Zeyad S. Tarawneh

Development of the MFI-UF in constant flux filtration

The MFI-UF, based on cake filtration, was developed to measure and predict the particulate fouling potential of feedwater to membrane filtration installations. The MFI-UF is determined in constant pressure filtration with the flux deceasing during the test. However, many membrane systems, e.g., reverse osmosis (RO), operate at constant flux with pressure increasing when fouling occurs. As both pressure and flux contribute to cake compression, determining the MFI-UF in constant flux with correction to the flux of an RO system is expected to more closely simulate particulate fouling Therefore, this research investigated the development of the MFI-UF test in constant flux filtration applying low (tap water) and high fouling (diluted canal water) feedwater. Preliminary experiments were promising; the fouling index (I) (and hence the MFI-UF) of all feedwater could be determined within 2 h under constant flux filtration. Cake filtration was demonstrated as (1) a minimum in the fouling indexvs time plot and (2) by linearity of the fouling index with feedwater particulate concentration. The fouling index increased with increasing applied flux due to cake compression. Further investigation at higher and lower applied flux is required to identify a reference test flux and to develop a method to correct the fouling index to the reference test flux and/or the flux of a membrane filtration system The fouling index can then be applied in a model to predict fouling.

Modified Fouling Indexultrafiltration to compare pretreatment processes of reverse osmosis feedwater

Existing fouling indices to measure the particulate fouling potential of reverse osmosis (RO) feedwater, the SDI and MFI0.45 do not include smaller colloidal particles. Therefore, the MFI using ultrafiltration (UF) membranes was developed (1000–100,000 Da pore size) to incorporate and measure smaller particles. A 13,000 Da membrane was selected as the most promising reference membrane for application in the MFI-UF test. This research investigates its application to (1) measure the particulate fouling potential of RO feedwater and (2) evaluate the efficiency of pretreatment processes on particle removal at two RO pilot plants. Where possible a comparison was made with the SDI, MFI0.45, and particle counts. Both RO plants use conventional pretreated surface water. Subsequently, the Rhine River plant uses ozonation, biological activated carbon filtration, and slow sand filtration while the Ijssel Lake plant uses ultrafiltration (150–200,000 Da). The MFI-UF of the influent feedwater was about 400–1400 higher than the corresponding MFI0.45 and SDI, due to the retention of smaller particles. A reduction in the particulate fouling potential, > -80%, was found by MFI-UF with pretreatment at both plants. For the larger particles the MFI0.45 gave a 90–≈100% reduction at the Rhine River plant, while the SDI gave more variable results: 70 > 90%.

Bias in return period of droughts estimated from tree-ring reconstructions

This article investigates the bias in return period of droughts of extreme duration evolved from trun-cating tree-ring reconstructed precipitation. 239 years of tree-ring reconstructed annual precipitation for Madaba region in Jordan, covering the period 1743–1981, was used to explore the bias. Furthermore, 100 traces of simulated annual precipitation, each of 239 years, were generated using stochastic simulation model for comparison purposes. The results show that the return period estimated from the analysis of the tree-ring reconstructed precipitation departs increasingly downward from the expected results provided by simulation or theoretical models as the drought duration increases (becomes more extreme). The bias in the estimated return period can be neglected when the drought duration is fairly short, i.e. 1–2 years for the case under study.