Monitoring of SUR to control and enhance the performance of dead-end ultrafiltration installations treating wwtp effluent

The variation of quality and fouling properties of wwtp effluent over time influences the performance of ultrafiltration (UF) plants. This research reports three experiments in which the specific ultrafiltration resistance (SUR) measurement is applied to obtain more insight in quality variation an impact on UF performance. Firstly the overall performance (flux, recovery and trans-membrane pressure) of a UF pilot was compared with the SUR values of the feedwater. Secondly the effect of pre treatment was investigated. At last the relation between the slopes of filtration cycles of a UF installation and SUR measurements of feedwater were compared. The results clearly indicate that the overall performance of the UF pilot depends on the SUR values of the feedwater. The SUR values should be less than 10×1012 m–2 for a stable UF performance. Also the effect of pre treatment depends on the SUR values of raw wwtp effluent. Very low SUR values (~4×1012 m–2) mean less effect compared to higher SUR values. The relation and correlation between SUR values of feed water and single filtration cycles of UF installations depends on the condition of the membranes in the units. Using fouled membranes the variation of SUR values corresponds to higher TMP variations than using cleaner membranes.

The overall performance of the UF installation at wwtp Horstermeer depends on the SUR values of the feed water. Good performance with fluxes of 57 and 71 l/m2h was only obtained when the SUR values were in the range of 9–13× 1012 m–2. With higher fluxes (80–90 l/m2h) the critical SUR becomes lower (9×1012 m–2). The overall effect of pretreatment depends on the SUR values of the raw wwtp effluent at Sas van Gent. The effect decreases with decreasing values of the SUR. Therefore, it may be considered and investigated if pre treatment is needed during a periods of lower SUR values. At the UF plant Sas van Gent a clear relation and correlation between SUR and TMP increase was found twice for UF unit 1. The relation and correlation were less for UF unit 4. Probably, this difference is caused by the life time and therefore performance of the membranes. Considering all findings it is firm that the SUR 0,04 Increase TMP (bar/filtration cycle) 0,035 0,03 0,025 y = 0,0041x + 0,002 R2 = 0,8952 0,02 0,015 0,01 0,005 0,0 1,0 2,0 3,0 4,0 5,0 6,0 7,0 8,0 9,0 SUR (10^12 m^-2) Fig. 6. Relation between SUR values of feedwater UF and TMP increase during one filtration cycle of UF unit 1. Measurements were performed in the period 13/10/2006–7/12/2006.