BIOMASS STUDY
5.3 ENVIRONMENTAL REVIEW .1 Introduction
The environmental criteria for the selection of biomass resources and energy conversion systems are presented, together with an analysis of the environmental issues relating to each system option. The criteria include environmental issues and impacts associated with agricultural and forestry practices, pollution control and environmental regulations relating to industrial waste discharges from processing facilities and global issues, such as greenhouse gas emissions.
5.3.2 Environmental Criteria
The following criteria are desirable in the selection of biomass resources and processing technologies for energy production and used in the assessment of the system options:
resource use sustainability carbon sequestration
net reduced Greenhouse Gas emissions
minimisation of impact on biodiversity and wildlife habitat minimisation of soil erosion and employ conservation practices enable re-afforestation of marginal/degraded agricultural land minimisation of the application of fertilisers/herbicides/pesticides conserve soil nutrient status and organic matter
maintenance and re-establishment of natural ecosystems low soil compaction harvesting techniques
avoidance of steep slopes
maximisation of plantation sites in catchment recharge zones suitability for effluent irrigation
minimisation of genetic pollution of native forests minimisation of crop water demand requirements minimisation of water requirements for processing
high standard of effluent wastewater treatment and discharge quality
minimisation of solid and liquid waste outputs
encourage options which include solid and liquid waste reuse minimisation of air emissions and solid outputs such as noxious gases, particulates and ash
minimisation of human exposure to toxic chemicals through the growing, handling and storage of biomass feedstocks and produced biofuels.
Land-use practices employed for the production of biomass for energy should be environmentally sustainable.
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If conventional agricultural and forestry land use management practices are employed, bioenergy would be unsustainable in the long-term, because present land use practices are not environmentally sustainable due to the degradation of soil and natural ecosystems.
Similarly the proposed biomass conversion technologies must incorporate state of the art technologies to ensure that the nature and volume of the waste output products to soil, water and air are environmentally acceptable.
The issues relating to biomass energy system options are discussed beiow with respect to their characteristic environmental impacts and government policy initiatives.
5.3.3 Lignocellulose Residues to Electricity
This option provides the most significant environmental benefits of all the options primarily because of its potential global impact in the reduction of Greenhouse gas emissions together with its potential to contribute to environmental policy on land revegetation and rehabilitation. This option has the potential to make a significant contribution to the Commonwealth Government's objective of stabilising greenhouse gas emissions based on 1988 levels by the year 2000 and reducing these emissions by 20% by the year 2005.
Electricity produced from lignocellulose residues through combustion and/or gasification technologies would be largely carbon neutral (excluding greenhouse gases emitted during feedstock growth, harvesting and transportation phases) since the carbon dioxide released during conversion would liberate only the carbon dioxide sequestered during the biomass growth phase. However this would only be the case where the biomass is grown as a renewable resource in plantations specifically established for harvesting on a continual rotation basis. Lignocellulose residues obtained from the logging of forest reserves which are not replaced would provide little benefit to the reduction of greenhouse gas emissions since the carbon released during conversion would not be balanced or offset by subsequent sequestration.
For this option to sustain the benefit of carbon neutrality it is necessary for the forestry practices to determine rotations such that carbon sequestration and release from the woody biomass and soil is optimised for the growth and harvest cycle.
A second major potential environmental benefit of this option is that it provides a suitable end use for woody biomass established on cleared and/or degraded lands as an environmental remediation or rehabilitation
BIOMASS IN T H E ENERGY C Y C L E
measure. Similarly significant regional environmental benefits could be achieved if woody biomass which w a s irrigated with regional sewage effluent wastewater were to be converted to electricity and/or cogeneration end uses.
This scenario contributes to a number of regional, state and national environmental policy objectives relating to sustainable agriculture, improved river and ocean water quality and environmental remediation.
Whilst there is the scope for significant environmental benefits, there is also the potential for substantial environmental impacts if sustainable agricultural and forestry land management practices are not widely used.
The primary issues relate to the clearance of native vegetation and habitat, a reduction of biodiversity and habitat diversity, a reduction in water quality through increased chemical use, and an increase in soil erosion and the area of land degradation.
The Greenhouse benefit would be significantly enhanced if the electrical energy produced displaced electricity produced from fossil fuels. This option could have a greater environmental benefit if the feedstock were derived from all lignocellulose resources rather than only residues.
There also remains the potential for air emission impacts related to the stack gases, particulates and solid ash waste emitted as a consequence of lignocellulose combustion similar to those produced by fossil fuel combustion. It is likely that the impact of air emissions produced by combustion technology would be comparable irrespective of feedstock and that substantial pollution control devices would be required on the stacks.
5.3.4 M u n i c i p a l Solid W a s t e to Electricity
This option provides for significant environmental benefits which relate mainly to improved urban waste disposal techniques and a reduction in pressure for the availability for land fill sites.
There is the potential for the development of highly efficient recycling processes for non-combustible municipal solid waste (MSW), since the quality of the M S W has an enormous impact on the emissions from the gasification/combustion conversion technology. Without extensive recycling and sorting of M S W the air emissions produced from the conversion to electricity can include lead, sulphur dioxide and highly toxic compounds such as dioxins, furans, heavy metals and hydrochloric acid. Air emissions from waste to energy combustion plants are at a higher rate per kWh generated than for coal fired plants. Consequently combustion of MSW is not a recommended option without
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comprehensive waste sorting and the development of specialised emission control devices.
However the extraction of landfill gas or biogas from landfill sites and its conversion through gasification has a benefit in the reduction of Greenhouse gas emissions by converting methane to carbon dioxide.
Since methane emissions have a proportionally greater impact on the atmosphere than carbon dioxide, this gas conversion is of benefit compared to the present leaking of methane rich biogas from landfill sites.
The overall effect on Greenhouse gas emissions would be a small reduction in the present total volume since only a slight offset or displacement of fossil fuel derived electricity would occur.
5.3.5 Animal and Human Wastes to Electricity
This option provides for environmental benefits through the utilisation of organic waste products which present a significant worldwide disposal problem due to their impact on water quality and nullification, the demand on available land for storage and disposal, and major community health problems.
Consequently, the use of human and animal wastes for conversion to electricity alleviates these problems. However, there remains the potential for localised and regional pollution associated with the storage and handling of these wastes. Generally, the conversion of these wastes is of significant environmental benefit at a local to regional level.
5.3.6 Lignocellulose to Ethanol
This option provides for almost the same level of significant environmental benefits lignocellulose residues to electricity except that the wastewater produced by the fermentation/hydrolysis conversion process could potentially have an extremely negative environmental impact. Since there are no operating conversion plants of this type the exact nature of the environmental outputs are unknown.
However, it is known from the waste outputs from pulp and paper mills that lignin is the most difficult compound to breakdown in the mill effluent wastewater. It is expected that a small quantity of lignin is likely to be discharged in the form of ligno sulphonates in waste process water, which present a serious environmental hazard to biota especially since they have an extremely high biological oxygen demand on the receiving water.
BIOMASS IN T H E ENERGY C Y C L E
The wastewater would also contain a high nutrient content (nitrogen, phosphorus and potassium) combined with a high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). To minimise the environmental impact the waste waters should be treated to produce biogas to cogenerate heat and power. It is likely that a lignocellulose to ethanol plant would require a comprehensive environmental impact assessment with approval dependent upon either provision for wastewater discharge to the ocean which is only marginally more desirable than to rivers.
Alternatively, significant environmental benefits as outlined in Section 5.3.3 relating to carbon-neutral energy sources and a reduction or offset of Greenhouse gas emissions, together with the contribution to environmental remediation/rehabilitation policy exist for this option.
There are also the added benefits of the ethanol fuel replacing or displacing fossil derived liquid fuels for industrial and transportation use.
This would have a significant impact on the reduction of global Greenhouse gas emissions, particulates, S Ox and CO emissions.
Aldehyde emissions from ethanol/gasoline blended fuel powered vehicles are thought to be similar in quantity to those from gasoline powered vehicles, and the aldehyde emissions increase with higher alcohol blends (BTCE, 1994).
A number of health and safety issues occur with the use of ethanol which stem from aldehyde emissions, alcohol vapours and direct contact with alcohol and the potential for fires. Increased production and widespread use of ethanol as a fuel would cause a greatly increased risk of environmental contamination from fuel spillage and toxicological problems from the increased risk of human contact as a result of spillage, inhalation of unburnt fuel and evaporative emissions (BTCE, 1994).
5.3.7 Lignocellulose to Methanol
The significant environmental benefits outlined for the lignocellulose to electricity option generally applies to this option, with the major benefit being a significant reduction in Greenhouse gas emissions. Methanol production from lignocellulose would eliminate the current practice of converting natural gas to methanol and the associated greenhouse gas emissions.
Consequently, this energy option would be carbon-neutral as long as the lignocellulose was derived from continual rotation harvested crops or forest plantations. Detailed assessment of the environmental outputs of this option are not possible since there are no operating conversion plants. However, there are significant environmental issues with methanol
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production, handling and use which relate to human health and safety and environmental contamination, and increased fire risk.
Methanol is toxic to humans and public exposure through the inhalation of unburnt fuel in exhaust emissions, of fuel evaporating during refuelling or accidental spills, or of hot vehicle evaporative emissions could be fatal or produce serious injury (BTCE, 1994).
5.3.8 Oilseeds to Oilseed Esters
This option provides for environmental benefits by potentially reducing the use of fossil fuels for transportation, thus reducing Greenhouse gas emissions from vehicles. There are no significant waste disposal issues.
There is some potential for related environmental impacts as a result of unsustainable agricultural land management practices as outlined in Appendix 5. Biofuels from oil seed esters provides a potential environmental benefit if they are used to power harbour, port and lake waterway vehicles as they are biodegradable if fuel spills occur.
5.3.9 Biomass to Oxygenates
This option provides comparable environmental benefits and costs to those outlined for the options, lignocellulose to ethanol and methanol.
The production of oxygenates incurs a Greenhouse penalty where the oxygenate product is produced by the combustion of natural gas and process by-products. The CO2 emission rate is estimated as 0.47 tonnes C 02 per tonne product.
5.4 SELECTION CRITERIA AND METHODOLOGY