RAW - Recovering nutrients from wastes: eco-innovative solutions to transform waste into resources

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Struvite quality assessment during electrodialytic extraction

Publication . Oliveira, V.; Kirkelund, Gunvor M.; Labrincha, J.; Ferreira, Célia

Struvite 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.

2020Book part

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Phosphorus flows in the Portuguese agriculture and livestock sectors

Publication . Rocha, Joana; Oliveira, V.; Ferreira, Célia

Phosphorus 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.

2020Book part

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Testing scenarios for municipal waste management chasing carbon neutrality

Publication . Fernández Braña, Álvaro; Feijoo-Costa, G.; Ferreira, Célia

A Life Cycle Assessment (LCA) of the municipal solid waste (MSW) management in a selected residential area of the Portuguese city of Aveiro was conducted. The results showed a poor environmental performance in terms of greenhouse effect gases (GHG) emissions, due to the high amounts of waste being landfilled and the low extent of separate collection. Alternative scenarios were tested, where separate collection is enhanced, in order to improve the environmental balance of GHG emissions until reaching a balanced situation between positive and negative effects. It was found that by using an adequate combination of several treatment options and increasing the separate collection of recyclable materials it is possible to turn MSW management neutral in terms of GHG emissions.

2020Book part

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Evaluation of a phosphorus fertiliser produced from anaerobically digested organic fraction of municipal solid waste

Publication . Oliveira, Verónica; Horta, Carmo; Ferreira, Célia

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 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.

2019Journal article

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Improving the energy efficiency of an electrodialytic process to extract phosphorus from municipal solid waste digestate through different strategies

Publication . 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.

2019-06Journal article

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