A preliminary study of metal distribution in three waterhyacinth biotypes

Two waterhyacinth (Eichhornia crassipes (Mart.) Solms) biotypes from Broward County, Florida, were collected and analyzed for chlorophyll content and metal distribution (potassium, calcium, magnesium, cobalt, copper, manganese and iron) in roots, stems and leaves. Two biotypes were distinguished by size (medium or “stunted”, and large or “super”) and by whether they were or were not eaten (“stunted” and ”super”, respectively) by the waterhyacinth weevil, Neochetina eichhorniae Warner. Results are compared with a third biotype (small or “normal”): i.e. plants from the Hillsborough and Peace Rivers where the weevils have not been released. The data indicate abnormal concentration of cobalt and iron in the leaves of the “super” plants relative to the third biotype. Fractions of calcium, magnesium, manganese, iron and copper in roots showed a significant, negative linear correlation coefficient, r, with solubility product constant (log K_sp) for metal carbonates of the small and medium biotypes.     

Sorption of organics on clay and synthetic humic-clay complexes simulating aquifer processes

Sorption/partition of several organic solute (contaminants) of a wide range of hydrophobicities was studied on clay and on clay-humic complexes representing aquifer-soil systems. The role of the mineral and of the organic (humic) fractions was elucidated and a model considering both fractions in the sorption process was proposed. The adsorption constants on humic (organic fraction), K_∝, were 8–20 times higher than on “pure” clay, K_m. But with soils with low to medium organic fractions (ƒ_∝ < 0.05) the contribution of the clay mineral to adsorption was quite significant, in spite of the fact that half of the sorption sites on the mineral surface were blocked by the humic. In the range of very low organic content in aquifer soil a non-linear pattern going through a minimum is observed between the overall partition coefficient and soil-organic fraction, transforming to the familiar linear relationship at higher ƒ_∝s. Both the K_∝ and K_m followed the linear-free energy relationship to the octanol-water partition coefficient K_ow.     

Compaction of flocculated material

The device used in the experiment consists of a flat-bottomed graduated cylinder and a coaxial plunger. A suspension flocculated with chemicals is sedimented after being mechanically worked within the graduate, and the supernatant water is removed with a pipette. The plunger is thrust into the sludge at a constant speed. The sludge is not only compressed but also flows into the annular gap between the plunger and the graduate, resulting in liberation of water. The liberated water is accumulated on the sludge in the annular gap. The “sludge bulkiness” β is used to describe the volumetric proportion of sludge and solids in it. The sludge bulkiness values before and after the “plunger test” are denoted as β_i and β_f, respectively. The values of β_i and β_j have been explored as a function of the time of the mechanical working. As a result, there is a definite time lag between the maximum value of β_i and the minimum value of β_f. The minimum value of β_j is obtained when the sludge consists of “pelleted flocs”.     

Simulation of water-bloom in a eutrophic lake—I. Photosynthetic characteristics of Microsystis aeruginosa

A perspective of how to simulate “emergence and/or disappearance of the water-bloom… dense population of a blue-green alga, Microcystis aeruginosa at the surface of eutrophic waters… ” was presented.The algal photosynthetic activity. Q_o2 as a function of irradiation light intensity. I, could be represented by the Blackman model, taking the algal content. C of chlorophyll-α and water temperature. 0 as parameters.When the cells that had been cultured under dim light were transferred to a new environment, wherein the light intensity was from 0 (dark) to the level much brighter than the dim light, the value of C exhibited various responses against time. Subtracting the rate of chlorophyll-α degradation from that of chlorophyll-α synthesis, the rate of change in C values during the light-adaptation period was studied.     

Shear fracture (Mode II) of brittle rock

Mode II fracture initiation and propagation plays an important role under certain loading conditions in rock fracture mechanics. Under pure tensile, pure shear, tension- and compression-shear loading, the maximum Mode I stress intensity factor, K_Imax, is always larger than the maximum Mode II stress intensity factor, K_IImax. For brittle materials, Mode I fracture toughness, K_IC, is usually smaller than Mode II fracture toughness, K_IIC. Therefore, K_Imax reaches K_IC before K_IImax reaches K_IIC, which inevitably leads to Mode I fracture. Due to inexistence of Mode II fracture under pure shear, tension- and compression-shear loading, classical mixed mode fracture criteria can only predict Mode I fracture but not Mode II fracture. A new mixed mode fracture criterion has been established for predicting Mode I or Mode II fracture of brittle materials. It is based on the examination of Mode I and Mode II stress intensity factors on the arbitrary plane θ,K_I(θ) and K_II(θ), varying with θ(−180°θ+180°), no matter what kind of loading condition is applied. Mode I fracture occurs when (K_IImax/K_Imax)<1 or 1<(K_IImax/K_Imax)<(K_IIC/K_IC) and K_Imax=K_IC at θ_IC. Mode II fracture occurs when (K_IImax/K_Imax)>(K_IIC/K_IC) and K_IImax=K_IIC at θ_IIC. The validity of the new criterion is demonstrated by experimental results of shear-box testing.Shear-box test of cubic specimen is a potential method for determining Mode II fracture toughness K_IIC of rock since it can create a favorable condition for Mode II fracture, i.e. K_IImax is always 2–3 times larger than K_Imax and reaches K_IIC before K_Imax reaches K_IC. The size effect on K_IIC for single- and double-notched specimens has been studied for different specimen thickness B, dimensionless notch length a/W (or 2a/W) and notch inclination angle α. The test results show that K_IIC decreases as B increases and becomes a constant when B is equal to or larger than W for both the single- and double-notched specimens. When a/W (or 2a/W) increases, K_IIC decreases and approaches a limit. The α has a minor effect on K_IIC when α is within 65–75°. Specimen dimensions for obtaining a reliable and reproducible value of K_IIC under shear-box testing are presented. Numerical results demonstrate that under the shear-box loading condition, tensile stress around the notch tip can be effectively restrained by the compressive loading. At peak load, the maximum normal stress is smaller than the tensile strength of rock, while the maximum shear stress is larger than the shear strength in the presence of compressive stress, which results in shear failure.     

A comprehensive study on the biological treatabilities of phenol and methanol—I. Analysis of bacterial growth and substrate removal kinetics by a statistical method

An unbiassed statistical method was developed to evaluate kinetic parameters in the biological oxidation of wastewaters. Through the statistical analyses of the biological oxidation kinetics, it was shown that the kinetic equations satisfactorily described the bacterial growth and substrate removal kinetics where X is biomass concentration, S is substrate concentration, t is time, a is cell yield coefficient, k_d is cell decay coefficient, K_s is Michaelis-Menten constant, and k is substrate removal rate coefficient. The coefficients K_s and a changed with temperature insignificantly while k and k_d were closely related to it. The temperature independent coefficients K_s and a were estimated to be 236 mg 1⁻¹ (standard deviation, σ = 70 mg 1⁻¹) and 1.21 (σ = 0.06) respectively for phenol, and 2330 mg 1⁻¹ (σ = 1410 mg 1⁻¹) and 1.25 (σ = 0.45) respectively for methanol based on total organic carbon (TOC) and volatile suspended solids (VSS). The oxygen utilization rate can be formulated as where Rr is the oxygen utilization rate (mg 1⁻¹ O₂ time⁻¹), as′ is a coefficient designating oxygen requirement per substrate utilized, and b′ is a coefficient designating oxygen requirement per biomass for endogeneous respiration. The coefficient a′ was 1.39 for phenol and 2.23 for methanol, and b′ was 1.42 k_d for both substances based on TOC and VSS.     

Essais d'aerateurs: Enseignements tires de 500 essais en eau claire effectues dans 200 stations d'epuration differentes—I. Methodologie

Aeration represents the main part of energy consumption in the activated sludge process and the evaluation of aeration systems efficiency is becoming more important, especially as energy cost increases. Since 1972, CEMAGREF teams have carried out more than 500 non-steady state clean water tests in sewage treatment plants. The first aim of these measurements was to compare the results collected in plants with those predicted by manufacturers.The distribution of the different types of aerators tested in the field by the CEMAGREF is given in Table 1. All tests are conducted using tap water under non-steady state conditions: the initial dissolved oxygen (DO) level is brought down to zero by adding cobalt chloride as catalyst and sodium sulfite. When all the sodium sulfite has been used, the increase in water dissolved oxygen content is monitored vs time in various places in the tank by means of membraned probes.The graphical procedure used for estimating the oxygen transfer coefficient (K_La) is shown in Fig. 1; this procedure is usually called “log deficit method”. The results are expressed for “standard conditions” (θ = 10°C; P = 760 mm Hg). The influence of temperature on oxygenation capacity is illustrated in Fig. 2.The water quality parameters that may affect oxygen transfer are investigated: it appears that only the presence of surfactants, flocculated suspended solids, or high salinity (conductivity > 1500 μS cm⁻¹—Table 2) are liable to have any appreciable effect on oxygen transfer. The unflocculated SS, pH and alkalinity have no effect on oxygenation results in the common range of values occurring in the tests (Table 3).Authors differ about the operational procedure in non-steady state clean water test. After 7 years' field-measurements the CEMAGREF teams have developed their own recommendations about test procedures; their main conclusions are the following:Dissolved oxygen analysis: the differences observed between the results ( ) obtained simultaneously by Winkler titration of piped samples and those from in-tank probes never exceed 4% (Table 4). Reliable dissolved oxygen probes are suitable for accurate measurements of oxygen transfer.The number of sampling points should be no smaller than three for aeration tanks with a volume below or equal to 500 m³. It should be recommended to add one sampling point for every additional 500 m³.Location of sampling points requires attention. Differences may appear according to the locations of probes in the basin (Tables 5, 6 and 7).Sulfite pre-dissolution has no influence on results and should be avoided whenever possible.     

Quantitative three-dimensional description of a rough surface and parameter evolution with shearing

The choice of a general criterion to determine the shear strength of rough rock joints is a topic that has been investigated for many years. The major problem is how to measure and then to express the roughness with a number (e.g., joint roughness coefficient) or a mathematical expression in order to introduce the morphology of the joint into a shear strength criterion. In the present research a large number of surfaces have been digitised and reconstructed using a triangulation algorithm. This approach results in a discretisation of the joint surface into a finite number of triangles, whose geometric orientations have been calculated. Furthermore, during shear tests it was observed that the common characteristic among all the contact areas is that they are located in the steepest zones facing the shear direction. Based on this observations and using the triangulated surface data, it is possible to describe the variation of the potential contact area versus the apparent dip angle with the expression A_θ^*=A₀[(θ_max^*−θ^*)/θ_max^*]^C, where A₀ is the maximum possible contact area, θ_max^* is the maximum apparent dip angle in the shear direction, and C is a “roughness” parameter, calculated using a best-fit regression function, which characterises the distribution of the apparent dip angles over the surface. The close agreement between analytical curves and measured data therefore suggests the possibility of defining the influence of roughness on shear strength by the simple knowledge of A₀, C and θ_max^*. Based on the samples studied here, the values of these parameters capture the evolution of the surface during shearing. Moreover, they tend to be characteristic for specific rock types, indicating that it might be possible to determine ranges for each rock type based on laboratory measurements on representative samples.     

A modified Hoek–Brown failure criterion for anisotropic intact rock

The Hoek–Brown criterion parameters (σ_ci, m_i and s) are significantly influenced by the strength anisotropy of intact rock. In the present study, the criterion was modified by incorporating a new parameter (k_β) to account for the effect of strength anisotropy, thus being able to determine the strength of intact anisotropic rock under loading in different orientations of the plane of anisotropy. The range of the parameter (k_β) for the rocks tested has been analytically investigated by carrying out triaxial tests, in different orientations of the foliation plane. The proposed modification was studied for metamorphic rocks (gneiss, schist, marble), but could also be applied to other rock types exhibiting “inherent” anisotropy, e.g. sedimentary as well as igneous rocks. The proposed modified criterion is intended for use for prediction of strength of intact rock, but can also be extended to rock masses.     

Hydraulic performance of percolating biological filters and consideration of oxygen transfer

A distinct difference exists between the experimentally measured and theoretically calculated values of residence time in percolating biological filters. From existing information it was shown that the measured values are usually at least three times higher than those calculated theoretically. Based on several premises, it was concluded that two liquid film layers should be distinguished. One “free” liquid film flowing on top of the biofilm, the second “captured” flowing through the biofilm.From experimentally measured residence time, it becomes evident that the total liquid film depth will be in the region of 150–550 μm for a hydraulic load range of 0.02–5 m³m⁻²m⁻¹. It can be proved that oxygen cannot penetrate up to such a depth, especially when the captured liquid film thickness is in the region of 110–380 μm. The largely anoxic conditions in the captured liquid film are in drastic contrast with the prevailing conditions close to oxygen saturation in the free flowing liquid layer. Due to the large developed surface the outflowing liquid can be saturated with oxygen. The measured oxygen concentration in filter effluent does not reflect the aerobic conditions neither in the captured liquid film nor in the biofilm as such.     

Coefficient of restitution and rotational motions of rockfall impacts

This paper presents experimentally obtained results for the coefficient of restitution for spherical boulders impacting on rock slopes. Plaster modeling material is used for casting both the boulders and slopes. It is observed that the normal component of the coefficient of restitution (R_n) increases with the slope angle α, which agrees with Wu's observations (Trans. Res. Rec. 1–5 (1985) 1031). However, there appears to be no clear correlation between the tangential component of the coefficient of restitution (R_t) and the slope angle α. When the ratio of the resultant velocities and the ratio of the kinetic energies before and after impacts are used to define the coefficient of restitution (i.e. R_V and R_E), a very clear increasing trend in the coefficient of restitution with α is observed. When all data are plotted onto the R_t−R_n space, our laboratory data fall into the rock slope regime proposed by Fornaro et al. (In: D.G. Price (Ed.), Proceedings of the Sixth International Congress IAEG, Amsterdam, Balkema, Rotterdam, 1990, p. 2173) and also agree with those data gleaned from literature. In addition, the rotational kinetic energy E_r, induced at each impact, increases with the slope angle α, achieves a maximum at about α=40°, before decreasing again to a negligible value at α=70°. A simple theoretical model is proposed to explain this observation based on the locking between the boulder and the slope during impact. The α-dependence of E_r differs from the recommendation by the Japanese Railway Association that the induced rotational energy is about 10% of that of the translational kinetic energy.     

The effects of copper on maximum respiration rate and growth rate of perch, Perca fluviatilis L.

Addition of copper to the ambient water of perch resulted in decreased daily maximum respiration rates (R_max) and growth rates. The time-course of the effect in R_max was characterized by: (1) an initial decrease over three additions; (2) a minimal “trough” lasting some 10–15 days; and (3) a phase of increasing R_max. The variation in R_max was due to copper concentration and exposure time. The decrease in growth rate was most dramatic initially and was correlated to copper concentration and perch weight. The subsequent increase in growth rate was constant and independent of copper concentration. The increase in R_max and in growth rate was interpreted as acclimatization. Up to a given sublethal copper concentration acclimatization resulted in a return to the control level of R_max but not of growth rate.     

Determination of no effect levels of heavy metals for rainbow trout using hepatic metallothionein

Rainbow trout (Salmo gairdneri) were exposed to various sublethal concentrations of a mixture of zinc, copper and cadmium for periods of time ranging from 4 to 16 weeks and the concentration of metallothionein (MT) in the livers was determined. The data were described by linear regressions of hepatic MT (with 95% confidence limits) against concentration of metal. From these data could be determined a “no observable effect” concentration for each metal at which the concentration of hepatic MT in exposed fish was not distinguishable from that in unexposed fish. The value thus determined was in close agreement with estimates of the “no observable effect” concentrations of zinc, copper and cadmium calculated for soft water by other authors. The elevation of hepatic MT in rainbow trout therefore appears to provide a useful biological response for the estimation of “no observable effects” of zinc, copper and cadmium in mixture in the natural environment.     

Toxicity of silver to rainbow trout (Salmo gairdneri)

The mean 96-h LC₅₀'s of silver with rainbow trout were 6.5 μg l⁻¹ and 13.0 μg l⁻¹ in soft water (approximately 26 mg l⁻¹ hardness as CaCO₃) and hard water (350 mg l⁻¹ hardness as CaCO₃), respectively. The long-term, “no effect” concentration for silver, added to the water as silver nitrate, was between 0.09 and 0.17 μg l⁻¹ after 18 months exposure in soft water. The “no effect” concentration is that concentration range which defines no observed effect. Based on mortalities different from the control, no mortalities attributable to silver occurred at 0.09 μg Ag l⁻¹, whereas 17.2% mortality occurred to fish exposed to 0.17 μg ll⁻¹. The “no effect” concentration does not reflect possible effects of silver on spawning behavior or reproduction, since female rainbow trout will not generally reach sexual maturity before 3 yr. At silver concentrations of 0.17 μg l⁻¹ or greater, silver caused premature hatching of eggs and reduced growth rate in fry. In one experiment, the eggs were completely hatched within 10 days of exposure; whereas, control eggs completed hatching after 42 days. The prematurely erupted fry were not well developed and frequently died. The growth rate of surviving fry was greatly reduced.     

Sorption of hydrophobic pollutants on natural sediments

The sorption of hydrophobic compounds (aromatic hydrocarbons and chlorinated hydrocarbons) spanning a concentration range in water solubility from 500 parts per trillion (ppt) to 1800 parts per million (ppm) on local (North Georgia) pond and river sediments was investigated. The sorption isotherms were linear over a broad range of aqueous phase pollutant concentrations. The linear partition coefficients (K_p) were relatively independent of sediment concentrations and ionic strength in the suspensions. The K_p ś were directly related to organic carbon content for given particle size isolates in the different sediments. On an organic carbon basis (K_{oc = Kp/fraction}) organic carbon), the sand fraction (> 50 μm particle size) was a considerably less effective sorbent (50–90% reduction in K_oc) than the fines fraction (> 50 μm particles). Differences in sorption within the silt and clay fractions were largely related to differences in organic carbon content. Reasonable estimates of K_ocś can be made from octanol/water distribution coefficients, which are widely catalogued or easily measured in the laboratory.     

Evaluation of geosmin and 2-methylisoborneol on the histidine dependence of TA98 and TA100 Salmonella typhimurium tester strains

Low (ca 0.01 ppb) concentrations of the naturally occurring terpene derivatives geosmin (1α, 10β-dimethyl-9α-decalol) and 2-methylisoborneol [(1-R-exo)-1,2,7,7-tetramethyl-bicyclo-(2,2,1)-heptan-2-ol] (MIB), impart earthy/muddy “off-flavors” to many water and food resources. The presence of these “off-flavors” often elicits public concern over the safety of the affected resources. The “Ames test”, assesses the induction of reverse mutation at the histidine locus in specially constructed Salmonella typhimurium tester strains, and is a widely used index of mutagenicity. This investigation indicated that neither MIB nor geosmin, when tested up to cytotoxic levels in both the presence and absence of exogenous metabolic activation, induced a mutagenic response in either strain TA98 or TA 100 compared to controls. Doses of MIB and geosmin above 45.2 and 18.1 ppm, respectively, inhibited tester strain growth, indicating that high concentrations of these metabolites may exhibit an antimicrobial activity, possibly by a mechanism similar to that reported for certain other terpene derived alcohols. Food or water resources containing similar concentrations of geosmin or MIB would be extremely unpalatable and would probably not be consumed.     

Shaft resistance of a pile embedded in rock

A rational calculation procedure is proposed for establishing the shaft resistance of a pile embedded in rock, based upon the Hoek and Brown failure model. The state of the art of the calculation of the pile shaft resistance is analysed. Nearly all the recommendations that have appeared in the technical literature, for calculating the ultimate shear strength of a shaft embedded in rock (τ_ult) propose that τ_ult=ασ_c^k(σ_c;τ_ulten MN/m²) where the coefficient α, considered as a constant dimensional value, ranges from 0.1 to 0.8, if the unconfined compressive strength (σ_c) is expressed in MN/m². In most cases, the exponent k is 0.5.A comparison is made between the results yielded and the different empirical theories that have been put forward with respect to this shaft resistance. It can generally be stated that the results obtained with this theory are reasonable for long and deeply socketed piles (high confining pressures) but the results are on the safe side in some cases where short piles (low confining pressures) are involved.This paper is a continuation of the works developed by the same authors with piles working at the tip, socketed in rock.     

Glucose mineralization activity and the use of the heterotrophic activity method in an acidified lake

This paper concerns bacterial glucose mineralization in Silver Lake sampled during the summer; specifically, whether or not it occurs, and whether or not the “heterotrophic activity method” can be used to measure it, in this acidified lake.For Sampling I, linearity between turnover time (t/f) and added substrate concentration (A) did not exist at the in situ pH (3.2) or the experimental pH's (5.5 and 7.0), even though time studies showed that glucose was being mineralized at measurable rates. For Sampling II, modifications were made to the concentrations of labelled glucose and the incubation time. A highly significant linear relationship between t/f and A was demonstrated, and the turnover time and V_max were calculated to be 472.3 h and 0.005 μm l⁻¹ h⁻¹, respectively. For Sampling III, even though the environmental conditions were similar to those for the previous sampling, a statistically-significant relationship between t/f and A did not result.