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BACKGROUND: Deinking is an important part of paper recycling that involves the removal of ink particles from the paper fibres. This industrial process is important so that the fibres can be recirculated back into paper production, which enables better sustainability as fewer fresh fibres are needed. In this study, we examined five different alternative fibre materials from different agricultural residues and industrial processes for the pilot production of papers. Papers containing fibres from invasive plants (Japanese knotweed), dedicated crops (miscanthus, acacia), agricultural residues (tomato stems), and industrial waste (jute - fibres from coffee bags) were printed with water-based flexo inks and deinked with two separate processes (chemical and enzymes). Mechanical (break and tensile index, breaking length) and optical properties (ISO whiteness, brightness and CIE L*a*b* values) were measured and ink elimination IR700 and deinking efficiency was calculated for the two deinking processes. RESULTS: Enzymatic treatment improved the mechanical properties of deinked pulp in comparison with the classic chemical treatment. Mechanical strength for almost all papers increased slightly (breaking length up to 20% in tomato and jute), and the optical result (brightness) increased similarly for both processes due to the bleaching action of the colour-shaded samples, whereas the deinking efficiency showed mixed results between chemical- and enzyme-type deinking (with chemical achieving better elimination measured at 700 nm) in the typical range of ink elimination values (15-35%) for flexographic inks. This indicates further optimization of the deinking with enzymes is needed due to different alternative fibre compositions and variations of residues in the delignification processes. CONCLUSION: Using a combination of adjusted enzymatic treatment as a precursor for deinking of paper-based packaging materials sourced from alternative fibres showed promising results regarding mechanical properties, whereas the optical properties need to be improved with cellulase optimization or by using mixes of different enzymes. These kinds of paper materials printed with flexo inks were found to be successfully deinkable with the chemical ISO-based deinking protocol. [ABSTRACT FROM AUTHOR]

Wastewater recycling and sludge removal in the paper industry account for about 60% of all process costs. New and environmentally friendly wastewater treatment techniques are, therefore, continually being developed. Cavitation exploitation is currently a well-investigated topic that is also interesting for the paper production industry. This study investigates efficiency of hydrodynamic cavitation alone and in combination with the addition of NaOH for the treatment of secondary pulp and paper mill sludge in order to enhance nutrient release. First, two laboratoryscale devices were tested: the blow-through and the rotating hydrodynamic cavitation generator. The latter set-up proved to be more efficient: therefore, further experiments were performed on its pilot-scale version. The results showed an increase of soluble chemical oxygen demand (CODs) by 514 mg/L, total nitrogen (Nt) by 17.4 mg/L, and total phosphorous (Pt) by 2.3 mg/L. To further increase nutrient release combination of cavitation and sludge sample alkalinization was tested. The addition of NaOH and 30 min cavitation of secondary sludge (500 L) significantly improved CODs and Nt release by 2400 mg/L and 120 mg/L, respectively. Microbiological photos revealed a definite disintegration of sludge flocks. According to our estimates, 1.9 kg of released CODs from alkaline pre-treated and cavitated sludge would cost only one euro. [ABSTRACT FROM AUTHOR]

In this study anaerobic digestion of selected lignocellulosic substrate, namely brewery spent grain (BSG), was studied In order to facilitate anaerobic digestion several types of pretreatment methods were tested such as: mechanical, chemical (alkali and acid) and thermo-chemical. The anaerobic digestion experiments were carried out in a semi-continuous stirred bioreactors with the organic loading rates between 2.9 and 3.9 kgCODm-3d-1 (1.9 and 2.5 kgVSS m-3d-1 respectively) and corresponding hydraulic retention times of 33-39 days. Biogas production and composition, pH, COD, TSS and VSS, short chain fatty acids and phenolic compounds were measured. A significant inhibition of biogas production occurred, depending on the type of substrate pretreatment. There are indications that p-cresol is responsible for process inhibition when its concentration in the reaction mixture exceeds critical value between 115 and 240 mg L . Anaerobic digestion of chemically pretreated BSG (acid and alkali) and untreated-raw BSG was inhibited between the days 56 and 63 of the experiment, followed by thermo-chemically pretreated BSG on day 112 and mechanically pretreated BSG on day 126. Analyses of the substrates showed no phenolic compounds either in raw-untreated BSG or pretreated substrates, therefore the recorded p-cresol is an intermediate degradation product, responsible for process inhibition. [ABSTRACT FROM AUTHOR]

The growth of oyster mushroom (Pleurotus ostreatus) on pulp and paper industry wastes was studied. Specifically, the question was investigated whether solid-state fermentation of P. ostreatus on paper-mill deinking sludge and primary sludge substrates is appropriate for production of enzymes, relevant to the pulp and paper industry. Following fermentation, extracellular protein was extracted and the specific activities of four enzymes were determined, namely, the cellulase, xylanase, lipase and peroxidase. Furthermore, the effects of the pH of the extraction buffer on these enzyme activities were determined, along with the effects of the incubation time. The data show that P. ostreatus can grow on solid wastes from the pulp and paper industry, which could help to minimize the waste volume and to decrease the ecological impact. Furthermore, the solid wastes in focus are good substrates for the production of commercially interesting enzymes. [ABSTRACT FROM AUTHOR]

In paper production industry, microbial contaminations of process waters are common and can cause damage to paper products and equipment as well as the occurrence of pathogens in the end products. Chlorine omission has led to the usage of costly reagents and products of lower mechanical quality. In this study, we have tested a rotation generator equipped with two sets of rotor and stator assemblies to generate developed cavitation (unsteady cloud shedding with pressure pulsations) or supercavitation (a steady cavity in chocked cavitation conditions) for the destruction of a persistent bacteria Bacillus subtilis. Our results showed that only supercavitation was effective and was further employed for the treatment of waters isolated from an enclosed water recycle system in a paper producing plant. The water quality was monitored and assessed according to the chemical (COD, redox potential and dissolved oxygen), physical (settleable solids, insolubles and colour intensity) and biological methods (yeasts, aerobic and anaerobic bacteria, bacterial spores and moulds). After one hour of treatment, a strong 4 logs reduction was achieved for the anaerobic sulphate reducing bacteria and for the yeasts; a 3 logs reduction for the aerobic bacteria; and a 1.3 logs reduction for the heat resistant bacterial spores. A 22% reduction in COD and an increase in the redox potential (37%) were observed. Sediments were reduced by 50% and the insoluble particles by 67%. For bacterial destruction in real industrial process waters, the rotation generator of supercavitation spent 4 times less electrical energy in comparison to the previously published cavitation treatments inside the Venturi constriction design. [ABSTRACT FROM AUTHOR]