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- Dataset of socio-economic and waste collection indicators for Portugal at municipal levelPublication . Oliveira, Verónica; Sousa, Vitor; Ferreira, CéliaThis data article presents demographic, socio-economic and wasterelated data at municipal level for Portugal. The dataset includes raw data collected from 4 main sources: (i) the annual reports of waste management companies; (ii) the database of the Portuguese water, sanitation and waste regulatory entity; (iii) the Portuguese Environmental Agency; and (iv) national statistical data. Relevant indicators for waste generation and for the separate collection of waste are proposed and calculated using the raw data. The dataset comprises municipalities with high, medium and low separate collection yields, providing socio-economic and waste infrastructures data that can be used for benchmarking. The dataset can also be used to define a baseline against which the progress of the collection of packaging waste can be assessed over time, or else serve as input to mathematical models predicting waste generation and collection. Moreover, data can serve as the base to calculate new waste-related indicators. In addition to being a valuable input to the waste topic, the dataset can also be used in a large range of other topics where demographic and socio-economic parameters are relevant. The data presented herein are associated with the research articles “Model for the separate collection of packaging waste in Portuguese low-performing recycling regions” [1] and “Artificial neural network modelling of the amount of separatelycollected household packaging waste” [2].
- Prediction performance of separate collection of packaging waste yields using support vector machinesPublication . Sousa, Vítor; Meireles, I.; Oliveira, Verónica; Ferreira, CéliaUnderstanding the drivers underlying waste production in general, and source-segregated waste in particular, is of utmost importance for waste managers. This work aims at evaluating the performance of support vector machines (SVM) models in the prediction of separate collection yields for packaging waste at municipal level. Two SVM models were developed for a case study of 42 municipalities simultaneously serviced by separate collection of packaging waste and by unsorted waste collection. The “SVM-fxed” model used a fxed set of 5 variables to predict collection yields, whereas the “SVM-optimal” model chose from a pool of 14 variables those that optimized performance, using a genetic algorithm. These SVM models were compared with 3 traditional regression models: the ordinary least square linear (OLS-L), the ordinary least square non-linear (OLS-NL) and robust regression. The robust regression model was further compared against the other regression models in order to assess the infuence of the dataset outliers on the model performance. The coefcient of determination, R2 , was used to evaluate the performance of these models. The highest performance was attained by the SVM-optimal model (R2=0.918), compared to the SVM-fxed model (R2=0.670). The performance of the SVM-optimal model was 42% higher than the best performing regression model, the OLS-NL model (R2=0.646). The diferences in performance among the 3 regression models are small (circa 3%), whereas the exclusion of outliers improved their performance by 13%, indicating that outliers impacted more on performance than the type of traditional regression technique used. The results demonstrate that SVM model can be a viable alternative for prediction of separate collection of packaging waste yields and that there are nine important drivers that all together explain roughly 92% (R2=0.918) of the variability in the separate collection yields data.
- Improving the energy efficiency of an electrodialytic process to extract phosphorus from municipal solid waste digestate through different strategiesPublication . Oliveira, Verónica; Kirklund, G.; Horta, Carmo; Labrincha, João; Ferreira, Célia; Kirkelund, Gunvor M.This work assesses the possibility of energy optimisation during the electrodialytic extraction of phosphorus from the municipal solid waste digestate. Strategies tested for energy optimisation consisted in (i) using a dualstage extraction approach; (ii) replacement of continuous stirring by pulse stirring and; (iii) utilisation of pulse electric current as an alternative to a constant current. Experiments were carried out using different stirring profiles (continuous stirring, pulsed stirring, manual stirring and no stirring) and different profiles for generating the electric field (continuous current and pulsed current). Dual-stage approach decreased the energy consumption by 30%. Energy was mainly used in the stirring operation (80%). Applying this strategy caused a faster acidification of the waste suspension and reduced the time required for the extraction. As for the second strategy, use of pulse stirring, it is possible to save energy by operating the stirrer 25% of the time, without compromising the phosphorus extraction values, which are close to 90%. Corresponding energy savings reached 70%. The third strategy tested, use of pulse current, had as side-effect a significant decrease of the phosphorus extracted, so the implementation of pulse current is not recommended. Overall, the energy efficiency of the electrodialytic extraction of phosphorus can be improved by 80% through the use of the dual-stage approach and the use of stirring for 25% of the time. There is also a potential in further reducing the energy use by further improving the stirring system.
- Synthesis of PPy-ZnO composite used as photocatalyst for the degradation of diclofenac under simulated solar irradiationPublication . Silvestri, Siara; Ferreira, Célia; Oliveira, Verónica; Varejão, Jorge M. T. B.; Labrincha, João; Tobaldi, David Maria
- Evaluation of a phosphorus fertiliser produced from anaerobically digested organic fraction of municipal solid wastePublication . Oliveira, Verónica; Horta, Carmo; Ferreira, CéliaWhen urban waste is not separately collected its phosphorus content cannot be recovered. The production of phosphorus-based fertilisers from urban waste could generate phosphorus added-value products, reduce environmental impacts from waste disposal and lower the consumption of virgin raw materials in the fertiliser industry. The main objective of this work was to evaluate the short-term agronomic value of a phosphorus fertiliser, which has the same chemical composition and mineralogical structure as struvite, but is artificially produced using phosphorus recovered from the anaerobically digested organic fraction of municipal solid waste (herein referred to as “secondary struvite”). To evaluate the release of phosphorus forms over time a 30 d incubation experiment was performed. Then the cultivation of rye (Secale cereale L.) was done in pot scale during 45 d to assess the phosphorus phytoavailability and the agronomic potential of secondary struvite, when compared with the commercial mineral fertiliser, single superphosphate. This work contributes to fill a knowledge gap about the effects of this secondary struvite as a source of phosphorus on soil phosphorus forms as well as on phosphorus’ soil and plant availability. At the end of the incubation experiment, a similar distribution of phosphorus forms in soil for both secondary struvite and single superphosphate was observed; however, the soil Olsen phosphorus was significantly higher in the soils fertilised using secondary struvite than in those fertilised by single superphosphate, which indicates that secondary struvite provided a higher amount of immediately phytoavailable phosphorus. The shoot biomass production (1.7 g dry-matter kg 1 soil) and the agronomic efficiency (66 g drymatter g 1 phosphorus) were similar for both fertilisers. But the crop's phosphorus uptake and the apparent phosphorus recovery were higher (5.9 mg phosphorus kg 1 soil and 45%) in the secondary struvite treatment than in the single superphosphate treatment (4.7 mg phosphorus kg 1 soil and 36%). The results suggest that the secondary struvite can be used as a phosphorus fertiliser and lower rates of the secondary struvite are required to achieve the same agronomic efficiency as the single superphosphate.
- Testing new strategies to improve the recovery of phosphorus from anaerobically digested organic fraction of municipal solid wastePublication . Oliveira, Verónica; Ferreira, Célia; Labrincha, João; Rocha, Joana; Kirkelund, Gunvor M.BACKGROUND: This work is focused on phosphorus (P) recovery from the anaerobically digested organic fraction of municipal solid waste (referred to as ‘digestate’) as a fertilizer. The main purpose was to propose and test modifications to the electrodialytic process that increase P extraction, improve the quality of the fertilizer by removing contaminants, and reduce hydraulic retention time to allow for smaller system footprints. Strategies tested were: (i) lowering the pH of the digestate suspension to <4.5 using the electrochemical reactions and enhance P solubilization from the waste; (ii) changing the configuration of the electrodialytic cell from three to two chambers; and (iii) stirring the sample to shorten the duration of the extraction. RESULTS: Results show that the acidification of digestate by the electrochemical reactions was effective to enhance P extraction yield. Three-chamber electrodialytic experiments enabled the removal of heavy metals from the digestate, producing P-rich solutions with low metal concentrations. This resulted in the production of high-quality fertilizer which can be used for agricultural applications. The modification of the electrodialytic cell set-up from three- to two-chamber neither resulted in an increase of the P extraction yields, nor contributed to the removal of metals from the liquid phase of digestate. Reduction of the hydraulic retention time of electrodialytic extraction of P from 16 days to 9 days was attained by the use of stirring and by electrodialytic acidification. CONCLUSIONS: An increase of P recovery was accomplished by modification of electrodialytic extraction, resulting in 90% of Pbeing successfully extracted from the digestate and transformed into struvite.
- Artificial neural network modelling of the amount of separately-collected household packaging wastePublication . Oliveira, Verónica; Sousa, Vitor; Ferreira, CéliaThis work develops an artificial neural network (ANN) model using genetic algorithms to estimate the annual amount (kg/inhabitant/year) of separately-collected household packaging waste. The ANN model comprises one input layer, one hidden layer with seven neurons and one output layer. Ten variables affecting the amount of separately-collected packaging waste were identified and used in the ANN model. These variables are related to the level of education of the population, the size and level of urbanisation of the municipality, social aspects related to poverty and economic power and factors intrinsic to the waste collection service. A comparison between ANN and regression models for the estimation of packaging waste is also carried out. The performance of the proposed ANN model for a data set of 42 municipalities located in the centre of Portugal, measured by the R2 , is 0.98. This value is 34% higher than the best regression model applied to the same data set (R2 ¼ 0.73), indicating that ANN has a significantly higher explanatory power than traditional regression techniques. Another advantage is that ANN is not as sensitive to outliers as regression. However, ANN is more complex, has a higher number of variables, and the model development and interpretation of the results are more difficult. Nevertheless, the higher performance of ANN makes it a valuable tool in the definition of strategies to increase recycling and achieve circular economy goals.