Taste and odor problem induced by algal proliferation in source water has become one of the aesthetic issue in drinking water. With the urbanization, lake/reservoir source water is becoming more and more important in our country. Compared to the river source water, the lake/reservoir source water is characterized with slow flow rate, long hydraulic retention time and low turbidity etc., which will facilitate algal proliferation and easily producing taste and odor problem, especially musty odor caused by 2-Methylisoborneol. This study aimed at reducing taste and odor in lake/reservoir source water. By combining field surveys, laboratory experiments and modelling, the algal population dynamic and related odor occurrence in Qingcaosha Reservoir and Nanping Reservoir were investigated. Two typical odor-producing cyanobacteria were selected for evaluating the algal growth and odor production characteristics in response to light change. The main work and results are summarized as follows:
1. Light response and application of one typical deep-living MIB-producing Plank-tothrix sp. was studied. The laboratory experiment revealed that the optimum light intensity for algal growth and MIB production were 36 and 85 μmol photons m2 s1, respectively. High light intensitywould inhibit the growth of Planktothrix sp.. The fitted result showed the minimum light requirement for Planktothrix sp. was 4:4 μmol photons m2 s1, while the result from in-situ experiment also showed Planktothrix sp. could not reproduce when the available underwater light was below the minimum light requirement. The historical data from Miyun Reservoir showed high concentration of MIB usually occurs in the region where underwater light intensity exceed the minimum light requirement for Planktothrix sp.. To reduce benthic/deep-living MIB-producing cyanobacterial growth in the field, it might be feasible to decrease the light availability by elevating water level or increasing turbidity.
2. The temporal-spatial distribution of one typical planktonic MIB-producing Pseu-danabaena sp. in QCS Reservoir and its light response was studied. One brown Pseudanabaena was identified as the MIB source in QCS Reservoir, while the other green one didn’t produce MIB. The optimum for growth and MIB production of brown Pseudanabaena sp. were 36 and 85 μmol photons m2 s1, respectively. The Pseudanabaena sp. was characterized by poor low light tolerance and sensitive to light inhibition, but its maximum growth rate (0:56 d1) under optimum light intensity was relative higher than other cyanobacteria. The light spectrum experiment further revealed that red light facilitate the growth of Pseudanabaena sp. while green light promote the MIB yield by promoting the synthesis of both chlorophyll-a and phycoerythrin. The photopigments composition of Pseudan-abaena sp. under different light color varied remarkably. The underwater light spectrum was affected by turbidity but independent of the size of particles. The spectrum peak would shift towards green when the turbidity decrease, which would facilitate the growth of the phycoerythrin containing cyanobacteria.
3. The effect of hydraulic retention time on growth of cyanobacteria and its application in reservoir management. The one-year survey in NP Reservoir in Zhuhai indicated that Pseudanabaena might be the source of MIB. The water level and hydraulic retention time are two key factor resulting in MIB episode. It was found that hydraulic retention time would affect the maximum cell density rather than the maximum growth rate based on the batch culture of different water renew period. This indicates that the effect of water renewal on algal growth is dilution.
The hydrodynamic model of NP Reservoir was further established using Delft3D,of which water age and flush time were used to evaluate the water exchangeability under different scenario. The modeling results showed that increasing discharge would significantly decrease the water age and flush time. And at the water level of 25:5 m, the south region would circulate interiorly. Wind has negative effect on the water exchange of NP Reservoir at lower water level, while the effect of different wind direction was unconspicuous. The diversion wall could enhance the water exchange at the water level of 25:5 m, while no significant effect was observed at the water level of 27 m. The results indicated that raising water level would be better to enhance the water exchange of south region in NP Reservoir.