Pilot-scale magnetic recovery of vivianite from digested sewage sludge. (1st April 2022)

• Record Type: Journal Article
• Authors: Wijdeveld, W.K.; Prot, T.; Sudintas, G.; Kuntke, P.; Korving, L.; van Loosdrecht, M.C.M.
• Is Part Of: Water research. Volume 212(2022)
• Publication Date: 2022-04-01
• Subjects: Vivianite -- Phosphorus recovery -- Magnetic separation -- Pilot scale operation -- HGMS; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2022.118131
• Languages: English
• ISSNs: 0043-1354

Abstract

Highlights: An urban mining concept is introduced to recover phosphorus from digested sludge. High gradient magnetic separators (HGMS) can recover vivianite from digested sludge. A pilot scale HGMS showed a vivianite recovery of 80% from digested sludge. Vivianite recovery allows for 60% recovery of phosphorus from influent wastewater. The concentrate had a vivianite content of 0.8 g/g and low heavy metal content. Abstract: Phosphorus (P) is an essential resource for food production and chemical industry. Phosphorus use has to become more sustainable and should include phosphorus recycling from secondary sources. About 20% of P ends up in sewage sludge, making this a substantial secondary P source. There is currently a technological gap to recover P from sludge locally at wastewater treatment plants (WWTP) that remove P by dosing iron. Vivianite (Fe3 (PO4 )2 8(H2 O)) is the main iron phosphate mineral that forms during anaerobic digestion of sewage sludge, provided that enough iron is present. Vivianite is paramagnetic and can be recovered using a magnetic separator. In this study, we have scaled up vivianite separation from lab-scale to bench- and pilot-scale. Bench-scale tests showed good separation of vivianite from digested sewage sludge and that a pulsation force is crucial for obtaining a concentrate with a high P grade. A pilot-scale magnetic separator (capacity 1.0 m 3 /h) was used to recover vivianite from digested sewage sludge at a WWTP. Recirculating and reprocessing sludge allows over 80% vivianite recovery within three passes. A concentrated P-product was produced with a vivianite content of up to 800 mg/g and a P content of 98 mg/g. P recovery is limited by the amount of P bound in vivianite and can be increased by increased iron dosing. With sufficient iron dosing, the vivianite content can be increased, and subsequently more P can be recovered. This would allow compliance with existing German legislation, which requires a P recovery larger than 50%. Graphical abstract: Image, graphical abstract