Browsing by Author "Oliveira, V."
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- Door-to-door collection of food and kitchen waste in city centers under the framework of multimunicipal waste management systems in Portugal: the case study of AveiroPublication . Rodrigues, J.; Oliveira, V.; Lopes, P.; Ferreira, CéliaSeparate collection of biowaste represents in Portugal only 2% of total collected biowaste. Even though higher quality compost can be obtained through the sepa rate collection of biowaste, this is generally regarded as more expensive and discarded as an option. In this work we assessed the viability of implementing the separate collection of biowaste targeting restaurants and canteens in city centers, using Aveiro as a case study. The current situation (no separate collection for biowaste) was com pared with an alternative scenario in which biowaste was separately collected and valorized. The costs, constrains and the producers’ attitude towards such a collection scheme are presented and discussed. On average 0.46 kg of biowaste were produced per meal served. The acceptance of separate biowaste collection was high (67 %) among producers, and it could be increased further through in formative campaigns and economic incentives such as pay as-you-throw tariffs. Door-to-door collection of biowaste could reduce the cost per ton as much as 37 %, when compared to collection as unsorted waste. The major constrains for the implementation of separate collection of biowaste were the selection of alternative legal destinations to the MBT unit (which has the exclusivity to treat col lected waste) and the lack of dedicated infrastructures at multimunicipal waste management facilities to handle separately collected biowaste.
- Effects of struvite recovered from wastes on crop cultivationPublication . Oliveira, V.; Horta, C.; Rocha, Joana; Ferreira, CéliaStruvite recovered from wastes has been considered a promising second generation fertiliser. The main objective of this work is to evaluate the effects of struvite fertilisation on i) rye (Secale cereale L.) cultivation (through a 45-d pot experiment), in terms of macronutrients, micronutrients and heavy metals and ii) on soil fertility (through a 30-d incubation experiment) in terms of available phosphorus and exchangeable bases (Ca2+, Mg2+ and K+). Struvite-fertilisation increased the soil available phosphorus resulting in improvement of the soil fertility class from low to medium class. In terms of exchangeable bases, the soil fertility class did not change. Furthermore, the struvite-fertilisation led to the highest concentration of total phosphorus in the plant. No relevant effects were found regarding the concentrations of Ca, Mg and K in the plant as well as the micronutrients. The levels of heavy metals on crop did not increase after soils fertilisation with struvite.
- Hospital food waste and environmental and economic indicators: a Portuguese case studyPublication . Ferreira, Célia; Santos, T.; Oliveira, V.This study presents a comprehensive characterization of plate waste (food served but not eaten) at an acute care hospital in Portugal and elaborates on possible waste reduction measures. Even though waste prevention is a priority in Europe, large amounts of food are still being wasted every day, with hospitals giving rise to two to three times more food waste than other foodservice sectors. For this work the plate waste arising at the ward level was audited during 8 weeks, covering almost 8000 meals, using a general hospital as case study. Weighing the food served to patients and that returned after the meal allowed calculating plate waste for the average meal, as well as for individual meal items. Comparison of food waste arising showed that differences exist among wards, with some generating more waste than others. On average each patient throws away 953 g of food each day, representing 35% of the food served. This equates to 8.7 thousand tonnes of food waste being thrown away each year at hospitals across Portugal. These tonnes of food transformed into waste represent economic losses and environmental impacts, being estimated that 16.4 thousand tonnes of CO2 (equivalent) and 35.3 million euros are the annual national indicators in Portugal. This means that 0.5% of the Portuguese National Health budget gets throw.n away as food waste. Given the magnitude of the food problem five measures were suggested to reduce food waste, and their potential impact and ease of implementation were discussed. Even though food waste is unavoidable the results obtained in this work highlight the potential financial and environmental savings for Portuguese hospitals, providing a basis to establish future strategies to tackle food waste
- Model for the separate collection of packaging waste in Portuguese low-performing recycling regionsPublication . Oliveira, V.; Sousa, V.; Vaz, J. M.; Ferreira, CéliaSeparate collection of packaging waste (glass; plastic/metals; paper/cardboard), is currently a widespread practice throughout Europe. It enables the recovery of good quality recyclable materials. However, separate collection performance are quite heterogeneous, with some countries reaching higher levels than others. In the present work, separate collection of packaging waste has been evaluated in a lowperformance recycling region in Portugal in order to investigate which factors are most affecting the performance in bring-bank collection system. The variability of separate collection yields (kg per inhabitant per year) among 42 municipalities was scrutinized for the year 2015 against possible explanatory factors. A total of 14 possible explanatory factors were analysed, falling into two groups: socio-economic/demographic and waste collection service related. Regression models were built in an attempt to evaluate the individual effect of each factor on separate collection yields and predict changes on the collection yields by acting on those factors. The best model obtained is capable to explain 73% of the variation found in the separate collection yields. The model includes the following statistically significant indicators affecting the success of separate collection yields: i) inhabitants per bring-bank; ii) relative accessibility to bring-banks; iii) degree of urbanization; iv) number of school years a ttended; and v) area. The model presented in this work was developed specifically for the bring-bank system, has an explanatory power and quantifies the impact of each factor on separate collection yields. It can therefore be used as a support tool by local and regional waste management authorities in the definition of future strategies to increase collection of recyclables of good quality and to achieve national and regional targets.
- Nutrient recovery from digestate using gas-permeable membrane technology and struvite formationPublication . Riaño, B.; Oliveira, V.; Ferreira, Celia; Molinuevo-Salces, B.; García-González, M. C.The performance of gas-permeable membrane (GPM) technology for nitrogen (N) recovery from digestate with subsequent struvite formation is evaluated in this work and compared with the recoveries obtained by centrifugation or direct struvite formation. Nearly 68% of the digestate N was recovered using GPM technology, which was almost 2-times higher than the recoveries achieved in solid form by centrifugation or direct struvite formation. In addition, the use of GPM as a first stage improved the P recovery by struvite formation from the N-trapping digestate up to 100%.
- Phosphorus flows in the Portuguese agriculture and livestock sectorsPublication . Rocha, Joana; Oliveira, V.; Ferreira, CéliaPhosphorus plays a vital role as a limiting nutrient for plant growth, but the majority of minable phosphate rock reserves are located in just a small handful of countries: South Africa, Jordan and Morocco. Therefore, Portugal is totally dependent on imports, with phosphate rock being added to the European Union list of critical raw materials it is essential to increase its sustainable use. Thus, the main objective of this work was to compute substance flow analysis of phosphorus in the agriculture and livestock production sectors in Portugal. The data was gathered from several statistical sources and computed into phosphorus contents employing mass conservation law. Phosphorus flows were computed and quantified using STAN software. As result, we identified phosphorus flows, losses, and sinks. We can conclude that, both in agriculture and livestock production sectors, it is possible to decrease losses and increase phosphorus efficiency use by applying best management practices.
- Separate collection of packaging waste: characterization and impactsPublication . Oliveira, V.; Vaz, João Miguel; Sousa, V.; Ferreira, CéliaThis study evaluates separate collection rate of packaging waste in the coastal area of the “Centro” region of Portugal, where collection is based on road-side waste containers. The area comprises 42 municipalities and the collection system of two waste management companies were studied: ERSUC and VALORLIS. In 2015, the average separate collection rate was 7.6% (30.7 kg person−1 year−1), in ERSUC, and 7.7% (29.2 kg person−1 year−1), in VALORLIS. Furthermore, separate collection rates varied significantly between municipalities, ranging from 4.5% to 12.6% of the total waste generated. Recyclables in unsorted waste represent a significant economic and environmental burden, and municipalities could save 8.1 million euros per year and avoid the emission of 86 thousand tonnes of CO2 equivalent. The implementation of door-to-door collection and adoption of variable waste tariffs are further efforts required to increase separate collection rate, in order to achieve national targets.
- Struvite quality assessment during electrodialytic extractionPublication . Oliveira, V.; Kirkelund, Gunvor M.; Labrincha, J.; Ferreira, CéliaStruvite recovered from anaerobically digested sludge can be conducted by a two – step process. The first step consists of electrodialytic extraction of phosphorus and heavy metals from the waste. The second step comprises the chemical precipitation of phosphorus as struvite. This work studied if the quality of phosphorus recovered as struvite is affected by the reduction of energy on the electrodialytic extraction step. Four electrodialytic experiments were carried out to assess the effect of the energy reduction through stirring time. This was followed by four struvite-precipitation experiments. The efficacy of the electrodialytic extraction of heavy metals is not affected by reducing the stirring from continuous mode to just 25% of the time. XRD analysis confirmed that the precipitates were constituted by pure struvite, while no significant accumulation of heavy metals was found in produced struvite. The struvite meets the requirements for use as phosphorus-based fertiliser.
- Valorisation of phosphorus extracted from dairy cattle slurry and municipal solid wastes digestates as a fertilizerPublication . Oliveira, V.; Ottosen, Lisbeth M.; Labrincha, J. A.; Ferreira, CéliaPhosphorus is a vital cell component and an essential and irreplaceable element. Yet at the current rate of exploitation, the phosphate’s reserves will be fast depleted. Dairy cattle slurry and digestates from anaerobic digestion of municipal solid wastes (MSW) are organic wastes containing phosphorus which can potentially be used as a secondary source of this nutrient. The present study investigated the effect of pH in phosphorus release from these wastes using acid and base extraction followed by phosphorus recovery via precipitation, targeting the production of a fertilizer. Results showed that when using HNO3, 100 % of P content was extracted from dairy cattle slurry (2.0\pH\3.3) and 90 % from MSW digestates (1.2\pH\1.5). The maximum extraction was obtained after 2.5 h for dairy cattle slurry and 48 h for MSW digestates. The extraction efficiencies using NaOH were only 22 % for dairy cattle slurry (12.9\pH\13.4) and 9 % for MWS digestates (13.0\pH\13.4). Phosphorus precipitation from extracted solutions was carried out at a molar ratio of 1:1:1 for Mg:N:P and at pH around 8.0. Analysis of the harvested precipitates by XRD and SEM–EDS ruled out the formation of struvite, but validated the formation of amorphous calcium phosphates, a potential fertilizer that can help to close the cycle of this nutrient. During the process, heavy metals might become enriched in the precipitates. In the perspective of producing a fertilizer this is an undesirable process, and one that should be taken into account when considering phosphorus recovery from wastes.