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A socio-economic based survey of household waste characteristics in the city of Dublin, Ireland. I. Waste composition
resources,
ELS E V I E R
Resources,
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and Recycling
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(I 996) 227-244
conservation andrecycling
A socio-economic based survey of household waste characteristics in the city of Dublin, Ireland. I. Waste composition G. J. Dennison* a, V.A. Dodda, B. Whelanb ‘Department of Agricultural and Food Engineering, University College Dublin, Beljield, Dublin 4, Ireland bEconomic and Social Research Institute, 4 Burlington Road, Dublin 4, Ireland
Received 4 May 1995; revision received 25 August 1995; accepted 14 September
1995
The importance of reliable information on both the quantity and composition of municipal solid waste for the effective planning of waste handling infrastructure has long been recognised. Much of the data currently available in Ireland, and specifically the Dublin region, is either old or unreliable. The present study sought to address the problem of unreliable waste composition data with regard to the city of Dublin. In late 1992 a representative sample of 1500 households was generated at random from the computerised record of the Electoral Register for the city. Each household was visited by trained interviewers and key demographic and socioeconomic data was obtained on the 1036 households that agreed to participate in a survey of waste arisings. Waste was subsequently collected in uncompacted form from 857 of these households and hand-sorted into 12 main categories and 36 categories in total including all subdivisions. Both total waste and individual waste fractions for each household were weighed. An overall total of 12 tonnes of waste was analysed in this manner over a 5week period in October/November 1992. The physical data revealed substantial differences in the relative composition of the waste stream as compared with both previous studies undertaken in Dublin in the late 1970s. In particular the proportion of organic waste was found to be in excess of 45% by wt. in the 1992 study as compared with 34% in 1977/78. However, the present findings were supported by the results of a more limited survey of waste composition carried out separately in 1993/94 for the Dublin green-box recycling service. The physical weight data and the corresponding social, economic and demographic data for all households were amalgamated in electronic format. Statistical techniques were used to test the relationship between socioeconomic factors and the composition of generated waste. The results in* Corresponding
author.
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dicated a clear divide between the more prosperous section of the city’s population and the less prosperous in relation to overall waste generation and the generation of individual components of the waste stream. Keyworris: Household waste; Composition analysis; Socio-economics; Ireland
1. Introduction Reliable current information on both the quantity and composition of the municipal waste stream is of considerable importance in the planning of waste services and infrastructure. In Dublin the waste stream information currently available is both old and unreliable but is perforce widely quoted in the absence of alternative data. The demand for reliable data on waste has grown in recent years in Dublin as elsewhere in response to the higher priority accorded to waste-related matters in general. Furthermore, Irish domestic legislation requires local authorities to prepare waste management plans and it is accepted that such plans involve ‘the assessment of present waste arisings, an accurate idea of their constituents and a forecast of the future position’ [ 11. A need therefore existed in Dublin for the creation of a waste arisings database to provide credible information for waste managers and planners into the medium term. Although data are required on all the principal elements of municipal waste (i.e. domestic, commercial, industrial and construction wastes) limitations on resources has restricted investigations to date to the household component of the waste stream only. The study reported here was the most comprehensive of its kind undertaken in Ireland to date. The data generated are therefore likely to prove of value and interest not only in the local Dublin context but also nationally and internationally. 2. The Dublin Region Dublin is the capital city of Ireland and is located on the eastern seaboard of the island. In terms of municipal administration the ‘the Dublin region’ is a notional entity comprising the city of Dublin (Dublin County Borough) and the three adjoining counties of Fingal, Belgard (South Dublin) and Dun Laoghaire-Rathdown (Fig. 1). The latter three authorities were created on 1 January 1994 from the administrative area of the former Dublin County Council. The present study was undertaken within the administrative area of the city of Dublin, The urban area has grown considerably over the past 30 years. Today the built-up area covers an expanse of approximately 20 000 ha on both banks of the river Liffey and along the Irish Sea coast. The rapid growth of the metropolitan region in the past generation or so has entailed a transformation from the compact relatively highdensity city of the 19th and early 20th centuries to a ‘low-rise, low density, sprawling agglomeration’ [2].
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The population of the region is now just over 1 million having risen from 636 000 in 1946. In 1991 about one-half of this total resided in the city of Dublin with the remainder more or less evenly divided amongst the three Dublin counties [3]. The combined Dublin population represents approximately 29% of the national population or some 50% of Ireland’s urban population [3]. 3. Development of waste analysis procedures Interest in the analysis of solid wastes can be traced to at least the earlier years of the century. Irish practice has tended to follow closely on developments in the United Kingdom. The first serious efforts at systematic analysis in the UK were undertaken in the 1920s and 30s. The apparent catalyst for this work was the publication in 1929 of the Dawes Report into the Public Cleansing of the Administrative County of London [4]. Following the publication of the Dawes Report the Institute of Public Cleansing (IPC) appointed a sub-committee to undertake a thorough investigation of waste analysis procedures [5]. Dawes proposed the use of rateable valuations as the basis for his procedure placing households into three valuation bands with a fourth category to take account of trade premises and this was adopted in the IPC approach. The IPC system was updated in 1965 and 1982 [6] and this procedure has continued to be employed in both the UK and Ireland until recently. Previous waste analysis studies in Dublin, such as that undertaken in 1977178, was based broadly on this approach [l]. A comprehensive hand-sorting analysis of the contents of over 2000 dustbins representing 1277 individual households was carried out in the Birmingham area in 1982-3 and was reported by Pocock and Rufford [7]. The households selected were representative of the area studied. Work of a similar nature has been undertaken in Athens [8] and in Denmark [9]. A common system for classifying the components of household waste in the European Community was proposed by an EC-appointed Working Group in 1984 with the objective of ensuring compatibility of data between member states [lo]. The need for such compatibility has been lent urgency in the interim as definitive waste recovery/recycling targets have been set by both the EU (in the Directive on Packaging and Packaging Waste) and by individual member states. 4. Outline of approach adopted 4.1. Household counts A system of household classification was sought which would permit differences in household size, economic status or other potentially key demographic variables to be identified. The most comprehensive dataset available in Ireland, in this context, is the Small Area Population Statistics (SAPS) produced every 10 years by the Central Statistics Office (CSO) using census information. SAPS provide a large body of information
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Table I City of Dublin demography No. of Wards No. of Households Population (1991) Average household size
162 159 775 478 389 2.99
Source: Ref. [3]
on demographics, housing and other socio-economic parameters at the level of the District Electoral Division (DED) and as it is available in both electronic and paper format it is readily accessible. The DED (termed a ward in city areas) provides a useful unit for the purposes of household aggregation. There are 3440 DEDs/Wards in the state and 162 within the city of Dublin. Table 1 summa&es the principal demographic data concerning Dublin city as derived from the 1991 Census of Population. These data show that the typical Dublin city ward has a population of almost 3000 living in about 1000 households. 4.2. Sampling framework As noted above the SAPS database provides ease of access to important information on the demographic and so&o-economic characteristics of Dublin’s households - at least down to ward level. A sampling framework for the collection of waste arisings data was required which allowed sample data collected on individual households to be expanded to the full population. A process was sought which was capable of identifying individual households for inclusion in the sample. Access to census data on individual households is denied on grounds of privacy and a suitable alternative was therefore required. Attention was focused on the Electoral Register with a view to establishing a sample listing of households. The electoral register holds the names and addresses of every citizen over the age of 18 registered as eligible to vote in local, general and European elections. A franchise department attached to each local authority has the responsibility of ensuring that all eligible persons are registered and that the list is updated annually. Whelan [l l] lists some deficiencies in the Irish electoral register from the standpoint of the ‘perfect’ sampling frame. Age restriction: Under current law the register excludes those under the age of 18. Thus, a sample which includes persons under 18 cannot be obtained directly from the register. Missing efemenfs: Individuals over 18 may fail to appear in the register. The same is true of those who have just reached their 18th birthday. Superfluous elements: The register includes the names of some deceased electors and of some who have left the district without cancelling their previous registration. In spite of these drawbacks Whelan concludes that ‘the Electoral Register is still
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the most appropriate list for use as a sampling frame to select representative samples at reasonable cost’. Each year the Survey Unit of the Economic and Social Research Institute (ESRI) in Dublin transfers the Electoral Register to computer. ESRI has developed a computer-based system called RANSAM for drawing random samples from the register at low cost. The system uses multi-stage sampling so that it is possible to draw on names restricted to certain geographical areas, e.g. the city of Dublin. According to Whelan, an important feature of the RANSAM design is that it is ‘epsem’, i.e. each element (elector) in the population has an equal probability of selection. Epsem procedures offer important advantages, notably the fact that the estimates derived are self-weighting. The ESRI’s RANSAM programme was selected as the means of providing a sample of Dublin’s households for inclusion in the proposed waste analysis study. Accordingly a list of names and addresses were generated from the Dublin city Register of Electors of 1992. The addresses produced were located at random in all parts of the city. 4.3. Sample size Statistical theory suggest that a sample size may be estimated using a formula applicable to estimating proportions for a large population [12]: n=r(l
- T) z2te2
where n is the estimated number of individuals necessary in the sample for the desired precision and confidence; r is the preliminary estimate of the proportion in the population; Z is the two-tailed value of the standardised normal deviate associated with desired level of confidence. e is the acceptable error, or half the maximum acceptable confidence interval. A maximum error of 0.05 with an associated 95% confidence were set as the desired reliability. The value of Z was thus equal to 1.96. As the value of r was not known the maximum value of x = 0.50 was assumed. Substituting into the equation gives the required sample size as 384.2. It was anticipated that at most two-thirds of households approached would probably agree to participate in the survey. Further losses from the sample were anticipated during the operational phase of the survey. Accordingly it was decided to select an initial total of 1500 names and addresses at random from the Electoral Register as the basis for the survey. 4.4. Timing of survey Time of year is an important consideration when sampling In general, average household waste generation rates (in weight some 20-25% lower in summer than winter [13]. During April/May and October/November generation rates in Dublin
solid waste arisings. terms) in Dublin are the two periods of are broadly equiva-
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lent to annual average rates. For this reason it was decided to carry out the analysis during one or other of these ‘average’ periods. The period selected was the late autumn/early winter of 1992. 5. Execution
of the
study
5.1. Questionnaire survey A questionnaire survey was conducted in order to establish the socio-demographic characteristics of each of the households represented on the selected list of elector’s names and addresses. The survey had the additional purposes of seeking the householder’s agreement to participate in the analysis programme and the determination of public attitudes to a range of issues relating to waste management in Dublin. The questionnaire was designed jointly by the authors in consultation with Dublin Corporation technical staff. Care was required in the design of this document as sufficient data of an appropriate nature had to be generated to allow the demographic and economic circumstances of the household and its members to be adequately described. The experience of previous researchers, in particular Pocock and Rufford [7], was found to be of value in this task. Trained interviewers visited the individual households and obtained the necessary information from a responsible adult. The fieldwork for this phase of the study took place in early October 1992. Households agreeing to participate were provided with special yellow plastic refuse sacks marked with a four-digit code unique to that household. Householders were asked to place all their normal weekly production of waste in the sacks provided for a four-week period and place them, in the usual manner and at the usual time, on the kerb for collection. Householders were advised that the sacks would be removed either by the survey team or by the normal refuse collection system. Householders were not told in which of the four weeks their waste would be collected for analysis. Special arrangements were made for participants residing in multi-storey buildings. In many instances waste from multi-storey dwellings is deposited by the householder in a chute which discharges into communal bins stored at ground level. Clearly this procedure was inconsistent with the requirements of the survey and householders were therefore requested to retain their tilled sacks in their own properties for doorstep collection by the survey team. Collection of sacks from participants in high-rise flats or apartments was accorded a priority during the survey in order to minimise inconvenience to the householders concerned. A total of 1036 households out of the original list of 1500 agreed to participate in the survey representing a response rate of 69%. 5.2. Waste collection and analysis The main collection duties were carried out by two teams of city council employees using non-compacting 10 tonne tipping trucks.
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Following their collection yellow sacks were delivered for analysis to one of the city’s depots where space had been provided for the purpose. The sorting was carried out by two teams consisting of three general operatives each with a postgraduate engineering student to supervise, assist and ensure the required standards of accuracy were met and sustained in both sorting and weighing operations. In addition to the above personnel three other people were involved in the sorting process; a ‘bagman’ to sort out incoming sacks and dispose of analysed material; a recorder to log the weights of sacks and individual sack content fractions; the authors provided overall supervision and lent assistance when and where required. A total of 11 persons were therefore involved, almost continuously, for 5 weeks in the sorting operations. 5.3. Sorting procedure Incoming sacks were first weighed individually on electronic scales capable of recording weights up to 60 kg in 0.02 kg steps. Where more than one sack was collected from an individual household the aggregate weight was recorded. Once weighed the sacks were split open on benches and the contents sorted into 12 principal categories and 36 categories in total including all sub-categories. The individual fractions were then weighed on either the large scales or, for the lighter fractions, on one of two smaller electronic scales capable of recording in the range O-2 kg in steps of 1 g. All the scales used were new and were checked for accuracy before use. Checks on accuracy were also carried out periodically by the survey teams. Weights associated with a given household, i.e. both the aggregate sack weights and the individual fraction weights, were recorded together with the household’s unique identifying four digit code. The sorting team leaders were thoroughly briefed prior to the commencement of the project on the fraction categories to be used and the identification of materials. Material categories were selected based on the advice of specialists in the packaging and other relevant industries and to reflect the anticipated requirements of the (then) draft EU Directive on Packaging and Packaging Waste 1141. A total of 12 principal categories was employed although the total number of individual categories used was 36 when all subdivisions are included. This was the time certain categories, such as ‘batteries’ or ‘disposable nappies’ (diapers) were employed in an Irish waste analysis. As noted the collection and sorting of waste from the participating households continued for a period of 5 weeks extending over October and early November 1992. Table 2 Summary of households participating and collected Target households Participating households Percentage of target list Collected households Percentage of target list Percentage of participating list
1500 1036 69 857 57.1 82.7
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Of the 1036 participating households yellow sacks were finally collected and analysed from 857 households representing an 83% collection rate. This number corresponds to 57O/oof the original 1500 target list of selected households. The remaining households were omitted for various operational reasons, e.g. sacks continuously not left out for collection, householder withdraws from participation, etc. Details of the household numbers participating and sorted are given in Table 2. 6. Results 6.1. Composition of household waste
The average size of the 857 households in the sample was 3.78 persons. This is 26% higher than the actual average size of households in Dublin city which the 1991 Census of Population records as 2.99 persons [3]. Details are available on the distribution of household sizes in the population in 1991. These are tabulated below in Table 3 and compared with the distribution found in the sample. One- and two-person households comprised nearly 52% of all households in Dublin in 1991. This proportion has risen from 48% in 1986 and is likely to represent part of a continuing trend. These smaller households are under-represented in the sample. Further analysis revealed that this was mainly due to an underrepresentation of flat- and apartment-dwellers in the sample. The 1991 Census of Population shows that the average household size of those residing in flats (incl. apartments) is only some 57% that of those residing in houses. Some 25% of the city population resides in flats/apartments while only 8.5% of the sample population was found to be in this category [3]. The waste arisings data for the sample were weighted to reflect the actual proportions of the different household sizes in the population and therefore the actual overall average household size. The procedure used will be described more fully in Part II [22]. The post-weighting analysis data are shown in Table 4. One of the most interesting and unexpected results is the relatively high proportion of organics in Dublin’s
Table 3 Household size distribution in sample and population Household size (no. of persons)
Sample (%)
Population (%)
I
8.2 18.6 19.1 20.2 15.7 18.2
28.3 23.5 15.3 13.7 9.5 9.7
2 3 4 5 6+
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Table 4 Post-weighting constituent analysis of household waste Material Newspaper Magazines Coloured card (P) Old corrugated cardboard (P) Foil-lined laminates (e.g. juice cartons) (P) Polymer-lined laminates (e.g. milk cartons) (P) Other paper (tissue, etc.) Total paper
Weight % 8.44 0.98 3.32 0.70 0.16 1.16 6.33 21.09
Polyethylene sacks (e.g. bin liners, supermarket bags) (P) PET bottles (P) Polyethylene bottles (P) PVC bottles (P) Polystyrene containers (e.g. meat trays) (P) Polyethylene film (P) Snack food wrappers (e.g. crisp packets) (P) Non-packaging plastics Other plastic Total plastic
4.90 0.55
Textiles
2.32
Disposable nappies
2.71
Clear bottles (P) Green bottles (P) Brown bottles (P) Jars (P) Other glass Total glass
2.06
Food cans (tins) (P) Ferrous beverage cans (P) Altinium beverage cans (P) Foil (P) Other ferrous materials Other non-ferrous materials Total metals
2.43 0.17 0.47
Batteries
0.03
Food waste Garden waste Total organics Miscellaneous combustible (e.g. timber) Miscellaneous non-combustible (primarily cinders) Fines (primarily ash) Household chemicals (incl. of packaging) Total packaging (P) Total non-packaging Overall total
1.18 0.17 0.01 0.01 0.65 0.11 0.10 8.79
0.78 0.61 1.45 0.12 5.02
0.36 0.18 0.10 3.70
40.48 5.13 45.62 1.70 7.68 1.22 0.11 $2.25 77.75 100.00
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Fig. 1. Dublin city (county borough) and surrounding counties.
household waste stream. Organics account for nearly half of all waste arisings from domestic sources. On average one-ninth of all putrescible waste consists of garden waste; the rest is of kitchen origin. Packaging waste, of all types, comprises over one-fifth of the total waste stream according to these data. The largest single contributor to packaging waste are PE sacks and plastics in general constitute nearly 4O?h of the total arisings under this heading. The relative composition of waste packaging is shown in Fig. 2. The present data may be compared with waste analysis information from a previous Dublin study on household waste composition [I]. The latter involved five separate sampling exercises undertaken in the summer and autumn of 1977, the winter of 1977/78 and the spring and summer of 1978. In each case a total of 400-500 properties comprised of blocks of 20-180 dwellings of varied social and economic circumstances were sampled and between 4.26 and 6.2 tonnes of waste collected for analysis. Aggregated results for this study are presented in Table 5 and it is evident that there are quite distinct differences between the results obtained in the late 1970s
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22.67%
39.68%
Fig.2. Relativecompositionof packagingwastefractionof householdwastestream.
and the present data. The reasons for these differences are unclear at present. The 1970s data are more broadly representative, in theory, of the average annual composition of the city’s waste. However, more recent seasonally-adjusted data tend to confirm the findings of the present survey (see below). The most likely explanation is that these differences reflect the differences in the sampling and analytical methodologies employed in the 1970s and the present study. The findings of the present study may also be compared with the results obtained by a separate waste analysis programme undertaken in Dublin by Kerbside Dublin in 1993194. Kerbside Dublin is a private company which provides a pilot green-box type kerbside recycling service to some 25 000 private households in the south-western section of Dublin city and suburbs. The company was founded in 1991 and is funded by local and central government, industry and by the European Recovery and Recycling Association (ERRA) [15].
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Table 5 Comparative waste analysis results, weight%
Paper Plastic Textiles Disposable nappies Glass Metals Fe Non-Fe Organics Miscellaneous combustibles Miscellaneous non-combustibles Fines Batteries
Dublin 1992
Dublin 1977/78
Kerbside Dublin 1993l94
21.09 8.79 2.32 2.71 5.02 3.70 2.77 0.93 45.62 1.70 7.68 1.22 0.03
33 12 3 No Data 10 4
24.8 8.3 1.8 3.7 5.4 3.8
34 No Data No Data 4 No Data
49.6 1.5 0.2 0.8 0.1
Kerbside Dublin commissioned an independent study of the composition of both the recyclable and non-recyclable fractions of the waste stream in its area of operation. The analysis procedure followed was designed by ERRA [16] and was aimed at producing samples representative of the socio-economic mix of the area serviced. The first three of four seasonally determined samples were undertaken in June 1993, September 1993 and May 1994, respectively. The aggregated average results of these three surveys are shown in Table 5 [17] together with national average data [18]. Both the Kerbside Dublin results and national average data reflect very closely the Endings of the present study. Comparisons between Dublin and other cities or countries in terms of waste composition data are probably invidious and may be misleading given known differences in sampling and analytical methodologies in addition to those related to demographics, social and economic circumstance and climate. For whatever reason, it is clear that the Dublin data are substantially different to those pertaining to other European countries and cities, particularly in relation to the organic content of household waste. For example, UK national average composition data for household waste 1191suggest that organics and paper account for about 20% and 32%, respectively of arisings in this sector. In Geneva Leroy et al. [20] report that organics comprise 30% of household arisings while paper accounts for 24% of the total. Slightly different proportions are reported for Vienna by Amfelser [21] where the organic content is -23% and that of paper is 33.6%. The glass content of household waste in the UK, Geneva and Vienna is also uniformly higher than in Dublin. The Dublin figure of 5.02% may be compared with that of the UK (9.2%), Geneva (8.5%) and Vienna (10.4%). Plastic content, on the other hand, in both Geneva (8%) and Vienna (7.5%) is closer to that in Dublin (8.79%) than is the UK national average of 12%.
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6.2.
Influence
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of socio-economic factors
The waste data were paired with the corresponding questionnaire information for each of the sampled households and the combined data files were transferred to a VAX computer for analysis using the SPSS 4.1 statistical software package. Correlation analysis was used to test the level of inter-relation between pairs of datasets, i.e. socio-demographic parameters and physical waste data. The socioeconomic parameters employed included those relating to the household size, tenure and type of accommodation, home heating arrangements, employment status, social class and education level attained by head of household and age profile of residents. The significance of the correlation coefficent calculated in this exercise is summarised in Table 6. The picture that emerges from the above analysis is, as expected, one of distinct differences in waste production patterns between different sectors of the population and in general the findings coincide with intuitive expectations. For example the use of open fires or solid-fuel central heating (SFCH) is a strong predictor for the production of miscellaneous non-combustible material (primarily cinders) and fines (primarily ash). One apparent anomaly evident in the results is the strong positive correlation between the production of garden waste and apartment dwelling. One possible explanation for this could be the inclusion of grounds maintenance waste in the material collected from apartments. A divide clearly exists between the more prosperous section of society, as represented generally by those people in employment and living in detached or semidetached dwellings, and the less prosperous. The latter may be characterised as including the unemployed, students and the sick or retired. The divide between these two broad sectors is evident in the data for waste composition and quantity. While many of the features associated with the former group are strong positive predictors of both overall waste generation and the generation of individual components of the waste stream many of those associated with latter group are the reverse. Interestingly social class per se does not appear to be a strong determinant in waste generation (see Appendix I for definitions of ‘Social Class’ as used in Ireland for demographic purposes). Social class 1 appears as a predictor of metals and garden waste and social class 6 is likewise a predictor of miscellaneous material (i.e. miscellaneous combustible/non-combustible and fines). These are among the few references to social class to emerge from the statistical analysis. In general the relative composition of the household waste stream was found to be remarkably consistent across the social class spectrum. Household size is seen to be a reasonably consistent influence on waste generation. It not only appears as a positive influence in live out of the 11 variables assessed above but probable analogues of household size such as flat dwelling, retired or student households are also common strong correlation factors. Various forms of tenure appear in the analysis including private rented, tenant purchase or local authority rented. All of these might be regarded as being associated with the less prosperous section of society and all except tenant purchase appear as
Semidetached Terrace Local authority flat Private apartment Owner occupier Tenant purchase Local authority rented Private rented Other rented Non SFCH SFCH Open tire Electric heating Bottled gas Pets At work
Household size Detached
** ???
?? ??
**
Neg*
Neg**
+*
*
Neg.*
??
Neg*
Neg**
St
Neg** ?? *
Neg**
z
Neg**
Neg*
**
?? ??
Other paper
Newspaper
Neg**
Neg*
* +*
Neg.*
??
*
Neg**
*
**
Total Waste
Table 6 Significance table based on correlation analysis
?? *
22
Neg**
Neg*
**
Neg**
*
Neg**
???
?? ??
Total plastic
*
*
Neg*
???
Textiles
**
??
?? ??
Blass
Total
???
**
Beverge cans
???
?? ??
??
Other metal
Neg.
?? ??
?? ?
Neg** Neg**
?? ??
Neg**
**
**
Garden waste
Neg**
?? ??
???
Neg**
?? ??
Neg**
?? ??
**
Food waste
??
Neg*
Neg** ** **
???
?? ??
Misc.
?? * **
Neg** Neg** Neg**
*
Neg*
Neg**
Neg**
Neg*
Neg**
**
?? * 22
Neg*
Neg**
Neg** Neg.
Neg**
Neg.*
*
Neg**
?? ??
**
**
*
Neg* t
*
??
*
?? ??
** **
Neg.
?? ??
Neg** Neg*
Neg** Neg*
??
Neg*
Neg** *
??
Neg*
**
Neg**
**
?? , Positive Correlation at the 95% level. **, Positive Correlation at the 99% level. Neg., Negative Correlation at the 95% level. Neg**, Negative Correlation at the 99% level.
Unemployed Student Retired Home duty Sick Social Class 1 Social Class 2 Social Class 3 Social Class 4 Social Class 5 Social Class 6 Primary education Secondary education Third level Age O-4 Age 5-15 Age 16-29 Age 30-64 Age 65+ Sink disposal unit Deep freeze Fridge freezer
212
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strong negative determinants on waste generation rates. Owner occupation is not represented as such. However, probable analogues such as detached, semi-detached or terraced dwellings do appear in the list of strong positive determinants. 7. coIlclusions The present study sought to address the problem of unreliable waste composition data with regard to the city of Dublin. The physical data revealed substantial differences in the relative composition of the waste stream as compared with both previous studies undertaken in Dublin in the late 1970s and with more recent UK national data. In particular the proportion of organic waste was found to be in excess of 45% by wt. in the 1992 study as compared with 34% in 1977178(Dublin) and - 20% (UK). However, the present findings were supported by the results of a more limited survey of waste composition carried out separately in 1993/94 for the Dublin green-box recycling service. Following the amalgamation of the physical weight data and the corresponding social, economic and demographic data for all households in electronic format statistical techniques were used to test the relationship between socio-economic factors and the composition of generated waste. In general the results of this exercise tended to confirm anecdotal observation. For example it was found that household size (and its analogues) was a key positive determinant not only - as might be anticipated - in overall waste production, but also with regard to the relative proportions of the components of the generated waste stream. Similarly, more affluent households were found to be more likely to produce larger quantities of waste, including all components, than the less aftluent. This was the first Irish waste analysis survey to investigate the subject to this degree of detail and it is anticipated that the results obtained will provide a baseline against which future change can be assessed. Further work is required to establish with greater certainty the influence of seasonal factors on both waste generation rates and relative composition. The sampling programme should also be extended in future to include the commercial and industrial waste streams so that a comprehensive assessment of the combined inputs to the municipal waste stream may be facilitated. Acknowledgements The practical, financial and technical assistance of the Dublin City Engineer and his staff in the planning and execution of this study is gratefully acknowledged. Appendix 1: List of social classes used in Ireland for demographic purposes and tbe occupations assigned to them Social Class 1 Higher professional, higher managerial, proprietors more acres (> 80 ha).
and farmers farming 200 or
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Social Class 2 Lower professional, lower managerial, proprietors and farmers farming lOO- 199 acres (40-80 ha). Social Class 3 Other non-manual and farmers farming 50-99 acres (20-40 ha). Social Class 4 Skilled manual and farmers farming 30-49 acres (12-20 ha). Social Class 5 Semi-skilled manual and farmers farming less than 30 acres (< 12 ha). Social Class 6 Unskilled manual. Unemployed and retired persons are classified according to their last employment. References [l] McGee, R., 1980. Municipal refuse including domestic and trade wastes litter and packaging. In: Proceedings of Seminar on Today’s and Tomorrow’s Wastes, National Board for Science and Technology, Dublin, pp. 23-28. [2] Cosgrove, A. (Ed.), 1988. Dublin Through the Ages. College Press, Dublin, 256 pp. [3] Central Statistics Office, 1992. Census of Population of Ireland for 1991, Dublin. [4] Dawes, J.C., 1929. Report on an Investigation into the Public Cleansing service in the Administrative County of London, HMSO, London. [5] Gulley, B.W., 1984. An Overview of UK Waste Analysis Experience, Wastes Management, April, pp. 210-216. [6] Higginson, A.E., 1982. The Analysis of Domestic Waste. IWM Publication No. 10, Northampton, UK. [7] Pocock, R.L. and Rufford, N.M., 1983. A New Approach to Household Waste Analysis and Forecasting. Paper to Department of the Environmentinstitute of Waste Management One-day Joint Seminar, Aston University, Birmingham, 20th September, 1983. [8] Skordilis, A., 1985. Household waste analysis in the greater Athens region using generally acceptable statistical methods. In: M.P. Ferranti and G.L. Ferrer0 @is.), Sorting of Household Waste and Thermal Treatment of Waste, Elsevier, London, 521 pp. [9] Mortensen, H., 1985. Low-technology sorting of presorted household waste. In: M.P. Ferranti and G.L. Ferrer0 @Is.), Sorting of Household Waste and Thermal Treatment of Waste, Elsevier, London, 521 pp. [lo] Williams, H.E., 1984. Recommendations for the Classification and Description of Household Waste and Refuse-derived Fuel. Report by Ecotec, Birmingham, UK to EC Commission. [I I] Whelan, B., 1979. RANSAM: A random sample design for Ireland. Economic and Social Review, IO (2, Jan.), 169-174 pp. [12] McCall, C.H. Jr., 1982. Sampling and Statistics: Handbook for Research, Iowa, 340 pp. [I31 Dermison, G.J., 1991. Municipal Solid Waste Management in Greater Dublin 1986-2001, M.Eng.Sc. Thesis, University College Dublin. [I41 Commission of the European Commission, 1992. Draft Proposal for a Council Directive on Packaging and Packaging Waste, Brussels. 1151 Madden, N., 1993. Recycling Experiences: Kerbside Dublin. Paper to Addressing the Challenge: The National Recycling Conference, Wexford, Ireland, 9-10 December 1993.
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[16] ERRA, 1993. Waste Analysis Procedure, Brussels. [17] DeBurca, D., Dodd, V.A., Dennison, G.J., Cullinan, N. and Madden, N., 1994. Assessing the role of kerbside recycling in municipal waste management in the Dublin region. Paper to the 10th International Conference on Solid Waste Management and Secondary Materials, Philadelphia, PA, 14-16 Nov., 1994. [I81 Department of the Environment (Ireland), 1994. Recycling for Ireland, Dublin. [I91 Materials Reclamation Weekly, May I, 1993. Assessing the Recyclables in British Dustbins, p. 6. [20] Amfelser, F., 1992.Systems and Facilities for the Collection of Household Wastes in Vienna. Waste Management and Research, 10 (Dec.), pp. 535-541. [21) Leroy, D., Giovannoni, J.-M. and Maystre, L.-Y., 1992. Sampling Method to Determine a Household Waste Composition Variance. Wastes Management and Research, IO (Feb.), pp. 3-12. (221 Dennison, G.J., Dodd, V.A. and Whelan, B., 1996. A socio-economic based survey of household waste characteristics in the city of Dublin, Ireland - II. Waste quantities. Resour. Conserv. and Recyc., 17, 245-257.
ELS E V I E R
Resources,
Conservation
and Recycling
17
(I 996) 227-244
conservation andrecycling
A socio-economic based survey of household waste characteristics in the city of Dublin, Ireland. I. Waste composition G. J. Dennison* a, V.A. Dodda, B. Whelanb ‘Department of Agricultural and Food Engineering, University College Dublin, Beljield, Dublin 4, Ireland bEconomic and Social Research Institute, 4 Burlington Road, Dublin 4, Ireland
Received 4 May 1995; revision received 25 August 1995; accepted 14 September
1995
The importance of reliable information on both the quantity and composition of municipal solid waste for the effective planning of waste handling infrastructure has long been recognised. Much of the data currently available in Ireland, and specifically the Dublin region, is either old or unreliable. The present study sought to address the problem of unreliable waste composition data with regard to the city of Dublin. In late 1992 a representative sample of 1500 households was generated at random from the computerised record of the Electoral Register for the city. Each household was visited by trained interviewers and key demographic and socioeconomic data was obtained on the 1036 households that agreed to participate in a survey of waste arisings. Waste was subsequently collected in uncompacted form from 857 of these households and hand-sorted into 12 main categories and 36 categories in total including all subdivisions. Both total waste and individual waste fractions for each household were weighed. An overall total of 12 tonnes of waste was analysed in this manner over a 5week period in October/November 1992. The physical data revealed substantial differences in the relative composition of the waste stream as compared with both previous studies undertaken in Dublin in the late 1970s. In particular the proportion of organic waste was found to be in excess of 45% by wt. in the 1992 study as compared with 34% in 1977/78. However, the present findings were supported by the results of a more limited survey of waste composition carried out separately in 1993/94 for the Dublin green-box recycling service. The physical weight data and the corresponding social, economic and demographic data for all households were amalgamated in electronic format. Statistical techniques were used to test the relationship between socioeconomic factors and the composition of generated waste. The results in* Corresponding
author.
Tel: +353
I 7061867; fax: +353 I 7061155.
0921~3449196/$15.00 @ 1996 Elsevier Science B.V. All PII 0921-3449(96)01070-l
rights reserved.
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dicated a clear divide between the more prosperous section of the city’s population and the less prosperous in relation to overall waste generation and the generation of individual components of the waste stream. Keyworris: Household waste; Composition analysis; Socio-economics; Ireland
1. Introduction Reliable current information on both the quantity and composition of the municipal waste stream is of considerable importance in the planning of waste services and infrastructure. In Dublin the waste stream information currently available is both old and unreliable but is perforce widely quoted in the absence of alternative data. The demand for reliable data on waste has grown in recent years in Dublin as elsewhere in response to the higher priority accorded to waste-related matters in general. Furthermore, Irish domestic legislation requires local authorities to prepare waste management plans and it is accepted that such plans involve ‘the assessment of present waste arisings, an accurate idea of their constituents and a forecast of the future position’ [ 11. A need therefore existed in Dublin for the creation of a waste arisings database to provide credible information for waste managers and planners into the medium term. Although data are required on all the principal elements of municipal waste (i.e. domestic, commercial, industrial and construction wastes) limitations on resources has restricted investigations to date to the household component of the waste stream only. The study reported here was the most comprehensive of its kind undertaken in Ireland to date. The data generated are therefore likely to prove of value and interest not only in the local Dublin context but also nationally and internationally. 2. The Dublin Region Dublin is the capital city of Ireland and is located on the eastern seaboard of the island. In terms of municipal administration the ‘the Dublin region’ is a notional entity comprising the city of Dublin (Dublin County Borough) and the three adjoining counties of Fingal, Belgard (South Dublin) and Dun Laoghaire-Rathdown (Fig. 1). The latter three authorities were created on 1 January 1994 from the administrative area of the former Dublin County Council. The present study was undertaken within the administrative area of the city of Dublin, The urban area has grown considerably over the past 30 years. Today the built-up area covers an expanse of approximately 20 000 ha on both banks of the river Liffey and along the Irish Sea coast. The rapid growth of the metropolitan region in the past generation or so has entailed a transformation from the compact relatively highdensity city of the 19th and early 20th centuries to a ‘low-rise, low density, sprawling agglomeration’ [2].
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The population of the region is now just over 1 million having risen from 636 000 in 1946. In 1991 about one-half of this total resided in the city of Dublin with the remainder more or less evenly divided amongst the three Dublin counties [3]. The combined Dublin population represents approximately 29% of the national population or some 50% of Ireland’s urban population [3]. 3. Development of waste analysis procedures Interest in the analysis of solid wastes can be traced to at least the earlier years of the century. Irish practice has tended to follow closely on developments in the United Kingdom. The first serious efforts at systematic analysis in the UK were undertaken in the 1920s and 30s. The apparent catalyst for this work was the publication in 1929 of the Dawes Report into the Public Cleansing of the Administrative County of London [4]. Following the publication of the Dawes Report the Institute of Public Cleansing (IPC) appointed a sub-committee to undertake a thorough investigation of waste analysis procedures [5]. Dawes proposed the use of rateable valuations as the basis for his procedure placing households into three valuation bands with a fourth category to take account of trade premises and this was adopted in the IPC approach. The IPC system was updated in 1965 and 1982 [6] and this procedure has continued to be employed in both the UK and Ireland until recently. Previous waste analysis studies in Dublin, such as that undertaken in 1977178, was based broadly on this approach [l]. A comprehensive hand-sorting analysis of the contents of over 2000 dustbins representing 1277 individual households was carried out in the Birmingham area in 1982-3 and was reported by Pocock and Rufford [7]. The households selected were representative of the area studied. Work of a similar nature has been undertaken in Athens [8] and in Denmark [9]. A common system for classifying the components of household waste in the European Community was proposed by an EC-appointed Working Group in 1984 with the objective of ensuring compatibility of data between member states [lo]. The need for such compatibility has been lent urgency in the interim as definitive waste recovery/recycling targets have been set by both the EU (in the Directive on Packaging and Packaging Waste) and by individual member states. 4. Outline of approach adopted 4.1. Household counts A system of household classification was sought which would permit differences in household size, economic status or other potentially key demographic variables to be identified. The most comprehensive dataset available in Ireland, in this context, is the Small Area Population Statistics (SAPS) produced every 10 years by the Central Statistics Office (CSO) using census information. SAPS provide a large body of information
230
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Table I City of Dublin demography No. of Wards No. of Households Population (1991) Average household size
162 159 775 478 389 2.99
Source: Ref. [3]
on demographics, housing and other socio-economic parameters at the level of the District Electoral Division (DED) and as it is available in both electronic and paper format it is readily accessible. The DED (termed a ward in city areas) provides a useful unit for the purposes of household aggregation. There are 3440 DEDs/Wards in the state and 162 within the city of Dublin. Table 1 summa&es the principal demographic data concerning Dublin city as derived from the 1991 Census of Population. These data show that the typical Dublin city ward has a population of almost 3000 living in about 1000 households. 4.2. Sampling framework As noted above the SAPS database provides ease of access to important information on the demographic and so&o-economic characteristics of Dublin’s households - at least down to ward level. A sampling framework for the collection of waste arisings data was required which allowed sample data collected on individual households to be expanded to the full population. A process was sought which was capable of identifying individual households for inclusion in the sample. Access to census data on individual households is denied on grounds of privacy and a suitable alternative was therefore required. Attention was focused on the Electoral Register with a view to establishing a sample listing of households. The electoral register holds the names and addresses of every citizen over the age of 18 registered as eligible to vote in local, general and European elections. A franchise department attached to each local authority has the responsibility of ensuring that all eligible persons are registered and that the list is updated annually. Whelan [l l] lists some deficiencies in the Irish electoral register from the standpoint of the ‘perfect’ sampling frame. Age restriction: Under current law the register excludes those under the age of 18. Thus, a sample which includes persons under 18 cannot be obtained directly from the register. Missing efemenfs: Individuals over 18 may fail to appear in the register. The same is true of those who have just reached their 18th birthday. Superfluous elements: The register includes the names of some deceased electors and of some who have left the district without cancelling their previous registration. In spite of these drawbacks Whelan concludes that ‘the Electoral Register is still
G.J. Dennison et al. /Resources,
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231
the most appropriate list for use as a sampling frame to select representative samples at reasonable cost’. Each year the Survey Unit of the Economic and Social Research Institute (ESRI) in Dublin transfers the Electoral Register to computer. ESRI has developed a computer-based system called RANSAM for drawing random samples from the register at low cost. The system uses multi-stage sampling so that it is possible to draw on names restricted to certain geographical areas, e.g. the city of Dublin. According to Whelan, an important feature of the RANSAM design is that it is ‘epsem’, i.e. each element (elector) in the population has an equal probability of selection. Epsem procedures offer important advantages, notably the fact that the estimates derived are self-weighting. The ESRI’s RANSAM programme was selected as the means of providing a sample of Dublin’s households for inclusion in the proposed waste analysis study. Accordingly a list of names and addresses were generated from the Dublin city Register of Electors of 1992. The addresses produced were located at random in all parts of the city. 4.3. Sample size Statistical theory suggest that a sample size may be estimated using a formula applicable to estimating proportions for a large population [12]: n=r(l
- T) z2te2
where n is the estimated number of individuals necessary in the sample for the desired precision and confidence; r is the preliminary estimate of the proportion in the population; Z is the two-tailed value of the standardised normal deviate associated with desired level of confidence. e is the acceptable error, or half the maximum acceptable confidence interval. A maximum error of 0.05 with an associated 95% confidence were set as the desired reliability. The value of Z was thus equal to 1.96. As the value of r was not known the maximum value of x = 0.50 was assumed. Substituting into the equation gives the required sample size as 384.2. It was anticipated that at most two-thirds of households approached would probably agree to participate in the survey. Further losses from the sample were anticipated during the operational phase of the survey. Accordingly it was decided to select an initial total of 1500 names and addresses at random from the Electoral Register as the basis for the survey. 4.4. Timing of survey Time of year is an important consideration when sampling In general, average household waste generation rates (in weight some 20-25% lower in summer than winter [13]. During April/May and October/November generation rates in Dublin
solid waste arisings. terms) in Dublin are the two periods of are broadly equiva-
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lent to annual average rates. For this reason it was decided to carry out the analysis during one or other of these ‘average’ periods. The period selected was the late autumn/early winter of 1992. 5. Execution
of the
study
5.1. Questionnaire survey A questionnaire survey was conducted in order to establish the socio-demographic characteristics of each of the households represented on the selected list of elector’s names and addresses. The survey had the additional purposes of seeking the householder’s agreement to participate in the analysis programme and the determination of public attitudes to a range of issues relating to waste management in Dublin. The questionnaire was designed jointly by the authors in consultation with Dublin Corporation technical staff. Care was required in the design of this document as sufficient data of an appropriate nature had to be generated to allow the demographic and economic circumstances of the household and its members to be adequately described. The experience of previous researchers, in particular Pocock and Rufford [7], was found to be of value in this task. Trained interviewers visited the individual households and obtained the necessary information from a responsible adult. The fieldwork for this phase of the study took place in early October 1992. Households agreeing to participate were provided with special yellow plastic refuse sacks marked with a four-digit code unique to that household. Householders were asked to place all their normal weekly production of waste in the sacks provided for a four-week period and place them, in the usual manner and at the usual time, on the kerb for collection. Householders were advised that the sacks would be removed either by the survey team or by the normal refuse collection system. Householders were not told in which of the four weeks their waste would be collected for analysis. Special arrangements were made for participants residing in multi-storey buildings. In many instances waste from multi-storey dwellings is deposited by the householder in a chute which discharges into communal bins stored at ground level. Clearly this procedure was inconsistent with the requirements of the survey and householders were therefore requested to retain their tilled sacks in their own properties for doorstep collection by the survey team. Collection of sacks from participants in high-rise flats or apartments was accorded a priority during the survey in order to minimise inconvenience to the householders concerned. A total of 1036 households out of the original list of 1500 agreed to participate in the survey representing a response rate of 69%. 5.2. Waste collection and analysis The main collection duties were carried out by two teams of city council employees using non-compacting 10 tonne tipping trucks.
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Following their collection yellow sacks were delivered for analysis to one of the city’s depots where space had been provided for the purpose. The sorting was carried out by two teams consisting of three general operatives each with a postgraduate engineering student to supervise, assist and ensure the required standards of accuracy were met and sustained in both sorting and weighing operations. In addition to the above personnel three other people were involved in the sorting process; a ‘bagman’ to sort out incoming sacks and dispose of analysed material; a recorder to log the weights of sacks and individual sack content fractions; the authors provided overall supervision and lent assistance when and where required. A total of 11 persons were therefore involved, almost continuously, for 5 weeks in the sorting operations. 5.3. Sorting procedure Incoming sacks were first weighed individually on electronic scales capable of recording weights up to 60 kg in 0.02 kg steps. Where more than one sack was collected from an individual household the aggregate weight was recorded. Once weighed the sacks were split open on benches and the contents sorted into 12 principal categories and 36 categories in total including all sub-categories. The individual fractions were then weighed on either the large scales or, for the lighter fractions, on one of two smaller electronic scales capable of recording in the range O-2 kg in steps of 1 g. All the scales used were new and were checked for accuracy before use. Checks on accuracy were also carried out periodically by the survey teams. Weights associated with a given household, i.e. both the aggregate sack weights and the individual fraction weights, were recorded together with the household’s unique identifying four digit code. The sorting team leaders were thoroughly briefed prior to the commencement of the project on the fraction categories to be used and the identification of materials. Material categories were selected based on the advice of specialists in the packaging and other relevant industries and to reflect the anticipated requirements of the (then) draft EU Directive on Packaging and Packaging Waste 1141. A total of 12 principal categories was employed although the total number of individual categories used was 36 when all subdivisions are included. This was the time certain categories, such as ‘batteries’ or ‘disposable nappies’ (diapers) were employed in an Irish waste analysis. As noted the collection and sorting of waste from the participating households continued for a period of 5 weeks extending over October and early November 1992. Table 2 Summary of households participating and collected Target households Participating households Percentage of target list Collected households Percentage of target list Percentage of participating list
1500 1036 69 857 57.1 82.7
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Of the 1036 participating households yellow sacks were finally collected and analysed from 857 households representing an 83% collection rate. This number corresponds to 57O/oof the original 1500 target list of selected households. The remaining households were omitted for various operational reasons, e.g. sacks continuously not left out for collection, householder withdraws from participation, etc. Details of the household numbers participating and sorted are given in Table 2. 6. Results 6.1. Composition of household waste
The average size of the 857 households in the sample was 3.78 persons. This is 26% higher than the actual average size of households in Dublin city which the 1991 Census of Population records as 2.99 persons [3]. Details are available on the distribution of household sizes in the population in 1991. These are tabulated below in Table 3 and compared with the distribution found in the sample. One- and two-person households comprised nearly 52% of all households in Dublin in 1991. This proportion has risen from 48% in 1986 and is likely to represent part of a continuing trend. These smaller households are under-represented in the sample. Further analysis revealed that this was mainly due to an underrepresentation of flat- and apartment-dwellers in the sample. The 1991 Census of Population shows that the average household size of those residing in flats (incl. apartments) is only some 57% that of those residing in houses. Some 25% of the city population resides in flats/apartments while only 8.5% of the sample population was found to be in this category [3]. The waste arisings data for the sample were weighted to reflect the actual proportions of the different household sizes in the population and therefore the actual overall average household size. The procedure used will be described more fully in Part II [22]. The post-weighting analysis data are shown in Table 4. One of the most interesting and unexpected results is the relatively high proportion of organics in Dublin’s
Table 3 Household size distribution in sample and population Household size (no. of persons)
Sample (%)
Population (%)
I
8.2 18.6 19.1 20.2 15.7 18.2
28.3 23.5 15.3 13.7 9.5 9.7
2 3 4 5 6+
G.J. Dennison ef al. /Resources,
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and Recycling
17 (19%)
Table 4 Post-weighting constituent analysis of household waste Material Newspaper Magazines Coloured card (P) Old corrugated cardboard (P) Foil-lined laminates (e.g. juice cartons) (P) Polymer-lined laminates (e.g. milk cartons) (P) Other paper (tissue, etc.) Total paper
Weight % 8.44 0.98 3.32 0.70 0.16 1.16 6.33 21.09
Polyethylene sacks (e.g. bin liners, supermarket bags) (P) PET bottles (P) Polyethylene bottles (P) PVC bottles (P) Polystyrene containers (e.g. meat trays) (P) Polyethylene film (P) Snack food wrappers (e.g. crisp packets) (P) Non-packaging plastics Other plastic Total plastic
4.90 0.55
Textiles
2.32
Disposable nappies
2.71
Clear bottles (P) Green bottles (P) Brown bottles (P) Jars (P) Other glass Total glass
2.06
Food cans (tins) (P) Ferrous beverage cans (P) Altinium beverage cans (P) Foil (P) Other ferrous materials Other non-ferrous materials Total metals
2.43 0.17 0.47
Batteries
0.03
Food waste Garden waste Total organics Miscellaneous combustible (e.g. timber) Miscellaneous non-combustible (primarily cinders) Fines (primarily ash) Household chemicals (incl. of packaging) Total packaging (P) Total non-packaging Overall total
1.18 0.17 0.01 0.01 0.65 0.11 0.10 8.79
0.78 0.61 1.45 0.12 5.02
0.36 0.18 0.10 3.70
40.48 5.13 45.62 1.70 7.68 1.22 0.11 $2.25 77.75 100.00
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236
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Fig. 1. Dublin city (county borough) and surrounding counties.
household waste stream. Organics account for nearly half of all waste arisings from domestic sources. On average one-ninth of all putrescible waste consists of garden waste; the rest is of kitchen origin. Packaging waste, of all types, comprises over one-fifth of the total waste stream according to these data. The largest single contributor to packaging waste are PE sacks and plastics in general constitute nearly 4O?h of the total arisings under this heading. The relative composition of waste packaging is shown in Fig. 2. The present data may be compared with waste analysis information from a previous Dublin study on household waste composition [I]. The latter involved five separate sampling exercises undertaken in the summer and autumn of 1977, the winter of 1977/78 and the spring and summer of 1978. In each case a total of 400-500 properties comprised of blocks of 20-180 dwellings of varied social and economic circumstances were sampled and between 4.26 and 6.2 tonnes of waste collected for analysis. Aggregated results for this study are presented in Table 5 and it is evident that there are quite distinct differences between the results obtained in the late 1970s
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22.67%
39.68%
Fig.2. Relativecompositionof packagingwastefractionof householdwastestream.
and the present data. The reasons for these differences are unclear at present. The 1970s data are more broadly representative, in theory, of the average annual composition of the city’s waste. However, more recent seasonally-adjusted data tend to confirm the findings of the present survey (see below). The most likely explanation is that these differences reflect the differences in the sampling and analytical methodologies employed in the 1970s and the present study. The findings of the present study may also be compared with the results obtained by a separate waste analysis programme undertaken in Dublin by Kerbside Dublin in 1993194. Kerbside Dublin is a private company which provides a pilot green-box type kerbside recycling service to some 25 000 private households in the south-western section of Dublin city and suburbs. The company was founded in 1991 and is funded by local and central government, industry and by the European Recovery and Recycling Association (ERRA) [15].
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Table 5 Comparative waste analysis results, weight%
Paper Plastic Textiles Disposable nappies Glass Metals Fe Non-Fe Organics Miscellaneous combustibles Miscellaneous non-combustibles Fines Batteries
Dublin 1992
Dublin 1977/78
Kerbside Dublin 1993l94
21.09 8.79 2.32 2.71 5.02 3.70 2.77 0.93 45.62 1.70 7.68 1.22 0.03
33 12 3 No Data 10 4
24.8 8.3 1.8 3.7 5.4 3.8
34 No Data No Data 4 No Data
49.6 1.5 0.2 0.8 0.1
Kerbside Dublin commissioned an independent study of the composition of both the recyclable and non-recyclable fractions of the waste stream in its area of operation. The analysis procedure followed was designed by ERRA [16] and was aimed at producing samples representative of the socio-economic mix of the area serviced. The first three of four seasonally determined samples were undertaken in June 1993, September 1993 and May 1994, respectively. The aggregated average results of these three surveys are shown in Table 5 [17] together with national average data [18]. Both the Kerbside Dublin results and national average data reflect very closely the Endings of the present study. Comparisons between Dublin and other cities or countries in terms of waste composition data are probably invidious and may be misleading given known differences in sampling and analytical methodologies in addition to those related to demographics, social and economic circumstance and climate. For whatever reason, it is clear that the Dublin data are substantially different to those pertaining to other European countries and cities, particularly in relation to the organic content of household waste. For example, UK national average composition data for household waste 1191suggest that organics and paper account for about 20% and 32%, respectively of arisings in this sector. In Geneva Leroy et al. [20] report that organics comprise 30% of household arisings while paper accounts for 24% of the total. Slightly different proportions are reported for Vienna by Amfelser [21] where the organic content is -23% and that of paper is 33.6%. The glass content of household waste in the UK, Geneva and Vienna is also uniformly higher than in Dublin. The Dublin figure of 5.02% may be compared with that of the UK (9.2%), Geneva (8.5%) and Vienna (10.4%). Plastic content, on the other hand, in both Geneva (8%) and Vienna (7.5%) is closer to that in Dublin (8.79%) than is the UK national average of 12%.
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6.2.
Influence
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239
of socio-economic factors
The waste data were paired with the corresponding questionnaire information for each of the sampled households and the combined data files were transferred to a VAX computer for analysis using the SPSS 4.1 statistical software package. Correlation analysis was used to test the level of inter-relation between pairs of datasets, i.e. socio-demographic parameters and physical waste data. The socioeconomic parameters employed included those relating to the household size, tenure and type of accommodation, home heating arrangements, employment status, social class and education level attained by head of household and age profile of residents. The significance of the correlation coefficent calculated in this exercise is summarised in Table 6. The picture that emerges from the above analysis is, as expected, one of distinct differences in waste production patterns between different sectors of the population and in general the findings coincide with intuitive expectations. For example the use of open fires or solid-fuel central heating (SFCH) is a strong predictor for the production of miscellaneous non-combustible material (primarily cinders) and fines (primarily ash). One apparent anomaly evident in the results is the strong positive correlation between the production of garden waste and apartment dwelling. One possible explanation for this could be the inclusion of grounds maintenance waste in the material collected from apartments. A divide clearly exists between the more prosperous section of society, as represented generally by those people in employment and living in detached or semidetached dwellings, and the less prosperous. The latter may be characterised as including the unemployed, students and the sick or retired. The divide between these two broad sectors is evident in the data for waste composition and quantity. While many of the features associated with the former group are strong positive predictors of both overall waste generation and the generation of individual components of the waste stream many of those associated with latter group are the reverse. Interestingly social class per se does not appear to be a strong determinant in waste generation (see Appendix I for definitions of ‘Social Class’ as used in Ireland for demographic purposes). Social class 1 appears as a predictor of metals and garden waste and social class 6 is likewise a predictor of miscellaneous material (i.e. miscellaneous combustible/non-combustible and fines). These are among the few references to social class to emerge from the statistical analysis. In general the relative composition of the household waste stream was found to be remarkably consistent across the social class spectrum. Household size is seen to be a reasonably consistent influence on waste generation. It not only appears as a positive influence in live out of the 11 variables assessed above but probable analogues of household size such as flat dwelling, retired or student households are also common strong correlation factors. Various forms of tenure appear in the analysis including private rented, tenant purchase or local authority rented. All of these might be regarded as being associated with the less prosperous section of society and all except tenant purchase appear as
Semidetached Terrace Local authority flat Private apartment Owner occupier Tenant purchase Local authority rented Private rented Other rented Non SFCH SFCH Open tire Electric heating Bottled gas Pets At work
Household size Detached
** ???
?? ??
**
Neg*
Neg**
+*
*
Neg.*
??
Neg*
Neg**
St
Neg** ?? *
Neg**
z
Neg**
Neg*
**
?? ??
Other paper
Newspaper
Neg**
Neg*
* +*
Neg.*
??
*
Neg**
*
**
Total Waste
Table 6 Significance table based on correlation analysis
?? *
22
Neg**
Neg*
**
Neg**
*
Neg**
???
?? ??
Total plastic
*
*
Neg*
???
Textiles
**
??
?? ??
Blass
Total
???
**
Beverge cans
???
?? ??
??
Other metal
Neg.
?? ??
?? ?
Neg** Neg**
?? ??
Neg**
**
**
Garden waste
Neg**
?? ??
???
Neg**
?? ??
Neg**
?? ??
**
Food waste
??
Neg*
Neg** ** **
???
?? ??
Misc.
?? * **
Neg** Neg** Neg**
*
Neg*
Neg**
Neg**
Neg*
Neg**
**
?? * 22
Neg*
Neg**
Neg** Neg.
Neg**
Neg.*
*
Neg**
?? ??
**
**
*
Neg* t
*
??
*
?? ??
** **
Neg.
?? ??
Neg** Neg*
Neg** Neg*
??
Neg*
Neg** *
??
Neg*
**
Neg**
**
?? , Positive Correlation at the 95% level. **, Positive Correlation at the 99% level. Neg., Negative Correlation at the 95% level. Neg**, Negative Correlation at the 99% level.
Unemployed Student Retired Home duty Sick Social Class 1 Social Class 2 Social Class 3 Social Class 4 Social Class 5 Social Class 6 Primary education Secondary education Third level Age O-4 Age 5-15 Age 16-29 Age 30-64 Age 65+ Sink disposal unit Deep freeze Fridge freezer
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strong negative determinants on waste generation rates. Owner occupation is not represented as such. However, probable analogues such as detached, semi-detached or terraced dwellings do appear in the list of strong positive determinants. 7. coIlclusions The present study sought to address the problem of unreliable waste composition data with regard to the city of Dublin. The physical data revealed substantial differences in the relative composition of the waste stream as compared with both previous studies undertaken in Dublin in the late 1970s and with more recent UK national data. In particular the proportion of organic waste was found to be in excess of 45% by wt. in the 1992 study as compared with 34% in 1977178(Dublin) and - 20% (UK). However, the present findings were supported by the results of a more limited survey of waste composition carried out separately in 1993/94 for the Dublin green-box recycling service. Following the amalgamation of the physical weight data and the corresponding social, economic and demographic data for all households in electronic format statistical techniques were used to test the relationship between socio-economic factors and the composition of generated waste. In general the results of this exercise tended to confirm anecdotal observation. For example it was found that household size (and its analogues) was a key positive determinant not only - as might be anticipated - in overall waste production, but also with regard to the relative proportions of the components of the generated waste stream. Similarly, more affluent households were found to be more likely to produce larger quantities of waste, including all components, than the less aftluent. This was the first Irish waste analysis survey to investigate the subject to this degree of detail and it is anticipated that the results obtained will provide a baseline against which future change can be assessed. Further work is required to establish with greater certainty the influence of seasonal factors on both waste generation rates and relative composition. The sampling programme should also be extended in future to include the commercial and industrial waste streams so that a comprehensive assessment of the combined inputs to the municipal waste stream may be facilitated. Acknowledgements The practical, financial and technical assistance of the Dublin City Engineer and his staff in the planning and execution of this study is gratefully acknowledged. Appendix 1: List of social classes used in Ireland for demographic purposes and tbe occupations assigned to them Social Class 1 Higher professional, higher managerial, proprietors more acres (> 80 ha).
and farmers farming 200 or
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243
Social Class 2 Lower professional, lower managerial, proprietors and farmers farming lOO- 199 acres (40-80 ha). Social Class 3 Other non-manual and farmers farming 50-99 acres (20-40 ha). Social Class 4 Skilled manual and farmers farming 30-49 acres (12-20 ha). Social Class 5 Semi-skilled manual and farmers farming less than 30 acres (< 12 ha). Social Class 6 Unskilled manual. Unemployed and retired persons are classified according to their last employment. References [l] McGee, R., 1980. Municipal refuse including domestic and trade wastes litter and packaging. In: Proceedings of Seminar on Today’s and Tomorrow’s Wastes, National Board for Science and Technology, Dublin, pp. 23-28. [2] Cosgrove, A. (Ed.), 1988. Dublin Through the Ages. College Press, Dublin, 256 pp. [3] Central Statistics Office, 1992. Census of Population of Ireland for 1991, Dublin. [4] Dawes, J.C., 1929. Report on an Investigation into the Public Cleansing service in the Administrative County of London, HMSO, London. [5] Gulley, B.W., 1984. An Overview of UK Waste Analysis Experience, Wastes Management, April, pp. 210-216. [6] Higginson, A.E., 1982. The Analysis of Domestic Waste. IWM Publication No. 10, Northampton, UK. [7] Pocock, R.L. and Rufford, N.M., 1983. A New Approach to Household Waste Analysis and Forecasting. Paper to Department of the Environmentinstitute of Waste Management One-day Joint Seminar, Aston University, Birmingham, 20th September, 1983. [8] Skordilis, A., 1985. Household waste analysis in the greater Athens region using generally acceptable statistical methods. In: M.P. Ferranti and G.L. Ferrer0 @is.), Sorting of Household Waste and Thermal Treatment of Waste, Elsevier, London, 521 pp. [9] Mortensen, H., 1985. Low-technology sorting of presorted household waste. In: M.P. Ferranti and G.L. Ferrer0 @Is.), Sorting of Household Waste and Thermal Treatment of Waste, Elsevier, London, 521 pp. [lo] Williams, H.E., 1984. Recommendations for the Classification and Description of Household Waste and Refuse-derived Fuel. Report by Ecotec, Birmingham, UK to EC Commission. [I I] Whelan, B., 1979. RANSAM: A random sample design for Ireland. Economic and Social Review, IO (2, Jan.), 169-174 pp. [12] McCall, C.H. Jr., 1982. Sampling and Statistics: Handbook for Research, Iowa, 340 pp. [I31 Dermison, G.J., 1991. Municipal Solid Waste Management in Greater Dublin 1986-2001, M.Eng.Sc. Thesis, University College Dublin. [I41 Commission of the European Commission, 1992. Draft Proposal for a Council Directive on Packaging and Packaging Waste, Brussels. 1151 Madden, N., 1993. Recycling Experiences: Kerbside Dublin. Paper to Addressing the Challenge: The National Recycling Conference, Wexford, Ireland, 9-10 December 1993.
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[16] ERRA, 1993. Waste Analysis Procedure, Brussels. [17] DeBurca, D., Dodd, V.A., Dennison, G.J., Cullinan, N. and Madden, N., 1994. Assessing the role of kerbside recycling in municipal waste management in the Dublin region. Paper to the 10th International Conference on Solid Waste Management and Secondary Materials, Philadelphia, PA, 14-16 Nov., 1994. [I81 Department of the Environment (Ireland), 1994. Recycling for Ireland, Dublin. [I91 Materials Reclamation Weekly, May I, 1993. Assessing the Recyclables in British Dustbins, p. 6. [20] Amfelser, F., 1992.Systems and Facilities for the Collection of Household Wastes in Vienna. Waste Management and Research, 10 (Dec.), pp. 535-541. [21) Leroy, D., Giovannoni, J.-M. and Maystre, L.-Y., 1992. Sampling Method to Determine a Household Waste Composition Variance. Wastes Management and Research, IO (Feb.), pp. 3-12. (221 Dennison, G.J., Dodd, V.A. and Whelan, B., 1996. A socio-economic based survey of household waste characteristics in the city of Dublin, Ireland - II. Waste quantities. Resour. Conserv. and Recyc., 17, 245-257.