Ultrafiltration of digestate liquid fraction by hollow-fiber membranes: Influence of digestate pre-treatment on hydraulic capacity and nutrient removal efficiency

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2023-10, Vol.473, p.145426, Article 145426
• Main Authors: Chuda, Aleksandra, Ziemiński, Krzysztof
• Format: Article
• Language: English
• Subjects: Coagulation; Digestate pre-treatment; Flocculation; Membrane fouling; Permeate flux; Ultrafiltration
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2023.145426

[Display omitted] •Pre-treated digestate was effectively ultrafiltered by hollow-fiber membranes.•Pre-treatment mitigated membrane fouling and alleviated permeate flux decline.•The most effective pre-treatment method was centrifugation and flocculation with PAM.•Biocoagulant chitosan can replace synthetic flocculants in digestate pre-treatment.•Type and dose of coagulant and flocculant greatly affected digestate pre-treatment. With the growing interest in anaerobic digestion as a processing method of agro-food waste, proper disposal of digestate has become a prominent problem. In the study, ultrafiltration of the sugar beet pulp digestate was conducted using hollow-fiber membranes with a cut-off of 150 kDa operating in an outside-in system. The effect of different pre-treatment strategies of digestate i.e. centrifugation alone or in combination with coagulation with polyaluminium chloride, biocoagulation with chitosan and flocculation with polyacrylamide on mitigation of membrane fouling and permeate quality was investigated. High ultrafiltration performance was obtained using centrifugation followed by flocculation with 416 mg/dm3 of polyacrylamide as digestate pre-treatment. Removal efficiencies of chemical oxygen demand (COD), total solids, phosphorus and nitrogen were 89.80, 90.08, 88.37 and 64.12%, respectively. Permeate flux and total membrane resistance averaged 22.33 dm3/m2/h and 5.32 • 1011 m−1. Hydraulic parameters and removal rates determined during ultrafiltration preceded by centrifugation and biocoagulation with 100 mg/dm3 of chitosan did not differ significantly from the values mentioned above for the pre-treatment consisting of centrifugation and flocculation with polyacrylamide. The results indicate the possibility of filtering the liquid fraction obtained by centrifugation, coagulation or flocculation of the digestate, and using natural auxiliary agents during its pre-treatment.