Recycled Materials and Byproducts in Highway Applications—Manufacturing and Construction Byproducts, Volume 8 (2013)

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46 Background Waste paper mill sludge is the byproduct of the paper produc- tion process. The major byproducts from the pulp and paper waste stream are (Bird and Talberth 2008): • Waste water treatment plant (WWTP) residuals • Boiler and furnace ash • Causticizing residuals. The primary residuals, approximately 40% of the WWTP, including de-inking residuals (paper recycling operations), consisting mostly of processed wood fiber and inorganic or mineral materials (e.g., kaolin clay, CaCO3, and TiO2). Sec- ondary (activated waste sludge) is mostly bacterial biomass (nonpathogenic) and makes up about 1% of the WWTP residu- als. Dewatering the WWTP residual produces a byproduct of between 30% and 40% solids and once dewatered, the material is not considered hazardous as defined by RCRA. A few facil- ities can dry the WWTP to produce a byproduct with 70% to 95% solids. Chlorinated organic compounds tend to concen- trate in the solids that can be an environmental concern. Boiler and furnace ash (energy recovery) is produced from wood, coal, or a combination of wood, coal, and other solid fuels (most common) used in the pulp and paper processes. Causticizing residues have three components: lime mud, green liquor dregs, and slaker grit. Lime mud (calcium carbonate and water) is burned in a lime kiln to regenerate the byproduct to lime (CaO). This byproduct may also contain unreacted calcium hydroxide, unslaked calcium oxide, magnesium, and sodium. The lime mud is about 70% to 80% solids. Green liquor dregs are composed of nonreactive and insol- uble materials remaining after the inorganic process chemi- cals (smelt) from the recovery furnace are mixed with water. The dregs are removed by gravity clarification, resulting in a byproduct with 45% to 55% solids. The major components are carbonaceous material along with calcium, sodium, mag- nesium, and sulfur. Slaker grits are produced by mixing lime (burned or unburned) with the green liquor dregs and contain between 70% and 80% solids. The solid portion is approximately 50% fibers and up to 50% minerals with a pH about 12, which is neutralized before disposal. The solids can also contain tita- nium oxide and calcium sulfate. usage and Production united states Production in the United States generates about 16.5 mil- lion dry tons of solid wastes and byproduct solids that are used and/or disposed of in a number of ways (Table 59). There are about 6.1 million dry tons of WWTP residuals pro- duced annually. For the 104 U.S. mills, this works out to an average byproduct production of about 28,660 dry tons per year per plant. However, WWTP rates of production vary widely between mills, ranging from 31 to 309 pounds per ton of pulp produced. Causticizing residuals production, as of 1995, was 1.8 million dry tons per year and consisted of lime mud (59%), green liquor dregs (28%), and slaker grit (14%). The Wisconsin Department of Natural Resources (DNR) (2010) summarized the beneficial usage of paper sludge byproducts. These byproducts were regulated under the waste- water program, so that there were no generators requesting initial or annual certification under DNR Chapter NR538. The wastewater program only accounted for a portion of the total pulp and paper processing waste either generated or used ben- eficially. One recycler that received paper mill sludge from a group of mills reported the annual amount of sludge pro- cessed by the facility as approximately 1.2 million tons of which approximately 445,000 tons were beneficially used (38% of sludge). The Wisconsin Paper Council reported to the DNR that about 1.73 million tons of paper mill sludge was produced annually in the state, with about 1.15 million tons being ben- eficially used (66%). These numbers included material land spread and used in energy recovery at the facilities. european Dunster et al. (2005) noted that European pulp and paper mills produce more than 1 million tons per year from recy- cling operations. Paper sludge was thought to be a signifi- cant resource but not without significant modifications. The major post-processing needed was dewatering. Waste paper sludge was considered to have potential as a value-added component for lightweight concrete products and nonaer- ated blocks. Limited research showed it reduced density but also reduced compressive strength. It was suggested that the usefulness could be improved with chemical bonding to form chapter three Waste PaPer MiLL sLudge

47 TABLE 59 DISPOSAL OF WASTE PAPER SLUDGE ByPRODUCTS After Bird and Talberth (2008). Use Percent of Byproduct per Use, % WWTP residuals Boiler and furnace ash Causticizing residuals U.S. Europe Lime mud Green liquor dregs Slaker grits Landfill or Lagoon 50 10 65 70 95 91 Land Application 10 40 10 9 3 6 Incineration for Energy Production 20 30 — — — — Reuse in Mill 1 0 3 Other Beneficial Use 10 20 25 2 2 1 TABLE 60 TyPICAL CONCENTRATIONS OF NUTRIENTS AND MINERALS IN LIME MUD FROM PULP AND PAPER MILLS COMPARED WITH AGRICULTURAL LIME Minerals Lime Mud* Agricultural Lime Nitrogen, % 0–0.2 0.01 P2O5, % 1–1.2 0.06 K2O, % 0.2–1.4** 0.13 Calcium, % 28–50** 31 CCE, % 91–100 NA Magnesium, % 0.2–1.0** 5 Sulfur, ppm 0.19*** NA Boron, ppm 7.91*** NA Copper, ppm 3–66 10 Zinc, ppm 4–93 113 After IRC (2010). *Data from Morris et al. (2000) except where noted. **Data from South Carolina mills. Camberato et al. (1997). ***Data from Alabama mills. Muse and Mitchell (1995). NA = not available. TABLE 61 TRACE METAL CONTENT IN LIME MUD Minerals Lime Mud* Agricultural Lime Arsenic, ppm 1.71** <1–3 Cadmium, ppm bd–0.5 <0.1–1.1 Lead, ppm bd 1.3–130 Mercury, ppm <0.05** <0.01–0.02 Molybdenum, ppm bd–0.1 0.3–0.5 Nickel, ppm 3.3–71 7.0–17 Selenium, ppm bd–7.6 <1 After IRC (2010). *Data from Morris et al. (2000) except where noted. **One sample from a Georgia mill. ***Data from McBride and Spiers (2001). bd = below detection. aggregates. The authors recommended examination of the feasibility of adapting, binding, or otherwise modifying the paper sludge or paper sludge ash as an aggregate replacement. PhysicaL and cheMicaL ProPerties Wastewater treatment Plant Little was found in the literature with regard to the material or chemical properties of the WWTP residuals. IRC (2010) noted the WWTP can provide paper fiber content that will reduce the hydraulic conductivity (permeability) of a treated soil. Lime Mud The University of Maine publication Beneficial Use of Solid Waste in Maine (2006) provided a summary of lime mud properties reported in the literature, which only provided lim- ited information. Particle sizes reported in previous research for Wisconsin mill paper sludge showed that the lime mud had a 94% CaCO3 content, with 100% passing the 0.15 mm sieve. A subsequent study reported that only 88% passed the 0.15 mm sieve. When the lime mud was taken from the dewatering storage facility the moisture content was about 17%, with a bulk density of 66.55 lb/ft3. When used in soil modification, the sodium levels increased with the addition of lime mud. The magnesium levels were raised at a slower rate than when using limestone, whereas the calcium level rose faster than with limestone. A 1993 study by Dorris eval- uated the longest linear dimension using an image analysis technique. The results generally showed that the lime mud particles were larger and more spherical than hydrated lime but were less reactive. Clemson University (2010) research showed that although lime mud reacts faster than agricultural lime, it was not typi- cally used because of the need to dredge from holding ponds, dry the material, and crush it so that it can be spread with conventional dry lime spreaders. IRC (2010) reported that as long as lime mud had a ben- eficial use it was not considered a hazardous material by the Georgia DNR. Typical mineral and trace metal contents for lime mud are shown in Tables 60 and 61. Moisture con- tents of the lime mud were typically around 30%, but could be as high as 50%, which were difficult to spread for soil stabilization. The application rates needed to be adjusted for water content. The pH was also found to increase with increasing lime mud concentrations, hence its usefulness for soil stabilization.

48 Boiler ash, like other burned ash byproducts (e.g., fly ash and boiler ash) can be used in road construction and concrete brick manufacture (Table 62). As with the other byproducts, the physical and chemical properties are dependent on fuel source. Significant differences have been noted in dioxin and furan levels between ash from inland mills and ash from salt- laden coastal mill fuels. Causticizing residuals have been used for soil stabiliza- tion and erosion control. The potential uses identified by Bird and Talberth (2008) are shown in Table 63. cement and concrete Vegas et al. (2006) reported that Spain produced about 441,000 tons of paper mill sludge per year, which would yield about 165,400 tons a year of pozzolanic material. The paper mill sludge used in the study consisted mainly of calcite, kaolinite, talc, and other philosilicates (illite, chlorite). There aPPLications Applications for the beneficial reuse of WWTP residuals include use in clinker production, as a cement additive, and in roadbed construction, soil improvement, and erosion control. WWTP has also been preliminarily investigated in the production of synthetic aggregates. The basic raw materials in WWTP are consistent with those traditionally used in cement clinker production. Early research suggests that the wood fiber content can potentially serve as a con- crete admixture to potentially improve durability, pump- ability, and salt-scaling resistance while reducing shrinkage cracking. However, the concrete may need a high range water reducer to mitigate an increase in water demand and loss of compressive strength. When used in roadbed, soil improvement, and erosion control, the WWTP needs to be post-process-treated, otherwise trace amounts of heavy metals may not meet soil environmental standards. Syn- thetic lightweight aggregates can be produced by mixing with fly ash and pelletizing in a rotary kiln. TABLE 62 PAPER PROCESSING BOILER ASH USES IN HIGHWAy APPLICATIONS Market or Beneficial Uses Description Manufactured Soil Component Wood ash is more appropriate for land application. Ashes provide alkalinity to soil. Cement and Brick Feedstock Boiler ash from wood and WWTP residues is suitable for cement and brick manufacture. Concrete Additive Coal fly ash is used as an additive in concrete for highways and other applications. A state DOT approved use of coal wood fly ash for use in concrete after short- and long-term evaluation of the product. With wood fly ash added, concrete is stronger, more durable, more resistant to water er osion in saltwater conditions, and is less expensive. Coal wood bottom ash is used as aggregate in concrete blocks. Flowable Fill (CLSM) CLSM is a self-compacting soil replacement and has become a popular material for projects such as structural fill, foundation support, pavement base, and conduit bedding. Soil Stabilization Can be used as potting or liming agent Earthen Construction Boiler ash may increase the strength of the structure if it is cementitious. Asphalt Aggregate/Road Building Component Coal or wood bottom ash is used as aggregate in asphalt mixes. After Bird and Talberth (2008). CLSM = controlled low strength material. TABLE 63 PAPER PROCESSING CAUSTICIzING RESIDUAL USES IN HIGHWAy APPLICATIONS Market or Beneficial Uses Description Cement and Brick Feedstock The basic raw materials required to make cement are calcium, silicon, aluminum, and iron. Causticizing materials have high percentages of calcium, aluminum, and iron. Manufactured Soil Ingredient Causticiz ing residuals provide lime to soil. Soil Stabilization/Earthen Construction Lime slaker grits have been used as an additive. Road Dust Control Lime slaker grits have also been shown to be effective as a dust suppressant on unpaved roads. Asphalt Additive Lime mud, lime slaker grits, and green liquor dregs have been used successfully as a substitute for fine aggregate in roads. After Bird and Talberth (2008).

49 was a significant kaolinite content (20.83%) that is the pre- cursor of reactive metakaolin, which can be obtained under certain temperature and kiln time conditions. Typically, higher kaolinite content resulted in a more reactive calcined product. The study evaluated a blend of 90% cement and 10% cal- cined paper sludge. Calcined materials were produced using three temperatures (700°C, 750°C, and 800°C) and one of two kiln times (2 or 5 h) and ground to a maximum particle size of 0.045 mm before use in the cement mixtures. Results showed that the pozzolanic activity declined with increasing calcination so the optimum activation of the paper mill waste was found to be achieved with calcining for 2 h at 700°C. Initial set times were 127.5 min for the control and 97.5 min for the blend. Science Daily (2009) reported research in Portugal that showed pulp waste could be useful in cement production. The preliminary research evaluated clinkers made with 0.13% and 0.25% grits and dregs and compared them with conventional clinkers. Gas emissions measured during clin- ker production showed no significant effect as a result of including the paper byproducts in production. This research used the process as more of a disposal process rather than clinker enhancement. hot Mix asphalt Torres (2007) reported on research conducted by the Forest Products Research and Development Institute of the Depart- ment of Science and Technology (FPRIDI-DOST), which investigated the use of paper mill sludge in stone matrix asphalt. The dried, ground, and sieved sludge material was used as the fiber additive. The processed sludge was mixed with aggregates and asphalts and then used to prepare stan- dard Marshall mix design samples. The results showed that at between 5% and 6% asphalt, mixtures with 0.3% to 0.5% paper mill sludge would provide mixes that would meet the requirements of the stone matrix asphalt for both medium and high traffic level roadways. Successful implementa- tion of the post-processing of the sludge could provide a beneficial use for 92,600 tons of sludge that is currently landfilled. agency survey resuLts Only Kentucky reported they had used paper pulp or lime mud in HMA applications. No comments were provided on its experiences. suMMary of Waste PaPer sLudge inforMation List of candidate Byproducts The list of the most commonly researched and used byprod- ucts include: • WWTP residuals • Boiler and furnace ash • Causticizing residuals. About 50% of these byproducts were used in land applica- tion, for energy production (incineration), or landfilled. There had been limited research for use in highway applications and only one agency reported using this byproduct. Potential future use of these byproducts will likely focus on soil modification (lime mud), cement or concrete addi- tives, or aggregate replacement (bottom ash). test Procedures No specific test methods were cited in the literature for using this byproduct in highway applications. It is anticipated that traditional environmental (leaching), material (physical, chem- ical), and application test methods would be used. suMMary of other toPics There was too little usage in highway applications to provide information for the following topics: • Materials Preparation and Byproduct Quality Control • Materials Handling Concerns • Design Adaptations • Construction Concerns • Failures, Causes, and Lessons Learned • Barriers • Costs • Gaps.