Presentation on theme: "Bioremediation of Soils in Afrrica"— Presentation transcript:
1Bioremediation of Soils in Afrrica Africa-US Network of Centers of Excellence in Water & Environmental Science & Technol.Bioremediation of Soils in AfrricaRamble O. Ankumah. Ph.D.Tuskegee University1
2Overview of Soil As Media For Biological & Chemical Reactions 1. Soils contain solids and fluids2. The solids are various inorganic and organic compounds3. The fluids are liquids (water being the solvent) and gases4. The volume of the components of agricultural soils at optimum soil moisture for plants is approximately as follows:
4Field View of Soil a. Soil vs. Regolith Regolith: Unconsolidated material above bedrock: Quite universal1. Can be negligible (shallow) or hundreds of feet thick2. May be material weathered from underlying rock or might have been transported by H2O or wind and deposited upon the bedrock or upon other material covering bedrock.
10Oxides, Hydroxides and Oxyhydroxides Hydrous Oxides of Iron and AluminumpH Dependent and variableAmphoteric i.e. can have positive or negative chargesPositive charge under low pHNegative charge under high pH (0-4mmolc/100g)
14Soil Colloids: Organic Colloids pH Dependent and variableStructure has Carboxylic(–COOH), Phenolic, and hydroxyl (-OH) groups.Dissociation of this groups at various pH results in negative charge.Charge always negative (150 and 550 cmolc/kg)
18Carbon Cycle on Soil Organic Matter (SOM) A. Organic Constitution of Plants:Divided into six broad categories1. Cellulose -most abundant %2. Hemicellulose %3. Lignin %4. Water soluble fraction(simple sugars, amino acids,and aliphatic acids) %
19Carbon Cycle: Assimilation/Mineralization 5. Ether and alcohol soluble (Waxes, fats oilsresins and a number of pigments)6. Protein (have N and S)7. Mineral Component-usuallyestimated by ashing %As plant ages the content of water soluble fraction decreases and the percentage of cellulose, hemicelluose and lignin rises.
20Carbon Cycle: Assimilation/Mineralization B. Carbon Assimilation1. Organic Matter serves two functionsa. Provides energyb. Supplies C for new cell materialsProducts: CO2, CH4, organic acids, Alcohol
21Carbon Cycle: Assimilation/Mineralization Assimilation: Process of converting substrate to protoplasmic carbonMost microbial cells contain 50%Under aerobic conditions 20-40% of substrate C is assimilated and remainder released as CO2.Fungal flora more efficient in C transformation than other groups and releases less CO2.
22Carbon Cycle: Assimilation/Mineralization Fungi and actinomycetes more efficient than Bacteria.During Decomposition Fungi 30-40% C metabolized is used to form new mycelium.Actinomycetes 15-30%Aerobic Bacteria less efficient, assimilates to 5-10%Anaerobic Bacteria 2-5% assimilated
23Carbon Cycle: Assimilation/Mineralization Immobilization: Assimilation of inorganic substrates into complex organic molecules.Determined by utilization of nutrients elements for cell synthesis.Magnitude is proportional to net microbial cells or filament formed and is related to C assimilated by a factor governed by C:N, C:P, C:K, or C:S ratio of the newly generated protoplasm.
24Carbon Cycle: Assimilation/Mineralization C. Decomposition and CO2 Evolution:Most important function of microbial flora is decomposition of organic matter and release of CO2.Degradation is a property of organotrophs (heterotrophs).
25Carbon Cycle: Assimilation/Mineralization D. Process in Organic Matter Transformation.1. Plant and animal constituent disappear under influence of microbial enzyme.2. New microbial cells are synthesized.3. Certain end products of the breakdown are excreted to the surroundings.
26Carbon Cycle: Assimilation/Mineralization E. Decomposition of Soil Organic MatterRate of CO2 release during mineralization of humus varies with soil typeFactors governing humus decomposition area. Organic Matter Level in soilb. Cultivation
27Carbon Cycle: Assimilation/Mineralization c. Temperatured. pHe. Depthf. Aeration
28Carbon Cycle: Assimilation/Mineralization Fresh substrates sometimes accelerate and sometimes reduce humus decomposition.Enhancement is known as priming.2-5% C present in humus can be mineralized per annum.Cultivation enhances O. M. Decomposition.
29Carbon Cycle: Assimilation/Mineralization E. Breakdown of Added Carbonaceous Materials:Factors affecting breakdown of added organic materials.a. Type of materialb. Temperaturec. O2d. pHe. Inorganic nutrientsf. C/N ratio of plant tissue
30Carbon Cycle: Assimilation/Mineralization Nitrogen is the key substrate for microbial growth and hence organic matter breakdown.If the N content is high and the substrate is easily metabolized, organism satisfies N needs from this source.If substrate is poor in N, decomposition is slow, and C mineralizes will be stimulated by the supplement.
31Carbon Cycle: Assimilation/Mineralization F. Mineralization of the Materials and C:N Ratio.1. During mineralization of the compounds containing little N, the C:N ratio tends to decrease with time.2. This results in gaseous loss of C while N remains in organic combinations for as long as C:N ratio in wide.
32Carbon Cycle: Assimilation/Mineralization 3. Thus % of N in residue continues to rise as decomposition progresses.4. Curve approach approximately ratio of 10:1.5. C:N ratio of soil is roughly 10:16. Microbial cells have C:N ratio between 5 to 15 parts C to 1 parts N. approximately 10:1.
33Carbon Cycle: Assimilation/Mineralization Arrangement of plants in order of decreasingrate of Mineralization.1. Sweet Clover %2. Alfalfa %3. Red Clover %4. Soybeans %5. Millet %6. Flax %7. Corn Stalks %8. Sudan Grass %9. Wheat %10. Oat Straw %
34Carbon Cycle: Assimilation/Mineralization Low N content or a wide C:N ratio is associated with slow decay.Example: Incorporation of a residue having a wide C:N ratio.1. Microbes will develop to the extent of available N and other inorganic nutrients.2. All immediately available N will be
35Polysacharides: Cellulose: Introduction Insoluble polymer of β(1-4) linked glucoseThe most abundant organic carbon material in natureMolecular weight appox. 20, millionMost bugs hydrolyze α-linkagesBecause it occurs with other materials and is resistant to degradation it impedes enzymatic attack
37Cellulose: Introduction Generally animals don't metabolize it.Older plant tissues have a lot of it.Cotton fibres about 90% cellulose.About 14,000 isolates can degrade it.Bugs degrading it need supply of N.Decomposition faster under aerobic conditions when N-fertilizers are applied.
38Factors Affecting Cellulose Degradation Occurs from freezing to 65 C, Slow in frozen stateThermomophiles optimumMesophiles C, tolerate CPsychrophiles < 20 CMost soil microbes are mesophilesCellulose not available as source of energySlow type of release, conversion to glucose is very slow.
39Microbiology of Cellulose Degradation Microbes growing on it don't grow fast on cellulose.Ability to degrade cellulose is common in fungi but unusual with bacteria and actinomycetes.Fungi Degrading Cellulose:Aspergillus, Fusarium, Chaetomium, PhomaBacteria:Most popular is Cytophaga, Pseudomonas spp.
40Cellulose Degradation: Microbiology Actinomycetes:e.g. Streptomyces*, Norcodia*, Micromonospora. * Very versitileAll cellulose degrading bacteria and actinomycetes can be isolated at pH 5.5.Montmorillonite reduces activity of cellulases.Cellulose exploited in industry by breaking and fermenting it to ethanol
41Hemicellulose Chemistry: Not a polymer of just glucose but a mixture of glucose, galactose, mannose, glucoronic acid, galactoronic acid, arabinose, and xylose.Hemicellose, generally 50 to 200 units.Polysacharide may exist as a linear chain as with cellulose. Usually branched.
43Degradation of Hemicellulose Only few sugars and uronic acids are common. These are:Pentoses (5 C sugars)-Xylose and Arabinose;Hexoses (6 C sugars)- Mannose, glucose, and galactose;Uronic acids-glucouronic acid and galactouronic acids.
44II. Degradation of Hemicellulose a. Easily degraded than cellulose;b. Hemicellulose disappears initially at a rapid rate and may be due to degradation of part which is physically available.c. Converted to CO2 and microbial cells.
45Degradation of Hemicellulose: Factors 2. Factors Affecting Decompositiona. pH approximately 7b. O2 limitingc. Age Older plant more resistant to decomposition.d. Availability of inorganic nutrientse.g. N
46Microbiology of Hemicellulose Degradation More microbes can degrade it;Microbes not specific, can degrade other things.Microorganisms Utilizing Hemicelloluse:1. BacteriaOrganism SubstrateBacillus Mannan, galactomannan, xylanCytophaga GlactanErwinia XylanPseudomonas XylanStreptomyces Mannan, Xylan
49Lignin: Introduction a. Lignin is the third most abundant plant tissue Most common in woody plants, i.e. about 15-35%.they are slowly degraded.Woody plants contribute most of the lignin which are degraded by the microflora.
50Lignin : I. Introduction b. Lignin is chemically complex and is found in cell walls and also in the middle lamella.c. Lignin can also be found in certain fungi and algaed. Not much known about the biochemistry of lignin degradation.
52Lignin: Decomposition a. Very resistant to degradation (enzymatic)b. Occurs in the presence of oxygen.c. Rate observed far less than cellulose, hemicellulose, and other carbohydrates.d. Well decomposed material has high percentage of lignin.
53Lignin Decomposition e. Aerobic decomposition of corn stalks. 2/3 of total dry matter lost in 6 months and 1/3 of lignin in 6 months.f. Lignins of young tissues disappear more rapidly than mature plants.g. Lignin protects the decomposition of associated polysaccharides by mechanically separating the microorganisms from CHO.
54Factors Affecting Rate and Extent of Lignin Decomposition. 1. TemperatureOptimum temperature is 30oCNo degradation less than 7oC or greater than 37oC.2. Availability of nitrogen3. Aeration4. Plant residue undergoing decayMethoxy groups first-more under anaerobiosis and least under aerobic conditions
55V. Microbiology of Lignin Degradation Numbers of microbes capable of breaking down lignin are small.1. Major microflora are FungiDecomposition of lignin is primarily by fungi.color of the decayed substrate is indicative of the mode of attack.
56Microbiology of Lignin Degradation i. White-rot-Fungi:White rot-fungi are the most active lignin-degrading microorganisms.Their degradation leads to CO2 and H2OSpecies involved are mainly basidiomycetes (Phanerochaete sp., most studied) and a few ascomycetes.
57Microbiology of Lignin Degradation a. Basidiomycetes-Agaricus, Armillaria, Fomes, Pleurotus, Coriolus etc.b. Ascommycetes: Xylaria, Libertella and HypoxylonWhite rot fungi are thought to degrade lignin only in the presence of other degradable substrates which they use as primary energy source
58V. Microbiology of Lignin Degradation ii. Brown-rot Fungi.These degrade the polysaccharides associated with lignin and remove the CH3 subgroups, and R-O-CH3 side chains.This leaves the phenol behind which turn brown upon oxidation.Representative groups include Poria and Gloeophyllum
59V. Microbiology of Lignin Degradation iii. Soft-rot Fungi.Important in wet situations and appear to degrade hardwood lignin more effectively than soft woods.Representative groups are Chaetomium and Preussia2. Aerobic bacteria e.g. Arthrobacter, Pseudomomas, Xanthomonas, Flavobacterium, and Micrococcus.
60V. Microbiology of Lignin Degradation 3. Actinomycetes have been implicated e.g. Streptomyces and Norcardia.Actinomycetes and Bacteria such as Streptomyces and Norcardia and anaerobic G- bacteria such as Azotobacter and Pseudomonas , depolymerize the lignin structure and lower the molecular size.
62VI. Biochemistry of Lignin Degradation: 4. To obtain energy and carbon from the transformation, the ring is opened and the cleavage products either enter the metabolic pathway or are used in biosynthesis.5. Ring opening proceeds by 3 ways.A. Ortho fissionB. Meta Ring FissionC Gentisic Acid Pathway
63VI. Biochemistry of Lignin Degradation: 1. All 3 pathways require molecule O2.2. Reason not much aromatic degradation in anaerobic environment.3. Oxygenase involved is mainly dioxygenase i.e. in ortho Fission.4. Meta Fission limited to alkyl substituted rings.
66Soil Organic Matter (SOM) Degradation of Plant ResiduesMineralization of less resistant C compounds leads to CO2Less resistant C compounds persistRate of decomposition influenced by C/N ratio of material
68Organic Matter Equilibrium C = bm/kWhere:C= The % of soil organic carbon in Equilibrium (tons/ha)b= The annual amount of fresh organic matter added (tons/ha)m= Conversion rate of fresh organic matter in to soil carbon (percent).
69Organic Matter Equilibrium k= the annual decomposition rate of the soil organic carbon (percent)a= the annual addition of organic matter (tons/ha)a = bm
71k and m values k is primarily a function of temperature Values range from 2-5 % in tropical forest to about 1.5 in tropical savannahs.Temperate forest values range from 0.4-1%m is about 30-50% per year
75Organic Matter Effect1. Direct physical/Chemical- soil structure and chemical properties2. Direct biological Effect- Mineralization/Immobilization3. Indirect Biological Effect- Alter/Modify physical and chemical processes
76Organic Matter Management 1. Manipulate existing organic matter through tillage or soil drainage2. Crop residue placement on or in soiland burning to enhance management operations
77Organic Matter Mgt.3. Augment in situ production using green manure, cover or sod crops4. Amendment with organic matter sources such as animal waste and or compost
81In Situ Production of Organic Crops 1. Legume crops2. Green crops3. Animal manure
82Use of Enzyme Activity in Evaluation Bioremediation Evaluation of the use of soil enzyme activities and microbial diversity in determining agricultural and environmental impacts of “soil quality”.Tillage Practices: Conventional vs ConservationOrganic Farming
86Bioremediation of Contaminated Soil-Approaches Bioremediation strategy uses microbes, plants or microbial or plant enzymes to detoxify contaminants.BiodegradationMineralizationCometabolism
87Criteria for Bioremediation Organisms must have catabolic activity to degrade contaminant at a reasonable rateTarget contaminant must be bioavailableSite must have soil conditions conducive to microbial and plant growth
88Bioremediation Strategies Passive or intrinsic bioremediationBiostimulationBioventingBioaugmentationLandfarmingCompostingPhytoremediation