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- A novel approach for nutrients recovery from municipal waste as biofertilizers by combining electrodialytic and gas permeable membrane technologiesPublication . Oliveira, Verónica; Ferreira, Célia; González-García, Isabel; Labrincha, João; Horta, Carmo; García-González, María CruzThe recovery of valuable materials from waste fits the principle of circular economy and sustainable use of resources, but contaminants in the waste are still a major obstacle. This works proposes a novel approach to recover high-purity phosphorus (P) and nitrogen (N) from digestate of municipal solid waste based on the combination of two independent membrane processes: electrodialytic (ED) process to extract P, and gas permeable membranes (GPM) for N extraction. A laboratory ED cell was adapted to accommodate a GPM. The length of waste compartment (10 cm; 15 cm), current intensity (50 mA; 75 mA) and operation time (9 days; 12 days) were the variables tested. 81% of P in the waste was successfully extracted to the anolyte when an electric current of 75 mA was applied for 9 days, and 74% of NH4 + was extracted into an acid-trapping solution. The two purified nutrient solutions were subsequently used in the synthesis of a biofertilizer (secondary struvite) through precipitation, achieving an efficiency of 99.5%. The properties of the secondary struvite synthesized using N and P recovered from the waste were similar to secondary struvite formed using synthetic chemicals but the costs were higher due to the need to neutralize the acid-trapping solution, highlighting the need to further tune the process and make it economically more competitive. The high recycling rates of P and N achieved are encouraging and widen the possibility of replacing synthetic fertilizers, manufactured from finite sources, by secondary biofertilizers produced using nutrients extracted from wastes.
- Two-phase nutrient recovery from livestock wastewaters combining novel membrane technologiesPublication . González-García, Isabel; Oliveira, Verónica; Molinuevo-Salces, Beatriz; García-González, María Cruz; Ferreira, Célia; Riaño, BertaThe application of new technologies in the agro-industrial sector is needed to close the loop of the nutrient cycle in the food chain. The aim of this work is to study the feasibility of the combination of two nutrient recovery technologies. In a first step, the novel gas-permeable membrane technology recovers N from the wastewater as an ammonium sulfate solution (a bio-based fertilizer). Secondly, the electrodialytic process recovers P, as an electrolyte solution, from which P can then be precipitated as struvite (a slow-release fertilizer). The process was tested in two different livestock wastewaters: swine manure (SM) and anaerobically digested SM (digestate). Recovery efficiencies for N were 53% for SM and 92% for digestate; for P the efficiencies were 100% and 74% for SM and digestate, respectively. The results showed a great potential of combining these novel membrane technologies in livestock wastewaters, promoting the sustainability of the sector in the realm of the bioeconomy.
- 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.