Understanding fouling and optimizing cleaning for membranes used for rainwater harvesting

Abstract

This master degree thesis project focuses on assessing the performance of flat-sheet ceramic silicon carbide (SiC) microfiltration membranes used for rainwater purification. The rainwater roof runoff samples were collected from a sedimentation tank installed in the Pilot Hall at Kemicentrum, Faculty of Engineering, Lund University, Sweden. Two membranes were tested in multiple varying fouling and cleaning sequences obtained through a design of experiments (DoE). A suction pressure applied through a peristaltic pump installed on the permeate side created a driving force for this membrane filtration. Experiments assessed the influence of sodium hydroxide and citric acid as cleaning agents chosen through a literature review.
The theoretical part of the project covers information on rainwater harvesting systems, including contaminants commonly found in the roof runoff. Pressure driven membrane processes and water quality requirements for both potable and non-potable applications have been described. Moreover, different fouling mechanisms and cleaning approaches divided into physical and chemical methods were discussed.
The experimental part of the project involves examining the membrane performance through a series of fouling and cleaning tests. The fouling layer was analysed through selected analytic methods: scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDS), atomic force microscopy (AFM), Brunauer-Emmett-Teller (BET). Visual differences between the active layer and the porous support of the membrane were described, along with elemental characterisation. Membrane roughness and area were assessed.
Conducted project shows that the optimal cleaning of membranes is achieved through the application of sodium hydroxide at the highest used concentration of 1.5 wt.%. Citric acid exhibits a negative influence on the process, with the highest cleaning effectiveness achieved in the absence of the agent. Time has little influence, with medium values of approximately 61 minutes exhibiting the best results. Although the applied cleaning strategy was successful at improving the flux, there is still room for improvement, and future recommendations have been proposed.

Popular Abstract

Membranes for the cleaner future of rainwater: performance restoration
Can rainwater from rooftops become a sustainable and safe water source? This project explored the performance of ceramic silicon carbide membranes during repeated contaminant accumulation and chemical cleaning in roof rainwater treatment.
Rainwater collected from rooftops is increasingly considered to be a valuable alternative water source. Before use, it has to be purified, as it contains contaminants that can pose a serious health risk. Ceramic membranes, which act as filters separating substances based on their size and other properties, seem to be a promising technology applied for this purpose due to their durability in changing conditions. They are, however, prone to clogging – fouling – and should therefore be cleaned to keep their effectiveness at a high level.
In this project, the process of rainwater microfiltration using flat-sheet ceramic silicon carbide membranes has been studied. Sodium hydroxide, which is a component that can be found in strong household cleaners designed to dissolve clogs, and citric acid, commonly found in lemons, have been proposed as the cleaning agents. Duration of the process was also varied, and flux of the water going through the membrane – permeate – was measured. More blocked pores would result in a lower permeate flux, which allowed for the assessment of the effectiveness of different applied cleaning sequences.
Membrane samples were then analysed through different imaging and gas adsorption methods to further understand fouling. Visual examination and elemental composition were assessed, along with the roughness of the surface and its area expressed per unit of mass.
This project suggests that ceramic silicon carbide membranes perform best at the highest concentration of sodium hydroxide and in the absence of citric acid. Cleaning duration showed little influence, with the optimal results obtained while running the process for approximately 61 minutes. Irregular formations were visible on the surface, with membranes exhibiting a certain roughness value. Aluminium and iron were found on the surface, and the measured membrane area was relatively small, confirming that fouling is the issue.
In summary, membranes can play a meaningful role in purifying rainwater to meet existing water quality standards. They experience performance issues which can be further optimised. Their durability and ease of modifying the cleaning strategies are important advantages that shall be seen as an opportunity for meeting the sixth United Nations Goal aimed at sustainable water management.

• author: Nowak, Natalia
• supervisor: Mariona Battestini Vives
• organization: Chemical Engineering (M.Sc.Eng.)
• course: METM01 20261
• year: 2026
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: ceramic membranes, silicon carbide, rainwater harvesting systems, membrane fouling, chemical cleaning, design of experiments, membrane technology
• language: English
• id: 9238988
• date added to LUP: 2026-06-22 09:28:25
• date last changed: 2026-06-22 09:28:25