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Advanced Technologies for the Removal of Refractory Contaminants from Pulp and Paper Mill Wastewater
Published in Maulin P. Shah, Removal of Refractory Pollutants from Wastewater Treatment Plants, 2021
These days, the P&P industry is more focused on the use of recovered fibers as raw materials due to environmental pollution issues. Recycling of recovered fibers can be achieved through processes like pulping, screening, and deinking. Pulping involves the conversion of wastepaper into recovered fibers, deinking involves the removal of ink from the fibers, and screening includes the segregation of fibers based on density. The most important stage in recovered fiber recycling is the deinking step which not only involves the removal of ink particles from cellulose fibers but also includes the removal of ink particles from pulp slurry by adopting washing or flotation techniques (Zhenying et al. 2009). Zhang et al. (2008) reported various toxic chemicals and surfactants which are used as deinking agents to increase the pulp brightness which is difficult to remove. Therefore, enzyme-based deinking using enzymes like cellulase, pectinase, hemicellulose, and xylanase is found to be a better solution which helps in decreasing the overall cost of wastewater treatment. Compared to the chemical deinking process, enzyme-based deinking is eco-friendly as it decreases the COD and BOD values of effluents produced in the case of only partial (50%) replacement of deinking chemicals with the enzyme-based deinking process (Singh et al. 2012).
Solid Waste Source Reduction and Recycling
Published in Charles R. Rhyner, Leander J. Schwartz, Robert B. Wenger, Mary G. Kohrell, Waste Management and Resource Recovery, 2017
Charles R. Rhyner, Leander J. Schwartz, Robert B. Wenger, Mary G. Kohrell
High-grade deinking papers are generally defined as office type papers of high quality. Print free grades are classified as pulp substitutes. The bulk of these high quality papers are recycled into tissue products and fine printing and writing papers, as Table 4.5 indicates. The major suppliers of these grades of paper are commercial operations and institutions, such as government offices. Mills have either added or upgraded deinking facilities to accommodate the growing supplies of these paper grades, and to allow them to meet growing government mandates for tissue and writing papers with recycled content.
Microbial Enzymes for Eco-friendly Recycling of Waste Paper by Deinking
Published in Ram Chandra, R.C. Sobti, Microbes for Sustainable Development and Bioremediation, 2019
Sanjeev Balda, Aarjoo Sharma, Neena Capalash, Prince Sharma
The principal process steps in deinking plants are pulping, deflaking, deinking (flotation or washing), and final product. Pulping being the first step aims at defibring the paper for detachment of ink from fibers to produce dispersed ink particles of the size and geometry that can be efficiently removed in subsequent ink removal steps. Smaller ink particles cause problem, as these can be redeposited on fibers. Devices used for pulping are low-consistency pulpers, medium-consistency pulpers, and drum pulpers. Due to the nature of chemicals involved in this step, it is analogous to sulfite “cooking.” For deflaking, machines are used which defiber flakes by fiber-to-fiber rubbing or hydraulic shear to form individual fibers. Most deflakers can handle consistencies of 3%–6%. For removal of staples and heavy materials, high-density cleaning is performed. Deinking is the most crucial step in waste paper recycling, which helps in detachment and removal of ink from fibers. It is done by two methods: flotation and washing. Flotation is preferred as in the case of washing fiber loss is more (up to 40%) as compared to flotation (up to 10%). Flotation works on the principle of difference of surface physicochemical properties between the ink and fiber for removal of hydrophobic particles (e.g., ink particles), where the ink particles conjoin with air bubbles and float up to the surface where these are removed. Flotation aids such as surfactants can be added to improve the attachment of ink particles with air bubbles. Washing is based on the principle of filtration and separation, which causes higher fiber losses. Some modern plants use a combination of flotation and washing for effective ink removal. Flotation or washing is followed by chemical deinking followed by thickening, kneading, dispersion, and final processing. Steps involved in waste paper recycling are shown in Figure 2.3.
Fast dewatering of high nanocellulose content papers with in-situ generated cationic micro-nano bubbles
Published in Drying Technology, 2021
Hamidreza Ahadian, Elaheh Sharifi Zamani, Josphat Phiri, Thaddeus Maloney
In this study, cationic bubbles as dewatering aids are examined for MNFC containing furnishes. The generated bubbles are in three different size range. This idea has its origins in dissolved air flotation, which is commonly used to separate fine ink particles in paper mill deinking plants. We have also been encouraged by several studies showing that foam bubbles can be used to increase dewatering and improve paper properties in MNFC containing furnishes.[39,40,42] In this study, the cationic bubbles attach to the fibers surfaces and cause them to move upward and separate from the suspension. Consequently, a two-phase structure is formed which significantly improves the dewatering. This phenomenon works based on the electrostatic interaction of cationic bubbles and fibers, and the changes in buoyancy of the fibers.[45,50–52]
Investigation into the Ozone Reactivity during the O3/O2 Flotation of Recovered Cellulosic Fiber: Does Ozone Affect the Papermaking Properties of Fibers?
Published in Ozone: Science & Engineering, 2021
A. Ghorbel, N. Marlin, M. Aurousseau, A. Boyer
The raw material used for the production of recycled graphic papers is a mixture of old magazine (OMG), old newspaper (ONP), and mixed office waste (MOW). The recycling process starts with the disintegration of the recovered papers in a pulper followed by non-cellulosic fiber component (stones, staples, plastics, adhesives …) purification through the well-known cleaning and screening unit operations. Printed ink should then be removed to target a high level of brightness. That is why the key unit operation in recycling lines for graphic grade production is deinking (Kemper 1999; Labidi et al. 2007; Lothar and Heikki 2000). Deinking aims at removing ink particles from the fiber suspension to obtain white pulp. The flotation process is becoming the most common practice for removing inks from wastepaper (Kemper 1999). It is a process for selectively separating hydrophobic material from hydrophilic. After the ink-fiber separation, occurring during the pulping operation, hydrophobic ink particles are collected by air bubbles injected at the bottom of the flotation cell, and stabilized by a surface-active agent. Air bubbles then carry the ink particles to the top of the cell leading to the formation of aerated gray foam which is mechanically removed from the fiber suspension (Vashisth et al. 2011). Aside from containing ink particles, the flotation rejects (foam) also comprise some cellulosic fines and mineral components (ash) (Marlin and Carré 2016). This operation exhibits an average fiber yield of 80–90% depending on the printed substrate and on the operating conditions applied. Solid rejects are generally landfilled but also used in agriculture, in cement products (Yan, Sagoe-Crentsil, and Shapiro 2011) or incinerated (Villanueva and Wenzel 2007). On the other hand, aqueous rejects containing strong COD due to the release of mineral and organic materials in the effluent should be treated in a water treatment plant (Latorre et al. 2007).
Drying of industrial sludge waste in a conical spouted bed dryer. Effect of air temperature and air velocity
Published in Drying Technology, 2019
M. J. San José, S. Alvarez, R. López
The production of pulp and paper using newsprint paper as a substitute for raw wood fibers is an economically and ecologically favorable alternative. However, paper manufacturing generates a large amount of waste, approximately 70% of which is deinking sludge.[1] Deinking sludge is generated in the process of removing inks and coatings from waste paper at newsprint mills and tissue mills. The composition and amount of generated deinking sludge depend on the characteristics of the recycled paper and the used deinking process. Thus, 160 to 500 kg of wet deinking sludge is produced per ton of paper,[2] which requires proper management. Deinking sludge not only consists of cellulose and mineral charges but also inks, extraction substances, and deinking additives, and has a high moisture content, a high ash content, and a low calorific value.[3] This waste, after dewatering, presents different management alternatives. The main destination of this waste is the landfills (48%), followed by application in agricultural activities (28%), the generation of compost (6%),[456] and the manufacturing of fiberboard.[7] In the ceramic sector, this waste is valorized as secondary matter, such as in the cement industry, where it serves as a raw substitute for clinker because of its content of kaolinite, the base of metakaolinite, a highly pozzolanic product more ecological than clinker.[8] In the manufacture of cement mortar products, the addition of up to 2.5 wt% deinking sludge in cement mortar does not significantly affect its physical and mechanical properties.[9] Despite its low heating value (9.40 MJ/kg of dry residue) de-inking sludge is used as fuel derived from waste as an alternative to fossil fuels (i.e. as refuse derived fuel), in pyrolysis[2] and in gasification of de-inking sludge blended with wood chips.[3]