Replacing traditional pretreatment in one-step UF with natural short-distance riverbank filtration: Continuous contaminants removal and TMP increase relief.

Scientists have been focusing on applying more natural processes instead of industrial chemicals in drinking water treatment to achieve the purpose of carbon emissions reduction. In this study, we shortened the infiltration range of riverbank filtration, a natural water purification process, to form the short-distance riverbank filtration (sRBF) which retained its ability in water quality improvement and barely influenced the groundwater environment, and integrated it with ultrafiltration (UF) to form a one-step sRBF-UF system. This naturalness-artificiality combination could realize stable contaminants removal and trans-membrane pressure (TMP) increase relief for over 30 days without dosing chemicals. Generally, both sRBF and UF played the important role in river water purification, and the interaction between them made the one-step sRBF-UF superior in long-term operation. The sRBF could efficiently remove contaminants (90 % turbidity, 60 % total nitrogen, 30 % ammonia nitrogen, and 25 % total organic carbon) and reduce the membrane fouling potential of river water under its optimum operation conditions, i.e., a hydraulic retention time of 48 h, an operation temperature of 20 °C, and a synergistic filter material of aquifer and riverbank soil. Synergistic adsorption, interception, and microbial biodegradation were proved to be the mechanisms of contaminants and foulants removal for sRBF. The sequential UF also participated in the reduction of impurities and especially played a role in intercepting microbial metabolism products and possibly leaked microorganisms from sRBF, assuring the safety of product water. To date, the one-step sRBF-UF was a new attempt to combine a natural process with an artificial one, and realized a good and stable product quality in long-term operation without doing industrial chemicals, which made it a promised alternative for water purification for cities alongside the river.

Generalization and Expansion of the Hermia Model for a Better Understanding of Membrane Fouling.

One of the most broadly used models for membrane fouling is the Hermia model (HM), which separates this phenomenon into four blocking mechanisms, each with an associated parameter n. The original model is given by an Ordinary Differential Equation (ODE) dependent on n. This ODE is solved only for these four values of n, which limits the effectiveness of the model when adjusted to experimental data. This paper aims extend the original Hermia model to new values of n by slightly increasing the complexity of the HM while keeping it as simple as possible. The extended Hermia model (EHM) is given by a power law for any n ≠ 2 and by an exponential function at n = 2. Analytical expressions for the fouling layer thickness and the accumulated volume are also obtained. To better test the model, we perform model fitting of the EHM and compare its performance to the original four pore-blocking mechanisms in six micro- and ultrafiltration examples. In all examples, the EHM performs consistently better than the four original pore-blocking mechanisms. Changes in the blocking mechanisms concerning transmembrane pressure (TMP), crossflow rate (CFR), crossflow velocity (CFV), membrane composition, and pretreatments are also discussed.

Alleviation of Ultrafiltration Membrane Fouling by ClO2 Pre-Oxidation: Fouling Mechanism and Interface Characteristics.

In order to alleviate membrane fouling and improve removal efficiency, a series of pretreatment technologies were applied to the ultrafiltration process. In this study, ClO2 was used as a pre-oxidation strategy for the ultrafiltration (UF) process. Humic acid (HA), sodium alginate (SA), and bovine serum albumin (BSA) were used as three typical organic model foulants, and the mixture of the three substances was used as a representation of simulated natural water. The dosages of ClO2 were 0.5, 1, 2, 4, and 8 mg/L, with 90 min pre-oxidation. The results showed that ClO2 pre-oxidation at low doses (1-2 mg/L) could alleviate the membrane flux decline caused by humus, polysaccharides, and simulated natural water, but had a limited alleviating effect on the irreversible resistance of the membrane. The interfacial free energy analysis showed that the interaction force between the membrane and the simulated natural water was also repulsive after the pre-oxidation, indicating that ClO2 pre-oxidation was an effective way to alleviate cake layer fouling by reducing the interaction between the foulant and the membrane. In addition, ClO2 oxidation activated the hidden functional groups in the raw water, resulting in an increase in the fluorescence value of humic analogs, but had a good removal effect on the fluorescence intensity of BSA. Furthermore, the membrane fouling fitting model showed that ClO2, at a low dose (1 mg/L), could change the mechanism of membrane fouling induced by simulated natural water from standard blocking and cake layer blocking to critical blocking. Overall, ClO2 pre-oxidation was an efficient pretreatment strategy for UF membrane fouling alleviation, especially for the fouling control of HA and SA at low dosages.

Adsorption-Enhanced Ceramic Membrane Filtration Using Fenton Oxidation for Advanced Treatment of Refinery Wastewater: Treatment Efficiency and Membrane-Fouling Control.

With the development of the refining industry, the treatment of refinery wastewater has become an urgent problem. In this study, a ceramic membrane (CM) was combined with Fenton-activated carbon (AC) adsorption to dispose of refinery wastewater. The effect of the combined process was analyzed using excitation-emission matrix (EEM), ultraviolet-visible (UV-vis) and Fourier transform infrared spectroscopies (FTIR). Compared with direct filtration, the combined process could significantly improve the removal of organic pollution, where the removal rate of the COD and TOC could be 70% and the turbidity removal rate was above 97%. It was found that the effluent could meet the local standards. In this study, the membrane fouling was analyzed for the impact of the pretreatment on the membrane direction. The results showed that Fenton-AC absorption could effectively alleviate membrane fouling. The optimal critical flux of the combined process was increased from 60 to 82 L/(m2·h) compared with direct filtration. After running for about 20 d, the flux remained at about 55 L/(m2·h) and the membrane-fouling resistance was only 1.2 × 1012 m-1. The Hermia model revealed that cake filtration was present in the early stages of the combined process. These results could be of great use in improving the treatment efficiency and operation cycle of refinery wastewater.

Effect of particle size distribution on filtration performance of cell culture medium.

Cell culture media used in CHO-based biologic processes are typically sterile filtered to prevent microbial contamination prior to inoculation. In this study, the impact of common sterile filter throughput on a different, commercially available cell culture media was evaluated from the intermediate-adsorption fouling model of the filtration model. The key particle size range for optimum filter performance was discussed and identified by measuring the submicron order particle size distribution. It may be possible to predict the performance of filter capacity with size-exclusive separation by understanding the media particle counts and size distribution.

Fouling Mechanisms Analysis via Combined Fouling Models for Surface Water Ultrafiltration Process.

Membrane fouling is still the bottleneck affecting the technical and economic performance of the ultrafiltration (UF) process for the surface water treatment. It is very important to accurately understand fouling mechanisms to effectively prevent and control UF fouling. The rejection performance and fouling mechanisms of the UF membrane for raw and coagulated surface water treatment were investigated under the cycle operation of constant-pressure dead-end filtration and backwash. There was no significant difference in the UF permeate quality of raw and coagulated surface water. Coagulation mainly removed substances causing turbidity in raw surface water (including most suspended particles and a few organic colloids) and thus mitigated UF fouling effectively. Backwash showed limited fouling removal. For the UF process of both raw and coagulated surface water, the fittings using single models showed good linearity for multiple models mainly due to statistical illusions, while the fittings using combined models showed that only the combined complete blocking and cake layer model fitted well. The quantitative calculations showed that complete blocking was the main reason causing flux decline. Membrane fouling mechanism analysis based on combined models could provide theoretical supports to prevent and control UF fouling for surface water treatment.

Effect of metabolic uncoupler, 2,4­dinitrophenol (DNP) on sludge properties and fouling potential in ultrafiltration membrane process.

Energy uncoupling technology was applied to the membrane process to control the problem of bio-fouling. Different dosages of uncoupler (2,4­dinitrophenol, DNP) were added to the activated sludge, and a short-term ultrafiltration test was systematically investigated for analyzing membrane fouling potential and underlying mechanisms. Ultrafiltration membrane was used and made of polyether-sulfone with a molecular weight cut off (MWCO) of 150 kDa. Results indicated that low DNP concentration (15-30 mg/g VSS) aggravated membrane fouling because more soluble microbial products were released and then rejected by the membrane, which significantly increased cake layer resistance compared with the control. Conversely, a high dosage of DNP (45 mg/g VSS) retarded membrane fouling owing to the high inhibition of extracellular polymeric substances (proteins and polysaccharides) of the sludge, which effectively prevented the formation of cake layer on the membrane surface. Furthermore, analyses of fouling model revealed that a high dosage of DNP delayed the fouling model from pore blocking transition to cake filtration, whereas this transition process was accelerated in the low dosage scenario.

Model assessment of the prevailing fouling mechanisms in a submerged membrane anaerobic reactor treating low-strength wastewater.

Three models (blocking laws, combined and resistance-in-series) were applied to identify the prevailing fouling mechanisms in a submerged membrane in an up-flow anaerobic sludge blanket reactor treating municipal wastewater. Experimental runs were carried out at lab-scale with filtration periods of 4 and 10 min, followed by relaxation periods of one minute with and without nitrogen bubbling. In all conditions excepting one (IF4R), the blocking laws model showed a predominance of cake formation. With the combined model, cake formation coupled with intermediate, standard and complete fouling had the better fits in all conditions, excepting IF4 and IF4R. When sewage was fed, both models pointed at intermediate fouling in the absence of gas bubbling. The resistance-in-series model identified the positive effect of gas bubbling and a post-cake fouling behavior, not shown by the other two models. This modeling approach could be applied for achieving longer filtration runs in submerged UF membranes.

Investigation of the treatability of molasses and industrial oily wastewater mixture by an anaerobic membrane hybrid system.

In this study, the anaerobic treatability of automotive industry wastewater and its treatment in the subsequent membrane system were examined by using molasses, which is a waste of the sugar industry, as a co-substrate. Organic loadings of 3-3, 5-4, and 5gCOD/L/day were applied to a UASB reactor made of steel with a working volume of 7 L. The hydraulic retention time (HRT) was kept constant at 2 days. Temperature, pH, COD, alkalinity, Volatile Fatty acid (VFA) and biogas were monitored. The best COD removal was achieved at the value of 4 gCOD/L/day. The average COD removal rate was 77%. The effluent from the UASB reactor was transferred to the membrane system. The flux reductions of the PW10 kDa UF membrane at different concentrations were 1.717 gCOD/L, 1.934 gCOD/L, 2.257 gCOD/L, 4 gCOD/L, and 8 gCOD/L, and they were 90.78%, 42.69%, 45.88%, 51.00%, and 56.60%, respectively, at the input concentrations. The flux reductions of the UE50 100 kDa UF membrane at the input concentrations of 4 gCOD/L and 8 gCOD/L were 76.00% and 66.25%, respectively. It was determined that the UE50 100 kDa membrane caused more fouling compared to the PW 10 kDa UF membrane. Pore fouling models were determined for the flux reduction in the membranes and the mechanism behind it. Heavy metal and organic matter removals were examined in the effluent obtained from the membrane experiments.