Burying Black Carbon (Char): Moving Carbon Dioxide from the Atmosphere to Stable Soil Compounds

Transcription

1 Burying Black Carbon (Char): Moving Carbon Dioxide from the Atmosphere to Stable Soil Compounds Presented at: Mountain Resource Management in a Changing Environment Kathmandu, Nepal May, 2012 John M. Galbraith Virginia Tech Blacksburg, VA USA

2 Objectives Identify carbonaceous materials formed from pyrolysis of fresh biological materials, Discuss the role that soot and biochar play in climate change, Summarize the production, properties, and benefits of biochar as a soil amendment, Compare long-term (stable) carbon forms in soils, their ability to offset CO 2 emissions, and ideas for storing carbon in the soil. 8

3 Defining Terms Black carbon is defined here as a by-product from natural and human-controlled pyrolysis of carbon-containing materials, such as fresh animal and plant tissue, manure, hydrocarbons, and fossil fuels Pyrolysis is incomplete combustion in oxygendeprived environments Products are airborne soot and a solid residue 8

4 Soot Soot particles are aromatic compounds such as graphite that stay in the atmosphere days to weeks

5 Biochar and Charcoal Biochar is the solid, moderate carbon (< 60%) residue of pyrolysis of fresh animal and plant tissue. Properties vary considerably but this is a product we are interested in making and using 3 Charcoal is biochar plus ash 9

6 Solid Combustion Products Ash is residue from nearly complete combustion of organic material. Ash contains elements (Ca, Mg, P, Mn, Al, Fe, and Si) that do not combust 11 Carbon content of ash is low, and ash has little intact tissue structure left Activated carbon is high carbon biochar or charcoal treated with O 2, CO 2, or steam to expose carbon atoms

7 Sources of Soot The majority of soot emissions come from the nations that do not have burning or soot emissions policies or enforcement 8 Open fire burning, uncontrolled diesel engine exhaust, and emissions from power plants and smokestacks are the primary (72%) sources of soot. All of these have uncontrolled emissions Pyrolysis under controlled conditions produces almost no soot

8 Impact From Atmospheric Soot Soot strongly absorbs sunlight, which is why it has such a black color 2 Sunlight absorption leads to warming in the atmosphere, and on surfaces where the soot settles. Black carbon is found worldwide, but its presence and impact are particularly strong in Asia. 5

9 Impact From Soot Deposition Warmer air raises Himalayan temp. by ~ 0.6 C. On the Tibetan side, by > 1 C 1 Soot on snow warms the planet about three times more than radiative forcing of CO 2 in snow-covered areas 14 Soot emitted upwind is carried into the snowcovered glacial areas and accelerates melting, glacial lake outburst flooding, and alteration of the hydrology lower in the watersheds. 7, 15

10 Global Warming CO 2 lets sunlight through but traps the heat from reradiating, whereas soot absorbs sunlight directly. These result in radiative forcings of the climate, making it warmer. Soot is second only to CO 2 in net forced warming. A dramatic decrease in emissions of soot would rapidly slow the global warming rate by about half, because it lasts such a short time in the atmosphere.

11 Carbon Cycle Carbon lost as CO 2 exceeds carbon stored in the soil each year, yet soil carbon content is a prime measure of soil quality, and must be preserved (adapted from Brady, N. and R. Weil. The Nature and Property of Soils. 2008)

12 Soil Carbon Sequestration Atmospheric levels of CO 2 will not be decreased unless photosynthesis exceeds CO 2 emissions for a few hundred years, the residence time of CO 2 in the atmosphere 8 18 To effectively and sustainably sequester and store carbon in the soil long-term, you must add and incorporate more organic material than is lost from the soil, and that organic material must be very slowly decomposable

13 The Case for Biochar Humus, charcoal and biochar all have very slow decomposition rates in soil, but conversion from organic matter to humus is a very slow process Only 10-30% of organic matter incorporated into a soil becomes humus, which is 60% carbon, leaving 6-18% of the original carbon in the soil But we can preserve 35-50% of the original 60% organic carbon if we carefully produce biochar and incorporate it into the soil, leaving 20-30% of the original carbon there

14 Picturing Biochar Roughly 40% of the mass is lost and shrinkage occurs during production, but biochar retains much of the physical structure of the source material 9

15 Up Close

16 How Biochar is Made Under Control The organic materials are pre-heated without exposure to flame, releasing water vapor and gasses. An updraft pulls the vapor and gasses away from the plant tissue. The flame and O 2 are pulled away also, producing little soot or smoke. However, the process must be stopped when the gasses are consumed. CO 2, CO, and CH 4 are released during pyrolysis, but this can be minimized by slow burning at low temperatures (400 C).

17 Biochar and Soot Out of Control

18 Biochar Under Control Source: Carbolea

19 Industrial Biochar Production 21

20 Biochar Properties Bulk density = 0.25 g/cm 3 (charcoal ~1.00 g/cm 3 ) Water holding capacity = higher than organic matter Surface area = low temp 15 m 2 g -1, high temp 300 Chemistry = 10-60% C as graphite; rest N, Ca, Mg, P, Mn, Al, Fe, Si 7, 27 ph = 5 at low temp, 8-9 at high temp Base sat = mod. high (Ca, Mg present, not K, Na) C/N ratio = ~ 44:1

21 Biochar Properties Temperature Dependency 20

22 CEC of Biochar CEC ~8 at ph 5, CEC ~15-25 cmol kg -1 at ph The CEC should increase over time. 24 CEC in whole soils = < 10 low ph, low OC like tropical soils 23 but up to 40 in other soils with high clay, OC, or ph. The low ph, low OC, low CEC benefit most from adding biochar rather than humus.

23 Benefits of Adding Biochar to Soil Stores carbon in a long term, stable form Suppresses GHG emissions (CH 4, N 2 O, NH 4+ ) 29 Increases aggregation - increased fungal hyphae Reduces soil acidity, aluminum toxicity as ph rises Increases availability of nutrients as ph rises Increases nutrient storage, so less fertilizer needed Water in tubes is more available than some clays Adsorbs chemicals and pollutants for degradation

24 Likely Sources of Organic Material for Making Biochar 1. Biomass left after processing perennial non-food biofuels on non-arable, non-forested land 2. Agricultural waste coffee bean or rice husks corn husks seed hulls from grains and coffee fruit pits, nut shells, coconut husks, etc 3. Tall grasses 4. Certain reeds, bamboo, cane 5. Sprouting shrubs

25 6. Pruned branches from palm banana, plantain tea coffee 7. Plants hand-harvested for weed control Unpalatable or noxious weeds and brush Invasive plants that need control to prevent seeding/spread

26 Improving Biochar Properties Biochar in pure form is not inherently fertile and soil microbes rapidly remove any labile carbon Therefore, renewable sources of fertility should be mixed with the biochar before application: compost type A biosolids urine by-products from food processing bones metal, hormone and antibiotic-free manure

27 EX: Improve Compost With Biochar Source: Biochar Farms

28 Aggregating Powdery Biochar Powdery biochar that is inhaled is a health hazard, so it should not be applied dry Powdery biochar should be mixed with a binder wet manure wet compost wet soil The wet mix should be stirred into clumps or pressed into pellets or aggregates

29 Pellets and Briquettes pellets Photo: alextiller/flickr

30 Rates of Biochar Application 50 t ha -1 ( kg m -2 ) needed to completely change the soil chemistry in farm fields or forests lb ft 2 (1-5 kg m -2 ) gardens 25 Simple formula: mix 50% soil, 25% biochar, 25% compost or fertility source by volume Use soil tests before and after to determine soil properties, and repeat timing

31 Field Scale

32 Spot Applications International Biochar Institute

33 Slash-and-char Instead of Slash-and-burn Slash-and-burn (hot fires) leaves about 5% of the carbon behind, but slash-and-char (cool, humid, nonwindy, low litter) leaves about 50% carbon 20 If humans are to burn, then they should burn as infrequently as necessary Char Burn

34 Soil Carbon Storage Potential Soil humus is made of more resistant compounds like like fulvic and humic acids and humin 31 Humin humic acid fulvic acid s 100s < 100 Some of the humin may be the residue of burned carbon 31 Organic materials trapped inside of oxide-coated aggregates (true in many tropical soils) may last up to 5000 years 31

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36 (Spodic) Al-humus Complexes, + Fe Metals such as Al or Fe or their oxides may form complexes with low molecular weight organic compounds in acid, sandy soils The age of some of the complexes has been measured at < 500 yr, but cemented versions may take approximately 3,000 to 8,000 yr to form, then last indefinitely 29

37 Biochar Biochar as a soil amendment has been known to persist for several hundreds to thousands of years in (terra preta) soils 32 The carbon source may have been a combination of burned litter, bones and other cooking/eating waste, possibly manures The soils have properties that reverse the infertility and acidity of dominant soils in wet tropical regions, and are still being farmed today sustainably, even sold as topsoil 31, 32

38 Terra Preta Soils Tropical Acidic Soils Transformed into Fertile Soils These soils occur on the same landform. Additions of char, bones, and organic waste

39 Summary of Organic Carbon in Soil All three of the organic carbon forms mentioned last longer in the soil than CO 2 does in the atmosphere Humus very slowly forms from some of the organic matter added into the soil, but only 10-30% of organic matter becomes humus And we cannot recreate the soil forming processes that allow humus to form complexes with a metal such as Al or Fe But we can save up to 5 times the carbon of humus, and produce and incorporate biochar rapidly

40 Consider In Japan, about 9% of the charcoal is used for agriculture. Estimates say that by 2100 we could store as much carbon in the form of biochar as we emit in CO 2 34, 35

41 Inconvenient and Costly The world community is suffering from malpractices, and the world community must invest in change Producing biochar (and clean heat) can be done with subsidized stoves for households Landowners must be compensated AT A FAIR MARKET PRICE for returning carbon to the soil as organic matter or biochar at the proper equivalent rate, or no change in current practices will take place Other people can sell biochar on the open market Proof of carbon added can come from soil tests provided. IT IS THE ONLY PROOF for Selling CCredits

42 Conclusions Biochar lasts at least 10 times longer in the soil than CO 2 does in the atmosphere, so reducing soot and adding biochar or 3-5x the organic matter to soil could eventually reduce warming Biochar can be more easily produced than any of the other carbon forms that store carbon for long periods in the soil Biochar can be enhanced, benefits the soil, and the production can be done with little harm to the atmosphere if done under controlled conditions

43 Isn t This a Good End?