Controlling toxic cyanobacteria: effects of dredging and phosphorus-binding clay on cyanobacteria and microcystins

Sediment dredging and Phoslock^® addition were applied individually and in combination in an enclosure experiment in a Dutch hypertrophic urban pond. These measures were applied to control eutrophication and reduce the risk of exposure to cyanobacterial toxins. Over the 58 days course of the experiment, cyanobacteria (predominantly Microcystis aeruginosa) gradually decreased until they dropped below the level of detection in the combined treated enclosures, they were reduced in dredged enclosures, but remained flourishing in controls and Phoslock^® treated enclosures. Cyanobacteria were, however, less abundant in the enclosures (medians chlorophyll-a 30-87 μg l⁻¹) than in the pond (median chlorophyll-a 162 μg l⁻¹), where also a thick surface scum covered one-third of the pond for many weeks.Soluble reactive phosphorus (SRP), total phosphorus and total nitrogen concentrations were significantly lower in the combined dredged and Phoslock^® treated enclosures than in controls. Median SRP concentrations were 24 μg P l⁻¹ in the combined treatment, 58 μg P l⁻¹ in dredged enclosures, and 90 μg P l⁻¹ in controls and 95 μg P l⁻¹ in Phoslock^® treated enclosures. Hence, the combined treatment was most effective in decreasing SRP and TP, and in lowering cyanobacterial biomass.Microcystin (MC) concentrations were analyzed by LC-MS/MS. MC concentrations and cyanobacterial biomass were positively correlated in all treatments. Mean MC concentrations in controls (71 μg l⁻¹), Phoslock^® treated enclosures (37 μg l⁻¹) and dredged enclosures (25 μg l⁻¹) exceeded the provisional guideline of 20 μg l⁻¹, whereas mean MC concentrations were 13 μg l⁻¹ in the combined treated enclosures. All samples contained the MC variants dmMC-RR, MC-RR, MC-YR, dmMC-LR and MC-LR; traces of MC-LY and nodularin were detected in few samples. The different treatments did not change the relative contribution of the variants to the MC pool; MC profiles in all treatments and the pond showed dominance of MC-RR followed by MC-LR. In the surface scum of the pond, total MC concentration was extremely high (64000 μg l⁻¹ or 1300 μg g⁻¹ DW), which poses a serious health hazard to children playing on the banks of the pond. Based on our results and pond characteristics, we propose combined sediment dredging and Phoslock^® addition, fish removal and strong reduction of duck feeding by the neighborhood as most promising measures controlling cyanobacterial hazards in this pond.     

Total dissolved phosphorus: Effects of two molecular weight fractions on phosphorus cycling in natural phytoplankton communities

Although ³²P-uptake kinetics enable the closed mathematical treatment of the phosphorus cycle, several P pools, other than PO₄, do not achieve isotopic equilibrium. This means that the P system could be open to P sources not labelled by the tracer. We tested whether such sources supporting an open system could produce significant changes in phytoplankton biomass in two lakewater communities. Two fractions were concentrated from natural lakewaters ranging from 2 × 10³ to 10⁴ daltons (fraction I) and 10⁴–10⁵ daltons (fraction II). These were then reintroduced to the natural communities at three concentration levels. During the incubation that followed, we assessed the capacity of the added organic matter to deliver phosphorus to the P cycle by monitoring known keypoints: phosphatase activity, ³²PO₄-uptake rate constant, and chlorophyll a. These measurements allowed us to estimate respectively the potential for hydrolysis, the actual product of hydrolysis PO₄ (which disrupts ³²PO₄-uptake rates) and the long-term net uptake of P (growth). Although the fractions did cause decreases in growth, and also increased both phosphatase activity and PO₄ uptake rate constants, none of these could be attributed to an additional delivery of P to the community. Under all conditions tested, the P system remained closed to organic P additions. However, the observed effects could be explained by non P organic matter such as dissolved humic materials acting either directly upon the community, or on phosphorus kinetics. The effects appeared to be pH dependent. We suggest that outside Spring P loading or other sporadic P inputs, the natural community tends to operate within a closed P system, where community dynamics are more strongly affected by non P organic matter than by organic phosphate inputs.     

Growth and nutrient uptake of green alga, Scenedesmus dimorphus, under a wide range of nitrogen/phosphorus ratio—I. Experimental study

In order to elucidate the relation between algal growth and nutrients such as nitrogen and phosphorus, a chemostat culture experiment using Scenedesmus dimorphus was performed under the conditions of T-N/T-P ratio of 2–50 mg N mg⁻¹ P and dilution rate of 1–4 day⁻¹. It was ensured from the results that nitrogen and/or phosphorus is the limiting nutrient for the growth of this alga under these conditions. The optimum T-N/T-P ratio for its growth was observed to change from 20 to 5 mg N mg⁻¹ P as the dilution rate varied from 1 to 4 day⁻¹ and, in most of the range of T-N/T-P ratio and dilution rate, its growth rate was not regulated by only one of the available nitrogen and phosphorus concentrations in the medium and algal nitrogen and phosphorus contents. Based on these facts, the multiplicative effect rather than the threshold effect of these two nutrients on its growth was considered to exist. It has been suggested, however, that algal nitrogen and phosphorus contents, especially nitrogen content, are the most important factors regulating its growth. Nitrogen uptake rate of this alga increased at a given concentration of available nitrogen in the medium as T-N/T-P ratio decreased down to 2 or 5 mg N mg⁻¹ P. It is also suggested that a multiplicative effect of nitrogen and phosphorus on uptake of these nutrients by S. dimorphus may exist.     

Variation of ATP content in Scenedesmus dimorphus cells grown in a chemostat culture and its comparison with chlorophyll-A content

The variations of ATP and chl-a contents in Scenedesmus dimorphus cells grown in a chemostat culture under nutrient limitation were investigated. ATP and chl-a contents per algal dry weight varied in the ranges of 0.15–1.64 μg mg⁻¹ (0.33–3.82 μg mg⁻¹ as ATP/C ratio) and 0.32–1.32% (7.8–30.8 μg mg⁻¹ as chl-a/C ratio), respectively, under the conditions of T-N/T-P ratio of 2–50 by weight and dilution rate of 1–4 per day. At every T-N/T-P ratio, both ATP and chl-a contents increased as dilution rate increased. At a given dilution rate, ATP content decreased systematically as T-N/T-P ratio increased, with the only exception at dilution rate of 4 per day. It was considered based on the result that ATP or chl-a can hardly be used successfully as an indicator of algal biomass.     

聚丙烯酸钠对透水混凝土物理力学性能影响研究

为使透水混凝土更好地为海绵城市及道路建设服务,在具有良好透水性的前提下,兼有一定的保水性,从而改善道路交通与生态环境,选取不同掺量的聚丙烯酸钠和水灰比作为配合比设计参数,对透水混凝土的物理力学性能进行测试分析。结果表明,聚丙烯酸钠掺量一定时,随着水灰比的增加,透水混凝土的软化系数及保水率均先升高后降低;水灰比一定时,随着聚丙烯酸钠掺量的增加,透水混凝土的软化系数和28 d抗折强度都先升高后降低,而保水率逐渐提高。综合而言,水灰比0.3,聚丙烯酸钠掺量0.4%为最优配合比。     

Influence of sampling depth on Escherichia coli concentrations in beach monitoring

While the US Environmental Protection Agency's (EPA) Beaches Environmental Assessment and Coastal Health (BEACH) Act requires coastal and Great Lakes’ states to implement plans for monitoring bacterial contamination of recreational beach water, exactly how this monitoring should occur has not been regulated. This study examined differences in concentration of Escherichia coli in water collected from different depths and from different horizontal locations across the beach. E. coli concentrations were significantly different (p<0.05), when water from different depths was compared. Sampling water at depths of 30, 60, and 120 cm resulted in significantly lower E. coli concentrations as depth increased. Had the State of Wisconsin chosen to collect beach water monitoring samples at a shallower or deeper depth, numbers of beach closures and the potential risk to public health would have changed substantially. These data imply that a revised and standardized protocol for monitoring beach water should be adopted by all states of a monitoring region to better compare microbial contamination of beaches and protect public health.     

氯化钠溶液对膨胀土膨胀力及孔隙分布影响的研究

利用常规三轴固结仪,进行了一系列膨胀力实验,研究了不同浓度氯化钠溶液对不同初始干密度试样的膨胀力的影响,并且利用核磁共振仪,探究了完成膨胀力试验后试样孔隙分布的情况。试验结果表明:在干密度不变的情况下,随着盐浓度增加,膨胀力逐渐减小;盐浓度越大,T_2曲线分布整体往右移,说明大孔隙体积增加,小孔隙体积减小。分析试验结果认为:在相同干密度下,随着盐浓度增加,Donnan渗透压逐渐减小,导致膨胀力降低;在体积保持恒定的情况下,由于膨胀力降低,必然导致内部膨胀力相应减小,所以孔隙被填充的体积减小,使得大孔隙较多,因此随着盐溶液浓度增加,同一干密度试样的T_2曲线向右移动。     

Effects of lanthanum and lanthanum-modified clay on growth, survival and reproduction of Daphnia magna

The novel lanthanum-modified clay water treatment technology (Phoslock^®) seems very promising in remediation of eutrophied waters. Phoslock^® is highly efficient in stripping dissolved phosphorous from the water column and in intercepting phosphorous released from the sediments. The active phosphorous-sorbent in Phoslock^® is the Rare Earth Element lanthanum. A leachate experiment revealed that lanthanum could be released from the clay, but only in minute quantities of 0.13-2.13 μg l⁻¹ for a worst-case Phoslock^® dosage of 250 mg l⁻¹. A life-history experiment with the zooplankton grazer Daphnia magna revealed that lanthanum, up to the 1000 μg l⁻¹ tested, had no toxic effect on the animals, but only in medium without phosphorous. In the presence of phosphorous, rhabdophane (LaPO₄ · nH₂O) formation resulted in significant precipitation of the food algae and consequently affected life-history traits. With increasing amounts of lanthanum, in the presence of phosphate, animals remained smaller, matured later, and reproduced less, resulting in lower population growth rates. Growth rates were not affected at 33 μg La l⁻¹, but were 6% and 7% lower at 100 and 330 μg l⁻¹, respectively, and 20% lower at 1000 μg l⁻¹. A juvenile growth assay with Phoslock^® tested in the range 0-5000 mg l⁻¹, yielded EC₅₀ (NOEC) values of 871 (100) and 1557 (500) mg Phoslock^® l⁻¹ for weight and length based growth rates, respectively. The results of this study show that no major detrimental effects on Daphnia are to be expected from Phoslock^® or its active ingredient lanthanum when applied in eutrophication control.     

硫酸钠溶液和硫酸钠盐渍土的冻结温度及盐晶析出试验研究

为了探索硫酸钠盐渍土的盐胀与冻胀机理,对硫酸钠溶液分别在环境温度-20℃和变环境温度-5℃～-10℃下进行降温试验;并对硫酸钠盐渍土在环境温度-20℃下进行降温试验,通过试验研究了硫酸钠溶液和硫酸钠盐渍土中芒硝的析出规律及各自的冻结温度。试验表明：在相同外界环境温度下,浓度大的溶液,芒硝更容易析出;具备一定浓度的溶液,在环境温度变化缓慢条件下更容易析出但溶液的冻结温度的趋势一致;相同浓度硫酸钠盐渍土的冻结温度均低于硫酸钠溶液的冻结温度,随着含盐量增加,其冻结温度降低;在相同外界环境温度下,盐晶在土体中更容易析出。     

双龙湖初级生产力测定及其模型研究

双龙湖是浅水型城市湖泊,一度为重富营养化湖泊。经综合治理其水质得到明显改善。通过黑白瓶法测定双龙湖浮游植物水柱日净产量时空分布,认为双龙湖营养水平较高,且初级生产力同水温、透明度、溶解氧、溶解性总磷呈显著正相关。根据模型计算双龙湖全年浮游植物净产量为1815033 kg,理论产鱼潜力9075.2 kg。与实际情况符合较好。定期收获鱼产品可以从湖泊生态系统中移出氮、磷等营养元素,从而减轻双龙湖富营养化。     

Algal growth in warm temperate reservoirs: kinetic examination of nitrogen, temperature, light, and other nutrients

Nutrient limited growth of the phytoplankton assemblage in two Texas reservoirs was studied by a combination of nutrient addition experiments and statistical modeling. Dilution bioassays were run to ascertain the qualitative and quantitative patterns in nutrient limitation. Algal growth was frequently and strongly nutrient limited, particularly when temperature was >22°C. By itself, N was more often stimulatory than P, though strong additional enhancement of growth by P and trace nutrients was often detected. Monod growth kinetics indicated that half-saturation constants for N limited growth for the entire algal assemblage were in the range 20–200 μg N/L, relatively high compared to literature values, and increased with increasing temperature. Maximal growth was also an increasing function of temperature. A single temperature-dependent model was fit to the growth dynamics for all experiments showing N-limitation. The model μ=0.0256·T([DIN]/66.0+[DIN]) where μ is specific growth rate (d⁻¹), T is temperature (°C) and [DIN] is dissolved inorganic N (μmol/L) fit the experimental results reasonably well (r²=0.82). However, only a modest predictive power for growth in the controls (our best estimate of growth in situ) was achieved (r²=0.26). Thus, even with unusually detailed, site-specific fitting of model parameters, accurately modeling algal growth in natural ecosystems can remain a challenge.     

碱集料反应中当量碱计算问题探讨

设计了2种集料、4种水泥、2种试验方法的AAR膨胀试验。通过对试验数据进行聚类分析和作图分析，提出当前普遍使用的当量碱计算公武Na2Oeq=Na2O 0．658K2O中K2O的系数偏大，并初步得出该系数应为0．4--0．5。     

乙酸钠对厌氧段释磷过程的影响研究

以乙酸钠为唯一碳源,分别在污泥浓度为2 000和3 000 mg/L时,研究了乙酸钠投配量对厌氧/好氧SBR生物除磷系统厌氧段释磷过程的影响。结果表明:当乙酸钠负荷约为0.15gCOD/gVSS时,厌氧段聚磷菌释磷量相对最大,当乙酸钠负荷小于或大于此值时释磷量都相对较小;并且当乙酸钠负荷<0.24 gCOD/gVSS时,释磷时间随着碳源负荷的增加而越来越长,超过这个值之后,系统中周期内没有明显的厌氧释磷和好氧吸磷现象,其原因归结为乙酸钠浓度增大引起pH值过高,造成厌氧段聚磷菌不释磷,从而导致后续好氧吸磷过程遭到破坏。     

Effects of aluminum treatment on phosphorus, carbon, and nitrogen distribution in lake sediment: a 31P NMR study

The effects of aluminum (Al) treatment on sediment composition of carbon (C), nitrogen (N) and phosphorus (P) were investigated in sediment representing pre- and post-treatment years in the Danish Lake S?nderby. 31P NMR spectroscopy analysis of EDTA-NaOH extracts revealed six functional P groups. Direct effects of the Al treatment were reflected in the orthophosphate profile revealing increased amounts of Al-P in the sediment layers representing the post-treatment period, as well as changes in organic P groups due to precipitation of phytoplankton and bacteria at the time of Al addition. Furthermore, changes in phytoplankton community structure and lowered production due to the Al treatment resulted in decreased concentrations of sediment organic P groups and total C. Exponential regressions were used to describe the diagenesis of C, N, and P in the sediment. From these regressions, half-life degradation times and C, N, and P burial rates were determined.     

高效减水剂中硫酸钠间接滴定法的研究

本文研究了用EDTA间接滴定法测定高效减水剂中Na2SO4的含量，该方法简单、易行，快速，回收率99％以上，相对标准偏差小于1．5％，同标准方法对照及样品测定令人满意。     

次氯酸钠对微囊藻毒素释放及降解特性的研究

选用铜绿微囊藻为处理对象,研究了NaClO在藻类处理过程中藻毒素释放和降解的特性。结果表明：NaClO作用于藻细胞后会破坏其完整性,导致藻毒素释放,同时次氯酸钠投加量及藻浓度对藻毒素释放及降解量有较大影响。应避免在藻类大量暴发时（藻浓度〉6．96×10^6个／mL）预氧化中使用次氯酸钠,而在一般藻细胞浓度较低的水厂采用该种预氧化方法除藻,不会造成藻毒素的释放扩散。     

硫酸钠激发超细矿粉的性能研究

碱激发材料因其低碳排放特性受到广泛关注。为了克服硫酸钠激发矿粉体系抗压强度发展缓慢的缺陷,本文通过降低矿粉粒径,提高硫酸钠对矿粉的激发效率,实现增强抗压强度的效果。结果表明,在常温条件下,中值粒径为4.3μm的矿粉被9%的硫酸钠激发后,胶砂的28d和90d抗压强度可达到44MPa和71.8MPa。     

Effects of sedimentation on removal of faecal coliform bacteria from effluents in estuarine water

Faecal coliform deposition rates with estuary type suspended solids have been examined in laboratory experiments. Faecal coliform deposition rates in estuary water increased proportionately with suspended solids concentration, whereas faecal coliform deposition rates in effluent/seawater mixture showed no correlation with suspended solids concentration.

Deposition of estuary water suspended solids showed correlation with time, whereas deposition of effluent suspended solids showed no correlation with time. The adsorption efficiency experiments suggested immediate adsorption of some of the faecal coliforms onto both types of suspended solids and no difference in adsorption potential.

Therefore, it appears that the contrasting effects on faecal coliform deposition can be attributed to the different deposition potential of each type of suspended solids and not to the adsorption process.     

改性钢渣的制备及其吸附除磷性能

研究了改性钢渣吸附除磷影响因素、等温吸附线特征和吸附动力学,并对生物处理后的出水进行吸附除磷研究。结果表明:在初始磷浓度10mg/L,投加量10g/L、pH为7时,改性钢渣吸附后总磷浓度为0.687mg/L,去除率达93%;改性钢渣对磷的吸附符合Langmuir模型,理论饱和吸附量是1.977mg/g,吸附动力学符合准二级动力学模型(R20.99);实际生活污水的吸附除磷中,投加量为50g/L,反应2h后出水总磷浓度达到《城镇污水处理厂污染物排放标准》(GB18918—2002)一级B标的排放要求。     

Effects of the nuisance algae, Cladophora, on Escherichia coli at recreational beaches in Wisconsin

Recreational beaches constitute a large part of the 12 billion dollar per year tourism industry in Wisconsin. Beach closures due to microbial contamination are costly in terms of lost tourism revenue and adverse publicity for an area. Escherichia coli (E. coli), is used as an indicator of microbial contamination, as high concentrations of this organism should indicate a recent fecal contamination event that may contain other, more pathogenic, bacteria. An additional problem at many beaches in the state is the nuisance algae, Cladophora. It has been hypothesized that mats of Cladophora may harbor high concentrations of E. coli. Three beaches in Door County, WI were selected for study, based on tourist activity and amounts of algae present. Concentrations of E. coli were higher within Cladophora mats than in surrounding water. Beaches displayed an E. coli concentration gradient in water extending away from the Cladophora mats, although this was not statistically significant. Likewise, the amount of Cladophora observed on a beach did not correlate with E. coli concentrations found in routine beach monitoring samples. More work is needed to determine the impact of mats of Cladophora on beach water quality, as well as likely sources of E. coli found within the mats.