Layer-by-Layer (LbL) technology was used to coat alumina ceramic membranes with nanosized polyelectrolyte films. The polyelectrolyte chains form a network with nanopores on the ceramic surface and promote the rejection of small molecules such as pharmaceuticals, salts and industrial contaminants, which can otherwise not be eliminated using standard ultrafiltration methods. The properties and performance of newly developed hybrid membranes are in the focus of this investigation. The homogeneity of the applied coating layer was investigated by confocal fluorescence microscopy and scanning transmission electron microscopy (STEM). Properties such as permeability, bubble point, pore size distribution and Zeta potential were determined for both pristine and LbL coated membranes using various laboratory tests. Subsequently, a thorough comparison was drawn. The charging behavior at solid-liquid interface was characterized using streaming potential techniques. The retention potential was monitored by subjecting widely used pharmaceuticals such as diclofenac, ibuprofen and sulfamethoxazol. The results prove a successful elimination of pharmaceutical contaminants, up to 84% from drinking water, by applying a combination of polyelectrolyte multilayers and ceramic membranes.

Hybrid ceramic membranes (i.e., membranes with a layer-by-layer (LbL) coating) are an emerging technology to remove diverse kinds of micropollutants from water. Hybrid ceramic membranes were tested under laboratory conditions as single-channel (filter area = 0.00754 m²) and multi-channel (0.35 m²) variants for the removal of pharmaceuticals (sulfamethoxazole, diclofenac, clofibric acid, and ibuprofen) and typical wastewater pollutants (i.e., COD, TOC, PO₄-P, and TN) from drinking water and treated wastewater. The tests were conducted with two low transmembrane pressures (TMP) of 2 and 4 bar and constant temperatures and flow velocities, which showed rejections above 80% for all the tested pharmaceuticals as well for organic pollutants and phosphorous in the treated wastewater. Tests regarding sufficient cleaning regimes also showed that the LbL coating is stable and resistant to pHs between 2 and 10 with the use of typical cleaning agents (citric acid and NaOH) but not to higher pHs, a commercially available enzymatic solution, or backwashing. The hybrid membranes can contribute to the advanced treatment of water and wastewater with low operational costs, and their application at a larger scale is viable. However, the cleaning of the membranes must be further investigated to assure the stability and durability of the LbL coating.

Layer-by-layer (LbL) modification of porous membranes for water filtration has become an active research field in the past few years. Different mechanisms regarding polyelectrolyte film growth, swelling and smoothing, transport through these films, etc., have been studied. Although there are conjectures, it is not yet fully understood where the polyelectrolyte layering takes place when modifying porous membranes, either within the pores or on top of the porous material. This study presents a theoretical approach to investigate the dominant layer buildup regime between pore-dominated vs. layer-dominated growth of polyelectrolytes on porous membranes without mechanically interfering or damaging the membrane material. For this, fouling mechanism processes are used as an analogy. The presented approach gives a new insight into layering conformation and might be helpful to investigate the interaction between the membrane surface and the PE film. Moreover, the MgSO₄ rejection behavior of two types of modified membranes was investigated: one with an initial pore-dominated layer growth followed by a layer-dominated film growth; the other one with a completely layer-dominated film growth. The data confirm that a rejection for MgSO₄ could only be achieved in the regime of layer-dominated film growth. Additionally, when layer-dominated film growth prevails from the early stages of the coating process, permeability values are higher at similar MgSO₄ rejection rates compared to an initial pore-dominated and then layer-dominated film growth. Accordingly, the interaction between the membrane pore size and molecular weight of the polyelectrolytes in the coating solutions plays an important role during LbL coating.