Landfill gas (LFG) is a renewable source of useful energy. Its world wide annual energy potential is in the range of a few hundred TWh. Today it is only marginally exploited. LFG is also an important contributor to the atmospheres CH4-content, it can be estimated to contribute about 25% of the methane coming from anthropogenic sources. In comparison to many other sources of methane emissions such as peat bogs, rice paddies, termites and sheep, landfills can be considered to be point sources, i.e. they are stationary and of limited extension. For this reason landfill gas (LFG) utilisation is one of the most cost effective ways to combat the greenhouse effect. The aim of the IEA activity on LFG is to promote information exchange and co-operation between national programmes in order to promote the proliferation of landfill gas utilisation. During the period 1992–1994 the LFG activity has had six participating countries: Canada, Denmark, Norway, The Netherlands, Sweden, UK and USA. In the past three-year period, the activity has been mainly directed towards establishing networks and obtaining an over-view of data related to LFG in the member countries. Numerous contacts have been established and perhaps of most importance for the future of the activity are the links towards organisations involved in the development of landfill technology, such as ISWA and SWANA. The gathering and evaluation of data within the LFG area from the member countries has resulted in a number of documents that are to be published within the near future. These documents cover information on LFG utilisation, landfill research, landfill gas potentials, landfill emission assessment and also non-technical barriers to LFG utilisation.
9th consecutive edition of the textbook for the Landfill technology course
Revised edition of the 9th consecutive edition of the textbook for the Landfill technology course
The addition of cellulolytic enzymes to MSW has been tried under methanogenic and acidogenic conditions in 0.1 m3 landfill models. An enhanced degradation seems to follow the enzyme addition in both cases. During acidogenic conditions the observed conversion of cellulose was 42 and 29% respectively, with and without enzyme addition. The enzyme addition did not result in a change from methanogenic to acidogenic conditions. A similar conversion of VS can be achieved during methanogenic and acidogenic conditions; at the completion of this experiment the conversion of VS was in excess of 50% in the methanogenic models and somewhat lower than 40% in the acidogenic models (the latter still yielding strong leachates). The results of some standard waste-water analyses were compared and it is concluded that especially acid leachates may cause analytical problems.
Återcirkulation av lakvatten kombinerar avfallsbehandling med lakvattenbehandling. Flera olika processer kan påverka lakvattenkvalitén vid återcirkulation såsom biologisk nedbrytning, utfällning, avsättning, adsorption och jonbyte. Samtidigt som vissa ämnen avlägsnas från lakvattnet löses ämnen i avfallet av lakvattnet. Syfte: Att belysa den intensifiering av olika processer som sker vid recirkulation av lakvatten samt diskutera möjliga tillämpningar. Resultat och slutsatser: Tillämpning av återcirkulation kan bl a medföra:Temperaturen i deponin kan sjunka vid kraftig återcirkulation av lakvatten.Förhöjt vatteninnehåll kan sänka nedbrytningshastigheten i deponin.Näringsämnen kan tillföras och fördelas.Mikroorganismer kan tillföras och/eller fördelas. Homogenisering av deponimiljön sker. Nedbrytbart organiskt material i lakvattnet kan brytas ned i deponin. Metanogent avfall i deponin kan kvarhålla metaller, fosfor och svavel från t ex acidogent lakvatten. Denitrifikation kan erhållas vid återcirkulation.
Waste is generated in all processes. According to the laws of thermodynamics , materials and energy can be transformed but never destroyed. Even if material is substantially transformed, all matter which is introduced in any kind of process will come out of the process in exactly the same number of kilograms, either as products, by-products , or waste. Waste may be solid, liquid, or gaseous. In many cases, gaseous waste is a dominating outflow when processing solid matter. However, the focus in this article is on solid waste.Waste is often perceived as the remains from consumption. However, the major part of all solid waste is generated already by consumers' demand for products, i.e., before the products were consumed and thrown away. In general, the extraction of natural resources and industrial production processes produce massively more solid waste than the consumer products amount to, e.g., about 20 times according to European waste data [14]. As material flows through society, waste is formed in each step, as illustrated in Fig. 1. The material wastes can either end up in landfills or they can be dispersed in water, air, or soil. The dispersion in liquid phases typically exits the material from the waste management domain and turns it into pollution, albeit solid wastes can also form pollution, such as the floating plastic of the oceans.
Under periodenn 1992-94 har gasemissioner studerats vid testceller ingående i projektet "Samordnad deponigas-FUD" (i Malmö, Helsingborg och Upplands Bro). Syftet med dessa mätningar har varit att bestämma gasbildningen och gasutvinningens effektivitet i olika celler
The cementitious properties of many wood ashes makes them a potential stabilising agent for roads that can substitute cement. A test is presently performed using a 30% ash addition to natural soils for reinforcing a forestry road near Timrå, central Sweden. The bearing capacity of forestry roads in Sweden has become increasingly problematic in recent years, due to warmer winters, and in order to get timber out from the forests, road stabilisation is needed, usually adding cement to the road body. Wood ash has similar properties, and may substitute cement. An added advantage of using wood ash is the saving of landfill space. In the ongoing study, laboratory tests on leaching and mechanical stability, frost-sensitivity et c has been performed and a test road was built in June 2009, and will be monitored with regard to environmental impact and mechanical properties. The results so far indicate a strong stabilizing effect of ash additions to the road shoulder material.
A conventional 1300 m3 continuously stirred anaerobic tank reactor at the city of Boden, north Sweden, which was receiving a feed of both sewage sludge and food waste, was put out of operation due to the build-up of a float phase. The reactor was emptied and cleaned. At start-up there was no methanogenic sludge available, so an unconventional start-up procedure was applied: The reactor was rapidly (8 days with 1200 kg of total solids (TS) added daily) filled with thickened, and slightly acidic sewage sludge, showing only slight methane generation, which was subsequently heated to 55 °C. Then compressed air was blown into the digester and within a month a fully functional methanogenic culture was established. The transfer from acidogenic to methanogenic conditions happened in about one week. As a start-up technique this is fast and cost efficient, it only requires the access of a compressor, electricity and a source of air. In total, about 16 tonnes of oxygen were used. It is proposed that this method may also be used as an operational amendment technique, should a reactor tend to acidify.
The use of industrial residues as raw materials in construction raises concerns over the potential leaching and dispersal of hazardous constituents from them into the environment. Their leaching behaviour has been studied in laboratory assays, but leaching processes in the field over larger spatial and temporal scales are more complex due to variations in the conditions the materials are exposed to, and less well understood. Hence, estimates of the potential environmental loads associated with the use of such materials based on laboratory tests may be inaccurate. This thesis addresses the environmental implications of using recycled materials in road and landfill cover constructions. The focus is primarily on the leaching of inorganic constituents from six types of materials: incineration ashes, copper smelter slag, blast-furnace slag, recycled concrete, natural rock and contaminated soil. The leaching behaviour of constituents from these materials were assessed in both laboratory batch leaching tests and monitoring programs in which the water percolating through them in field applications were sampled over one to ten years. Leaching data were evaluated using statistical and geochemical modelling. In addition, assessment methods and criteria to judge the environmental suitability of substituting natural materials for recycled materials in construction were reviewed. It was found that leachates from recycled materials in the constructions contain higher concentrations of several constituents than natural water and leachates from conventional materials. However, the rates and extent of constituent leaching were affected by the application methods in various ways that are explored and discussed. The results of simplified leaching tests did not always reflect the leaching behaviour in the field, which highlight the importance of developing assessment methods that allow case-specific factors to be taken into account. The environmental impacts of leaching must also be considered in relation to the expected impacts of the default alternative, i.e. landfilling of industrial residues and exploitation of natural resources. Combinations of case-specific assessments and system analyses would be the ideal approaches to evaluate impacts at both local and regional scales.
Process industry, construction and other comparable activities produce large quantities of waste with potential use in geotechnical applications. Prior to utilisation, an acceptably low risk of contamination to humans and the environment must be demonstrated. This work focuses on the identification and evaluation of critical factors for environmental assessments of secondary construction materials. The market potential and the main barriers for usage of industrial wastes were analysed and showed a good potential especially in urban areas. The main obstacle is the long and complicated permit process involved. Further, the lack of a general procedure to investigate the suitability of intended usage leads to inconsistent assessments. An evaluation of leachate emissions from a large-scale test road demonstrated the importance of construction design and site-specific field conditions on the potential environmental impacts. It was also shown that pollutant concentrations in leachate from secondary construction materials tend to become comparable, or for some pollutants, even lower than from rock materials. Different assessment methods and criteria to judge the acceptability of an intended use were reviewed and various methods were identified. However, a generic method to evaluate materials under various environmental conditions is lacking.
Air-cooled blast-furnace slag is commonly utilised as a construction material in roads, fill and embankments. Materials used in such constructions do not remain continuously wetted, but is often subjected to cyclic wetting and drying under various exposure conditions. However, its leaching behaviour is often assessed based on tests performed under continuous wetting. This work was conducted to evaluate the leaching behaviour of an air-cooled blast-furnace slag under intermittent and continuous wetting. Four different leaching tests were performed, including a static leaching test without leachant renewal and three dynamic leaching tests: a column leaching test with continuous flow of the leachant, a tank leaching test with sequential renewal of the leachant and an intermittent leaching test with periodical flow of leachant. Leaching of the studied material under cyclic wetting and drying led to less alkaline and more oxidised eluates than leaching under continuously wetted conditions. The eluates are expected to maintain a mildly alkaline pH for long time periods during wetting, drying and oxidation of the material because the material has considerable acid neutralising potential. The leaching of soluble elements such as Ca and S was lower under intermittent than under continuous flow of the leachant which could be due to the shorter contact time between the leachant and material, and the precipitation of secondary phases on the particle surfaces during intermittent leaching. During exposure of the BFS to cyclic wetting and drying, the leaching of these elements decreased and the speciation of S in the eluates shifted towards more oxidising forms. The leached amounts of constituents were low in all performed tests, which indicate that the material was resistant to leaching under the conditions that were investigated here.
Air-cooled blast-furnace slag (ACBFS) has suitable physical properties for use as an unbound aggregate in road bases. Results of laboratory leaching tests have also indicated that ACBFS can be used without posing any risk of negative environmental impacts. However, monitoring of drainages from a full-scale road test section with ACBFS has indicated that acid leachates (pH<6) with associated increased releases of constituents can occur under field conditions. In this paper, the potential and responsible mechanisms for acid leachate formation from ACBFS used in road construction are discussed. Analysis of a 10-year time series of drainage samples and 12 year old ACBFS from the road section indicates that acidity might develop from the oxidation of reduced sulphides released from the ACBFS. Currently, the impact of intermittent wetting and drying conditions on the weathering of minerals and leaching over time from ACBFS is investigated under controlled laboratory conditions to verify the field observations. A combination of chemical and mineralogical analyses is used to analyse the results.
Process industry, construction and other comparable activities generate large quantities of wastes, which are potentially suitable for use in geotechnical applications. This review presents the current status of reuse and recycling of secondary construction materials in Sweden. Also, different assessment methods to judge the environmental suitability of different utilisations are overviewed. Several driving forces for reuse and recycling of wastes have been introduced recently. For example, the alternative costs, e.g. for landfilling, have increased due to raised taxes on waste deposited on landfills. However, the amounts of wastes made use of as construction materials are lower than the potential. Uncertainties about potential risks and demanding permit processes are often hindering recycling. Approval practices also vary in different regions, causing confusion for users as well as authorities. Wastes of high utilisation rates are commonly produced in urban areas where the demand for construction materials is high and are released from the permit obligation based on earlier experience. Current environmental assessment practice is unfavourable to the use of secondary materials. The surrounding environment is often not considered which may lead to environmental damage of sensitive recipients. The methods applied vary and the results are rarely related to corresponding investigations of conventional materials, although shown to have a high leachability of certain pollutants. The lack of a general procedure to assess the suitability of an intended use leads to inconsistent assessments. Laboratory leaching tests can be used to assess fundamental leaching properties of materials, but do not necessarily reflect the actual field conditions. Risk assessments can provide a link between the leaching behaviour of a material and the recipient/-s of concern, but requires large amounts of data. Life-cycle assessments can be used for comparative studies of different materials, but are often irrelevant for specific utilisation scenarios. Further work is needed on how to improve the quality and the consistency in environmental assessments. The effect of different factors on the release and transport of contaminants from different materials in different utilisation scenarios need to be evaluated. Also, simplified assessment methods are lacking to account for characteristics in the surrounding environment and to address resource management at the strategic level.
Three years of leachate emissions from municipal solid waste incineration bottom ash and crushed rock in a full-scale test road were evaluated. The impact of time, construction design, and climate on the emissions was studied, and the predicted release from standard leaching tests was compared with the measured release from the road. The main pollutants and their respective concentrations in leachate from the roadside slope were Al (12.8-85.3 mg l-1), Cr (2-125 μg l-1), and Cu (0.15-1.9 mg l-1) in ash leachate and Zn (1-780 μg l-1) in crushed rock leachate. From the ash, the initial Cl- release was high (≈20 g l-1). After three years, the amount of Cu and Cl- was in the same range in both leachates, while that of Al and Cr still was more than one order of magnitude higher in ash leachate. Generally, the release was faster from material in the uncovered slopes than below the pavement. Whether the road was asphalted or not, however, had minor impacts on the leachate quality. During rain events, diluted leachates with respect to, e.g., salts were observed. The leaching tests failed to simulate field leaching from the crushed rock, whereas better agreement was observed for the ash. Comparisons of constituent release from bottom ash and conventional materials solely based on such tests should be avoided.
The use of municipal solid waste incineration (MSWI) bottom ash in road construction may possess a risk to the environment due to the release of e.g. salt and heavy metals. In this study, two years of leachate data from a test road built of MSWI bottom ash and crushed rock in northern Sweden were evaluated. It was found that Cu, Cr, Al, Na, and Cl- were leached in higher amounts from the bottom ash, while the release of Zn, Mg, Ba, and Ca was higher from the crushed rock. The difference between ash and crushed rock leachates decreased over time, mainly due to changes in the ash leachate composition. The road pavement reduced the release rate of most pollutants from the bottom ash compared to the release from the uncovered parts of the road, whereas the release of pollutants from the crushed rock was less affected by the presence of a pavement.
The use of secondary materials in geotechnical applications is regarded as favourable but is often hindered by uncertainty about the potential environmental impact of the utilisation. In this paper, the main hurdles restricting the use of waste derived construction materials in Sweden are analysed, and means to overcome these are discussed. Standard test procedures and limit values for the assessment of environmental compliance of waste materials have not yet been established in the legislation. This has lead to confusion both for prospective users and for authorities. Also, a risk assessment system developed for the use of the secondary materials is lacking. Formalising the way data on e.g. material properties is collected and structured facilitates the judgement if and how a waste derived material can be used in a specific project. A web based information system could be used to gather, store and communicate information regarding secondary materials used for construction purposes. The proposed information system may form a basis for a simplified evaluation of risks related to the use.
The leaching behaviour of a road construction with fayalitic copper slag, recycled concrete and crushed rock as sub-base materials was monitored over ten years. All studied materials used in the road construction, including crushed rock, contained concentrations of several elements exceeding the guideline values recommended by the Swedish EPA for total element concentrations for waste materials used in constructions. Despite that, leaching from the road construction under field conditions in general was relatively low. The leachates from the recycled materials contained higher concentrations of several constituents than the leachates from the reference section with crushed rock. The leaching of the elements of interest (Cr, Mo, Ni, Zn) reached peak concentrations during the second and fourth (Cu) years and decreased over the observation period to levels below the Swedish recommended values. Carbonation of the concrete aggregates caused a substantial but short-term increase in the leaching of oxyanions such as chromate. The environmental risks related to element leaching are highest at the beginning of the road life. Ageing of materials or pre-treatment through leaching is needed prior to their use in construction to avoid peak concentrations. Also, the design of road constructions should be adjusted so that recycled materials are covered with low-permeability covers, which would minimize the exposure to atmospheric precipitation and weathering.
Chemical stabilisation of trace element contaminated soil may be used as pre-treatment prior to landfilling or re-utilisation. Three different treatments with iron amendments were evaluated for their efficiency in reducing trace element mobility in chromate copper arsenate (CCA) contaminated soil. The amendments tested were two industrial by-products from steel production industries, viz. blaster sand, containing mainly zerovalent iron (Fe0), and oxygen scarfing granulate, with mainly iron oxides. Batch, column, and lysimeter leaching tests were conducted on untreated and treated soils. The tests were used to firstly evaluate the potential of the amendments as stabilising agents, and secondly to assess the potential management of the treated soil. Soil amendments lowered concentrations of As, Cu, Cr, and Zn in soil pore water and leachate, whereas Fe, Mn, and Ni showed tendencies towards increased concentrations. The treatment efficiency can be ranked as 1% Fe0 < 4% iron oxides < 8% iron oxides. While iron oxides may be used as effective amendments to reduce As leaching from soil, their effects on leaching of e.g. Ni warrant careful consideration. Further, impurities of the iron oxides increased soil concentrations of e.g. Cr, potentially limiting re-utilisation of the treated soil. Lowered As leaching from column and lysimeter tests on treated soil indicated aerobic soil conditions and, hence, stability of iron oxides. This may, however, be an artefact of a too short testing period for anaerobic conditions to establish.
The medium-term (5-10 years) elemental leaching from five different materials used in full-scale road applications was evaluated. Two materials, fayalite slag and blast-furnace slag, leached high concentrations of trace metals such as Cu and Zn throughout the study period. At several occasions, the blast-furnace slag generated leachates with acidic pH-values (<4). Leachate from crushed concrete and MSWI bottom ash contained elevated concentrations of e.g. Cr and Cu during the first 2-3 years. Enrichment of trace elements occurred in sediments of roadside drainage ditches, but the respective contribution from leachate and road surface runoff is unclear. Migration of the elements through subsoil and plants in the ditches was limited, but clear anthropogenic signals were observed for e.g. Cu and Zn at the BA section. Further studies are recommended to verify if laboratory tests used for impact assessments are able to predict the observed field leaching and how the road environment is affected by leaching from the road materials in the longer term.
Two industrial by-products with high iron contents were tested for their effectiveness in the stabilisation of arsenic and trace metals in chromated copper arsenate (CCA)-contaminated soil. Steel abrasive (SA; 97% Fe0) and oxygen scarfing granulate (OSG; 69% Fe3O4) were applied at levels of 1% and 8% (w/w) respectively to two soils with different organic matter contents. Field lysimeter measurements indicated that SA and OSG treatments decreased the arsenic concentration in pore water by 68% and 92%, respectively, for the soil with low organic matter content, and by about 30% in pore water of soil with high organic matter content. At pH ≤6, the amended soil with low organic content contained elevated levels of manganese and nickel in their pore water, which were sufficient to induce cytotoxic effects in L-929 mouse fibroblast cells. The industrial by-products have significant potential for soil amendment at field-scale, but caution is required because of the potential release of their chemical contaminants and their reduced capacity for sorption of arsenic in organic-rich soils.
Exploiting the full biogas potential of some types of biomass is challenging. The complex structures of lignocellulosic biomass are difficult to break down and thus require longer retention times for the nutrients to become biologically available. It is possible to increase the digestibility of the substrate by pre-treating the material before digestion. This paper explores a pre-treatment of ley crop silage that uses electrical fields, known as electroporation (EP). Different settings of the EP equipment were tested, and the results were analyzed using a batch digestion setup. The results show that it is possible to increase the biogas yield with 16 % by subjecting the substrates to 65 pulses at a field strength of 96 kV/cm corresponding to a total energy input of 259 Wh/kg volatile solid (VS). However, at 100 pulses, a lower field strength of 48 kV/cm and the same total energy input, no effects of the treatment were observed. The energy balance of the EP treatment suggests that the yield, in the form of methane, can be up to double the electrical energy input of the process.