Performance and Cost Evaluations of Synthetic Resin Technology for the Removal of Methyl Tert-Butyl Ether from Drinking Water

This study investigated the performance of synthetic carbonaceous resin technology for the treatment of methyl tert-butyl ether (MTBE) contaminated waters using rapid small-scale column tests (RSSCTs). The RSSCTs were conducted using Ambersorb 563 carbonaceous resin (Rohm and Haas Corp., Philadelphia, Pa.) under multisolute conditions of typical municipal water source, soluble fuel components or additive/by-product, and MTBE. Specifically, one RSSCT column run was conducted with groundwater from Arcadia Wellfield, Santa Monica, Calif., with tert-butyl alcohol (TBA) and MTBE, while the other RSSCT column run was performed with surface water from Lake Perris, Calif., with benzene, toluene, p-xylene (BTX) and MTBE. The results obtained were compared to RSSCTs performed using PCB coconut shell granulated activated carbon (GAC) (Calgon Corp., Philadelphia, Pa.). The adsorbent comparisons indicate that the performance (as characterized by indicators such as carbon usage rates or integrated column capacity) of the Ambersorb 563 synthetic resin in multisolute conditions of TBA or BTEX with MTBE in typical municipal water source is significantly superior to that of the coconut shell PCB GAC. Cost comparison for the coconut shell GAC and synthetic resin system was also performed. Under multisolute conditions of typical municipal water source, flow rates, and influent MTBE concentrations, the cost of the resin system, for most of the scenarios evaluated, is demonstrated to be significantly lower than the complementary GAC system under the costing procedure used. Further, when soluble fuel components such as BTX or fuel additives/byproducts such as TBA were present along with MTBE, the predicted higher adsorbent usage rates for the coconut shell GAC were translated into significantly higher treatment costs relative to the synthetic carbonaceous resin system.     

Granular Activated Carbon Adsorption of 2-Methylisoborneol (MIB): Pilot- and Laboratory-Scale Evaluations

Pilot- and laboratory-scale granular activated carbon (GAC) studies were conducted to determine the extent of 2-methylisoborneol (MIB) removal from two conventionally treated waters. Two different GACs were evaluated, a wood-based carbon and a coal-based carbon. Greater MIB removal was observed with the wood-based GAC which contradicts previous studies using the powdered forms of the carbons. Equilibrium and kinetic parameters were derived from laboratory-scale adsorption isotherm and short bed adsorber (SBA) experiments, respectively, and used to describe the adsorption of MIB. However, the derived parameters were unable to accurately predict the removal of MIB in the pilot-scale columns using the homogenous surface diffusion model. This suggested that there were inherent limitations with the SBA experiments, in particular, the small volume of GAC and high filtration rates employed. Larger laboratory column experiments were shown to accurately simulate the pilot-scale columns. Adsorption still played a vital role in the removal of MIB, even though the GAC had been exhausted for the removal of organics in terms of dissolved organic carbon and ultraviolet absorbance measurements. Even after a 6-month operation, complete MIB removal was observed with up to 80% attributed to adsorption, and the remaining 20% attributed to biodegradation.     

Modeling the Transformation of Chromophoric Natural Organic Matter during UV/H2O2 Advanced Oxidation

This research developed a differential kinetic model to predict the partial degradation of natural organic matter (NOM) during ultraviolet plus hydrogen peroxide (UV/H2O2) advanced oxidation treatment. The absorbance of 254?nm UV, representing chromophoric NOM (CNOM) was used as a surrogate to track the degradation of NOM. To obtain reaction rate constants not available in the literature, i.e., reactions between the hydroxyl radical (?OH) and NOM, experiments were conducted with “synthetic” water, using isolated Suwannee River NOM, and parameter estimation was applied to obtain the unknown model parameters. The reaction rate constant for the reaction between ?OH and total organic carbon (TOC), k?OH,TOC, was estimated at 1.14(±0.10)×104??L?mg-1?s-1, and the reaction rate constant between ?OH and CNOM, k?OH,CNOM, was estimated at 3.04(±0.33)×104??L?mol-1?s-1. The model was evaluated on two natural waters to predict the degradation of CNOM and H2O2 during UV/H2O2 treatment. Model predictions of CNOM degradation agreed well with the experimental results for UV/H2O2 treatment of the natural waters, with errors up to 6%. For the natural water with additional alkalinity, the model also predicted well the slower degradation of CNOM during UV/H2O2 treatment, owing to scavenging of ?OH by carbonate species. The model, however, underpredicted the degradation of H2O2, suggesting that, when NOM is present, mechanisms besides the photolysis of H2O2 contribute appreciably to H2O2 degradation.     

Treatment of MTBE-Contaminated Water in Fluidized Bed Bioreactor

Methyl tertiary-butyl ether (MTBE) biodegradation was evaluated in a laboratory-scale granular activated carbon (GAC)-based fluidized bed bioreactor system. The reactor was operated in seven distinct phases during which the MTBE loading rate, hydraulic retention time, cocontaminant loading [butyl, toluene, ethylbenzene, and xylene (BTEX) and tertiary-butyl alcohol (TBA)] and temperature were varied. The reactor was able to treat MTBE to less than 20 ug/L at 25°C and total organic carbon (TOC) loading rates between 0.01 and 1.1 kg/m3 of expanded GAC bed per day (kg/m3?day). Net biomass yield in the reactor under high loading conditions was approximately 0.55 g of total suspended solids (TSS) per gram of TOC consumed. This high yield under the higher loading rates necessitated that biomass be removed from the reactor to control bed expansion. At a loading rate of 1.5 kg/m3?day, MTBE effluents exceeded 20 ug/L. Reactor performance decreased as the reactor temperature was reduced from 25 to 15°C, but even at the lower temperatures MTBE removal efficiency exceeded 99%. Methyl tertiary-butyl ether treatment efficiency was not affected by the addition of TBA or BTEX under the conditions evaluated. Results of this study demonstrate that fluid bed bioreactors inoculated with an appropriate microbial culture can efficiently treat MTBE-contaminated water.     

Adsorption of RDX and HMX in Rapid Small-Scale Column Tests: Implications for Full-Scale Adsorbers

The high explosive (HE) compounds royal demolition explosive or hexahydro-1,3,5-trinitro-1,3,5-triazocine (RDX) and high melting explosive or octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) have been detected as groundwater contaminants at many military facilities. This research evaluated adsorption of RDX and HMX with granular activated carbon (GAC) to provide guidance for the design and operation of GAC adsorbers for treatment of HE-contaminated groundwater. Five GACs were screened using rapid small-scale column tests (RSSCTs), after which additional tests were performed with the two GACs that most effectively treated mixtures of RDX and HMX (Calgon F400 and Northwestern LB-830). GAC service life as a function of empty-bed contact time (EBCT) was determined using RSSCTs for a range of simulated full scale EBCTs with influent concentrations of 2,200 μg RDX/L and 350 μg HMX/L. Increasing the influent concentration of either contaminant significantly reduced the predicted service life, as did preloading GAC with groundwater natural organic matter. In batch isotherm tests, RDX was less adsorbable than HMX under all conditions studied. Concurrent loading of natural organic matter reduced the Freundlich K for RDX, whereas adsorption of HMX was not affected. Of the GACs tested, Calgon F400 most effectively removed RDX and HMX.     

Effects of Particle Stratification on Fixed Bed Absorber Performance

The effects of adsorbent particle size distribution (PSD) and the layering of particles in stratified and reverse stratified modes on the performance of fixed bed adsorber were investigated. Using trichloroethylene as the adsorbate and granular activated carbon as the adsorbent, experimental studies were conducted in stratified beds for different flow rates and influent concentrations. The homogeneous solid diffusion model was modified to take into account PSD and was used to simulate breakthrough curves. The PSD-based model was validated using experimental data and was found to be more accurate in predicting the breakthrough curves than the non-PSD-based model. The validated model was used to conduct simulations to examine the effects of key variables on performance in the stratified and reverse stratified modes. In the reverse stratified mode, the adsorbent particle size decreases gradually in the direction of flow. Model simulations indicate that this mode of operation increases breakthrough time, decreases the time to reach saturation, and thereby increases the overall adsorbent capacity utilization. The mass transfer zone for the reverse stratified bed was found to be narrower and sharper than that for the stratified bed. These model predictions have important ramifications to the water and wastewater industry in terms of reducing the overall cost of treatment using granular activated carbon adsorption.     

Effects of Moisture on Warming of Activated Carbon Bed during VOC Adsorption

Thermal waves resulting from the dynamic adsorption of organic vapor present in air on a granular activated carbon (GAC) filter were studied. An experimental design was carried out to determine the influential factors among the relative humidity of air (0–60%), the initial water content of the activated carbon (0–9.8%), and the volatile organic compound (VOC) concentration (0–50 g?m?3, i.e., 0–20,700 ppmv for acetone). The temperature increase is a function of the initial VOC concentration as well as the energy flux released. The warming of the adsorber is shown to be important for the adsorption of high VOC concentrations on a dry carbon bed, but the thermal amplitude is distinctly reduced when the GAC is initially wet because of water desorption. The moisture content of the air in the range of 0–95% is not found to be a prominent factor affecting both the adsorption capacity and the warming of the GAC bed for the high VOC concentration tested (20,700 ppmv of acetone). Temperature monitoring provides interesting information about the adsorption process, and the mechanisms involved are discussed.     

Rapid Small-Scale Column Tests for Arsenate Removal in Iron Oxide Packed Bed Columns

Arsenate breakthrough in column studies with a porous granular ferric hydroxide (GFH) was investigated in model waters and groundwaters. In this study, the use of rapid small-scale column tests (RSSCTs) initially designed for simulating the removal of organic compounds by granular activated carbon was extended for arsenate adsorption onto GFH. Adsorption kinetic studies and a comparison of laboratory RSSCT performance versus pilot-scale performance suggests that proportional diffusivity (PD) RSSCT scaling approaches are more valid than constant diffusivity (CD) approaches for arsenate onto GFH. Adsorption densities from column tests (qcolumn) were calculated at the point in the breakthrough curve when arsenate equaled 10 μg/L in the column effluent. For a simulated 2.5 min empty-bed contact time (EBCT), a model water (pH=8.6) had qcolumn values of 0.99 to 1.5 mgAs/gGFH versus 0.02 to 0.28 mgAs/gGFH with a comparable pH and EBCT in a natural groundwater. The differences were attributed to the silica, phosphate, vanadium, and other adsorbable inorganics in the groundwater. At pH 7.6 to 7.8, qcolumn values from PD-RSSCTs in the three natural waters were comparable (1.5±0.3 mgAs/gGFH) and higher than CD-RSSCT qcolumn values (0.57±0.26 mgAs/gGFH) in the three natural waters. All the RSSCTs captured changes in water quality (source water and pH) and operational regimes (e.g., EBCTs) and could be used to aid in the selection and design of arsenic removal media for full-scale treatment facilities.     

Characteristics of Ground Granular Activated Carbon for Rapid Small-Scale Column Tests

The rapid small-scale column test (RSSCT) has become a popular method for sizing granulated activated carbon (GAC) systems and columns for water treatment facilities. In this procedure, the GAC is ground and a specific size fraction is used for the RSSCT. Since GAC is produced and activated using different processes from different starting materials (e.g., bituminous, lignite, wood, etc.), the possibility exists that the extent of activation and, hence, the adsorptive capacity and surface reactivity may vary throughout the GAC particles. This would be the case if there were less activated inner cores in the GAC particles. If there is a variation in the sorption properties throughout the GAC particles, then grinding the GAC may result in smaller particles that have different properties than the bulk GAC. This study was carried out to test this commonly assumed hypothesis that the limited-sized ground particles represent the same adsorptive properties as the bulk GAC. Four activated carbons (manufactured from different source carbons) were studied. Gas adsorption tests determined the physical morphology, Boehm’s titrations checked the chemical nature of the surface oxides, and the Mohs hardness test was performed on all bulk GACs and ground fractions. No apparent differences were found in the total surface area, cumulative pore volume, or pore size volume of fractions generated by grinding activated carbons. In addition, the Boehm technique did not identify any significant differences in the chemical nature of the surfaces of the various size fractions of GAC. The Mohs hardness test did not indicate any variations in the hardness of the bulk GAC, the ground fractions, and the unground core. Based on the methods and materials used, the underlying assumption in the RSSCT analysis—that there are no variations in the different size fractions of the ground GAC—appears to be correct.     

Adsorption of Carbon Disulfide (CS2) in Water by Different Types of Activated Carbon—Equilibrium, Dynamics, and Mathematical Modeling

Adsorption equilibrium and kinetics of carbon disulfide in water by granular activated carbon (GAC), powdered activated carbon (PAC), and activated carbon fiber (ACF) were investigated and compared in an effort to elucidate the fundamentals for optimizing the control process design. It has been shown that the BET expression can satisfactorily describe the adsorption equilibrium of carbon disulfide (CS2) on GAC, PAC, and ACF and the corresponding kinetic experimental data properly correlated with the second-order kinetic model, which indicates that the CS2 adsorption is the rate-limiting step. A two-phase mathematical model was developed to simulate CS2 transfer in fixed-bed operation filled with the GAC, PAC, and ACF, and the equilibrium and kinetics information is subsequently used in the model to characterize the dynamics of adsorption. The model includes mechanisms such as axial dispersion, advection, liquid-to-solid mass transport, and intraparticle mass transport by pore and surface diffusion. It is manifested that the model was able to predict the dynamic breakthrough curve of CS2 in a fixed-bed adsorption column filled with GAC, PAC, and ACF at varied conditions (standard deviations for 1.5?cm/min is 12.13% and for 2.2?cm/min is 16.12%), based on BET-3 equilibrium and second-order kinetics, which indicates that the methodology proposed by this work could be employed for adsorbents selection, adsorption design, and process optimization for CS2 waste-water emission control.     

Dynamic Modeling of Bentazon Removal by Pseudo-Moving-Bed Granular Activated Carbon Filtration Applied to Full-Scale Water Treatment

A model for the removal of pesticides by granular activated carbon (GAC) filtration in full-scale water treatment is presented. The model describes GAC filtration in a pseudo-moving-bed configuration, where two filters are operated in series and after breakthrough the first filter is regenerated and becomes the second filter. The influent of the second filter is changing due to gradual breakthrough of the first filter. Therefore, a dynamic model is developed based on kinetics, equilibrium, and mass balance equations. The model is calibrated and validated on data of full-scale and pilot plants. Operational strategies are evaluated of two different cases. From this study it can be concluded that a dynamic mathematical model can be successfully used to evaluate the performance and operation of full-scale GAC filters for pesticide removal and can be used for operational decision support. Data obtained from practice can be used for calibration without additional laboratory work.     

Sorption of Cr (VI) onto Olive Stone in a Packed Bed Column: Prediction of Kinetic Parameters and Breakthrough Curves

This paper investigates the ability of olive stone to remove chromium (VI) ions from aqueous solution in a packed bed up-flow column with an internal diameter of 1.5 cm. The experiments were performed with a bed height of 15 g (13.4 cm) and a flow rate of 2 mL/min. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Adams-Bohart, Thomas, Yoon-Nelson, and Dose-Response models were applied to the experimental data. All models were found suitable for describing the whole or a definite part of the dynamic behavior of the column. The simulation of the whole breakthrough curve was effective with the Dose-Response model, but the initial part of the breakthrough was best predicted by the Adams-Bohart model. On the other hand, the results indicated that, at pH values of this work, approximately 50% of Cr (VI) is biosorbed by olive stone and the other 50% is reduced to Cr (III), both processes being of equal importance. Therefore, a two-stage biosorption process was developed. The goal of these final experiments was to confirm that Cr (III) [the Cr (VI) reduction product] was also effectively sorbed by olive stone in a second column.     

Prediction of Carbon BTEX Adsorption Capacity Using Field Monitoring Data

The need for predicting adsorption capacity for benzene, toluene, ethylbenzene, and xylenes (BTEX) onto granular-activated carbon (GAC) is a problem commonly associated with petroleum-spill remediation. In this study, monitoring data are compiled from operational records of ground-water pump and treat remediation sites where GAC adsorption is utilized as a primary treatment mechanism for BTEX. The monitoring data are reduced to adsorbed and equilibrium concentrations from which Freundlich isotherms and various linear and multivariate models are calibrated for prediction of BTEX capacity on GAC. The models are employed by themselves and with Ideal Adsorbed Solution Theory to predict capacity for total BTEX and benzene. Several models are selected based on prediction ability and are tested with independent data. Two simple models, a multivariate model and a Freundlich isotherm, are recommended. Complex empirical models and Ideal Adsorbed Solution Theory did not perform as well as the selected models and were rejected. From the Freundlich isotherm, new Freundlich constants are reported that describe adsorption of total BTEX on GAC from gasoline-contaminated ground water.     

Orthophosphate Adsorption Equilibrium and Breakthrough on Filtration Media for Storm-Water Runoff Treatment

Total phosphorus (TP) in storm-water runoff is a common regulatory target for maintaining the quality of receiving surface water. Previous storm-water treatment studies show that it is difficult to consistently achieve TP removal higher than 40%, whereas regulatory goals of 50–65% removal are becoming common. To meet these goals, storm-water filtration technologies utilizing an expanding array of filtration media are being deployed, especially in areas with protected water bodies such as Puget Sound and Chesapeake Bay. One challenge is that if the media has no adsorption capacity, particulate phosphorus can redissolve into solution and form liberal orthophosphate (Ortho-P), resulting in lower overall TP removal. Therefore, effective Ortho-P adsorption capacity in filtration media is crucial to meet more stringent TP removal goals. Additional media characteristics that should be considered include gradation, permeability, surface area, morphology, cost, and toxicity. In response to these requirements, an engineered media (EM) was developed and evaluated by Ortho-P adsorption isotherms and breakthrough in typical storm-water runoff conditions. Three other media, perlite, zeolite, and granular activated carbon (GAC), widely used in storm-water treatment, were also investigated under the same experimental conditions. With adsorption isotherms, EM showed the highest adsorption capacity of 7.82??mg/g, nearly seven times that of GAC (1.16??mg/g). In adsorption breakthrough testing, overall removal efficiency decreases as the number of treated empty bed volumes (EBVs) increases. To reach 50% overall removal, EM provided 838 EBVs, whereas GAC could only treat 12 EBVs. In addition, for the lifetime of media, EM outlasted GAC with 2,297 EBVs, compared to 1,000 EBVs, respectively. Results indicate that EM is an adsorptive filtration media for treating storm-water phosphorus.     

Hydraulic Conductivity and Compressibility of Soil-Bentonite Backfill Amended with Activated Carbon

Flexible-wall permeability tests and rigid-wall consolidation/permeability tests were performed to evaluate the hydraulic conductivity and compressibility of a model soil-bentonite (SB) backfill amended with granular activated carbon (GAC) or powdered activated carbon (PAC). The tests were performed as part of an assessment of enhanced SB backfill with improved attenuation capacity for greater longevity of barrier containment performance. Backfill specimens containing fine sand, 5.8% sodium bentonite, and GAC or PAC (0, 2, 5, and 10% by dry weight) were prepared to target slumps of 125±12.5?mm. Hydraulic conductivity (k) and compressibility of backfill test specimens were measured in consolidometers as a function of effective stress, σ′ (24 ? σ′ ? 1,532?kPa), whereas flexible-wall k was measured for backfill specimens consolidated to σ′ = 34.5?kPa. The results indicate that addition of GAC has little impact on the hydraulic and consolidation properties of the backfill, whereas addition of PAC causes a decrease in k and consolidation coefficient (cv) and a slight increase in compression index (Cc). Differences in behavior between GAC-amended backfills and PAC-amended backfills are attributed primarily to differences in GAC and PAC particle size.     

Modeling As(V) Removal in Iron Oxide Impregnated Activated Carbon Columns

Iron oxide impregnated onto an activated carbon (FeAC) has a high arsenic (As) removal capacity with the potential to be used in existing activated carbon column systems. Objectives of this research were to investigate As(V) removal from aqueous-phase systems using fixed-beds packed with FeAC and to determine if the triple layer model (TLM) with the homogeneous surface diffusion model (HSDM) could describe As(V) removal in the columns. Rapid small-scale column tests (RSSCT) were conducted at various empty bed contact times (EBCT). Effluent As(V) breakthrough (10?μg/L) was incipient for the 0.20-min EBCT experiment, whereas ～ 2300 bed volumes of water at 1-mg/L inlet concentration of As(V) was treated at an EBCT of 2.1?min before breakthrough occurred. The TLM with three As(V)-FeAC surface reactions coupled with the HSDM provided accurate prediction of As(V) removal in the RSSCT.     

Particulate and THM Precursor Removal with Ferric Chloride

Pilot-scale experiments were performed to investigate the effectiveness of enhanced coagulation in removing particles and trihalomethane (THM) precursors from two surface source waters: California State Project water and Colorado River water. The removal of suspended particles and natural organic matter at various ferric chloride doses and coagulation pHs was assessed through source water and filter effluent measurements of turbidity, particle count, UV254, TOC, and THM formation potential. Overall, it was found that optimal removal of particles and THM precursors by enhanced coagulation with ferric chloride is obtained at high coagulant doses (>16 mg∕L) and low pH conditions. Generally, turbidity removal is more efficient and head loss is more moderate at ambient pH compared with pH 5.5. Additionally, filter effluent particle counts were found to be consistent with residual turbidity data. The removal of THM precursors by enhanced coagulation is significantly enhanced at pH 5.5 compared with ambient pH. The reduction in THM formation potential is consistent with the trends observed for the THM precursor removal data (i.e., UV254 and TOC data). Furthermore, specific UV absorbance was used to estimate the proportion of humic substances in the raw waters. Enhanced coagulation was found to be less effective for the source water with the lower specific UV absorbance.     

High-Density Polyethylene Membrane Containing Fe0 as a Contaminant Barrier

To improve the performance of polymer-based containment barriers with respect to the breakthrough of chlorinated solvents, a high-density polyethylene (HDPE) membrane containing zero-valent iron (Fe0) nanoparticles was developed as a reactive barrier. The performance of the reactive membrane was evaluated by challenging it with carbon tetrachloride in a diaphragm cell apparatus. In a Fe0/HDPE system, reaction between carbon tetrachloride and Fe0 did not occur due to a lack of water in the polymer matrix. A glycerol-modified Fe0/HDPE membrane successfully increased the lag time before breakthrough by 13–16 fold compared to HDPE alone. Calculations estimate that only 2.5–3.0% of the Fe0 initially present in the membrane reacted before breakthrough of carbon tetrachloride. Extrapolations of these results to practical situations with larger membrane thicknesses and lower contaminant concentrations predict lag times on the order of years.     

Effect of Adsorbent Particle Layering on Performance of Conventional and Tapered Fixed-Bed Adsorbers

Experimental and modeling studies were conducted for the adsorption of phenol from aqueous solutions onto activated carbon in fixed beds with the adsorbent particles layered according to particle size. In the conventional stratified cylindrical adsorber (SCA), the particles were layered according to natural stratification, and increased in size with column depth. In the reverse stratified tapered adsorber (RSTA), the particle size decreased with column depth, and the fluid velocity decreased in the direction of flow. Experimental data indicate that for a uniform particle size distribution, the breakthrough time for the RSTA was about 60% higher than for the SCA under identical carbon loading and flow conditions. The homogeneous solid phase diffusion model with Linear-Freundlich isotherm was used to model the layered adsorbers. It provides excellent predictions for breakthrough curves at various column depths. Bed capacity utilization can be increased with the RSTA due to the sharpening of the solute front, and this will translate into lower capital and operating costs for the carbon adsorption system due to the smaller unit required, lower carbon inventory, and lower pumping costs.     

Process Optimization of an Aerobic Upflow Sludge Blanket Reactor System

Response of an aerobic upflow sludge blanket (AUSB) reactor system to the changes in operating conditions was investigated by varying two principle operating variables: the oxygenation pressure and the flow recirculation rate. The oxygenation pressure was varied between 0 and 25?psig (relative), while flow recirculation rates were between 1,300 and 600% correspondingly. The AUSB reactor system was able to handle a volumetric loading of as high as 3.8?kg total organic carbon (TOC)/m3?day, with a removal efficiency of 92%. The rate of TOC removal by AUSB was highest at a pressure of 20?psig and it decreased when the pressure was increased to 25?psig and the flow recirculation rate was reduced to 600%. The TOC removal rate also decreased when the operating pressure was reduced to 0 and 15?psig, with corresponding increase in flow recirculation rates to 1,300 and 1,000%, respectively. Maintenance of a high dissolved oxygen level and a high flow recirculation rate was found to improve the substrate removal capacity of the AUSB system. The AUSB system was extremely effective in retaining the produced biomass despite a high upflow velocity and the overall sludge yield was only 0.24–0.32?g VSS/g TOC removed. However, the effluent TOC was relatively high due to the system’s operation at a high organic loading.