Hazardous Industrial Waste Treatment - Chapter 10 potx

This chapter addresses three major subsections of the entire industry: a wood preserving, both steaming and Boulton processes; b insulation board manufacturing; and c both wet – wet S1S

Treatment of Timber Industry Wastes

Lawrence K Wang

Zorex Corporation, Newtonville, New York, U.S.A., and

Lenox Institute of Water Technology, Lenox, Massachusetts, U.S.A

The timber products processing industry encompasses manufacturers and processors who use forest materials to produce their goods and merchandise Fifteen distinct subcategories of manufacturers and/or processors are engaged in the utilization of timber This chapter addresses three major subsections of the entire industry: (a) wood preserving, both steaming and Boulton processes; (b) insulation board manufacturing; and (c) both wet – wet (S1S or smooth one side) and wet – dry (S2S or smooth two side) hardboard manufacturing

The number of dischargers in the timber products processing industry in the United States can be broken down as follows: (a) 19 direct dischargers; (b) 55 indirect dischargers; and (c) 172 zero dischargers

The timber industry treats timber and wood products with chemical preservatives to protect the wood from degradation due to various organisms including fungi, and insects such as borers and termites This treatment extends the range of applications and the service life of the wood By design, the chemicals used to protect wood must be toxic to the target organisms, but they may also affect nontarget organisms and the environment [1]

The following groups of preservatives are commonly used for wood preservation: (a) copper chrome arsenate (CCA); (b) copper-based alternatives to CCA [ammoniacal copper quaternary (ACQ) and copper azole]; (c) boron; (d) creosote; and (e) pyrethroid- and metal-based light organic solvent preservatives (LOSPs) Section 10.2.1 presents a complete list of toxic chemicals used in wood preservation in the United States

Copper chrome arsenate (also known as CCA or chromated copper arsenate) consists of three metals: copper, chromium, and arsenic All three metals pose a risk to the environment Both hexavalent chromium and arsenic can cause cancer in humans The CCA concentrate is diluted with water to create a working solution that is used in the pressure treatment of timber CCA-treated timber is commonly a greenish color, but this is also often the case with the other copper-based preservatives CCA-treated timber is registered for use by the industrial countries under their laws The registered uses include internal building uses and external uses such as decks, walkways, fences, playground equipment and retaining walls, and some marine water applications such as wharfs and jetty piles

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10.1.2 Air Pollution and Health Hazards Published results of scientific studies indicate that copper, chromium, and arsenic slowly leach from CCA-treated timber products All three metals pose a risk to human health and the environment, but also exist naturally in the environment in varying concentrations

Based on currently available evidence, CCA-treated wood does not pose any significant risk to the public However, as arsenic is a known human carcinogen, it would be prudent to avoid unnecessary exposure to it Some common sense tips to minimize unnecessary exposure to CCA-treated timber are: (a) treated wood should never be burned in open fires, stoves, fireplaces,

or residential boilers; (b) hands should always be washed thoroughly after contact with any treated wood, especially before eating and drinking; (c) food should not come into direct contact with any treated wood; and (d) precautions should be taken to wear protective gear when working with CCA-treated wood

Small quantities of household CCA-treated timber waste (e.g., offcuts from a small job) could be placed in the owner’s rubbish bin, with the rest of owner’s household waste CCA-treated timber waste from larger household building and demolition jobs is classified as inert waste, and can be disposed of to most suburban landfills

CCA-treated timber waste from industrial sources should only be disposed of to certain landfills CCA-treated timber waste must not be burned or used as such

The timber industry is moving away from using pesticides such as CCA and creosote The United States and Canada have moved to phase out the use of CCA to treat timbers intended for residential uses after December 2003 and Europe after June 2004 This trend appears to be driven by recent European risk assessments of arsenic, the application of the “precautionary principle,” and by perceived consumer demand shifts in North America [1]

The United States Environmental Protection Agency (USEPA) granted the cancellation of CCA registration for most residential uses of treated timber following an application to do so from the wood preservation industry From January 1, 2004, the USEPA will not allow CCA products to be used to treat timber intended for most residential uses The USEPA is continuing

an assessment of the risks posed to children by arsenic leaching from CCA-treated timber The European Commission has announced a partial prohibition on the use of CCA-treated timber, to take effect after June 2004 In addition to the residential uses being restricted in the United States and Canada, CCA preservatives will also not be used in the EU for timber destined for marine and most agricultural uses

The New Zealand Environmental Risk Management Authority (ERMANZ) has decided not to change the registration of CCA following a recent review of the potential public health risks arising from the continuing use of CCA-treated timber ERMANZ found that the extent of any risk to public health arising from CCA remains unclear but is considering further investigation into the possible environmental and occupational health risks arising from CCA

The Ministry of Environment and the Ministry of Health of Manatu Hauora [2] announced their Guidelines for Selected Timber Treatment Chemicals in 1997

10.1.5 Cleaner Production and Economy

Cleaner production aims at avoiding the generation of waste and emissions, by making more efficient use of materials and energy, through modifications in the production processes, input materials, operating practices, and/or products and services [3,4] Van Berkel [4] illustrates how the timber industry and other industries were able to implement cleaner production practices and technologies

Aruna and Mercer [5] state the timber economy of the Mid-Atlantic Region in the United States Specifically, the health and sustainability of ecosystems in an eight state region for the forest industries (including the timber industry) have been assessed Wang and colleagues [6], meanwhile, present the costs of various wastewater treatment systems

General descriptions and process descriptions for the major subcategories of the timber products processing point source category are introduced in this section

Creosote, pentachlorophenol (PCP), and formulations of water-soluble inorganic chemicals are the three most prevalent types of preservatives used in wood preserving The most common of inorganic chemicals are the salts of copper, chromium, and arsenic Fire retardants are formulations of salts, the principal ones being borates, phosphates, and ammonium compounds

Of plants in the United States, 80% use at least two of the three types of preservatives Many plants treat with one or two preservatives plus a fire retardant

There are two basic steps in the wood preserving process: (a) preconditioning the wood to reduce its natural moisture content and to increase permeability; and (b) impregnating the wood with the desired preservatives

The preconditioning step may be performed by one of several methods including (a) seasoning or drying wood in large, open yards; (b) kiln drying; (c) steaming the wood at elevated pressure in a retort followed by application of a vacuum; (d) heating the stock in a preservative bath under reduced pressure in a retort (Boulton process); or (e) vapor drying, heating of the unseasoned wood in a solvent to prepare it for preservative treatment All of these preconditioning methods have, as their objective, the reduction of the moisture content in the unseasoned stock to a point where the requisite amount of preservative can be retained in the wood

Conventional steam conditioning (open steaming) is a process in which unseasoned or partially seasoned stock is subjected to direct steam impingement at an elevated pressure in a retort The maximum permissible temperature is set by industry standards at 1188C and the duration of the steaming cycle is limited by these standards to no more than 20 hours Steam condensate formed in the retort exits through traps The condensate is discharged to oil – water separators for removal of free oils Removal of emulsified oils requires further treatment

In closed steaming, a widely used variation of conventional steam conditioning, the steam needed for conditioning is generated in situ by covering the coils in the retort with water from a reservoir and heating the water by passing process steam through the coils The water is returned

to the reservoir after oil separation and reused during the next steaming cycle There is a slight increase in volume of water in the storage tank after each cycle due to water exuded from the

wood A small blowdown from the storage tank is necessary to remove this excess water and to control the level of wood sugars in the water

Modified closed steaming is a steam conditioning process variation in which steam condensate is allowed to accumulate in the retort during the steaming operation until it covers the heating coils At that point, direct steaming is discontinued and the remaining steam required for the cycle is generated within the retort by utilizing the heating coils Upon completion of the steaming cycle, and after recovery of oils, the water in the cylinder is discarded

Preconditioning is accomplished in the Boulton process by heating the stock in a preservative bath under reduced pressure in the retort The preservative serves as a heat transfer medium After the cylinder temperature has been raised to operating temperature, a vacuum is drawn, and water, which is removed in vapor form from the wood, passes through a condenser to

an oil – water separator At this point low-boiling fractions of the preservative are removed The Boulton cycle may have a duration of 48 hours or longer for large poles and piling This fact accounts for the lower production per retort day as compared to plants that steam condition The vapor-drying process consists of exposing wood in a closed vessel to vapors from any one of the many organic chemicals that are immiscible with water and have a narrow boiling range

The following is a summary of toxic pollutants found in significant quantities in the wood preserving category [7,8]:

Insulation board is a form of fiberboard, which in turn is a broad generic term applied to sheet materials constructed from ligno-cellulosic fibers Insulation board is a “noncompressed” fiberboard, which is differentiated from “compressed” fiberboards, such as hardboard, on the basis

There are more than 16 insulation board plants in the United States with a combined annual production capacity of over 330 million square meters (3600 million square feet) on a

13 mm (0.5 in.) basis Sixteen of the plants use wood as a raw material for some or all of their production One plant uses bagasse exclusively, and one plant uses waste paper exclusively for raw material Four plants use mineral wood, a nonwood-based product, as a raw material for part

of their insulation board production Five plants produce hardboard products as well as insulation board at the same facility

Insulation board can be formed from a variety of raw materials including wood from softwood and hardwood species, mineral fiber, waste paper, bagasse, and other fibrous materials

In this section, only those processes employing wood as raw materials are considered Plants utilizing wood may receive it as roundwood, fractionated wood, and/or whole tree chips Fractionated wood can be in the form of chips, sawdust, or planer shavings

The toxic pollutants found in significant quantities in insulation board manufacturing wastewater are:

Hardboard is a form of fiberboard, which is a broad generic term applied to sheet materials constructed from ligno-cellulosic fibers Hardboard is a “compressed” fiberboard, with a density

13 mm (nominal 1/12 to 7/16 in.)

Production of hardboard by the wet process method is usually accomplished by thermomechanical fiberization of the wood furnish One plant produces wet – dry hardboard using primarily mechanical refining

Dilution of the wood fiber with fresh or process water then allows the formation of a wet mat of a desired thickness on a forming machine This wet mat is then pressed either wet or after drying Chemical additives help the overall strength and uniformity of the product The uses of manufactured products are many and varied, requiring different processes and control measures The quality and type of board are important in the end use of the product

Hardboard that is pressed wet immediately following forming of the wet-lap is called wet – wet or smooth-one-side (S1S) hardboard; that which is pressed after the wet-lap has been dried is called wet – dry or smooth-two-side (S2S) hardboard

There are about 16 wet process hardboard plants in the United States, representing an annual production in excess of 1.5 million metric tons per year Seven of the plants produce only S1S hardboard Nine plants produce S2S hardboard Of these nine, five plants also produce insulation board, while three plants also produce S1S hardboard

The toxic pollutants found in significant quantities in the hardboard manufacturing wastewater are [8]:

Nickel

The timber products processing industry was analysed in a screening program for the 129 USEPA priority pollutants Those pollutants detected in screening were further analyzed in a verification sampling analysis The minimum detection limit for toxic organics is 10 mg/L and for toxic metals, 2 mg/L Any concentration below its detection limit is presented in the following tables as BDL, below detection limit

The quantity of wastewater generated by a wood preserving plant is a function of the method of conditioning used, the moisture content of the wood being treated, and the amount of rainwater draining toward the treating cylinder Most wood preserving plants treat stock having a wide range of moisture contents Although most plants use predominantly one of the major conditioning methods, many plants use a combination of several conditioning methods, and the actual quantity of wastewater generated by a specific plant may vary considerably The average wastewater volume from 14 Boulton plants is reported to be 21,200 L/day (5600 gal/day) or

wastewater volume for 10 plants that treat significant amounts of dry stock is 13,300 L/day

Tables 1A and B present the concentrations of toxic pollutants found in streaming

presents the concentrations of toxic pollutants found in both streaming and Boulton subcategory treated effluent (Source: USEPA)

Insulation board plants responding to the data collection portfolio reported fresh water usage rates ranging from 95,000 to 5,700,000 L/day for process water (0.025 – 1.5 MGD) One insulation board plant that also produces hardboard in approximately equal amounts, uses over

15 million L/day (4 MGD) of fresh water for process water

Water becomes contaminated during the production of insulation board primarily through contact with the wood during fiber preparation and forming operations The vast majority of pollutants are fine wood fibers and soluble wood sugars and extractives More specifically, potential sources of wastewater in an insulation board plant include: (a) chip washwater; (b) process whitewater generated during fiber preparation (refining and washing); (c) process whitewater generated during forming; and (d) wastewater generated during miscellaneous operations (dryer washing, finishing, housekeeping, etc.)

The average unit flow for an insulation board mechanical refining plant is 8.3 L/kg (2000 gal/ton), assuming the plant produces a full line of insulation board products and practises

found in insulation board manufacturing raw wastewater [8]

Table 1A Concentrations of Toxic Pollutants Found in Streaming Subcategory

Raw Wastewater

Metals and inorganics

Phthalates

Phenols

Monocyclic aromatics

Polycyclic aromatic hydrocarbons

Halogenated aliphatics

BDL, below detection limit.

Source: USEPA.

Table 1B Concentrations of Toxic Pollutants Found in Boulton Subcategory Raw Wastewater

Metals and inorganics

Phthalates

Phenols

Monocyclic aromatics

Polycyclic aromatic hydrocarbons

Halogenated aliphatics

BDL, below detection limit.

Source: USEPA.

Table 1C Concentrations of Toxic Pollutants Found in Both Streaming and

Boulton Subcategory Treated Effluent

Metals and inorganics

Phthalates

Phenols

Monocyclic aromatics

Polycyclic aromatic hydrocarbons

Halogenated aliphatics

BDL, below detection limit.

Source: USEPA.

10.3.3 Hardboard Manufacturing Wastewater Significant amounts of water are required for production of hardboard by wet process Plants responding to the data collection portfolio reported fresh water usage rates for process water ranging from approximately 190,000 to 19 million L/day (0.05 – 5 MGD) One plant produces both hardboard and insulation board in approximately equal amounts, and reported fresh water use of over 15 million L/day (4 MGD)

Process water becomes contaminated during the production of hardboard primarily through contact with the wood raw material during the fiber preparation, forming, and, in the case of S1S hardboard, pressing operations The vast majority of pollutants in the wastewater consist of fine wood fibers, soluble wood sugars, and extractives Additives not retained in the board also add to the pollutant load

Process whitewater is the water used to process and transport the wood from the fiber preparation stage through mat formation Process whitewater produced by the dewatering of stock at any stage of the process is usually recycled to be used as stock dilution water However,

in order to avoid undesirable effects in the board when elevated concentrations of suspended solids and dissolved organic materials occur, excess process whitewater is discarded

Potential wastewater sources in the production of wet process hardboard include: (a) chip washwater; (b) process whitewater generated during fiber preparation (refining and washing); (c) process whitewater generated during forming; (d) hot press squeezeout water; and (e) wastewater generated during miscellaneous operations (dryer washing, finishing, housekeeping, etc.)

A unit flow of 12 L/kg (2800 gal/ton) is considered to be representative of an S1S hardboard plant that produces a full line of hardboard products and that practises internal

Table 2 Concentrations of Toxic Pollutants Found in Insulation Board Subcategory Raw Wastewater, USEPA Verification Data

Toxic pollutant (mg/L)

Number of

Metals and inorganics

Toxic organics

BDL, below detection limits.

Source: USEPA.