved organic carbon (DOC) in a treated effluent from a CTMP mill consisted of 87% hydrophobic material (primarily humic substances), 5% hydrophilic acids and 3 to 4% nitrogenous compounds. At least 95% of the DOC was isolated using three different macroporous resins. The chlorine demand of the biotreated CTMP effluent was two to three times higher than is typical for natural organic matter from surface water. This indicated that the organic material in the CTMP effluent was highly reactive with chlorine and will likely be reactive with other oxidants such as ozone, which is also applied in the drinking water industry. Moreover, the disinfection by-products chloroform and trichloroacetic acid were formed in high concentrations as a result of chlorination. The biotreated CTMP effluent had a high chemical oxygen demand (at least 1,100 mg/L) but a relatively low biochemical oxygen demand (less than 100 mg/L), which was to be expected after biological treatment. Hence, discharge of these effluents could release high concentrations of non- or slowly biodegradable organic matter into the downstream aquatic environment. Water pollution control policies should therefore consider the potential impact of treated effluents from CTMP mills with regard to their high DOC and the potential for chlorinated by-product formation upon drinking water disinfection.

Resin acid degradation by bacterial strains grown on CTMP effluent

All resin acids are diterpenoid carboxylic acids that are components of softwood extractives and they are known to contribute to much of the toxicity of pulp mill effluents. Although biological treatment systems can efficiently remove resin acids during normal operating conditions, resin acid breakthroughs occasionally occur. Recently we isolated five bacterial strains from bleach kraft effluents that degrade dehydroabietic acid (DHA), a resin acid commonly found in effluents. In this study we examined the ability of two bacterial strains (BKME 5 and BKME 9) to grow on chemithermomechanical pulping (CTMP) effluent and degrade DHA. Both of the strains could grow on CTMP effluents, but did not degrade DHA. COD measurement showed that both strains used other organic substrates in CTMP effluent. When nutrients (NH4⊕, PO43−, minerals and vitamins) were added to the effluent, both growth and DHA degradation increased significantly. The strains used DHA and other organic sources in the CTMP effluent simultaneously. The stimulated growth resulting from use of other organic material did not increase the rate of DHA degradation. It was found that ammonium played an important role in the DHA degradation of both strains. Without added ammonium, DHA degradation did not occur. Other nutrients also played important roles in DHA degradation by BKME 9.