Distribution, Dynamics And Degradation Of Algae-producing Odorous Compounds In The Freshwater Bodies

Off-flavor problems caused by algae-producing odorous compounds have been one of the focuses in drinking water industry and aquaculture. Knowledge on the property of odorous compounds, their origins and the eco-physiological functions has been accumulated in some developed countries, however, this has not been the case in China. With the growing demand for higher quality of drinking water and aquatic products, it is anticipated there will be an urgent need for the understanding and control of odorous compounds in China. Based on this consideration, the present dissertation was designed to conduct the study on the odorous compounds in the following aspects: 1. identifications of odor compounds in the freshwater bodies and in the isolated algal strains; 2. Diurnal dynamics of odorous compounds in Dalianhua Lake and annual dynamics in Dianchi Lake; 3. correlation between toxin production and odorous compounds production in Microcystis aeruginosa; and 4. degradation of odorous compounds by UV photolysis and nano-TiO2 photocatalysis.. The main results were summarized as follows: 1. Three major odorous compounds were determined by coupling HSPME with GC-MS. The highest absorption of the odorous compounds were obtained under the following conditions of 30%(W/V)NaCl , stirring at 60℃for 40 min , using 65μm PDMS/DVB coated fibre. Under the optimal conditions of HSPME-GC-MS, the limits of detection for Geosmin , ?-cyclocitral and MIB in water were 1.0 , 1.3 , 1.7 ng/L , and the relative standard deviations for them were 4.9% , 8.4% , 6.2% , respectively. There were good linear correlation for the three odorous compounds in the range of 5～1000 ng/ L (the calibration coefficients were all above 0. 997). Therefore, trace levels of the odorous compounds at ng/L in water could be quantified accurately.. 2. Among the 10 municipal water treatment plants(WTPs) in Wuhan, MIB was detected in 3 WTPs,Geosmin in 3 WTPs and 2,4-Decadienal in 6 WTPs. 2,4-Decadienal was probably produced by some strains of bacillariophyta or chlorophyta in the river. MIB, Geosmin and ?-cyclocitral were found in both lakes and ponds. ?-cyclocitral-producing Microcystis aeruginosa strains were isolated from Lake Dianchi, Lake Taihu and Lake Donghu, respectively. It could be inferred that ?-cyclocitral in these lake water might be produced by Microcystis. In the whole,the algal biomass in lakes and ponds were much higher than in the rivers, as well as the frequency and concentration of MIB and Geosmin in the lakes and ponds were bigger than that in the rivers. This suggested that off-flavor episodes in the lakes and ponds may occurred more frequently than in the rivers. 3. Two Geosmin-producing strains(Anabaena cylindrica and Lyngbya kuetzingii), three MIB producing strains(Oscillatoria raciborskii, Oscillatoria sp. and Phormidium mucicola) and eleven β-Cyclocitral and β-Ionone producing Microcystis strains were screened out from 35 cyanobacterial monoculture. Even though all the strains were isolated from Lake Dianchi, some of them yielded strong odor, while others produced no odor, suggesting that odor-producing property is strain-specific. Most part of these odor compounds were pounded in cell. β-Ionone was the main contributor to the odor of Microcystis. 4. During the growth of Microcystis aeruginosa FACHB905 and Microcystis aeruginosa PCC7806, all the contents of intracellar β-Cyclocitral, β-Ionone and microcystin were correlated with Chla, however, the concentration of β-Cyclocitral,β-Ionone,microcystin had no significant correlations each other, either inside cell or in the medium. This may be due to the fact that the three compouds were produced through different metabolic pathways. No significant correlation was found between intracellular concentration and dissolved concentration in the medium of β-Cyclocitral and β-Ionone. 5. Microcystis aeruginosa was the dominant genus in the pilot area of Lake Dianchi. Both the concentration of particulate ?-Cyclocitral and that of ?-Ionone correlated significantly with the annual variation of Chla, biomass of total phytoplankton, ,cyanobacteria and Microcystis. The concentration of particular Geosmin correlated significantly with the cell number of Anabaena, while the concentration of particulate MIB correlated significantly with the cell number of Oscillatoria. Off-flavor in the pilot area was found to be caused by ?-Cyclocitral-and ?-Ionone-producing Microcystis, MIB-producing Oscillatoria and Geosmin-producing Anabaena together. ?-Ionone, MIB and Geosmin contributed together to the odor intensity in the lake water. 6. The diurnal variation of environmental parameters, algae and odorous compounds in Lake Dalianhua, Wuhan city, were investigated. Microcystis dominated in the lake. The diurnal highest concentration of soluble MIB, ?-Cyclocitral and ?-Ionone reached 69.1ng/L, 32.6ng/L and 453.9ng/L, respectively. MIB and ?-Ionone were mainly responsible for the strong off-flavors in the lake. Averagely, particulate MIB, ?-Cyclocitral and ?-Ionone accounted for 70.9%, 74.4%, 81.4% of its total content, respectively. All the dissolved, particulate and total ?-Cyclocitral correlated significantly with the biomass of total algae and Microcystis, particulate ?-Cyclocitral and ?-Ionone correlated significantly with total algae and light intensity, and particulate MIB had a significant correlation with Anabaena biomass. 7. Illuminated with UVC, UVB and sunlight respectively, ?-Cyclocitral and ?-Ionone in pure water could be effectively degraded, but not for MIB. However, upon the addition of nano-TiO2,MIB,?-Cyclocitral and ?-Ionone all degraded rapidly. It was proved that nano-TiO2 photocatalysis could be more effetively than UV photolysis on the removal of the three odorous compounds. Both the nano-TiO2 photocatalysis and the UV photolysis of the odorous compounds can be depicted by pseudo first order reaction kinetics. The solar/nano-TiO2 photocatalysis system was also effective degradation method of the three odorous compounds in lake water, which showed the great potential application on the removal of off-flavors in the aquatic environments.