Tracking 14C-Labeled Organic Micropollutants to Differentiate between Adsorption and Degradation in GAC and Biofilm Processes

Strategy for repurposing waste anion exchange resins to construct a biofilter for removing dissolved organic matter: performance and mechanism

Anion exchange resins are widely employed in wastewater and drinking water treatment plants to remove dissolved organic matter (DOM). However, the degradation of resin performance necessitates the discontinuation of these treatment projects, resulting in the idling of underperforming resins, referred to as waste anion exchange resins (WAER). Given the substantial investment in operational costs, determining how to economically utilize WAER is essential for restarting the treatment projects. Therefore, this study proposed a strategy for repurposing WAER to construct a biofilter for DOM removal. A biofilter, termed biological anion exchange resin (BAER), was developed using WAER and compared with two conventional biofilters: biological activated carbon (BAC) and sand filter. After the acclimatization period, the BAER biofilter achieved a removal of up to 21.42 % of dissolved organic carbon (DOC), which is 5.8 times greater than the removal rate of the sand filter and comparable to the BAC. Notably, BAER exhibited the highest removal rate of aromatics, achieving 41.04 % UV254 removal, which are precursors to disinfection byproducts (DBPs). Consequently, BAER demonstrated superior control of DBPs, with a removal efficiency of 39.59 %. Additionally, BAER demonstrated effective removal of humic substances due to the bioregeneration of its adsorption sites, which led to significant differences in both the structural composition and functional expression of the biological community in BAER compared to other biofilters. This study also revealed that the bioregenerated adsorption sites primarily capture DOM through electrostatic attraction rather than ion exchange. Overall, these findings confirm the promising application of the BAER biofilter constructed with WAER and offer valuable insights into the associated removal processes.

Anaerobic digestion and biochar/hydrochar enhancement of antibiotic-containing wastewater: Current situation, mechanism and future prospects

The increasing consumption of antibiotics by humans and animals and their inappropriate disposal have increased antibiotic load in municipal and pharmaceutical industry waste, resulting in severe public health risks worldwide. Anaerobic digestion (AD) is the main force of antibiotic-containing wastewater treatment, and the adaptability of biochar/hydrochar (BC/HC) makes it an attractive addition to AD systems, which aim to promote methane production efficiency. Nevertheless, further studies are needed to better understand the multifaceted function of BC/HC and its role in antibiotic-containing wastewater AD. This review article examines the current status of AD of antibiotic-containing wastewater and the effects of different preparation conditions on the physicochemical properties of BC/HC and AD status. The incorporation of BC/HC into the AD process has several potential benefits, contingent upon the physical and chemical properties of BC/HC. These benefits include mitigation of antibiotic toxicity, establishment of a stable system, enrichment of functional microorganisms and enhancement of direct interspecies electron transfer. The mechanism by which BC/HC enhances the AD of antibiotic-containing wastewater, with focus on microbial enhancement, was analysed. A review of the literature revealed that the challenge of optimization and process improvement must be addressed to enhance efficiency and clarify the mechanism of BC/HC in the AD of antibiotic-containing wastewater. This review aims to provide significant insights and details into the BC/HC-enhanced AD of antibiotic-containing wastewater.

Biodegradation of organosulfur with extra carbon source: Insights into biofilm formation and bacterial metabolic processes

Organosulfur compounds are prevalent in wastewater, presenting challenges for biodegradation, particularly in low-carbon environments. Supplementing additional carbon sources not only provides essential nutrients for microbial growth but also serves as regulators, influencing adaptive changes in biofilm and enhancing the survival of microorganisms in organosulfur-induced stress bioreactors. This study aims to elucidate the biodegradation of organosulfur under varying carbon source levels, placing specific emphasis on functional bacteria and metabolic processes. It has been observed that higher levels of carbon supplementation led to significantly improved total sulfur (TS) removal efficiencies, exceeding 83 %, and achieve a high organosulfur CH3SH removal efficiency of ~100 %. However, in the reactor with no external carbon source added, the oxidation end-product SO42- accumulated significantly, surpassing 120 mEq/m2-day. Furthermore, the TB-EPS concentration consistently increasedwith the ascending glucose concentration. The analysis of bacterial community reveals the enrichment of functional bacteria involved in sulfur metabolism and biofilm formation (e.g. Ferruginibacter, Rhodopeudomonas, Gordonia, and Thiobacillus). Correspondingly, the gene expressions related to the pathway of organosulfur to SO42- were notably enhanced (e.g. MTO increased by 27.7 %). In contrast, extra carbon source facilitated the transfer of organosulfur into amino acids in sulfur metabolism and promoted assimilation. These metabolic insights, coupled with kinetic transformation results, further validate distinct sulfur pathways under different carbon source conditions. The intricate interplay between bacteria growth regulation, pollutant biodegradation, and microbial metabolites underscores a complex network relationship that significantly contributes to efficient operation of bioreactors.

Biological degradation of organic micropollutants in GAC filters-temporal development and spatial variations

The capacity for organic micropollutant removal in granular activated carbon (GAC) filters for wastewater treatment changes over time. These changes are in general attributed to changes in adsorption, but may in some cases also be affected by biological degradation. Knowledge on the degradation of organic micropollutants, however, is scarce. In this work, the degradation of micropollutants in several full-scale GAC and sand filters was investigated through incubation experiments over a period of three years, using 14C-labeled organic micropollutants with different susceptibilities to biological degradation (ibuprofen, diclofenac, and carbamazepine), with parallel 16S rRNA gene sequencing. The results showed that the degradation of diclofenac and ibuprofen in GAC filters increased with increasing numbers of bed volumes when free oxygen was available in the filter, while variations over filter depth were limited. Despite relatively large differences in bacterial composition between filters, a degradation of diclofenac was consistently observed for the GAC filters that had been operated with high influent oxygen concentration (DO >8 mg/L). The results of this comprehensive experimental work provide an increased understanding of the interactions between microbial composition, filter material, and oxygen availability in the biological degradation of organic micropollutants in GAC filters.

New Perspectives on the Interactions between Adsorption and Degradation of Organic Micropollutants in Granular Activated Carbon Filters

The removal of organic micropollutants in granular activated carbon (GAC) filters can be attributed to adsorption and biological degradation. These two processes can interact with each other or proceed independently. To illustrate the differences in their interaction, three 14C-labeled organic micropollutants with varying potentials for adsorption and biodegradation were selected to study their adsorption and biodegradation in columns with adsorbing (GAC) and non-adsorbing (sand) filter media. Using 14CO2 formation as a marker for biodegradation, we demonstrated that the biodegradation of poorly adsorbing N-nitrosodimethylamine (NDMA) was more sensitive to changes in the empty bed contact time (EBCT) compared with that of moderately adsorbing diclofenac. Further, diclofenac that had adsorbed under anoxic conditions could be degraded when molecular oxygen became available, and substantial biodegradation (≥60%) of diclofenac could be achieved with a 15 min EBCT in the GAC filter. These findings suggest that the retention of micropollutants in GAC filters, by prolonging the micropollutant residence time through adsorption, can enable longer time periods for degradations than what the hydraulic retention time would allow for. For the biologically recalcitrant compound carbamazepine, differences in breakthrough between the 14C-labeled and nonradiolabeled compounds revealed a substantial retention via successive adsorption-desorption, which could pose a potential challenge in the interpretation of GAC filter performance.

Chemically enhanced primary treatment, microsieving, direct membrane filtration and GAC filtration of municipal wastewater: a pilot-scale study

Chemically enhanced primary treatment (CEPT) followed by microsieving and direct membrane filtration (DMF) as ultrafiltration, was evaluated on pilot scale at a municipal wastewater treatment plant. In addition, a granular activated carbon (GAC) filter downstream of DMF was evaluated for the removal of organic micropollutants. Up to 80% of the total organic carbon (TOC) and 96% of the total phosphorus were removed by CEPT with microsieving. The additional contribution of subsequent DMF was minor, and only five days of downstream GAC filtration was possible due to fouling of the membrane. Of the 21 organic micropollutants analysed, all were removed (≥ 98%) by the GAC filter until 440 bed volumes, while CEPT with microsieving and DMF removed only a few compounds. Measurements of the oxygen uptake rate indicated that the required aeration for supplementary biological treatment downstream of CEPT with microsieving, both with and without subsequent DMF, was 20-25% of that in the influent wastewater. This study demonstrated the potential of using compact physicochemical processes to treat municipal wastewater, including the removal of organic micropollutants.

Assessment of full-scale 4th treatment step for micro pollutant removal in Sweden: Sand and GAC filter combo

This study focuses on the 4th treatment step in Degeberga WWTP treatment plant, the first full scale GAC filter in Sweden installed in April 2020 for removal of micropollutants. The two GAC filters, containing two different carbon types, has operated flawlessly for three years (30,000 bed volumes) without requiring backwashing. The results indicate that the sand filter provides effective protection to the carbon filters, preventing solids from reaching the carbon and reducing the growth of organic matter. Additionally substantial biodegradation was observed for several substances. During the first year of operation, the two filters (at 8500 and 5700 bed volumes respectively) achieved >98 % removal of 24 substances. By the end of the second year (at 19,000 and 12,600 bed volumes respectively), fluconazole and sulfamethoxazole broke through completely, and the number of compounds below 80 % removal increased. The average removal of micro pollutants decreased over time. Compounds with positive charges generally exhibited higher adsorption capacities, while negatively charged compounds had lower removals. On average the investigated 24 compounds was removed by 89 % in the 4th treatment step over three years. The study suggests that biodegradation may contribute to the removal of some micropollutants in GAC filters, similar to observations made in the sand filter. Both Swiss and suggested EU regulations aim for at least an 80 % removal in micropollutant concentration. The study evaluated the performance of the filters based on this guideline and the presented technique is after a total of eight years of investigation and evaluation a proven performer. Overall, the 4th treatment combination of sand and GAC filters in WWTPs has shown promising results in removing organic micropollutants, addressing the need for efficient treatment strategies targeting these emerging pollutants. Degeberga WWTP serves as an example of successful implementation of advanced treatment for improving water quality and protecting human and aquatic health.

Assessing the potential of a membrane bioreactor and granular activated carbon process for wastewater reuse - A full-scale WWTP operated over one year in Scania, Sweden

A full-scale membrane bioreactor (MBR) with ultrafiltration, followed by granular activated carbon (GAC), was examined to determine the potential of reusing treated water as a source of drinking water or for irrigation. The major part of the bacteria removal took place in the MBR, whereas the GAC removed substantial amounts of organic micropollutants. Annual variations in inflow and infiltration resulted in a concentrated influent during summer and a diluted influent in the winter. The removal of E. coli was high throughout the process (average log removal 5.8), with effluent concentrations meeting the threshold for class B water standards for irrigation (EU 2020/741) but exceeding those for drinking water in Sweden. The total bacterial concentration increased over the GAC, indicating the growth and release of bacteria; however, E. coli concentrations declined. The effluent concentrations of metals met the Swedish criteria for drinking water. The removal of organic micropollutants decreased during the initial operation of the treatment plant, but after 1 year and 3 months, corresponding to 15,000 bed volumes, the removal increased. Maturation of the biofilm in the GAC filters might have resulted in biodegradation of certain organic micropollutants, in combination with bioregeneration. Although there is no legislation in Scandinavia with regard to many organic micropollutants in drinking water and water for irrigation, the effluent concentrations were generally in the same order of magnitude as to those in Swedish source waters that are used for drinking water production.

Key constructed wetland design features for maximized micropollutant removal from treated municipal wastewater: A literature study based on 16 indicator micropollutants

The removal of micropollutants from wastewater by constructed wetlands (CWs) has been extensively studied and reviewed over the past years. However, most studies do not specifically focus on the removal of micropollutants from the effluent of conventional wastewater treatment plants (WWTP) that still contains micropollutants, but on the removal of micropollutants from raw wastewater. Raw wastewater has a significantly different composition compared to WWTP effluent, which positively or negatively affects micropollutant removal mechanisms. To determine the optimal CW design for post-treatment of WWTP effluent to achieve additional micropollutant removal, this review analyzes the removal of 16 Dutch indicator micropollutants for post-treatment technology evaluation from WWTP effluent by different types of CWs. It was concluded that CW systems with organic enhanced adsorption substrates reach the highest micropollutant removal efficiency as a result of adsorption, but that the longevity of the enhanced adsorption effect is not known in the systems studied until now. Aerobic biodegradation and photodegradation are other relevant removal mechanisms for the studied micropollutants. However, a current knowledge gap is whether active aeration to stimulate the aerobic micropollutant biodegradation results in an increased micropollutant removal from WWTP effluent. Further knowledge gaps that impede the wider application of CW systems for micropollutant removal from WWTP effluent and allow a fair comparison with other post-treatment technologies for enhanced micropollutant removal, such as ozonation and activated carbon adsorption, relate to i) saturation of enhanced adsorption substrate; ii) the analysis of transformation products and biological effects; iii) insights in the relationship between microbial community composition and micropollutant biodegradation; iv) plant uptake and in-plant degradation of micropollutants; v) establishing design rules for appropriate hydraulic loading rates and/or hydraulic retention times for CWs dedicated to micropollutant removal from WWTP effluent; and vi) the energy- and carbon footprint of different CW systems. This review finishes with detailed suggestions for future research directions that provide answers to these knowledge gaps.

Fate of emerging contaminants in a sequencing batch reactor and potential of biological activated carbon as tertiary treatment for the removal of persisting contaminants

The study aims to understand the occurrence and removal of 20 emerging contaminants (ECs) in each unit process of a sequencing batch reactor-based wastewater treatment plant (WWTP) and explore the potential of biological activated carbon (BAC) for the treatment of residual ECs and organic matter in the secondary effluent. Analgesic-acetaminophen, anti-inflammatory drug-ibuprofen, and stimulant-caffeine were detected at high concentrations in the influent. Most of the removal was observed in the biological treatment stage in the SBR basins. The mass load of the ECs was 2.93 g/d in the secondary effluent and 0.4 g/d in the final sludge, while the total removal of the mass load of ECs till the secondary treatment stage was 93.22%. 12 of the 20 ECs were removed by more than 50%, while carbamazepine (negative removal), sulfamethoxazole, and trimethoprim were removed by less than 20%. As a polishing step and to remove residual ECs, two BAC units were studied for 11,000 bed volumes (324 days). Packed column studies on granular activated carbon were conducted, and GAC development to BAC was monitored. SEM and FTIR were used to confirm and characterize the BAC. The BAC appeared to be more hydrophobic than the GAC. The BAC removed 78.4% and 40% of the dissolved ECs and organic carbon at an optimum EBCT of 25 min. Carbamazepine, sulfamethoxazole, and trimethoprim were removed by 61.5, 84, and 52.2%, respectively. Parallel column tests revealed adsorption as an important mechanism for the removal of positively charged compounds. The results indicate that the BAC is an effective tertiary/polishing technique for removing organic and micropollutants in the secondary wastewater effluent.

Predicting and improving the microbial removal of organic micropollutants during wastewater treatment: A review

Organic micropollutants (OMPs) consist of widely used chemicals such as pharmaceuticals and pesticides that can persist in surface and groundwaters at low concentrations (ng/L to μg/L) for a long time. The presence of OMPs in water can disrupt aquatic ecosystems and threaten the quality of drinking water sources. Wastewater treatment plants (WWTPs) rely on microorganisms to remove major nutrients from water, but their effectiveness at removing OMPs varies. Low removal efficiency might be the result of low concentrations, inherent stable chemical structures of OMPs, or suboptimal conditions in WWTPs. In this review, we discuss these factors, with special emphasis on the ongoing adaptation of microorganisms to degrade OMPs. Finally, recommendations are drawn to improve the prediction of OMP removal in WWTPs and to optimize the design of new microbial treatment strategies. OMP removal seems to be concentration-, compound-, and process-dependent, which poses a great complexity to develop accurate prediction models and effective microbial processes targeting all OMPs.

Mechanistic studies on the effect of easy degradable carbon on pharmaceuticals removal in intermittently fed moving bed biofilm reactors

This study was conducted to provide for the first time systematic data on how intermittent feeding with carbon (ethanol) affects the kinetics of pharmaceuticals degradation in a moving bed biofilm reactor (MBBR). The relationship between the degradation rate constants (K) of 36 pharmaceuticals and the length of famine was tested with 12 different feast-famine ratios: For 17 pharmaceuticals, intermittent feeding increased K with a factor of 3-17, while for six other pharmaceuticals, it decreased K. Concerning intermittent loading, three dependencies were detected: 1) for some compounds (e.g., valsartan, ibuprofen, iohexol), the K decreased linearly with carbon loading, 2) for three compounds (2 sulfonamides and benzotriazole) K increased linearly with carbon loading 3) for most compounds (e.g., beta blockers, macrocyclic antibiotics, candesartan, citalopram, clindamycin, gabapentin) K had a maximum around 6 d famine (with 2 d feast). Optimizing processes on MBBRs need therefore be conducted based on a prioritization of compounds.

Microbial communities and processes in biofilters for post-treatment of ozonated wastewater treatment plant effluent

Ozonation is an established solution for organic micropollutant (OMP) abatement in tertiary wastewater treatment. Biofiltration is the most common process for the biological post-treatment step, which is generally required to remove undesired oxidation products from the reaction of ozone with water matrix compounds. This study comparatively investigates the effect of filter media on the removal of organic contaminants and on biofilm properties for biologically activated carbon (BAC) and anthracite biofilters. Biofilms were analysed in two pilot-scale filters that have been operated for >50,000 bed volumes as post-treatment for ozonated wastewater treatment plant effluent. In parallel, the removal performance of bulk organics and OMP, including differentiation of adsorption and biotransformation through sodium azide inhibition, were carried out in bench-scale filter columns filled with material from the pilot filters. The use of BAC instead of anthracite resulted in an improved removal of organic bulk parameters, dissolved oxygen, and OMP. The OMP removal observed in the BAC filter but not in the anthracite filter was based on adsorption for most of the investigated compounds. For valsartan, however, biotransformation was found to be the dominant pathway, indicating that conditions for biotransformation of certain OMP are better on BAC than on anthracite. Adenosine triphosphate analyses in the media-attached biofilms of the pilot filters showed that biomass concentrations in the BAC filter were significantly higher than in the anthracite filter. The microbial communities (16S rRNA gene sequencing) appeared to be similar with respect to the types of organisms occurring on both filter materials. Alpha diversity also exhibited little variation between filter media. Beta diversity analysis, however, revealed that filter media and bed depth substantially influenced the biofilm composition. In practice, the impact of filter media on biofilm properties and biotransformation processes should be considered for the design of biofilters.

Is In-Service Granular Activated Carbon Biologically Active? An Evaluation of Alternative Experimental Methods to Distinguish Adsorption and Biodegradation in GAC

In-service granular activated carbon (GAC) may transform into biological activated carbon (BAC) and remove contaminants through both adsorption and biodegradation, but it is difficult to determine its biodegradative capacity. One approach to understand the GAC biodegradative capacity is to compare the performance between unsterilized and sterilized GAC, but the sterilization methods may not ensure effective microbial inhibition and may affect adsorption. This study identified the ¹⁴C-glucose respiration rate as the best metric to evaluate the effectiveness of three sterilization methods: sodium azide addition, autoclaving, and γ irradiation. The sterilization protocols were refined, including continuously feeding 300 mg/L of sodium azide, three cycles of autoclaving, and 10-12 kGy of γ irradiation. Parallel minicolumn tests were conducted to identify sodium azide addition as the most broadly effective sterilization method with an insignificant effect on adsorption in most cases, except for the adsorption of anionic compounds under certain conditions. Nevertheless, this problem was solved by decreasing the azide dosage as long as it is still sufficient to provide effective microbial inhibition. This study helps to develop an approach that differentiates adsorption and biodegradation in GAC, which could be used by future studies to advance our understanding of BAC filtration.

Ozonation of 14C-labeled micropollutants - mineralization of labeled moieties and adsorption of transformation products to activated carbon

Ozonation transformation products (OTPs) are largely unknown compounds that are formed during the ozonation of micropollutants, and it is uncertain to which extent these compounds can be removed by subsequent adsorption to activated carbon. Thus, ¹⁴C-labeled micropollutants were ozonated to generate ¹⁴C-labeled OTPs, for which the adsorption of the sum of all ¹⁴C-labeled OTPs to activated carbon could be determined, based on the adsorption of the labeled carbon. Further, ¹⁴CO₂ traps were used to examine the mineralization of ¹⁴C-labeled moieties during ozonation. ¹⁴CO₂-formation revealed a partial mineralization of the ¹⁴C-labeled moieties in all compounds except for propyl-labeled bisphenol A and O-methyl-labeled naproxen. A similar degree of mineralization was noted for different compounds labeled at the same moiety, including the carboxylic carbon in diclofenac and ibuprofen (∼40% at 1 g O₃/g DOC) and the aniline ring in sulfamethoxazole and sulfadiazine (∼30% at 1 g O₃/g DOC). Aromatic ring cleavage was also confirmed for bisphenol A, sulfamethoxazole, and sulfadiazine through the formation of ¹⁴CO₂. The adsorption experiments demonstrated increased adsorption of micropollutants to powdered activated carbon after ozonation, which was connected to a decreased adsorption of dissolved organic matter (DOM). Conversely, the OTPs showed a substantial and successive decline in adsorption at increased ozone doses for all compounds, likely due to decreased hydrophobicity and aromaticity of the OTPs. These findings indicate that adsorption to activated carbon alone is not a viable removal method for a wide range of ozonation transformation products.

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.

Characterization of Ziziphus lotus’ Activated Carbon and Evaluation of Its Adsorption Potential

This study aims to prepare activated carbon from an interesting biomaterial, corresponding to the cores of Ziziphus lotus, for the first time to the best of our knowledge, according to a manufacturing process based on its chemical and thermal activation. These cores were chemically activated by sulfuric acid for 24 h and then carbonized at 500°C for 2 hours. The obtained activated carbon was characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and Brunauer–Emmett–Teller (BET) analysis. The adsorption of methylene blue (MB) on the activated carbon was evaluated, by Langmuir and Freundlich models examination, in order to explain the adsorption efficiency in a systematic and scientific way. Moreover, pseudo-first-order and pseudo-second-order kinetic models were used to identify the mechanisms of this adsorption process. The characterization results showed an important porosity (pore sizes ranging from 10 to 45 µm), a surface structure having acid groups and carboxylic functions, and a specific surface of 749.6 m²/g. Results of the MB adsorption showed that this process is very fast as more than 80% of MB is adsorbed during the first 20 minutes. In addition, increasing the contact time and temperature improves the MB removal process efficiency. Moreover, this adsorption's kinetic modeling follows the pseudo-second-order model. Furthermore, data on the adsorption isotherm showed a maximum adsorption capacity of 14.493 mg/g and fit better with the Langmuir model. The thermodynamic parameters (∆G₀, ∆S₀, and ∆H₀) indicate that the adsorption process is endothermic and spontaneous. Therefore, Ziziphus lotus can be used as a low-cost available material to prepare a high-quality activated carbon having a promising potential in the wastewater treatment.

Understanding adsorption and biodegradation in granular activated carbon for drinking water treatment: A critical review

Drinking water treatment plants use granular activated carbon (GAC) to adsorb and remove trace organics, but the GAC has a limited lifetime in terms of adsorptive capacity and needs to be replaced before it is exhausted. Biological degradation of target contaminants can also occur in GAC filters, which might allow the GAC to remain in service longer than expected. However, GAC biofiltration remains poorly understood and unpredictable. To increase the understanding of adsorption and biodegradation in GAC, previous studies have conducted parallel column tests that use one column of GAC (potentially biologically active) to assess overall removal via both adsorption and biodegradation, and one column with either sterilized GAC or biological non-adsorbing media to assess adsorption or biodegradation alone. Mathematical models have also been established to give insight into the adsorption and biodegradation processes in GAC. In this review, the experimental and modeling approaches and results used to distinguish between the role of adsorption and biodegradation were summarized and critically discussed. We identified several limitations: (1) using biological non-adsorbing media in column tests might lead to non-representative extents of biodegradation; (2) sterilization methods may not effectively inhibit biological activity and may affect adsorption; (3) using virgin GAC coated with biofilm could overestimate adsorption; (4) potential biofilm detachment during column experiments could lead to biased results; (5) the parallel column test approach itself is not universally applicable; (6) competitive adsorption was neglected by previous models; (7) model formulations were based on virgin GAC only. To overcome these limitations, we proposed four new approaches: the use of gamma irradiation for sterilization, a novel minicolumn test, compound-specific isotope analysis to decipher the role of adsorption and biodegradation in situ, and a new model to simulate trace organic adsorption and biodegradation in a GAC filter .