Aluminum salts final content: chapter 2.2
2. Summary of information critical to assessment of toxic under CEPA 1999
2.2 Entry characterization
2.2.1 Production, import, export and use
Aluminum sulphate and aluminum chloride are produced in Canada, while aluminum nitrate is imported. Information on sources and emissions of aluminum salts or aluminum resulting from the use of aluminum salts was initially obtained through an industry survey carried out under the authority of section 16 of Canadian Environmental Protection Act (CEPA) (CEPA 1988; Environment Canada 1997). Information regarding the use of aluminum chloride and aluminum sulphate in water treatment plants was obtained on a voluntary basis from Canadian municipalities with the help of provincial and territorial authorities. In 2007, additional research was conducted in order to review use patterns and quantities of aluminum derived from sources identified in the original assessment, as well as to identify and quantify potential new sources of aluminum to the environment resulting from the application of aluminum salts in Canada (Cheminfo Services Inc. 2008).
Table 2.2 provides estimated production, import, export and consumption values for the year 2006, based largely on input from Canadian aluminum salt producers. Unless otherwise stated, quantities reported in table 2.2 and the accompanying text represent the amount of elemental aluminum present in the respective salts rather than the total amount of the salt. Polymeric forms of the chloride and sulphate are detailed separately, as these salts were found to be commonly used individually or in combination with other salts in water treatment processes. No producers or users of aluminum nitrate were identified for 2006 and, therefore, while it is likely that very small quantities were being imported into Canada in that year for a variety of low volume applications, no numerical data were available. Total Canadian consumption of aluminum as aluminum salts in 2006 was estimated at 16.1 kilotonnes, with aluminum sulphate accounting for approximately 80% of this demand, and polyaluminum chloride (PAC) for the majority of the remainder (Cheminfo Services Inc. 2008). Approximately 80% of the total aluminum demand was for the treatment of drinking water and wastewater at municipalities. Industrial fresh water and wastewater treatment facilities accounted for the majority of the remaining demand in Canada.
|Demand: municipal drinking water treatment plants||4.3||0.1||2.4||6.8|
|Demand: municipal wastewater treatment plants||5.7||0.03||0.07||5.8|
|Demand: industrial fresh water treatment||0.3||0.03||0.67||1.0|
|Demand: industrial wastewater treatment||0.5||0.03||0.44||0.9|
|Demand: pulp and paper additive||1.1||0.01||0.16||1.3|
|Demand: total domestic consumption||12.0||0.3||3.8||16.1|
Five companies produced most of the aluminum salts used in Canada in 2006 (Cheminfo Services Inc. 2008). Imports and exports were roughly in balance, with imports representing approximately 10% of 2006 domestic consumption and exports representing approximately 14% of 2006 production. Alum, PAC and aluminum chlorohydrate (ACH) were the major imported aluminum salts, while PAC and alum were exported.
Total Canadian demand for aluminum salts remained relatively constant between 2000 and 2006 (Cheminfo Services Inc. 2008). Canada's salt producers indicate that the demand for alum and sodium aluminate declined during this period, while PAC, aluminum chlorohydrate (ACH) and polyaluminum silicate sulphate (PASS) increased in use. While overall aluminum salts demand for municipal water treatment has increased slightly, use in the pulp and paper industry has dropped. The overall total amount of aluminum contained in the salts used in Canada has remained constant at close to 16 kilotonnes per year (Cheminfo Services Inc. 2008).
188.8.131.52 Aluminum chloride
Aluminum chloride is used in either anhydrous or hydrated form. In the anhydrous form, it is used as a catalyst, in Friedel-Crafts reactions, in the manufacture of rubber, the cracking of petroleum, and the manufacture of lubricants. In its hydrated form, it is used by the pharmaceutical industry as an active ingredient in deodorants and antiperspirants, as well as in wood preservation, and in the manufacture of adhesives, paint pigments, resins, fertilizers and astringents (Germain et al. 2000; Pichard 2005; Merck 2006). Polymeric forms, primarily polyaluminum chloride (PAC) and the more concentrated and highly charged ACH, are used as coagulants and flocculants in water treatment.
PAC has the highest Canadian production and use volumes of the three aluminum chloride salts. PAC demand increased over the period 2000 to 2006, with greatest quantities being used in the treatment of drinking water (Cheminfo Services Inc. 2008). Similar increased demand was evident in other applications, including industrial freshwater treatment, municipal and industrial wastewater treatment, and as a pulp and paper additive (Cheminfo Services Inc. 2008). Production and demand were substantially lower for both aluminum chloride and ACH. Canadian consumption of aluminum chloride remained stable from 2000 to 2006, while ACH demand increased substantially (Cheminfo Services Inc. 2008). Most of the increased demand was associated with increased applications in industrial wastewater treatment, with slower rates of growth in other applications.
184.108.40.206 Aluminum nitrate
Aluminum nitrate is used as a chemical reagent (catalyst), in the leather tanning industry, as an antiperspirant, as a corrosion inhibitor, and in the manufacture of abrasives, refractories, ceramics, electric insulation, catalysts, paper, candles, pots, artificial precious stones and heat-resistant fibres (Budaveri et al. 1989; Pichard 2005). It is also used as an adsorbent in chromatography for the production of filter membranes, in radiation protection dosimetry in the uranium extraction sector, and as a nitrating agent in the food industry (Merck 2006).
There are no known producers of aluminum nitrate in Canada, and only one user was identified in a survey done in 1997 by Environment Canada (1997). This user reported that less than 400 kg of aluminum nitrate was included in fertilizers for export to the United States. It is likely that very small quantities of aluminum nitrate are being imported into Canada for a variety of low volume applications, including laboratory uses, leather manufacturing, manufacturing of fire works, and other minor applications (Cheminfo Services Inc. 2008).
220.127.116.11 Aluminum sulphate
In Canada, aluminum sulphate is used primarily as a coagulant and flocculant in water and wastewater treatment. There are other applications, however, in the leather industry, the paper industry, as a mordant in dyeing, in the fireproofing and waterproofing of textiles, in resin manufacture, and in the preparation of fertilizers and paint pigments (Germain et al. 2000; Pichard 2005; Merck 2006). The Canadian Fertilizers Product Forum advises that aluminum sulphate (alum) is used as a soil potential of hydrogen (pH) adjuster in the Lawn and Garden industry (2008 email from The Canadian Fertilizers Product Forum to J. Pasternak, Environment Canada; unreferenced). Aluminum sulphate can also be used to waterproof concrete, decolorize petroleum products, and as a formulant in antiperspirants and pesticides (Budaveri et al. 1989). Aluminum sulphate or alum is used in the treatment of eutrophic or mesotrophic lakes, to reduce the amount of nutrients present in the water. Both alum (Al2(SO4)3) and sodium aluminate (Na2Al2O4) are highly effective coagulants and flocculants that adsorb and precipitate soluble phosphorus and other compounds such as organic matter, forming clumps that settle to the bottom of the lake. In saturated solutions, aluminum sulphate is considered a mild corrosive and can be applied to ulcers in concentrations of 5% to 10% to prevent mucous secretion (Pichard 2005). The substance is also used as a food additive and some foods, such as baking powder.
It is estimated that approximately 276 kilotonnes of aluminum sulphate (11.9 kilotonnes on an aluminum basis) were produced in Canada in 2006, 15 kilotonnes (0.6 kilotonnes of aluminum) were imported and 12 kilotonnes (0.5 kilotonnes of aluminum) exported (Table 2.2). Municipal drinking water and wastewater treatment plants were the main users, comprising almost 84% of the total demand for that year. Industrial water treatment facilities and the pulp and paper sector accounted for most of the remaining consumption (15.8%).
2.2.2 Sources and releases
Aluminum sulphate minerals such as aluminite and alunite occur naturally in Canada in certain restricted geological environments. Aluminum chloride and aluminum nitrate do not occur naturally in the environment. Aluminum can be released from natural aluminum sulphate minerals . Since aluminum is a common constituent of rocks, where it occurs dominantly in aluminosilicate minerals (such as kaolinite, boehmite, clay, gibbsite, feldspar, etc.), weathering can slowly release aluminum to the surface environment. Aluminum present in surface waters due to human activites cannot be distinguished from natural aluminum released during weathering of aluminum-bearing minerals.
While aluminum chloride, aluminum nitrate and aluminum sulphate have many commercial applications in Canada, releases of aluminum to the environment from most commercial applications are expected to be small. However, there is potential for release of relatively large amounts of aluminum resulting from the use of aluminum chloride and aluminum sulphate in water treatment plants (industrial water, drinking water or wastewater). In this application, aluminum will react rapidly, producing sludge, usually in the form of aluminum hydroxide (Al(OH)3). Most sludge produced by municipal wastewater treatment plants (MWWTPs) or industries is sent to landfills or spread on land, with the remainder being composted, held in permanent lagoons, or incinerated prior to landfilling (Germain et al. 2000). Most provinces control drinking water treatment plant (DWTP) waste flows through their respective systems of permits and/or approvals. Sludge purged from clarifiers or accumulated in sedimentation basins of drinking water treatment plants (DWTPs) cannot be released directly to the aquatic environment in many provinces. It may be sent to sewers, incinerated with wastewater sludge and landfilled, held in permanent lagoons, spread on land or landfilled. Likewise, backwash waters (used to clean filters) cannot be discharged directly into open water bodies in many provinces where these discharges are often subjected to requirements for pretreatment (diversion to sedimentation ponds) or diversion to MWWTPs. While many provinces do not generally allow direct discharge to surface water of any DWTP effluents containing sludges or backwash waters (Alberta, Manitoba, Ontario and New Brunswick), some of their existing plants may continue to discharge effluents directly to surface waters. Communication with provincial agencies indicates that these provinces are generally requiring some type of environmental impact assessments of the subject discharges with consideration of alternatives to direct discharge. Some existing large plants in these provinces have recently removed their DWTP direct discharges from surface water (Britannia DWTP and Lemieux Island DWTP in Ottawa, ON), or are developing plans for alternatives to direct discharge to surface waters (certain plants in Alberta). In other provinces, direct discharge may be allowed through provincial approvals systems if it is shown that the discharge results in no adverse effects (defined based on varying criteria) on the receiving body of water (Saskatchewan, Nova Scotia and Newfoundland). It should be noted that some provinces and territories either do not have any coagulant usage for drinking water treatment, or they only use very small amounts and have requirements for DWTP effluent treatment destined for surface water (Prince Edward Island, Yukon Territory, Northwest Territories and Nunavut Territory) (Environment Canada unpublished 2008a)
While most aluminum is released in particulate form, a certain proportion occurs as the dissolved metal and it is this form that is considered easily absorbed and therefore bioavailable to aquatic organisms. The following section therefore discusses aluminum releases in general, with additional emphasis given to dissolved forms. This approach was necessary because very few studies examine monomeric aluminum levels in the environment or in anthropogenic releases.
18.104.22.168 Natural sources
Atmospheric deposition of aluminum on land or water is small compared with internal releases by weathering and erosion of rock, soil and sediment (Driscoll et al. 1994). Weathering and erosion of "alum"-containing rocks will release aluminum into soils and streams, in part as Al3+ and other dissolved cationic and anionic species, depending on pH and the availability of complexing ions (Garrett 1998). These releases will be small, however, in relation to releases from weathering and erosion of aluminosilicate minerals.
There are no reliable estimates of the quantities of aluminum released to the environment by natural processes on a global scale, most of which comes from natural aluminosilicate minerals. Quantification of total or dissolved aluminum releases in Canada and elsewhere is very difficult and can provide only a rough estimate. Using Garrels et al.'s (1975) proposed global stream flux of 2.05 g/m² per year, total aluminum releases (including particulate material) were estimated to be approximately 20.45 million tonnes per year for Canada. Studies of weathering flux in selected Canadian and U.S. catchments (Likens et al. 1977; Kirkwood and Nesbitt 1991) yield similar or somewhat lower estimates (2 to 20 million tonnes per year) when extrapolated to the whole of Canada.
22.214.171.124 Anthropogenic sources
Very limited information is available on historical releases of the three aluminum salts. Accidental releases are reported to Environment Canada's National Analysis of Trends in Emergencies System (NATES) database and, more recently, the National Enforcement Management Information System and Intelligence System (NEMISIS). Between 1974 and 1991, 24 events released 316.2 tonnes of aluminum sulphate, mainly to land, and approximately 80% of the spilled material was recovered. Four accidental releases of aluminum chloride occurred in 1986 and 1987, and the product was not recovered on two occasions, resulting in a total release of 18.18 tonnes (Environment Canada 1995). Six spills involving the three aluminum salts subject to this assessment were reported from 1992 to 2008, all for aluminum sulphate. Approximately 40,000 liters of aluminum sulphate were released during these events, to both land and surface water, with no identified recovery of the spilled material. None of the reported incidents related to municipal or industrial effluent discharges (Environment Canada 2008b).
Municipal drinking water and wastewater treatment plants are the main users of aluminum sulphate, aluminum chloride and other aluminum-based polymeric products. Aluminum salts are used as coagulants and flocculants to cause fine materials that are suspended, soluble or both to agglomerate, for subsequent removal via sedimentation and filtration. As part of this agglomeration or coagulation process, most of the aluminum associated with the added aluminum salt hydrolyses to aluminum hydroxide, which precipitates and becomes part of the floc structure. As such, it makes up a part of the sludge generated by the treatment process. A small amount of the aluminum added may stay with the finished water in either colloidal particulate (Al(OH)3) or soluble form (e.g., AlOH2+, Al(OH)2+, Al(OH)3, Al(OH)4-), dictated by the conditions of the treatment process and in particular, the pH (see Figure 2.1 and from Stumm and Morgan 1981) .
While no comprehensive inventory of releases of aluminum associated with commercial use of aluminum salts exists, order-of-magnitude estimates derived from information provided by Canadian producers and users confirm that most releases are associated with wastewater treatment processes (approximately 43% in 2006), with drinking water treatment plants accounting for the majority of the remainder (about 36%; Table 2.3; Cheminfo Services Inc. 2008). All other sources are relatively minor. Again, most quantities are reported in terms of the elemental aluminum present in the respective salts. Approximately three quarters of the releases are to land, including: landfill, application on farms, and permanent lagoons. It is estimated that 5% of the aluminum used at pulp and paper mills for paper sizing is released to water courses (rivers or lakes), while 95% is contained on the paper, which is assumed to receive eventual disposal to landfills and composting in a minor, but growing proportion (2008 email from Canadian Wastewater Association to J. Pasternak, Environment Canada; unreferenced).
in lagoon (land)
|Landfill (land)||Farms (land)
|Municipal drinking water treatment plantsFootnote b.1||0.1||3.2||0.1||2.2||5.7|
|Municipal wastewater treatment plantsFootnote c||0.4||0.06||2.0||4.5||6.9|
|Industrial fresh water treatment||0.02||0.5||0.02||0.4||1.0|
|Industrial wastewater treatment||0.06||0.01||0.3||0.6||0.9|
|Pulp and paper additive||0.1||1.2||1.2|
in lagoon (land)
|Landfill (land)||Farms (land)
|Municipal drinking water treatment plants||1%||20%||1%||14%||36%|
|Municipal wastewater treatment plants||3%||0.4%||12%||28%||43%|
|Industrial fresh water treatment||0.1%||3%||0.1%||2%||6%|
|Industrial wastewater treatment||0.3%||0.05%||2%||4%||6%|
|Pulp and paper additive||0.4%||7%||8%|
Most of the aluminum releases are from the use of aluminum sulphate, which is the aluminum salt having the highest quantity of consumption in Canada (Table 2.4; Cheminfo Services Inc. 2008).
|Drinking water||Receiving water||Storage in lagoon||Landfill||Farms||Total|
Approximately 2% of the total aluminum used by municipalities for drinking water treatment (6.8 kilotonnes; see Table 2.2) ends up in drinking water (Table 2.3; Cheminfo Services Inc. 2008). A survey of 102 Canadian water treatment facilities conducted in 2006 found that over 80% of drinking water treatment plants (DWTPs) that use aluminum salts as coagulants and flocculants measure the concentration of aluminum in the treated water. The survey considered data from municipal drinking water and wastewater treatment facilities across Canada, primarily from larger municipalities (population > 100,000), although a small sample of small-to-medium sized municipalities was included (population range 20,000-100,000; Cheminfo Services Inc. 2008). Outlet concentrations in drinking water at the surveyed DWTPs which used aluminum ranged from 0.005 to 0.2 mg/L, with an average value of 0.067 mg/L. For comparison, Health Canada's Guidelines for Canadian Drinking Water Quality are 0.1 mg/L for conventional treatment plants using aluminum-based coagulants and 0.2 mg/L for other treatment systems using aluminum-based coagulants (Health Canada 2007a).
Less than half of the aluminum used at drinking water plants is released to receiving waters - mostly as solid aluminum hydroxide sludge (Cheminfo Services Inc. 2008). Notable examples of this practice occur in water treatment plants in Toronto. Most of the remaining aluminum is contained in sludge that is sent to landfill. Some of the sludge from drinking water facilities (commonly called "filter backwash solids"), in dilute form, may also be sent to wastewater treatment facilities in the municipality. Results from the 2006 survey suggest that approximately 16% of the aluminum used at drinking water treatment facilities is contained in sludge sent to nearby wastewater treatment facilities. A very small portion (~2%) remains permanently stored in lagoons, which for assessment purposes has been assumed to be a land destination. The 2006 survey did not identify any sludge from drinking water treatment plants going to farms; however, it is possible that some disposal by this method may be occurring in Canada as a small proportion of DWTP sludge was identified for landfarming in the earlier survey conducted for 1995 and 1996 (Germain et al. 2000).
In a study done with sludge from Calgary and Edmonton, AEC (1987) found that less than 0.02% of aluminum bound with sludge (containing 78,187 mg Al/kg dw) was released in water (0.20 to 0.32 mg/L). Srinivasan et al. (1998) studied the speciation of aluminum at six different stages of water treatment at Calgary's DWTP. Total aluminum concentrations ranged from 0.038 to 5.760 mg/L, and dissolved inorganic aluminum concentrations varied from 0.002 to 0.013 mg/L. George et al. (1991) measured monomeric aluminum concentrations of less than 0.06 mg/L in alum sludge from ten different DWTPs containing up to a total of 2,900 mg Al/L; Calgary's DWTP was one of the plants studied.
Calgary's DWTP reported the aluminum content in backwash water following the cleaning of its filters. Dissolved aluminum levels ranged from 0.07 to 0.44 mg/L, and total aluminum concentrations varied from 0.76 to 3.3 mg/L. The backwash waters from this DWTP were not released to the river but were treated and sold as fertilizer (Do 1999).
Most of the aluminum discharged from municipal wastewater treatment plants (MWWTPs) surveyed in the 2006 study is associated with sludge. Approximately two thirds of the aluminum in MWWTP sludge is applied to farmland, with most of the balance (around 30%) being sent to landfill. About 5% of total aluminum releases are to surface waters and a very small proportion (less than 1%) is stored permanently in lagoons (Table 2.3). In Quebec City, the sludge from the drinking water treatment plant is directed to MWWTP where the resulting sludge is dried and incinerated with residential waste (co-incineration). The mineral and non-combustible component of the sludge is then landfilled (2008 email from Canadian Wastewater Association to J. Pasternak, Environment Canada; unreferenced). In most cases, the sludge sent to landfills was first sent for anaerobic digestion (where methane gas is generated from the organic content and used for plant energy) and the remaining solids concentrated to remove excess water. Some provinces (e.g., Alberta, Ontario and Quebec) have guidelines for the disposal of sewage sludge on agricultural land; spreading on agricultural land is permitted only when the pH is greater than 6.0 or when liming and fertilization (if necessary) are done. Although not a common practice, a few of the municipalities participating in the 2006 survey provided measured concentrations for aluminum present in sludge solids from their plants. In general, these values were in the range of 10 to 60 mg per gram of solids (dry basis) (Cheminfo Services Inc. 2008).
Final effluent concentrations of aluminum were not always available for MWWTPs participating in the 2006 survey (Cheminfo Services Inc. 2008). Where data were available, reported concentrations ranged from 0.013 to 1.200 mg/L, with an average value (weighted by water volume treated) of 0.816 mg/L. The form of the aluminum measured was not specified. Many of the MWWTPs surveyed relied on substances other than aluminum to treat wastewater, such as iron salts (ferrous and ferric chloride) and/or polyacrylamides, while others did not use any chemicals in their water treatment process.
Only two respondents to the 2006 survey provided information on aluminum concentrations in receiving waters in the vicinity of their effluent outfalls. The typical background level of dissolved aluminum in Lake Ontario in the vicinity of Toronto was reported to be approximately 0.010 mg/L, while typical concentrations in the North Saskatchewan River near Edmonton were 0.020 to 0.040 mg/L (Cheminfo Services Inc. 2008). These data are insufficient to determine in a useful way the contribution of aluminum from aluminum salt consumption in receiving waters. In the original State of the Science (SOS) report (Environment Canada and Health Canada 2000), it was determined that while extensive data on total aluminum concentrations in Canadian surface water are available, few data exist in areas close to sites where releases occur. The situation for sediment and soil is similar, in that data exist for the Canadian environment in general, but not for areas where releases occur. The state of available relevant concentration data has not changed since 2000.
In addition, changes in policies and procedures relating to the direct release of treatment plant effluents into surface waters have occurred since the publication of the original SOS report. In 1993, a total aluminum concentration of 36 mg/L was measured just downstream of the Regional Municipality of Ottawa-Carleton's (RMOC) DWTP discharge pipe, while the concentration 200 m downstream of the plant was 0.5 mg/L (Germain et al. 2000). Similarly, in 1998, sediment concentrations in the Ottawa River were 125,160, 51,428 and 41,331 mg/kg dw at points closest to, 300 m, and 500 m downstream of the DWTP, respectively, and were significantly elevated compared with control and upstream values of 17,543 and 20,603 mg/kg dw, respectively. In 2008, all wastes from the plant were diverted to a nearby MWWTP, effectively eliminating the direct discharge of aluminum-bearing sludge into the river (Environment Canada 2008c). However, it will likely take some time before conditions in bottom sediment in the vicinity of the DWTP outfall return to those in line with non-impacted areas.
Germain et al. (2000) reported mean total aluminum levels in the effluent of some MWWTPs using aluminum salts. Concentrations varied from 0.03 to 0.84 mg/L, and the maximum value reported by one plant reached 1.8 mg/L. These figures are in the same order of magnitude as those reported by Orr et al. (1992) for 10 Ontario MWWTPs and by MEF and Environnement Canada (1998) for 15 Quebec MWWTPs, and agree well with those of Cheminfo Services Inc. (2008) reported above. Some plants do not use aluminum-based coagulants and flocculants but still reported aluminum levels in their effluents; their mean total aluminum levels ranged from 0.003 to 0.90 mg/L (Germain et al. 2000). Many wastewater treatment plants, such as those in Quebec, receive influents from combined sewers which collect both wastewater and stormwater. In these cases, part of the solids content of the influent will come from urban drainage that could contain aluminum-bearing solids from erosion processes and other sources. The content of wastewater treatment plant influents is determined by the nature and proportions of their primary inputs (residential, commercial, institutional, industrial) and contaminants present in these waters may also appear in the effluent, depending on the treatment process (2008 email from Canadian Wastewater Association to J. Pasternak, Environment Canada; unreferenced).
Federal, provincial/territorial and municipal governments all play a role in managing treated drinking water quality in Canada (Cheminfo Services Inc. 2008). Voluntary guidelines have been established for aluminum concentrations in drinking water, and while provincial/territorial and municipal government authorities recognize these guidelines, they have not been adopted as mandatory standards. For example, in British Columbia, Alberta, Newfoundland and Manitoba, the Guidelines for Canadian Drinking Water Quality - Technical Documents: Aluminum as specified by Health Canada (0.1 mg/L for conventional treatment plants using aluminum-based coagulants and 0.2 mg/L for other treatment systems using aluminum-based coagulants) are recognized, but specific standards have not yet been fully incorporated into operating permits for treatment facilities. In Ontario, Certificates of Approval with a limit of 0.1 mg/L are issued to drinking water treatment plants; however, this limit is included as a guideline rather than a standard. In Quebec, no limits on aluminum content in drinking water are found in the provincial regulations (including the Regulation Respecting the Quality of Drinking Water), and operating approvals are not required by wastewater treatment facilities (Cheminfo Services Inc. 2008).
Similarly, no federal legislation specific to municipal wastewater effluent discharges is in place (Cheminfo Services Inc. 2008). The federal government enforces CEPA (1999) that governs the releases of toxic substances to the environment, and the Fisheries Act that protects Canadian waters against the deposit of deleterious substances into fish habitat. In recent years, federal, provincial, and territorial governments have been working to develop a Canada-wide Strategy for the Management of Municipal Wastewater Effluent through the Canadian Council of Ministers of the Environment (CCME 2008); however, release standards for aluminum are not currently proposed or under development under the Strategy.
Less information is available on industrial releases of aluminum salts. The pulp and paper sector is the primary industrial user of aluminum salts, with applications in water treatment and as a paper additive. Alum is more commonly used for water treatment at mills in the warmer months of the year, while polyaluminum chloride (PAC) and polyaluminum silicate sulphate (PASS) have been found to be more effective winter coagulants. Recent quantitative release data for industrial uses are not available, although average concentrations of residual aluminum in treated water are estimated to be in the range of 0.02 mg/L (Cheminfo Services Inc. 2008). A 35% to 40% decrease in use of aluminum salts as a pulp and paper additive has been reported for the period 2000 to 2006, indicating a significant reduction in demand for this application (Cheminfo Services Inc. 2008).
Germain et al. (2000) reported mean total aluminum levels ranging from 0.46 to 4.8 mg/L in wastewaters released into rivers by the pulp and paper industry over the period 1990 to 1997. Mean total aluminum levels measured for other types of industries ranged from 0.01 to 2.3 mg/L. Since 1995, pulp and paper mills have been subject to the Pulp and Paper Effluent Regulations passed in 1992 under the Fisheries Act. In Quebec, for example, implementation of these regulations has led to a mean reduction of approximately 60% in total aluminum concentrations present in effluents (Germain et al. 2000). Environmental effects monitoring (EEM) reports published by the pulp and paper industry provide information on the distance from point of discharge that is required to dilute an effluent to less than 1% in the receiving water body. In some cases, only a few metres were needed, while in others, up to 300 km was required. In these cases, water input from other watercourses was needed to achieve dilution to 1%.
Sludge containing aluminum from the salts used in industrial water treatment can be sent to landfill or to steam boilers and co-generation units that handle bark, sludge, or other fuels (Cheminfo Services Inc. 2008). Aluminum may be present in the fly ash after burning of the sludge, although a small portion may also be emitted to air along with particulate matter (PM) emissions. No data are available on aluminum concentrations in fly ash; however, potential PM emissions are usually controlled with baghouses, electrostatic precipitators or other PM control systems.
The use of sludge derived from aluminum-based water treatment facilities as a soil amendment is the primary pathway by which aluminum salts enter the terrestrial environment. It is likely that the amount of aluminum added to soil through this practice is small in comparison with aluminum naturally present in soil. Sludge disposal guidelines specifying maximum application rates and soil pH requirements exist for a number of provinces. In Ontario, sludge application rates cannot exceed 8 tonnes solids/ha/5 years and the pH of the receiving soil must be greater than 6.0 or liming is required (ME and MAFRA 1996). Still, potential exists for the release of aluminum into soil due to high amounts of the metal present in sludge residuals (Mortula et al. 2007). In addition, a shift in soil pH at the site of sludge application could mobilize aluminum in the sludge by shifting the chemical equilibrium towards more soluble forms of the metal. Soil acidification may occur during high water discharge events (storm events), when water entering the sludge deposition area has interacted with organic matter or travelled through more acidic upper mineral soils (Pellerin et al. 2002). Aluminum solubilized in this process is then available to be transported to adjacent soils or water bodies along shallow flow paths in the soil.
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