涂铁铝砂对水中有机物去除效果研究

在实验室条件下,以石英砂为载体,制备了涂铁铝砂.研究表明,涂铁铝砂的表面物理化学性质比石英砂滤料有很大改善：比表面积是原石英砂滤料的10倍,等电点时的pH值由0.2-2.2提高到8.8;表面粗糙,孔隙增多;对有机物的静态吸附效果由石英砂的8%提高到100%,过滤时对有机物的去除率由9.5%提高至45.2%,对藻类藻毒素的去除效果也明显优于石英砂滤料.进水有机物浓度、pH值、浊度和空床停留时间是涂铁铝砂去除有机物的主要影响因素.涂铁铝砂对有机物的去除效率随过滤时间会逐渐衰减,用0.5 mol.L的NaOH溶液再生,可以使其恢复对有机物的去除能力.最后分析了涂铁铝砂去除有机物的作用机理.

Environmental abundance and microcystin-LR production ability of toxic Microcystis in Nanquan region of Lake Taihu

The variations of environmental abundance and microcystin-LR （MC-LR） production ability of toxic Microcystis in the Nanquan region of Lake Taihu are investigated by real-time quantitative PCR （RTQ-PCR） and high performance liquid chromatography （HPLC） from May to December in 2009. Simultaneously, degrees of water pollution and eutrophication are monitored. The results indicate that the water quality in the Nanquan region of Lake Taihu is in a moderate degree of pollution and eutrophication. Algal density exceeds the threshold of bloom from May to November. The environmental abundance of toxic Microcystis is more than 40% from May to October and then significantly declines to 5.66% due to the obvious reduction in the water temperature in December. From May to December, the MC-LR production ability of toxic Microcystis ranges from 1.661 to 9.293 μg/108cells. With the significant drops in water temperature and algal density, the MC-LR production ability of toxic Microcystis is obviously increased from November to December. It is concluded that the lake presents Microcystis bloom and the toxic Microcystis becomes dominant during most of the year. The environmental abundance and the MC-LR production ability of toxic Microcystis have a close relationship with water temperature. The effective control of toxic Microcystis should be considered in both the bloom period and the non-bloom period of winter since the MC-LR production ability of toxic Microcystis obviously increases in winter.

Negative effects of Phaeocystis globosa on microalgae

The potential allelopathic effects of the microalga,Phaeocystis globosa Scherffel,on three harmful bloom algae,Prorocentrum donghaiense Lu,Chattonella marina(Subrahmanyan) Hara et Chihara and Chattonella ovata Hara et Chihara were studied.The growth of C.marina and C.ovata was markedly reduced when the organisms were co-cultured with P.globosa or cultured in cell-free spent medium.Haemolytic extracts from P.globosa cells in the senescence phase had a similar inhibitory effect on the three harmful bloom algae.However,P.globosa had less influence on the brine shrimp,Artemia salina.These results indicate that P.globosa may have an allelopathic effect on microalgae,which would explain the superior competitive abilities of P.globosa.Because the addition of the haemolytic toxins from P.globosa had similar effects on algae as spent media,these compounds may be involved in the allelopathic action of P.globosa.

Survival,recovery and microcystin release of Microcystis aeruginosa in cold or dark condition

Microcystis often dominates phytoplankton in eutrophic lakes and must survive a long period of cold or dark conditions. However, the survival strategies of Microcystis to withstand cold or dark stress are less well known. In this study, we conducted experiments on the responses of two toxic Microcystis aeruginosa strains （FACHB-905 and FACHB-915） and their microcystin release in conditions of low temperature （15℃ or 4℃, with illumination） or darkness, and subsequent recovery in standard conditions （25℃ with illumination）. On exposure to 15℃, a small decrease in cell viability was observed, but the cell number increased gradually, suggesting that M. aeruginosa FACHB-905 and FACHB-915 cells seem in general tolerant in 15℃. Interestingly, our results show that a higher carotenoid content and microcystin release potentially enhance the fitness of surviving cells at 15℃. M. aeruginosa cells exposed to lower temperature light stress （4℃） did not completely lose viability and retained the ability to reinitiate growth. In darkness, the maximum quantum yield （Fv/Fm） and the maximum electron transport rate （ETRmax） values and cell viability of M. aeruginosa cells gradually decreased with time. During the recovery period, the photosynthetic efficiency of M. aeruginosa reverted to the normal level. Additionally, M. aeruginosa FACHB-905 and FACHB-915 exposed to low temperature had increased caspase-3-1ike activity and DNA fragmentation, which suggests the occurrence of a type of cell death in M. aeruginosa cells under cold stress similar to programmed cell death. Overall, our findings could confer certain advantages on the Microcystis for surviving cold or dark conditions encountered in the annual cycle, and help explain its repeated occurrence in water blooms in large and shallow lakes.

Escherichia coil Removal in Tropical Oligotrophic and Eutrophic Lakes

The mechanisms by which oligotrophic and eutrophic lakes rid itself of Escherichia coli or faecal coliforms are still not clearly understood. This study sought to review the various means by which E. coli or faecal coliforms are inactivated or removed in lakes. The review cited temperature, solar radiation, predation, starvation, attachment and sedimentation as key factors that aid the removal of E. coli in lakes. In eutrophic lakes additional factors such as the role of algal biomass may play a role due to increased pH and dissolved oxygen levels attributed to algal presence. Algal toxins or exudates may also play a role although this is still under debate. The interactive effect of two or more of these factors on E. coli inactivation and the relative importance of these mechanisms on E. coli removal are still not known. Areas for further research include the role of algae in sedimenting E. coli or faecal coliforms and the possible role of algal exudates on E. coli inactivation.