SUMMARIZED INTERIM REPORT Q3/2019
25 years after the technology invention, 20 ceramic flat sheet membrane producers have been identified. Especially over the past few years, several new suppliers in China have established large-scale production facilities.
As of today, CERAFILTEC has tested 11 different ceramic flat membranes and characterized their performance in clean water and under application conditions.
CLEAN WATER TESTS
Filtration pressure (TMP) as well as backwash pressure have been characterized. All results are normalized to standard temperature of 20 °C. The illustrated TMP curves are based on a set flux of 400 LMH. At minute 34 the membranes were backwashed at a 3.5 times higher flow.
New membranes have been used (as received from the producers) without any additional cleaning prior to the clean water tests. Dust deposits and remaining air inside the pores during first minutes of filtration usually affect the performance readings. Consequently, for the benchmark evaluation only the last recorded values after executed backwash and re-stabilized TMP are considered.
To conduct more benchmarks against membrane quality and material features the permeabilities have been additionally normalized to a standard pore size of 0.1 µm based on pore diameter pressure loss calculation.
INORGANIC CAKE LAYER FILTRATION TESTS
The active cake layer filtration process is one of the unique features of the ceramic flat sheet membrane technology. A cake layer can function as additional filter bed for enhanced removal of very small particles and colloidal fractions. It can also be used to adsorb dissolved water contents. A formed cake layer can also function as protective coating to minimize membrane biofouling and scaling effects.
Common cake layer particles or flocs are based on metal oxides, e.g. from Fe and Mn but they can also be based on Alum or hardness precipitants.
Cake layer particle sizes below 0.4 µm are common. Membranes with larger pores sizes or a wide pore size distribution range will be affected by performance declines, e. g. due to pore blockages or reduced filtered water quality.
In general, the smaller the pore size and the tighter the pore size distribution the better the suitability for cake layer filtration processes.
FOULING FILTRATION TESTS
The membrane biofouling behaviour is key knowledge needed for a proper plant projection and a stable process performance.
To evaluate the fouling potential organically contaminated water was used to simulate typical water characteristic of TSE or river water. The filtration flux has been set to a reduced but still high value of 200 LMH in order to record prospective fouling potential within a short time. The backwash flow is set at 700 LMH which is 3.5 times the filtration flux. At minute 34 the backwash has been executed.
Reversible and irreversible fouling are illustrated based on TMP decline. The lower the decline the lower the susceptibility to fouling.