Drinking Water Biofilters Research Articles

Development of biomass in a drinking water granular active carbon (GAC) filter

Indigenous bacteria are essential for the performance of drinking water biofilters, yet this biological component remains poorly characterized. In the present study we followed biofilm formation and development in a granular activated carbon (GAC) filter on pilot-scale during the first six months of operation. GAC particles were sampled from four different depths (10, 45, 80 and 115 cm) and attached biomass was measured with adenosine tri-phosphate (ATP) analysis. The attached biomass accumulated rapidly on the GAC particles throughout all levels in the filter during the first 90 days of operation and maintained a steady state afterward. Vertical gradients of biomass density and growth rates were observed during start-up and also in steady state. During steady state, biomass concentrations ranged between 0.8 –1.83 x 10 −6 g ATP/g GAC in the filter, and 22% of the influent dissolved organic carbon (DOC) was removed. Concomitant biomass production was about 1.8 × 10 12 cells/m 2h, which represents a yield of 1.26 × 10 6 cells/μg. The bacteria assimilated only about 3% of the removed carbon as biomass. At one point during the operational period, a natural 5-fold increase in the influent phytoplankton concentration occurred. As a result, influent assimilable organic carbon concentrations increased and suspended bacteria in the filter effluent increased 3-fold as the direct consequence of increased growth in the biofilter. This study shows that the combination of different analytical methods allows detailed quantification of the microbiological activity in drinking water biofilters.

Biodegradation studies and sequencing of microcystin-LR degrading bacteria isolated from a drinking water biofilter and a fresh water lake

The presence of microcystin-LR -degrading bacteria in an active anthracite biofilter and in Lake Mead, Nevada was investigated. Four bacterial isolates from enrichment culture were identified using 16S rRNA analysis. Microcystin biodegradation tests were performed with both, the enrichment cultures and the respective isolates, using microcystin alone and acetate as carbon sources. A newly recognized microcystin-degrading bacterium, Morganella morganii, was isolated from the biofilter and from Lake Mead. The results of the biodegradation tests indicated that addition of a carbon source (acetate), significantly repressed the degradation of microcystin-LR. The findings of this study inform on the prevalence of microcystin-degrading bacteria in the environment indicating bioaugmentation may not be needed, if biofiltration is used to remove microcystin from waters. The results also imply that, in a biofilter, biodegradable naturally organic matter (NOM) and microcystin will compete and therefore lower toxin removals are likely in waters with higher NOM content. The feasibility of removing microcystin by biofiltration depends on the toxin concentration and the concentration of biodegradable carbon sources in the biofilter.

PLFA profiles of drinking water biofilters with different acetate and glucose loadings

The biofilters fed with acetate or glucose and their phospholipid fatty acid (PLFA) profiles were investigated to observe the impact of organic matter concentrations on the microbial community structure in the drinking water production system. PLFA markers for bacteria were predominant in all of the biofilters and made up over half of the total PLFA content. PLFA diversity was compared and the biofilters fed with glucose had higher diversity. The Shannon-Wiener (or sometimes known as just Shannon diversity index) indices in the biofilters fed with acetate were from 0.68 to 0.97, while the indices in the biofilters fed with glucose were from 0.95 to 1.25. Principle components analysis showed that carbon sources and media depth were responsible for 68 and 17% of the total PLFA variance, respectively. The results indicated that PLFA analysis could be useful in illustrating microbial community structure in drinking water bioreactors, and microbial community structure was impacted by carbon substrates.

Modeling of NOM-removal in drinking water biofilters

The application of biofiltration is a hot topic in the drinking water treatment field, and the mathematical modeling of biofilters has received considerable attention. However, no practical model is available for designing the biofiltration process. The aim of this research is to develop a representative model which simulates NOM (natural organic matter) removal in water treatment biofilter. A steady-state model was applied. Monod-type substrate utilization was used and the external and internal mass transfer was neglected in this model. The model described the process of substrate biodegradation, bacterial attachment onto filter media and detachment of suspended bacteria. It simulated the NOM and biomass profiles in a biofilter as a function of filter depth and filtration velocity. The key biokinetic parameters k and Ks were estimated through a special experiment. The results of the model testing show that the model prediction agrees well with the experimental data. It is possible to adapt the model under various conditions by changing the parameters such as flow rate, bacteria and DOC concentration et al. Therefore, the model is an effective tool for designing and operation.

Accumulation and fate of green fluorescent labeled Escherichia coli in laboratory-scale drinking water biofilters

Biological filters combining microbial activity and rapid sand filtration are used in drinking water treatment plants for enhanced biodegradable organic matters (BOM) removal. Biofilms formed on filter media comprised of bacteria enclosed in a polymeric matrix are responsible for the adsorption of BOM and attachment of planktonic microorganisms. This study investigated the removal of Escherichia coli cells injected into laboratory-scale biofilters and the role of biofilm in retaining the injected E. coli. Green fluorescent protein was used as a specific marker to detect and quantify E. coli in the biofilms. About 35% of the total injected E. coli cells were observed in the filter effluents, when initial cell concentrations were measured at 7.4×106CFU/mL and 1.6×107CFU/mL in two separate experiments. The results from real-time PCR and plate count analysis indicated that 95% of the E. coli retained inside the filters were either non-viable or could not be recovered by colony counting techniques. Injected cells were unevenly distributed inside the filter with more than 70% located at the top 1/5 of the filter. Images obtained from an epifluorescent microscope showed that E. coli cells were embedded inside the biofilm matrix and presented mainly as microcolonies intertwined with other microorganisms, which was consistent with findings from standard plate count methods and qPCR.

Factors affecting the removal of geosmin and MIB in drinking water biofilters

Bench‐scale experiments were conducted using four parallel dual‐media filter columns containing biologically active anthracite or granular activated carbon media and sand. The factors under investigation were low‐ (8°C) and high‐ (20°C) temperature operations, geosmin and 2‐methylisoborneol (MIB) concentration, media type, and biodegradable organic matter (BOM) level. Source water consisted of dechlorinated tap water to which geosmin and MIB were added, as well as a cocktail of easily biodegradable organic matter (i.e., typical ozonation by‐products). Phase 1 experiments used a high BOM level (280 μg/L carbon [C]) to simulate water that had been subjected to ozonation before filtration. Phase 2 experiments used a low BOM level (28 μg/L C) to simulate nonozonated water. Factorial design experiments showed that all four main factors (temperature, concentration, media, and BOM level) were important to both geosmin and MIB removal. Temperature and media interaction and concentration and BOM level interaction were significant for geosmin removal only. Temperature and BOM level interaction as well as media and BOM level interaction were significant for the removal of both geosmin and MIB. Overall, removals of geosmin and MIB were lower in phase 2 (low BOM level), in particular in the anthracite media filters. Biomass levels in the filters appeared to have a significant effect upon the removal efficiencies of both odor compounds.

Biodegradation Behavior of Ozonated Natural Organic Matter in Sand Filters

Natural organic matter (NOM) in drinking water is a complex mixture of organic compounds. Some of the compounds are not biodegradable, while others are quickly biodegradable and a third group is more resistant to biodegradation. To have a better understanding of the biofiltration process in drinking water treatment, it is important to identify the elements of the quickly and slowly biodegradable NOM and to characterize the biodegradation rate of each element. In this study, an ozonated NOM solution was used as the substrate. The NOM was isolated from a groundwater in Germany using ion-exchange resins. The ozone dose was 0.35 mg O3/mg DOC (dissolved organic carbon). Previously bioacclimated sand was used as filter media and biomass source and was homogeneously distributed in the filter prior to each run. The substrate removal was evaluated by DOC, biodegradable DOC (BDOC), assimilable organic carbon (AOC), aldehyde and ketoacid analyses. When expressed in terms of the empty bed contact time (EBCT), the results showed that filter velocity in the range of 1.5 to 15 m/hr had no impact on substrate removal. This implies that substrate utilization, not external mass transfer, is the rate limiting step for substrate removal in drinking water biofilters. In this study, compounds or NOM fractions are termed quickly biodegradable if they are removed in the first three minutes of EBCT. 15% of the DOC was removed by the biofilter within three minutes of EBCT and was termed the quickly biodegradable fraction. The BDOC fraction of the ozonated solution was determined to be 40 to 45% of the DOC. In terms of BDOC, about one third of the total BDOC was quickly biodegradable. The AOC results show that about 90% of the total AOC was utilized by Spirillum sp. NOX (AOC-NOX). Most of the AOC was quickly biodegradable and was removed within one minute of EBCT. For aldehydes, glyoxal and methyl glyoxal were removed to below the detection limit after two minutes of EBCT. However, only 60% of formaldehyde removal was achieved in the first two minutes of EBCT, and no additional removal was achieved with increasing EBCT. Additionally, no significant removal of acetaldehyde was observed. The results of ketoacids show that their utilization rates were very high. More than 90% of glyoxylic acid and pyruvic acid were removed within one minute of EBCT.

Removal of selected ozonation by-products in pilot scale drinking water biofilters: compound interactions and mass transfer considerations

Biofilters are finding increasing use in drinking water treatment. Among the substances they remove are ozonation by-products such as low molecular weight aldehydes and carboxylic acids. Because a number of these compounds also participate in or are produced by major bacterial metabolic pathways, their behaviour in biofilters may be complex. This pilot scale study investigated biodegradation relationships between methylglyoxal and pyruvate. A second objective was to determine the impact of mass transfer on removals. The formation of pyruvate was observed when methylglyoxal was the sole easily biodegradable compound fed in the filter influent. The removal rates of formaldehyde and methylglyoxal were found to be comparable when each was the sole easily biodegradable compound fed. When fed alone, complete removals of methylglyoxal were obtained under steady-state conditions. When fed alone, the removal rate of pyruvate was more than twice than that of either formaldehyde or methylglyoxal. The removal rate of pyruvate was reduced by more than 50% when it was fed together with methylglyoxal. The reduced rate was probably due both to competition and to the formation of pyruvate from methylglyoxal. Backwashing was shown to have essentially no effect on removals of the compounds investigated. The mass transfer investigations showed that neither external nor internal mass transfer was limiting. Therefore removals were governed by biodegradation rates. The lack of importance of mass transfer is significant because it simplifies modelling for the removal of easily biodegradable substances in drinking water biofilters.

Factors Affecting Drinking Water Biofiltration

This research examined several important factors affecting the removal of biodegradable organic matter in drinking water biofilters. Laboratory‐scale biofilters were used and were fed a cocktail of easily biodegradable compounds. The factors investigated were chlorine or chloramine in the backwash water, air scour during backwashing, anthracite/sand versus granular activated carbon (GAC)/sand media, and low (5°C) versus high (20°C) temperature operation. Factorial design experiments showed that the three main factors (chlorine in the backwash water, temperature, and media type) and their interactions were significant in most cases. The temperature effect was more significant when chlorine was present. The GAC filters were much more resistant to chlorinated backwash water than were anthracite filters. Air‐scour effects were generally negligible except in some cases at low temperature with chloramine in the backwash water. Glyoxal removal was more sensitive to unfavorable biofiltration conditions than were removals of acetate, formate, and formaldehyde.

The transient-state, multiple-species biofilm model for biofiltration processes

We describe the transient-state, multiple-species biofilm model (TSMSBM), which is a novel synthesis of key modeling features needed to describe multiple-species biofilms that experience time-varying conditions, particularly including periodic detachment by backwashing. The TSMSBM includes six features that are essential for describing multiple-species biofilms that undergo changes over time: (1) four biomass types: heterotrophs, ammonia oxidizers, nitrite oxidizers, and inert biomass; (2) seven chemical species: input biodegradable organic material (BOM), NH 4 +-N, NO 2 −-N, NO 3 −-N, utilization-associated products, biomass-associated products, and dissolved oxygen; (3) eight reactions that describe the rates of consumption or production of the different species, as well as the stoichiometric linkages among the rates; (4) reaction with diffusion of all the soluble species in the biofilm; (5) growth, decay, detachment, and flux of each biomass type by location in the biofilm; and (6) constant or periodic detachment of biofilm, both of which allow for protection of biomass deep inside the biofilm. The last two features of the TSMSBM provide novel additions to biofilm modeling, and the synthesis of all features is a unique advancement. A series of examples illustrates insights that the TSMSBM can provide about the transient development of multiple-species biofilms; the roles of soluble microbial products and detachment in controlling the distribution of biomass types and process performance; and how backwashing affects the biofilm in drinking-water biofiltration.

Comparative measurements of microbial activity in drinking water biofilters

Tetrazolium reduction assays, phospholipid analysis, and 16S rRNA (rDNA) sequence analysis were applied to assess the distribution, composition and activity of microbial communities developing in biofilters treating non-ozonated and ozonated drinking water. The response of media-attached biomass to both operating temperature (3°C vs. >12°C) and ozone application point was assessed. As judged by 2-( p-iodo-phenyl)-3-( p-nitrophenyl)- s-phenyl tetrazolium chloride (INT) reduction, the dehydrogenase activity in biofilter systems that were operated with non-ozonated water was 55% lower than in identical filters operating with ozonated water. There was no significant difference between the microbiological activity measured in a biofilter series treating ozonated water and an identical series where ozonated water was introduced at an intermediate point. The biomass levels in biofilter systems that were operated with ozonated water were 47% higher on average than identical systems operated with non-ozonated water. Operating temperature had no significant impact on total biomass levels; however , specific dehydrogenase activity was 70% higher in systems operated at ambient temperatures (>12°C) than in systems held at 3°C. Phospholipid and rDNA analysis suggests that there was a community structure response to ozone application and operating temperature, but no response to different ozone application points.

Spatial Distribution of Microorganisms and Measurements of Oxygen Uptake Rate and Ammonia Uptake Rate Activity in a Drinking Water Biofilter

The biofilm characteristics (population dynamics and biofilm composition) in a biological filter for the removal of iron, manganese and ammonium were studied in a drinking water treatment plant. The objective was to examine the spatial distribution and biological composition of active biomass that grows in a biological filter and to verify the effect of the backwashing on the quantity of fixed biomass and on the density and activity of the biological population. Heterotrophic microorganisms activity was higher in the upper layer of the filter. Nitrifying microorganisms colonized the biofilter in a stratified manner and their activity was higher in the second layer of the filter. A total of 14 species of ciliated protozoa and 7 species of filamentous microorganisms were found in the biofilters. Ciliates were concentrated in the filterbed layer in which the heterotrophic activity was higher. The grazing activity of ciliates on heterotrophic bacteria reduced the competition pressure on nitrifying microorganisms, supporting their growth and thus raising the ammonium removal efficiency. In general, filamentous microorganisms appeared to be indifferent to operating changes in the plant such as backwashing and filtering cycles. Crenothrix was the prevalent filamentous microorganism in terms of both frequency and abundance; it was found prevalently in the first layer where the oxidisation of iron and manganese occurred.

Measurement of biomass activity in drinking water biofilters using a respirometric method

A simple respirometric method was developed and applied for the measurement of biomass activity in bench-scale drinking water biofilters. The results obtained with the new method, i.e. biomass respiration potential (BRP), indicated a high sensitivity allowing the quantification of the activity of low amounts of biomass. The analysis of duplicate samples showed a reasonable reproducibility, i.e. average coefficient of variation of 14% ( n=19). The calculation of the ratio between biomass activity and the amount of viable biomass (phospholipid) at different filter depths indicated a substantial increase of this ratio with filter depth. This indicated an increased biomass activity per unit amount of viable biomass deeper in the biofilters, where biofilm thickness is low. The comparison of the filter profiles of biomass activity and dissolved biodegradable organic matter (BOM), expressed as theoretical oxygen demand, showed a high correlation between these profiles. Consequently, BRP results appear to be good indicators of the BOM removal capacity of the filter biomass. Therefore, BRP results can potentially be used in certain cases instead of BOM measurements for the assessment of the BOM removal capacity of drinking water biofilters, operated under different conditions. This is important because of the relative complexity of the measurements of BOM surrogates, e.g. assimilable organic carbon and biodegradable dissolved organic carbon, and BOM components.

Non-steady state simulation of BOM removal in drinking water biofilters: Model development

A numerical model was developed to simulate the non-steady-state behavior of biologically-active filters used for drinking water treatment. The biofilter simulation model called “BIOFILT” simulates the substrate (biodegradable organic matter or BOM) and biomass (both attached and suspended) profiles in a biofilter as a function of time. One of the innovative features of BIOFILT compared to previous biofilm models is the ability to simulate the effects of a sudden loss in attached biomass or biofilm due to filter backwash on substrate removal performance. A sensitivity analysis of the model input parameters indicated that the model simulations were most sensitive to the values of parameters that controlled substrate degradation and biofilm growth and accumulation including the substrate diffusion coefficient, the maximum rate of substrate degradation, the microbial yield coefficient, and a dimensionless shear loss coefficient. Variation of the hydraulic loading rate or other parameters that controlled the deposition of biomass via filtration did not significantly impact the simulation results.

Non-steady state simulation of BOM removal in drinking water biofilters: applications and full-scale validation

A biofilter model called “BIOFILT” was used to simulate the removal of biodegradable organic matter (BOM) in full-scale biofilters subjected to a wide range of operating conditions. Parameters that were varied included BOM composition, water temperature (3.0–22.5°C), and biomass removal during backwashing (0–100%). Results from biofilter simulations suggest a strong dependence of BOM removal on BOM composition. BOM with a greater diffusivity or with faster degradation kinetics was removed to a greater extent and also contributed to shorter biofilter start-up times. In addition, in simulations involving mixtures of BOM (i.e. readily degradable and slowly degradable components), the presence of readily degradable substrate significantly enhanced the removal of slowly degradable material primarily due to the ability to maintain greater biomass levels in the biofilters. Declines in pseudo-steady state BOM removal were observed as temperature was decreased from 22.5 to 3°C and the magnitude of the change was significantly affected by BOM composition. However, significant removals of BOM are possible at low temperatures (3–6°C). Concerning the impact of backwashing on biofilter performance, BOM removal was not affected by backwash resulting in biomass removals of 60% or less. This suggests that periodic backwashing should not significantly impact biofilter performance as observed biomass removals from full-scale biofilters were negligible. In general, the simulation results were in good qualitative and quantitative agreement with experimental results obtained from full-scale biofilters.

Impact of Temperature on Drinking Water Biofilter Performance and Microbial Community Structure

Seasonal changes in removal of natural organic matter (NOM) by drinking water biofilters are often attributed to temperature differences. Bench-scale sand biofilters treating NOM isolated from a surface water source were operated in parallel at 5, 20, and 35 °C to isolate the effect of temperature from other water quality and operational parameters, which also vary seasonally. The biofilter operated at 5 °C achieved significantly lower removal of NOM and the NOM fraction that reacts with disinfectants (disinfection byproduct precursors) compared to the filters operated at 20 and 35 °C, which had similar performance levels. Viable biomass, measured as lipid phosphate, was significantly higher at the top and bottom of the filter operated at 20 °C. Phospholipid fatty acid (PLFA) profiles indicated an increasing gradient in markers for Gram-negative bacteria and microeukaryotes as biofilter operation temperature decreased, replacing general fatty acids and markers for Gram-positive bacteria and sulfate-reduci...

Assessment of drinking water filter microbial communities using taxonomic and metabolic profiles

Biofiltration is used in drinking water treatment to oxidize the biodegradable fraction of natural organic matter (NOM), thus controlling disinfection byproducts (DBP), DBP formation and microbial regrowth. Most work to date has focused on assessing drinking water biofilter performance; the microbial dynamics of biofilters have not been examined and are poorly understood. The objective of this research was to provide baseline information about the impact of design, operational and water quality parameters on NOM and DBP precursor removal, and microbial biomass and community structure profiles of biologically active drinking water rapid media filters. Phospholipid fatty acid (PLFA) profiles and the BIOLOG system for detecting the metabolism of sole carbon sources were found to be useful for characterizing the microbial communities in drinking water biofilters. Substrate removal was impacted most by ozonation, contact time, backwashing with water containing disinfectants, and low temperature. Using the PLFA technique, it was found that ozonation, contact time, and backwashing with water containing disinfectants had the greatest impact on microbial community structure. The BIOLOG system differentiated communities based on ozonation, contact time, pH, and temperature.

Assessment of drinking water filter microbial communities using taxonomic and metabolic profiles

Biofiltration is used in drinking water treatment to oxidize the biodegradable fraction of natural organic matter (NOM), thus controlling dtsinfection byproducts (DBP), DBP formation and microbial regrowth. Most work to date has focused on assessing drinking water btofilter performance; the microbial dynamics of biofilters have not been examined and are poorly understood. The objective of this research was to provide basehne information about the impact of design, operational and water quality parameters on NOM and DBP precursor removal, and rrucrobral biomass and community structure profiles of biologically active drinking water rapid media filters. Phospholipid fatty acid (PLFA) profiles and the BIOLOG system for detecting the metabolism of sole carbon sources were found to be useful for characterizing the microbial communities in drinking water biofilters. Substrate removal was impacted most by ozonation, contact time, backwashing with water containing disinfectants, and low temperature. Using the PLFA technique, it was found that ozonation, contact time, and backwashing with water containing disinfectants had the greatest impact on microbial community structure. The BIOLOG system differentiated communities based on ozonation, contact time, pH, and temperature

Microbial characterization of biological filters used for drinking water treatment.

The impact of preozonation and filter contact time (depth) on microbial communities was examined in drinking water biofilters treating Ohio River water which had undergone conventional treatment (coagulation, flocculation, sedimentation) or solutions of natural organic matter isolated from groundwater (both ozonated and nonozonated). With respect to filter depth, compared to filters treating nonozonated waters, preozonation of treated water led to greater differences in community phospholipid fatty acid (PLFA) profiles, utilization of sole carbon sources (Biolog), and arbitrarily primed PCR fingerprints. PLFA profiles indicated that there was a shift toward anaerobic bacteria in the communities found in the filter treating ozonated water compared to the communities found in the filter treating nonozonated settled water, which had a greater abundance of eukaryotic markers.