Recycling Paper Mill By-products 193 Chapter 

# 30

Recycling Paper Mill By-products on Forest Lands:

By-product Composition, Potential Applications, and Industry Case Studies

ERIC D. VANCE National Council for Air and Stream Improvement, Inc. (NCASI), P.O. Box 13318, Research Triangle Park, NC

27709-3318

Abstract—Large quantities of wastewater treatment plant (WTP) residuals and boiler ash are generated as by-products from the U.S. pulp and paper industry. These by-products have the potential to enhance forest growth and long-term site productivity when land-applied and are generally environmentally benign. Land application may be a particularly valuable tool for replenishing nutrients and organic matter removed from whole-tree harvesting or other intensive forest management practices and could also be used to rejuvenate marginal sites that are naturally infertile or degraded from past land use practices or other anthropogenic factors.

Despite the demonstrated and potential benefits of forest land application, 50-70% of mill by-products continue to be disposed of in landfills at considerable costwhile only 10-12% are land applied. Factors that impede companies from initiating land application programs include logistic challenges, particularly when a variety of landowners, contractors, and regulators are involved; time requirements and costs associated with the permitting process; uncertainties associated with tree and forest responses; and real and perceived risks of future liability.

Case studies of successful company land application programs demonstrate the value of the practice and showthat such impediments can be overcome. Economic benefits of land application programs to the mills involvedinclude reduced landfill disposal costs, delayed construction of new landfills, reduced fertilizer costs, and increased forest productivity. Clear communication of the intent and potential benefits to all relevant parties is a common element of successful company programs. They
also often include field research and demonstration trials conducted by the company itself or in cooperation with local landowners, university scientists, cooperative extension specialists, and state regulators. Additional
research and more effective communication of the benefits and environmental safety associated with land application should facilitate the development of new programs, hasten the permitting process, and increase incentives for forest landowners to adopt land application as a management tool. The U.S. pulp and paper industry generated 5.3 million dry Mg of WTP residuals and 2.5 million dry Mg of boiler ash as by-products in 1995 (NCASI 1999). An additional 1.2 million Mg of wood ash (1990 estimate) is generated annually from the wood products sector of the U.S. forest products industry (Someshwar 1996). Mill WTP residuals are comprised largely of wood fiber and, in some cases, microbial by-products remaining after
wastewater treatment while boiler ash is derived from the incineration of wood, coal, and other fuels for energy.

Rapidly rising landfill costs and scarcity in recent years
have resulted in a concerted effort to find beneficial use alternatives for mill by-products. A logical alternative is land application, since mill by-products are significant sources of organic matter (WTP residuals) and nutrients (WTP residuals and ash) required for the growth of trees and crops. Paper mill WTP residuals and boiler ash alsohave generally low concentrations of heavy metals, organic compounds, and other constituents of concern and are environmentally benign when used in reasonable quantities under standard management practices (Vance 1996, Camberato et al. 1997, Mitchell and Black 1997). Forest land application is a particularly attractive use for these materials because many companies own forest landsthat are in close proximity to mill sites where by-products are generated. Land application is also consistent with the concepts of sustainable forestry, because it can be used to replace woody biomass and nutrients removed during forest harvest and contribute to long-term site productivity.194 Vance Despite the apparent advantages of land application as a beneficial use, only about 12% of paper mill WTPresiduals and 11% of mill-generated boiler ash are currently land-applied, while the proportion of WTP residuals and ash disposed of in landfills is about 50% and 70%, respectively (NCASI 1999). Here I summarizethe composition of WTP residuals and boiler ash, review forest responses to these by-products when landapplied, and describe potential applications of the practice to improve forest growth and site productivity. Several case studies which highlight the some of the practical aspects, impediments, and benefits associated with successful company forest land application programs are
described.



### MILL RESIDUAL TYPES
AND COMPOSITION

Wastewater Treatment Plant Residuals

About 40% of by-product WTP residuals generated by the pulp and paper industry are derived from primary clarification treatment (i.e., primary residuals) (NCASI1999) and are comprised primarily of wood fibers. Because of their high wood-fiber content, primary residuals have low N concentrations (Table 1) with C:N ratios often ranging from 100:1 to 300:1. Primary residuals can be a significant source of other nutrients, however. Secondary residuals, the second major WTP residualscategory, are derived from biological treatment of effluents during which N and P are often added. Secondary residuals thus consists largely of microbial biomass and have higher concentrations of N and P and lower C:N ratios (e.g., 5:1 to 20:1) than do primary residuals. Bothprimary and secondary WTP residuals can provide significant sources of other macro- and micronutrients, although concentrations vary widely (Table 1). Although secondary residuals as a category represent only about 1% of the total paper industry residuals generated, they are most often mixed with primary residuals. These mixedresiduals represent the largest single WTP residuals category, about 54% of total residuals production (NCASI 1999).

Paper mill residuals are also generally low in potential environmental contaminants. Metals contained inresiduals, for example, are largely derived from the original wood fiber. The U.S. Environmental Protection Agency (EPA) has established metal loading limits for land-applied municipal biosolids, which generally havehigh metal concentrations compared to paper mill residuals (Table 1). Concentrations of leachable organic compounds as determined by the toxicity characteristicleaching procedure (TCLP) have also been below detection limits on analyzed residuals (Camberato et al. 1997). Despite their generally safe levels, concentrations of metals and potential organic contaminants should bedetermined before establishing a forest application program.

Dioxins have been a traditional environmental concern for WTP residuals derived from chlorine-based bleaching processes. Over the last decade, however, newtechnologies have dramatically reduced dioxin concentrations in bleaching mill effluents and WTP residuals.As of 1996, total industry export of tetrachlorodibenzodioxin and -furan (TCDD/TCDF)) was reduced by 94% on a toxic equivalent (TEQ) basis relative to 1988 levels (NCASI 1997). Median TCDD/TCDF concentrations for bleached kraft mill residuals are 1.6 ng kg -1 (ppt) TEQ, based on 1997 survey data (NCASI 1997, Table 2), which is below the maximum soil concentration of 10 ng kg -1 TEQ specified in an U.S. EPA/Industry Memorandum of Understanding for land-applied paper mill residuals. For mills employing complete substitution of chlorine dioxide for chlorine in pulp bleaching, WTP residual full congener data had mean values ranging from 1.8 to 5.2 ng kg -1 TEQ. Analytical needs related to these constituents should be left up to the discretion ofthose knowledgeable of the processes used, in cooperation with regulatory authorities.



### Boiler Ash

Paper industry boiler ash is derived from incineratingwood and other fuels for energy. Pure wood ash comprises about 22% of the total ash generated, while pure coal ash as a category comprises about 15% (NCASI1999). The other categories of ash are derived from mixtures of wood and coal, WTP residuals, and tire-derived fuels. While coal can be a valuable soil amendment, itgenerally has lower nutrient concentrations and less predictable composition than pure wood ash (Carlson and Adriano 1993, Bilski et al. 1995). This is also likely thecase with mixed fuel ashes, particularly since the relative proportion of the different fuels may change over

time.

Boiler ash derived from wood is comprised largely of
oxides and carbonates of K and Ca but also contains significant amounts of P, Mg, and some micronutrients(Table 3). Boiler ash does not provide significant quantities of N due to volatilization losses during combustion. One of the most important characteristics of ash as asoil amendment is its effect in raising soil pH, as demonstrated by its effective substitution for agricultural lime. The ability of an ash to neutralize soil acidity, defined

in terms of its CaCO
3 equivalence, varies widely (Table 3) and depends on the proportion of wood and otherRecycling Paper Mill By-products 195 NCASI*

 Wisconsin I

 Maine ?

 Alabama§

 Municipal #

 Range Median Range Mean Range Median Range Mean Range Median Ref.**

Macronutrients (g kg -1 )
N 0.51 - 87.5 8.98 1.4 - 41 29 0.1 - 61 1.1 3.0 - 15.5 8.76 <1.0 - 210 32.0 1
P 0.01 - 25.4 2.35 1.3 - 5.8 3.4 0.01 - 3.1 0.85 0.19 - 2.57 1.2 <1.0 - 150 14.0 1
K 0.12 - 10 2.2 0.37 - 6.0 1.37 0.08 - 3.4 0.46 0.15 - 2.65 0.96 0.2 - 650 2.3 1
Ca 0.28 - 210 14.0 2.7 - 90.2 29.5 0.001 - 81 4.2 13.0 - 148 60.0 1.0 - 250 27.0 1 Mg 0.2 - 19.0 1.55 0.11 - 1.0 0.65 0.05 - 3.7 1.8 0.72 - 5.07 2.30 0.3 - 25.0 4.0 1
S 0.2 - 20.0 4.68 NA NA 0.3 - 6.5 0.50 0.1 - 10.5 4.1 6.0 - 15 11.0 2

Micronutrients/metals (mg kg -1 ) Ag <0.1 - <11 0.55 NA NA 0.003 - 10 1.06 NA NA NA NA NA Al 590 - 59,000 13,400 15 - 22,000 19,500 120 - 16,00 0 6,190 790 - 40,700 13,100 1,000 - 13,500 4,000 2
As <0.07 - 8.3 1.2 NA NA NA NA NA NA 0.3 - 315.6 6 3 B <1 - 491 25.0 8.5 - 21.1 13.3 NA NA 5.11 - 28.2 13.5 4 - 1,000 33 4 Ba 17.9 - 1,800 160.0 NA NA NA NA 0.0 - 289 144 <0.01 - 9,000 200 2 Cd <0.09 - 56 1.2 1.6 - 9.4 3.9 0.008 - 7.7 1.16 0.1 - 3.69 1.01 0.7 - 8,220 7 3
Co 0 - 9.7 NA 1.8 - 4.5 2.5 NA NA 1.6 - 9.7 4.36 1 - 260 10 4 Cr 3.0 - 2,250 42.0 29.2 - 55.8 39.6 0.02 - 172 11.4 17.9 - 789 145 2.0 - 3,750 40 3 Cu 3.9 - 1,590 52.0 2.2 - 90.9 67.4 2.0 - 204 48.0 10.3 - 69.6 34.3 6.8 - 3,120 463 3 Fe 97.1 - 10,800 1,540 675 - 7,162 2,930 162 - 5,120 1,670 790 - 12,800 3,040 1,000 - 15,400 1,700 4 Hg 0.0009 - 3.52 0.35 3.9 3.9 0.003 - <2 0.17 NA NA 0.2 - 47.0 4 3 Mn 13 - 2,200 155.0 22.9 - 286.4 119.0 9.8 - 1, 500 99.0 40.0 - 2,555 900 32 - 9,870 260 4
Mo <2.5 - 14.0 NA 5.2 - 8.9 6.7 NA NA 2.44 - 32.2 11.9 2.0 - 67.9 11 3 Na 300 - 66,700 2,200 490 - 4,120 1,730 219 - 14,60 0 585 440 - 48,000 7,750 100 - 30,700 2,400 2
Ni 1.3 - 133 18.3 NA NA 1.7 - 97 10.6 0 - 41.0 15.2 2.0 - 976 29 3 Pb <0.05 - 880 28 37.8 - 129.3 81.9 0.05 - 1,000 14.3 9.5 - 116 48.6 9.4 - 1,670 106 3
Se <0.01 - <31 0.21 NA NA NA NA NA NA 0.5 - 70.0 5 3
Sn <70.6 NA NA NA 5.07 - 135 10.7 NA NA 40 - 700 150 4 Zn 13 - 3,780 188.0 41.3 - 214 127.0 9.8 - 843 62.0 50.2 - 695 215 38 - 68,000 725 3 Table 1

. Macronutrient and micronutrient concentrations in pulp and paper manufacturing wastewater treatment plant (WTP) residuals. Concentrations of some metals in WTP residuals have declined in recent years due to reductions in metal concentrations in inks and more careful scrutiny of raw materials and processing chemicals. For this reason, metal concentrations in samples collected before 1990, particularly maximum values, may be higher than those in present-day residuals and should be interpreted with caution. (Not available—NA.)

* NCASI 54 mill survey (Thacker 1984). An assortment of primary, secondary and combined treatment residuals. The median N and P concentrations and range (g kg -1 ) for individual residual types were primary, 2.7 (0.51 - 9.0) for N and 1.6 (0.01 - 4.0) for P; secondary, 23.3 (6.2 - 87.5) for N and 4.2 (0.4 - 16.7) for P; combined, 8.5 (1.1 - 59) for N and 0.67 (0.1 25.4) for P. Survey also reported Cl (range <0.06-8,500 mg kg -1 , median 383) and Ti (range 3,100-76,000 mg kg -1 ).

† Seven combined residuals from Wisconsin (McGovern et al. 1983).

‡ Twelve residuals from Maine (Rock and Beyer 1982).

§ Sixteen residuals from Alabama (Muse 1993).

# Municipal sewage biosolids. EPA loading limits for land-applied municipal wastewater treatment biosolids have been established for As, Ba, Cd, Cr, Cu, Mo, Ni, Pb, Se, and Zn ( see Table 4 ). ** 1—Hue 1995; 2—Sommers 1977; 3—Kuchenrither and McMillan 1991; 4—Chaney 1980. † ‡

All values are in ng kg -1 (ppt)

Max 90 th %* Mean Median

TCDD 92 (1,390) 17 (161) 7 (72) 1 (16) TCDF 735 (17,100) 65 (1,300) 33 (607) 6 (78)
TEQ I 165 (3,100) 24 (291) 10 (133) 1.6 (24) Table 2 . Concentrations of 2,3,7,8 TCDD/Fs in bleached kraft mill wastewater treatment residuals from 1996 NCASI survey data (NCASI 1997). Data in parentheses from previous 1988 NCASI survey (NCASI 1990).

* Ninetieth percentile concentration.

† Expressed as toxic equivalents of the most toxic isomer (2,3,7,8-TCDD) calculated as TCDD + (0.1 × TCDF). †196 Vance fuels being incinerated and the combustion efficiency
of the boiler.

Although K contained in wood ash is relatively available, P availability is more complex and depends on its
form and on other soil chemical characteristics. Theproportion of ash-derived P available to plants determined from direct measures of plant uptake and soil indices has been estimated to range from less than 2% to 40% (Naylor and Schmidt 1986, 1989, Ohno andErich 1990). In one comparison with monocalcium phosphate fertilizer (mixed with CaCO
3 in an amount equivalent to the neutralizing capacity of the ash), ash:fertilizer availability ratios ranged from 30 to 70%, depending on Median Range No. samples
pH* 12.3 7.8 – 13.1 23

CCE I 48.1 13.2 – 92.4 18

Macronutrients (g kg -1 )

P 4.2 0.3 – 14.4 24
K 27.9 1.9 – 130 25

Ca 180 35.9 – 966 25 Mg 9.7 3.2 – 24.7 25

N 0.6 0.2 – 0.9 8

Micronutrients (mg kg -1 ) Mn 2,430 0.33 – 7,820 25
Cu 70.4 37.7 – 207 25 Zn 316 35.2 – 1,250 25
B 91 7.7 – 290 6

Mo 12.6 3.0 – 123 16 Table 3

. pH, calcium carbonate equivalence, and nutrient concentrations of wood-fired boiler ashes from different sources. Adapted from Vance (1996). Data compiled from Naylor and Schmidt (1986), Campbell (1990), Etiegni et al. (1991), and Muse (1993).

* Measured on an ash:water paste.

† Expressed as percent CaCO

3 equivalence. †

the soil type used (Erich and Ohno 1992).Wood ash metal concentrations are generally low relative to EPA loading limit guidelines for land-applied municipal biosolids (Table 4). Coal-derived ash has morevariable composition and generally higher metal concentrations than pure wood ash (Someshwar 1996, 1999). Organic compounds in ash are normally not significant. Elevated polychlorinated dibenzo-dioxins and furans (PCDD/Fs) can sometimes occur when extraneoussources of chlorine are present, however, as when saltladen wood or WTP residuals from mills using chlorine bleaching are part of the fuel mix (Someshwar 1996, 1999).

Wood ash* (kg ha -1 ) EPA limits I (kg ha -1 ) Metal No. samples Median Range Annual Cumulative

As 2 0.06 0.03-0.10 2.0 41
Ba 19 0.59 0.27-1.19 NA NA
Cd 25 0.02 0.00-0.26 1.9 39 Cr 25 0.36 0.09-1.6 150 3,000 Cu 25 0.70 0.38-2.1 75 1,500
Pb 25 0.70 0.34-6.7 15 300

Mo 16 0.13 0.03-1.2 0.90 18 Hg 5 Not detected 0.85 17
Ni 25 0.21 0.06-0.64 21 420

Se 2 0.05 0.00-0.11 5.0 100 Zn 25 3.2 0.35-12.5 140 2,800 Table 4

. Comparison of metals added from 10 Mg ha -1 wood-fired boiler ash with U.S. EPA annual and cumulative metal loading limits for municipal biosolids. (Not applicable—NA).

* From Vance (1996). Data compiled from Lerner and Utzinger (1986), Naylor and Schmidt (1986), Campbell (1990), Etiegni et al. (1991), Muse (1993), and Muse and Mitchell (1995).

† From U.S. EPA (1993). †Recycling Paper Mill By-products 197 

### FOREST RESPONSES TO LAND-APPLIED
MILL BY-PRODUCTS

Wastewater Treatment Plant Residuals

Land-applied paper mill residuals are a source of both organic matter and a range of nutrients. Because of their organic matter content and slow nutrient release, millresiduals (and municipal biosolids) may have more potential to enhance long-term site productivity than dochemical fertilizers if an appropriate balance of nutrients is supplied (Cole et al. 1990). Forest responses to WTP residuals are often dictated by their N content and availability, which is tied to their C:N ratio. For example, forest nursery studies have shown positive growth responses of cottonwood ( Populus deltoides Batr.), Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco), noble fir ( Abies procera (Rehd.), and white pine ( Pinus strobus L.) seedlings to paper mill residuals and municipal biosolids when residual C:N ratios were 20:1, fair responses with C:N ratios between 30:1 and 40:1, and low or negative responses with C:N ratios >100 (Henry 1986). Harrison et al. (1996) found a significant ( P <0.05) negative correlation between soil C:N ratio, as influenced by different land-applied pulp and paper mill residuals, and height and diameter growth of Douglas-fir and western white pine seedlings grown in nursery beds. Positive tree growthresponses have also been reported for mill residuals having C:N ratios of 100:1 to 150:1, however (Harringtonand DeBell 1984). In agricultural nursery and field trials, fertilizers have been successfully used to compensate for N deficiencies in paper mill residuals (Bellamy et al. 1995).

Nitrogen in residuals can also have negative effects when applied in excessive amounts. While a 32 Mg ha -1 application of a 1:1 primary:secondary residual mixture significantly increased red pine ( Pinus resinosa Ait.) basalarea growth, higher application rates either had no effect or reduced it (Bockheim et al. 1988 a ). This was attributed to increased growth of lateral branches and foliage at the expense of the stem. In a later study onthe same site, investigators speculated that increased incidence of shoot blight and canker disease in the crowns of pines on residual-treatment plots may have been caused by moisture stress induced by competing vegetation (Stanosz and Trobaugh 1996).

Land application at establishment, particularly forWTP residuals, poses unique challenges. The most common problem is an increase in herbaceous or woody competition, which can increase mortality and reduce growth of tree seedlings (Henry 1986, Shields et al. 1986, Torbert and Johnson 1993). In field seedling trials in Maine, for example, primary/secondary residual and secondary residual/ash mixtures reduced black spruce ( Picea mariana (Mill.) B.S.P.) and red pine seedling growthbecause of increased competition, even though herbicides were used (Shepard 1997). A third trial conductedby the same investigator showed positive effects of a primary/secondary residual mix on the growth of larger red pine seedlings, however, because they were able to withstand competitive pressures. In addition to allowing a longer period for seedlings to become established, weedcompetition can sometimes be reduced from the mulching effect provided by surface-applied residuals (Shieldset al. 1986, Torbert and Johnson 1993). Because seedling responses are highly variable and sensitive to the particular residuals and sites used, experimental trials can be valuable for predicting responses and identifying potential problems before an operational-scale program is implemented.

Mill residuals applied to forests in moderate quantities appear to have little potential to affect water qualitysignificantly. For nutrient-enriched mill sludges, N loading is often the factor limiting application rates. Studies using sewage biosolids and high-N paper mill residuals on mid-rotation loblolly pine ( Pinus taeda L.) have shown no additional benefit of adding more than 390 kg N ha

1 , which may also be a reasonable limit to avoid water quality concerns (Brockway et al. 1986, Dickens 1993). Studies of nutrient-enriched paper mill residuals appliedto red and white pine stands in Michigan showed positive effects at about 560 kg N ha -1 , and a potential for significant NO
3 -leaching only at rates exceeding about 840 kg N ha -1 (Brockway 1983, Brockway and Urie 1983).
Elevated NO
3 -concentrations were found in groundwater following heavy applications (63 and 94 dry Mg ha-1 ) of a 2.5:1 primary:secondary residual mixture to a red pine plantation (Bockheim et al. 1988 b ). In another study, the effects of 40 dry Mg ha-1 of a combined primary/secondary residual mix applied to a mixed northern hardwood/conifer stand in Maine on soil solutionchemistry were temporary and small relative to the effects from harvesting operations (Kraske and Fernandez 1993). Shields et al. (1986) found that application rates up to 456 dry Mg ha -1 of a 1:1 primary:secondary residual mix applied to a poorly drained alluvial soil in Oregon only slightly and temporarily increased tannin, sodium, and iron concentrations in groundwater but had no apparent effect on NO
3 -or other constituents.

Model-simulated threshold application rates for highN residuals have been estimated to be 720 kg N ha -1 (for the Pacific Northwest, 340 kg N ha -1 for the Southeast, and 470 kg N ha -1 for the Great Lakes regions (Brockway198 Vance et al. 1986). These estimates are based on limiting soil

NO
3 --N leachate concentrations to below the EPA standard for groundwater (10 mg l -1 ), and are likely conservative due to dilution of soil leachates entering groundwater. While total N-loading limits for low-N residuals (e.g., primary WTP residuals) could probably be higher without risking water quality degradation from NO

3 - leaching, it is likely that other factors such as induced N deficiencies, metal loading, or the sheer physical effects of the residuals would limit suitable application rates.

Field studies have shown little effect of land-applied paper mill residuals on forest wildlife communities (Thiel et al. 1989, Vera and Servello 1994, Sherman 1995). These studies have shown that any changes in wildlife populations that do occur likely result from shifts in the amount or composition of understory vegetation or from changes in soil moisture. Field studies have not shown any ecological effects resulting from trace quantities of TCDDs/Fs in land-applied residuals (Thiel et al. 1989, Vera and Servello 1994, McFadden et al. 1995, Sherman 1995). Concerns over dioxins other chlorinated organiccompounds should also diminish in the future as residual concentrations of these constituents continue to
decline.



### Boiler Ash

Effects of forest application of wood ash have been most widely studied in Scandinavia, where substantial, long-term growth responses have been demonstrated on Histosols (Weber et al. 1985, Silfverberg and Hotanen1989, Ferm et al. 1992). Positive responses in these systems have been attributed to increased K and B supply and improved availability of N and other nutrients due to more rapid microbial mineralization of soil organic matter. Forest responses to wood ash application in the U.S. have not been well documented. One study showed increases in the productivity of poplar cuttings up to40% following ash application in Idaho, which was attributed to increased availability of P, K, and B (Etiegni et al. 1991). There is also evidence that boiler ash can significantly improve loblolly pine growth on some sites in the South, probably due to increased P supply ( see industry case studies below ). Agricultural studies have alsoshown that ash has the potential to stimulate weed competition by reducing the effectiveness of some herbicides (Mueller-Warrent et al. 1993). As with WTP residuals, responses of trees and factors such as weed competition will be highly influenced by the rate, timing, and mode (e.g., surface applied vs. incorporated) of application.

Effects of coal ash on tree growth have not been widely reported. A greenhouse study in Finland showed that coal ash did not significantly affect birch seedling growth but that the seedlings could be successfully grown on spoil heaps when peat and N fertilizer were added (Veijalainen et al. 1994). The investigators concluded that coal ash might be beneficial on sites that exhibited K, Mg, or B deficiencies. Coal ash has been successfullyused to increase productivity of agricultural crops, although high application levels can have detrimental effects on some crops due to salt and B accumulation (Carlson and Adriano 1993, Bilski et al. 1995).

Considering the low concentrations of metals (Table 3) and organic compounds of concern (Camberato et al. 1997) in wood ash, effects on water quality should not be detrimental when ash is applied at rates consistent with its use as a forest fertilizer. Wood ash applied to a harvested forest site in South Carolina had only verysmall, temporary effects on groundwater chemistry (Williams et al. 1996) and no appreciable effect on heavy metal body burdens of small mammals (Sweeney et al. 1994). Investigators in Maine showed that ash applied at rates of 13 and 20 Mg ha -1 to an acidic, forested Spodosol caused transient increases in soil solution basecations, pH, and anions (Kahl et al. 1996). They suggested an ash application rate of 6 Mg ha -1 to favorablyalter soil exchange chemistry without affecting soil solution chemistry at the site. With some exceptions, Scandinavian studies have shown that ash generally increasessoil microbial biomass and activity, which has been primarily attributed to its effect in raising soil pH (Weber et al. 1985, Hyvönen and Huhta 1989, Bååth and Arnebrant 1994, Bååth et al. 1995, Fritze et al. 1995). In Finland, the amount of Cd contained in 1-5 Mg ha -1
wood ash was 20-100 times less than critical levels found to reduce microbial respiration in laboratory studies (Fritze et al. 1995). The study also showed that the ash decreased the toxicity of added Cd due to an increase insoil pH and also increased soil cation exchange capacity. Although coal ash has more variable composition and can have elevated concentrations of some metals, a
review of its use as a soil amendment concluded that there was little risk of contaminating groundwater when applied at moderate rates (Bilski et al. 1995).

There have been concerns that 137 Cs, the radionuclide generated from nuclear bomb testing and concentratedin wood, could pose environmental risks when land applied as ash (Hess et al. 1997). These concerns havebeen alleviated, however, by studies showing that landapplied wood ash does not add a significant amount of

137 Cs to the soil (Hess et al. 1997). In fact, a recent study in Finland found that wood ash applied to a Scots pine
stand reduced 137 Cs accumulation in understory berries on a site monitored for possible contamination follow-Recycling Paper Mill By-products 199 ing the Chernobyl nuclear accident (Levula et al. 2000). It is thought that K contained in the ash, which is a chemical analogue to Cs, reduced plant 137 Cs uptake.



### SITUATIONS WHERE LAND-APPLIED
MILL BY-PRODUCTS MAY BE BENEFICIAL

There are a number of situations where land-applied mill by-products might have particularly positive effectson forest productivity. In the South, loblolly pine is typically fertilized with N and P both at establishment and in mid-rotation stands (NC State Forest Nutrition Coop. 1995). Nutrient-enriched WTP residuals and boiler ash could be used as N and P fertilizers, respectively, with additional, positive effects of residuals on soil organicmatter. K contained in ash could also improve productivity of sites with deep, sandy surface soils in the region (Allen et. al. 1990) and could also increase the cation exchange capacity of coarse-textured soils (Fritze et al.1995). Although ash effects on soil pH may limit application rates to pine stands, there is evidence that loblolly pine can do well at relatively high pH values on some sites ( see industry case studies below ). Experimental trials are recommended when by-products, particularly WTP residuals, are to be applied to sites before or shortlyafter planting to determine their effects on weed competition, seedling growth, and seedling survival.

Nutrient-enriched WTP residuals also have the potential to increase productivity of Douglas-fir stands in the Pacific Northwest, since N often limits productivity and N fertilization is commonly practiced (Edmonds et al. 1989, Peterson and Hazard 1990, Stegemoeller and Chappell 1990, 1991, Hopmans and Chapell 1994). P has also been recommended for young Douglas-fir standson low-P soils and along some areas of coastal Washington (Edmonds and Hsiang 1987, Radwan et al. 1991,Radwan 1992). Consequently, a mixture of WTP residuals and ash could have beneficial effects on some sites.Mill residuals can also supply S, which limits productivity and responses to N fertilizer on some Pacific Northwest sites (Edmonds and Hsiang 1987, Blake et al. 1990). In addition, ash can supply K and Mg, which can limit Douglas-fir productivity as stand leaf area index increases (Velazquez-Martinez et al. 1992).

There are other specific situations where mill by-products might enhance forest growth or long-term site productivity. A prime example is intensively managed forests, where high proportions of biomass may be removedover short rotation intervals and where genetically improved, faster growing tree species may be used. Intensive management regimes will undoubtedly become more prevalent in the future and have the potential to affect long-term site productivity by depleting site nutrient capital and soil organic matter (Federer et al. 1989, Hornbeck et al. 1990, Johnson 1994, Olsson et al. 1996, Ranger and Nyes 1996). Both WTP residuals and boiler ash could be used to replace these constituents and help sustain productivity of intensively managed stands.

Boiler ash could also be used to alleviate K deficiencies in pine and spruce stands in the northeastern U.S. (Heiberg and White 1951, Stone and Leaf 1967, Leaf et al. 1975) and in sugar maple stands in southern Quebec (Ouimet and Fortin 1992). Heavy N fertilization has also been found to induce K (and likely Mg) deficiencies in spruce stands of British Columbia (van den Driessche and Ponsford 1995). In the eastern U.S., Europe, and other regions, ash could be used to replace Ca and other base cations depleted by acidic deposition or past land uses (Huettl 1989, Joslin et al. 1992, Joslin and Wolf 1994, Van Miegroet et al. 1993, Johnson et al. 1994, Cronan and Grigal 1995, Lawrence et al. 1995, Meiwes 1995, Likens et al. 1996, Wilmot et al. 1996). Mill WTPresiduals and boiler ash might also help address micronutrient deficiencies noted in a range of tree species,which also may be induced by macronutrient fertilization or high growth rates resulting from intensive management (Stone 1968, 1990, Boardman and McGuire 1990, Jokela et al. 1991, NC State Forest Nutrition Coop.1992). Because they can promote microbial N immobilization, high C:N ratio residuals might benefit sites whereconcerns about over-excessive N (i.e., “nitrogen saturation”) have been reported (Aber et al. 1989, 1991, Kahl et al. 1993). Mixtures of enriched residuals and ash alsomight provide a more complete amendment with respect to nutrients and organic matter than either byproduct alone. Ash could also enhance the physical properties of residuals, improving their effects on tree growth and facilitating their application (Carpenter and Beecher 1997).



### LAND APPLICATION WITHIN THE
U.S. PULP AND PAPER INDUSTRY

While there are clear economic incentives for pulpand paper mills to consider land application as a beneficial use option, landfilling continues to be the most common fate for mill by-products. Four reasons why mills do not initiate land application programs are commonlycited. One is the logistic and technical difficulty associated with coordinating activities between the mill andforestry operations and with local landowners and contractors. This added coordination and planning places aburden on company managers and reduces the time available for their primary responsibilities.200 Vance A second reason that some companies are reluctant to initiate a land application program is the time and cost associated with the permitting process. Several years areoften required to develop experimental field trials, conduct analytical testing, and organize site visits with regulators before a new program is approved. This process is complicated by the fact that many states do not have regulations specific to land application and that more than one agency is often involved. Because of a lack ofscientific data and experience with the materials, agencies can also be overly cautious and require individual permits and intensive sampling and reporting for each potential site. Companies with land holdings spanningmultiple states must also face disparate sets of regulations, requirements, and permitting procedures.

A third reason that more companies are not developing their own forest land application program is the uncertainty surrounding how the forest will respond. Tree seedlings are particularly sensitive to the composition ofmill by-products and their mode of application. By-products with high nutrient concentrations can stimulate weedcompetition and reduce tree seedling growth and survival, while low-N, primary residuals can also impair seedling establishment by inducing N deficiencies. Nutrient deficiencies or imbalances can also result from changes(usually increases) in soil pH following land application, and data on tree species tolerance to changes in soil pH are scarce. Surface-applied mill by-products can also have much different effects on nutrient availability, soil moisture and temperature, and weed competition than by-products tilled into the soil. Unfortunately, many of these relationships are site-specific and unpredictable due to a lack of comparable data across a wide range of sites. If positive tree growth responses cannot be assured,it can be difficult to justify the operational and regulatory costs associated with implementing a land application program and forest landowners external to the company may not have an incentive to cooperate.

A fourth reason that land application is not more widely considered is the risk of future liability. Even with comprehensive analytical testing, field experiments, and full permitting by the appropriate state agencies, there remains a legitimate fear that new information, whether or not based on sound science, may result in litigation at some future date. This has been cited as a genuine concern among some companies and a primary reason that they are unwilling to initiate a program. Some companies are even considering discontinuingexisting, successful programs because the economic benefits are viewed as not worth the liability risks. 

### INDUSTRY CASE STUDIES

The case studies described here depict actual company experiences in developing land application programs.
Most of the information from these studies comes from internal company reports and direct consultation with company personnel. Because study designs, replication,
and scientific documentation of such studies is often incomplete or inadequate for a full scientific analysis,
case studies are not often found in the scientific literature. They do, however, elucidate some of the practical considerations associated with land application and can provide valuable information for generating scientific hypotheses and identifying research needs.



### Georgia-Pacific Leaf River Mill, New Augusta, Mississippi

Georgia-Pacific’s Leaf River mill is a bleached kraftpulp mill producing 54 dry Mg of by-product WTP residuals d -1 , consisting of a mixture of primary (50-90%) and secondary (10-50%) residuals, and about 25 dry Mg
of wood-fired boiler ash d -1 (Smith et al. 1996). The millbegan its land application program in 1985, shortly after beginning operations and after obtaining a state permit for the practice. Since the program began, WTP residuals produced by the mill have been applied to agricultural fields within a 40-m radius and, beginningin 1989, residuals have also been applied to companyowned forest land. Before obtaining a permit for spreading wood ash on forest land, an average of 1,300 truckloads (12,000 Mg) of ash was disposed of in landfills annually.

Success of the agricultural program can be attributed to acceptance by local farmers, which was facilitated by the establishment of farm test plots. Agricultural demand for WTP residuals has since continued, with one farmer receiving the 1993 National Corn Yield Contest Award (no-till, irrigated class) using plots to which residuals had been applied 4 months before planting. Beginningin 1986, a series of field trials were established to determine the effects of land-applied residuals and ash on the growth of loblolly pine. These trials showed that over an 8-year period, both residuals and ash generallyincreased early pine growth despite increased weed competition (herbicides were not used in the trial) (Table 5). Treatment differences were not statistically significant ( P <0.05), largely because the power of the analysis wasreduced due to the confounding effect of several different soil types without replicate plots within each. Seedling survival rates tended to be lower in plots to which the by-products were applied, however, which was likely due to increased weed competition (Table 5).Recycling Paper Mill By-products 201 Treatment (Mg ha -1 ) Survival (%), yr 1* Height (m), yr 3* I

Control 84 ±7 1.4 ±0.3
Treatment residuals - 30 56 ±10 1.8 ±0.3
Ash – 28 83 ±4 1.9 ±0.03
Ash – 56 78 ±4 2.2 ±0.04
Ash – 112 70 ±4 2.1 ±0.05 Treatment residuals (30) + ash (28) 59 ±8 1.9 ±0.1 Table 5 . Leaf River 3-year pine growth data, 1993 trial (data obtained across two soil series, four site types).

* Mean ± SE, n = 4.

† No statistically significant effect ( P <0.5) of treatment on height. †

Addition of P is most likely the reason for the positive effects of WTP residuals and ash on pine growth, sincemost soils in the area are P-deficient. Tree foliar analyses from the 1993 trial support this hypothesis, with foliar P concentrations averaging 0.11% in control plots, 0.15% in the residual plots, and 0.13% in ash plots. The total P supplied by 30 dry Mg ha -1 of residuals or 28 dry Mg ha -1 of ash is about twice as much as the recommended rate of fertilizer P at the time of planting (generally 56 kg P ha -1 ), although fertilizer P is likely to be more readily available. Only the residuals provided a significant source of N, with 30 Mg ha -1 of residuals supplying about 112 kg of plant-available N (estimated as 20% of total N). Foliar N concentrations were 1.33,1.39, and 1.20% for control, residual, and ash plots, respectively. Similar seedling responses to the residual + ash treatment and either by-product alone also supports the hypothesis that P was the primary limiting factor on
these sites.

A surprising finding from another replicated Leaf River trial was that ash application rates as high as 110 Mg ha -1 had positive effects on pine growth for 2 years, despite soil pH outside of the range commonly thought optimal for loblolly pine growth. A longer monitoring period should allow firmer conclusions to be made aboutthe effects of high pH on pine. Based on field trial results, company foresters are recommending that residuals or ash not be applied on highly productive sites because nutrients are already sufficient and due to the potential for increased weed competition. Weed control isa major focus of current research, and improved planning, equipment, and site-specific prescriptions for forest application are also being developed.

In the operational program, by-products are applied to forest land following harvesting and site preparation (i.e., shearing and raking), and incorporated by disking or bedding prior to planting. The forest land base for the Leaf River mill is about 120,000 ha. About 54 dry Mg d -1 of combined WTP residuals are now land-applied, with 80% applied to company forest lands and most of the remaining 20% applied to surrounding forest and farm lands. Mill residuals are applied to about 600 ha each year, and annual ash application to 300- 400 ha is projected. Application rates for both residuals and ash are based on soil nutrient deficiencies and crop requirements, with N the constituent that most limits residual application rates during the growing season.

Although the Leaf River program has demonstrated that forest application on an operational scale is more logistically intensive than agricultural application, an advantage of forest application is the reduced liabilityrisk because company-owned lands are used. One regulatory hurdle the company faced was obtaining permission to apply wood ash to forest land. With the agricultural land application permit renewal of 1993, a request to the DEQ to allow forest ash application was initiallydenied. The request was eventually approved after a series of meetings between company personnel and state regulatory officials for several years, and after test plots were established and showed positive effects of ash on pine growth.

Leaf River’s land application program has significantly reduced the mill’s landfill requirements and is projected to double on-site landfill life once the ash application program is fully implemented. The mill saves $600,000 to $700,000 annually when costs of land application are compared to potential landfill disposal costs. Significantincreases in wood production resulting from the program are also projected. Positive tree and crop responses have been a primary reason for the program’s successand continuance. A more detailed account of by-products generated by the mill and other management alternatives is provided by Smith et al. (1996).



### Weyerhaeuser Pulp and Paper Mill, Plymouth,
North Carolina

Two boilers at Weyerhaeuser’s Plymouth mill generate about 24,000 dry Mg of bottom ash annually, utilizing a combination of bark, coal, de-watered primary WTP residuals, recycled fiber (old corrugated container) re-202 Vance jects, and waste oils as fuels. In the past, this material was disposed of in an on-site company-owned landfill. Beginning in 1995, about 14,000 dry Mg of the ash hasbeen recycled back to Weyerhaeuser timberlands annually, replacing commercial P fertilizers applied duringestablishment of intensively managed loblolly pine plantations. P fertilizer is critical for loblolly pine to be successfully established on Weyerhaeuser’s eastern North
Carolina timberlands because soils are P-deficient.

In 1990, experimental ash application trials in previously thinned loblolly pine plantations were initiated.The trials were designed to assess the effects of ash applications (up to 72 dry Mg ha -1 ) on tree growth and nutrition, soils, and groundwater. State regulators and NC State University scientists were involved from the beginning of the program and were instrumental to its success. Two study sites were monitored intensively forthe next 2 years, during which time no impacts on groundwater were measured and significant decreases in soil acidity and increases in soil nutrient capital and foliar
nutrient concentrations were observed.

During summer 1992, Weyerhaeuser sought authorization from the North Carolina Division of Solid WasteManagement to evaluate spreading and handling equipment and to assess the economic implications of ash application on an operational scale. Before expanding the operation, the ash had to be registered with the NCDepartment of Agriculture as a liming agent or fertilizer, which required agricultural field trial data. Agricultural field trials at two local farms showed that ash wasas effective as commercial lime in neutralizing soil acidity and increased yields of winter wheat and ryegrassclover to a greater extent than lime, presumably due to
the additional nutrients contained in the ash.

Following conditional registration of the ash for useon Weyerhaeuser land, an additional 3-year greenhousefield study with the NC State University Soil ScienceDepartment (F. Cox) led to full registration. The Division of Solid Waste Management then assembled a working committee comprised of representatives from industrial wood-ash generators, the NC Department of Agriculture, and NC State University’s Departments of Soil Science and Biological and Agricultural Engineering to adopt procedures for ash characterization, application rates, best management practices, and reporting.

In 1993, Carolina Silvi-Ash (Weyerhaeuser’s tradename) was approved for land application by the Division of Solid Waste Management. In addition to obtaining regulatory approval, Weyerhaeuser also invited representatives from local and national environmentalgroups to a meeting where research results were presented, environmental concerns were discussed, and mill facilities and landfill sites were visited. Local hunting clubs that lease Weyerhaeuser lands were also informedof the program. No adverse public reaction to the program has been expressed.

Additional operational pilot trials and logistical adjustments increased the efficiency of the program by 45%, making land application of ash economically superior to landfill disposal. Growth trial data showed that ash applied (13 and 27 dry Mg ha -1 ) and incorporated prior to planting increased pine seedling growth 15% after two growing seasons on P-deficient sites. This response was similar to that obtained from triple super phosphate fertilizer. Soil and foliar analyses indicated significant
increases in available P on the sites.

Carolina Silvi-Ash has since been applied toWeyerhaeuser timberlands as a year-round, 5-day-perweek silvicultural operation. During 1996, 15,600 dry Mg of Carolina Silvi-Ash were land applied on 1,800 ha
within an 80 km radius of the mill. About half the ash is applied to “post-thin” plantations and the other halfis applied to “pre-plant” plantations. Although the response of post-thin plantations is minimal at the operational ash application rate used (6.7 dry Mg ha -1 ), these stands continue to be used during the wet season when pre-plant applications are less feasible. The operational, fertilizer replacement rate for pre-plant sites is 28 dry Mg ash ha -1 . Silvicultural use of the ash has proven to be beneficial for two Weyerhaeuser businesses: the Pulp,Paper, and Packaging Division has delayed capital expenditures associated with new landfill construction, and
the Timberlands Division has reduced fertilizer costs.



### Jefferson-Smurfit Mill, Fernandina Beach,
Florida

This kraft mill produces about 180 wet Mg day -1 of aprimary/secondary (80/20) WTP residual mix. Beginning in 1983, forest WTP residual application trials were implemented to determine the effects of the residuals on slash pine ( Pinus elliottii Engelm.) growth (Carr and Gay 1997). Seedling mortality rates exceeded 90% in initial trials when residuals were applied in a 6-inch(15.2 cm) layer to harvested forest land and incorporated before planting. Poor survival rates were attributed to inadequate mineral soil contact with the seedling root systems, resulting in excessively wet and dry conditionsfor the roots. In some cases, bedding appeared to exacerbate the problem by concentrating the residuals where the seedlings were planted. Herbicides were not usedin initial seedling trials and weed competition also reduced seedling growth and increased mortality. BecauseRecycling Paper Mill By-products 203of these problems, 5-8-year-old plantations were subsequently used for the trials, although problems occurred in these stands as well due to the physical effects of the residuals and equipment on tree branches and boles.

To answer questions raised in earlier trials and to address regulator concerns about the benefits and environmental impacts of residual application, an additional pilot study was initiated in plantations ranging in age from 12 to 18 years. One, two, and three annual WTP residual applications (about 9 dry Mg ha -1 ) were used and compared to a control area where residuals were not applied. Three years after the study began, tree height growth was more than 14% greater and volume growthalmost 7% greater after two successive residual applications compared to plots where no residuals had been applied. Foliar analyses indicated negative effects of the residuals on N availability and positive effects on P, K,Mg, and Ca availability (29, 26, 40, and 19%, respectively, greater than on control plots).

Forest WTP residual application has been regulatedunder the mill’s wastewater permit, which requires quarterly testing of residuals. Additional residual characterization studies have also been initiated in conjunctionwith the Florida Pulp and Paper Association, and a formal groundwater monitoring plan for 2 years has beendeveloped for the Florida Department of Environmental Protection. Residual metal concentrations were found to be well below state limits for land-applied municipal biosolids, and a preliminary leachate study found low potential for significant groundwater impacts.

About 55% of primary WTP residuals are currently spread on company-owned forest lands up to 64 km from the mill site. The typical annual application rate is 27 wet Mg ha -1 in three consecutive years on 12-18-year-oldplantations. Buffers are maintained for wetlands, adjacent home sites, and potable water wells. Although theresiduals stimulate weed growth in areas exposed to sunlight, weed competition has not been a significant factor affecting these mid-rotation stands. Forest land application is now a significant component of the mill’sbeneficial use program, which also includes using byproducts in mine reclamation, roadside stabilization,landfill covers, pelletized fuel, and as horticultural media. Additional information on the mill’s solid waste program is described by Carr and Gay (1997).



### CONCLUSIONS

Paper mill by-products have considerable potential forenhancing forest growth and site productivity. The primary benefits of land-applied WTP residuals are relatedto the organic matter and nutrients they provide. N content and availability often dictate rates at which these residuals can be applied to forest lands. The C:N ratio of a residual provides a good first approximation of whether it will be a N source or sink and may be useful in indicating where conservative application rates are advisable prior to initiating field trials. Approximate application rates for WTP residuals can be based on forest response and nutrient uptake data reported in the literature and a practical understanding of the sites in
question.

Although not widely studied, there is evidence thatland application of boiler ash can enhance the productivity of some tree species. Positive effects of ash on loblolly pine growth in the southern U.S. likely result from P added in the ash. Long-term positive effects of ash on the productivity of Scandinavian forests growing on Histosols have been attributed to increased supplies of P, K, and B. Ash application could be particularly beneficial for deciduous tree species, which tend to have higher pH and base cation requirements than conifers. Soil pH optimal ranges for individual tree species are not well documented, however. Although loblolly pine is commonly assumed to grow best at soil pH values below 6.5, there is evidence that ash may promote the growth of this species on some sites with higher soil pH
values.

The response of tree seedlings to land-applied by-products can be particularly difficult to predict due to theirsusceptibility to nutrient deficiencies and weed competition. Consequently, conservative application rates are
recommended until more is known about these factorsand seedling responses for the particular sites in question. Residual quality can sometimes be improved by mixing residuals with fertilizers or with other industrial, municipal, or agricultural by-products. Tree seedling and forest responses can also be greatly influenced by the mode (e.g., surface applied vs. incorporated) and timing of application.

Industry land application programs have shown economic benefits for company waste management and forestry operations. Case studies of successful company programs demonstrate the importance of developing experimental trials and communicating with landowners and regulators early in the process. They also show approaches for addressing logistic and regulatory impediments to land application. Field trials are most effective when a valid experimental design and replicated treatment andcontrol plots are used. Interacting effects of land application treatments and specific management practices should also be assessed, and trials should be extended long enough to determine whether enhanced soil chemi-204 Vance cal and physical properties will contribute to sustainableforest productivity. Some benefits provided by land application may not be revealed in short-term studies.

A major regulatory hurdle facing companies interestedin developing a land application program is the requirement by some states for individual site permits. Individual site permitting can be particularly difficult forcompanies dealing with a large number of small landowners. An alternative to permitting each site to whichby-products are applied may be to register the by-products themselves and to define application rates, buffer zone widths, and other management practices that should be adopted for their safe and effective use across a range of sites. Specific management practices could also bedesignated for by-products or site types where environmental risks are higher.



### ACKNOWLEDGMENTS

I appreciate the information and documentation provided by Quentin Still and Jerry Brelend (Georgia-Pacific Corp.), Pete Steponkus (Weyerhaeuser Co.), and John Carr (Jefferson Smurfit Corp.). I also thank Alan Lucier,Jim Shepard, Reid Miner, and Bill Gillespie for reviewing earlier versions of the manuscript.



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