Environmental damage resulting from intensive, large scale farming falls into three areas: destruction of natural vegetation, loss of organic matter and subsequent erosion due to wind and rain as well as saturation of the soil water by excess nitrogen from fertiliser application or manure deposition. Passage of surface water contaminated with soluble nitrogen to rivers, lakes and other surface reservoirs causes eutrophication (excess growth of aquatic algae and higher plants), whilst increased levels of contamination of ground water have resulted in water which fails to meet EC requirements in some (nitrate sensitive) regions. These problems have been accepted in the past as a necessary consequence of the successful drive to establish self sufficiency in food production within the Community.

Since the early 1970s a combination of plant breeding, intensive management techniques and high chemical inputs have resulted in EC yields of conventional arable crops, grown for food use, which are among the highest in the world. These include wheat and sugar beet which could be used as feedstock for bioethanol production and rape which is currently attracting attention for the production of methyl (or ethyl) esters of the vegetable oil as a substitute diesel fuel. However, the high costs of crop production means than such biofuels require significant subsidies. At the same time the cost of support of agriculture through the Common Agricultural Policy (CAP) and global problems resulting from over production and generation of surpluses has led to a policy of land set aside with the possibility of millions of hectares of productive farm land being taken out of food production. This land could be used to grow large amounts of biomass using either high yielding arable crops such as Miscanthus and sweet sorghum or fast growing trees grown under short rotation or coppiced. However, the environmental penalties and economic costs which were justified in providing food cannot be extended to cover plants grown for energy.

Wastes and residues

At the same time the EC is faced with increased problems associated with the management and disposal of organic wastes from farms, forestry, the agro-food industry, commerce and domestic activities. Although non organic products made of metal, glass and some plastics (as well as a proportion of the paper, card and fabric wastes generated) may be reused or recycled this is not true for a wide range of readily biodegradable materials which include wood waste, straws, manures, food processing residues and effluents, sewage sludge and the organic components of municipal solid waste (MSW). Many of these wastes are wet and hence will not burn. If placed in landfills they make the major contribution to leachate and gas (methane) generation, contaminating ground water and contributing to the burden of greenhouse gases released to the atmosphere unless costly preventative actions (liners and gas collection systems)

The controlled biological consolidation of such wastes can generate large amounts of organic fertiliser in the form of compost from aerobic processes or digestate from anaerobic processes. However, neither process is entirely satisfactory for the treatment of sludges or manures with a high content of nitrogen which may be released into the atmosphere as ammonia. High levels of phosphate may limit the amount which can legally be spread each year per hectare of land. Such wastes may require additional chemical treatment, but have the potential to produce fertilisers with higher levels of inorganic nutrients as suitable conversion techniques are developed. In theory the use of such materials for fertilisation of biomass crops could both help solve the problem of disposing of unpleasant organic wastes and improve the economics of energy crop production. The feasibility of achieving this depends on the amount, availability and quality of the wastes.

The total wastes produced within the EC have been estimated at around 2500 million tonnes, comprising municipal solid waste (MSW), agricultural residues, manures, agrofood processing wastes, forest and yard wastes, sewage sludge and industrial wastes. Of the available wastes some 75 % will be organic in origin or include organic components as a significant proportion of their solids. However, this total resource bears little resemblance to the actual amounts of wastes which might actually be used to generate composts and organic fertilisers. The actual amount will vary with some many factors that estimates are of little value. These factors will reflect changes in both processes which generate wastes and residues and methods used for treating such materials. The amount and composition of wastes will vary with geography and population density (rural or urban), the extent to which they can be used will reflect technical ability, whilst the amounts which are used will reflect economic factors and investment in plant. This in turn will vary between farm, forest, industrial and domestic sectors and within each of these depend on local availability of by products and residues from local processing of specific raw materials.

Each opportunity will have its own site specific characteristics which may be influenced by local markets and national legislation. Hence, rather than attempt the impossible task of deciding what percentage of the above might become available, the factors influencing each area of consideration are as follows: changes in time, reflecting changes in practice and legislation; geographical availability, as transport costs are high waste must be locally available; technical availability, the waste must be suitable for treatment and a process to treat them must exist; economic availability, the net benefit of treating the waste and selling any product has to attract investment in a process plant with transport costs, tipping fee and net product value the most important factors; sectorial availability, reflects the extent to which a given industry accumulates treatable wastes as an unavoidable consequence of normal business practice; local availability, a consequence of cropping patterns, animal husbandry techniques and the nature and extent of agro industrial processing; legal availability, depending on constraints on waste use reflecting the degree of contamination, especially by heavy metals, xenobiotics and soluble plant nutrients.

The level of heavy metals is only one factor which can be used to characterise the wastes as clean or dirty. Other parameters include contamination with pesticide residues, antibiotics and other man made chemicals; the possibility of contamination with human, animal or plant pathogens and contamination with inerts generated from mechanical sorting of domestic wastes (fragments of metal, plastic and glass). The second way in which quality may be assessed is in terms of the levels of potential plant nutrients (NPK) and digestibility. A highly putrescible waste, or one with low level of inorganic plant nutrients is of less value since the final product will be of low bulk and low nutrient status. Such problems can be overcome by admixing wastes. In particular wastes with a high lignocellulose content (wood chips, bark or straw) can be mixed with liquid wastes of higher nutrient content (sewage sludge or manures). Such mixing also improves the waste treatment process.

Processes

Both composting and anaerobic digestion (AD) have particular benefits in organic waste consolidation with composting preferred for waste with a higher content of lignocellulose and anaerobic digestion preferable for liquid manures and sludges. Wastes can be mixed to suit either process. AD has the extra advantage of generating methane which may be used to increase the revenue to the process plant by sale of gas, electricity or heat. AD plant costs may be higher, control more difficult and failure of the plant irreversible - even a bad composting process cannot fail in totality, whereas anaerobic digestion plant may. Composting has the advantage that it takes place at a lower moisture content and tends to dry as a consequence of the heat generated by, microbial metabolism. In contrast AD occurs at solid levels of below 30% and digesters require an external source of heat, especially when the incoming wastes are at ambient temperature in the winter. The digestate may require further aerobic treatment and mechanical dewatering.

To process large amounts of waste requires large plant or areas of hard standing for open composting. Capacities may range from 10s to 1000s of tonnes per day wet weight of input material. Composting may accommodate this in windrows or in a large enclosed hall. However, the capacity of anaerobic digestion plant is generally increased by adding to the number of tanks, which may be between 500 and 3000 m3 in volume. In the past the main activities have been small on farm or garden composting, small on farm anaerobic digestion plant for manures, large composting plant receiving mixed MSW for mechanical sorting prior to composting and large industrial digesters treating site specific liquid effluents from food processing (sugar, starch, brewing and distilling, cheese production) as well as secondary treatment of sewage. Current expansion in biological waste processing is occurring in the following areas: large joint biogas plant receiving manure from a number of farms and also receiving selected agro industrial wastes; composting of source selected wastes (particularly garden, landscaping and horticultural residues).

Products

The value of products as replacements for conventional chemical fertilisers, with defined levels of the primary nutrients (NPK), depends on the level of these nutrients. In general these are only high (of comparable levels to synthetic fertilisers) in products which are derived from special wastes associated with animal processing, pectin extraction, etc., or are based on manures and (sewage) sludges. The availability of animal by products is limited and they may attract a higher price as special inputs into home garden and horticultural products such as 'hoof and bone' and dried blood. The low nutrient level of such materials can be compensated for by increasing the level of application. However, this may reach levels of tonnes per hectare, rather than kg/ha, increasing transport and spreading costs.

Where large amounts of waste derived materials are applied to the land there may be associated problems and cause for concern as a result of the composition the balance between components and the levels of trace constituents. Such problems reflect the fact that final composition reflects the original composition of the waste materials used and the conversion process, whereas chemical fertilisers are formulated. It may be possible to formulate composts and digestates on the small scale and products of this type are coming onto the market as peat substitutes for home and horticultural use. In particular coir (imported coconut waste) is used to increase the stability and minerals may be added to increase the level of inorganic nutrients. The nutrient value of lignocellulosic derived composts can be improved by co composting of straw or wood chips with manures or sludges. This has the added advantages of diluting concentration of contaminants (but not the total amount) and increasing solids content. Problems of contamination by inerts (glass, metal, plastics) of MSW derived composts are well known.

Product quality

The quality of such organic fertilisers will determine their market value and market penetration. Where these products have a low nutrient content their monetary value is low. Higher quality products will be used in the home, garden, horticultural and amenity markets since these command much higher prices. As a result it will be the bulk, low quality materials which cannot find other uses which will be used with energy crops. Due to costs of transport these will have to be used on a local basis, or the costs will have to be covered by a disposal fee. In other words the primary driving force behind an increased use of waste derived organic fertilisers will be waste disposal rather than plant nutrition. Set aside land, or land devoted to plants grown for non food use will be used for such disposal, since this represents the minimum direct threat to human health.

Environment

The key questions then concern the degree of contamination of such materials which can be tolerated by the soil, the impact of these on plant growth, the extent to which heavy metals are assimilated by energy crops and the overall long term distribution of these added contaminants in both the local and global environment. A considerable amount of information is available from field trials of agricultural crops treated with approved levels of sludges and manure as well as from plot or pot trials using indicator plants with higher amounts or concentrations of contamination. The uptake of metals and growth response resulting from application of sludges in trees and forests, including potential energy crops has been investigated in some situations. This extends to studies which aim to establish the benefit of growing trees and other plants as methods of selectively removing heavy metals from contaminated soil, as well as studies related to the establishment of vegetation on highly contaminated areas such as mine spoilage tips. Detailed studies on fast growing arable energy crops are not available, although some work has been started as part of the activities of the Miscanthus network supported by the CEC under the AIR programme.

Irrespective of the standard of management, plant design and precautions taken, many waste treatment plants built in the past have been unpleasant, to varying degrees, due to odours, leachate, wind blown fines, etc. This has engendered the well known NIMBY (not in my backyard) syndrome, which in turn has resulted in significant improvements in more recent plant, but also raised costs considerably. Anaerobic digestion plant have the advantage that they can be more or less totally enclosed, with liquid waste introduced (and digestate removed) by specifically designed tankers through ports fitted with valves, minimising gas and liquid escape. Composting systems are more difficult to enclose. However, odour can be reduced to a minimum by operating in halls at negative pressure with the swept volume recycled through the heap, scrubbed through a water filter or passed though a soil bed (bio filter). The off gas from anaerobic digestion may also require scrubbing to remove hydrogen sulphide to prevent engine damage. Such plant are facing increasing problems in terms of planning consent and environmental impact assessments may be required, as well as guarantees of zero emissions in terms of odours.

The most serious concerns about the widespread use of waste derived organic fertilisers and composts relate to the levels of heavy metals which may be accumulated and, to a lesser extent, the possibilities of disease transmission. Both anaerobic digestion and composting should provide adequate sanitation and where the risk is significant for liquid wastes an additional heat sterilisation stage can be added. Sludge consolidation by settling, composting or digestion leads to concentration of any heavy metals present in the solids. The only way to reduce the heavy metal problem is to limit the amounts of heavy metals entering the agro food and industrial processing chains. Suggestions have been made that sludges can be washed or heavy metals complexed by ion exchangers. This only transfers the problem of disposal to a new medium and increases processing costs.

Crop yields

Conventional agricultural wisdom accepts that crop yields are proportional to nutrient availability, which means nutrient inputs where high crop yields are harvested on an annual basis. The response of plants to such increased nutrition continues until some other factor, water supply, light, temperature, competition from other plants (weeds) or disease, limits this. The market value of CAP supported agricultural crops, reflected in the increase in yield, has in general exceeded the cost of chemical inputs. As a result use of soluble chemical fertilisers has increased in all Member States over the last 2-3 decades. Since nitrogen fertilisers have a high solubility and are not immediately assimilated by the plant leaching has contributed to nitrate levels in ground water. A second source of this nitrogen has been the decay of organic residues as a result of conversion of long term pasture to arable use.

The use of organic fertilisers does not necessarily overcome such problems of environmental contamination by macro nutrients unless these are complexed in some way providing slow release of nutrients as a result of microbial action. A number of processes for generating such slow release fertilisers are under investigation. However, these only represent one option, which may not be feasible with many wastes. Unlike food crops, where yields benefits can be measured in terms of the gross financial benefit per hectare and year, energy crop yields can be judged in terms of GJ harvested per annum per hectare compared with the energy inputs, expressed in similar terms. This reduces the value of bulky fertilisers with high distribution and spreading costs.

Political concerns and legislation

Political and environmental groups have expressed concern about the use of high chemical inputs to generate crops for fuel use, as well as aspects of waste generation, waste disposal, ground water contamination and environmental impact, including effects of large husbandry, harvesting and transport machinery.

These opinions can be viewed In respect of the increased environmental legislation which has been proposed or adopted as a response to environmental concerns. However, legislation and political considerations which impact on the use of organic fertilisers for production of energy crops go far beyond purely the environmental. In particular aspects of the Common Agricultural Policy (including set aside) and General Agreements on Tariffs and Trade (GATT) affect the availability of land and possible end use or marketing of crops such as rape. The feasibility of marketing biofuels depends on tax concessions, or improved competitiveness with fossil fuels resulting from the possible imposition of a carbon tax. The movement of some biomass materials in their raw state may be affected by legislation on plant product movements related to disease control. The nature and availability of wastes for composting or digestion, as well as the chosen route, will be affected by pending legislation covering landfilling and packaging. The application of sludges and manures, as well as derived products, to land is already covered by a wide range of national legislation, reflecting in part EC Directives. Legislation and quality standards for organic fertilisers are currently under discussion, whilst various alternative farming organisations have their own standards.

Fiscal measures

The deciding factor which determines the extent of energy cropping and hence the extent to which waste derived organic fertilisers are used in this respect will be economic. In terms of current market value biofuels cannot compete with fossil fuels and organic fertilisers cannot compete with chemical fertilisers. As indicated above legislation may distort these facts by fiscal means or subsidies. Some Member States have already introduced lower taxes on biofuels (eg France, Italy), whilst others offer preferential prices for electricity generated from renewable resources (eg UK, Denmark, Italy). Alternatively the difference may be paid for as part of the cost of waste disposal. This cost may be collected under local or regional taxes, paid for by governments, recovered as a tipping fee charged at the gate of the disposal site or be built into complex waste/packaging systems as in Germany. Irrespective of the route of payment the cost of waste disposal to acceptable standards, to meet ever more stringent environmental legislation, is growing.

Economics

Generating energy or organic fertilisers for sale, as a by product of waste treatment, reduces the net cost of disposal, especially for difficult wastes such as those derived from fish and meat processing, sewage sludge and liquid manures. However, again there is a balance between the direct use of wastes and residues for energy production (as in straw combustion or manure digestion) and the application of waste derived products to the land to generate energy crops. In the short term the true energy potential of many wastes and residues has yet to be realised. Energy crops are attractive where they offer the opportunity for income generation from set aside land or where they provide a superior feedstock which facilitates the use of more efficient conversion technology or a higher value product (eg liquid transport fuel). The feasibility and economics of growing and processing the most likely candidates (Sorghum and Miscanthus) are still under investigation. Until this work is completed and decisions made the main energy crops grown will be trees where applications of waste derived materials present fewer problems.

Needs

The main needs, apart from a viable biomass energy cropping industry to take the waste derived organic fertilisers, relate to information on amounts, distribution, availability and composition of wastes and residues which might be used as well as agreed methods of analysis, product definitions, product standards and agreement on terminology. Some aspects are being addressed by national government bodies, trade associations, professional institutes of waste management, common interest groups supported by industry, agricultural unions, scientific and academic institutes, environmental organisations and similar bodies. However, each group has its own particular vested interests, action programme and targeted recipients of selected information. There is a role for the CEC in maintaining a central position amongst these activities by a continuation and expansion of previous activities supported under DGXII within the Recycling Programme. This could be incorporated into environmental, regional or renewable energy programmes. However, the scope probably falls outside the specific activities of the AIR.

Community support of research and development

Areas of activity which could be supported under AIR, or future agricultural and forestry programmes and/or JOULE or future renewable energy programmes should obviously concentrate respectively on aspects of plant nutrition, plant yield, heavy metal accumulation and the fate of these heavy metals during subsequent combustion or processing to generate heat, liquid fuels or electricity. Due to the importance of soil composition, structure and physical properties as well as impact of climate and cropping practices investigations would be required covering a broad range of sites, using the preferred species matched to soil and climate.

Other needs for research into waste availability, waste management techniques, waste composition and changes within industrial practices designed to minimise waste and contamination by heavy metals lie outside the remit of AIR or JOULE and can best be funded by national initiatives, the environmental directorate of DG Xll or by DG Xl. However, a suitable dialogue should be maintained between these interests, which may extend to DG XVI in terms of regional development or planning and to DG Vl in respect of agricultural policy.