Carbon Accounting and Embedded Carbon
Carbon accounting is a means of measuring the direct and indirect emissions to the Earth’s biosphere of carbon dioxide and its equivalent gases from industrial activities. Hence if a water turbine is installed in a pipe to recover energy from excessive pressure the generated energy represents a carbon reduction benefit through the reduced carbon output from a conventional generation source. There will be a capital carbon cost, mainly due to the embedded carbon in the materials and workmanship used to manufacture and install the turbine and associated equipment. A Life Cycle Analysis (LCA) would show how long it would take for the capital carbon cost of the water turbine to be repaid by the outputs. LCAs are sometimes complicated by environmental benefits which may accrue beyond the site boundaries or beyond the conventional project life, such as into the demolition phase, so it is important to draw boundaries consistently in time, financial, commercial and geographic terms. For consistency, values used for direct and embedded carbon for different materials are usually taken from approved databases such as the Inventory of Carbon and Energy (ICE), Version 2.0 (Hammond, 2011).
For water treatment processes energy is a major direct carbon cost but the normal fossil fuel element can be effectively reduced by buying electricity from renewable sources, such as wind power companies.
It is sometimes difficult to find carbon information about chemicals since the production methods vary, however, a material such as granular activated carbon, as used for adsorption, will obviously have a high carbon cost, both from its manufacture and its periodic generation; liquid oxygen is another example.
Chemicals introduced in one part of the treatment process incur direct carbon and financial cost, but can also have a detrimental effect on another part of the process, often requiring further treatment, more chemicals and energy to address as well as the consequences of increased waste generated. The overall multiple effects of adding chemicals should, therefore, be taken into account.
Carbon values for construction materials are also available so comparisons can be made for different building techniques. Some surprises have resulted: glass fibre reinforced plastic kiosks and control cabins were frequently used but their end-of-life disposal is difficult as they cannot readily be recycled due to the hazards of raw glass fibres. In contrast, timber framed and insulated buildings, or even bricks, can be easily demolished and the materials reused or recycled.
When assessing process carbon costs it is not usual to include fugitive emissions unless specifically requested. These include odorous air from aeration or sludge treatment; however, any boiler stack emissions should be accounted for. For clean water treatment and pumping, the main fugitive emissions would relate to diesel powered generators primarily used for standby generation (resilience measure). However, like all standby systems, they need to be run regularly under load and maintained in order to minimize emissions and reduce the risk of failure.
In financial terms a project is sometimes considered viable if the capital cost is paid back within about 5 years; however, the acceptable carbon payback period is much longer. Regulation is tending towards longer term planning, typically 25 years, with renewed focus on balancing capital and operating costs (WLC and Totex; Section 2.10); new principles need to be established on carbon capital cost payback since this can be significantly different. There are also wider potential benefits to carbon accounting since changes in metrics can lead to completely new thinking on project concepts and execution. It has been found that such approaches can have significant financial benefits over conventionally managed projects. Broad scope and early adoption are critical. A predefined project scope presented with a carbon reduction objective at detail design stage is not likely to yield many benefits. If project objectives are considered within a broad brief at concept stage, then the risk is that the initial concept may change but the potential benefits could be much greater. For example a pipeline project will realize some benefit from arranging deliveries of pipes to small stockpiles along the route since this will reduce on-site transport and double handling. With a wider brief and perhaps a change of materials the pipes could be manufactured on site with huge savings in long distance transport costs, cheaper installation and major carbon credits. Different attitudes also encourage staff and contractors at all levels to make carbon and cost savings in their daily tasks so the gains can become cumulative. One benefit across the industry has been the increased use of recycled crushed concrete, since cement is a major carbon emitter due to quarrying and firing cement kilns. The financial benefits are apparently marginal but the carbon saving is significant. Careful reuse of trench excavation material has also reduced landfill volumes and costs significantly. Separation of waste material on site for recycling has also become an accepted norm; rather than all waste being dumped in one skip for discharge to landfill.
At a project level carbon accounting has led to evaluating and managing projects against a set of parameters designed to result in carbon credits. Options may be selected on the basis of least carbon expenditure and/or best carbon payback over whatever term is chosen. In a regulated industry this allows a utility’s investment plan to be assessed and scored against other companies with, in some cases, financial penalties for unsatisfactory performance. However, energy is the main source of carbon emissions and the water industry only uses about 1–3% of national energy demand so the industry’s contribution to national carbon reduction targets is relatively small. It is nevertheless an important example for other industries and one with a close public connection.
To help establish carbon accounting as an alternative to financial accounting for evaluating and prioritizing projects a nominal price of carbon was established by international agreement under the Kyoto Protocol in 1997. The hope was that this would raise the profile of climate change and the carbon emissions so that, through regulation, an artificial shortage would cause an effective carbon price rise. This would make projects with carbon benefits, such as renewable energy devices and their large scale deployment, more attractive. Some countries, such as the UK, committed to reducing carbon emissions by other means but full international agreement was never achieved. The price has not risen enough to influence commercial decisions; its value on the open market has not reflected the long-term importance of the issue and commercial decision making remains dominated by the habitual short-term focus of the financial markets.
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Carbon Accounting and Embedded Carbon