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Contém referências bibliográficas
Dissertação para obtenção do grau de Mestre em Gestão de Empresas, apresentada ao Instituto Politécnico de Castelo Branco
Dissertação apresentada ao Instituto Politécnico de Castelo Branco para cumprimento dos requisitos necessários à obtenção do grau de Mestre em Gestão de Empresas.
When 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 dry-matter 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.
Contém referências bibliográficas
Contém referências bibliográficas
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.
