Geosmin Degradation Research Articles

Radiolytic degradation of 2-methylisoborneol and geosmin in water: Reactive radical species and transformation pathways

Water radiolysis can serve as a useful tool to study the degradation of organic pollutants in water. Manipulation of the radiolytic system enables the selective production of reactive species (RS) with known yields. Our aim was to explore the effects of the radiolytically produced RS on commonly occuring water taste and odor compounds (T&O), 2-methylisoborneol (MIB) and geosmin (GSM). Observed degradation rate constants differ among experimental conditions/dominant RS and follow the order: HO•>H•>>eaq−>(O2−•/HO2•), ranging from 0.002 Gy−1 (O2−•/HO2•) to 0.083 Gy−1 (HO•) for MIB and from 0.006 Gy−1 (O2−•/HO2•) to 0.068 Gy−1 (HO•) for GSM. Degradation by HO• was very efficient, requiring 1.14 and 1.49 μmoles of HO• for each degraded μmole of MIB and GSM, respectively. The oxidative degradation of MIB by HO• proceeds with the production of carbonyl- and hydroxyl‑containing transformation products (TPs), leading to linear structures, while for GSM degradation proceeds with ring opening, followed by formation of carboxyl-groups. Fewer TPs are produced by HO2•, while degradation with H• led to numerous TPs, via dehydroxylation, dehydration and ring opening. Degradation with eaq−, yielded demethylated and rearranged TPs with formation of double bonds.

Comparison of OH and NaClO on geosmin degradation in the process of algae colonies inactivation at a drinking water treatment plant

• OH equipment was developed to install in drinking water system of 12000 m 3 /day. • OH degraded GSM in the process of algae colonies inactivation within 20 s. • OH inactivated algae colonies to individual intact ones without IOM release. • OH mineralized GSM through the crucial ring opening reactions. • All water quality and DBP indexes satisfied the limits of Chinese Standards. Excessive proliferation of cyanobacteria blooms resulting in metabolic musty-earthy odor materials such as geosmin (GSM) pose potential risks to aquatic ecosystems and human health. In this paper, a high-yield OH equipment was developed to be installed in drinking water treatment system with a capacity of 12,000 m 3 /day in the Xiang’an Water Plant, Xiamen, China, and the comparison of OH and NaClO on GSM degradation in the process of algae colonies inactivation were studied. The results showed that with OH inactivation at 1.0 mg/L within 20 s algae colonies were scattered to individual algae that still had intact shape, while with the NaClO inactivation at 2 h algae still mainly existed as colonies form but were deformed and ruptured due to extensive damage of cell membrane. After the coagulation sedimentation with injection of OH at 1.0 mg/L and the sand filtration at 0.5 mg/L, the GSM were both degraded to below 10 ng/L (Chinese standard limit) within only 20 s, while the NaClO degraded GSM slightly until 2 h later. Based on the intermediates analyses with mass spectra database, pathways of GSM degradation by OH or NaClO were obtained. With OH disinfection at 0.5 mg/L, all water quality and disinfection by-product indexes satisfied the limits of Chinese Standards. Therefore, the OH method based on the strong ionization discharge showed great prospect for large-scale industrial application in inactivation of algae colonies meanwhile degradation of odorous material GSM.

Development of a liquid chromatography atmospheric pressure chemical ionization mass spectrometry method for determining off-flavor compounds and its application toward marine recirculating aquaculture system monitoring and evaluation of aeration as a depuration approach

The off-flavor compounds geosmin and 2-methylisoborneol (2-MIB) are well-known to impact the quality of farmed freshwater fish species, but little is known about off-flavors in marine aquaculture. To begin addressing this knowledge gap, a method for determining geosmin and 2-MIB using LC with atmospheric pressure chemical ionization (APCI) MS detection was developed. While 2-MIB was readily detected using LC-APCI/MS, geosmin exhibited on-column degradation that was independent of column chemistry and could not be eliminated. Optimized conditions were identified that balanced the separation and ionization efficiency of 2-MIB and geosmin while minimizing geosmin degradation, but the overall method sensitivity for geosmin was reduced by the on-column losses. The method was used with direct aqueous injections to determine the volatilization rates of geosmin and 2-MIB at ppb levels during aeration under laboratory conditions in both salt water and pure water to simulate marine and fresh water aquaculture, respectively. The volatilization rates of both compounds were 30% faster in salt water than in fresh water with or without aeration, but aeration was found to enhance the rate by a factor of 2.5 in both water types. The LC-APCI/MS method was combined with stir bar sorptive extraction (SBSE) to achieve greater sensitivity for determining off-flavors in recirculating aquaculture system (RAS) water. Using SBSE-LC-APCI/MS, the LODs for geosmin and 2-MIB were 70 ng/kg (part per trillion) and 6 ng/kg, respectively. The on-column losses resulted in a relatively high LOD for geosmin that renders this method unsuitable for determining geosmin at the low ng/kg levels expected in RAS. SBSE using both grab water samples and an in-situ diving unit were used to evaluate 2-MIB levels in the culture water of two separate marine RAS that were supporting the growth of European sea bass but had differing levels of water treatment. 2-MIB was readily detected using both SBSE approaches in the RAS with less sophisticated treatment when the animal stocking density was at its highest (50 kg/m3) but was not detected in the more sophisticated RAS regardless of stocking density. Geosmin was not detected in either system, but the results were inconclusive given its higher LOD. These limited results suggest that the anaerobic water treatment components, present only in the more sophisticated RAS, maintained the level of 2-MIB below the LOD.

Effect of the wavelength on the pathways of 2-MIB and geosmin photocatalytic oxidation in the presence of Fe-N co-doped TiO2

In this study, 2-methylisoborneol (2-MIB) and geosmin (GSM) were degraded through photocatalytic oxidation process. For 2-MIB degradation under visible light irradiation, the highest removal rate was obtained in the presence of the 0.001% Fe – 0.5% N co-doped TiO2 calcined at 500 °C. The removal rates of 2-MIB and GSM were significantly affected by the wavelength of the lamp used during the oxidation, with the effective order of 254 nm > 365 nm > 420 nm > 475 nm. Higher steady-state concentration of ·OH, which was obtained at shorter wavelength, led to higher T&O removal efficiency. The degradation intermediates of 2-MIB and GSM during the photocatalytic oxidation, including a series of alcohols, aldehydes and ketones, were associated with the dehydration and ring-opening pathways. In most cases, for 2-MIB photocatalytic degradation, intermediates with ring structure were yielded under visible light, while the chain compounds tended to be generated under UV irradiation. However, intermediate products of GSM were not varied from each other significantly when the wavelength changed. The abundances of the GSM degradation intermediates were larger than those of the 2-MIB degradation intermediates because GSM was easier to be oxidized than 2-MIB. The apparent degradation rates of 2-MIB and GSM in real water were lower than those in deionized water, and the humic substances in real water were decomposed into low-molecular weight substances.

Removal of 2-MIB and geosmin by electrogenerated persulfate: Performance, mechanism and pathways

In this study, the degradation of 2-methylisoborneol (2-MIB) and geosmin (GSM) was evaluated by electrochemical oxidation (EO) using boron-doped diamond (BDD) electrode. Both 2-MIB and GSM could be degraded efficiently in sulfate electrolyte compared to inert nitrate or perchlorate electrolytes, implying that in-situ generated persulfate may be responsible for contaminants degradation. The observed linear relationship between 2-MIB (GSM) degradation rates and persulfate generation rates further proved that the in-situ generated persulfate enhanced 2-MIB (GSM) degradation. Moreover, a divided electrolytic cell was employed to investigate the effect of cathodic reactions on contaminants degradation and persulfate generation, and results confirmed that both anodic and cathodic reactions participated in 2-MIB (GSM) degradation. High current density and low solution pH were found to be favorable for 2-MIB and GSM degradation. The degradation intermediates were identified and the possible pathways of 2-MIB and GSM degradation were proposed. This study indicated that the EO process with BDD anode could be considered as a potential alternative for the removal of 2-MIB and GSM.

Photocatalytic degradation of geosmin by Pd nanoparticle modified WO3 catalyst under simulated solar light

Geosmin (GSM), a typical musty odor compound, causes undesirable earthy off-flavors and is a serious concern in the drinking water and aquaculture industries. Here, we employed a novel palladium (Pd) modified tungsten trioxide (WO3) photocatalyst to remove GSM from water under simulated solar light. We also investigated the effect of catalyst loading, GSM initial concentration, light intensity, pH and dissolved oxygen (DO) for GSM destruction. The Pd/WO3 catalyst almost completely degraded GSM within 20min under optimum conditions, with GSM degradation conforming to a pseudo-first-order reaction. This catalyst also exhibited a superior reuse performance. Photocatalytic degradation rate of GSM decreased in the presence of hydroxyl radical trapping reagent, implying oxidation by hydroxyl radicals plays a very significant role in the photo-degradation mechanism. Some possible intermediates were also identified. These results could provide helpful information for constructing a new efficient system for rapid GSM removal under solar light.

Removal of 2-MIB and geosmin using UV/persulfate: Contributions of hydroxyl and sulfate radicals

2-methylisoborneol (2-MIB) and geosmin are two odor-causing compounds that are difficult to remove and the cause of many consumer complaints. In this study, we assessed the degradation of 2-MIB and geosmin using a UV/persulfate process for the first time. The results showed that both 2-MIB and geosmin could be degraded effectively using this process. The process was modeled based on steady-state assumption with respect to the odor-causing compounds and either hydroxyl or sulfate radicals. The second order rate constants for 2-MIB and geosmin reacting with the sulfate radical (SO4−) were estimated to be (4.2 ± 0.6) × 108 M−1s−1 and (7.6 ± 0.6) × 108 M−1s−1 respectively at a pH of 7.0. The contributions of the hydroxyl radical (OH) to 2-MIB and geosmin degradation were 3.5 times and 2.0 times higher, respectively, than the contribution from SO4− in Milli-Q water with 2 mM phosphate buffer at pH 7.0. The pseudo-first-order rate constants (kos) of both 2-MIB and geosmin increased with increasing dosages of persulfate. Although pH did not affect the degradation of 2-MIB and geosmin directly, different scavenging effects of hydrogen phosphate and dihydrogen phosphate resulted in higher values of kos for both 2-MIB and geosmin in acidic condition. Bicarbonate and natural organic matter (NOM) inhibited the degradation of both 2-MIB and geosmin dramatically through consuming OH and SO4− and were likely to be the main radical scavengers in natural waters when using UV/persulfate process to control 2-MIB and geosmin.

Parameters Influencing the Photocatalytic Degradation of Geosmin and 2-Methylisoborneol Utilizing Immobilized TiO2

Geosmin and 2-methylisoborneol (MIB) are taste and odor compounds that negatively impact potable water and freshwater aquaculture species. Conventional water treatment methods are generally ineffective for the removal of these compounds. Prior studies using TiO2 photocatalysts have shown promising results, but are primarily limited to laboratory scale batch slurry systems. Immobilization of TiO2 is essential for the effective scale-up and conversion to a flow through system. In this study, the degradation of MIB and geosmin from laboratory spiked and naturally tainted water samples was demonstrated utilizing an immobilized TiO2 photocatalyst. The benefits of TiO2 photocatalysis, in comparison to photolysis, are discussed. Further, the influence of pH on the degradation rates was analyzed to optimize process location in an aquaculture production facility. Geosmin degradation reached a maximum near a pH of 6. While MIB degradation is highest at low pH, there is an inflection in this trend above the pH at which TiO2 has a zero surface charge. Photocatalytic processing is recommended to occur after nitrification and before base addition to maximize MIB and geosmin removal rates. The findings of this work have been incorporated into a larger project, which assesses the continuous operation of TiO2 photocatalyst in a recirculating aquaculture system.

Geosmin degradation by seasonal biofilm from a biological treatment facility

Initial geosmin degradation was closely related to water temperature and natural geosmin concentration of sampling environment. Here, for the first time, we evaluated the biodegradation of geosmin by microorganisms in biofilm from biological treatment unit of actual potable water treatment plant. At an initial geosmin concentration of 2,500 ng/l, efficient geosmin removal was confirmed throughout the year. Furthermore, in the presence of mixed musty odor compounds (geosmin and MIB) as carbon source, geosmin degradation was enhanced compared to sole carbon source (geosmin alone). PCR-DGGE analysis revealed a rich community structure within the biofilm during rapid geosmin removal period, April. PCA revealed that the significant change in bacterial communities occurred from day 1 to day 2. Two novel geosmin-degrading bacteria were isolated from the biofilm of the biological treatment unit of Kasumigaura Water Purification, Waterworks Department, Japan. They belong to Methylobacterium sp. and Oxalobacteraceae bacterium, respectively. These studies provide further insights into the unknown microbiological processes that occur during the biological removal of geosmin through water treatment and could facilitate the geosmin bioremediation in contaminated habitats.

Isolation and identification of novel geosmin-degrading bacteria

Three novel geosmin-degrading bacteria were isolated from the sediments of Lake Kasumigaura, Japan. All strains were identified as Acinetobacter spp. by 16S rRNA gene sequence analysis and can biodegrade geosmin at an initial geosmin concentration of 2 mg/L after 2 days. Furthermore, at an initial geosmin concentration of 40 microg/L, geosmin removal was more than 68per cent by GSM-2 strain, and the degradation mechanism followed a pseudo-first-order mode. A rate constant of 0.026 reveals rapid geosmin degradation. This is the first report on geosmin degradation by by Acinetobacter spp.

Electrochemical degradation of geosmin using electrode of Ti/IrO 2–Pt

Electrochemical degradation of geosmin was assessed at a typical anode Ti/IrO 2–Pt, as a treatment method in musty odor compounds. The influences of dosage of NaCl, current density, initial geosmin concentration and initial solution pH on electrochemical geosmin degradation were investigated. HOCl formed during electrolysis would play an important role on the oxidation of geosmin. For the Ti/IrO 2–Pt anode, geosmin concentration decreased from around 600 to 8 ng/L after 60 min of electrolysis with 3.0 g/L NaCl as supporting electrolyte at the current density of 40 mA/cm 2. Moreover, efficient degradation of geosmin solution with different initial pH was found and the electrochemical oxidation ability of Ti/IrO 2–Pt anode will not drop after serviced for long hours under the present experimental condition. These results suggested that electrochemical degradation would be a promising treatment for effective and rapid removal of musty odor compounds.

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.

Cooperative biodegradation of geosmin by a consortium comprising three gram-negative bacteria isolated from the biofilm of a sand filter column

To isolate and identify bacteria from a sand filter column capable of degrading the taste and odour compound, geosmin. In doing so, to investigate if these organisms degrade geosmin either individually or if an alternative mechanism is utilized. Geosmin-degrading bacteria from a biologically active sand filter column were enriched by their growth in a minimal medium supplemented with geosmin as the sole carbon source. By day 51, 21.7 mg l(-1) of geosmin had been degraded as determined by solid-phase microextraction gas chromatography/mass spectrometry, and was accompanied by a 2.12 log(10) increase in active bacterial numbers as measured using the BacLight(TM) bacterial viability kit and flow cytometric enumeration. During the onset of geosmin degradation, the predominance of three bacteria, most similar to previously cultured species of Sphingopyxis alaskensis, Novosphingobium stygiae and Pseudomonas veronii based on 16S rRNA gene sequences was detected by denaturing gradient gel electrophoresis. Subsequent isolation of these organisms revealed that degradation of geosmin, when present as either the sole carbon source (ranging from 40 ng l(-1) to 20 mg l(-1)) or when spiked into sterile reservoir water (37 and 131 ng l(-1)), occurred only when all three isolates were present. None of the isolates was shown to be capable of degrading geosmin either individually or in any combination of two. This study has reported, for the first time, the cooperative degradation of geosmin by a consortium comprising three gram-negative bacteria isolated from a biologically active sand filter column. These results are important for researchers currently employing molecular-based approaches to further understand the biodegradation of geosmin by bacteria, as such studies may be complicated by the discovery of geosmin degradation occurring by a consortium. This study also advances the knowledge surrounding the types of bacteria capable of degrading the taste and odour compound, as investigations to date regarding this are limited.

Biological Control: Isolation and Bacterial Oxidation of the Taste‐and‐Odor Compound Geosmin

Research has revealed that Bacillus species readily degrade geosmin. Bacillus cereus ATCC 9139 and Bacillus subtilus strains were found to be as effective as Bacillus cereus strain 10876. This last organism had been previously reported as the best strain for geosmin degradation in both laboratory and field studies.