Using ceramic nanofiltration membranes for treatment of municipal sewage is upcoming. However, the knowledge on fouling control methods for this application are very limited. The most commonly used fouling control method, chemical cleaning, has disadvantages. Chemical cleaning negatively impacts (i) the glass seal layer of tubular ceramic nanofiltration membranes and (ii) the environment, especially when using sodium hypochlorite for removal of organic fouling. Therefore, the use of chemical cleaning should be limited as much as possible. In this research, first, the well-known fouling control methods for polymeric micro- and ultrafiltration membranes, were studied on ceramic nanofiltration membranes: hydraulic backwash and forward flush. Second, a precoat method was combined with a chemical reaction to aid the detachment of the formed cake layer. In this method, a precoat layer was filtered atop of the membrane surface before the start of filtration. The precoat layer then acts as a barrier between the foulants and the membrane surface. After filtration, the precoat layer reacts with the cleaning reagent underneath the fouling layer to enable fast removal of fouling. Results showed that hydraulic backwash was not effective to be used for this type of membranes. Forward flush was able to maintain a higher flux but the relative production downtime was high. Reaction based precoat was most effective in maintaining a high flux and resulted in the highest net water production. Two reaction based precoat methods were tested of which the reaction of calcium carbonate with citric acid was more effective than a Fenton reaction.@en

Worldwide population growth, water scarcity, and climate change contribute to an urgent need for alternative water sources for irrigation water, industry water, and, in some countries even, drinking water. The implementation of municipal sewage reclamation is an upcoming trend in water treatment. The use of municipal sewage has the advantage of keeping the water circles small. Moreover, more is to gain from municipal sewage: nutrients and energy are abundantly present in this water and could potentially be recovered too. The purpose of this research was to study the potential of the application of ceramic nanofiltration for treatment of municipal sewage. Ceramic nanofiltration membranes were chosen because of their high mechanical strength and high chemical and thermal resistance. These membranes are expected not to be damaged by high pressures, temperatures, concentration of chemicals, which enables vigorous chemical cleaning of the membranes, and they are prone to less irreversible fouling compare to polymeric nanofiltration NF. This research was divided into four parts. First, a preliminary pilot study showed that ceramic nanofiltration membranes have potential for direct treatment of municipal sewage as pretreatment for reverse osmosis. Second, the quality and robustness was thoroughly researched and was lower than expected. Third, the phosphate retention during ceramic NF was notable effected by pH, multivalent counter ions, and a fouling layer on the membrane surface. Fourth, several fouling control method were tested using ceramic nanofiltration: the highest flux was maintain when applying reaction based precoat, resulting in the net highest water production.@en

One of the perceived benefits of ceramic membranes is their robustness, which makes them suitable for treating high organic load waste streams. In particular, ceramic tight ultrafiltration (tUF) and nanofiltration (NF) form an important barrier against small colloids and organic molecules. In order to achieve this barrier, the quality of the membranes should be uncompromised. An extension on a commonly used size exclusion method was developed in order to quantify defects in membranes and calculate the MWCO accurately excluding the defects. This approach gives a better representation of the membrane quality than the original method. The quality of a broad range of commercial ceramic membranes was investigated by determining the (i) hydraulic permeability, (ii) molecular weight cut-off, and (iii) quantitative defects. Several membranes – both tubular and disc membranes, selected from various suppliers – were tested to investigate their variability. Furthermore, the robustness of tubular NF membranes was studied by monitoring the effect of long-term exposure to sodium hypochlorite, which is commonly used to mitigate organic fouling. The results showed that batches of both tubular and disc membranes of different pore size and suppliers included membranes with defects. Furthermore, the long-term treatment of tubular ceramic membranes with sodium hypochlorite negatively affected, beyond expectation, the quality of the membranes. The separation layer in these membranes was not notably compromised by sodium hypochlorite exposure, but the end seal layer was damaged.@en