This work aimed to test both energy production and the recovering of phosphorus from high solid content digestate by coupling microbial electrochemical technologies (MET) with a crystallization process. Digestate coming from an anaerobic digester was used as the feeding substrate for a Microbial Fuel Cell (MFC) and a Microbial Electrolysis cell (MEC) to produce electricity and H2, promoting P removal (as struvite: MgNH4PO4∙6H2O) as consequence of the pH increase at the cathode level. MECs were equipped with low cost stainless steel mesh cathodes to be compared with a benchmark cathode, i.e. Pt electrode, and used to reduce the METs cost. The effluents coming from METs were then treated to further reduce P content by promoting struvite precipitation in a crystallization device, by adding either pure Mg salt (MgCl2) or an Mg by-product (seawater bitterns). MFC tests showed a Coulombic efficiency of 35%, with a volumetric power produced of 14.2 ± 0.15Wm 3. MEC (þ1.07 V vs SHE) systems produced 1.90 ± 0.04 LH2 L-1 d-1 using a stainless steel mesh (SSM) and 2.02 ± 0.03 LH2 L-1d-1 using a platinum cathode. Both MET treatments led to a phosphate (PO4 3-) reduction of between 21% and 30% and an organic load reduction (chemical oxygen demand) of between 27% and 44% of the digestate. The addition of MgCl2 * 6H2O or seawater bitterns, in the molar ratio of 1.6: 1 (Mg:P) led to a further reduction of phosphate (PO4 3-) of between 60% and 70% with an overall reduction of phosphate (PO4 3-) of z90%. These results show how the MET systems could be used for COD and nutrients reduction as well as H2 or electricity production from digestate. Moreover, the SSM cathode gave a similar performance to the Pt cathode, while seawater bitterns seem to be useful in substituting MgCl2 * 6H2O. The results obtained showed that the combination of the system proposed in this work with a biogas plant could be a low cost solution for the recovery of nutrients and for hydrogen or electricity generation from digestate.
|Titolo:||Nutrient recovery and energy production from digestate using microbial electrochemical technologies (METs)|
PEPE' SCIARRIA, TOMMY (Corresponding)
|Parole Chiave:||Digestate valorization Electricity production Hydrogen production Microbial electrochemical technologies (MET) Phosphorus recovery Seawater bitterns|
|Settore Scientifico Disciplinare:||Settore AGR/13 - Chimica Agraria|
|Data di pubblicazione:||2019|
|Digital Object Identifier (DOI):||10.1016/j.jclepro.2018.10.152|
|Appare nelle tipologie:||01 - Articolo su periodico|