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Canadian Wood Ash Chemistry Database

This database contains information on the chemical composition of wood ashes sampled from 17 Canadian biomass boilers. The goal of the database is to provide information about the levels and variation in the element concentrations of fly and bottom ashes formed during the combustion of woody biomass, and how they compare with the trace element limits established by the Canadian Council of Ministers of the Environment (CCME) noted in Hannam et al. Regulations and guidelines for the use of wood ash as a soil amendment in Canadian forests (2016)

The database includes the results of chemical analyses of wood ashes collected from 17 boilers: 10 pulp and paper mills and seven bioenergy co-generation facilities. At seven of these facilities, separate samples of bottom and fly ash were collected for analysis. The data presented in the tables and figures below summarize the chemistries of 16 bottom ash samples and nine fly ash samples.

If you have wood ash chemistry data that you can contribute to this database, or ash samples that we could analyze to add new data, please contact Paul Hazlett.

This graph shows that elements volatilized at lower boiler temperatures had lower fly and bottom ash concentrations. Nitrogen, sulphur and phosphorus concentrations were lower in comparison to magnesium, potassium and calcium. Mean nutrient concentrations of fly ash were greater than bottom ash.

Figure 1. pH, carbon and nutrient concentrations of Canadian fly and bottom wood ashes in grams per kilogram (g kg-1). Data represent mean and standard deviation.

Graph data
Table displays the pH, carbon and nutrient concentrations of Canadian fly and bottom ashes in grams per kilogram (g kg-1). Data represent mean and range (in brackets).
pH, carbon and nutrients Fly ash Bottom ash
pH in H2O 11.3 (8.6 – 13.8) 10.8 (7.2 – 12.9)
Total C (g kg-1) 180.9 (27.3 – 429.9) 203.6 (5.0 – 517.7)
Total N (g kg-1) 1.71 (0.40 – 3.84) 0.94 (<0.01 – 2.63)
Total P (g kg-1) 6.3 (3.2 – 10.6) 4.9 (0.1 – 11.9)
Total K (g kg-1) 33.1 (13.5 – 90.8) 24.1 (0.8 – 50.8)
Total Ca (g kg-1) 153.5 (92.0 – 247.9) 103.7 (3.9 – 211)
Total Mg (g kg-1) 14.6 (6.4 – 29.4) 11.8 (0.6 – 33.1)
Total S (g kg-1) 11.0 (0.0 – 47.4) 3.7 (0.0 – 25.9)
 
This graph shows mean concentrations of arsenic, cadmium, molybdenum and selenium for fly and bottom ash were generally greater than Category A Compost limits but less than Category B Compost limits. Wood ash with these levels of trace elements is classified as “restricted”. This ash could be used for land application but would be required to follow provincial and territorial regulations. Guidance documents outlining these regulations are listed in Hannam et al., 2016 (Hannam, K.D., C. Deschamps, M. Kwiaton, L. Venier and P.W. Hazlett.) 2016. Regulations and guidelines for the use of wood ash as a soil amendment in Canadian forests. Information Report GLC-X- 17.

Figure 2. Trace element concentrations of Canadian fly and bottom wood ashes in milligrams per kilogram (mg kg-1). Data represent mean and standard deviation.

Graph data
Table displays trace element concentrations of Canadian fly and bottom ashes in milligrams per kilogram (mg kg-1) for arsenic, cadmium molybdenum and selenium. Data represent mean and range (in brackets). It also displays the Canadian Council of Ministers of the Environment trace metal limits for category A and category B compost.
Trace element Fly ash Bottom ash Category A Compost Category B Compost
Arsenic (mg kg-1) 13.5 (3.6 – 27.9) 20.9 (<0.1 – 139.0) 13 75
Cadmium (mg kg-1) 8.9 (2.3 – 17.8) 2.8 (0.1 – 8.3) 3 20
Molybdenum (mg kg-1) 7.9 (2.9 – 36.9) 3.1 (0.2 – 6.2) 5 20
Selenium (mg kg-1) 9.6 (1.5 – 20.0) 6.0 (<0.1 – 24.2) 2 14
Notes

Category A Compost: Wood ash with trace element concentrations that fall below the limits set for Category A compost by the CCME is considered “unrestricted” and can be used as a soil amendment in any application.

Category B Compost: Wood ash with trace element concentrations that fall above CCME limits for Category A Compost but below the limits for Category B Compost has “restricted” use and “may require additional control when deemed necessary by a province or territory”. Wood ash with trace element concentrations above the limits for Category B Compost “must be used or disposed of appropriately ”.

 
This graph shows mean concentrations of chromium, cobalt, copper, lead and nickel in fly and bottom ash were less than Category A Compost limits.  Wood ash with these levels of trace elements is classified as “unrestricted”, and can be used in any land application. Mean zinc concentrations in fly ash were greater than Category A Compost limits placing these ashes in the “restricted” category. This ash could be used for land application but would be required to follow provincial and territorial specific regulations. Guidance documents outlining these regulations are listed in Hannam et al., 2016 (Hannam, K.D., C. Deschamps, M. Kwiaton, L.

Figure 3. Trace element concentrations of Canadian fly and bottom wood ashes in milligrams per kilogram (mg kg-1). Data represent mean and standard deviation.

Graph data
Table displays trace element concentrations of Canadian fly and bottom ashes in milligrams per kilogram (mg kg-1) for chromium, cobalt, copper, lead, nickel and zinc. Data represent mean and range (in brackets). It also displays the Canadian Council of Ministers of the Environment trace metal limits for category A and category B compost.
Trace element Fly ash Bottom ash Category A Compost Category B Compost
Chromium (mg kg-1) 35.2 (15.0 – 67.9) 41.8 (7.8 – 182.0) 210 1060
Cobalt (mg kg-1) 11.5 (4.8 – 20.1) 9.2 (0.1 – 15.6) 34 150
Copper (mg kg-1) 83.5 (35.0 – 144.6) 62.0 (0.1 – 205.0) 400 757
Lead (mg kg-1) 20.3 (3.3 – 61.3) 55.7 (0.5 – 369.0) 150 500
Mercury (mg kg-1) n/a n/a 0.8 5
Nickel (mg kg-1) 41.5 (10.4 – 184.4) 24.0 (3.3 – 47.0) 62 180
Zinc (mg kg-1) 1178.9 (388.9 – 2661.5) 439.2 (32.1 – 1504.0) 700 1850
Notes

Category A Compost: Wood ash with trace element concentrations that fall below the limits set for Category A compost by the CCME is considered “unrestricted” and can be used as a soil amendment in any application.

Category B Compost: Wood ash with trace element concentrations that fall above CCME limits for Category A Compost but below the limits for Category B Compost has “restricted” use and “may require additional control when deemed necessary by a province or territory”. Wood ash with trace element concentrations above the limits for Category B Compost “must be used or disposed of appropriately ”.

CCME trace element limits in milligrams per kilogram (mg kg-1). These limits were originally developed for compost. Trace element limits for chromium and copper were not established but would be 1060 mg kg-1 and 757 mg kg-1, respectively, if calculated with the same method used to establish limits for the other nine trace elements (Canadian Council of Ministers of the Environment 2005).

Graph. For ashes sampled from the same biomass boiler, trace element concentrations in fly ash were predominately greater than trace element concentrations in bottom ash. Zinc concentrations differed the most between fly ash and bottom ash. Cobalt and nickel were exceptions, with higher concentrations in bottom ash at four of the seven boilers.

Figure 4. Differences in trace element concentrations between paired fly ash and bottom wood ash sampled from seven Canadian biomass boilers. (Different symbols represent individual biomass boilers)

Graph data
Table showing differences in trace element concentrations between paired fly ash and bottom wood ash sampled from seven Canadian biomass boilers.
  Boiler #1 Boiler #2 Boiler #3 Boiler #4 Boiler #5 Boiler #6 Boiler #7
Arsenic 9.0338 3.0292 17.5794 0.1843 -5.3172 -0.7628 3.5364
Cadmium 8.3431 5.1443 13.4973 1.9982 5.1276 8.3074 17.6696
Chromium 4.3652 0.3292 27.6719 -6.503 -4.7022 -3.0197 60.1079
Cobalt 7.9241 -1.3959 8.9762 -4.7974 -0.4784 -1.8794 12.3809
Copper 43.7913 23.6275 43.7123 0.8982 9.1122 -19.8927 142.2584
Lead 14.9886 5.9771 43.6978 3.8695 1.4917 2.134 21.0371
Molybdenum 2.0742 1.6636 3.4668 33.8473 -0.0759 1.0197 3.8438
Nickel 156.5232 -0.4009 16.6552 -4.5393 -1.0324 -3.0928 26.3957
Selenium -1.8575 13.8838 9.4604 -2.9942 4.1309 -4.2297 1.5112
Zinc 1137.6927 561.2883 1777.5209 337.1577 598.3535 565.9733 2629.3787
Notes

Data represent calculated differences between fly ash and bottom ash trace element concentrations for individual boilers. Values that are greater than zero indicate that trace elements were more concentrated in fly ash; values that are less than zero indicate that trace elements were more concentrated in bottom ash.

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