Determination of phosphate in wastewaters by ion-exclusion chromatography with flow coulometric detection

Ion-exclusion chromatography of PO₄³⁻ in wastewaters has been investigated on a cation exchange resin in the H⁺-form. Phosphate ion was chromatographed by ion-exclusion as H₃PO₄ formed by cation exchange, and monitored with a flow coulometric detector based on the electrochemical reaction of H⁺ ion from H₃PO₄ and p-benzoquinone at a constant applied potential (+0.45 V vs Ag-AgI) or a conductometric detector. A reasonable separation of PO₄³ from strong acid anions (Cl⁻ SO₄²⁻ and NO₃⁻) and CO₃²⁻ as coexisting anions could be accomplished by isocratic elution with 60% (v/v) acetone-water. The calibration graph for PO₄³⁻ with the flow coulometric detector was linear over the concentration range 1–150 ppm (slope = 0.982), but not with the conductometric detector. The agreement of the analytical results of PO₄³⁻ between the ion-exclusion chromatography with the flow coulometric detector and the colorimetry (molybdenum-blue method) was excellent for some industrial wastewater and domestic sewage samples.     

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.     

pH adjustment in anaerobic digestion

In the pH range 6·0–7·5, the pH in anaerobic processes is controlled by the interaction of the carbonic system and a net strong base. The acid-base state of a digestor can be monitored by only measuring pH and CO₂ partial pressure. Shock doses of strong bases and carbonates causes temporary undersaturated CO₂ conditions and excessively high pH. Bicarbonate dosing leaves the CO₂ solubility equilibrium unchanged. In the absence of a CaCO₃ precipitation inhibiting agent. CaCO₃ solubility limits the pH, and Ca(OH)₂ dosing is unable to raise the pH significantly. Orthophosphates inhibit CaCO₃ precipitation. With [PO₄] > 1·0 × 10⁻³mole·1⁻¹. CaCO₃. precipitation is partially inhibited. Ca(OH)₂ dosing being approximately 45 per cent effective for doses up to 15000 mg 1⁻¹ as CaCO₃. At [PO₄] < 1·0 × 10⁻³moles·1⁻¹ orthophosphates eventually precipitate out during Ca(OH)₂ dosing, thus removing the inhibition mechanism: pH is then limited by the CaCO₃ solubility. Most wastes contain [PO₄] > 2·0 × 10⁻³moles·1⁻¹ making pH adjustment with Ca(OH)₂ possible to a pH of about 7·2 although the dosages will be very high. The pH changes in a process following dosing can be predicted by the graphical representation of the carbonic and net strong base systems.     

Effects of salinity on synthesis of DNA, acidic polysaccharide, and growth in the blue-green alga, Gomphosphaeria aponina

A blue-green alga, Gomphosphaeria aponina, was grown in artificial sea water at salinities 20–36%. Fair to good growth was obtained at all salinities, and growth constants (K_e) were obtained. A parabolic relationship was obtained for the growth salinity relationship, e.g. (S−S_max)² = −2p(K_e−K′_e), where S and S_max is the given salinity and the maximum salinity, respectively, for which growth constants K_e and K_e^′ were obtained; p is a constant. The rate of DNA synthesis increased linearly with growth constant above K_e = 0.95 day⁻¹. Linear correlation coefficients were obtained for rate of polysaccharide synthesis and the rate of DNA synthesis, as well as for the rate of DNA synthesis and the rate of synthesis of aponin. The latter is material isolated from G. aponina and has cytolytic activity toward the Florida red tide organism, Gymnodinium breve, an unarmoured dinoflagellate.     

Biologically induced phosphorus precipitation in aerobic granular sludge process

Aerobic granular sludge is a promising process for nutrient removal in wastewater treatment. In this work, for the first time, biologically induced precipitation of phosphorus as hydroxyl-apatite (Ca₅(PO₄)₃(OH)) in the core of granules is demonstrated by direct spectral and optical analysis: Raman spectroscopy, Energy dispersive X-ray (EDX) coupled with Scanning Electron Microscopy (SEM), and X-ray diffraction analysis are performed simultaneously on aerobic granules cultivated in a batch airlift reactor for 500 days. Results reveal the presence of mineral clusters in the core of granules, concentrating all the calcium and considerable amounts of phosphorus. Hydroxyapatite appears as the major mineral, whereas other minor minerals could be transiently produced but not appreciably accumulated. Biologically induced precipitation was responsible for 45% of the overall P removal in the operating conditions tested, with pH varying from 7.8 to 8.8. Major factors influencing this phenomenon (pH, anaerobic phosphate release, nitrification denitrification) need to be investigated as it is an interesting way to immobilize phosphorus in a stable and valuable product.     

Fatty acid fouling of reverse osmosis membranes: implications for wastewater reclamation

Effluent organic matter (EfOM) contributes significantly to organic fouling of reverse osmosis (RO) membranes in advanced wastewater reclamation. In this study, the effect of feed solution chemistry (solution pH and Ca²⁺ concentration) on the fouling of RO membranes by octanoic acid—selected to represent fatty acids in EfOM—is investigated. Crossflow fouling experiments demonstrate that RO membrane fouling is much more significant at solution pH below the pK_a of the octanoic acid (pK_a = 4.9) than at an elevated pH. Octanoic acid permeates across the membranes more readily at solution pH below its pK_a than at elevated pH. At pH below the octanoic acid pK_a, fouling behavior is not affected by calcium ions, whereas at elevated pH, the rate of flux decline decreases with higher calcium ion concentration. The effect of calcium on the fouling behavior was further verified from foulant-foulant adhesion forces, determined by atomic force microscopy (AFM) force measurements under solution chemistries identical to those of the crossflow fouling experiments. To investigate the implications of octanoic acid fouling for wastewater reclamation, the effect of octanoic acid on membrane fouling by a combination of organic foulants in the presence of calcium ions is studied. At a solution chemistry simulating that of typical wastewater effluents, the addition of octanoic acid to a feed solution containing alginate, bovine serum albumin, and Suwannee River natural organic matter, does not enhance membrane fouling behavior. This observation could be attributed to the significant contribution of the alginate-calcium complexes within the fouling layer to the total membrane resistance.     

A kinetic model of steady state phosphorus fixation in a batch reactor—II. Effect of pH

Measurements of phosphorus fixation at the soil/solution ratio of 250 mg 500^?1 ml at pH = 2, 3, 5, 7 and 8 in a batch reactor with steady input of phosphate were carried out. All results reached a steady state and followed a Michaelis-Menten type equation as predicted for the catalytic process. Maximum rate of reaction showed a decrease with increase of pH due to the competitive effect between OH^? and H₂PO^?₄. The maximum value of 1/K at pH = 5 showed H₂PO^?₄ may be required in phosphorus adsorption for some specific-bonding mechanism with soil.     

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.     

Towards a better understanding of high rate biological film flow reactor theory

On the assumption that performance of biological film flow reactors is independent of oxygen transfer, a theoretical extension of a mathematical model (after Ames) is described. This predictive and interpretive model incorporates both mass transfer-limitations between biomass and liquid film, and kinetic biological reaction rate of organic “food” utilization.Given general boundary conditions for the differential equations describing the mass transfer process, it is shown that: C_e = C_r + (C_l − C_r.exp(−K_m D/Q) where by definition: C_t = α C_s + C_r1/K_m = 1/K_LA_γ + α/Kx.For an influent concentration biochemical oxygen demand (C_i) and resultant effluent concentration (C_e) obtained during film flow through a packed media depth (D), the Model proposes that the residual concentration (C_r) is a function of surface irrigation rate (Q) and biomass activity. If this term is negative, adsorption occurs; while if positive, desorption from the biomass film at concentration (C_s) takes place.An overall mass transfer coefficient (K_m) is defined by a series equation where the usual mass transfer coefficient (K_L) is primarily a function of Reynolds Number [surface irrigation rate (Q) and specific surface area (A_V)], Schmidt Number (diffusivity of organic “Food”) and concentration. “Food” utilization at active sites on the biological film is governed by a specific adsorption coefficient (α) and explained by a Langmuir analogy. Biological conversion of “food” is described by a kinetic rate constant (K), while the necessary oxygen is defined by (X).This predictive model was developed from a wide range of pilot plant data, successfully tested further on a variety of published results and on actual full scale operating plants.Parameters derived from this Model, in terms of Height of Transfer Unit and Kinetic Reaction coefficient, characterize organic “treatability” for a variety of wastes.     

Equilibrium approaches to natural water systems—6. Acid-base properties of a concentrated bog-water and its complexation reactions with aluminium(III)

A filtered bog-water, concentrated by means of a freezing technique, has been studied with respect to acid-base properties and aluminium(III) complexation reactions. Sampling was performed during autumn and winter periods with a resulting acidity or alkalinity due to oxic (autumn) or anoxic (winter) conditions. The measurements were performed as potentiometric titrations in constant ionic media (0.02, 0.1 and 0.6 M NaCl) with the use of a glass electrode. The samples show buffer ranges at 3 pH 5 and pH 7.5. The first is ascribed to the presence of carboxylate groups and is characterized by fast equilibria. The second is due to phenolic OH⁻ groups and precipitation reactions with resulting sluggish equilibria. For one sampling period comprehensive measurements were undertaken to study the possible polyelectrolytic character of the organic acids. Due to the small increase in apparent carboxylate pKa-values with the degree of dissociation at low (0.02 M) as well as at high (0.6 M) ionic strength, the possible polyelectrolytic feature of the acids was neglected. Instead, a good fit to data was obtained by introducing a di-protic acid (H₂L) as a model compound. Furthermore the medium dependence of the two acidity constants could satisfactorily be fitted to the expression:

Full-size image (1K)

, where K is the constant at infinite dilution, a and b parameters of which b has been adjusted to present data. The following K values were obtained: pK₁ = 3.65 and pK₂ = 4.30. The complexation with Al(III) could be described by the formation of AlL⁺, AlL₂⁻ and the ternary species AlLH₋₁. The stability constants (log k₁ = 4.4 (winter), 4.2 (autumn); log k₂ = 4.2, 4.7; pKa (AlL⁺) = 4.2, 4.2) show no significant trend with sampling period but indicate a stability of the complexes greater than for phtalic acid but lower than for oxalic acid. Finally, the theoretical solubility of the clay mineral kaolinite in the presence of bog-water was computer modelled. The calculations show up on a 10-fold increase with respect to soluble aluminium at pH = 5.     

Effects of lignin and chlorolignin in pulp mill effluents on the binding and bioavailability of hydrophobic organic pollutants

The partition coefficients (K_p) of benzo(a)pyrene (BaP), 3,3′,4,4′-tetrachlorobiphenyl (TCB) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to dissolved kraft lignin (Indulin AT), chlorolignin isolated from a bleached kraft mill effluent (BKME) and dissolved organic matter (DOM) in a lake receiving BKME were measured by equilibrium dialysis. The K_p values of kraft lignin were 28.2 × 10⁵, 6.5 × 10⁵ and 15.9 × 10⁵ and those of chlorolignin were 8.3 × 10⁵, 2.9 × 10⁵ and 2.2 × 10⁵ for BaP, TCB and TCDD, respectively. In addition, DOM in a series of lake water samples collected from the southern part of Lake Saimaa, SE Finland, receiving BKME revealed higher binding capacities to all of the three model compounds than natural DOM in water upstream from the pulp mill. An important phenomenon related to the environmental transport and fate of xenobiotics was almost the full reversibility of the binding between chlorolignin and model compounds. The obtained K_p values of chlorolignin after a 4 day dissociation period were 12.6 × 10⁵ and 4.6 × 10⁵ for BaP and TCDD, respectively.In short-term (24 h) accumulation experiments with Daphnia magna the effects of kraft lignin and chlorolignin on the bioavailability of three model compounds was very clear. The bioconcentration factors of the xenobiotics in the chlorolignin containing water (DOC = 10 mg C/l) were 20–30 and 25–35% of those organic-free control and upstream reference waters (DOC = 7.2 mg C/l), respectively. The effect of chlorolignin of BKME on the bioavailability of model compounds was also seen in the lake water series of Lake Saimaa.     

A comprehensive study on the biological treatabilities of phenol and methanol—III Treatment system design

The effects of temperature, pH, salinity, and nutrients on bacterial activities were investigated and evaluated using a statistical method. The substrate utilization rate coefficient (k) decreased as pH deviated from neutral and as salinity increased, and the unfavorable pH and salinity alleviated the temperature effect on k. The modified Arrhenius equation, k_T2 = k_T1 θ(^T2−T1), was not effective in describing the temperature effect on k: the temperature coefficient (θ) ranged between 1.0–1.4 depending on the temperature range, pH, salinity, and substance (phenol or methanol). The endogeneous respiration activity was affected by various environmental factors such as pH, temperature, and salinity; however, the cell decay coefficient (k_d) turned out to be correlated to a single parameter, k. Thus, k_d = 0.066 k^0.87 and k_d = 0.0115 k^0.634, where k and k_d are based on the unit of h⁻¹, were proposed for the prediction of cell decay coefficient for phenol and methanol acclimated activated sludge, respectively. In batch treatment of 770 mg l⁻¹ of phenol and 1000 mg l⁻¹ of methanol as TOC, nitrogen and phosphorus did not have any recognizable effect on k, while trace elements such as Fe²⁺, Mg²⁺, Mn²⁺, Ca²⁺, and Zn²⁺, etc. showed a slightly perceptible effect on it. The absence of extra-cellular nitrogen and phosphorus resulted in a greater cell yield; however, the cells in this condition decayed more rapidly than normal cells. The primary factor affecting the substrate decomposition rate in natural systems was pH: phenol decomposition resulted in a considerable decrease in pH so that the buffering capacity of the water was the most important factor, and methanol decomposition did not affect pH significantly so that the initial pH of the water was the most important factor. An initial lag phase was observed in 8 out of 115 phenol batch tests and 31 out of 66 methanol batch tests.     

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.     

Conditions required for the precipitation of aluminium in acidic natural waters

Laboratory and field studies were carried out in order to define the conditions necessary for the precipitation of Al in natural waters of pH 4–6. It is concluded that if precipitation does occur it involves the formation of Al(oxy)hydroxide, not aluminosilicates or basic aluminium sulphates. The solubility product of the Al(oxy)hydroxide is highly temperature dependent (ΔH = −30.5 kcal⁻¹). It is also sensitive to concentrations of SO₄²⁻ and, more markedly, humic substances (HS); both of these decrease solubility, HS by more than an order of magnitude at a concentration of approx. 5 mg l⁻¹ (equivalent to approx. 2.5 mg l⁻¹ dissolved organic carbon). A semi-empirical equation is proposed that allows the prediction of the effective solubility product at different temperatures and at humic concentrations in the range 0–7 mg l⁻¹. Of the 113 natural water samples analysed, only one was calculated to be oversaturated with respect to Al(oxy)hydroxide.     

Études des transformations des formes du carbone, azote, phosphore, soufre et des principaux éléments minéraux au cours de la mesure de la demande totale en oxygene—III transformation des formes du soufre

Previous experiments carried out with the laboratory TOD meter Ionics 225 of the DOW Chèmical made it possible (after a high temperature catalytic action) to characterize the stable forms of organic and inorganic carbon and nitrogen (NH₄⁺, NO₂⁻, NO₃⁻), and the principal cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) in the course of the total oxygen demand (TOD) measurement.The object of this study is firstly to compare the oxidation capability of different techniques of organic pollution (particularly the COD and TOD) in relation to the constituent elements of the organic matter C, N, P, S, and to calculate the possible interferences of the inorganic compounds at the time of TOD test.These investigations warrant the application of this technique to measure the amount of organic pollution in relatively mineralized conditions (Industrial wastewater, sea-water…). The present publication is concerned more with the study of the transformation of the organic and inorganic sulphur forms (S²⁻, SO₃²⁻. SO₄²⁻) in the course of the TOD measurement.The study of the oxidizability of the organic sulphur compound type C_xH_yO_zS, made it possible to establish a specific relation with a ratio of 0–50 mg of organic sulphur l⁻¹, between the oxygen demand of this element [TOD (S)] and its concentration (TOD (S) = 0.97 [S]).These tests showed a partial oxidation of the sulphur to SO₂ and SO₃ as the literature claimed. On the other hand, the oxidation of the same compounds during the COD tests varies greatly and although it is not possible to establish a correlation between these two measurements, as applies in the case of organic nitrogen, nevertheless these experiments showed a greater reliability of the TOD compared with the COD in the oxidation of organic matter in general. We then carried out experiments on the different mineral forms of sulphur in order to distinguish the possible effects and to recommend simple improvements.A relative study on sulphate ions had been carried out with standard solutions which have the same TOD (the basic TOD is obtained using potassium phthalate acid) and the same increasing concentration of the salt M₂SO₄ type. The experiments showed that the basic TOD decreases when the concentration of sulphate ions is increased (Fig. 3). Therefore, the interference is negative and taking into consideration the specific oxygen demand of the cation, we can propose an evaluation of this interference (ΔTOD (SO₄²⁻) = 0.203 [SO₄²⁻]). The same experiments have been conducted with a salt of M₂SO₃ type and similar results obtained (Fig. 5).The specific interference of the sulphite ion is negative and can be estimated by the following equation (ΔTOD (SO₃²⁻) = 0.132 [SO₃²⁻]). In both cases, we have to note that the transformation of these inorganic anions occurs between those relative to the theoretical dissociation reaction corresponding to the appearance of the oxide SO₂ and SO₃. For sulphurous on the contrary, the interference is positive and therefore corresponds to an extra oxygen demand (Fig. 8).The experiments were conducted directly with the M₂S salts (M representing K or Na) in aqueous solution.The evaluation of this interference had been made in the consideration of two concentration ranges of the sulphurous ions (0–35 mg S²⁻ l⁻¹): TOD (S²⁻) = 0.4 [S²⁻] and (35–100 mg S²⁻ l⁻¹): TOD (S²⁻) = 1.2 [S²⁻] − 30.Therefore this study confirms a better oxidation of the organic matter by TOD test in comparison with COD test.But sulphate and sulfite have a negative interference in the TOD measurement, whereas sulphurous is positive.The evaluation model of these interferences allows a correction to be made of the TOD value or to verify TOD measurement of organic pollution obtained by this technique.     

Kinetic study for phosphate removal from water by recycled date-palm wastes as agricultural by-products

The presence of excessive amounts of nutrients including phosphates in water is undesirable. They cause the deterioration of water quality and problems in many natural and engineering systems. The recycling of agricultural waste materials as biosorbents for contaminants removal provides a cheap and ecological means to reduce wastes. This study explored the use of date palm wastes for the effective removal of phosphate from aqueous solutions. Granular date stones (GDS) and palm surface fibres (PSF) as raw abundant waste materials were examined for PO₄ ^-3 removal from aqueous solution. The experimental work was performed in a batch mode to investigate the influence of initial phosphate concentration, contact time, and pH of solution on phosphate biosorption. The FT-IR spectra for the waste materials display many adsorption peaks, confirming the complex nature of the GDS and PSF. Phosphate percentage removal up to 87 and 85% were obtained at initial PO₄ ^-3 concentration of 50 mg as P/L using GDS and PSF, respectively. Due to their low cost and high capability, these types of waste can be used for cost-effective removal of phosphate from wastewater.     

Detoxification of seawater used for gas scrubbing in the steel industry

Cyanide ion present in seawater after scrubbing blast furnace and coke ovens gases can be removed by sedimentation of hexacyanoferrate complexes followed by oxidation of residual cyanide with Caro's acid. Zinc ion is removed at the same time by adsorption on the hexacyanoferrate/hydrous ferric oxide precipitate.Sulphide is precipitated as ferrous sulphide, then oxidised by atmospheric oxygen. At 25°C and using an Fe/CN ratio of 1·00, initial concentrations of 50 mg l⁻¹ of CN⁻ and 10 mg l⁻¹ of Zn²⁺ in seawater are reduced to 5–7 mg l⁻¹ and 0·1 mg l⁻¹. Subsequent treatment with H₂SO₅/CN = 1·2 reduces the [CN⁻] to 0·1 mg l⁻¹.Treatment of a combined blast furnace/coke ovens effluent ([CN⁻] = 24 mgl⁻¹, [Zn²⁺] = 4·0 mgl⁻¹) with Fe/CN = 1·5 reduced [CN⁻] to 0·2 mg l⁻¹ and [Zn²⁺] to <0·1 mgl⁻¹. Subsequent treatment with H₂SO₅/CN = 2·0 reduced [CN⁻] to 0·2 mg l⁻¹. The process operates best in the pH range 7–9 and so is not affected by the buffer characteristics of seawater.     

Floatation extraction of thinly-emulsified tributyl phosphate stabilized by silicic acid

We have studied regularities of floatation extraction of fine-emulsion tributyl phosphate stabilized by silicic acid. Most completely the floatation process occurs at pH 5–6. At the concentration of silicic acid 500–550 mg/dm³ the degree of floatation extraction of tributyl phosphate (α) reaches 70% (floatation time of tributyl phosphate is 10 min). In the presence of HNO₃ (1–5 mol/dm³) the value α passes through the maximum at \(C_{HNO_3 } \)= 3 mol/dm³. A conclusion was made about an important role in the studied floatation process of not only electrical, but also structural-mechanical properties of the surface of the air drops and bubbles.     

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.