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Applied Environmental Geoscience (ESE 3.22) Dr. Bill Dudeney Room B339 RSM Department of Earth Science and Engineering

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Presentation on theme: "Applied Environmental Geoscience (ESE 3.22) Dr. Bill Dudeney Room B339 RSM Department of Earth Science and Engineering"— Presentation transcript:

1 Applied Environmental Geoscience (ESE 3.22) Dr. Bill Dudeney Room B339 RSM Department of Earth Science and Engineering Spring term 2006 Tuesday – Keynote lectures Friday – Coursework One day field work at Silwood Park Session 7 (3 hours) – Soil and waste management

2 Objectives This lecture considers the science and technology of bulk mineral and organic materials in the biosphere, and their sustainable management to minimise despoilation of the environment. In this context, the main materials are Soils, soil amendments and artificial soils Waste mineral matter: mine and quarry waste, construction and demolition (C&D) waste, incinerator ash and general industry waste Waste organic matter: municipal and industrial sludge, green waste, and domestic and industrial rubbish Anthropological use, re-use and release of materials to the environment is regulated by law, particularly integrated pollution, prevention and control legislation (IPPC) covering land, air and water. Concentrations in the environment are governed partially by natural physicochemical and biological processes and partially by man-made environmental control processes. As the medium of microbes (water) occurs throughout the biosphere, their activities figure prominently

3 Soil formation and horizons Primary soil formation is by weathering of rocks, and movement of fine-sized products by interactive geological and hydrological processes, involving diverse physicochemical and biological (mainly microbiological) change Mature soil may be described in terms of three distinctive horizons: A: 5-10 cm topsoil containing most organics and microbes B: subsoil with solubles and fines leached from the topsoil C: weathered rocks, often from which the soil originated Bedrock or other strata underlie these horizons. Sometimes there is a humus layer on the surface After Manahan

4 Typical interactions in soil formation Soil is formed primarily by disruption of rock matrices and mineral debris (regolith) by weathering and transportation of products by erosion. These processes occur mostly at or near the surface to form mixtures of small particles (having large surface area), many of which are hydrated, porous and surface-active. Five environmental factors determine soil development: climate, organic activity, relief of land, parent material and time. Weathering is a complex physical, chemical and biological phenomenon. It may be exemplified as follows. - Physical: rocks are wedged apart along planes of weakness by thermal expansion and contraction, e.g., during freeze-thaw cycles - Chemical: mainly acid dissolution, oxidation and hydrolysis. For example, feldspars hydrolyse to clay minerals, e.g., orthoclase forms kaolinite and potash 2KAlSi 3 O 8 + 2H + + 9H 2 O = Al 2 Si 2 O 5 (OH) 4 + 2K + + 4H 4 SiO 4 - Biological: mainly microbial catalysis of processes, e.g., oxidation of iron in basalt. In relatively soft ground, animals burrow, aerate and mix mineral/organic material

5 Microbes in soil formation Exposed rocks and monuments are frequently inhabited by algae, lichens and/or mosses. These organisms are able to remain dormant when the surface is dry and grow when moisture is present. As we have seen, they are phototrophic and produce organic matter which can be used by chemoorganotrophs Chemoorganotrophs produce carbon dioxide during respiration, which leads to an acidic medium. Some also produce metabolic acids. Acidity causes slow incongruent rock dissolution Cracks and crevices collect the resulting ‘raw’ soil, which becomes a medium for pioneering higher plants. Their roots penetrate further into planes of weakness and increase rock fragmentation. Root excretions then promote the development of a rhizosphere (soil around plant roots) and accompanying microflora When the plants die, their remains are added to the soil and become nutrients for more extensive microbial development. As water percolates it carries metabolites downwards, which aid further weathering. As the soil layer deepens, larger plants are accommodated and soil animals invade to mix and aerate. The course of hundreds of years gravitation of materials results in the formation of a soil profile Lichens on monument After J.R. Laundon

6 Soil as a microbial habitat Measurements with microelectrodes have shown that oxygen concentrations can vary over the full scale (0-10 mg/l) within a few mm and thus form a number of pseudo-concentric microenvironments within single small soil particles - see next slide. Other microbial nutrients may also vary over very short distances (and times) Thus, various physiological types of microbes could co-exist in single soil particles: - anaerobes near the centre - microaerophiles further out - aerobes in the surface 2-3 mm - facultative organisms throughout The most extensive microbial growth takes place on the surfaces of soil particles, usually within the rhizosphere - see slide after next Soil aggregates are composed of mineral and organic components, together with water (soil solution) and air. Concentrations of microbes are immobilised on the particles (not in soil solution) - see next slide. These concentrations depend upon the nutrient status, i.e., availability of N,P&K, etc.

7 Soil particles and aggregates After Brock Typical O 2 % contours in a soil particle Typical soil aggregate with air, water and microbial colonies

8 Microbes on soil particles (a) SEM images of soil microbes: (a) rod-shaped bacteria, 1-2 μm (b) Actinomycetes spores, 1-2 μm (c) fungal hyphae, 4 μm

9 Soil particle size and composition Soil has the particle size range and composition suited to, and provides the site for, most plant growth and food production Particle sizes in soils are classified as: - gravel >1.5 mm - sand mm - silt 2-50  m - clays <2  m Particle size distribution largely determines soil texture, e.g., loam is about 40, 40 and 20% of sand, silt and clay, respectively. The triangular diagram shows different textures, e.g., following the heavy lines shows the position of a soil containing 60, 20 and 20% silt, clay and sand Soil contains a wide and variable range of mineral, organic and aqueous components (alive and dead) and receives a diverse range of additives, both useful (e.g., air, water, fertilisers and organic conditioners) and contaminating (e.g., acid rain and wind-blown dust). Contaminated soil is studied in ESE After Pipkin, Trent & Hazlett

10 Soil classification 1. Weathering loosens grains 3. Stream transports grains 4. Stream deposits grains on beach 1. Rain erodes the grains and washes them into the stream The word soil has different meanings to different professional groups. - geologists observe weathered rock and mineral grains, discuss residual and transported soils, e.g., loess (wind blown silt), and often classify soil on a grand scale according to climatic origin, i.e., pedalfers and pedacols of humid and desert temperate regions; laterites of the tropics; and tundra of near polar conditions - agriculturists concern themselves with what will grow in prevailing climatic conditions; with soil texture (see previous slide), humus content, fertility, pH, workability, drainage and the balance between coarse and fine-sized components - engineers see easily moved material with suitable mechanics for groundwork and construction Despite different opinions, three generally useful broad classes of soil can be identified by applied geoscientists: mineral (primarily rock and mineral weathering), organic (sedimentation in bogs and marshes) and formulated (anthrologically altered, balanced or mixed). A detailed a international classification is available for professional soil scientists, having: - a non-genetic basis (physical characteristics are highlighted, not origin) - a comprehensive system (anthropologically modified soils are classified with natural ones) - consistent nomenclature (soil names convey information about physical characteristics) After Pipkin, Trent and Hazlett

11 Amended and formulated soil media Available soils. Most soils in populated areas have been much altered by use and re-use. In former industrial areas, e.g., mine sites, topsoil may be absent because of historical removal. During restoration, artificial topsoil (ATS) may be required Conditioners and fertilisers. Compost, e.g., from sewage sludge and green waste, is a typical soil conditioner (improvement of drainage, workability, nutrient retention and ion exchange for enhancement of microbial and plant growth) and source of fertilisers (provision of balanced N,P&K and trace elements). For example, humates in soils retain potash by ion exchange but also make it to available to plant roots by further exchange with metabolic hydrogen ion Lime. The pH of ‘sour’ or acidic soils can be increased from 3-5 to 6-8 with lime (the least costly alkaline reagent). Physical workability of heavy (clay-rich) material is also greatly improved. In engineering terms clay soil becomes stabilised, i.e., clay particles are flocculated and lose their plasticity. Larger quantities of lime (and higher pH up to about 12) have a ‘pozzolanic’ or hardening effect. This involves re- crystallization of aluminium and calcium silicates and produces ground of improved mechanical strength on which buildings can be constructed. Minerals. ATS formulations can be based on bulk mineral mixtures, e.g., coal spoil, which would otherwise be un-marketable or waste. For legislative reasons, the result of mixing such materials with organics must an identifiable and economic product, not just a way of disposing of mixed wastes. The next two slides show trials carried out at the former Woolley coal mine (aerial view given in Lecture 4) involving coal spoil, ochre and sewage sludge.

12 Yellow lagoon ochre Brown wetland ochre Shale, lagoon ochre and compost Coned and quartered mixture ATS trial at the Woolley mine

13 Artificial top-soil cells General view of 24 Cells Top: with ochre Below: without ochre

14 Re-vegetation of coal or metal mining tips Natural re-vegetation. Spoil heaps from former and current mining activity are a common feature of industrial landscapes. In some cases, they become vegetated naturally because roots can extract potash and micro-nutrients (e.g., phosphate) from spoil minerals like coal shale, and leguminous pioneer plants, e.g., clover, provide N via root nodules containing nitrogen-fixing bacteria. However, natural re- vegetation is a lengthy process, which is easily disrupted by acid generation and heating, e.g., via pyrite bio-oxidation, and by physical damage, e.g., by bikers Enhanced re-vegetation. This may sometimes be achieved by: - nutrient spraying or injection (e.g., with digested sewage sludge) and/or liming - applying a surface layer of ATS and sowing with a suitable ‘restoration mix’, i.e., one containing resistant grasses such as Festuca rubra and leguminous clovers such as Trifolium repens. Small trees, e.g., alders and silver birch are also planted. After the first few years, plant litter and surface minerals are supposed to provide a new top soil layer in which ‘normal’ microflora and microfauna become established for sustained seasonal growth of restoration and ‘ruderal’ (indigenous) plants. See next slide Phosphate availability. In some restoration systems phosphate availability can become limiting, particularly if precipitated chemically in stable compounds, e.g., iron or calcium phosphate, or leached out of the soil. Ochre can be considered as a ‘slow release’ phosphate fertiliser. See slide after next

15 Restoration studies The Duhamel tip (Saarland, Germany): 300 m high. Unrestored coal shale (top right); restoration trees (top middle); recent restoration with ATS (main view) - being excavated to install a piezometer ATS ‘wedge’ trials on the RSM roof using Duhamel spoil, sewage sludge and restoration plants

16 Ochre, phosphate and fungi The element P is available to plants as phosphate, usually H 2 PO 4 - or HPO 4 2-, from the breakdown of polyphosphate or phosphatic biopolymers in plants or fertiliser compounds. Metal phosphates, e.g., Ca 3 (PO 4 ) 2 and FePO 4, usually have very low solubility products and strong adsorption onto particle surfaces. As a result, phosphate deficiencies in crops are common. However, phosphate is not usually lost to groundwater. In order to increase phosphate availability, mycorrhizal fungi may be added. These form a symbiotic relationship with plant roots: the fungi grow out from the roots, take up phosphate and transport it to the roots, while the roots supply carbohydrate to the fungi. This mechanism is only operative if phosphate is in short supply The question arises that if ochre (a particular amorphous form of iron(III) oxide) is mixed with a good source of organic phosphate, e.g., sewage sludge or compost, will there still be sufficient P available for healthy plant growth, and will the ochre have a net beneficial effect of allowing P availability without significant loss to groundwater. The trials (still ongoing) introduced several slides back were designed to answer this question for coal tip restoration After D.J. Read: Brock Pine seedling Suillus bovinus symbiotic fungus

17 Possible applications for mine water ochre Mine water sytems. As the UK Coal Authority is now constructing some eight new minewater treatment systems each year, a large quantity of ochre sludge is building up in former mining areas in England, Scotland and Wales. For instance, see next slide. Much research is being directed towards marketing this ochre Markets for ochre. In addition to possible use in ATS, ochre can be considered for use in cement and coagulant formulations. Coagulant production by acid dissolution remains a matter for research Ochre in cement. About 1 million tonnes of cement are produced each year by calcining together limestone and clay. The product must have the correct elemental ratio of Fe:Al:Si to achieve the most favourable setting and final hardness properties when used to make concrete, etc. This ratio is achieved by mixing appropriate mineral additives to cement feed. For instance, in Wiltshire the feed is deficient in iron. In this case ochre or iron-rich water treatment waste are a useful additives Process details. The process of utilising ochre in cement is shown in three slides. Sludge is pumped from a sedimentation lagoon, dewatered by centrifuge, conveyed to the Glacier ARM works at Sheffield by wagon container, and mixed with PFA to form a free flowing mixture suitable as an additive. The elemental balance is adjusted with the aid of ICP-AES spectrometry

18 © Imperial College London The occurrence of waste ochre

19 Pumping and centrifuging ochreous sludge

20 Glacier ARM plant, Sheffield Recovering ochre sludge Conveying ochre sludge to mixing with other wastes, e.g., pulverised fuel ash

21 Glacier ARM plant: mixture for cement works

22 Material mass balance and waste The diagrammatic weighing scales represent estimates of bulk material flows in the UK economy: inputs versus outputs. Inputs are shared between imports and local production to satisfy our needs. Outputs are consumer products that are dominated by waste. The economy is traditionally based on profit and loss, but is (hopefully) becoming more geared towards efficient use and re-use, i.e., geotechnical application and recycling, of resources through a consideration of overall material balance. A major objective is to highlight and minimise environmental impacts of waste, particularly disposal to landfill In this lecture we will briefly consider landfill, and alternatives to new landfill, particularly integrated treatment of rubbish and carbon sequestration. As landfill must decrease by up to 80% in the next 10 years and global warming by CO 2 is a fact, safe sequestration and recycling become crucial developments General recycling and the energy economy will be considered in level 5 courses After Peter Jones, Biffa Waste Services

23 Landfill Because recycling is currently inefficient, huge quantities of rubbish are buried. The environmental security of a landfill is primarily set by geological and hydrogeological conditions but also by transportation and constructed containment facilities Until about 20 years ago, most landfill sites were open to the air and based on the ‘dilute and disperse’ principle, i.e., were not contained within a liner. Now they are governed by the EU Landfill Directive, which requires sites to be fully contained and effectively isolated from the outside environment. Just over a year ago, new legislation prohibited the co-disposal of wastes in landfill, i.e., hazardous (toxic) and normal (municipal) waste must now be kept separate The Biffa site at Skelton Grange (see next slide) deals with rubbish from the whole Leeds area. It is on the former NCB Ox Bow open cast coal mine (later used for dumping power station ash to a depth of 60 m), which worked the carboniferous (Westphalian) lower coal measures (inter-layered with mudstones, siltstones and sandstones). Coal spoil was used to prepare embankments for the site. It is regulated by the EA under a PPC permit as a non-hazardous site, although one ‘cell’ takes asbestos waste. The site is taking 4 x 10 6 m 3 rubbish to a depth of 45 m between The site has a complex containment system (analogous to that in the slide after next) which allows water (leachate) collection at the perimeter for recycle despite compression of the 60 m depth of PFA by the overlying waste

24 Biffa Waste Services Skelton Grange Landfill, Leeds

25 Waste management by landfill After Pipkin, Trent and Hazlett

26 Leachate treatment Under EU legislation, degradation products, particularly leachate and landfill gas, must be properly managed to prevent groundwater and air pollution. Leachate is re-cycled as far as possible to promote microbial activity (particularly hydrolysis, fermentation and methanogenesis) but must otherwise be treated, e.g., as below

27 Alternatives to new landfill sites Integrated recycling. In principle this recovers many products, including energy. An example is shown in the next slide. However, the methodology has yet to be widely adopted Incineration of organics. With properly designed and managed equipment, incineration provides heat which can be converted partially to electricity for the national grid. Combustion also leads to a relatively small volume of ash, which might find application in construction. However, incineration also augments CO 2 to atmosphere and has the risk of toxic emissions. Yorkshire water have four incinerators burning nearly 40% of their total produced sewage sludge, with all ash planned to go sub-surface pipe production at nearby Hepworth Building Products Monolith engineering. Judicious mixing of organic and mineral waste, and compaction on restoration areas, with proper containment, lead to stable foundations for amenities and construction. Up to 1% of the total UK land area is classed as brownfield land and could be suitable. The Biostore project is introduced several slides on Landfill mining and space re-use. Old landfills, which have stabilised for >25 years and which remain accessible, can be re-opened. The contents can be excavated and recycled as far as possible to yield space for renewed landfill.

28 Integrated treatment of rubbish After Boyle Facilities in Florida for: - metals recovery - plastics removal - combined heat and power recovery from methane and solid waste incineration

29 Carbon sequestration Carbon is continually sequestered in new biological growth, as calcium carbonate in the sea and as peat and similar materials. However, as is well known, consumer combustion overwhelms these processes and global warming continues. In order to reduce the net emission of carbon dioxide to the atmosphere the options are to reduce combustion of fossil fuels, store carbon dioxide in porous geological formations, e.g., mature oil fields, or store condensed forms of carbon at or near the surface Drax power station could be replaced by solar cells or wind turbines if these covered most of Nottinghamshire. More realistically, the carbon dioxide could be concentrated and pumped into old coal or petroleum horizons if the geology is suitable An alternative is to grow and bury trees or stabilised sewage sludge with minerals (cf replacing coal seams) Drax Power Station, Yorkshire, produces huges volumes of CO 2 and PFA

30 Biostore is a way of storing organics (particularly sewage sludge) with minerals to produce stable ground that can be used as an amenity or built upon. A 100 tonne pilot scale emplacement (at Skelton Grange) developed by ESE is shown In this case the objective is to minimise microbial activity Biostore


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