Peter M. Huck

The objective was to develop and apply an improved, comprehensive biofilm characterization protocol for cellular and extracellular polymeric substances in drinking water biofilters.

The performance of conventional and advanced processes with regard to the reduction of the biopolymer fraction of natural organic matter (NOM) at two large adjacent full-scale drinking water treatment plants was compared and evaluated. Both plants were fed with the same surface water source, however, they differed in configuration and type of coagulant used. The biopolymer fraction, although of critical importance for low-pressure membrane fouling, is only a relatively small percentage of the overall NOM. Therefore, to provide context and comparison, the removal of humic substances, the largest NOM fraction, was also investigated. It was observed that the plant using aluminum sulfate slightly outperformed the one dosing polyaluminum chloride for biopolymer and humic substance removal when the coagulants were dosed at average concentrations of 0.68 ± 0.23 mg Al/L and 1.10 ± 0.63 mg Al/L, respectively. Under the conditions investigated, coagulation, flocculation, and sedimentation may be a better pre-treatment option for ultrafiltration membranes in terms of biopolymer removal compared to ozonation and biofiltration. However, as confirmed by Liquid Chromatography-Organic Carbon Detection analysis, biopolymer removal through biofiltration with prior ozonation was less than expected, suggesting that the process pairing was not optimized. This research illustrates the value of biopolymer quantification with respect to assessing its impact on membrane fouling.

A pilot-scale study investigated the effect of phosphorus addition on a drinking water biofilter used to reduce fouling of an ultrafiltration membrane. Biofiltration without pre-treatment (BF_wp) has been shown to be an effective pre-treatment for the removal of natural organic matter (NOM) components that cause membrane fouling. However, the river source used in this study was found to have low phosphorus concentrations that could potentially affect biofilter biomass levels and NOM biodegradation. The river water source (Saugeen River located at Walkerton, Ontario, Canada) had a high total organic carbon (4.34–6.61 mg/L) of primarily humic content, variable turbidity, and seasonal changes in water temperature (9.7–19.9°C) as measured over the study period. Phosphorus was added to the biofilter influent at 0.01 mg P/L, and later at 0.05 mg P/L, over a four-month period. Biofilter activity, NOM removal, and membrane performance were compared to a control system operating under identical conditions but without nutrient addition. Filter biomass measured by ATP and fluorescein diacetate hydrolysis (overall enzyme activity) was stable over time, with no difference between control and phosphorus-amended biofilters. As well, phosphorus addition did not improve the removal of NOM fractions, especially biopolymers that are important for membrane fouling. There was a small initial increase in the removal of dissolved organic carbon and humic substances after phosphorus addition, but this effect diminished over time. The effluent from each biofilter was used to operate an ultrafiltration membrane system using conditions similar to full scale. Membrane fouling for each experiment was measured over 1.5 d, and operating cycles included 30-min permeation followed by backwashing/air sparging. Results showed that there was no difference in hydraulically reversible or irreversible fouling of membranes fed with the effluent from control or phosphorus-amended biofilters. It was found that biofilter nutrient feed requirements are likely site specific, and affected by factors including biomass and NOM characteristics.

: Aqueous chlorination kinetics of the lipid regulator gemfibrozil and the formation of reaction products were investigated in deionized water over the pH range 3 to 9, and in two wastewater matrices. Chlorine oxidation of gemfibrozil was found to be highly dependent on pH. No statistically significant degradation of gemfibrozil was observed at pH values greater than 7. Gemfibrozil oxidation between pH 4 and 7 was best represented by first order kinetics. At pH 3, formation of three reaction products was observed. 4′‐ClGem was the only reaction product formed from pH 4–7 and was modeled with zero order kinetics. Chlorine oxidation of gemfibrozil in two wastewater matrices followed second order kinetics. 4′‐ClGem was only formed in wastewater with pH below 7. Deionized water rate kinetic models were applied to two wastewater effluents with gemfibrozil concentrations reported in literature in order to calculate potential mass loading rates of 4′ClGem to the receiving water.

Fouling remains one of the major constraints on the use of low pressure membranes in drinking water treatment. Work over the last few years has shown the importance of biopolymers (carbohydrates and protein-like material) as foulants for ultrafiltration (UF) membranes. The purpose of this study was to investigate at pilot scale the use of rapid biofiltration (without prior coagulation or ozone addition) as an innovative pretreatment to reduce fouling of UF membranes. The investigation was carried out on a water with a higher than average DOC and significant temperature variation. The biofilters, each operated at a hydraulic loading of 5 m/h, had empty bed contact times of 5, 10 and 15 minutes. The membrane unit was operated at a flux equivalent to 60 LMH at 20°C. The investigation confirmed the encouraging results obtained in an earlier smaller scale study with essentially the same water. Increased biofiltration contact time (i.e. increased bed depth) led to lower rates of hydraulically irreversible fouling. The initial biofiltration backwash procedure, involving air scour as is common in chemically assisted filtration, led in some cases to an increased rate of membrane fouling immediately after the backwash. An alternative backwashing strategy was developed, however the feasibility of operating with this approach over very long periods of time needs to be confirmed. To assist in full-scale implementation of this “green” and simple pretreatment, the design and operating conditions for the biofilters should be optimized for various types of waters. It is expected that biofiltration pretreatment will be of particular interest for small and/or isolated systems where a higher initial capital cost may be acceptable because of operational simplicity and reduced chemical requirements.

The natural organic matter (NOM) components causing fouling of nanofiltration membranes used in drinking water applications consists in a complex mixture of humic and fulvic acids, proteins, and carbohydrates of various molecular size and functional groups. Understanding the characteristics of NOM fractions such as humic substances (HS) and biopolymers (proteins and polysaccharides) as foulants is of paramount importance to develop fouling control strategies. Fluorescence spectroscopy is becoming an increasingly popular method for characterizing NOM and shows good potential for online monitoring, as minimal sample pre-treatment and preparation is required, high instrumental sensitivity is available and the technique is non-destructive in nature. In this research an innovative approach involving both fluorescence and LC-OCD analyses is used to identify and to characterise organic membrane foulant.

This study investigated the impact of coagulated/flocculated particulate matter on low-pressure (LP) UV inactivation of spiked Escherichia coli under drinking water conditions using a standard bench scale collimated beam apparatus. The effect of floc particles in both coagulated river water and coagulated process (treatment plant) water was assessed. Laboratory grade water and uncoagulated river water were used as controls. The dose-response curves of spiked E. coli were determined at UV doses of 5, 10, 15, 25, and 40 mJ/cm². The results indicated that surface water particles (turbidity from 12 to 32 NTU essentially have no influence on UV inactivation of spiked E. coli if they are appropriately accounted for in the UV transmittance determination. However, the presence of floc particles formed by coagulation and flocculation led to significantly lower inactivation of E. coli by LP UV. A limited investigation of medium pressure UV inactivation undertaken as part of the study indicated that shielding effects for medium pressure UV warrant further investigation. The support for the inactivation results provided by the particle size analysis carried out suggests that criteria related to particle size may be very useful in addition to turbidity for UV regulation and operation. The results emphasize the need for UV disinfection/inactivation to be placed following filtration, because a sedimentation upset (i.e. where some floc particles may reach a downstream UV unit) could potentially compromise disinfection/inactivation.

Chemical and microbiological analyses were performed in an attempt to obtain a better understanding of the reduction of membrane fouling via the use of feed pretreatment. Biofiltration was chosen as pretreatment due to its potential to be a sustainable process coupled with membrane filtration. Biofiltration effectively reduced the concentration of organic and biological matter in the feed solution, decreasing the material deposited on the membrane surface approximately by half. More importantly, it reduced the loss of permeability during the operation of UF and NF membranes. However, it is believed that the performance of biofiltration as membrane pretreatment can be further improved with a greater understanding of the material that causes membrane fouling. This way the biofilter design and operation can be optimized to specifically minimize the concentration of this fouling material.