Direct Biofiltration As A Pretreatment To Control Fouling In Ceramic Membranes In Drinking Water Treatment

Ceramic membranes have been widely and successfully used in the food and beverage processing industry. Despite their success, ceramic membranes are not commonly employed in drinking water treatment due to their high initial capital cost. Polymeric membranes, on the other hand, have gained widespread use in drinking water treatment in the last few decades due to their ability to meet stringent water quality regulations. Ceramic membranes have a number of advantages over polymeric membranes, which include high chemical and thermal stability, higher fluxes and longer operational life. Advances in membrane technology in recent years coupled with innovative design have made the life cycle cost of implementing ceramic membranes competitive with that of polymeric membranes. This has resulted in a number of drinking water treatment plant installing ceramic membranes as part of the treatment process, especially in Japan. The biggest challenge facing membrane filtration (polymeric or ceramic) is fouling. To control fouling, coagulation prior to ceramic membrane filtration is often implemented and has been shown to be effective in controlling both hydraulically reversible and irreversible fouling. Direct biofiltration without pretreatment (BFWP) (coined by Huck et al., 2015) has been shown to be another effective “green” pretreatment to control fouling in polymeric membranes. High molecular weight natural organic matter (NOM) such as biopolymers have been found to be directly related to the hydraulically reversible fouling and to play a key role in hydraulically irreversible fouling of polymeric membranes and biofiltration is able to reduce the concentration of this NOM fraction. Given the effectiveness of BFWP in controlling fouling in polymeric membranes, there is an opportunity to investigate its applicability to ceramic membranes. Therefore, the goals of this study were to investigate the efficacy of BFWP as a pretreatment to control fouling in ceramic membranes and characterize the fouling of the membranes over time. The effects of Empty Bed Contact Time (EBCT) of the biofilters, membrane materials and pore sizes (Microfiltration (MF) vs. Ultrafiltration (UF)) on the fouling rates were also investigated in the study.

The goal of drinking water treatment is to produce and deliver safe water to the consumers. To achieve these objectives water treatment plants are designed based on the concept of the multibarrier approach which combines several drinking water treatment processes in order to increase the reliability of the system. The presence of pharmaceutically active compounds (PhACs), personal care products (PCPs) and endocrine disrupting compounds (EDCs) in drinking water sources is becoming a concern, because of chronic and indirect human exposure to contaminant mixtures at sub-therapeutic levels via drinking water consumption. Membrane filtration can be an efficient treatment process to remove microorganisms and/or trace organic contaminants from drinking water sources. However, membranes are confronted by a major limitation: membrane fouling. Fouled membranes suffer from a loss in performance either leading to a reduction in flux or a higher pressure requirement. Generally, membrane fouling increases the need for membrane maintenance measures such as backwashing and chemical cleaning which has a negative impact on the operating costs and membrane life time. Severe membrane fouling may even impact permeate quality and/or compromise membrane integrity. The aim of this study was to establish if biofiltration pretreatment without prior coagulation would be able to control membrane fouling in natural waters. The second objective investigated the removal of trace organic contaminants by individual treatment processes (i.e. biofiltration and membrane filtration). Parallel to this work, the presence and concentration of selected trace organic contaminants in Grand River (Ontario, Canada) were determined. The trace organic contaminants investigated included atrazine, carbamazepine, DEET, ibuprofen, naproxen, and nonylphenol.

Membrane filtration is growing in popularity as a viable technology for drinking water treatment to meet high demand and regulatory requirements. While many improvements have been made to the technology in the past decade, fouling continues to be one of the major operational challenges associated with membranes as it increases operating costs and reduces membrane life. Fouling control typically requires some form of pre-treatment. Biofiltration is a “green” technique that can minimize chemical usage and waste during water treatment and is a relatively new application as a pre-treatment for membranes. Proteins and polysaccharides (biopolymers) have been found to contribute most to fouling of low pressure polymeric membranes. Biofiltration has recently been demonstrated as an effective pre-treatment method for reducing biopolymer-associated fouling of this type of membrane (Hallé et al., 2009). Given that the concentration and composition of organic matter in water is variable, there is an opportunity to explore the applicability of this robust technology for different water types. The primary goals of this research were to assess the effectiveness of direct biofiltration in minimizing ultrafiltration polymeric (PVDF) membrane fouling and at the same time evaluate the biofilter development, biofilter performance based on organics removal potential, and the effect of phosphorus addition (as a nutrient) to the biofilter influent. A pilot-scale treatment train was constructed at the Technology Demonstration Facility at the Walkerton Clean Water Centre. It included two parallel dual media (sand/anthracite) biological filters (preceded by roughing filters), followed by an ultrafiltration membrane unit. Experiments were conducted using water from the Saugeen River (Ontario, Canada) whose primary form of carbon is humic material. The biofilters were allowed to acclimate and biofilter performance and organics removal were tested over a fourteen month period, the last four months of which were dedicated to phosphorus enhancement experiments. The membrane fouling experiments started seven months following the start-up of the biofilters, after confirmation of steady-state operation. Biofilter water samples were analyzed for natural organic matter constituents along with other water quality parameters, and biomass quantity and activity in the media were measured. Biomass activity in the biofilter media and biopolymer removal through the biofilter indicated a rapid acclimation period, and also demonstrated similar performance of the parallel biofilters during start-up and steady-state operation. The biofilters achieved 21% removal of the biopolymers on average following acclimation, while reduction of the humic fractions was not observed. A linear relationship between biopolymer removal and its concentration in the river water was observed (first-order process). Membrane fouling experiments were conducted using both untreated and biofiltered river water. The fouling rates were computed by monitoring changes in transmembrane pressure over time. Analysis of the samples with liquid chromatography-organic carbon detection confirmed the significant contribution of biopolymers to irreversible and reversible membrane fouling rates even when only present at low concentrations. During the phosphorus enhancement phase, two different phosphorus doses were fed into the influent of one of the parallel biofilters in order to achieve a target C:N:P ratio of roughly 100:10:1. Although initially (first month of the dosing period) an increase in the removal of dissolved organic carbon and ultraviolet-absorbance was observed in the phosphorus-enhanced biofilter, this was not sustained. Phosphorus addition did not affect biopolymer removal or biomass quantity and activity in the biofilter, and the membrane fouling experiments during this period did not show any significant effect of phosphorus addition.

Biofiltration is a promising green drinking water treatment technology that can reduce the concentration of biodegradable organic matter (BOM) in water. Direct biofiltration or biofiltration without pretreatment (BFwp) limits the use of chemicals such as coagulants or ozone commonly employed with conventional biofiltration, making BFWP a more environmental friendly pre-treatment. BFWP was proven to be an efficient pretreatment to reduce fouling of low pressure membranes, and can also improve the biological stability of the final treated drinking water to limit bacterial regrowth in the distribution system. One major operational problem for high pressure membranes (i.e. nanofiltration and reverse osmosis membranes) is membrane biofouling due to biofilm growth inside the feed channel of the membrane module, resulting in higher energy requirements and more frequent membrane cleaning. BFWP can potentially be applied to reduce biofouling of nanofiltration membranes, which can reduce the energy requirements of high pressure membranes. Three pilot-scale parallel biologically active filters with different empty bed contact times, and bench-scale nanofiltration membrane fouling simulators, were designed and constructed in this study. A challenging surface water source (the Grand River in Kitchener, ON) was used as source water for the investigation. Initial work assessed the effect of biofiltration on the treated water quality and how the biofilter performance is affected by changes in water temperature. A protocol was developed to better characterize the biofilter attached biomass and extracellular polymeric substances (EPS), in order to understand their possible relationship to biofilter performance. Flow cytometry was applied to measure both planktonic cell concentrations in water and also to perform assimilable organic carbon (AOC) analysis using a natural microbial inoculum. BFWP was found to be an efficient pre-treatment for the removal of large molecular weight biopolymers and AOC over a wide range of water temperatures. Lower water temperatures had a significant impact on biopolymer removal, unlike AOC which was efficiently removed at lower water temperatures, and this proved the robustness of such a pre-treatment technology. Other fractions of the natural organic matter (NOM) such as humic substances, buildings blocks and low molecular weight organics were removed to a lower extent than biopolymers or AOC. Empty bed contact time (EBCT) as a design parameter had a limited effect on the biofilter performance. Most of the observed removal for BOM and total cell count happened at the shortest EBCT of 8 minutes, and increasing the EBCT up to 24 minutes had a significant but less proportional impact on biofilter performance. Regarding biofilter attached biomass, no direct linkage was found between biofilter performance and attached biofilter biomass characteristics using any of the commonly used analytical methods such as adenosine triphosphate (ATP) or biofilm cell count, however, cellular ATP content was found to be indicative of biofilm activity. Biofilm EPS composition was not related to biofilter performance but it was largely affected by the water temperature. Through community level physiological profiling (CLPP) analysis it was evident that the microbial community was changing due to a drop in water temperature, however, this was a minor effect and it is likely that the overall drop in biomass activity was the main reason behind the drop in biofilter performance. Finally, BFWP was tested as a potential pre-treatment technology to control high pressure membrane biofouling, which is a major operational problem. BFWP was able to reduce the amount of available nutrients measured as AOC, reduce the presence of conditioning molecules such as large molecular weight biopolymers, and modify the microbial community of the feed water. A 16 minute EBCT biofilter was able to extend the lifetime of nanofiltration membranes by more than 200% compared to the river water without biofiltration, both at low and high water temperature conditions. The 16 minute EBCT biofilter performance was also comparable to that of a full scale conventional biofilter with prior coagulation, sedimentation and ozonation. The biofiltration pre-treatment efficiently affected the amount of biomass present in the biofouling layer and affected the biofilm microbial community as determined using CLPP analysis. The findings of this study provide the basis upon which further and larger scale testing of the BFWP as a pre-treatment for membrane applications can be done. A sound technology could include a hybrid membrane system with a high pressure membrane proceeded with a low pressure membrane. BFWP can then be used at the start of the treatment train to limit both low pressure membrane fouling at the same time limit the biofouling of the pressure membrane. This treatment train can provide a high water quality with limited footprint compared to conventional treatment trains and long service time. Monitoring of the treatment unit performance can be efficiently done using some of the proposed analytical methods presented in the study, such as AOC monitoring and flow cytometry to study microbiological water quality and biofilter biomass. Fluorescence spectroscopy and size exclusion chromatography can also be used to monitor large molecular weight biopolymers, which are responsible for several operational problems in water treatment in general and specifically for membrane applications.

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The use of ultrafiltration membrane technology for drinking water treatment has seen a marked increase in the past few decades, however, membrane fouling remains the top technological hurdle in the way of its widespread use. Multiple membrane pretreatment methods exist to alleviate this issue, however, they can be complicated and involve the addition of chemicals to the system. A novel method, known as biofiltration without pretreatment, is a green alternative to conventional membrane pretreatment, and has been shown effective at both the laboratory and bench scale in proof of concept studies. It is unknown if the conventional biofiltration operational experience, applies to biofiltration without pretreatment especially as it relates to filter backwashing. To this end, the goal of this study was to investigate the performance of biofiltration without pretreatment as a membrane pretreatment under varying water quality conditions, as well as to test the effect of various backwashing parameter settings on the system performance. To perform this study, a pilot plant was constructed at the Mannheim water treatment plant in Kitchener Ontario. This plant consisted of multiple identical biofilter columns running in parallel. For this study, dual identical biofilters run in parallel were used, with one being a control and run under constant backwashing conditions, while the other, an experimental filter, was run over a range of backwashing conditions according to a statistical experiment design. The dual media filters (anthracite over sand) used in this study were run with a 7 minute empty bed contact time. This study was divided into two parts. In the first part, focus was placed on the performance of the biofilters and in the second part the combined process, that is the use of biofilters without pretreatment as a membrane fouling reduction pretreatment, was investigated. In both cases, the effect of changing inlet water quality parameters, as well as the effect of backwashing parameters (collapse pulsing time, wash time, wash expansion and membrane run delay) was investigated. Performance of both sections of the plant was monitored through a combination of online and laboratory measured parameters. Biofilter turbidity, temperature, headloss, as well as membrane temperature and transmembrane pressure were monitored online. In the laboratory, liquid chromatography with organic carbon detection was used to measure the concentrations of various water constituents. Fluorescence emission and excitation matrices were also used for this purpose. In addition, dissolved organic carbon, and ultraviolet light absorption were also measured. The consumption of dissolved oxygen by biofilms attached to biofilter media was quantified as a means to determine biological activity within the biofilter. In terms of biofilter performance, the backwashing factors studied were found to have no effect on the biological activity, either through the removal of nutrients, or by the amount of biomass on the biofilter media. However, these factors were found to influence turbidity removal and headloss accumulation by the biofilters as well as the removal of suspected membrane foulants, namely biopolymers and protein-like material In terms of membrane performance, the irreversible fouling rate was found to be correlated to the amount of biopolymers applied to the membranes and reversible fouling was found to not be correlated to any of the parameters studied. The amount of turbidity applied to the membranes was shown to a play a complex, role in this fouling as well. Backwashing was also shown to have an effect on irreversible fouling, suggesting that the backwashing regime may be optimized for the reduction of irreversible fouling. Although the backwashing procedure was found to have an effect on both the reduction of irreversible membrane fouling and the headloss buildup (hence biofilter run time), these two parameters were found to be affected in opposite , meaning that one may be optimized at the expense of the other. Therefore process optimization must be undertaken with specific goals in mind. It was found however, that the filter run time of the biofilters may be extended by optimizing the biofilter backwashing procedure. The results of this study provide a frame work for which to further study the influence of backwashing on biofiltration without pretreatment used as a membrane pretreatment by pointing to the backwashing parameters which have the greatest effect on performance. Moreover, the results of this study may be used as a starting point for more in depth optimization exercises.

Over the last decade polymeric membranes have emerged as an economically viable treatment option to produce drinking water. Due to higher capital costs, the use of ceramic membranes has generally been limited to industrial applications that deal with challenging water quality. Ceramic membranes are superior to polymeric membranes in their physical and chemical resistance, which allows for higher fluxes and backwash pressures as well as rigorous chemical cleaning. As a result, these membranes can potentially operate for longer periods of time, which can decrease the lifetime cost of the membrane. Furthermore, decreased production costs coupled with an increased desire for economical sustainability may open the door for the use of ceramic membranes in drinking water treatment, particularly for highly polluted waters. The loss of membrane permeability as a result of fouling remains one of the biggest challenges for sustainable membrane operation. Therefore, a thorough understanding of fouling behavior and the identification of key foulants is essential for optimizing membrane performance. However, fouling has not been researched in detail for ceramic membranes in drinking water treatment, particularly ultrafiltration, since most research has focused on ceramic microfiltration membranes combined with coagulation. The thesis is divided into four main stages. The first stage involved developing a factorial design to establish a procedure to determine sustainable flux that can adequately compare the fouling between a ceramic and polymeric membrane without compromising the functional potential or operating parameters of either membrane. In this stage, the significance of three different variables (interval length, increment increase, and a hydraulic backwash) in determining sustainable flux were statistically analyzed following a factorial design and consequently included or removed from the sustainable flux determination approach. The increment increase was not significant while the backwash was the most significant variable. The method established was used in later experiments to allow for a comparison of fouling behavior and performance between a polymeric and ceramic membrane. The second stage investigated the fouling behavior of flat-sheet ceramic membranes with model solutions at constant pressure to identify foulants of concern and likely fouling mechanisms for ceramic membranes as well as perform surface characterization techniques not possible with tubular membranes. In this stage the contributions of different model foulants (bovine serum albumin i.e. a protein, alginate i.e. a carbohydrate, humic acid, and colloidal silica) to reversible and irreversible fouling on a flat-sheet ceramic membrane at constant pressure were quantitatively evaluated. Both single foulant solutions and all possible combinations of mixtures of model foulants were investigated. The bovine serum albumin and humic acid were main contributors to hydraulically irreversible fouling and their removal mechanism is postulated to be largely through adsorption. Colloidal silica was the most influential factor governing fouling behavior and diminished the irreversible fouling effect of these organics, thus increasing hydraulic reversibility. Additionally, synergistic fouling effects were also observed. The third stage investigated the same model solutions with tubular ceramic membranes at constant flux to determine the fouling behavior under different conditions and quantitatively assess the effectiveness of different fouling mitigation techniques. The rate of fouling was very high for bovine serum albumin but extremely low for humic acid; however, they both showed high irreversible fouling. The results obtained were consistent with the previous stage using flat-sheet ceramic membranes; particularly regarding the significant role colloidal silica plays in fouling. The ability to compare these two very different configurations and operating parameters is largely due to the use of a hydraulic backwash in both configurations. Therefore, this highlights the importance of investigating fouling reversibility, especially in simplified experiments. The last stage investigated tubular ceramic fouling behavior and organic matter rejection with surface water at constant flux. Tubular ceramic membrane fouling behavior was investigated for river water. A very high initial organic carbon removal was observed at the initial stages of filtration and after each backwash cycle indicating a high affinity of organics to the membrane surface as well as partially reversible adsorption. Humic acid rejection decreased throughout the filtration cycle. On the contrary, biopolymer rejection remained constant indicating size exclusion as a primary removal mechanism. After several modifications to the design and setup, the sustainable flux method established in Stage 1 could not be applied to the ceramic membrane or to the polymeric membrane using highly turbid water; a few hypotheses were made as to why this occurred. It is likely that one or more variables that were not included in the sustainable flux method were influencing the fouling rate over time. Overall, the robustness of ceramic membranes opens the door for some creative fouling mitigation techniques to be used such as backwash pulses and chemical maintenance cleaning.

Ceramic membrane processes are a rapidly emerging technology for water treatment, yet virtually no information on the performance and fouling mechanisms is available to the industry. Ceramic microfiltration of model feed solutions and a synthetic river water was examined, and a systematic comparison with polymeric counterpart was performed. The results suggested that the models which have been applied to polymeric membranes agreed well with the ceramic membrane filtration data. The fouling was characterized by the initial pore blocking mechanism and transition to the cake filtration mechanism at a later phase. Cake resistance was dominant and readily removable by physical cleaning. The effects of solution chemistry including ionic strength, divalent ion concentration and pH on the flux behavior were comparatively evaluated for ceramic and polymeric ultrafiltration of synthetic water containing model natural organic matter. Experimental evaluations further included resistance-in-series model analysis, organic matter fouling visualization using quantum dots, batch adsorption test, and contact angle measurement, and provided a quantitative a quantitative comparison of fouling characteristics between ceramic and polymeric membranes. The results collectively suggested that the effects of solution chemistry on the fouling behavior with ceramic membranes were mostly similar with polymeric membranes in terms of trends, while the extents varied depending on water quality parameters. Less fouling tendency and better cleaning efficiency were observed with the ceramic membranes, which was a promising finding for ceramic membrane application to surface water treatment. The study further examined a coagulation-ceramic membrane process as a robust option for surface water treatment. The performance of the hybrid system was evaluated using selected surface waters by varying coagulation conditions and types of coagulants. Results suggested that ceramic membranes experienced relatively less fouling and had better cleaning efficiency than polymeric counterpart. The results of this study provide critical information to guide the industry practitioners, consultants, and regulatory agents considering early adoption of this new technology as well as fundamental knowledge upon which further in-depth studies can be built.

carbon (DOC), surrogates of disinfection by-products (DBPs), were reduced by 60 and 30 percent, respectively. With coagulant pretreatment, DBP concentrations were effectively reduced below their maximum contaminant levels. Optimized coagulation pretreatment with ferric chloride reduced the rate of membrane fouling by approximately 92 percent. Removals of surrogates of DBPs were approximately 20 to 30 percent higher than for the control (no coagulation) experiment. Attempts to optimize the system with aluminum chlorohydrate (ACH) were unsuccessful. In some cases an increase in the rate membrane fouling was observed as a result of the addition of ACH.The overall results demonstrated that both aluminum sulfate and ferric chloride can potentially be used for the coagulation pretreatment of ceramic membrane systems. However, aluminum sulfate was found to be more flexible and consistent at controlling the rate of membrane fouling. Under optimized coagulation conditions, current drinking water standards can be met, typically at coagulant dosages lower than those required for a conventional treatment process.