Pulp and Paper Industry

Microbiological Issues in Papermaking

Pratima Bajpai

• Publisher: Elsevier
• Year: 2015
• ISBN:
  9780128034262
• Topic: Ciencias biológicas
• Subtopic: Microbiología

Pulp and Paper Industry: Microbiological Issues in Papermaking features in-depth and thorough coverage of microbiological issues in papermaking and their consequences and the current state of the different alternatives for prevention, treatment and control of biofilm/slime considering the impact of the actual technological changes in papermaking on the control programmes. The microbial issues in paper mill systems, chemistry of deposits on paper machines, the strategies for deposit control and methods used for the analysis of biofouling are all dealt in this book along with various growth prevention methods. The traditional use of biocides is discussed taken into account the new environmental regulations regarding their use. Finally, discusses the trends regarding the future of the microbiological control in papermaking systems.

• In-depth coverage of microbiological issues in papermaking and their consequences
• Discusses eco-efficient processes (green processes) for biofilm/slime control
• Offers a thorough review of the current literature with links to the primary literature
• Comprehensive indexing
• Author is an authority in the pulp and paper industry

Chapter 1

General Introduction

Abstract

Paper manufacturing today is characterized by increased closure of the water system, conversion to neutral/alkaline systems, changes in chemical additives, and increased recycled fiber use, all of which may worsen the microbiological problems and decrease mill performance. Running the process under closed conditions leads to accumulation of nutrients and higher oxygen demand, which in turn rapidly results in anaerobic conditions. This favors fermenting organisms that form low-chain fatty acids, causing malodors. Under such conditions, microbially influenced corrosion is also favored and this can affect electrical control equipment causing serious operational problems. The general background of microbiological issues in paper mill systems is presented.

Keywords

Chemical additives; Electrical control equipment; Malodors; Microbially influenced corrosion; Microbiological problems; Nutrients; Recycled fiber; Water closure

1.1. Global Pulp and Paper Industry

The pulp and paper industry is one of the largest industrial sectors in the world. It is also an important source of employment in many countries. A sustainably managed pulp and paper industry can bring many benefits to the local economy and people, particularly in rural areas. Pulp and paper is produced in every part of the world. The largest producer countries, United States, China, Japan, and Canada, make up more than half of the world’s paper production, which is 400 million tons a year. Around the world we use more than 1 million tons of paper every day. Our paper consumption is escalating, particularly in emerging markets such as China. Pulp and paper is primarily made from wood fibers originating from natural forests or pulpwood plantations. Recycled fiber and other fiber sources such as agricultural residue are also used, and recycled fiber is becoming more commonly used in pulp and papermaking. Many global pulp and paper companies are moving their production to southern regions because lower production costs and proximity to fast-growing pulpwood plantations. Hence, responsible pulpwood plantations practices are urgently required.

Pulp and paper mills are big business around the world, generating $563.6 billion in revenue during 2013. Over the past 5 years, revenue from the global pulp and paper industry is expected to increase at an average annual rate of 0.4%, driven by strong performance in paperboard packaging and tissue products. During the global economic downturn in 2009, however, industry revenue dropped a sharp 19.2% because of a severe drop in pricing and shipment volumes. Demand for printing and writing paper dropped from a structural change toward digital media and lower advertising spending from the global recession, particularly in mature markets in Europe and North America. Paper mills are generally large and contain sizable and heavy machinery used in the production of pulp, paper, and paperboard. The mills are large because small-scale production is too costly on a per-output basis. The sort of machinery required for large-scale production is expensive and therefore capital expenditure in the industry is substantial. That is the main reason for a high level of capital intensity; an estimated $0.86 of capital is required for every $1.00 spent on labor. The industry’s capital intensity has increased slightly since 2008, mainly from increased capital investment in more efficient manufacturing machinery with lower energy requirements.

1.2. Microbial Problems in the Paper Industry: General Aspects

The pulp, paper, and board industry is continuously seeking to improve its economic and environmental performance (Bajpai, 2010). The efficient use of virgin and recycled wood fibers, efficient water reuse, and control of emissions to environmental media are some of the key factors in this respect. In these contexts, the awareness of microbiological issues can be crucial to production performance. Table 1.1 shows industry changes resulting in increased microbial problems (Gudlauski, 1996; Mattila-Sandholm and Wirtanen, 1992; Klahre et al., 1997; Dexter, 1996; Cantrell, and Lefevre, 1989; Robertson, 1995). The most significant and recent papermaking trends include (Rice, 2001):

• Conversion from acidic to neutral/alkaline papermaking

• Increased use of chemical additives

• Increased use of recycled fiber

• Closure of water systems

There are several benefits of conversion from acidic to neutral/alkaline papermaking. These include improved stability on aging, reduced costs, higher strength properties, reduction in energy consumption, decreased corrosion, increased productivity, and less complex systems. The most important aspect of this conversion is the replacement of alum and clay and titanium dioxide fillers with calcium carbonate. In addition, new retention aids, sizing and wet strength resins have become essential. Problems reported include reduced drainage and dryer efficiency and sheet quality, with an increase of holes, web breaks and pitch deposition problems. As the pH shifted toward the 7.0–8.0 range, the microbial populations shifted, and the population of freshwater microorganisms increased. Consequently, many of the common slime-control programs became less cost-effective or, in some cases were not effective at all.

New chemical strategies have become important for effective and well-organized management of the wet-end process for meeting the requirements of improved paper quality and increased productivity, taking into consideration the recent papermaking trends. Several types of chemical products are being used for sizing, retention, formation, drainage, distribution of fines, and microbiological and deposit control. Papermaking chemicals, namely processing chemicals and functional additives, account for more than 20% of world pulp and paper producers’ total raw material expenditures.

Table 1.1

Industry changes resulting in increased microbial problems

Conversion from acidic to neutral/alkaline conditions

High-speed machines

Closure of water system

Increased use of recycled pulp

Increased use of fillers

Increased use of chemical additives

Lighter weight grades

Boilout interval changes

Based on Robertson (2009).

Recycled fiber is an inexpensive source of fiber. Today, more than half of the global amount of fibers used in papermaking is recycled fibers. However, recycled fibers consist of increased amounts of short fiber and is often contaminated with deinking chemicals, glue, and other substances. This results in increased deposit problems, such as slime and stickies. The contaminants can also lead to an increased consumption of chemical additives. The use of retention aids is also required to maintain the stable paper quality.

The amount of water required to make 1 ton of paper has decreased significantly over the past 20 years. The benefits of water systems closure include reduced treatment costs; increased system temperature; lower losses of fibers, fillers, and chemicals; and more stable operating conditions. Increased whitewater closure changes the environment and growth conditions for microorganisms in the papermaking process. The changes such as lower dissolved oxygen content, longer retention time, increased temperature, and increased total solids create conditions for microbial growth which result in product quality, runnability, and safety issues. Microbiological growth can result as either slime deposition, formation of volatile gases, or spoilage-producing acids that affect the bonding of organic compounds, which lead to material degradation, such as additives and wood fibers. The buildup of higher concentrations of dissolved and colloidal materials within the system, leads to pitch problems and increase of suspended solids, buildup of thermal energy, microbial activity, and corrosion. These problems result in poor utilization or an increased consumption of chemical additives. The paper quality and the performance of machine are also affected.

These process modifications may make microbiological problems worse and decrease mill performance. Running the process under closed conditions leads to accumulation of nutrients and higher oxygen demand, which in turn rapidly results in anaerobic conditions. This favors fermenting organisms that form low-chain fatty acids, causing malodors (Bennett, 1985). Maukonen et al. (2006) observed Desulfovibrionales-related bacteria in paper mill environments. Under such conditions, microbially influenced corrosion is also favored and this can affect electrical control equipment causing serious operational problems (Blanco et al., 1996).

Microbial problems in papermaking have been understood for decades (Beckwith, 1931; Appling, 1955), and the expansion of production plants has provided more space and opportunities for microbial growth. Paper consists of a web of pulp fibers derived from wood or other plants from which lignin and other noncellulose components are separated by cooking with chemicals at a high temperature (Smook, 1992). Before pulp is made into paper, it undergoes several steps called stock preparation. This is conducted to convert raw stock into finished stock which is known as furnish for the paper machine. The pulp is prepared for the paper machine including the blending of different pulps, dilution, and t...