A structured methodology to understand municipal waste generation at local level with minimized effort: development and case study

Understanding municipal solid waste (MSW) generation is a key requirement for designing and optimizing MSW collection services. The present contribution proposes a statistical methodology to identify MSW generation patterns from MSW collection records. The methodology aims at finding statistically distinct household waste generation patterns within the days of the week and within months (seasonal variation). It is based on standard statistical methods (ANOVA complemented by non-parametric tests and cluster analysis). The methodology was applied to a Portuguese neighbourhood to assist in the definition of a waste sampling campaign to support the implementation of a pilot PAYT. The results showed the existence of groups with statistically distinct MSW generation patterns both at the weekly and monthly time scales. Three clusters of days of the week, with high, medium and low generation, and two clusters of months, with high and low generation, were identified. These results allowed to design and implement a customized field waste sampling campaign to estimate the MSW generated at the study site with minimal field work. Instead of implementing a homogeneous sampling campaign (equal number of samples for every day of the week and for every month), the samples were collected from the days and months that showed statistically distinct MSW generation pattern. The systematic procedure can be easily adapted to any given location, thus being a useful tool that combines statistical analysis with field collected data.

Looking beyond the banning of lightweight bags: analysing the role of plastic (and fuel) impacts in waste collection at a Portuguese city

The purpose of this work is to assess the environmental impacts of the collection of mixed municipal solid waste (MSW) in a selected neighbourhood of the Portuguese city of Aveiro. To this purpose, the main elements necessary for the collection process (carrier bags, dustbins, street containers and vehicles) were analysed applying the life cycle assessment methodology, making use of locally gathered data. The main impacts associated with this activity are mostly related to the use of polyethylene plastic bags to carry the waste from the household to the waste container, and to the fuel consumption of collection vehicle that picks MSW from street containers and transports it to the treatment facility. The impacts associated with the plastic bags were primarily due to their disposal in a sanitary landfill after use and secondarily to the consumption of fossil raw materials required for their production. Given the relative high impact of the plastic bags, alternative scenarios were tested: using bags entirely produced with recycled polyethylene and bags produced with bio-based plastics derived from starch (TPS) and from wastewater (PHA). PHA bio-based bags were found to perform slightly better than conventional high-density polyethylene (HDPE) bags, but HDPE bags with 100% recycled content remained as the environmentally best option. A sensitivity analysis was performed to check the influence of bag size. Regarding the fuel consumption by collection vehicles, a comparison was performed to check how site-specific conditions can influence the impact of this activity, resulting in remarkably higher consumptions when local data were used instead of reference databases.

Are municipal waste utilities becoming sustainable? A framework to assess and communicate progress

A framework of indicators to assess the progress towards sustainability of municipal waste management utilities is developed. Its purpose is to fulfil the need for assessing the performance of municipal waste (MW) management in a simple but comprehensive way-unlike indicators based on individual aspects such as recycling-and including aspects not well considered before, such as waste prevention. The framework is composed of a set of six single indicators, concerning the three dimensions of sustainability: reduction of effectively landfilled MW and reduction of MW generation (environmental component), balance between expenses and revenues and reduction of costs (economic component), accessibility to separate collection and number of complaints (social component). Each indicator consists of an evaluation of the current status of the variable in contrast to a previous situation, with a positive value in case of improvement or negative in case of decline. Then, the values of the individual indicators are combined to obtain a global result. This approach focuses on dynamic progress towards sustainability, complementing the common static indicators. Contrarily to the existing performance indicator schemes, the proposed framework aims at measuring the progress and not the absolute or relative achievement of a waste management utility. The framework was tested on two Portuguese municipalities, proving to be a straightforward application and reliable in guiding stakeholders. Results for the case study showed good performance on economic sustainability, while environmental and social performance were lower due to a lack of strategies for waste prevention and low source separation, affected by poor accessibility to separate collection.