Granular Activated Carbon Media Research Articles

Digging deep into a GAC filter – Temporal and spatial profiling of adsorbed organic micropollutants

A large pilot-scale granular activated carbon (GAC) filter was operated downstream in a full-scale wastewater treatment plant to remove organic micropollutants. To describe the spatial and temporal developments of micropollutant adsorption profiles in the GAC filter, micropollutants were extracted from GAC media taken at various filter depths and number of treated bed volumes. At a low number of treated bed volumes (2600 BVs), most micropollutants were adsorbed in the top layers of the filter. At increasing number of treated bed volumes (7300–15,500 BVs), the adsorption front for micropollutants progressed through the filter bed at varying rates, with sulfamethoxazole, fluconazole, and PFOS reaching the bottom layer before carbamazepine and other well-adsorbing micropollutants, such as propranolol and citalopram. Higher amounts of adsorbed micropollutants in the bottom layer of the filter bed resulted in decreased removal efficiencies in the treated wastewater. Mass estimations indicated biodegradation for certain micropollutants, such as naproxen, diclofenac, and sulfamethoxazole. A temporary increase in the concentration of the insecticide imidacloprid could be detected in the filter indicating that extraction of adsorbed micropollutants could provide an opportunity for backtracking of loading patterns.

Acetaminophen and caffeine removal by MnOx(s) and GAC media in column experiments

The objective of this study was to investigate the application of manganese oxide [MnOx(s)] and granular activated carbon (GAC) media for the removal of caffeine and acetaminophen from water.

Chemical-Free Greywater Treatment Using Aeration, Sedimentation, Followed by Granular Activated Carbon Filter (GAC) -A Case Study of Baghdad city household

Greywater is a possible water source that can be improved for meeting the quality required for irrigation. Treatment of greywater can range from uncomplicated coarse filtration to advanced biological treatment. This article presents a simple design of a small scale greywater treatment plant, which is a series of physical and natural processes including screening, aeration, sedimentation, and filtration using granular activated carbon filter and differentiates its performance with sand filter. The performance of these units with the dual filter media of (activated carbon with sand) in treatment of greywater from Iraqi house in Baghdad city during 2019 and that collected from several points including washbasins, kitchen sink, bathrooms, and laundry, was recorded in terms of removal efficiency of particular pollutants like Turbidity 94%, chemical oxygen demand (COD) 93%, and oil 91%. Dual filter was the most effective filter for decreasing these pollutants, while sand indicates the lowest removal efficiency. In general, granular activated carbon media seemed to be the most proper medium to improve greywater quality for reaching the quality of irrigation within the terms of organic matter decrease. Accordingly, this technology may be reliable for greywater treatment in a residential area.

Implementing Ozone‐BAC‐GAC in potable reuse for removal of emerging contaminants

AbstractRemoval of contaminants of emerging concern (CECs) is an important consideration in potable reuse. The effectiveness of ozonation, biologically activated carbon (BAC) filtration, and granular activated carbon (GAC) adsorption was assessed in the removal of 96 CECs. During phase 1, O3/total organice carbon (TOC) was varied between 0 and 1.5. Ozone was successful in removing CECs, achieving a total CEC concentration of 20.5 μg/L at an O3/TOC of 1.5 compared with 70 μg/L in absence of ozone. CECs such as iohexol, meprobamate, sucralose and flame retardants, tris(2‐carboxyethyl)phosphine (TCEP), tris(1‐chloro‐2‐propyl) phosphate (TCPP), and tris(1,3‐dichloro‐2‐propyl)phosphate (TDCPP) were detected in the ozone effluent even at the highest ozone dose. BAC filters did not contribute measurably to CEC removal, while the 20‐min empty bed contact time (EBCT) GAC removed 57.6% of the influent CEC concentration, even though the adsorption capacity had been exerted through previous operation. During phase 2, the average O3/TOC ratio was 0.64, and the impact of new GAC media on CEC removal was studied. EBCT was maintained at 15 min for both GAC contactors, while the used GAC (133,600 bed volume [BV]) was replaced with new media in one GAC contactor. The GAC with new media removed CECs below the limit of quantitation, up to 10,000 BV, while removal decreased to 70% after 20,000 BV, with seven CECs—sucralose, iohexol, acesulfame‐k, meprobamate, cotinine, primidone, and acetaminophen—being detected. Ozone doses for CEC removal and BV needed for adsorption of CECs on activated carbon can be determined from this study. Thus, the results from this study can help design and optimize ozone, BAC, and GAC systems used for potable reuse to target the removal of specific CECs.

Efficient removal of manganese from aquatic solutions by amphistegina filter

Mono-media filtration vessels of amphistegina and conventional granular activated carbon filters in an assembled semi-pilot filtration unit had been carried out to represent the efficient removal of manganese ions from hydrous solution in a comparison study. Amphistegina tests surfaces have been characterized for the first time in compared to conventional granular activated carbon media by X-ray diffraction, Fourier Transform Infrared spectroscopy and Brunauer–Emmett–Teller surface area analysis. Also, the surface morphology of granular activated carbon and amphistegina media with manganese chloride adsorption was observed by Atomic Force Microscopy analysis. The filtration unit had been operated at different working conditions such as; flow rates (20, 30, 40, 50 and 60 l/min), operating temperatures (293, 303 and 313 k), initial manganese(II) concentrations (15–105 mg/l), constant pH (7.5) and calculated adsorbent mass for granular activated carbon (34.1 g/l) and amphistegina media (115 g/l). The maximum adsorption capacities of manganese ions by amphistegina (1.17 mg/g) and granular activated carbon (3.36 mg/g) filters had been produced at a temperature of 313 k and at a higher flow rate (60 l/min); while at a lower flow rate (20 l/min), the maximum adsorption capacities were 2.83 mg/g for granular activated carbon filter and 3.42 mg/g for amphistegina filter. The adsorption performance was verified by Freundlich and Langmuir adsorption isotherms.

Transport of Enterococcus faecalis in granular activated carbon column: Potential energy, migration, and release

An increasing number of water purification plants use granular activated carbon filtration as an advanced treatment technology. One of the main constraints of carbon filtration is bacterial leakage, which can impact public drinking water safety. In this study, Enterococcus faecalis, commonly detected in natural water, was employed as the target bacteria for investigating the mechanism of deposition and migration of bacteria in granular activated carbon medium. The repulsive barrier, secondary potential well and potential energy change curve under various conditions were depicted by DLVO theory. Moreover, the influence, including ionic strength, ionic charge and flow rate, on bacterial transport was comprehensively discussed. The Enterococcus faecalis penetration curve was in accordance with the van der Waals force and electrostatic repulsion force under different conditions. Finally, 8%–11% of Enterococcus faecalis was released into the effluent when ionic strength declined.

The Water Microbiome Through a Pilot Scale Advanced Treatment Facility for Direct Potable Reuse

Advanced treatment facilities for potable water reuse of wastewater are designed to achieve high removal levels of specific pathogens, as well as many other constituents. However, changes to the microbial community throughout treatment, storage, and distribution of this water have not been well characterized. We applied high-throughput amplicon sequencing, read-based, assembly-based, and genome-resolved metagenomics, and flow cytometry to investigate the microbial communities present in a pilot-scale advanced water treatment facility. Advanced treatment of secondary-treated wastewater consisted of ozonation, chloramination, microfiltration, reverse osmosis (RO), advanced oxidation (UV/H2O2), granular activated carbon (GAC) filtration, and chlorination. Treated water was fed into bench-scale simulated distribution systems (SDS). Cell counts and microbial diversity in bulk water decreased until GAC filtration, and the bacterial communities were significantly different following each treatment step. Bacteria grew within GAC media and contributed to a consistent microbial community in the filtrate, which included members of the Rhizobiales and Mycobacteriaceae. After chlorination, some of the GAC filtrate community was maintained within the SDS, and community shifts were associated with stagnation. Putative antibiotic resistance genes and potential opportunistic pathogens were identified before RO and after advanced oxidation, although few if any members of the wastewater microbial community passed through these treatment steps. These findings can contribute to improved design of advanced treatment trains and management of microbial communities in post-treatment steps.

A comparison of gravity-driven membrane (GDM) reactor and biofiltration + GDM reactor for seawater reverse osmosis desalination pretreatment

In this study, permeate quality, membrane performance, and microbial community in a gravity-driven microfiltration (GDM) reactor and a biofiltration (BF) + GDM reactor for seawater reverse osmosis (RO) desalination pretreatment were compared at both lab-scale and pilot-scale. The presence of BF column was more efficient in removing soluble organic substances by biosorption/biodegradation, leading to superior permeate quality from BF + GDM and subsequently lower RO fouling than GDM. Compared to the biofilm-saturated anthracite media, the granular activated carbon media in BF improved the assimilable organic substances removal in BF + GDM. Although less organic substances and microbial cells were accumulated on the membrane in BF + GDM, its permeate flux was 10–20% lower than GDM. Furthermore, BF lowered the amounts and diversity of prokaryotes (due to less organic substances) and eukaryotes (due to BF media rejection and lacking of prokaryotic preys) in the membrane biofilm of BF + GDM, but did not cause significant shifts of predominant species. Thus, the lower flux in BF + GDM was attributed to the limited predation and movement of eukaryotes in membrane biofilm, which may result in the formation of less porous and compact biofilm layer. The cost analysis indicated that BF + GDM-RO requires 5.2% less operating cost and 1.5% less water production cost than GDM-RO.

Using upstream oxidants to minimize surface biofouling and improve hydraulic performance in GAC biofilters

The combination of biological growth and particle loading can adversely affect hydraulic performance in drinking water biofilters. In this study, upstream oxidant addition was used to distribute biologically-derived filter clogging in granular activated carbon (GAC) biofilters. Oxidant penetration was assessed during pilot-scale operation and backwashing of dual media (GAC/sand) and multimedia (GAC/anthracite/sand) biofilters. Influent chlorine (HOCl), monochloramine (NH2Cl), and hydrogen peroxide (H2O2) residuals were optimized to react with the GAC surface in the upper portion of the filter media bed (depth < 0.5 m) to attenuate biomass development. As the oxidant residual was quenched by surface-mediated reaction with the filter media, biomass growth was promoted deeper in the filter bed (depth > 0.5 m). The oxidant-induced effects on biomass and hydraulic performance were monitored through measurements of adenosine triphosphate (ATP) and head loss accumulation at different media depths. Addition of oxidants (e.g., 0.6 mg Cl2/L HOCl) could decrease terminal head loss by 20% in dual media filters and 40% in multimedia filters. These hydraulic benefits were achieved without significantly affecting removal of assimilable organic carbon (AOC), total organic carbon (TOC), turbidity, and particle counts. Oxidant type, residual concentration, media type, media age, and media depth influenced the passage of oxidant residuals and distribution of filter biomass. When oxidants were added during backwashing, oxidant residual was quenched through the bed depth from a combination of reactions with GAC media and biofilm degradation. This attenuation of residual oxidant may prevent the oxidant residual from penetrating the entire bed depth, potentially compromising backwashing objectives.

Paclobutrazol removal from irrigation water using a commercial-scale granular activated carbon system

Abstract A commercial-scale granular activated carbon (GAC) system was evaluated for removal of the plant growth regulator paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol] from recaptured irrigation water in an ornamental greenhouse operation. This greenhouse collected and re-used irrigation drain water from 8.1 ha of subirrigated greenhouse production space, resulting in approximately 5.4 million L of recycled irrigation water filtered annually by GAC. Recaptured water was pre-filtered with polyester bag filters and then passed through three 1000 L (454 kg) GAC vessels in series before being recycled for irrigation purposes. Each GAC filter contained 8 × 30 US mesh (595–2380 μm) bituminous coal-based GAC. In Experiment 1, paclobutrazol concentration was analyzed in pre- and post-GAC filtration samples approximately weekly with a total of 55 samples between March 2015 and August 2016. The highest concentration of paclobutrazol found in recycled irrigation water was 72.5 μg L−1, whereas residual concentration after GAC was below a target 5 μg L−1 in all samples. In Experiment 2, water samples collected pre- and post-GAC filtration four times over a ten-week period during a peak period of plant production and included chemical analysis and a broccoli bioassay. The GAC filtration in Experiment 2 was effective at paclobutrazol removal despite wide variation in flow rates and resulting contact times (11–31 min) through the filter. In Experiment 3, samples were taken in a random order from the outlet of each individual GAC filter with contact times of 0, 10, 21, or 31 min. After 31 min of GAC contact time, broccoli bioassay plants were 7% (0.22 cm) shorter than control plants that received 0 μg L−1 paclobutrazol. There was a 30% average reduction in paclobutrazol concentration with the addition of each GAC filter or approximately 10 additional minutes of contact time with each GAC filter, reduced from 16.3 μg L−1 for the control to 1.7 μg L−1 after 31 min contact time. A partial budget showed GAC media replacement to be the highest operating cost item associated with treating recaptured irrigation water, contributing approximately 30% of the total annual cost of $13,020. There was no indication of reduced effectiveness of GAC paclobutrazol removal after approximately one year of filtration without GAC replacement.

Fluorescence spectroscopy for monitoring reduction of natural organic matter and halogenated furanone precursors by biofiltration

The application of fluorescence spectroscopy to monitor natural organic matter (NOM) reduction as a function of biofiltration performance was investigated. This study was conducted at pilot-scale where a conventional media filter was compared to six biofilters employing varying enhancement strategies. Overall reductions of NOM were identified by measuring dissolved organic carbon (DOC), and UV absorbance at 254 nm, as well as characterization of organic sub-fractions by liquid chromatography–organic carbon detection (LC-OCD) and parallel factors analysis (PARAFAC) of fluorescence excitation-emission matrices (FEEM). The biofilter using granular activated carbon media, with exhausted absorptive capacity, was found to provide the highest removal of all identified PARAFAC components. A microbial or processed humic-like component was found to be most amenable to biodegradation by biofilters and removal by conventional treatment. One refractory humic-like component, detectable only by FEEM-PARAFAC, was not well removed by biofiltration or conventional treatment. All biofilters removed protein-like material to a high degree relative to conventional treatment. The formation potential of two halogenated furanones, 3-chloro-4(dichloromethyl)-2(5H)-furanone (MX) and mucochloric acid (MCA), as well as overall treated water genotoxicity are also reported. Using the organic characterization results possible halogenated furanone and genotoxicity precursors are identified. Comparison of FEEM-PARAFAC and LC-OCD results revealed polysaccharides as potential MX/MCA precursors.

Quaternary nitrogen activated carbons for removal of perchlorate with electrochemical regeneration

Positively charged nitrogen functional groups were introduced onto the surface of granular activated carbon (GAC), and these increased perchlorate anion removal from drinking water sources. Nitrogen functionalization involved three treatment steps: (1) introducing oxygen groups onto the GAC, (2) incorporating nitrogen groups by thermal treatment in ammonia flow to replace O with N, and (3) quaternerizing pyridine-like groups to create positively charged pyridinium-like groups. Functionalized bituminous GAC provided 6 times more perchlorate removal than its predecessor, pristine bituminous GAC. The conversion of pyridine-like groups (after step 2) to pyridinium-like groups by quaternization (step 3) was confirmed by analysis of the XPS N 1s signals and surface charge analysis. Redox peaks, observed during cyclic voltammetry analysis of the functionalized GAC, evidenced that these nitrogen functional groups were electrochemically active, so that they sorbed perchlorate when they were oxidized, and then desorbed perchlorate when reduced. Moreover, after sorbing perchlorate onto pyridinium-GAC in RSSCTs, the GAC media could be regenerated by electrochemical reduction, and its capacity for perchlorate adsorption was mostly restored. This tailored functionality and redox regeneration of a relatively inexpensive media such as activated carbon could offer novel opportunity to the adsorption industry.

Microbial activity in biofilter used as a pretreatment for seawater desalination

Biofilters as a pretreatment process in seawater desalination can reduce biofoulants through adsorption and biodegradation. In this study, the performance of granular activated carbon (GAC) biofilter with three different filtration velocities was studied in terms of dissolved organic carbon (DOC) removal. This apart, the microbial activities in the biofilters were measured in terms of concentration of active biomass (adenosine tri-phosphate; ATP) and total cell count. Biofouling potential in biofilter effluents were assessed in terms of transparent exopolymer particles (TEP) and assimilable organic carbon (AOC) concentration. AOC was carried out using a new rapid bioluminescence method. Upon reaching mature stage, the GAC biofilters achieved high DOC removal efficiency of more than 60%, especially the low molecular weight organics. This organic removal was mostly attributed to active biomass on the GAC media. In addition, GAC biofilters led to significant reduction of the AOC and TEP concentration amounting to only 0.6±0.2μg-C glucose/L and 5.3±1.1μg-C/L, respectively in effluents. Thus, GAC biofilter is an effective pretreatment in reducing biofouling potential.

The effect of nitrate on ethylene biofiltration

This study investigated the effects of filter media types and nitrate (NO3−) concentrations in nutrient solutions on C2H4 biofiltration. A new nutrient solution with zero NO3− concentration was supplied to two perlite-bed biotrickling filters, two perlite-bed biofilters, and two GAC (Granular Activated Carbon)-bed biofilters, while the other with 2gL−1 of NO3− was used for the other two GAC biofilters. All reactors underwent a total test duration of over 175 days with an EBRT (Empty Bed Residence Time) of 30s, inlet gas flow rate of 7Lmin−1, and inlet C2H4 concentrations of 20–30mgm−3.NO3− concentration and media type significantly affected the C2H4 removal efficiencies in all types of biofiltration. The perlite media with no NO3− achieved C2H4 removal efficiencies 10–50% higher than the others. A NO3− concentration as high as 2gL−1 in the original nutrient solution may act as an inhibitor that suppresses the growth or activity of C2H4 degraders. In addition, the perlite media resulted in higher C2H4 removal efficiencies than GAC media, because the hydrophilic surface of the perlite leads to a higher moisture content and thus to favorable microbial growth.

Arsenic adsorption via iron‐preloaded activated carbon and zero‐valent iron

This research focused on removing arsenic (As) from groundwater by coupling iron‐tailored activated carbon with iron solubilization. This was achieved by solubilizing iron grains that were interspersed within the tailored activated carbon. A commercially available bituminous coal carbon was preloaded with iron by an evaporation method. With natural groundwater as the source, the media processed 25,000 bed volumes (BV) of water before 10‐μg/L As breakthrough occurred. In comparison, when 30% zero‐valent iron (ZVI) grains were interspersed with iron‐preloaded bituminous coal carbon, As breakthrough &gt; 10 μg/L occurred at 45,000 BV. The As breakthrough corresponded to when most of the ZVI source had become visibly corroded. Although some solubilized iron escaped through the granular activated carbon media, this iron could be captured in a subsequent sand or activated carbon filter in order to yield water that would meet both primary and secondary drinking water standards. Field‐scale tests are required to determine whether results at large scale corroborate the laboratory findings.

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.

Denitrification with external carbon source utilizing adsorption and desorption capability of activated carbon

The adsorption-desorption capability of activated carbon was incorporated into biological denitrification process with the addition of external carbon source for nitrogen removal in water and wastewater treatment. Laboratory scale column packed with granular activated carbon (GAC) was fed with nitrate and sucrose in various modes. Other than continuous organic carbon addition (continuous mode), two different dynamic feeding modes, namely intermittent and injection modes were investigated. Under intermittent mode, organic carbon source was added in accordance with cycles consisting of two stages: an organic carbon feeding stage and an organic carbon starvation stage. Three cycle schedules in terms of duration of feeding stage and starvation period were examined. In injection mode, concentrated organic substrate was fed into the columns for 10 min at frequencies of 1, 2 or 3 times per day. With substrate C:N ratio of 1.88, influent NO 3N level of 20 mgl −1 and empty bed contact time (EBCT) of 80 min, intermittent mode produced high overall N removal efficiencies ranging from 89 to 95% which are comparable with levels attainable under continuous mode. Injection mode achieved slightly lower but reasonably high denitrification efficiencies. Under the conditions employed, once per day organic substrate injection was sufficient to remove 87% of the influent NO 3N. The performance of anthracite media was also compared with GAC under both continuous and intermittent modes using identical set of conditions. Anthracite performed equally well under continuous mode where organic carbon source was always available. However, under intermittent mode, anthracite gave a poor N removal efficiency of 29% during the starvation period due to the lack of adsorption and desorption capability in comparison with 90% obtained in GAC media. The adsorption and desorption property of activated carbon was also applied in denitrification process for the treatment of water or wastewater with fluctuating influent NO − 3 concentration levels. Two cases of NO − 3 fluctuation were examined and in both cases, overall N removal efficiencies of more than 93% were achieved.

Biofiltration performance: part 1, relationship to biomass

Many factors could account for the good performance of coal‐based GAC biofilters, including the quantity of biomass attached to the media.A phospholipid analytical technique was used to measure the amount of biomass attached to the surfaces of drinking water filter media. The method was reproducible and able to detect significant differences in biomass concentrations in different filters and at various depths within filters. The amount of attached biomass decreased as filter depth increased, suggesting that most removal of natural organic matter occurred at the top of the biofilters. The results show that granular activated carbon media were able to hold more biomass than were anthracite and sand media and that concentrations of biomass in anthracite‐sand filters were lower with chlorine in the backwash water.

Organic carbon supplement influencing performance of biological nitritification in a fluidized bed reactor

A three-phase draft-tube fluidized-bed bioreactor packed with granular activated carbon (GAC) was employed to start up a nitrification process for high-strength ammonium (500 mg/l as N) wastewater. Supplement of sucrose into the ammonium wastewater was expected to enhance the attachment of nitrifier biofilm on GAC medium, and also to promote a high rate of ammonium conversion to predominant nitrite, i.e. nitrification process. In this study, various concentrations of sucrose provided various COD/NH4+-N ratios (0 to 1) to the fluidized bed bioreactor with an extremely high loading of 2.0 kg NH4+-N/m3-day and a limited air supply at the dissolved oxygen level of 3.0 mg/l. The results clearly indicated that the addition of organic carbon would inhibit the bioactivity of ammonium oxidizer (Nitrosomonas sp.) and nitrite oxidizer (Nitrobacter sp.). When the COD/NH4+-N ratio was increased to 0.33, the applied sludge loading to the nitrite oxidizer was greater than the specific substrate utilization rate, so the intermediate product, nitrite was accumulated without further nitratification. While the COD/NH4+-N ratio was increased to 1.0, a significant nitrite accumulation above 95% was achieved with the high ammonium feeding concentration of 500 mg/l NH4+-N. Meantime, the addition of sucrose in the start-up stage promoted heterotrophic growth and biofilm attachment on GAC surface. The filamentous structure of heterotrophs provided a biofilm surface on which the discrete nitrifying bacteria could be easily entrapped. In this fluidized-bed reactor, a large amount of entrapped nitrifier and a high efficiency of oxygen transfer rate had contributed to a high removal loading rate of ammonium with short hydraulic retention time of 6 hours.

A comparison of media types in acetate fed expanded-bed anaerobic reactors

A synthetic feed, containing acetate as the only carbon source, was used to start-up four different anaerobic expanded-bed reactors containing three different types of microbial attachment media. The media types used were low-density anthracite, granular activated carbon (GAC) and two sizes of sand. All media types were of the same average diameter, 0.7 mm, except for a smaller sand, 0.35 mm. These media types were chosen to compare surface roughness, macroscopic shear stresses due to upflow velocity and sphericity. The 0.7 mm sand required the greatest upflow velocity, 16 cm/s, while the other reactors had upflow velocities of 5.5–6.0 cm/s. Sand had the least surface roughness and GAC had the roughest surface, while anthracite had the most angular shape. At steady-state, the GAC reactor retained 3.75–10 times the attached biomass retained on the other media tested and the GAC reactor accumulated biomass at a faster rate during start-up. Shear losses reflected the biomass accumulation with the two sand and anthracite media having shear loss coefficients 6–20 times greater than that of the GAC medium. Sand induced the formation of sludge granules in both sand reactors with two species of methanogens and stability of the sludge blankets was critical to reactor performance. Scanning electron microscopy demonstrated that attached growth developed in crevices where biomass was protected from shear forces. Attached growth on the sand and anthracite media was located only in crevices, while the GAC medium is completely covered with crevices and biofilm developed on the entire GAC particle. Surface roughness was critical to biofilm development with the rougher surface providing the better attachment medium.