Recycled Paperboard Mill Waste

Posted April 19, 2016 in Pulp and Paper Industry by Elizabeth Tischer

Mill shrink and the proper handling of mill sludge is imperative when it comes to the paper and pulp industry. According to numerous studies, a wide assortment of solid wastes and sludges are created. The solid waste is produced, mainly, from the pulping process, the deinking process, and the treatment of wastewater. Waste generation is directly proportional to the overall production processes and the technologies associated with wastewater treatments. According to statistics, approximately 50 kg of sludge is created per 1 ton of paper produced. 70% of this sludge is considered to be “primary”, and the other 30% is considered to be “secondary”. In a mill that creates newsprint, the sludge rate is 20%. In a mill that creates tissue products, the sludge rate is approximately 40%. In this article, we will expound on the waste that is produced, specifically, from recycled paperboard mills.


What is a Recycled Paperboard Mill?


In order to understand mill shrink techniques and to take the steps necessary to reduce mill sludge, one must first have a solid understanding of what a recycled paperboard mill is and what they do for the paper and pulp industry. In these mills, heavy papers are used as a source of feedstock. The paper is mixed with water in a very large vessel that is typically referred to as a “pulper”. This blends the components in order to separate the various fibers contained in each of the paper sheets from one another. The slurry that is then produced passes through an assortment of screens and other items in order to remove various types of contaminants. Examples of these include metals, clay, and plastic.


The fiber that is recovered from this process is then used to create new types of paper products that are composed, entirely, from content that has been 100% recycled. According to numerous studies, fiber is not endlessly used in the recycled paperboard mills. It can, however, be used up to seven times to create new products. Furthermore, products that contain long cellulose-based fibers are considered to be the highest of quality and may be used more often to create new paper products. Products that contain only short cellulose-based fibers do not hold the same level of value.


Reducing Mill Shrink by Handling Rejects Appropriately


There are several types of rejects that are seen in recycled paperboard mills. Examples of these rejects include the following:


  • Sand, bark, and wood from virgin pulps
  • Lumps of various fibers from the ring binders
  • Ink particles
  • And, Others….


In order to reduce mill shrink, all types of rejects must be handled in the most effective manner possible. In some instances, rejects in the paper and pulp industry may be used or reused in order to create new types of paper-based products. In other instances, rejects that are present in a recycled paperboard mill may be sold to other industries for a profit that will aid in reducing mill shrink. The following outlines various techniques for handling reject mill sludge in order to reduce the amount of mill shrink that is experienced in the facility:


  1. 1.     Rejects that stem from virgin-based pulp that contain residues from sand, various types of bark, and wood are considered to be highly unfit for the creation of paper products. These types of rejects have a very low amount of moisture, but, a high heating value. In order to reduce mill shrink, it is best to use these rejects in the bark boiler unit at the mill in order to enhance energy efficiency and recovery.
  2. 2.     Screen-based rejects that come from the paper and pulp industry often have a large amount of cellulose fiber. This mill sludge reject may be used to create high-quality, recyclable paperboard.
  3. 3.     Rejects that contain short fibers, particles of ink, and various types of coatings may be sold to other industries, such as the cement industry and/or the ceramic industry.
  4. 4.     Primary mill sludge has a high level of fines and fillers. It is considered to be very easy to dewater. As a result, this type of reject may be used in the creation of boards or may be diluted with secondary mill sludge to create additional types of paper products.
  5. 5.     Mill sludge that contains a lot of organic and microbial content may be provided to landfills in order to break down the debris that is present in the area.




If you are the owner or operator of a recycled paperboard mill, mill shrink should consistently be placed as a high priority. You have, at your disposal, a vast array of rejects that could aid in the paper and pulp industry, and other industries, as well! All it takes is a little creativity and you could transform all that excess mill sludge into a useable product to reduce mill shrink at your mill, or sell off the mill sludge to another industry in order to optimize your profits!

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