Geosmin Concentrations Research Articles

Effect of stocking biomass on solids, phytoplankton communities, common off-flavors, and production parameters in a channel catfish biofloc technology production system

The effect of initial channel catfish (Ictalurus punctatus, Rafinesque, 1818) fingerling biomass (1.4, 1.8, or 2.3 kg m−3) on phytoplankton communities, common off-flavours and stocker catfish production parameters was evaluated in biofloc technology production tanks. Stocker catfish size (145.5–172.6 g fish−1) at harvest did not differ among treatments, but net yield increased linearly as initial biomass increased (R2 = 0.633). Mean total feed consumption increased linearly with initial catfish biomass (R2 = 0.656) and ranged from 10.7 to 15.8 kg m−3. Total suspended solids (TSS) in all treatments increased linearly with total feed addition, and high TSS appeared to impact negatively daily feed consumption. Initial phytoplankton populations were dominated by small colonial green algae and diatoms, and later transitioned to populations dominated by a small, filamentous cyanobacteria and diatoms. Low, variable concentrations of 2-methylisoborneol and geosmin were present in biofloc tank water during most of the study and two tanks yielded catfish with 2-methylisoborneol or geosmin concentrations that might be classified as off-flavour. One isolate of actinomycete was isolated sporadically from some biofloc tanks, but its abundance was not correlated with 2-methylisoborneol concentration in tank waters. The microbial sources of 2-methylisoborneol and geosmin in biofloc tanks remain unidentified.

UV-based advanced oxidation processes for the treatment of odour compounds: Efficiency and by-product formation

The occurrence of the taste and odour compounds geosmin and 2-methyl isoborneol (2-MIB) affects the organoleptic quality of raw waters from drinking water reservoirs worldwide. UV-based oxidation processes for the removal of these substances are an alternative to adsorption and biological processes, since they additionally provide disinfection of the raw water. We could show that the concentration of geosmin and 2-MIB could be reduced by VUV irradiation and the combination of UV irradiation with ozone and hydrogen peroxide in pure water and water from a drinking water reservoir. The figure of merit EE/O is an appropriate tool to compare the AOPs and showed that VUV and UV/O3 yielded the lowest treatment costs for the odour compounds in pure and raw water, respectively. Additionally, VUV irradiation with addition of ozone, generated by the VUV lamp, was evaluated. The generation of ozone and the irradiation were performed in a single reactor system using the same low-pressure mercury lamp, thereby reducing the energy consumption of the treatment process. The formation of the undesired by-products nitrite and bromate was investigated. The combination of VUV irradiation with ozone produced by a VUV lamp avoided the formation of relevant concentrations of the by-products. The internal generation of ozone is capable to produce ozone concentrations sufficient to reduce EE/O below 1 kWh m−3 and without the risk of the formation of nitrite or bromate above the maximum contaminant level.

Evaluation of Off‐Flavor in Pond‐Raised Channel Catfish following Partial Crop Harvest

AbstractPonds used to raise channel catfish Ictalurus punctatus in the southeastern United States often contain more food‐sized catfish than processors can accept at one time. Fish remaining after initial harvest are returned to the pond and harvested again as soon as possible based upon processor demands. Some catfish farmers report that catfish crops initially declared “on‐flavor” appear to develop off‐flavors soon after the first harvest, which postpones harvest of the remaining population and delays subsequent production. We conducted a 9‐month study on a commercial catfish farm in northwest Mississippi to determine whether fish systematically develop off‐flavors after partial fish harvest and, if so, the type and origin of the flavor. Channel catfish and water samples were obtained from 12 ponds before initial harvest and then at intervals for 2 weeks after harvest. Water and catfish fillet samples were analyzed for geosmin and 2‐methylisoborneol (MIB). Phytoplankton were identified and counted microscopically. Catfish fillets were also used in sensory analysis to determine quality and intensity of off‐flavor. In most ponds, MIB levels decreased or remained unchanged in pond water after the first seining while geosmin levels remained very low (<10 ng/L) in all ponds. Analysis indicated that mean MIB concentrations in catfish fillets either decreased or were unchanged after the initial harvest. Similar results were found for geosmin concentrations in catfish fillets. There was also no systematic change in fillet flavor quality as determined by sensory analysis. The MIB‐producing cyanobacterium Planktothrix perornata was found in only three ponds, and the abundance of P. perornata decreased in two ponds after initial harvest and transiently increased in the third pond. Overall, we found no systematic changes in fish flavor quality after partial fish harvest and no indication that harvest activities changed ecological conditions that would cause an increase in odor‐producing cyanobacteria.

Removal of geosmin and 2-methylisoborneol during managed aquifer recharge: batch and column studies

Managed aquifer recharge is a robust barrier in the multi-barrier approach to supply safe drinking water. The removal performance of gesomin and 2-methylisoborneol through managed aquifer recharge was investigated using batch and column experiments. Batch experiments were carried out to investigate the removal of geosmin and 2-methylisoborneol (MIB) in the presence of different types of biodegradable organic matter using different types of water. Five different types of water spiked with 70–293 ng/L of geosmin and MIB were used in batch reactors, and complete removal of geosmin and MIB (down to the detection limit) was achieved in all cases. Soil column studies showed that biodegradation contributed to the removal of geosmin and MIB by 23 and 31%, respectively (empty bed contact time: 17 hours). The removal of geosmin and MIB appeared to be influenced more by microbial activity than the initial concentrations of geosmin and MIB. Adsorption was found to be the dominant mechanism (major role) followed by biodegradation (minor role) for geosmin and MIB removals during soil passage. Managed aquifer charge can therefore be used as a robust barrier to remove taste and odor (T&O) causing compounds.

Determination of the Microbial Origin of Geosmin in Chinese Liquor

Geosmin is the major cause of the common earthy off-flavor in light-aroma type Chinese liquor and, thus, highly detrimental to the aromatic quality. To find out its origin, the evolving process of geosmin in light-aroma type liquor making was monitored, and microbial analysis of Daqu containing geosmin was carried out. The results showed that geosmin appeared in all the fermented sorghums at different fermentation periods. About 57% geosmin in the fermented sorghums was distilled into liquor. During the distillation process, the peak of geosmin concentration appeared when alcohol content was 50-60% vol. More importantly, high geosmin content was observed during the Daqu-making process. Furthermore, five Streptomyces strains were isolated from different types of Daqu used for the fermentation of light-aroma type liquor. All of them produced only geosmin as the main volatile metabolite but no 2-methylisoborneol (2-MIB). It appears that microorganisms developing in Daqu are responsible for the presence of geosmin in liquor. Because of the relatively low detection threshold estimated at 110 ng/L in 46 vol % hydroalcoholic solution, the presence of geosmin in Daqu may pose a risk for Chinese liquor producers.

Modelling geosmin concentrations in three sources of raw water in Quebec, Canada

The presence of off-flavour compounds such as geosmin, often found in raw water, significantly reduces the organoleptic quality of distributed water and diverts the consumer from its use. To adapt water treatment processes to eliminate these compounds, it is necessary to be able to identify them quickly. Routine analysis could be considered a solution, but it is expensive and delays associated with obtaining the results of analysis are often important, thereby constituting a serious disadvantage. The development of decision-making tools such as predictive models seems to be an economic and feasible solution to counterbalance the limitations of analytical methods. Among these tools, multi-linear regression and principal component regression are easy to implement. However, due to certain disadvantages inherent in these methods (multicollinearity or non-linearity of the processes), the use of emergent models involving artificial neurons networks such as multi-layer perceptron could prove to be an interesting alternative. In a previous paper (Parinet et al., Water Res 44: 5847-5856, 2010), the possible parameters that affect the variability of taste and odour compounds were investigated using principal component analysis. In the present study, we expand the research by comparing the performance of three tools using different modelling scenarios (multi-linear regression, principal component regression and multi-layer perceptron) to model geosmin in drinking water sources using 38 microbiological and physicochemical parameters. Three very different sources of water, in terms of quality, were selected for the study. These sources supply drinking water to the Québec City area (Canada) and its vicinity, and were monitored three times per month over a 1-year period. Seven different modelling methods were tested for predicting geosmin in these sources. The comparison of the seven different models showed that simple models based on multi-linear regression provide sufficient predictive capacity with performance levels comparable to those obtained with artificial neural networks. The multi-linear regression model (R(2) = 0.657, <0.001) used only four variables (phaeophytin, sum of green algae, chlorophyll-a and potential Redox) in comparison with ten variables (potassium, heterotrophic bacteria, organic nitrogen, total nitrogen, phaeophytin, total organic carbon, sum of green algae, potential Redox, UV absorbance at 254 nm and atypical bacteria) for the best model obtained with artificial neural networks (R(2) = 0.843).

Process Window Determination for Biofiltration by the Taguchi Method

Raw water from the Yantian Reservoir in Southern China was used for this study. Several process parameters of biofiltration, temperature, media, empty bed contact time, ozone dosage and concentration of geosmin and MIB, were adopted in order to determine their effects. Experiments were conducted using the Taguchi method and 9 experiments were needed to obtain the best process parameter settings and parameter effects. The results of these experiments indicate the use of biological filtration as a method of geosmin and MIB removal, to be satisfactory. In addition, the results show that temperature impacts the removal rate of both geosmin and MIB. Useful insights into the effects of the filter media on such as, empty bed contact time, ozone dosage and concentration of geosmin and MIB were also obtained.

Chemical and Sensory Quantification of Geosmin and 2-Methylisoborneol in Rainbow Trout (Oncorhynchus mykiss) from Recirculated Aquacultures in Relation to Concentrations in Basin Water

Globally, aquaculture systems with water recirculation experience increasing problems with microbial taste and odor compounds (TOCs) such as geosmin and 2-methylisoborneol (MIB). This study investigated the content of geosmin and MIB in water and the flesh of 200 rainbow trouts from eight recirculated aquaculture systems in Denmark. TOC content in the fish flesh was measured by a dynamic headspace extraction method and was evaluated by a sensory panel. The results showed significant correlations between TOC content in water and fish and between chemical analysis and sensory perception. When geosmin exceeded 20 ng/L in the water, 96% of the fish had an intense muddy flavor, but below 10 ng geosmin/L, 18% of the fish (only 3% in special depuration ponds) had an intense muddy flavor. The results indicate that TOC levels <10 ng/L will ensure that a negligible portion of the fish obtains an unpalatable taste and flavor due to TOCs.

The management of undesirable cyanobacteria blooms in channel catfish ponds using a constructed wetland: Contribution to the control of off-flavor occurrences

An exploratory study on the management of undesirable cyanobacteria blooms with respect to off-flavor problems using an integrated vertical-flow constructed wetland (CW) was performed at a small commercial-scale channel catfish farm from 2004 to 2007. The results of the three-year experiment indicated that water treatment by the CW could reduce the possibility of dominance by undesirable cyanobacteria species that often cause off-flavor problems. A detailed investigation in 2007, showed that the concentrations of geosmin, MIB (2-methylisoborneol), and β-cyclocitral in the water of the recirculating pond (4.3 ng L −1, U.D. (undetected) and 0.2 ng L −1, respectively) treated by the CW were significantly lower than those in the control pond (152.6 ng L −1, 63.3 ng L −1 and 254.8 ng L −1, respectively). In addition, the relationships among the cyanobacteria species, the off-flavor compounds and ten environmental variables were explored by canonical correspondence analysis (CCA). The results showed that Oscillatoria sp., Oscillatoria kawamurae and Microcystis aeruginosa were the main sources of off-flavor compounds in the catfish ponds. The successful manipulation of undesirable cyanobacteria species potentially resulted in lower concentrations of odorous compounds in the water of the recirculating pond. An investigation of the concentrations of geosmin and MIB in catfish fillets showed that the levels of odorous compounds were below the OTC (odor threshold concentration) values in the recirculating pond but were above the OTC values from July to October in the control pond. Water recycling by the CW could potentially be one of the best management practices to control off-flavor occurrences in aquaculture.

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.

Spatio-temporal distribution of cell-bound and dissolved geosmin in Wahnbach Reservoir: Causes and potential odour nuisances in raw water

In many lakes and reservoirs, problems caused by off-flavours are known to be particularly associated with the occurrence of planktonic and benthic cyanobacteria. Frequently observed objectionable taste and odorous products of cyanobacteria are geosmin and 2-methylisoborneol. Investigations focused on the littoral zone of Wahnbach Reservoir (Germany) revealed that benthic cyanobacteria were present in this oligotrophic drinking water reservoir. Benthic cyanobacteria were found in the depth horizon between 1.75 m and 11 m, particularly on south-exposed slopes. This spatial distribution indicates a possible key role of the underwater light climate. Moreover, cell-bound and dissolved geosmin were detected in corresponding littoral samples. Both fractions were subjected to spatial and primarily temporal variations with maximum concentrations at the end of summer. However, a substantial lowering of the water level caused a diminution of cyanobacterial growth. Due to the drawdown of the water level concentrations of cell-bound geosmin and pigments (as a proxy of cyanobacterial biomass) were remarkably reduced, and dissolved geosmin was never detected during this phase. Except for the influence of water level fluctuation no other abiotic variables had a significant influence on pigment and geosmin concentrations. From geosmin concentrations detected in the littoral zone, the probability of serious episodes of odour events in the raw water of the Wahnbach Reservoir was estimated. Hence, the probability that the raw water was affected by geosmin was minor, which was supported by routine flavour profiles. Nevertheless, the study shows that odorous episodes caused by benthic cyanobacteria are likely to develop even in an oligotrophic lake or reservoir when these cyanobacteria, and consequently odorous production, proliferate. In principle, such a proliferation cannot be excluded as nutrients are available from the sediment pore water, and underwater light at the sediment surface in the sub-littoral is sufficiently high due to very low phytoplankton-induced turbidity under oligotrophic conditions. Thus, management-induced fluctuations of the water level seem to be the main control variable to generate light conditions at the sediment surface fluctuating in a given depth horizon faster than cyanobacteria can develop there.

Detection of geosmin from Coelosphaerium kuetzingianum separated by a step density gradient medium from suspended materials in water in Lake Shinji, Japan

To identify the geosmin-producing organisms in Lake Shinji, Japan, we conducted preliminary chemical and biological investigations from April to July 2008, during which odor occurrence was observed. Geosmin was mainly detected in the suspended substance (SS) of lake water, and its concentration corresponded to the cell numbers of Coelosphaerium kuetzingianum (Cyanophyceae) and Monoraphidium contortum. C. kuetzingianum and Pseudodictyosphaeriumminusculum (Chlorophyceae; which occurred only in April) were separated from the lake water of 30 April to the lighter, interlayers in a step density gradient medium. The highest concentration of geosmin was detected in the portion of the lightest layer separated from the water sample by gas chromatography mass spectrometry (GC/MS). Observation under optical microscope confirmed that abundant C. kuetzingianum with some P. minusculum and a very rare unknown material was retained in this portion. Similarly C. kuetzingianum was separated by the step density gradient medium from the sediment of 7 May. Abundant C. kuetzingianum with rare bacteria was recognized in the portion of the lightest layer, which contained the highest concentration of geosmin. The cell numbers of C. kuetzingianum correlated with the concentration of geosmin in the separated portions of water samples. These results suggest that C. kuetzingianum probably produced geosmin, although there has been no report about this to now.

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.

Effect of Transmembrane Pressure on Geosmin Release from Cyanobacterial Cell During Microfiltration

The mechanisms of increase in geosmin concentration in MF permeate with filtration time were investigated when inflow to the MF contained cyanobacteria incorporating geosmin inside and outside their cells. Whereas the geosmin concentration in the MF permeate was almost the same as the extracellular geosmin concentration in the MF inflow at the beginning of filtration, it increased and exceeded the extracellular geosmin concentration in MF inflow after 2 h of filtration. A cell viability test using a double-staining method revealed that a portion of the intracellular geosmin, which was incorporated in the cyanobacterial cells and therefore retained on the MF membrane, was released from the cells. This occurred probably because increased transmembrane pressure (TMP) with filtration time forced the cells to compress. However, geosmin release was not explained simply by cell breakage: other possible factors were implied.

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.

Contribution of Streptomyces in sediment to earthy odor in the overlying water in Xionghe Reservoir, China

Musty and earthy odors frequently characterize the source water and fish of the Xionghe Reservoir in China. Although odorous compounds and odor-producing cyanobacteria have been analyzed in surface water, potential odorants in sediments and their contribution to the water body have remained uninvestigated. In this study, we examined the odorous compounds and possible odor-producers in the sediments and overlying water of Xionghe Reservoir from November 2007 to October 2008. High concentrations of geosmin (up to 5280.1 ng kg −1 dw −1) were detected in sediments, and eight strains of Streptomyces isolated from sediments were verified as producers of geosmin and/or 2-MIB in M liquid medium by HSPME-GC-MS. Geosmin concentrations in the overlying water were correlated with those in the sediments ( r = 0.838, p < 0.05). In vitro studies showed that geosmin in the overlying water was released from the sediment, and that within 12 days the amount released from the sediment was 21.4–51.4%. Concentrations of geosmin in sediments were positively correlated with organic matter ( r = 0.642, p < 0.01), total nitrogen ( r = 0.606, p < 0.01) and Chl a ( r = 0.674, p < 0.01), and were negatively associated with temperature ( r = −0.425, p < 0.05). This study indicates that odorous compounds that are released from sediments should be taken into account when assessing the sources of these odorants in waters.

Removal of geosmin (trans-1,10-dimethyl-trans-9-decalol) from aqueous solution using an indirect electrochemical method

Geosmin was effectively removed using an electrochemical method at the Ti/RuO 2–Pt anode in the presence of NaCl as a reactant. At a current density of 40 mA cm −2, the geosmin concentration decreased from 600 ng L −1 to 6 ng L −1 in 60 min in the presence of 3.0 g L −1 NaCl. HOCl formed during electrolysis would likely play an important role in the geosmin oxidation. The electrochemical method exhibited good performance for geosmin removal under various conditions. The geosmin removal rate increased with increasing current density, while the geosmin removal rates were similar at different initial pH values. The Ti/RuO 2–Pt anode also performed well for electrochemical degradation of geosmin at both low and high concentrations. According to the present experimental results, the electrochemical method should be a promising alternative for the efficient and rapid removal of musty odor compounds in a water treatment process.

Biological origins and annual variations of earthy-musty off-flavours in the Xionghe Reservoir in China

Research Article| June 01 2010 Biological origins and annual variations of earthy-musty off-flavours in the Xionghe Reservoir in China Ting Zhang; Ting Zhang 1State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China2College of Animal Science and Technology, Hunan Agriculture University, Changsha 410128, China Search for other works by this author on: This Site PubMed Google Scholar Lin Li; Lin Li 1State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China Tel.: +86-27-68780806 Fax: +86-27-68780871 lilin@ihb.ac.cn Search for other works by this author on: This Site PubMed Google Scholar Yanxia Zuo; Yanxia Zuo 1State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China3Graduate School of the Chinese Academy of Science, Beijing 100039, China Search for other works by this author on: This Site PubMed Google Scholar Quan Zhou; Quan Zhou 1State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China3Graduate School of the Chinese Academy of Science, Beijing 100039, China Search for other works by this author on: This Site PubMed Google Scholar Lirong Song Lirong Song 1State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China lrsong@ihb.ac.cn Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2010) 59 (4): 243–254. https://doi.org/10.2166/aqua.2010.019 Article history Received: January 15 2009 Accepted: December 02 2009 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 Ting Zhang, Lin Li, Yanxia Zuo, Quan Zhou, Lirong Song; Biological origins and annual variations of earthy-musty off-flavours in the Xionghe Reservoir in China. Journal of Water Supply: Research and Technology-Aqua 1 June 2010; 59 (4): 243–254. doi: https://doi.org/10.2166/aqua.2010.019 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex The annual variations in physicochemical parameters, algal abundance and odorous compounds in the Xionghe Reservoir were investigated, in order to identify the possible odorous compounds and their origins. From May 2007 to April 2008, the algal composition, cell number and earthy-musty odorous compounds both in the water and in the flesh of fish at Sites A, B and C were determined monthly. The physicochemical parameters such as total nitrogen (TN), total phosphorus (TP), dissolved oxygen (DO), pH, transparency, water temperature and chlorophyll a (chl a) were simultaneously determined. A statistical correlation was noted between the chl a and water temperature: 0.678 (P<0.05) for Site A, 0.831 (P<0.01) for Site B and 0.659 (P<0.05) for Site C. Geosmin and 2-methylisoborneol (2-MIB)—in the reservoir were identified by gas chromatography-mass spectrometry (GC-MS). We observed that a large amount of Anabaena circinalis bloomed in surface water during the off-flavour episodes. In July 2007, we detected the highest concentration of geosmin (2.7 μg/L in the water, 0.27 μg/kg in the silver carp and 0.10 μg/kg in the crucian carp), while no 2-MIB was detected, which indicated that geosmin was mainly responsible for the off-flavour episodes in summer. cyanobacteria, earthy-musty off-flavour, geosmin, reservoir, 2-methylisoborneol This content is only available as a PDF. © IWA Publishing 2010 You do not currently have access to this content.

Cyanobacterial population and harmful metabolites dynamics during a bloom in Yanghe Reservoir, North China

A significant outbreak of odorous and toxic cyanobacteria occurred in Yanghe Reservoir, North China, in the summer of 2007. The dominant species was Anabaena spiroides and it was accompanied with the occurrence of very high concentrations of the odor metabolite geosmin. The event included two cycles of growth of A. spiroides: the first one of approximately 16 days between 21 June and 8 July, with the peak density 70,000 cells mL −1 on 2 July, and the second smaller bloom of over 50 days between 9 July and the end of August. The bloom also included a range of species of Microcystis, predominantly M. aeruginosa, as the second largest population, which varied from 5800 cells mL −1 to 28,000 cells mL −1 in the first cycle and from 2000 cells mL −1 to 11,000 cells mL −1 in the second. Geosmin reached the peak value of 7100 ng L −1 on 3 July, which was the highest value ever reported. The average geosmin production potential for A. spiroides cells was approximately 0.1 pg cell −1, which was also very high and 85–97% of geosmin was found within the cells and in addition the dissolved geosmin did not increase even during the cyanobacterial decay period. In addition to odor metabolites, three microcystin variants MC-LR, MC-RR, MC-YR and anatoxin-a, most of which were intracellular, were detected, with MC-RR being the dominant cyanotoxin. The highest cyanotoxin concentrations were: dissolved: MC-RR 1.56 μg L −1, MC-YR 0.066 μg L −1, MC-LR 0.544 μg L −1, anatoxin-a 0.106 μg L −1; intracellular: MC-RR 70.1 μg L −1, MC-YR 3.76 μg L −1, MC-LR 24.6 μg L −1, anatoxin-a 0.184 μg L −1, and these occurred on 2 July. The correlation between geosmin and A. spiroides was excellent ( R 2 = 0.912), however the correlation between anatoxin-a concentrations and Anabaena densities and between MCs concentrations and Microcystis densities was not as strong. This study demonstrated the relatively complex requirement for monitoring cyanobacterial blooms in this lake in China, where both the range of odors and cyanotoxins can be produced in concentrations which can change rapidly over a short time along with the bloom composition. It also demonstrated that both odor compounds and cyanotoxins should be considered in terms of the potential hazard to public water supply when a bloom was dominated by Anabaena and Microcystis occurs.

Photocatalytic removal of taste and odour compounds for drinking water treatment

Photocatalytic degradation of geosmin and 2-methylisoborneol (MIB), which are two taste and odour compounds commonly found in drinking water supply sources, was investigated using an immobilised TiO2 photoreactor. It was found that the degradation of geosmin and MIB followed similar pseudo-first-order kinetics with reaction rate constants being approximately 0.025 min−1 for typical geosmin and MIB concentrations of 250 and 500 ng/L. The normalised formal quantum efficiency was calculated to be in the range of 162–182 L/mol. Influence of additives (i.e. sodium bicarbonate and alcohols) on the degradation process was also investigated. It was found that there was a small reduction in the degradation rate constants of geosmin and MIB with increasing sodium bicarbonate concentration. At 50 mg/L sodium bicarbonate the degradation rate constants decreased by approximately 5%. Similarly, for methanol and ethanol concentrations up to 35 and 50 mg/L, respectively, these constants were found to also decrease. While addition of sodium bicarbonate and alcohols was seen to have relatively small negative effects on the photocatalytic degradation performance, the magnitude of their influence was consistent with the hypothesis that the degradation mechanism of geosmin and MIB was predominately that of attack involving HO∙ radicals.