Agricultural Uses of By-Products and Wastes - ACS Publications

Chapter 13

Land Application of Boiler Wood Ash in the Southeastern United States 1

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C. C. Mitchell and E . D. Black 1

Downloaded by COLUMBIA UNIV on January 21, 2018 | http://pubs.acs.org Publication Date: July 1, 1997 | doi: 10.1021/bk-1997-0668.ch013

Department of Agronomy and Soils, 202 Funchess Hall, Auburn University, A L 36849-5412 122 West Lochwood Drive, Cary, NC 27511 2

Most agricultural soils in the southeastern U.S. require periodic application of ground limestone in order to maintain productivity. Using boiler wood ash and combination ash as an alternative to ground limestone is agronomically productive, environmentally safe, and fiscally sound for both the ash producer and the landowner/farmer. While plant nutrient content of ash is variable, it should be considered as an incidental source of plant nutrients, especially Κ and Mg, for field crops. An analysis of boiler ash from 14 Alabama pulp and paper mills averaged 38% CaCO equivalent (CCE) with a dry density of 500 kg m . Although popular concerns are often expressed about land application of metals in boiler wood ash and in combination ash, levels are well within EPA's guidelines for land application of biosolids. There are no published reports of metals being an environmental or crop production/crop quality problem, especially when ash is used at recommended rates as a soil liming material. An analysis of the CCE along with a routine analysis of plant nutrients and selected total metals is needed to utilize ash as a soil amendment. If growers follow a conscientious soil testing program and apply ash as a liming material, some variability in the ash can be tolerated, especially at the rates generally used. Because boiler wood ash is considered a non-hazardous waste, it is regulated by individual states. Where it is being utilized as an agricultural lime or plant nutrient source or soil amendment, the state departments of agriculture regulate its licensing. Hauling and spreading can be a logistical problem because of the physical condition of ash and collection and handling practices by the generator. Nevertheless, research and experience from Maine to Alabama suggest that land application is a safe and practical approach to utilization of boiler wood ash and mixed ash by-products. 3

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Every industry produces wastes, by-products or co-products that must be either disposed or recycled. Economics and government regulations usually determine how they are handled. With increased regulations on public and private landfills, the cost of disposal has increased dramatically over the past 10 years. In 1994, the costs of disposal in public 204

© 1997 American Chemical Society

Rechcigl and MacKinnon; Agricultural Uses of By-Products and Wastes ACS Symposium Series; American Chemical Society: Washington, DC, 1997.


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Use ofBoilerWood Ash

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landfills rangedfrom$8 per U.S. ton in New Mexico to $175 per U.S. ton in New Jersey (1). Industrial and private landfills would probably be more expensive. This has made the economics of alternative uses for some by-products more attractive. Tisdale et al. (2) made the following historical observations: The Bible records the value of wood ashes in its reference to the burning of briars and bushes by the Jews, and Xenophon and Virgil both report the burning ofstubble to clearfields and destroy weeds. Cato advised the vine keeper to burn prunings on the spot and to plow in the ashes to enrich the soil. Pliny states that.. . some farmers burned manure and applied the ashes to their fields. Columella also suggested the spreading of ashes or lime on lowland soils to destroy acidity. There are over 90 wood-fired, electrical cogenerating facilities consuming over 40 million metric tons of fuelwood each year in the 13 southeastern United States (3). Sometimes combinations of wood, coal, oil, or biosolids may be burned. The pulp and paper industry is one of the largest users of renewable, biomass energy sources in the United States. Much of the energy used in the pulping process is derived from the burning of bark, small sized trees, logging slash, andfibrousby-products in boilers (4). More wood may be consumed in the biomass boiler than in the paper making process itself (5). The ash generatedfromthese facilities is bottom ash from the base of the boiler,flyash from cyclones, ashfromwet scrubbers, or, more commonly, a mixture of two or more sources. All are referred to as "boiler wood ash". The U.S. pulp and paper industry is probably the largest generator of producing an estimated 3.6 million metric tons of boiler ash annually which is about evenly divided between coal ash and bark/wood ash (6). In addition, many public and private utilities and wood-using industries burn wood or wood wastes in boilers. The average pulp and paper mill in the southeastern U.S. can produce an average of approximately 18 metric tons pulp and paper products per day (7) 43 metric tons boiler ash per dayfromtheir boilers (8). A1991 survey of 88 pulp and paper mills (9) indicated that most of this ash isfromthe burning of hardwoods, a wood-coal mixture or a woodsludge mixture (Figure 1). Ashfrommixtures of wood, coal, and/or sludge is often referred to as mixed or combination ash. Most of the mills in the southeastern U.S. place their boiler ash in company-owned landfills. Only 5% are land-applying some of their boiler ash and much of the land application activity involves wood ash. Both the survey by Muse in the southeastern U.S. and a national survey by Miner and Unwin (6) report similarfiguresfor ash disposal. Other alternative disposal practices include lagoons, stockpiles, or reuse as construction materials. However, almost 60 percent of the mills contacted by Muse indicated that the company either approved or strongly approved a land application program. In the northeastern U.S., up to 80% of the boiler ash is land-applied (70). Land application of many by-products often seems to be an inexpensive alternative to rising disposal costs (11). However, there are some very practical considerations before committing to such a program whether the by-product is boiler wood ash or some other material. These are the types of considerations the authors have to address frequently when dealing with land application of by-products. Boiler wood ashes have a long history of successful, beneficial use when land applied. Extensive research has been conducted throughout North America and Europe, yet obstacles still are encountered whenever land application of boiler wood ashes are proposed.


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Coal


Sources

Disposition

Figure 1. Sources of boiler ash and methods of ash disposal estimatedfroma 1991 survey of 88 paper mills in the southeastern U.S. (Adaptedfromref. 9).

Environmentally Harmful Properties. Thefirstconsideration is, "Does my by-product have any obvious properties that could be potentially harmful to the environment (soil, plants, animals, water) if land applied?" This may be a difficult one to answer, particularly if it contains traces of metals, carcinogens, or organics that would be rate dependent. However, unless the answer is clearly, "Yes, it does", then it may be a candidate for land application and one can proceed. Most boiler wood ashes are low in metals, organics, and potential carcinogens. There are no cases of boiler wood ashes harming the environment when applied at reasonable rates (12,13,14). Magdoff et al. (14) reported overtiming injury in alfalfa when excess limestone was applied but not when excess ash was used. Research in Oregon has reported poor herbicide efficacy in perennial ryegrass or fescuefieldspreviously treated with "boiler fly ash" as a liming material (unpublished reportfromG.W. Mueller-Warrant, S. Aldrich-Markham, and M.E. Mellbye, USDA-ARS and Oregon State Univ.) Value of Ash. The second consideration is, "Does it have any value if land applied?" If it is inert and has no value as a source of plant nutrients, alternative soil liming material, source of soil organic matter, or other environmentally or agronomically advantageous properties, then one will have a difficult time selling the landowner, a regulatory agency or the public on a land application program. Boiler wood ash, on the other hand, has demonstrated properties of benefit to the land, primarily its neutralizing value as an alternative soil liming material (8,15,16,17) and its plant nutrient content (12,13, 15,18). Research is being conducted by the authors to evaluate its effect on soil physical properties such as bulk density and aggregate stability. Logistics of Application. A third consideration is, "Can we logistically and economically apply it to either our own land or offer it for public use?" Some materials may be too wet, too dusty, too bulky, or too odorous to move and spread economically. If the logistics of handling the materials cannot be economically overcome, then a land application program may not be the best alternative. Boiler wood ash is a product that can be handled and spread successfully (4, 6), but some companies are not willing to make the commitment. The bottom line is economics.



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Use of Boiler Wood Ash

Public Objections. Thefinalquestion to consider is, "Will there be any public objection to a land application program?" Often, there are some public or political objections to almost any activity that involves land application of a by-product. This has led to complicated regulations by many states. However, research and extensive practical experience has failed to identify negative environmental effectsfromapplication of boiler wood ash when used at reasonable agronomic rates. Sometimes, this last issue may be overcome by a good public relations campaign. However, if public objections and potential litigations seem insurmountable, then an alternative to land application may be appropriate. The following is a review of published research reports, journal articles, abstracts, and reports of practical experiences involving the beneficial use and recycling of boiler wood ash and combination ash as an agricultural and silvicultural soil amendment along with unpublished datafromthe authors. Ash Use as Lime From a land application standpoint, the most important property of ash is the total alkalinity, total neutralizing value or potential liming value most often reported as CaC0 equivalent (CCE). Although there have been alternatives to CCE proposed for wood 3

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Agricultural Uses of By-Products and Wastes - ACS Publications

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