Volume 7 Issue 3

Since the introduction of the water footprint concept in 2002, in the context of humankind’s ever-increasing awareness of the valuable global freshwater resources, it has received more and more attention. The application of this relatively new concept has been expected to provide ecological and environmental benefits. For the water-intensive papermaking industry, it seems that water footprint needs to be addressed. The water footprint of cellulosic paper can be divided into three components, including its green water footprint, blue water footprint, and grey water footprint, which may be accounted for by considering the individual contributions of wood or non-wood materials, pulp production processes, effluent discharge to the receiving water bodies, process chemicals and additives, energy consumption, etc. In the literature, the accounting of water footprint during the whole production chain of cellulosic paper is already available, and relevant research findings can provide useful insights into the application of the concept; however, further development of the accounting methodologies is much needed, so that the quantitative and qualitative evaluation of water footprint can be internationally recognized, certified, and standardized. Although there are ongoing or upcoming debates and challenges associated with the concept, its application to papermaking industry may be expected to provide various encouraging possibilities and impacts.

The removal of Cr(VI) from aqueous solutions was studied using a compost generated from carnation flowers waste. The highest percentage of removal achieved (ca. 99 %) was obtained at pH 2.0, using a 10 mg L-1 of Cr(VI) solution, a dose of 10 g L-1 of compost, and with an equilibrium time of 3 hours. Under these conditions, the kinetics and adsorption isotherm were examined varying the initial Cr(VI) concentration from 15 to 200 mg L-1. The maximum sorption capacity at equilibrium (Qm), from the Langmuir model, was found to be 6.25 mg g-1. The evaluation of Cr(VI) removal at pH 2.0 showed a second order kinetics and showed that the process mechanism can be modeled by the “adsorption-coupled reduction” hypothesis. Also, the monitoring of Cr(VI) and total Cr in aqueous solutions showed that Cr(VI) and total Cr were removed from solution, and that part of the Cr(III) was retained on the compost. According to the results, the removal of Cr(VI) with the assayed compost can be explained by the following steps: (i) adsorption of Cr(VI) species onto compost, (ii) Cr(VI) reduction to Cr(III), and (iii) adsorption of part of Cr(III) on the compost. Thus, this study suggests that the carnation flower waste compost can be used as a remediation system for water contaminated with Cr(VI).

The yield of monosaccharides after two-stage concentrated sulfuric acid hydrolysis of softwood (Scots pine) and hardwood (trembling aspen) was modeled using a generalized severity parameter with a time-independent rate constant. The severity parameter, which combines the major operating variables acid concentration, temperature, and reaction time in the decrystallization stage into a single reaction ordinate, was successfully used to describe monosaccharide yields after a standardized hydrolysis stage. Conversion of cellulose to glucose demanded a higher severity to reach maximum glucose yields than the conversion of hemicelluloses to their respective monosaccharides, and the conversion of pine demanded a higher severity to obtain maximum monosaccharide yields as compared to aspen. The results indicate that the generalized severity parameter can be a useful tool for the prediction of sugar yields in a two-stage concentrated sulfuric acid hydrolysis process.

A lignosulfonate was prepared from alkali-extracted corn stalk lignin (AEL) by oxidation under mild conditions and sulfomethylation. The oxidized AEL exhibited lower molecular weight, narrower molecular weight distribution, and higher phenolic hydroxyl content than AEL, demonstrating that oxidized AEL was more reactive than those before oxidation. The content of sulfonic groups was significantly increased with the increase in sodium sulphite to AEL ratio, while the content slightly decreased when the ratio was above 1:1. During the sulfomethylation, the content of sulfonic groups increased with time and then achieved a constant level with the increase in time. The content of sulfonic groups reached 1.29 mmol/g, the maximum value, at 5 h and a sodium sulphite to AEL ratio of 1:1. The solubility of AEL was obviously improved by sulfomethylation with the increase in the content of sulfonic groups. The surface activity of AEL was improved after sulfomethylation. The sulfomethylation products exhibited good dispersibility and showed potential for use as a dye dispersant.

Removal of Cd²⁺, Pb²⁺, and Ni²⁺ from aqueous solutions using cellulose-graft-acrylic acid (C-g-AA) hydrogels was investigated. Various factors affecting the adsorption capacity, such as pH, time, initial ions concentration, and competitive ions, were tested. The results showed that the adsorption of hydrogels was very pH dependent, and maximum adsorption was obtained at a pH of 5.0. The adsorption capacities of hydrogels for the heavy metal ions were 562.7 mg/g (Cd²⁺), 825.7 mg/g (Pb²⁺), and 380.1 mg/g (Ni²⁺), respectively. The adsorption behavior can be very well described by the pseudo-second-order kinetic model and the Langmuir isotherm model. The observed affinity order of competitive ions adsorption is Pb²⁺>Ni²⁺>Cd²⁺ in mmol/g. The hydrogels can be regenerated after releasing heavy metal ions and reused three times with 15% loss of adsorption capacity. Scanning electron microscope (SEM) images and Fourier transform infrared spectroscopy (FTIR) spectra before and after ion adsorption on the hydrogels revealed that the complexation between heavy metal ions and carboxyl groups on hydrogels was the main adsorption mechanism.

Paper sludge is a major waste by-product of the paper industry. Its disposal creates serious problems, as approximately 30% of treated sludge is not flammable. In this study, artificial lightweight aggregates (ALWAs) were synthesized from paper sludge by co-sintering with H3BO3. H3BO3acts as a flux to lower the sintering temperature below 900 °C, with co-melting occurring during the procedure. The decomposition gas is sealed within the ALWA during the glassy phase to form a porous structure. Water absorption, apparent porosity, bulk density, compressive strength, and weight loss after rinsing with Na2SO4 were tested to understand the physical properties of the manufactured ALWAs. The optimal method suggested is co-sintering with 18% H3BO3 flux at 890 °C for 30 min. The tested properties mentioned above gave the following results: 4.64 %, 2.77 %, 0.6 g/cm³, 13.2 MPa, and < 0.1 %, respectively. The ALWAs produced in this study have been compared to commercially available lightweight aggregates – Lytag and Arlita – with the examined ALWAs possessing better qualities than Lytag. Water absorption and compressive strength of ALWAs in this study met government requirements of pre-stressed concrete necessary for civil works, and could make useful building material.

The effects of a chelating surfactant and different foaming agents on the efficiency of cleaning process waters from a thermomechanical pulp (TMP) mill were studied in a Voith flotation cell. Turbidity measurements and gas chromatography were used to determine the removal extent and characteristics of dissolved and colloidal substances (DisCo). The metal ion content in the process waters before flotation and the metal chelate removal after flotation were determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). FiberLab™ equipment was used to characterize changes in the size of fibers present in the process waters. The results indicate that a decrease in turbidity of up to 91% and the removal of 80% of lipophilic extractives in the TMP water could be obtained using a single-stage flotation unit. Furthermore, the foam fraction was within 5% of the initial volume, and 100% of the Mn2+/chelating surfactant complex added to the TMP water was removed.

The heat treatment of softwood (i.e. spruce, pine, fir, and larch) may result in significant colour changes. During this study Scots pine and spruce samples were steamed and analysed for their altered hue and lightness. Treatments included: 0 to 22 days of steaming time at a temperature range of 70 to 100°C. The outcome included a variety of colours between the initial hues and brownish tint. These new colours are similar to that of aged furniture and indoor wooden structures. Consequently, properly steamed softwood may be used to repair historical artefacts and relic furniture. Besides restoration, steamed stocks are excellent sources for manufacture of periodical furniture, where the aged appearance has aesthetical value. Results however, indicated that steaming at a temperature above 90 ˚C has a bleaching effect, i.e. the coloured chemical components formed by moderate steaming may be removed. Furthermore, we observed a linear correlation between lightness and colour hue at all steaming times and temperatures.

Dark brown wood color is a current trend and widely appreciated by consumers in the furniture and decoration markets. Heat treatment is one of the most effective methods to darken wood’s appearance. The influence of steam-heat treatment on color change of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) was investigated within the temperature range from 170 to 230 °C and time from 1 to 5 hours in an air-tight chamber within an atmosphere comprising less than 2 percent oxygen. Saturated steam was used as a heating medium and a shielding gas. The results showed that the chroma difference (△C*) decreased gradually, while the color difference (△E*) and hue difference (△H*) increased with an increase in temperature and length of time. An analysis of variance (ANOVA) and a multi-comparison analysis revealed that the treatment temperature plays a more important role in darkening wood color during the process of steam-heat treatment in comparison with the treatment time. The results suggest that a more desirable wood color can be achieved with the technology of steam-heat treatment.

Sulfated titania (SO4^2-/TiO2) was prepared and used for catalytic fast pyrolysis of cellulose to produce levoglucosenone (LGO), a valuable anhydrosugar product. Analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) technique was employed in this study to achieve the catalytic fast pyrolysis of cellulose and on-line analysis of the pyrolysis vapors. Experiments were performed to investigate the effects of several factors on the LGO production, i.e. pyrolysis temperature, cellulose/catalyst ratio, TiO2 crystal type, and pyrolysis time. The results indicated that the SO4^2-/TiO2 catalyst lowered the initial cellulose decomposition temperature and altered the pyrolytic product significantly. Levoglucosan (LG) was the most abundant product in the non-catalytic process, while levoglucosenone (LGO) was the major product in the catalytic process. The maximal LGO yield was obtained at the set pyrolysis temperature of 400 °C, while the highest LGO content was obtained at 350 °C, with the peak area% over 50%. In addition, the SO4^2-/TiO2 (anatase) was confirmed the best catalyst for the LGO production.