Mass Balance Framework - Technical DetailsContents1 Classification SystemsThe fundamental goal of the mass balance framework is to track the flows of materials and products in the UK both geographically and economically. This requires that the data contained in the within the framework is referring to a well defined material or product and must be classified temporally, geographically and economically in a consistent manner. 1.1 Geographical RegionsThere are two principal regional classification schemes relevant to waste management and resource flows: Government Office Regions and Environment Agency regions. However, there appears to be an increasing convergence towards the use of Government regions 2 and, therefore, these regional boundaries have been adopted. As Government regions are formed from subsets of Local Authority areas they are a useful geographical unit for collating data regarding refuse collection and disposal. In total there are 12 separate regions: nine in England plus Scotland, Wales and Northern Ireland (see Table 1). In addition to these there are three likely regional groupings for which data may be generated: the United Kingdom, Great Britain and England and Wales. Table 1 shows the relationships between the levels of regional classification in the framework. The level of Government regions (Level 5) is the standard level for classification but a further level of disaggregation is included in the framework for Local Authority areas (Level 6). This allows studies focusing on specific sub-regional geographical areas to be included in the framework. For instance, the Biffaward 'Island State project calculating the Ecological Footprint of the Isle of Wight (Best Foot Forward, 2000) can be included in this way as the Isle of Wight is a Local Authority within the South East Region. This classification system for regions is compatible with NUTS 1 and NUTS 2 of the Nomenclature des UnitesTerritoriales Statistiques (nomenclature of territorial units for statistics) of the European Commission. 1.2 Industrial SectorsIndustrial sectors are classified according to the Division level of the Standard Industry Classification (SIC) codes defined by the Office for National Statistics (ONS). These are detailed in Table 2.The SIC codes Division 'Private households with employed persons' can be considered as 'Private households' as the employment status of the members of the household is irrelevant when considering a mass balance. This also applies to the classification of industries (section 3.2.4). 1.3 IndustriesIndustries are also be classified according to the UK Standard Industry Classification (SIC) codes. This scheme has 905 separate industrial classifications within a 5-tierhierarchy. These codes are widely implemented and accepted and provide a comprehensive scheme for classifying industrial activities. The US system of industry classification is also widely used in some industries However, it is felt that compatibility with the UK Input-Output accounts and Environmental accounts produced by the ONS is important and the UK SIC codes are, therefore, being used. 1.4 Materials No systems for material classification were found to
be widely accepted by either industry or the agencies involved in waste
management. Therefore, a system is being developed which differentiates
materials from products and which provides a hierarchical structure
for the classification of materials. The primary level of this classification
is composed of natural raw materials: non-metallic minerals, metal ores,
fossil fuels, water and organics. The definition of materials in sub-classifications
is that they are: Definition 1: mass not in its final processed form that is either a subset of the parent material classification or formed by the extraction of mass from its parent material. In other words, materials are directly derived from natural raw materials and when processed into final form or when different materials are combined they are considered as products. The distinction between materials and products requires knowledge of the process of manufacture. For this reason, and also given the number of material types, the material classification system is not being completely defined before the framework is implemented. Rather, definition and classification of materials is being carried out on a project by project basis in consultation with the project researchers. Therefore, non-ambiguous and objective criteria for classifying materials are necessary. These criteria are as follows:
The Combined Nomenclature is the system used by HM Customs and Excise to classify and monitor the movement of goods in the EU. This scheme is comprehensive (~10,000 types of product) and includes all the material and product types likely to be included in the mass balance framework. As industrial enterprises, particularly manufacturing industries with exports, will be familiar with these codes it is felt that this would be a good basis for the classification of materials and products in the mass balance framework. Table 3 gives some examples of the classification of materials using this scheme. As the Combined Nomenclature is a system for naming products rather than materials, the lowest level of material classification may have to be taken from the chapter heading rather than from the codes themselves. For example, the chapters relevant to copper are 'Ores, slag and ash' (chapter 26) and 'Copper and articles thereof' (chapter74). Copper as a material does not exist in the classification. Only products of copper, such as 'copper bars, rods and profiles' are included. However, the chapter heading code can be applied as an extension of the coding scheme to give the classification shown in Table 4. 1.5 ProductsProducts are defined as being materials in final processed form or created by the combination of two or more different materials. It is expected that products, rather than materials, will form the basis of much of the mass balance data framework. As for materials, the Combined Nomenclature provides the basis for the classification of products in the mass balance framework. The scheme is designed to classify products and it is, therefore, better suited to this task than the classification of materials, for which minor modifications to the scheme are required. Using the Combined Nomenclature (CN) for the classification of products makes the mass balance framework described in this report consistent with the recommendations presented in the Eurostat (2001). Eurostat (2001) states that the CN is more detailed than, but fully compatible with, the Harmonised commodity description and coding System (HS) and the Standard International Trade Classification (SITC), which would be the alternative systems. The draft UK Waste Classification Scheme, which is being developed by the Environment Agency, also has elements of material and product classification. This scheme is being incorporated into the framework to allow inclusion of product categories that are either not in the Combined Nomenclature or are more comprehensively defined in the Waste Classification Scheme. It is envisaged that much of the data concerning the mass of outputs from the anthroposphere will be from waste data and, therefore, may be more appropriately classified using this scheme. For instance, the classification of slags and ashes, which are important in elements of the mass balance of incinerated mass, is more comprehensive in the Draft UK Waste Classification Scheme. The classification of chemicals is also more comprehensive than in the Combined Nomenclature. The waste rather than product orientation of the waste classification scheme results in some 'catch all' categories that would not be ideal for a full mass balance e.g. 'commercial waste' and 'household waste'. For a full mass balance the amount of different materials and products that make up commercial or household waste would need to be identified. However, this will not be possible in all circumstances as data on the composition of waste is not readily available. In these circumstances the waste classification scheme may adequate to allow these material flows into the framework. The Combined Nomenclature, combined where necessary with the draft UK Waste Classification Scheme, is therefore being used as the basis of the classification of products. Owing to the number of products in the Combined Nomenclature decisions on product classification are take non a project by project basis, rather than including the whole classification system in the framework database. In cases where the detail of both classification systems is insufficient, a user defined product can be included in the framework as a subclass of either the Combined Nomenclature or the draft UK Waste Classification scheme with the relevant parent class defined in the metadata relating to that record in the database. Ensuring that user defined products or materials are i) a subset of the mass defined in the parent classification and are only allowed at the lowest level of the classification or ii) that the mass accounted for in that definition is not accounted for in a definition at the same level will prevent problems with double counting of mass. A major issue with the classification of materials and products is the form in which the data is available. It may not be possible to classify products and materials according to the scheme set out here if it is wholly incompatible with the schemes used in the relevant industry. In cases where this issue arises the classification of particular materials and products can be set by the project under the condition that the integrity of the data structure is maintained i.e. it does not lead to a situation where there is double counting of mass or multiple classifications for what is essentially the same material or product. Within the framework it is possible to define products in terms of their component materials and component products. For example, a television can be defined as a certain mass of glass, plastic, various metals etc. Defining products in this way allows the component definition to be relevant to the associated manufacturing industry, in terms of the products they use in their processes, or relevant to products and materials that are generally recovered or recycled from that product. However, if the database was complete all product components would be defined in terms of materials, the fundamental mass type, at some level of the data structure. Using the example of a television, amongst other components it would be defined as containing a certain proportion of glass. The mass balance for glass, however, would define glass in terms of proportions of silica sand and soda lime etc., which are materials. Fundamentally, therefore, the amounts of the various materials rather than products used to make televisions are defined. It is also possible to define the materials and products recovered and recycled from a particular product. These recovered/recycled components may, and in most cases probably will, differ from the materials and products used to manufacture it. For instance, rubber crumb can be mechanically recovered from tyres but is not a manufacturing component. 2 Accounting for Mass FlowsThe accounting period to be used in the framework is one year (January to December). In order to track resource flows in and out of a geographical or economic unit over this period eight categories of data need to be identified:
These data then allow the calculation of the 'stock' of the resource at the end of the period. To ensure that these components can be arithmetically manipulated they must all be in consistent units of metric tonnes. 2.1 Initial StockThe initial stock is the amount of a particular material or product within a specified geographical or economic unit at the start of the accounting period. For instance, for a regional classification the initial stock of tyres in the framework will specify the total tonnage of tyres in each region i.e. tyres on vehicles plus stockpiles of used tyres plus stocks held by tyre fitters etc. The initial stock of mass for an economic unit is the amount of that particular material/product owned by that industry or sector. Again using the example of tyres, for an industrial sector classification the mass of tyres owned by each industrial sector is specified. For the construction sector, for instance, the mass of tyres will primarily reflect the number of vehicles owned by the construction sector plus any tyres held as spares. Similarly, the initial stock of tyres within each of the industries listed in the SIC codes can be specified, although it is unlikely that the stock of a product such as tyres will be specified at this level of detail at this stage. 2.2 Total Flux InThe total flux into the geographical or economic unit is the total tonnage of the specified product or material that enters the unit over the accounting period, irrespective of whether or not it stays in the unit. 2.3 Produced & Extracted Material/ProductThe produced & extracted material/product category accounts for materials and products extracted and/or produced in the economic or geographical unit specified i.e. there is no movement of mass between units but tonnage is added to the 'stock' of the unit. This data category is particularly important as it is here that the mass of new material entering the anthroposhpere is quantified. 2.4 Total Flux OutThe total flux out of the geographical or economic unit is the total tonnage of the specified product or material that leaves the unit over the accounting period (excluding emissions, disposal and recycling). 2.4 Embodied Material/ProductThis data category shows the total mass of a product or material component that becomes embodied in other products but does not change its form. For example, in the process of furniture manufacture a mass of wood becomes embodied in the furniture but remains as wood. Whereas, before the wood is embodied its mass balance is explicit, it is now implicitly included as a component material. 2.5 Used Material/ProductWhen products or materials become transformed into another type of product or material they cannot necessarily be considered to have become embodied in that product(Section 3.3.1.5). In the same way as mass 'appears' in the produced/extracted category(Section 3.3.1.3), a category is needed where products 'disappear'. For instance, sheet stainless steel may be transformed into cutlery. The product 'sheet stainless steel' no longer exists and it cannot be considered to be embodied in the 'cutlery' product. The mass balance for stainless steel as a whole is, however, maintained as a new mass of stainless steel appears as cutlery in the produced/extracted category. This category can also be used to account for chemical transformations of materials and products. The distinction, therefore, between 'used' and 'embodied' is that a mass of material or product is embodied if it becomes a component of another product and, thus, its mass is explicitly retained in the framework. If it cannot be described as becoming a component of another product but is transformed into a different product it is accounted for in the 'used' category and the mass of the original material/product is only implicitly held in the framework. 2.6 Recycled & Recovered Material/ProductProducts that are recycled or recovered in some way are accounted for in terms of the materials or products that are recovered from them rather than the original product components. For example, the product components of tyres are mainly steel wire, synthetic rubber and textile. However, recovered/recycled products can be carbon black and oil from pyrolysis, rubber crumb from physical recovery and retreaded tyres. Incineration is treated in this category, not because of the energy recovery which it entails (as discussed earlier, energy flows are not relevant to a mass balance), but because the slag/ash materials can be recycled. In addition to the recovered and recycled products this category also includes the mass and type of solid, liquid and gas emissions during the recovery/recycling process. Emissions of the product mass that occur during the use of the product are also allocated here. For example, tyres that are incinerated emit a certain proportion of their mass as solid and gaseous emissions, the mass of which is allocated in the recovered/recycled category. Where possible, emissions will be listed by type (e.g. CO 2 , CH 4 , and SO 2 )and also categorised as solid, liquid and gas can be included. These emissions effectively add to the total going to final disposal. Mass that is accounted for through recovery or recycling is ultimately re-incorporated into the anthroposphere as 'produced & extracted material/product'. Therefore, recovery and recycling is a sink rather than a source of mass but the balance of mass is maintained when the produced/extracted category is considered. For example, used tyres that are retreaded are included in the recycled/recovered category. When retreaded this mass of tyres re-enters the mass balance through the produced/extracted category of the product tyres. Tyres that have mass recycled through pyrolysis are also included in the recycled/recovered category but the recovered mass re- enters the mass balance through the produced/extracted categories of the products steel, oil, carbon black etc. that are formed by pyrolysis. 2.7 Final disposalThe final disposal section of the framework accounts for the mass of materials or products sent to final disposal where there is no form of recovery of mass. This category is, therefore, mainly for mass going to landfill. Despite its inefficient use of resources, incineration is not considered as final disposal as some of the product's mass remains as ash or slag that could potentially be used as, for example, secondary aggregate. Incinerated mass, therefore, is included in the recovered/recycled category. Mass left after incineration is included in the mass balance as new product(ash or slag), which may or may not go straight to final disposal in landfill. As with the recycled/recovered category, solid, liquid and gas emissions resulting from the use of the product/material and the process of disposal are allocated in the final disposal category. Emissions are specified as CO2, SO2 ,PM10 etc. in addition to being categorised as solid, liquid and gas. 2.8 EmissionsThis category accounts for mass lost to the natural environment as solid, liquid and gas emissions. 2.9 Final StockThe final stock is the amount of a particular material or product within a specified geographical or economic unit at the end of the accounting period. It is, therefore, the initial stock for the next accounting period. It can be calculated as: final = initial + flux in + produced/extracted -flux out - embodied - used - final disposal -recovered/recycled - emissions 3 Double Counting of MassOne of the main problems in constructing this type of mass balance data framework is avoiding double counting of mass. This can be prevented by only counting materials and products that are not embodied in other products. For instance, if a mass balance of the products and materials in the manufacture of furniture is being carried out then the initial mass of furniture and the total initial mass of wood in the industry cannot both be counted as some of the wood is embodied in the furniture. By only allowing the mass of wood not embodied in furniture to be included this avoids double counting. However, this approach precludes the inclusion in the framework of comprehensive data on a single product which is a component of many other products. Therefore, it is important that each product has its component materials and products defined and the masses of the component materials and products are stored in the framework. These data are stored as absolute masses rather than being defined as a percentage of the parent product as this will allow for changes in the composition of the product over time. There are, therefore, two forms of product mass balance. In the preferred form, product mass balances are only explicit when the product is not a component of another product. When it becomes embodied the mass balance becomes implicit in that data is only stored on the product into which it has been embodied. This is the preferred form for the data because it precludes double counting i.e. all masses for different products can be summed to give the total mass. In the second form of product mass balance product masses are explicit even if embodied in other products. This data format is useful for presenting cross-product information on a particular resources of interest. For example, a mass balance of the total mass of steel in a region irrespective of the product it is contained within. Table 5 provides a simplified example of the relationship between the two types of mass balance. The hypothetical example presented is a mass balance of the manufacture of chairs made of 50% steel tubing and 50% plywood. Rows one and two contain the data for the product components of the chairs, i.e. steel tubing and plywood, which are not embodied in chairs. Row three contains the mass balance data for the chairs themselves. Rows four and five contain the data for all plywood and all steel tubing, i.e. both the mass in chairs and the mass that has not been embodied in chairs. Row six contains the total mass of chairs and is, therefore, effectively the same as row three. The 'embodied' category has been blacked out for rows four to six as it is irrelevant whether or not a materials/product is embodied when the total mass is being considered.
Table 1 Geographical Classification System
Table 2 Industrial Sector Classification
Table 3 Selected materials showing the Materials Classification Scheme
devised for the Mass Balance Data
Table 4 Example classification for copper
Table 5 Simplified table demonstrating an example framework table format
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