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 cost

while 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 show

that such impediments can be overcome. Economic benefits of land application programs to the mills involved

include 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 also

have 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 lands

that 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 WTP

residuals 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 summarize

the 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) (NCASI

1999) 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 residuals

category, 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. Both

primary 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 mixed

residuals 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 in

residuals, 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 have

high metal concentrations compared to paper mill residuals (Table 1). Concentrations of leachable organic

compounds as determined by the toxicity characteristic

leaching 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 be

determined 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, new

technologies 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 of

those knowledgeable of the processes used, in cooperation with regulatory authorities.

Boiler Ash

Paper industry boiler ash is derived from incinerating

wood 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% (NCASI

1999). 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, it

generally has lower nutrient concentrations and less predictable composition than pure wood ash (Carlson and

Adriano 1993, Bilski et al. 1995). This is also likely the

case 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 a

soil 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 CaCO3

 equivalence, varies widely (Table

3) and depends on the proportion of wood and other
Recycling Paper Mill By-products 195

NCASI*



WisconsinI



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 - 16,000 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 - 14,600 585 440 - 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 90th %* Mean Median

TCDD 92 (1,390) 17 (161) 7 (72) 1 (16)

TCDF 735 (17,100) 65 (1,300) 33 (607) 6 (78)

TEQI 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. The

proportion 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 and

Erich 1990). In one comparison with monocalcium phosphate fertilizer (mixed with CaCO3

 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

CCEI 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 CaCO3 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 more

variable 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 extraneous

sources 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 limitsI

 (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, mill

residuals (and municipal biosolids) may have more potential to enhance long-term site productivity than do

chemical 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 growth

responses have also been reported for mill residuals having C:N ratios of 100:1 to 150:1, however (Harrington

and 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.) basal

area growth, higher application rates either had no effect or reduced it (Bockheim et al. 1988a). This was

attributed to increased growth of lateral branches and

foliage at the expense of the stem. In a later study on

the 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 for

WTP 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 growth

because of increased competition, even though herbicides were used (Shepard 1997). A third trial conducted

by 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, weed

competition can sometimes be reduced from the mulching effect provided by surface-applied residuals (Shields

et 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 quality

significantly. 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 ha1

, 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 applied

to red and white pine stands in Michigan showed positive effects at about 560 kg N ha-1, and a potential for

significant NO3

-

 leaching only at rates exceeding about

840 kg N ha-1 (Brockway 1983, Brockway and Urie 1983).

Elevated NO3

-

 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. 1988b). 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 solution

chemistry 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 NO3

-

 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 (Brockway
198 Vance

et al. 1986). These estimates are based on limiting soil

NO3

-

-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 NO3

-

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 organic

compounds 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 Hotanen

1989, 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 to

40% 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 also

shown 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 successfully

used 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 very

small, 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 base

cations, pH, and anions (Kahl et al. 1996). They suggested an ash application rate of 6 Mg ha-1 to favorably

alter soil exchange chemistry without affecting soil solution chemistry at the site. With some exceptions, Scandinavian studies have shown that ash generally increases

soil 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 in

soil 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 137Cs, the radionuclide

generated from nuclear bomb testing and concentrated

in wood, could pose environmental risks when land applied as ash (Hess et al. 1997). These concerns have

been alleviated, however, by studies showing that landapplied wood ash does not add a significant amount of

137Cs 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 137Cs 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 137Cs 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 effects

on 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 organic

matter. 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 shortly

after 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 stands

on 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 removed

over 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 WTP

residuals 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 where

concerns 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 also

might 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 pulp

and 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 commonly

cited. One is the logistic and technical difficulty associated with coordinating activities between the mill and

forestry operations and with local landowners and contractors. This added coordination and planning places a

burden 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 are

often 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 of

scientific 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 spanning

multiple 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 of

mill by-products and their mode of application. By-products with high nutrient concentrations can stimulate weed

competition 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 discontinuing

existing, 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 kraft

pulp 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 mill

began 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, beginning

in 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. Beginning

in 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 generally

increased 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 was

reduced 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, since

most 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 about

the 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 is

a 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 liability

risk 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 initially

denied. 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. Significant

increases in wood production resulting from the program are also projected. Positive tree and crop responses

have been a primary reason for the program’s success

and 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 has

been recycled back to Weyerhaeuser timberlands annually, replacing commercial P fertilizers applied during

establishment 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 for

the 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 Waste

Management 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 NC

Department of Agriculture as a liming agent or fertilizer, which required agricultural field trial data. Agricultural field trials at two local farms showed that ash was

as 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 use

on Weyerhaeuser land, an additional 3-year greenhousefield study with the NC State University Soil Science

Department (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 trade

name) 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 environmental

groups 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 informed

of 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 to

Weyerhaeuser 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 half

is 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 a

primary/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 conditions

for the roots. In some cases, bedding appeared to exacerbate the problem by concentrating the residuals where

the seedlings were planted. Herbicides were not used

in initial seedling trials and weed competition also reduced seedling growth and increased mortality. Because
Recycling Paper Mill By-products 203

of 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 growth

almost 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 regulated

under the mill’s wastewater permit, which requires quarterly testing of residuals. Additional residual characterization studies have also been initiated in conjunction

with the Florida Pulp and Paper Association, and a formal groundwater monitoring plan for 2 years has been

developed 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-old

plantations. Buffers are maintained for wetlands, adjacent home sites, and potable water wells. Although the

residuals 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’s

beneficial 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 for

enhancing forest growth and site productivity. The primary benefits of land-applied WTP residuals are related

to 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 that

land 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 their

susceptibility to nutrient deficiencies and weed competition. Consequently, conservative application rates are

recommended until more is known about these factors

and 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 and

control 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 sustainable

forest productivity. Some benefits provided by land application may not be revealed in short-term studies.

A major regulatory hurdle facing companies interested

in developing a land application program is the requirement by some states for individual site permits. Individual site permitting can be particularly difficult for

companies dealing with a large number of small landowners. An alternative to permitting each site to which

by-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 be

designated 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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