Cristina Matos

Evaluation of operational, economic, and environmental performance of mixed and selective collection of municipal solid waste: Porto case study

This article describes an accurate methodology for an operational, economic, and environmental assessment of municipal solid waste collection. The proposed methodological tool uses key performance indicators to evaluate independent operational and economic efficiency and performance of municipal solid waste collection practices. These key performance indicators are then used in life cycle inventories and life cycle impact assessment. Finally, the life cycle assessment environmental profiles provide the environmental assessment. We also report a successful application of this tool through a case study in the Portuguese city of Porto. Preliminary results demonstrate the applicability of the methodological tool to real cases. Some of the findings focus a significant difference between average mixed and selective collection effective distance (2.14 km t-1; 16.12 km t-1), fuel consumption (3.96 L t-1; 15.37 L t-1), crew productivity (0.98 t h-1 worker-1; 0.23 t h-1 worker-1), cost (45.90 € t-1; 241.20 € t-1), and global warming impact (19.95 kg CO2eq t-1; 57.47 kg CO2eq t-1). Preliminary results consistently indicate: (a) higher global performance of mixed collection as compared with selective collection; (b) dependency of collection performance, even in urban areas, on the waste generation rate and density; (c) the decline of selective collection performances with decreasing source-separated material density and recycling collection rate; and (d) that the main threats to collection route efficiency are the extensive collection distances, high fuel consumption vehicles, and reduced crew productivity.

Domestic water uses: Characterization of daily cycles in the north region of Portugal

Nowadays, there is an increasing discussion among specialists about water use efficiency and the best measures to improve it. In Portugal, there have been a few attempts to expand the implementation of in situ water reuse projects. However, there is a lack of information about indoor water uses and how they are influenced by sociodemographic characteristics. There are several studies that investigate per capita global water usage, but the partitioning of this volume per domestic device and daily cycles is yet unknown. Identified as one of the key questions in sustainable building design, the water end-use is of primary importance to the design of hydraulic networks in buildings. In order to overcome this lack, a quantitative characterization of daily water uses for each domestic device was performed, based on a weekly monitoring program in fifty-two different dwellings in the northern region of Portugal (Vila Real, Valpaços and Oporto). For forty of them, each water usage of different domestic devices of each dwelling was recorded. At the same time, the remaining twelve dwellings were also monitored in order to register the volume of water consumed in each utilization of each domestic device. This paper presents the results of this complete monitoring program, using collected data to establish indoor water use patterns for each domestic device, aiming to support a more realistic approach to residential water use. The daily cycles in the different cities, where the monitoring program was performed, are also presented, in order to evaluate possible influences of sociodemographic characteristics.

An exploratory study on the influence of socio-demographic characteristics on water end uses inside buildings

Any strategy of water demand management needs the collaboration of the population involved and so it is important to know how characteristics as residence area, number of residents, presence/absence of children/elders, income level, and educational level, among others, may influence the use of water. Empirical studies that quantify relationship between socio-demographic factors and the water end use patterns inside buildings are still largely lacking. To help to fill this gap this paper gathers information about the characterization of water end use per domestic device in three regions of north of Portugal with different socio-demographic characteristics. The main research goal was to establish indoor water end use patterns per domestic device and to evaluate possible relations between these patterns with the socio-demographic characteristics of the area where the household is, namely the number of residents, the presence/absence of children/elders, the income level and educational level. The washbasin is in average the domestic device with more number of uses in a day (responsible for 34% of the total use), close followed by the kitchen sink (32%), the toilet flush (23%), the bathtub (6%) and finally the dishwasher (3%) and the washing machine (2%). The results found might reflect differences in rural and urban lifestyles once that, with the exception of the kitchen sink, Valpaços is the city that registers the lowest number of uses in the appliances monitored. Significant correlations were found in the following cases: between the residence area and the number of uses in washbasin and in the toilet flush; between the presence of children in the household and the use in the dishwasher; between the income level and the number of uses in the washbasin, in the bathtub, in the washing machine and in the dishwasher.

Impacts of climatic variability on rainwater tank outcomes for an inland city, Canberra

A daily water balance model is used for the performance analysis and design optimisation of household rainwater tank for an inland Australian city, Canberra. To investigate the climatic variabilities of rainwater tank outcomes nine representative years (three for each dry, average and wet condition) are selected from historical rainfall data. For the three climatic conditions, a number of rainwater tank outcomes (water savings, townwater augmentation, overflow and reliability) are presented in relations to tank volume, roof area, number of people in a house (i.e., water demand). It is found that 100% reliability cannot be achieved even in wet year with a large tank (10,000 L) connected with a large roof (300 m2). Also, it is observed that significant climatic variabilities exist in regards to studied rainwater tank outcomes, except for very few conditions having very large tank (10,000 L) connected with a small roof (100 m2). However, computed variabilities are still lower than the expected climatic variabilities in regards to annual water savings, annual townwater uses and reliabilities computed for Australian coastal cities, i.e., Sydney and Melbourne.

Assessment strategies for municipal selective waste collection schemes

An important strategy to promote a strong sustainable growth relies on an efficient municipal waste management, and phasing out waste landfilling through waste prevention and recycling emerges as a major target. For this purpose, effective collection schemes are required, in particular those regarding selective waste collection, pursuing a more efficient and high quality recycling of reusable materials. This paper addresses the assessment and benchmarking of selective collection schemes, relevant to guide future operational improvements. In particular, the assessment is based on the monitoring and statistical analysis of a core-set of performance indicators that highlights collection trends, complemented with a performance index that gathers a weighted linear combination of these indicators. This combined analysis underlines a potential tool to support decision makers involved in the process of selecting the collection scheme with best overall performance. The presented approach was applied to a case study conducted in Oporto Municipality, with data gathered from two distinct selective collection schemes.

Academics perception towards various water reuse options: University of Trás-os-Montes e Alto-Douro - UTAD Campus (Portugal) as a case study

Any strategy of water reuse has to achieve social acceptance to be successful. This paper presents the results of a multiple choice survey that attempted to establish the general attitude toward water reuse by asking academics in UTAD (Portugal) a wide range of questions. The survey included 20 reuse options, which were clustered into three reuse categories, specifically: low, medium and high contact levels. Correlation analysis between the level of support of low, medium and high contact options and demographic characteristics, personal and environmental beliefs was performed. Results show that a high proportion of the participants supported low and medium contact reuse options. Correlation was found to exist between the income classes and to the level of support of medium and high reuse options and between education level and the support for high contact reuse options. The responses to the survey suggested that some beliefs influence the level of support.

eTank and contemporary online tools for rainwater tank outcomes analysis

This paper presents development of a comprehensive decision support tool (eTank) to analyse and optimise a rainwater tank size. The developed tool enables a simple quantitative analysis of the expected water that can be saved based on daily water balance concept. The tool produces graphs showing cumulative yearly rainwater used, overflow and augmented townwater supply. To account for climate variability, provision has been made in the tool to analyse for a particular option in three different climatic conditions (dry, average and wet). Also, the tool enables a life cycle costing and payback period analysis of any particular tank size through the simulated expected water savings per year, initial construction costs and operational. The outcomes of eTank are compared with other contemporary online tools in regards to rainwater savings. It is revealed that most of the tools overestimate the potential savings due to not considering several influencing factors.

Generalised equations for rainwater tank outcomes under different climate conditions: a case study for Adelaide

Most of the studies on rainwater tanks focused on sizing and/or optimum design. Some studies proposed different methods of estimating rainwater tank outcomes. Several studies used monthly rainfall data to estimate rainwater tank outcomes. However, quantification using daily rainfall data will be much more realistic than using monthly rainfall data. This paper presents development of generalised equations for domestic rainwater tank outcomes for an Australian city, Adelaide, using a daily water balance model, which incorporates measured daily rainfall data. To investigate the climate variabilities of rainwater tank outcomes, 15 representative years (five for each dry, average and wet condition) are selected from historical rainfall data. For the three climate conditions, rainwater tank outcomes such as water savings and town water augmentation amounts are presented in relation to tank volume, roof area and rainwater demand. Eventually, six equations, one for each climate condition and one for each outcome, are proposed.

Equations for potential water savings through rainwater harvesting for different climatic conditions in Adelaide (Australia)

Among all the alternative options to minimise potable water demand, rainwater harvesting system has received the highest level of attention due to its easy collection and reuse potentials. However, available methods of quantifying potential water savings from rainwater tanks are questionable. This paper presents development of generalised equations for the quantification of potential water savings under different climatic conditions for an Australian city, Adelaide. An earlier developed daily water balance model, eTank, which can calculate potential water savings in three climatic conditions (dry, average and wet) was used for this purpose. Several relationship graphs of water savings were produced through model calculations for different input parameters.

Evaluation of different full scale landfill leachate treatment systems

Sanitary landfills are one of the most used disposal methods for municipal solid waste (MSW) disposal. Due to its high strength, these wastewaters need a combination of several treatment steps, which combine biological with physical-chemical processes. The main goal of this study was to assess the removal efficiency for specific treatment steps in three different full scale treatment facilities in Portugal. Results indicate a good BOD5 removal (75; 93; 96%) on all facilities but low TOC removal (2; 58; 64%) indicating that recalcitrant organic matter remains after treatment. Total dissolved nitrogen was poorly removed (0; 0.2 and 47%) possibly due to limited nitrate removal, even in the facility with an anoxic tank. This suggests biodegradable carbon limitations and salinity toxicity. The major cations, anions and heavy metals are only partially removed with advanced filtration. The heavy metal concentrations and the high conductivity (22-67 dS m−1) indicate the need for further treatment steps.