Patchy biofilm coverage can explain the potential advantage of BGAC reactors

Effects of running time on biological activated carbon filters: water purification performance and microbial community evolution

Ozone-biologically activated carbon (BAC) filtration is an advanced treatment process that can be applied to remove recalcitrant organic micro-pollutants in drinking water treatment plants (DWTPs). In this study, we continuously monitored a new and an old BAC filter in a DWTP for 1 year to compare their water purification performance and microbial community evolution. The results revealed that, compared with the new filter, the use of the old BAC filter facilitated a slightly lower rate of dissolved organic carbon (DOC) removal. In the case of the new BAC filter, we recorded general increases in the biomass and microbial diversity of the biofilm with a prolongation of operating time, with the biomass stabilizing after 7 months. For both new and old BAC filters, Proteobacteria and Acidobacteria were the dominant bacterial phyla. At the genus level, the microbial community gradually shifted over the course of operation from a predominance of Herminiimonas and Hydrogenophaga to one predominated by Bradyrhizbium, Bryobacter, Hyphomicrobium, and Pedomicrobium, with Bradyrhizobium being established as the most abundant genus in the old BAC filter. Regarding spatial distribution, we detected reductions in the biomass and number of operational taxonomic units with increasing biofilm depth, whereas there was a corresponding increase in microbial diversity. However, compared with the effects of time, the influence of depth on the composition of the biofilm microbial community was considerably smaller. Furthermore, co-occurrence network analysis revealed that the microbial community network of the new filter after 11 months of operation was the most tightly connected, although its modular coefficient was the lowest of those assessed. We speculate that the positive and negative interactions within the network may be attributable to symbiotic or competitive relationships among species. Moreover, there may have been a significant negative interaction between SWB02 and Acidovorax, plausibly associated with a competition for substrates.

Removal of organic micropollutants in biologically active filters: A systematic quantitative review of key influencing factors

Biofiltration utilizes natural mechanisms including biodegradation and biotransformation along with other physical processes for the removal of organic micropollutants (OMPs) such as pharmaceuticals, personal care products, pesticides and industrial compounds found in (waste)water. In this systematic review, a total of 120 biofiltration studies from 25 countries were analyzed, considering various biofilter configurations, source water types, biofilter media and scales of operation. The study also provides a bibliometric analysis to identify the emerging research trends in the field. The results show that granular activated carbon (GAC) either alone or in combination with another biofiltration media can remove a broad range of OMPs efficiently. The impact of pre-oxidation on biofilter performance was investigated, revealing that pre-oxidation significantly improved OMP removal and reduced the empty bed contact time (EBCT) needed to achieve a consistently high OMP. Biofiltration with pre-oxidation had median removals ranging between 65% and >90% for various OMPs at 10-45 min EBCT with data variability drastically reducing beyond 20 min EBCT. Biofiltration without pre-oxidation had lower median removals with greater variability. The results demonstrate that pre-oxidation greatly enhances the removal of adsorptive and poorly biodegradable OMPs, while its impact on other OMPs varies. Only 19% of studies we reviewed included toxicity testing of treated effluent, and even fewer measured transformation products. Several studies have previously reported an increase in effluent toxicity because of oxidation, although it was successfully abated by subsequent biofiltration in most cases. Therefore, the efficacy of biofiltration treatment should be assessed by integrating toxicity testing into the assessment of overall removal.

Study on the Changes in the Microcosmic Environment in Forward Osmosis Membranes to Reduce Membrane Resistance

Osmotic microbial fuel cells (OsMFCs) are an emerging wastewater treatment technology in bioelectricity generation, organic substrate removal, and wastewater reclamation. To address this issue, proton-conductive sites were strengthened after using the forward osmosis (FO) membrane by reducing the membrane resistance. The mechanism of improving electricity generation was attributed mainly to the unique characteristics of the membrane material and the water flux characteristics of the FO membrane. In particular, only when the concentration of catholyte was greater than 0.3 M was the membrane resistance the main contributor to the overall internal resistance. Meanwhile, through the simulation of the concentration inside the membrane, the changes in the membrane thickness direction and the phase transition of the internal structure of the membrane from the dry state (0% water content) to the expansion state (>50%water content) were analyzed, which were influenced by the water flux, further explaining the important role of the membrane’s microenvironment in reducing the membrane impedance. This further opens a novel avenue for the use of OsMFCs in practical engineering applications.

Biological activated carbon filter for greywater post-treatment: Long-term TOC removal with adsorption and biodegradation

Biological activated carbon (BAC) filters can be used to remove residual total organic carbon (TOC) from greywater after a membrane bioreactor. The two main TOC removal processes are adsorption to the granular activated carbon (GAC) and biological degradation. Biodegradation leads to the growth of microorganisms in the filter bed, which can lead to increased pressure loss over the filter bed. However, the roles of sorption and biodegradation in long-term TOC removal and how they complement each other are unclear. We monitored TOC removal from greywater in a BAC filter installed following a membrane bioreactor over more than 900 days. Removal performance depended on the operational time of the BAC filter, the influent TOC concentration, and in the upper part of the filter on the empty bed contact time (EBCT). Across the overall filter, the EBCT did not significantly influence TOC removal, showing that the filter was sufficiently large for the range of flow rates observed. Analysis of the long-term data revealed the equal importance of sorption and biodegradation over the whole operation period and the whole filter bed. Most of the TOC was removed in the upper part of the filter, where biodegradation was the dominant mechanism. In the lower part of the filter, sorption capacity remained and allowed high influent TOC concentrations to be buffered. The generous filter design with low average filtration rates ensured long-term TOC removal. The only maintenance needed was backwashing, which was required only after more than 800 days of operation. Backwashing effectively reduced the pressure loss but had no significant influence on the effluent water quality. Our study shows that BAC filters are a suitable post-treatment step for the treatment of greywater with highly variable flow and TOC concentrations.

Powdered Activated Carbon Exacerbates Fouling in MBR Treating Olive Mill Wastewater

Membrane fouling is a major obstacle in membrane bioreactors (MBRs) that treat wastewater. The addition of powdered activated carbon (PAC) is commonly suggested as a way to improve the MBR wastewater treatment process with respect to membrane fouling and effluent quality. Integrating the PAC addition into the MBR may also improve the stability of the acclimated microbial community for biodegrading the recalcitrant organic compounds that can also enhance membrane fouling. In this study, the ability of the MBR-PAC system to decrease membrane fouling was evaluated. Two pilot-scale reactors were operated: one reactor was supplemented with suspended PAC, and one was operated under similar conditions, without PAC. The feed to the reactors comprised domestic and olive oil mill wastewater. Surprisingly, the permeate flux and the membrane permeability decreased faster in the MBR supplemented with PAC compared to the control reactor. Corroborating these MBR fouling results, soluble microbial products (SMPs), originating from the PAC-supplemented reactor, were found to be more adhesive to an ultrafiltration membrane mimetic surface (polyether sulfone) as analyzed in a quartz crystal microbalance with dissipation monitoring (QCM-D). While the PAC had almost no effect on the dissolved organic carbon in the MBR, it altered the molecular weight distribution of the organic molecules in the SMP as observed with gel permeation chromatography: The fractions of 577–789 kDa and the one bigger than 4 × 103 kDa, were elevated and reduced, respectively, by the addition of PAC. A biofilm formation analysis using a confocal laser scanning microscopy showed a higher amount of biofilm on the membrane taken from the PAC reactor, but this membrane showed no traces of PAC particles when analyzed with a scanning electron microscope (SEM). Taken together, altering the composition of the dissolved organic matter in the MBR by PAC addition promoted its adhesion to the membrane, induced biofilm formation, and more prominently, decreased membrane permeability.

Real-time analysis of atrazine biodegradation and sessile bacterial growth: A quartz crystal microbalance with dissipation monitoring study

Biodegradation is a fundamental process for removal of the environmentally prevalent herbicide, atrazine, from contaminated waters. Biodegradation is more efficient when bacteria are attached on surface of an adsorbing carrier that supports the microbial population. However, for various reasons, biodegradation is almost always monitored in the liquid phase. In this study, we employ a novel Quartz Crystal Microbalance with Dissipation technique (QCM-D) for continuous, real-time monitoring of the attachment of atrazine-degrading bacteria to the surface, atrazine adsorption and degradation, and the consequent proliferation of the irreversibly attached sessile bacteria. The effect of atrazine biodegradation was observed in a batch mode of operation, in which a significant frequency decrease of the piezoelectric sensor was observed in the QCM-D, due to the proliferation of atrazine-degrading bacteria on the expense of atrazine. The latter was confirmed microscopically. Results also suggest that the viscoelastic properties of the atrazine-degrading consortium immediately changed in response to the presence of atrazine, whereas those of the non-degrading consortium were not affected. Importantly though, atrazine adsorption was similar regardless of the sessile consortia layers. When the QCM-D flow cell was exposed to a continuous flow of saturated atrazine solution, the degrading consortium layer was significantly more fluidic compared to batch mode conditions. The magnitude and kinetics of atrazine adsorption, which were monitored using QCM-D, were higher on bacterial cells comparing to the pristine, polystyrene-coated sensor. Findings from the current study can improve bioremediation design and open an avenue for studies on biodegradation and adsorption of micro-pollutants using QCM-D technology.

From urban municipalities to polar bioremediation: the characterisation and contribution of biogenic minerals for water treatment

Minerals of biological origin have shown significant potential for the separation of contaminants from water worldwide. This study details the contribution of biologically derived minerals to water treatment operations, with a focus on filtration media from urban municipalities and remote cold regions. The results support biofilm-embedded iron and manganese to be the building blocks of biogenic mineral development on activated carbon and nutrient-amended zeolites. The presence of similar iron and manganese oxidising bacterial species across all filter media supports the analogous morphologies of biogenic minerals between sites and suggests that biological water treatment processes may be feasible across a range of climates. This is the first time the stages of biogenic mineral formation have been aligned with comprehensive imaging of the biofilm community and bacterial identification; especially with respect to cold regions. Where biogenic mineral formation occurs on filter media, the potential exists for enhanced adsorption for a range of organic and inorganic contaminants and improved longevity of filter media beyond the adsorption or exchange capacities of the raw material.

A novel pilot-scale stacked microbial fuel cell for efficient electricity generation and wastewater treatment

A novel stacked microbial fuel cell (MFC) which had a total volume of 72 L with granular activated carbon (GAC) packed bed electrodes was constructed and verified to present remarkable power generation and COD removal performance due to its advantageous design of stack and electrode configuration. During the fed-batch operation period, a power density of 50.9 ± 1.7 W/m(3) and a COD removal efficiency of 97% were achieved within 48 h. Because of the differences among MFC modules in the stack, reversal current occurred in parallel circuit connection with high external resistances (>100 Ω). This reversal current consequently reduced the electrochemical performance of some MFC modules and led to a lower power density in parallel circuit connection than that in independent circuit connection. While increasing the influent COD concentrations from 200 to 800 mg/L at hydraulic retention time of 1.25 h in continuous operation mode, the power density of stacked MFC increased from 25.6 ± 2.5 to 42.1 ± 1.2 W/m(3) and the COD removal rates increased from 1.3 to 5.2 kg COD/(m(3) d). This study demonstrated that this novel MFC stack configuration coupling with GAC packed bed electrode could be a feasible strategy to effectively scale up MFC systems.

Next-generation pyrosequencing analysis of microbial biofilm communities on granular activated carbon in treatment of oil sands process-affected water

The development of biodegradation treatment processes for oil sands process-affected water (OSPW) has been progressing in recent years with the promising potential of biofilm reactors. Previously, the granular activated carbon (GAC) biofilm process was successfully employed for treatment of a large variety of recalcitrant organic compounds in domestic and industrial wastewaters. In this study, GAC biofilm microbial development and degradation efficiency were investigated for OSPW treatment by monitoring the biofilm growth on the GAC surface in raw and ozonated OSPW in batch bioreactors. The GAC biofilm community was characterized using a next-generation 16S rRNA gene pyrosequencing technique that revealed that the phylum Proteobacteria was dominant in both OSPW and biofilms, with further in-depth analysis showing higher abundances of Alpha- and Gammaproteobacteria sequences. Interestingly, many known polyaromatic hydrocarbon degraders, namely, Burkholderiales, Pseudomonadales, Bdellovibrionales, and Sphingomonadales, were observed in the GAC biofilm. Ozonation decreased the microbial diversity in planktonic OSPW but increased the microbial diversity in the GAC biofilms. Quantitative real-time PCR revealed similar bacterial gene copy numbers (>10(9) gene copies/g of GAC) for both raw and ozonated OSPW GAC biofilms. The observed rates of removal of naphthenic acids (NAs) over the 2-day experiments for the GAC biofilm treatments of raw and ozonated OSPW were 31% and 66%, respectively. Overall, a relatively low ozone dose (30 mg of O3/liter utilized) combined with GAC biofilm treatment significantly increased NA removal rates. The treatment of OSPW in bioreactors using GAC biofilms is a promising technology for the reduction of recalcitrant OSPW organic compounds.

Removal of micropollutants during tertiary wastewater treatment by biofiltration: Role of nitrifiers and removal mechanisms

The objective of this study was to determine the extent to which a suite of organic micropollutants (MPs) can be removed by biological filtration and the role of bioavailability and ammonia oxidizing microorganisms (AOMs) in the biodegradation process. During approximately one year, laboratory-scale columns with 8 min empty bed contact time (EBCT) and packed with anthracite as filter media were used for treating a tertiary effluent spiked with a broad range of MPs at a target concentration of 2 μg L(-1). In parallel columns, aerobic biomass growth was inhibited by using either the biocide sodium azide (500 mg L(-1) NaN3) or allylthiourea (5 mg L(-1) ATU), specifically inhibiting nitrifying bacteria. Once the biomass had colonized the media, around 15% of the dissolved organic carbon (DOC) contained in the untreated tertiary effluent was removed by non-inhibited columns. The removal of several MPs increased over time indicating the relevance of biological activity for the removal of MPs, while the negative control, the NaN3 inhibited column, showed no significant removal. Out of 33 MPs, 19 were recalcitrant (<25%) to biodegradation under aerobic conditions with the others exhibiting a diverse range of removal efficiency up to 95%. Through inhibition by ATU it was shown that nitrifying bacteria were clearly having a role in the degradation of several MPs, whereas the removal of other MPs was not affected by the presence of the nitrification inhibitor. A relationship between the qualitative assessment of sorption of MPs on granular activated carbon (GAC) and their removal efficiency by biodegradation on anthracite was observed. This result suggested that the affinity of the MPs for GAC media could be a useful indicator of the bioavailability of compounds during biofiltration on anthracite.

Encapsulation of Pseudomonas sp. ADP cells in electrospun microtubes for atrazine bioremediation

Electrospun hollow polymeric microfibers (microtubes) were evaluated as an encapsulation method for the atrazine degrading bacterium Pseudomonas sp. ADP. Pseudomonas sp. ADP cells were successfully incorporated in a formulation containing a core solution of polyethylene oxide dissolved in water and spun with an outer shell solution made of polycaprolactone and polyethylene glycol dissolved in a chloroform and dimethylformamide. The resulting microtubes, collected as mats, were partially collapsed with a ribbon-like structure. Following encapsulation, the atrazine degradation rate was low (0.03 ± 0.01 mg atrazine/h/g fiber) indicating that the electrospinning process negatively affected cell activity. Atrazine degradation was restored to 0.5 ± 0.1 mg atrazine/h/g fiber by subjecting the microtubes to a period of growth. After 3 and 7 days growth periods, encapsulated cells were able to remove 20.6 ± 3 and 47.6 ± 5.9 mg atrazine/g mat, respectively, in successive batches under non-growth conditions (with no additional electron donor) until atrazine was detected in the medium. The loss of atrazine degrading capacity was regained following an additional cell-growth period.

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(2)h, 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.

Fate of N-nitrosodimethylamine, trihalomethane and haloacetic acid precursors in tertiary treatment including biofiltration

The presence of disinfection by-products (DBPs) such as trihalomethanes (THMs), haloacetic acids (HAAs) and N-nitrosamines in water is of great concern due to their adverse effects on human health. In this work, the removal of N-nitrosodimethylamine (NDMA), total THM and five HAA precursors from secondary effluent by biological activated carbon (BAC) is investigated at full and pilot scale. In the pilot plant two filter media, sand and granular activated carbon, are tested. In addition, we evaluate the influence of ozonation prior to BAC filtration on its performance. Among the bulk of NDMA precursors, the fate of four pharmaceuticals containing a dimethylamino moiety in the chemical structure are individually investigated. Both NDMA formation potential and each of the studied pharmaceuticals are dramatically reduced by the BAC even in the absence of main ozonation prior to the filtration. The low removal of NDMA precursors at the sand filtration in comparison to the removal of NDMA precursors at the BAC suggests that adsorption may play an important role on the removal of NDMA precursors by BAC. Contrary, the precursors for THM and HAA formation are reduced in both sand filtration and BAC indicating that the precursors for the formation of these DBPs are to some extent biodegradable.

Characterization of natural organic matter adsorption in granular activated carbon adsorbers

The removal of natural organic matter (NOM) from lake water was studied in two pilot-scale adsorbers containing granular activated carbon (GAC) with different physical properties. To study the adsorption behavior of individual NOM fractions as a function of time and adsorber depth, NOM was fractionated by size exclusion chromatography (SEC) into biopolymers, humics, building blocks, and low molecular weight (LMW) organics, and NOM fractions were quantified by both ultraviolet and organic carbon detectors. High molecular weight biopolymers were not retained in the two adsorbers. In contrast, humic substances, building blocks and LMW organics were initially well and irreversibly removed, and their effluent concentrations increased gradually in the outlet of the adsorbers until a pseudo-steady state concentration was reached. Poor removal of biopolymers was likely a result of their comparatively large size that prevented access to the internal pore structure of the GACs. In both GAC adsorbers, adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly larger portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudo-steady state differed between the two tested GACs (18.9 and 28.6 g-C/kg GAC), and the percent difference in DOC uptake closely matched the percent difference in the volume of pores with widths in the 1-50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, individual NOM fractions were removed in similar proportions by the two GACs.

Biofiltration of wastewater treatment plant effluent: effective removal of pharmaceuticals and personal care products and reduction of toxicity

This study investigates biofiltration for the removal of dissolved organic carbon (DOC), pharmaceuticals and personal care products (PPCPs), and for the reduction of non-specific toxicity expressed as baseline toxicity equivalent concentration (baseline-TEQ). Two filtering media, sand and granular activated carbon, were tested. The influence of pre-ozonation and empty-bed contact time (EBCT, from 30 to 120 min) was determined. The experiments were performed at a pilot-scale with real WWTP effluent. A previous study showed that biological activity had developed on the filtering media and dissolved organic removal had reached a steady state before sampling commenced. The results show that biological activated carbon (BAC) has a good potential for the removal of DOC (35-60%), PPCPs (>90%) and baseline-TEQ (28-68%) even without pre-ozonation. On the contrary, the sand shows limited improvement of effluent quality. Varying the EBCT does not influence the performance of the BAC filters; however, dissolved oxygen concentration could be a limiting factor. The performances of the BAC filters were stable for over two years suggesting that the main mechanism of organic matter and PPCPs removal is biodegradation. It is concluded that BAC filtration without pre-ozonation could be implemented as a low cost advanced treatment option to improve WWTP effluent chemical quality.

Removal mechanisms of H(2)S using exhausted carbon in biofiltration

Exhausted carbon which comes from the H(2)S adsorption process may be a hazardous waste. In this study, exhausted carbon was re-used in biofiltration for H(2)S removal. Two identical columns were used for exhausted carbon (Column A) and fresh carbon (Column B). They were operated in the same mode with 35 ppmv of H(2)S gas at an empty bed residence time (EBRT) of 10s. The results show that the removal efficiency of H(2)S in the two columns was almost identical at 95-100%. The removal mechanisms of H(2)S was explored and explained by developing a mathematical model. The model incorporated mass transfer, biodegradation, adsorption, as well as biofilm growth. The developed model can predict the experimental results very well. The modeled results suggest that the removal of H(2)S in Column A was attributed to the adsorption mechanism much less than in Column B during the start-up stage, while the removal of H(2)S by the biodegradation in Column A was much higher. The removal of H(2)S by the adsorption was significantly affected by the biodegradation. The simulation results also suggest that column A achieved the steady-state biodegradation in a shorter time than in Column B. This could result from higher biomass concentration of biofilm in Column A, due to the extra sulfur source from pre-adsorbed sulfur on exhausted carbon besides H(2)S gas feeding.

Methanol removal efficiency and bacterial diversity of an activated carbon biofilter

Motivated by the need to establish an economical and environmentally friendly methanol control technology for the pulp and paper industry, a bench-scale activated carbon biofiltration system was developed. This system was evaluated for its performance in removing methanol from an artificially contaminated air stream and characterized for its bacterial diversity over time, under varied methanol loading rates, and in different spatial regions of the filter. The biofilter system, composed of a novel packing mixture, provided an excellent support for growth and activity of methanol-degrading bacteria, resulting in approximately 100% methanol removal efficiency for loading rates of 1-17 g/m(3) packing/h, when operated both with and without inoculum containing enriched methanol-degrading bacteria. Although bacterial diversity and abundance varied over the length of the biofilter, the populations present rapidly formed a stable community that was maintained over the entire 138-day operation of the system and through variable operating conditions, as observed by PCR-DGGE methods that targeted all bacteria as well as specific methanol-oxidizing microorganisms. Phylogenetic analysis of bands excised and sequenced from DGGE gels indicated that the biofilter system supported a diverse community of methanol-degrading bacteria, with high similarity to species in the genera Methylophilus (beta-proteobacteria), Hyphomicrobium and Methylocella (both alpha-proteobacteria).

Chemisorption of oxygen onto activated carbon can enhance the stability of biological perchlorate reduction in fixed bed biofilm reactors

Fixed bed biofilm reactors with granular activated carbon (GAC) or glass beads as support media were used to evaluate the influence of short-term (12h) and long-term (23 days) increases of influent dissolved oxygen (DO) concentrations on biological perchlorate removal. The goal was to evaluate the extent by which chemisorption of oxygen to GAC can enhance the stability of biological perchlorate reduction. Baseline influent concentrations were 50 microg/L of perchlorate, 2 mg/L of acetate as C, and 1mg/L of DO. Perchlorate removal in the glass bead reactor seized immediately after increasing influent DO concentrations from 1 to 4 mg/L since glass beads have no sorptive capacity. In the biologically active carbon (BAC) reactor, chemisorption of oxygen to GAC removed a substantial fraction of the influent DO, and perchlorate removal was maintained during short-term increases of influent DO levels up to 8 mg/L. During long-term exposure to influent DO concentrations of 8.5mg/L, effluent perchlorate and DO concentrations increased slowly. Subsequent exposure of the BAC reactor bed to low DO concentrations partially regenerated the capacity for oxygen chemisorption. Microbial analyses indicated similar microbial communities in both reactors, which confirmed that the differences in reactor performance during dynamic loading conditions could be attributed to the sorptive properties of GAC. Using a sorptive biofilm support medium can enhance biological perchlorate removal under dynamic loading conditions.

Visualization of active biomass distribution in a BGAC fluidized bed reactor using GFP tagged Pseudomonas putida F1

A favorable microenvironment for biofilm growth on GAC particles was shown using green fluorescent protein (GFP) as a marker for a phenol degrading bacterium, Pseudomonas putida F1. The dispersion of P. putida F1 in a biofilm covering granulated activated carbon (GAC) particles was monitored and compared to a biofilm on non-activated granular carbon particles. Laser scanning confocal microscopy (LSCM) micrographs of the biofilms taken from two fluidized bed reactors operating under identical conditions, showed higher fluorescent green areas in the GAC biofilm, especially close to the GAC surface. Quantitative analysis of the biofilm by COMSTAT, a three-dimensional biofilm structure analysis program, showed higher biomass concentration and higher viability in the GAC covered biofilm vs. the non-activated carbon biofilm. In addition, better effluent quality was measured for the BGAC reactor, which strongly suggests a significantly larger biofilm surface area available to the substrate, as opposed to that of the non-activated carbon carrier reactor.