A Crystal Clear Vision

A patented recycling process that allows paper companies to convert wastewater sludge into glass aggregate and power exemplifies the growing movement to lessen adverse environmental impacts

Benjamin Franklin once said, "When the well's dry, we know the worth of water." With that in mind, paper companies recognize it is not a question of whether they should treat and recycle their spent water -- the question is "How?" Some paper companies are not only finding environmentally friendly ways to take care of spent water, they are going a step further by putting the sludge from their wastewater treatment plants to beneficial use by converting it to glass aggregate, steam, and electricity. In fact, paper companies are leading the charge in using practices that reduce the consumption of resources and related emissions for themselves and their customers.

Converting Wastewater Sludge to Beneficial Uses
A growing number of paper companies have written policies that address the environmental impacts of their manufacturing processes. The companies mitigate these impacts by using auditable processes to reduce water usage, report recycling efforts, monitor quality, and by investigating the best available technology. Neenah Paper of Neenah, Wisc., is one example of a company that follows this path. Some of the written environmental policies at Neenah specifically concern water use. The company also employs auditable processes to reduce energy consumption and the waste sent to landfills.

Neenah Paper and other interested partners are using advanced technology developed in Neenah, Wisc., that recycles wastewater sludge. Their choice of recycling technology reflects the high priority the companies place on eliminating dependence on landfills to dispose of solids.

"The patented technology for converting wastewater sludge to glass aggregate, steam, and electricity provides a solution for recycling and establishing a truly long-term, beneficial reuse alternative," says Terry Carroll, general manager for Minergy in Neenah, which developed the process. "The primary purpose of this process is to reduce the load on landfills. It recycles some 350,000 tons of wastewater solids, which helps to preserve 10 acres of green space annually."

Community Snapshot: Adding Energy to the Power System

Neenah Paper and other partners are responsible for providing a dewatered sludge for the process. The technology not only solves a sludge disposal problem for 12 paper mills, but it also helps improve air quality. For example, by using the steam produced in this process, a nearby paper mill has reduced operation of its older, less efficient boilers, which have higher emission levels. Truck traffic and the resulting emissions also have decreased by approximately 450,000 miles per year.

How It Works
Once the plant receives the wastewater solids from a paper mill treatment facility, the solids are discharged into a receiving hopper and conveyed into a closed-loop drying system where they are dried.

Conveyors transport the solids from the dryers to a cyclone boiler, where the organic component burns off to provide the high temperatures required to melt the dry sludge into glass. The system builds upon the same glass furnace technology that has been used for centuries to melt minerals into glass. It consists of two furnaces lined with refractory, which is a material that has a high melting point and provides excellent insulation. The operating temperature inside the cyclones is 2,900 degrees Fahrenheit. At that temperature, the inorganic mineral component of the sludge melts and flows out of the furnace as a liquid glass. A steam generator traps the heat generated in the melting process and produces renewable energy. This energy dries the wastewater solids and co-generates electricity.

The liquid glass is collected and quickly cooled in a water quench system to form the glass aggregate product. Markets for the glass aggregate product include floor tiles, abrasives, roofing shingles, asphalt and chip seal aggregates, and decorative landscaping materials.

"The glass aggregate process can provide a service not only to paper companies, but also to municipal wastewater treatment systems and their surrounding communities," says Carroll. "We can provide significant environmental benefits for many companies and individuals."

Helping the Environment Through Paper Recycling
The overall benefits of wastewater recycling may be obvious. However, a useful tool is now available for measuring an individual company's efforts to reduce its environmental footprint. Called an Environmental Savings Account, the tool calculates the ecological savings of companies' environmentally responsible behavior in terms of water and other resources conserved.

For example, many companies wisely choose to purchase recycled products. In so doing, they support practices that are not only environmentally appropriate, but socially beneficial and economically viable.

The Environmental Savings Account uses data from a program developed by the Office of the Federal Environmental Executive and the U.S. Postal Service to calculate the savings associated with choosing papers with higher levels of post consumer fiber content. The data was developed by Environmental Defense and other organizations to promote the purchasing of environmentally responsible papers.

Community Snapshot: Uses in Asphalt and Concrete

Recycled papers are available in a variety of categories to suit virtually any environmental policy. These categories include:

  • 100 Percent Post-consumer Fiber. Papers made from 100 percent post-consumer fibers can be cleaned and decolorized without the use of any chlorine or chlorine-containing products. This alternative offers the most environmental savings in terms of energy, trees, and water consumed, as well as greenhouse gases produced.
  • FSC Certified. The Forest Stewardship Council (FSC) has established internationally recognized standards for ensuring that forests and waterways are well-managed and protected. To receive this accreditation, paper must contain a minimum of 17.5 percent FSC-certified content. The remainder is post-consumer recycled fiber.
  • Crop Residues. Papers made with alternative fiber, such as cotton, sugar cane bagasse, hemp, linen, and flax, often do not contain any new trees. Instead they are made from a combination of post- and pre-consumer materials.
  • 100 Percent Recycled. Papers in this category are assured to be recycled and contain anywhere from 10 to 50 percent post-consumer fiber. The higher the post-consumer content the better. Many environmentalists look for the highest post consumer content available. The Presidential Executive Order for uncoated papers requires that text and cover papers contain no less than 30 percent post-consumer content.

Sample environmental savings are listed in the following chart. Figures are based on 2,000 pounds of recycled papers:



Water (gals.)

Energy (000BTUs)

Solid Waste (lbs.)

Waterborne Waste


Atmospheric Emissions (lbs.)

PC 100 White*







FSC Ultra Bright White, 80% Post Consumer*








30% Post Consumer*







*Above are ENVIRONMENT® Papers, a recycled brand from Neenah Paper.

If the total area of biologically productive land and sea were divided by the number of people on Earth, we each would have about 4.5 acres to feed and clothe ourselves, and make all the materials needed to live. The average American footprint is an estimated 24 acres. Ever-increasing demand makes it unlikely that consumption of paper will decrease. However, advances in recycling are helping to make our consumed resources even more productive.


Community Snapshot: Adding Energy to the Power System
Without realizing it, thousands of Midwestern residents may have benefited from the wastewater recycling efforts of several paper companies including Neenah Paper. A Madison, Wis., energy company added to its power system 6.5 megawatts of electricity generated by converting wastewater sludge to steam. That's enough to power 2,500 average homes.

The energy supplier has had a successful relationship with Minergy for the last four years and is using the additional energy to offset increased electricity usage throughout peak summer months.

Another benefit is that the local county can potentially reduce its solid-waste stream by two-thirds.

Community Snapshot: Uses in Asphalt and Concrete
The glass aggregate ultimately produced from the wastewater sludge ends up in a number of unexpected places in the Wisconsin area. It is a cost-effective alternative that can replace the manufactured sand used in asphalt or can be added to concrete. This reduces the cost of the materials used in roads and sidewalks in two ways. First, the glass acts as an "extender" or filler, resulting in a substance that is less costly than pure asphalt or concrete. The second aspect involves the fact that concrete made with glass aggregate is whiter. Since white surfaces reflect light better than darker ones, this reduces the number of street lights needed on roads made using a glass aggregate concrete or asphalt mix.

Purchasing glass aggregate concrete or asphalt brings recycling virtually full circle. Although it is practical mainly for companies in or around Wisconsin (transporting it long distances would not be cost-effective), a lot is riding on this important recycling effort in more ways than one.

This article originally appeared in the 12/01/2004 issue of Environmental Protection.

About the Author

Gerry Rector is a chemical engineer and senior product development manager for Neenah Paper in Roswell, Ga.

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