Temporal and geographical patterns of solid waste collected at recycling centres.

Citizens increasingly dispose their waste at household waste recycling centres (HWRC). To enhance the collection of recyclables materials, local authorities and waste management companies invest considerable resources in planning. While the planning of these centres requires a comprehensive understanding of collected solid waste, only limited studies have consistently investigated waste data from HWRC. To fill this knowledge gap, historical data for HWRC from the Greater Copenhagen, Central Zealand, Silkeborg and Djursland in Denmark were analysed with regards to temporal and geographical variation. The results showed the mass of collected waste varies seasonally; this trend was consistently seen during the period 2010-2016. Moreover, the data revealed that the total waste collected was principally driven by the number of visitors. The geometric bar plot and ternary plot depicted an increase in the percentage of recyclable materials, whereas the percentage of incinerated waste decreased during the period 2010-2016. The waste characterisation study indicated that about 7% of small miscellaneous combustible waste was brought in black plastic bag, although these bags were forbidden; the results suggest that the percentage of misplaced recyclable materials could considerably decrease if citizens bring their waste in clear plastic bags.

Statistical analysis of solid waste composition data: Arithmetic mean, standard deviation and correlation coefficients.

Data for fractional solid waste composition provide relative magnitudes of individual waste fractions, the percentages of which always sum to 100, thereby connecting them intrinsically. Due to this sum constraint, waste composition data represent closed data, and their interpretation and analysis require statistical methods, other than classical statistics that are suitable only for non-constrained data such as absolute values. However, the closed characteristics of waste composition data are often ignored when analysed. The results of this study showed, for example, that unavoidable animal-derived food waste amounted to 2.21±3.12% with a confidence interval of (-4.03; 8.45), which highlights the problem of the biased negative proportions. A Pearson's correlation test, applied to waste fraction generation (kg mass), indicated a positive correlation between avoidable vegetable food waste and plastic packaging. However, correlation tests applied to waste fraction compositions (percentage values) showed a negative association in this regard, thus demonstrating that statistical analyses applied to compositional waste fraction data, without addressing the closed characteristics of these data, have the potential to generate spurious or misleading results. Therefore, ¨compositional data should be transformed adequately prior to any statistical analysis, such as computing mean, standard deviation and correlation coefficients.

Food waste from Danish households: Generation and composition.

Sustainable solutions for reducing food waste require a good understanding of food waste generation and composition, including avoidable and unavoidable food waste. We analysed 12tonnes of residual household waste collected from 1474 households, without source segregation of organic waste. Food waste was divided into six fractions according to avoidability, suitability for home-composting and whether or not it was cooked, prepared or had been served within the household. The results showed that the residual household waste generation rate was 434±18kg per household per year, of which 183±10kg per year was food waste. Unavoidable food waste amounted to 80±6kg per household per year, and avoidable food waste was 103±9kg per household per year. Food waste mass was influenced significantly by the number of occupants per household (household size) and the housing type. The results also indicated that avoidable food waste occurred in 97% of the households, suggesting that most Danish households could avoid or at least reduce how much they generate. Moreover, avoidable and unavoidable food waste was more likely to be found in houses containing more than one person than in households with only one occupant.

Source segregation of food waste in office areas: Factors affecting waste generation rates and quality.

Existing legislation mandates that the amount of waste being recycled should be increased. Among others, in its Resource Strategy Plan, the Danish Government decided that at least 60% of food waste generated by the service sector, including in office areas, should be source-sorted and collected separately by 2018. To assess the achievability of these targets, source-sorted food waste and residual waste from office areas was collected and weighed on a daily basis during 133 working days. Waste composition analyses were conducted every week to investigate the efficiency of the source-sorting campaign and the purity of the source-sorted food waste. The moisture content of source-sorted food waste and residual waste fractions, and potential methane production from source-sorted food waste, was also investigated. Food waste generation equated to 23 ± 5 kg/employee/year, of which 20 ± 5 kg/employee/year was source-sorted, with a considerably high purity of 99%. Residual waste amounted to 10 ± 5 kg/employee/year and consisted mainly of paper (29 ± 13%), plastic (23 ± 9%) and missorted food waste (24 ± 16%). The moisture content of source-sorted food waste was significantly higher (8%) than missorted food waste, and the methane potential of source-sorted food waste was 463 ± 42 mL CH4/g VS. These results show that food waste in office areas offers promising potential for relatively easily collectable and pure source-sorted food waste, suggesting that recycling targets for food waste could be achieved with reasonable logistical ease in office areas.

Municipal solid waste composition: sampling methodology, statistical analyses, and case study evaluation.

Sound waste management and optimisation of resource recovery require reliable data on solid waste generation and composition. In the absence of standardised and commonly accepted waste characterisation methodologies, various approaches have been reported in literature. This limits both comparability and applicability of the results. In this study, a waste sampling and sorting methodology for efficient and statistically robust characterisation of solid waste was introduced. The methodology was applied to residual waste collected from 1442 households distributed among 10 individual sub-areas in three Danish municipalities (both single and multi-family house areas). In total 17 tonnes of waste were sorted into 10-50 waste fractions, organised according to a three-level (tiered approach) facilitating comparison of the waste data between individual sub-areas with different fractionation (waste from one municipality was sorted at "Level III", e.g. detailed, while the two others were sorted only at "Level I"). The results showed that residual household waste mainly contained food waste (42 ± 5%, mass per wet basis) and miscellaneous combustibles (18 ± 3%, mass per wet basis). The residual household waste generation rate in the study areas was 3-4 kg per person per week. Statistical analyses revealed that the waste composition was independent of variations in the waste generation rate. Both, waste composition and waste generation rates were statistically similar for each of the three municipalities. While the waste generation rates were similar for each of the two housing types (single-family and multi-family house areas), the individual percentage composition of food waste, paper, and glass was significantly different between the housing types. This indicates that housing type is a critical stratification parameter. Separating food leftovers from food packaging during manual sorting of the sampled waste did not have significant influence on the proportions of food waste and packaging materials, indicating that this step may not be required.

Solid waste characterization in Ketao, a rural town in Togo, West Africa.

In Africa the majority of solid waste data is for big cities. Small and rural towns are generally neglected and waste data from these areas are often unavailable, which makes planning a proper solid waste management difficult. This paper presents the results from two waste characterization projects conducted in Kétao, a rural town in Togo during the rainy season and the dry season in 2010. The seasonal variation has a significant impact on the waste stream. The household waste generation rate was estimated at 0.22 kg person(-1) day(-1) in the dry season and 0.42 in the rainy season. Likewise, the waste moisture content was 4% in the dry season while it was 33-63% in the rainy season. The waste consisted mainly of soil and dirt characterized as 'other' (41%), vegetables and putrescibles (38%) and plastic (11%). In addition to these fractions, considerable amounts of material are either recycled or reused locally and do not enter the waste stream. The study suggests that additional recycling is not feasible, but further examination of the degradability of the organic fraction is needed in order to assess whether the residual waste should be composed or landfilled.