Monitoring settling of anaerobic digestates using low-field MRI profiling and NMR relaxometry measurements

Emanuel G Bertizzolo; Charlie G Gomes; Nicholas Ling; Fabiana Tessele; Michael L Johns; Einar O Fridjonsson

doi:10.1016/j.watres.2023.120660

Monitoring settling of anaerobic digestates using low-field MRI profiling and NMR relaxometry measurements

Water Res. 2023 Oct 15:245:120660. doi: 10.1016/j.watres.2023.120660. Epub 2023 Sep 21.

Authors

Emanuel G Bertizzolo¹, Charlie G Gomes², Nicholas Ling³, Fabiana Tessele⁴, Michael L Johns³, Einar O Fridjonsson⁵

Affiliations

¹ Department of Chemical Engineering, The University of Western Australia, 6009, Australia; Tessele Consultants, 6156, Australia.
² Chemical Metrology Laboratory, Federal University of Pelotas, 96010-900, Brazil.
³ Department of Chemical Engineering, The University of Western Australia, 6009, Australia.
⁴ Tessele Consultants, 6156, Australia.
⁵ Department of Chemical Engineering, The University of Western Australia, 6009, Australia. Electronic address: einar.fridjonsson@uwa.edu.au.

PMID: 37783175
DOI: 10.1016/j.watres.2023.120660

Abstract

Dewatering of anaerobic digestate from red meat processing was assessed using low field MRI profiling and NMR relaxometry. Samples were flocculated using a cationic flocculant (EM640CT) at dosing range (0 to 1.6% v/v) and monitored during the initial 30 min of settling via MRI profiling to assess changes in water fraction, settling time and initial settling velocity. The profiles showed decreasing settling time and increasing initial settling velocity with increased dosing, while sample porosity was observed to increase up to the optimal dosing point (0.8% v/v). Significant increases in sample variability were observed past this point due to flocculant overdosing. The samples were then analysed in terms of turbidity and NMR relaxometry. Increasing flocculant concentration caused turbidity to decrease from 210 to 13 NTU. The relaxation rate of free water showed a strong positive correlation with turbidity. T₂ peaks observed before overdosing could be assigned to different water structures (free, interstitial, vicinal and hydration). An additional T₂ population emerged in the T₂ distributions at the optimal dosing point. Multivariate exploratory data analysis (MEDA) showed that this T₂ population from the solids layer was strongly correlated with the total solids layer height and turbidity of the watery layer. This T₂ peak formation may therefore be used to study opaque flocculated solids to monitor for water structures associated with flocculant overdosing. Further studies using this technique will aim to assess the potential of low field T₂ relaxometry monitoring inline before mechanical dewatering, to monitor optimal flocculant dosing during continuous operations on systems with high solids concentration.

Keywords: Anaerobic digestate; Flocculation; NMR & MRI; Settling process; Water removal.

MeSH terms

Anaerobiosis
Flocculation
Magnetic Resonance Imaging*
Waste Disposal, Fluid* / methods
Water

Substances

Water