Abstract
Membrane filtration of biological suspensions is frequently limited by fouling. This mechanism is well understood for ultrafiltration of activated sludge in membrane bioreactors. A rather young application of ultrafiltration is the recovery of nutrients from anaerobic digestates, e.g., from agricultural biogas plants. A process chain of solid/liquid separation, ultrafiltration, and reverse osmoses separates the digestate into different products: an organic N-P-fertilizer (solid digestate), a recirculate (UF retentate), a liquid N-K-fertilizer (RO retentate) and water. Despite the preceding particle removal, high crossflow velocities are required in the ultrafiltration step to overcome fouling. This leads to high operation costs of the ultrafiltration step and often limits the economical application of the complete process chain. In this study, under-stoichiometric ozone treatment of the ultrafiltration feed stream is investigated. Ozone treatment reduced the biopolymer concentration and apparent viscosity of different digestate centrates. Permeabilities of centrate treated with ozone were higher than without ozone treatment. In a laboratory test rig and in a pilot plant operated at the site of two full scale biogas plants, ultrafiltration flux could be improved by 50–80% by ozonation. Nutrient concentrations in the fertilizer products were not affected by ozone treatment.
Highlights
Ultrafiltration (UF) is a state-of-the-art technology for municipal and industrial wastewater treatment, e.g., as membrane bioreactor in combination with activated sludge processes [1]
This leads to high operation costs of the ultrafiltration step and often limits the economical application of the complete process chain
In a laboratory test rig and in a pilot plant operated at the site of two full scale biogas plants, ultrafiltration flux could be improved by 50–80% by ozonation
Summary
Ultrafiltration (UF) is a state-of-the-art technology for municipal and industrial wastewater treatment, e.g., as membrane bioreactor in combination with activated sludge processes [1]. The interaction mechanisms between biological suspension and membrane surface are well understood and commonly classified into deposition, reversible and irreversible (bio-)fouling, and pore-blocking [1,2]. Particle size and structure as well as sludge rheology have an impact on membrane fouling [3,4]. Rather young applications for ultrafiltration of biological suspensions are anaerobic membrane bioreactors [7,8,9] and the recovery of nutrients from manure and anaerobic digestates [10,11]. Anaerobic digestate is a side product of sewage sludge, animal waste, or energy crop fermentation in biogas plants. Digestates are used as field fertilizer in Membranes 2020, 10, 64; doi:10.3390/membranes10040064 www.mdpi.com/journal/membranes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
