With the growing use of membranes in the water industry, different methods for using membranes to treat water is still occurring. Enhancing membrane performance is generally performed with extensive pretreatment methods before the feedwater is filtered by the membrane. With the utilization of direct membrane filtration (DF), no pretreatment is performed and the membrane is exposed to raw wastewater. While this may suggest that membrane performance and permeate quality would suffer in the process, DF testing with a 0.03 µm ultrafiltration PVDF membrane showed that relatively high membrane flux was sustained while producing a high quality effluent. Due to the rejection of the membrane, a highly concentrated fraction of the wastewater, which is significantly reduced in volume but high in solids and organic strength, is obtained and can be treated in other ways. A process is proposed to treat municipal wastewater by coupling a DF system with an anaerobic membrane bioreactor (AnMBR). AnMBRs generally treat industrial strength wastewater, which is high in chemical oxygen demand (COD), and may struggle with domestic wastewater, which is generally considered low strength in terms of COD. By coupling the DF with an AnMBR, the DF-AnMBR can be used to treat the low strength domestic wastewater. The DF portion can handle the bulk of the liquid fraction, while the highly concentrated fraction of wastewater is treated by the AnMBR stage, thus improving the energy profile of the AnMBR and enhancing performance. A series of flow and mass balance equations for the combined DF-AnMBR was developed, and used to shed insight on design parameters relevant to this novel treatment process. Since membrane fouling occurs gradually over weeks or months, it is difficult to systematically determine how processes changes may affect membrane performance. Hence, a method to rapidly determine the fouling propensity of wastewater was desired. The modified fouling index (MFI) was previously developed to test the fouling propensity of feedwater for seawater RO desalination, but has not been applied to membrane filtration of wastewater. The MFI method was adapted and used to test the fouling propensity of various treatment streams in the DF-AnMBR system, including raw domestic wastewater, concentrated domestic wastewater (20X by DF), and liquor from an active AnMBR. The effect of powdered activated carbon (PAC) on fouling propensity was also investigated. Raw wastewater had a fouling potential of about 25% of the AnMBR MFI, and with the utilization of PAC the fouling potential was further decreased to nearly 50% of the original fouling potential. The DF concentrated stream had a higher MFI value than liquor from the AnMBR, but presumably some of organics contributing to fouling would be degraded in the AnMBR. This study demonstrated that DF of raw wastewater is feasible, and the combined use of DF and AnMBR is highly promising.

Coagulation/flocculation/sedimentation is a common pretreatment process prior to microfiltration (MF) or ultrafiltration (UF) to alleviate membrane fouling, however there has been limited research on floatation as the pretreatment separation process. The main objective of this study is to compare sedimentation with floatation as part of the pretreatment for ultrafiltration of Ottawa River water (ORW) with relatively high natural organic matter (NOM) content. Water samples pretreated at two full-scale plants were subjected to multiple-day UF membrane fouling tests (constant flux with backwash and chemical cleaning) using an automated bench-scale UF hollow fiber membrane system. For all the experiments, the transmembrane pressure (TMP) increased sharply during the beginning of the operation (~10 h), which indicated the adsorption was significant. In the later cycles, the TMP showed a more linear constant increase, which indicated the built up of the cake layers. The total fouling index (TFI), hydraulically irreversible fouling index (HIFI) and chemical irreversible fouling index (CIFI) for floated water were much smaller than those of settled waters during both summer and winter testing. Thus, for this type of water coagulation/floatation pretreatment was superior process compared to coagulation/sedimentation, the decreased fouling appears to be linked to greater hydrophobic NOM removal by the coagulation/floatation. For all the tests, HIFI/TFIs were less than 0.1, which is to mean most of the fouling was reversible by hydraulic backwashing.Large fluctuation of backwash efficiencies with time were found for all the tested waters. Enhanced chemical backwash with 100 ppm chlorine and chemical clean with 0.1N NaOH & 200 ppm chlorine were found to be very effective at reducing fouling for pretreated ORW. As expected longer filtration cycles resulted in greater fouling but with a slightly greater degree of hydraulically reversible fouling.

Reverse osmosis operations are facing persistent fouling phenomenon that has challenged the integrity of these processes. Prediction of fouling potential by measuring a fouling index toward feed water is essential to ensure robust operation. Moreover, employing a reliable fouling index with good reproducibility and precision is necessary. Silt density index (SDI) is considered insufficient in terms of reliability and empirical theory, among other limitations. Nevertheless due its simplicity, SDI measurement is utilized extensively in RO desalination systems. The aim of this research is to assess the reliability of SDI. Methods include the investigation of different SDI membranes and study of the nature of the SDI filtration. Results demonstrate the existence of the membrane properties' variation within manufacturers, which then causes a lack of accuracy in fouling risk estimation. The nature of particles during SDI filtration provides information that particle concentration and size play a significant role on SDI quantification with substantial representation given by particles with size close to membrane nominal pore size. Moreover, turbidity assisted SDI measurements along with determination of UF pretreated and clean water fouling potential, establishes the indication of non-fouling related phenomena involved on SDI measurement such as a natural organic matter adsorption and hydrodynamic condition that alters during filtration. Additionally, it was found that the latter affects the sensitivity of SDI by being represented by some portions of SDI value. Keywords: Reverse Osmosis, Fouling index, Particulate Fouling, Silt Density Index (SDI), and Assessment of SDI.