Geosmin (GSM) and 2-methylisoborneol (2-MIB) are two characteristic odor-causing compounds encountered in drinking water treatment. Often associated with the activity of microorganisms such as cyanobacteria and actinomycetes, these substances can impart distinct earthy, musty, or stale odors to drinking water even at nanogram-per-liter (ng/L) concentrations, thereby negatively affecting consumers’ sensory perception of water quality.
As GSM and 2-MIB are difficult to remove adequately through conventional coagulation, sedimentation, and filtration processes, drinking water treatment systems often require additional treatment steps—such as activated carbon adsorption, ozonation, or the use of biologically active carbon (BAC)—or combinations thereof. Among these options, powdered activated carbon (PAC) allows for flexible dosing in response to seasonal odor events, whereas granular activated carbon (GAC) is better suited for continuous operation in fixed-bed systems or activated carbon filters.
What Are GSM and 2-MIB?
What is Geosmin (GSM)?
Geosmin is an organic compound characterized by a distinct earthy, musty odor. In natural water bodies, its presence is often associated with the growth and metabolic activities of microorganisms such as cyanobacteria.
A key characteristic of GSM is its extremely low odor threshold. This means that even minute quantities in water can be perceived by humans as a distinct, unpleasant odor. Consequently, for drinking water treatment plants, the challenge lies not necessarily in the presence of large amounts of GSM, but in the fact that even very low concentrations can cause noticeable sensory issues.
What is 2-MIB?
2-Methylisoborneol (2-MIB) is a common source of earthy and musty odors in drinking water. Since 2-MIB and GSM frequently co-occur, they are typically monitored and treated together as a group of characteristic taste and odor (T&O) compounds in practical water treatment processes.
Both GSM and 2-MIB have low odor detection thresholds. Studies have shown that, in certain instances, concentrations as low as approximately 10 ng/L—or even lower—can trigger consumer complaints regarding the taste and odor of the water.
How Does Activated Carbon Remove GSM and 2-MIB?
Conventional drinking water treatment primarily relies on coagulation, sedimentation, and filtration to remove suspended particles, algal cells, and other contaminants. However, once GSM and 2-MIB are present in water in a dissolved state, the challenge extends beyond the simple removal of algal cells; standard solid-liquid separation processes are often ineffective at removing these dissolved odor-causing compounds.
This is where activated carbon comes into play. Characterized by an extensive network of micropores and mesopores as well as a vast internal surface area, activated carbon utilizes mechanisms such as physical adsorption to transfer GSM and 2-MIB from the aqueous phase onto the carbon surface and into its internal pores, where they are adsorbed and retained. Consequently, in practical drinking water treatment, activated carbon typically serves as a barrier for advanced treatment and odor control, rather than simply replacing upstream conventional treatment processes.
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However, the actual process in water treatment is more complex than this simplified model suggests. Activated carbon requires not only a sufficient specific surface area but also a pore structure that matches the size and properties of the target molecules. Recent studies indicate a strong correlation between micropore volume and the adsorption capacity for taste- and odor-causing compounds such as GSM and 2-MIB.
Furthermore, during prolonged operation of activated carbon filters, a biofilm may form on the carbon surface, causing the system to gradually exhibit characteristics of biologically active carbon (BAC). Consequently, in long-term GAC system operations, the removal of GSM and 2-MIB does not necessarily rely solely on the initial physical adsorption capacity.
PAC & GAC for GSM and 2-MIB Removal
Both PAC and GAC can be used for the removal of GSM and 2-MIB, but they are suited to different process scenarios.
PAC for GSM and 2-MIB
PAC is a flexible option when GSM and 2-MIB levels in the water source exhibit significant seasonal fluctuations. For instance, during algal blooms, the PAC dosage can be adjusted based on the concentrations of GSM and 2-MIB in the raw water and experimental findings.
The advantage of PAC lies in the ability to rapidly adjust dosage without the need for large, permanent GAC contactors. However, PAC also has distinct limitations. Since PAC must ultimately be separated from the water, the system typically requires integration with coagulation, sedimentation, or filtration processes. Furthermore, the actual performance of PAC depends heavily on the type of carbon, particle size, contact time, and the level of natural organic matter (NOM) in the water.
PAC Parameters:
| Parámetro | Valor típico |
|---|---|
| Materia prima | Coal-based |
| Índice de yodo | 900-1100 mg/g |
| Adsorción de azul de metileno | 150–200 mg/g |
| Tamaño de las partículas | 200 mesh (≥90% through 75 μm, −325 mesh) |
| Contenido en cenizas | ≤5% |
| Humedad | ≤10% |
| pH | 8–11 |
| Surface area | 1000–1200 m²/g |
| Dosage (GSM/2-MIB) | 5–30 mg/L, typical 10–20 mg/L |
| GSM / 2-MIB removal | >90% (GSM); 80–95% (2-MIB) |
GAC for GSM and 2-MIB
For drinking water treatment plants facing persistent taste and odor (T&O) issues, granular activated carbon (GAC) is generally well-suited for establishing a continuous fixed-bed treatment system. GAC can be installed in dedicated activated carbon filters, contactors, or advanced treatment units. As operation continues, biologically active carbon (BAC) may develop alongside the adsorption process, enabling the removal of GSM and MIB through a combination of adsorption and biodegradation.
| Parámetro | Valor típico |
|---|---|
| Materia prima | Bituminous coal |
| Índice de yodo | 1000–1100 mg/g |
| Tamaño de las partículas | 8×30 mesh, 12×40 mesh (coconut) |
| Contenido en cenizas | ≤4% (coconut), ≤12% (coal-based) |
| Humedad | ≤5% |
| Densidad aparente | 450–520 g/L (coconut) |
| Surface area | 1050–1150 m²/g |
| Loading rate | 5–10 m/h |
| Service life (T&O) | 6–18 months (depending on water quality) |
| GSM / 2-MIB removal | >95% before breakthrough (fresh carbon) |
Conclusión
So in water treatment and drinking water purification processes, activated carbon serves a critical function in odor and taste contaminant control. It removes trace-level earthy-musty contaminants—including geosmin (GSM), 2-methylisoborneol (2-MIB), residual organic matter and odor-causing impurities—from raw and treated water, effectively improving water taste and mitigating common operational issues such as unpleasant earthy and musty odors triggered by microbial metabolites.
If you are looking for activated carbon solutions for GSM and 2-MIB removal in municipal water treatment and water purification units, please contact our technical experts for more customized, cost-effective filtration solution.
