A methodology for solid waste characterization based on diminishing marginal returns Mukesh Sharma a , Edward McBean b, * a Department of Civil Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India b University of Guelph, School of Engineering, Guelph, Ont., Canada N1G2W1 Accepted 3 February 2006 Available online 5 April 2006 Abstract A methodology is developed for estimating the number of waste sorts for characterizing solid wastes into categories based on dimin- ishing minimum incremental information. Convergence in the square of the coefficient of variation with successive waste sorts is used to indicate cost-efficient termination of sampling at substantially reduced numbers of sorts in comparison with existing methodologies. These findings indicate that the numbers of waste sorts beyond that determined using the proposed methodology do not add substantial marginal gains in information and/or reduction in the confidence interval of the estimate. The methodology is demonstrated using waste composition analyses from the Greater Vancouver Regional District where 22 waste sorts are examined. The proposed methodology is simple, and the number of waste sorts can be estimated with a hand-held calculator and utilized in the field. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction Knowledge of the percentages of solid waste within indi- vidual waste category types is important information for planning solid waste management programs. Planning ele- ments that may require an understanding of the percentages include (i) evaluation of the success, or lack thereof, of ongoing recycling programs, (ii) quantification of the degree of success of bans to exclude specific materials (e.g., gyproc) from the refuse stream, (iii) characterization of the waste as feedstock to an incinerator, and (iv) determination of quan- tities of organics in the waste stream which influence biogas production levels once the waste is landfilled. However, the number of waste sorts needed to answer (i)–(iv), to effi- ciently characterize percentages for individual categories of the waste, remains an important question. To quantify the percentages of solid wastes in individual categories, the Greater Vancouver Regional District (GVRD) authorized the completion of a number of waste sorts (CRA and CAS, 1999). Waste sorts divided the wastes into 9 primary categories and 31 secondary categories. From this substantial database, the research described herein assesses the information content from varying numbers of waste sorts, and develops a simple methodology for selecting efficient numbers of waste sorts to characterize solid wastes. 2. Literature review of current waste composition methodological approaches There are two general approaches taken to analyze solid waste stream composition, the ‘material flows approach’ and the ‘output method’ (McCauley-Bell et al., 1997). The material flows approach considers the production and expected lifecycles of products and, from these, esti- mates the waste stream percentages (by weight) within the various categories of waste. This approach considers waste as the end result of a production lifecycle. An advan- tage of the material flows approach is the broad geograph- ical scope for which the solid waste stream can be estimated, but criticisms of this method include its focus on product categories, and not on waste stream categories. Another problem with the material flows method is that it 0956-053X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2006.02.007 * Corresponding author. Tel.: +1 519824 4120x53923; fax: +1 519 836 0227. E-mail address: emcbean@uoguelph.ca (E. McBean). www.elsevier.com/locate/wasman Waste Management 27 (2007) 337–344