Removal Of Geosmin Research Articles

Pilot scale testing of advanced oxidation processes for degradation of geosmin and MIB in recirculated aquaculture

The presence of geosmin and 2-methylisoborneol (MIB) in recirculated aquaculture systems has a significant negative impact on the fish production due to poor flavour quality of produced fish and increased risk of rejection by fish processers. Advanced Oxidation Processes has a high potential for removal of geosmin and MIB in water and in this study UV/H2O2 and UV/O3 has been tested in pilot scale in real aquaculture process water. First order degradations constants were between 0.6 (UV/O3) and 1.2 (UV/H2O2) h−1 for geosmin and 1.3 (UV/O3)–1.5 (UV/H2O2) h−1 for MIB. This corresponded to average half-lives between 34–69 minutes for geosmin and between 28–32 minutes for MIB. These values were one order of magnitude higher than previously reported for degradation of geosmin and MIB in demineralised and tap-water. The slower degradation rates were caused by competitive and inhibitive processes from the water matrix. The influence of the water matrix also caused increased energy consumption with EEO values 16 to 38 times higher than previously reported for geosmin and MIB removal in tap water. Improved feasibility of removing geosmin and MIB in recirculated aquaculture systems by AOPs requires pre-treatment to minimize the impact of the water matrix on the degradation kinetics.

Removal of taste and odour from potable water by ozone and Powdered Activated Carbon (PAC)

The paper presents experimental evidence that selection and addition of an appropriate type of Powdered Activated Carbon (PAC) and alternatively or in combination ozonation of the water can be very effective in removal of both geosmin and 2-MIB from surface waters intended for supplying potable water. According to the experimental results, it was shown that the adsorptive capacity of the carbon is about five times greater in the case of geosmin when compared with 2-MIB. Furthermore, addition of ozone at doses in the range 1-3 mg/L for a period of 5-10 min can reduce odour to levels below threshold odour value.

Removal of geosmin and 2-methylisorboneol (2-MIB) in water from Zuikerbosch Treatment Plant (Rand Water) using â-cyclodextrin polyurethanes

Geosmin and 2-methylisorboneol (2-MIB) are major organic pollutants responsible for undesirable taste and odour in water. These compounds impact greatly on the aesthetic quality and general consumer acceptability of drinking water. The use of granular activated carbon (GAC) in the removal of geosmin and 2-MIB is generally ineffective since these compounds are present at very low concentrations (ngE.-1). Water treatment technologies that can remove geosmin and 2-MIB from water below human detection threshold (<10 ngE.-1) are highly sought by drinking water supplies, e.g. Rand Water. The removal of these odour-causing compounds from water samples using cyclodextrin- based nanoporous polyurethanes was investigated in our laboratory. Geosmin and 2-MIB were extracted from water samples by solid phase micro-extraction (SPME) and analysis was carried out using gas chromatography-mass spectrometry (GC-MS). Results from the analysis demonstrated that thesepolymers were highly effective in removing geosmin and 2-MIB.

Removal and transformation of odorous aldehydes by UV/H2O2

Removal of odorous aldehydes by UV/H 2 0 2 was compared to removal of geosmin and 2-MIB by the same process. Odour transformation was investigated by sensory test and by-products were monitored by a carbonyl derivatization method. Heptadienal, decadienal and nonadienal were removed faster than geosmin and 2-MIB. The primary mechanism was the direct UV photolysis in the UV/H 2 0 2 process. In sensory tests, new odours such as chalky or sweet odours were produced while the initial odour intensity of fishy/grassy-smelling aldehydes was reduced with increasing exposure time to UV/H 2 O 2 . New carbonyl compounds were detected from the UV photolysis of nonadienal and were not removed by further UV irradiation, which was thought to be related to production of new odours. Results indicate that new types of odour were produced from the oxidation of odorous aldehydes, and consequently, sensory tests coupled with chemical analysis should be considered in designing an oxidation process to control recalcitrant odorants.

Comparison of batch sorption tests, pilot studies, and modeling for estimating GAC bed life

Saint Paul Regional Water Services (SPRWS) in Saint Paul, MN experiences annual taste and odor episodes during the warm summer months. These episodes are attributed primarily to geosmin that is produced by cyanobacteria growing in the chain of lakes used to convey and store the source water pumped from the Mississippi River. Batch experiments, pilot-scale experiments, and model simulations were performed to determine the geosmin removal performance and bed life of a granular activated carbon (GAC) filter–sorber. Using batch adsorption isotherm parameters, the estimated bed life for the GAC filter–sorber ranged from 920 to 1241 days when challenged with a constant concentration of 100 ng/L of geosmin. The estimated bed life obtained using the AdDesignS model and the actual pilot-plant loading history was 594 days. Based on the pilot-scale GAC column data, the actual bed life (>714 days) was much longer than the simulated values because bed life was extended by biological degradation of geosmin. The continuous feeding of high concentrations of geosmin (100–400 ng/L) in the pilot-scale experiments enriched for a robust geosmin-degrading culture that was sustained when the geosmin feed was turned off for 40 days. It is unclear, however, whether a geosmin-degrading culture can be established in a full-scale filter that experiences taste and odor episodes for only 1 or 2 months per year. The results of this research indicate that care must be exercised in the design and interpretation of pilot-scale experiments and model simulations for predicting taste and odor removal in full-scale GAC filter–sorbers. Adsorption and the potential for biological degradation must be considered to estimate GAC bed life for the conditions of intermittent geosmin loading typically experienced by full-scale systems.

Photocatalytic Degradation of Algae and its By-product using Rotating Photocatalytic Oxidation Disk Reactor

This study examined the special technique of photocatalytic degradation (RPODisk) for removal of taste and odor causing materials, algae, and algal toxin. The RPODisk was effective for removal of these troublesome contaminants. It outperformed the fixed media and the UV irradiation for geosmin removal. The RPODisk performance was comparable to the combination of the UV irradiation with TiO₂. The RPODisk performance was affected by the rotating speed. The faster the speed was, the better the performance. The RPODisk was also effective for removal of algae and algal toxin. The algal activity reduced by 80% after 30 mins of the treatment. More toxic microcystin (MC)-LR was more difficult to remove than MC-RR. The times for 50% removal were 23.7 mins for MC-LR and 14.1 mins for MC-RR. Almost 100 mins of the contact time was required to completely remove MC-LR at the rotating speed of 260 rpm.

Removal of MIB and geosmin using granular activated carbon with and without MIEX pre-treatment

This study assessed the impact of MIEX pre-treatment, followed by either coagulation or microfiltration (MF), on the effectiveness of pilot granular activated carbon (GAC) filters for the removal of the taste and odour compounds, 2-methylisoborneol (MIB) and geosmin, from a surface drinking water source over a 2-year period. Complete removal of MIB and geosmin was achieved by all GAC filters for the first 10 months, suggesting that the available adsorption capacity was sufficient to compensate for differences in dissolved organic carbon (DOC) entering the GAC filters. Reduction of empty bed contact time (EBCT), in all but one GAC filter, resulted in breakthrough of spiked MIB and geosmin, with initial results inconclusive regarding the impact of MIEX pre-treatment. MIB and geosmin removal increased over the ensuing 12 months until complete removal of both MIB and geosmin was again achieved in all but one GAC filter, which had been pre-chlorinated. Autoclaving and washing the GAC filters had minimal impact on geosmin removal but reduced MIB removal by 30% in all but the pre-chlorinated filter, confirming that biodegradation impacted MIB removal. The impact of biodegradation was greater than any impact on GAC adsorption arising from DOC differences due to MIEX pre-treatment. It is not clear whether, at a lower initial EBCT, MIEX pre-treatment may have impacted on the adsorption capacity of the virgin GAC. The GAC filter maintained at the longer EBCT, which was also pre-chlorinated, completely removed MIB and geosmin for the period of the study, suggesting that the greater adsorption capacity was compensating for any decrease in biological degradation.

Optimising water treatment practices for the removal of Anabaena circinalis and its associated metabolites, geosmin and saxitoxins

The cyanobacterium Anabaena circinalis has the ability to co-produce geosmin and saxitoxins, compounds which can compromise the quality of drinking water. This study provides pertinent information in optimising water treatment practices for the removal of geosmin and saxitoxins. In particular, it demonstrates that pre-oxidation using potassium permanganate could be applied at the head of water treatment plants without releasing intracellular geosmin and saxitoxins from A. circinalis. Furthermore, powdered activated carbon (PAC) was shown to be an effective treatment barrier for the removal of extracellular (dissolved) geosmin and saxitoxins, with similar adsorption trends of both compounds. The relative removal of the saxitoxins compared with geosmin was determined to be 0.84 +/- 0.27, which implies that saxitoxin removal with PAC can be estimated to be approximately 60 to 100% of the removal of geosmin under equivalent conditions. Chlorine was shown to be effective for the oxidation of the saxitoxins with CT values of approximately 30 mg min l(-1) required for greater than 90% destruction of the saxitoxins.

Branched pore kinetic model analysis of geosmin adsorption on super-powdered activated carbon

Super-powdered activated carbon (S-PAC) is activated carbon of much finer particle size than powdered activated carbon (PAC). Geosmin is a naturally occurring taste and odor compound that impairs aesthetic quality in drinking water. Experiments on geosmin adsorption on S-PAC and PAC were conducted, and the results using adsorption kinetic models were analyzed. PAC pulverization, which produced the S-PAC, did not change geosmin adsorption capacity, and geosmin adsorption capacities did not differ between S-PAC and PAC. Geosmin adsorption kinetics, however, were much higher on S-PAC than on PAC. A solution to the branched pore kinetic model (BPKM) was developed, and experimental adsorption kinetic data were analyzed by BPKM and by a homogeneous surface diffusion model (HSDM). The HSDM describing the adsorption behavior of geosmin required different surface diffusivity values for S-PAC and PAC, which indicated a decrease in surface diffusivity apparently associated with activated carbon particle size. The BPKM, consisting of macropore diffusion followed by mass transfer from macropore to micropore, successfully described the batch adsorption kinetics on S-PAC and PAC with the same set of model parameter values, including surface diffusivity. The BPKM simulation clearly showed geosmin removal was improved as activated carbon particle size decreased. The simulation also implied that the rate-determining step in overall mass transfer shifted from intraparticle radial diffusion in macropores to local mass transfer from macropore to micropore. Sensitivity analysis showed that adsorptive removal of geosmin improved with decrease in activated carbon particle size down to 1 μm, but further particle size reduction produced little improvement.

Biodegradation of geosmin by a novel Gram-negative bacterium; isolation, phylogenetic characterisation and degradation rate determination

Biologically active sand filters within water treatment plants (WTPs) are now recognised as an effective barrier for the removal of geosmin. However, little is known regarding the actual microbiological processes occurring or the bacteria capable of degrading geosmin. This study reports the enrichment and isolation of a Gram-negative bacterium, Geo48, from the biofilm of a WTP sand filter where the isolate was shown to effectively degrade geosmin individually. Experiments revealed that Geo48 degraded geosmin in a planktonic state by a pseudo-first-order mechanism. Initial geosmin concentrations ranging from 100 to 1000 ng/l were shown to directly influence geosmin degradation in reservoir water by Geo48, with rate constants increasing from 0.010 h −1 ( R 2 = 0.93) to 0.029 h −1 ( R 2 = 0.97) respectively. Water temperature also influenced degradation of geosmin by Geo48 where temperatures of 11, 22 and 30 °C resulted in rate constants of 0.017 h −1 ( R 2 = 0.98), 0.023 h −1 ( R 2 = 0.91) and 0.019 h −1 ( R 2 = 0.85) respectively. Phylogenetic analysis using the 16S rRNA gene of Geo48 revealed it was a member of the Alphaproteobacteria and clustered with 99% bootstrap support with an isolate designated Geo24, a Sphingopyxis sp. previously described as degrading geosmin but only as a member of a bacterial consortium. Of the previously described bacteria, Geo48 was most similar to Sphingopyxis alaskensis (97.2% sequence similarity to a 1454 bp fragment of the 16S rRNA gene). To date, this is the only study to report the isolation and characterisation of a Gram-negative bacterium from a biologically active sand filter capable of the sole degradation of geosmin.

Submicron-sized activated carbon particles for the rapid removal of chlorinous and earthy-musty compounds

Research Article| December 01 2008 Submicron-sized activated carbon particles for the rapid removal of chlorinous and earthy-musty compounds Yoshihiko Matsui; Yoshihiko Matsui 1Division of Built Environment, Graduate School of Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan Tel.: & Fax: +81-11-706-7280; E-mail: matsui@eng.hokudai.ac.jp Search for other works by this author on: This Site PubMed Google Scholar Kenji Murai; Kenji Murai 1Division of Built Environment, Graduate School of Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan Search for other works by this author on: This Site PubMed Google Scholar Hiroshi Sasaki; Hiroshi Sasaki 1Division of Built Environment, Graduate School of Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan Search for other works by this author on: This Site PubMed Google Scholar Koichi Ohno; Koichi Ohno 1Division of Built Environment, Graduate School of Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan Search for other works by this author on: This Site PubMed Google Scholar Taku Matsushita Taku Matsushita 1Division of Built Environment, Graduate School of Engineering, Hokkaido University, N13W8, Sapporo, 060-8628, Japan Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2008) 57 (8): 577–583. https://doi.org/10.2166/aqua.2008.070 Article history Received: August 06 2007 Accepted: December 25 2007 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Cite Icon Cite Permissions Search Site Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsThis Journal Search Advanced Search Citation Yoshihiko Matsui, Kenji Murai, Hiroshi Sasaki, Koichi Ohno, Taku Matsushita; Submicron-sized activated carbon particles for the rapid removal of chlorinous and earthy-musty compounds. Journal of Water Supply: Research and Technology-Aqua 1 December 2008; 57 (8): 577–583. doi: https://doi.org/10.2166/aqua.2008.070 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Submicron-sized powdered activated carbon (PAC) was produced from a commercially available normal PAC by a bead mill. The submicron PAC decomposed dichloramine and nitrogen trichloride, impairing aesthetic quality with chlorinous odor, at a much faster rate than did normal PAC. Moreover, decomposition rates were faster for dichloramine and nitrogen trichloride than for monochloramine and free chlorine. Selective removal of chlorinous odors among chlorine compounds in a short time was thereby possible. The earthy–musty compound geosmin was also much more rapidly removed by adsorption on submicron PAC than on normal PAC. The increased removal rate was partly due to the adsorption capacity increase owing to the particle size reduction of PAC to submicron range, which accounted for 40% of the improvement of geosmin removal at a PAC contact time of 10 min. adsorption, drinking water, flavor, particles This content is only available as a PDF. © IWA Publishing 2008 You do not currently have access to this content.

Enhancing the biofiltration of geosmin by seeding sand filter columns with a consortium of geosmin-degrading bacteria

Geosmin is a secondary metabolite that can be produced by many species of cyanobacteria and Actinomycetes. It imparts a musty/earthy taste and odour to drinking water which can result in consumer complaints and a general perception that there is a problem with the water quality. As geosmin is recalcitrant to conventional water treatment, processes are sought to ensure effective removal of this compound from potable water. Biological filtration (biofiltration) is an attractive option for geosmin removal as this compound has been shown to be biodegradable. However, effective biofiltration of geosmin can be site specific as it is highly dependent upon the types of organism present and there is often an extended acclimation period before efficient removals are achieved. We report here, a novel approach to enhance the biofiltration of geosmin by seeding sand filter columns with a bacterial consortium previously shown to be capable of effectively degrading geosmin. Geosmin removals of up to 75% were evident through sand columns which had been inoculated with the geosmin-degrading bacteria, when compared with non-inoculated sand columns where geosmin removals were as low as 25%. These low geosmin removals through the non-inoculated sand columns are consistent with previous studies and were attributed to physical/abiotic losses. The presence of an existing biofilm was shown to influence geosmin removal, as the biofilm allowed for greater attachment of the geosmin-degrading consortium (as determined by an ATP assay), and enhanced removals of geosmin. Minimal difference in geosmin removal was observed when the geosmin-degrading bacteria were inoculated into the sand columns containing either an active or inactive biofilm.

Removal of geosmin and algae by ceramic membrane filtration with super-powdered activated carbon adsorption pretreatment

The musty-earthy taste and odour caused by the presence of geosmin and other compounds in tap water are major causes of consumer complaints. Although ozonation and granular activated carbon (GAC) adsorption have been practiced in water-treatment plants to remove these compounds effectively, two major problems associated with the application of these processes – formation of stringently regulated bromate ions by ozonation and unhygienic invertebrate colonisation of GAC filters – are still to be resolved. This research advanced the process of adsorption by powdered activated carbon (PAC) by reducing its particle size to the submicrometre range for microfiltration pretreatment. Adsorption pretreatment by using this super (S)-PAC removed the geosmin with vastly greater efficiency than by normal PAC. Removal was attained in a much shorter contact time and at a much lower dosage. The S-PAC was also beneficial in attenuating the transmembrane pressure rises that occurred between both physical backwashings and chemical cleanings.

Adsorptive removal of geosmin by ceramic membrane filtration with super-powdered activated carbon

Tap water free from unpleasant taste and odour is important for consumer satisfaction. We applied a super-powdered activated carbon (S-PAC) and microfiltration (MF) system to the removal of geosmin, a taste- and odour-causing compound. We used a specially pulverised PAC with a submicron particle size, much smaller than the normal PAC (N-PAC) particle size, as an adsorption pretreatment agent. MF and adsorption pretreatment with S-PAC removed geosmin with considerably greater efficiency and at a much lower dosage rate than with N-PAC. An S-PAC dosage of 2mg/L was equivalent to an N-PAC dosage of more than 20mg/L in the treatment of reagent-geosmin‐spiked feed water ‐ a dosage saving of 90%, with better removal. In experiments with feed water spiked with cultured Anabaena and geosmin, geosmin removal was attained with S-PAC at a dosage 10% of that of N-PAC. The superiority of S-PAC in removing naturally occurring geosmin from raw water was also confirmed. However, the dosage saving in this case was 75%. S-PAC also helped attenuate trans-membrane pressure increases in both physical backwash and chemical cleaning cycles. No significant trans-membrane pressure increase was observed during 4 months of MF operation with S-PAC addition, suggesting that S-PAC particles did not clog or foul the membrane.

Evaluation of Acid and Alkaline Processing to Remove Muddy Off-Flavors in Channel Catfish (Ictalurus punctatus)

ABSTRACT Conditions that optimize 2-methylisoborneol (MIB) and geosmin reduction by protein solubilization were evaluated in channel catfish. For both MIB and geosmin spiked fish, acid and alkaline solubilizations effectively (p < 0.001) reduced off-flavor. Average MIB and geosmin levels for untreated, unprocessed fish were 1.396 and 1.992 ppb, respectively. Pooled centrifuge levels for treated fish were: 0.194 ppb MIB and 0.398 ppb geosmin using citric acid; 0.104 ppb MIB and 0.258 ppb geosmin using phosphoric acid; 0.143 ppb MIB and 0.543 ppb geosmin using acetic acid; and 0.0987 ppb MIB and 0.426 ppb geosmin using alkaline (sodium hydroxide) conditions. Centrifugation did not significantly affect (p = 0.999) off-flavor removal for MIB, however it did significantly affect (p = 0.05) geosmin removal.

Kinetics Analysis on the Ozonation of MIB and Geosmin

The ozonation of 2-methylisoborneol (MIB) and geosmin was investigated in both pure and raw water. In a semi-batch reactor, a series of experiments was performed to determine the effect of pH on the ozonation of MIB and geosmin. The results show that pH has a significant effect on the ozonation of both compounds, which supports the theory that OH radical plays an important role on the destruction of MIB and geosmin. Compared with MIB, geosmin is more readily destroyed by ozonation. The ozonation kinetics follow approximately a first-order equation with respect to MIB and geosmin at the pH of 5, 7 and 9, and their rate orders of CO3 at pH 7 are 0.44 and 0.61, respectively. Ozonation of organic matters in the water decreases the ozone concentration leading to a lower removal of MIB and geosmin; at the same time, the formation of OH radical initiated by the organic matters accelerates the ozonation of MIB and geosmin. The ozonation of MIB and geosmin spiked in raw water, settled water and pure water shows that background organics have no significant effect on the removal of MIB and geosmin; hence, the simplified rate equations acquired in pure water may have potential application in real water.

Modification of granular activated carbon surface by chitosan coating for geosmin removal: sorption performances

This study presents the results of the sorption performances for geosmin removal by sorption onto granular activated carbons (GAC) manufactured from different raw materials of coconut shell and bituminous coal. The surface of GAC was modified by chitosan coating. The 90% deacetylated chitosan flakes were used for coating on GAC with the GAC: chitosan ratio of 5:1. The surface of GAC was characterised by scanning electron microscope (SEM) analysis, Fourier transform infrared spectroscopy and measurement of the pH solution of GAC samples. The sorption of geosmin onto the chitosan for both uncoated and coated GACs could be described by the Freundlich adsorption model. Data revealed that the sequence of Freundlich constant (K(F)) was chitosan coated bitominous coal (CB) > uncoated bituminous coal (UB) > chitos approximately equal to an coated coconut shell (CC) approximately equal to uncoated coconut shell (UC). The bituminous coal based GAC with chitosan coating had a maximum capacity of 23.57 microg/g which was approximately two-fold of uncoated bituminous coal based GAC. Two simplified kinetic models, pseudo-first order and pseudo-second order, were tested to investigate the sorption mechanisms. It was found that the intraparticle diffusion was a rate controlling step for the sorption and followed the pseudo-second order equation.

Effects of surface characteristics of activated carbon on the adsorption of 2-methylisobornel (MIB) and geosmin from natural water

Five powdered activated carbons (PACs), including one fruit-based, one wood-based, and three bituminous coal-based, were selected for the investigation of the effects of surface characteristics of activated carbon on the adsorption of 2-methylisobornel (MIB) and geosmin. Characterization of the carbons was performed using nitrogen adsorption, Fourier transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). All the carbons showed a broad absorption band in the 1300–1000 cm −1 region, which can be assigned to C–O stretching and O–H bending modes of alcoholic, phenolic, and carboxylic groups in FTIR spectra. The contents of O and C on the surfaces of carbons were acquired from the data of XPS analysis. Statistical analyses on the relationship between the adsorption capacities and different carbon surface parameters (O content, C O and C–O chemical group contents, the surface area, different pore volumes, iodine number and methylene blue number) were performed using Spearman rank correlation method. A good linear relationship between the adsorption capacities for MIB and geosmin and the micropore volumes was acquired. Both of iodine number and methylene blue number, the two most often used parameters for the evaluation of activated carbon quality, and other parameters, such as meso and total pore volumes, surface area, O and C–O contents were found to be insignificant in correlation with the adsorption capacities of MIB and geosmin. The volume of micropores could be used as an effective indicator for the selection of PAC for the removal of both MIB and geosmin.

Removal of geosmin and 2-methylisoborneol through biologically active sand filters

The removal of taste and odour compounds from drinking water is a constant challenge to water authorities. Although adverse odours do not present a risk to human health, their presence often leads to a misconception that the water is unsafe for drinking. 2-Methylisoborneol (MIB) and geosmin are the most common causes of earthy/musty odour, and are not easily removed by conventional treatment processes. MIB and geosmin can be removed through biologically active sand filters. Experiments were conducted using laboratory sand filter columns using sand taken from South Australian water treatment plants. Sand with a well-established biofilm taken from a 26 years old filter was capable of removing MIB and geosmin to below detection limit after 11 days of operation at an Empty Bed Contact Time (EBCT) of 15 min. Sand without an established biofilm removed 60% geosmin and 40% MIB after 154 days of operation at 15 min EBCT.

Removal of Geosmin and MIB by Biofiltration - an Investigation Discriminating Between Adsorption and Biodegradation

Geosmin and 2-methylisoborneol (MIB) are two substances causing earthy/musty odours that are difficult to remove by conventional chemical drinking water treatment. In this study removal of geosmin and MIB by biofiltration of untreated surface water was investigated using granular activated carbon (GAC) and crushed expanded clay (EC) as filter media. Biofiltration through both GAC and EC removed geosmin and MIB present at low (20 ng l−1) concentrations by at least 97 % at an empty bed contact time of 30 minutes and a temperature of 15°C. At lower temperature (6-12°C) and simultaneously lower biomass concentrations, removal efficiency was similar in the GAC but considerably lower in the EC biofilter, pointing to a second mechanism different from biodegradation. Consequently, microbial activity was suppressed with azide to enable discrimination between biodegradation and adsorption. During azide dosage, the GAC biofilters still removed geosmin and MIB nearly unaffectedly. In the EC biofilter, however, removal of both odorants ceased completely. Methylene blue adsorption confirmed that the GAC, even after almost four years of operation receiving surface water, had capacity to remove geosmin and MIB by adsorption. Since odour episodes commonly occur during the warm season when microbiological activity is high, EC constitutes a viable option as carrier medium for direct biological filtration of surface water. The additional GAC adsorption capacity however adds robustness to the removal process.