1. Background and Aim

Fouling remains a major challenge in membrane-based filtration applications, with biofouling accounting for 45 % of total fouling. Complete prevention of biofouling or removal of the biofilm has not yet been achieved in the long term and at a reasonable cost. The modification of the membrane surface with a thin hydrogel layer combines many approaches to reduce biofouling. A hydrogel consists of an insoluble three-dimensional macromolecular network that adsorbs large amounts of water. The hydration layer acts as a barrier layer for proteins and microorganisms. In this work, a thin hydrogel layer was applied to a membrane using the environmentally friendly technique of electron beam grafting without using toxic chemicals.^[1] In a first fundamental study, different hydrogels were immobilized on track-etched membranes to investigate different resulting properties (surface charge, swelling/crosslinking, surface hydrophilicity, roughness). Subsequently, the most promising hydrogel was immobilized on an ultrafiltration membrane, and the long-term performance was analyzed over a period of 11 months in a membrane bioreactor.

2. Materials and Methods

For the fundamental study, a track etched OxyDisc® membrane (polyethylene terephthalate PET, 0.4 µm, Oxyphen, Lachen, Switzerland) was used. In the applied study, the MicroPES™ membrane (0.03 µm) from 3M (Saint Paul, MN, USA) was used. Monomer solutions were prepared in different sample compositions. The membranes were modified with an electron accelerator under a nitrogen atmosphere at different irradiation doses. Voltage and current were set to 160 kV and 10 mA, respectively. The membranes were immersed in the monomer solution for 5 minutes, placed on a glass plate and irradiated in the electron accelerator. After irradiation, the membranes were washed in water three times for 30 minutes and dried overnight at room temperature.

The membranes were characterized using water contact angle measurements, atomic force microscopy, zeta potential measurements, scanning electron microscopy and biofouling tests with algae (Chlorella vulgaris). The unmodified and modified membranes were further processed by Weise Water GmbH (Hennigsdorf, Germany) to be implemented on two sides of a carrier plate (sandwich plate design) and operated in a membrane bioreactor over a period of 11 months. The total active membrane area was 1.5 m² per module.

3. Results

The charge and roughness had ....