A modified version of the sodium salicylate method for analysis of wastewater nitrates

The German sodium salicylate method for nitrate determination has been modified and improved by utilizing flocculating effect of the preservative HgCl₂ (1000 mg 1⁻¹). The method gives highly reproducible results in the range of 0·2–16 mg 1⁻¹ nitrate nitrogen and is applicable for routine analysis of untreated sewage. Interfering substances are chloride ions above 1500 mg 1⁻¹ and nitrite ions above 10 mg 1⁻¹N. The yellow color produced by sodium salicylate with nitrate ions obeys Beer's law and remains stable for several hours.     

The 10 m h rim-nut demonstration plant at West Bari for removing and recovering N and P from wastewater

The RIM-NUT, a new ion exchange-precipitation process for removing and recovering ammonium and phosphate ions from wastewater, has been tested on a 10 m³ h⁻¹ demonstration plant for tertiary treatment of West Bari domestic effluent. Natural zeolite clinoptilolite and a porous strong base resin, regenerated in a “closed-loop” fashion with 0.6 M neutral NaCl, ensure ≥90% removal of both nutrient species. Nutrients are precipitated from resin eluates as MgNH₄PO₄, a premium quality slow-release fertilizer.     

Recovery of chromium(VI) from wastewaters with iron(III) hydroxide—I: Adsorption mechanism of chromium(VI) on iron(III) hydroxide

Chromium(VI) [Cr(VI)] is adsorbed as HCrO⁻₄ on iron(III) hydroxide at pH below 8.5. The Cr(VI) adsorption is suppressed by the presence of other anions such as SO²⁻₄ and SCN⁻, and enhanced by the presence of metal ions such as Cd(II) and Pb(II). The suppression is due to the competitive adsorption of other anions, depending upon the stability of their iron complexes. The enhancement is probably due to the increase in adsorption sites as a result of coprecipitation of metal ion with iron(III) hydroxide.     

Some problems in the determination of total residual “chlorine” in chlorinated sea-water

In the determination of residual chlorine in sea-water by the amperometric titrimetric method, potassium iodide must be added to the sample before the addition of the pH 4 buffer, and the addition of these two reagents should not be more than one minute apart. Serious analytical error may arise if the order of the addition of the reagents is reversed. There is no evidence suggesting the formation of iodate by the reaction between hypobromite and iodide. For concentrations of residual chlorine below one mg 1⁻¹, iodate, which occurs naturally in sea-water, may cause serious analytical uncertainties. In sea-water, the preferred concentration unit of residual chlorine is μM. The unit, mg 1⁻¹, must be used with care and clear definition. The unit, ppm, should be avoided.     

Some practical aspects of the “biocarbon process”

In the presence of granular activated carbon the aerobic decomposition of organic compounds is facilitated (Koppe et al., 1974a,b). As could be shown by many laboratory tests several effects are given. First of all the faster adaptation of the bacteria has to be mentioned which is most important with substances which are difficult to be degraded like pentaerythrite. Additionally the degradation efficiency of the activated sludge process will be increased and equalized by granular activated carbon. Finally the effect of low temperatures can be compensated by the presence of granular activated carbon. With domestic wastewater for instance full nitrification could be obtained at a temperature of 4°C.Adsorption of organic compounds cannot be the explanation because the effect could be observed during several months whereas the calculated adsorption capacity had to be exhausted after two days. True causes are that specialized bacteria are retained in the pores and niches of the activated carbon in the lag-phase, that micro-organisms find area to grow in the log-phase (approximately 100 m²/m³ with 1 kg m⁻³ granular activated carbon) and that the enrichment of some exoenzymes at the activated carbon occurs (compare Figs. 1 and 2; and Müller & Sekoulov, 1975; Lue-Hing et al., 1976; Larsson et al., 1976; Rincke & Wolters, 1970). Since micro-organisms and activated carbon intimately react, this modification of the activated sludge process was called “biocarbon process” which has to be distinguished from the process with powdered activated carbon (de Walle & Chian, 1977).After completion of the laboratory tests, full-scale tests were started. In full-scale tests several difficulties had to be overcome. In some cases it was difficult to avoid the sedimentation of the granular activated carbon in the aeration tanks. Another task was the separation of the carbon from the surplus activated sludge. Finally it was of interest to determine how much carbon is lost by wet abrasion to be able to make a feasibility calculation. The full-scale tests have been performed in two wastewater treatment plants of the Ruhrverband: Nordenau and Günne.     

Effect of surfactants on the determination of sulphate in waters

The effects of pure cationic, anionic and non-ionic detergents, industrially prepared detergents, sodium tripolyphosphate, sodium pyrophosphate, soap and NTA, in quantities up to 1000 mg l⁻¹, on the analysis of soluble iron in water using the phenanthroline, tripyridine and biquinoline methods were investigated. The tripyridine method is superior to the other two methods for the determination of iron in the presence of up to 1000 mg l⁻¹ of various surfactants but not for up to 100 mg l⁻¹ of non-ionic detergents. The phenanthroline method can be used to determine iron in the presence of up to 1000 mg l⁻¹ of cationic, anionic and non-ionic detergents, but sodium tripolyphosphate interfered above 2 mg l⁻¹. The biquinoline method can be used for the determination of iron in the presence of up to 1000 mg l⁻¹ of cationic, 100 mg l⁻¹ of anionic and 70 mg l⁻¹ of non-ionic detergents, and 50 mg l⁻¹ of sodium tripolyphosphate.     

Investigation of the Folin-Ciocalteau phenol reagent for the determination of polyphenolic substances in natural waters

The methodology associated with the Folin-Ciocalteau phenol reagent was investigated and the performance characteristics of a method using sodium carbonate as the supporting medium were determined. Calibration curves using phenol, tannic acid, or l-tyrosine were linear up to at least 1000 μg l⁻¹. The limit of detection was 6 μg phenol l⁻¹ and the relative standard deviation at 100 μg phenol l⁻¹ was 5.2% and at 1000 μg phenol l⁻¹ was 4.1%. The absorbances obtained with equal amounts of a range of potential standards showed variations when compared with that of phenol: phenol (100%), l-tyrosine (62%), oak gall tannin (58%), tannic acid (48%), chestnut tannin (26%), oak tannin (24%), fulvic acid (5%). The method was applicable to a wide range of monohydric and polyhydric phenolic substances and interferences from inorganic and non-phenolic organic compounds were examined. Interference would be expected above 30 μg S²⁻ l⁻¹, 300 μg Mn(II) l⁻¹, or 400 μg SO₃²⁻ l⁻¹. Concentrations of iron >2 mg l⁻¹ as Fe(II) or Fe(III) formed the insoluble iron(III) hydroxide which increased the absorbance, but centrifugation could be used to remove this source of interference. Other potential sources of intereference (e.g. reducing agents and certain metabolic products) would be expected to have a negligible effect in unpolluted waters. Methods using diazotised sulphanilic acid or 4-aminoantipyrine (4-AAP) were found to be inferior when applied to natural water samples.     

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.     

The methanogenic toxicity and anaerobic degradability of a hydrolyzable tannin

Gallotannic acid was found to be highly toxic to methanogenic activity. Concentrations, representing 50% inhibition, approximated 700 mg l⁻¹. The toxicity was persistent despite the rapid degradation of gallotannic acid to volatile fatty acids and methane. A 72.5% loss of sludge activity was associated with a 1 day exposure of methanogenic granular sludge to 1000 mg l⁻¹ gallotannic acid. The toxicity of gallotannic acid was persistent over 2 month assay periods. The monomeric derivatives of gallotannic acid, gallic acid and pyrogallol were much less toxic. The 50% inhibition concentration of the monomers approximated 3000 mg l⁻¹ and their toxicities were not persistent. No activity losses were evident after sludge was exposed to 3000 mg l⁻¹ gallic acid for 19 days.The lower toxicities of the monomers compared to the gallotannic acid polymer suggests that the mechanism of toxicity was “tanning”, since data in the literature indicate that tannin polymers are more effectively adsorbed and precipitated with proteins compared to their monomeric counterparts. Functional proteins (enzymes) located at accessible sites in or on the methane bacteria are most likely disturbed by the tanning action.     

Anodic stripping voltammetric study of the lability of Cd, Pb, Cu ions sorbed on humic acid particles

The sorption of Cd, Pb and Cu by humic acid particles has been studied at μg l⁻¹ levels using A.S.V. on a Hg film electrode as the measuring technique. The variables examined included amount of solid present (0.01–0.2% w/v), initial metal ion concn (10–100 μg l⁻¹), systems pH (5.3, 6.35, 8.15) and base electrolyte composition. The calculated capacity for specific adsorption of the metal ions was a few mmol M²⁺ kg⁻¹, or less. The apparent lability of part of the sorbed material was examined by analysing the base solution before and after filtering, and by adding Chelex 100 particles to the suspension. Some sorbed Cd²⁺ was A.S.V. labile, another fraction transferred to the resin. The effect of solution reactions on uptake was studied by making the 1 M CH₃COONa base solution 0.2 M in a range of Na⁺ salts (8 different anions), or in carboxylic acid content (5 acids) or in compounds having S-type bonding groups. Formation of complex ions in solution altered the extent of metal ion uptake, and in the case of Cu A.S.V. peak size, shape and position were varied. It is suggested that natural waters containing suspended matter should be analysed by A.S.V. “as received”, as well as after filtration since response differences provide guidance in respect to the lability of sorbed ions.     

Nickel stimulation of anaerobic digestion

An acetate-enriched methanogenic culture was assayed for nutritional stimulation by nickel in combination with other inorganic and organic nutrients, i.e. iron, cobalt, yeast extract, riboflavin and vitamin B₁₂. Acetate was automatically maintained at 2–3 g l⁻¹ by a pH Stat system so that substrate was not limiting. In the absence of nickel, the specific acetate utilization rates were in the range of 2–4.6 g acetate g⁻¹ VSS day⁻¹. In the presence of nickel, this rate was as high as 10 and when both nickel and yeast extract were supplemented this rate temporarily increased to 12–15 g acetate g⁻¹ VSS day⁻¹ . The maximum acetate utilization rate was observed to be 51 g l⁻¹ day⁻¹ as compared to 3.3 g l⁻¹ day⁻¹ for conventional high-rate digestion. Daily phosphate additions were required to sustain these high acetate utilization rates. An acetate utilization rate of 20–30 g l⁻¹ day⁻¹ was maintained for over 25 days. Microscopic examination of the culture revealed a predominance of a sarcina whenever stimulation was noted.     

Mathematical analysis of the chemical system “cyanide-heavy metals” in water—determination of components and toxicity of the system—II. Solution by computer

An essentially new method of chemical analysis was developed and named “the non-experimental chemical analysis”. The subject of the method is the qualitative and quantitative analysis of chemical properties of the system of complex forming reagents and central atoms. The method is based on the application of the general system equation. An application of the general system equation for the toxic system “cyanide-heavy metals” in water solutions is advanced.     

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.     

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.     

Determination of ammonia and Kjeldahl nitrogen by indophenol method

The Berthelot reaction, based on development of a deep blue colour when ammonia reacts with phenol and alkaline hypochlorite, was investigated and modified. The reaction variables were studied, and a convenient and reliable analytical procedure was developed for ammonia and Kjeldahl nitrogen determination, well suited for routine analysis of fresh and waste water. The buffering system introduced into the reagents permits examination of domestic wastewater, without pH correction, in the 3–11·5 range. The method gives highly reproducible results in the range of 0.02–1 mg l⁻¹ ammonia nitrogen (1 cm light path). The solutions are ready for photometric measurement after 45 min of colour development at room temperature, and remain stable at least 48 h.Interfering substances likely to be present in domestic wastewater are hardness above 400 mg l⁻¹ and nitrite ions above 5 mg l⁻¹n. In high-ammonia wastewater samples, this interference is eliminated by the dilution required for photometric measurements.     

Comparison of iron(III) and aluminum in precipitation of phosphate from solution

The results of phosphate precipitation using iron(III) (Hsu, 1973a) and aluminum (Hsu, 1975) are compared. It is suggested that these two coagulants react with phosphate following the same mechanism. The observed differences in optimum conditions and effectiveness of phosphate precipitation are interpreted by assuming that Fe³⁺ has a stronger affinity for PO₄³⁻ and a stronger hydrolyzing power than Al³⁺.     

Toxicity of lipid-soluble copper(II) complexes to the marine diatom Nitzschia closterium: Amelioration by humic substances

Algal assays, using the marine diatom Nitzschia closterium, have established that humic acid (5 mg kg⁻¹) can ameliorate the toxicity of the lipophilic complex Cu(oxine)₂ (3 × 10⁻⁸ mol l⁻¹ in unsupplemented seawater). The toxicity of Cu(PAN)₂ is not ameliorated [PAN = 1-(2-pyridylazo)-2-napthol]. In conjunction with previous visible absorption spectrophotometry and polarographic measurements it was established that humic acid sequesters copper(II) from the hydrophobic complexes, releasing a ligand molecule. The copper(II) toxicity may be ameliorated provided the ligand itself is not toxic.Fulvic acid was significantly less effective in ameliorating toxicity. Because of the significant competition from Ca(II) and Mg(II) in seawater, it is inferred that humic substances may be more effective in ameliorating toxicity of hydrophobic copper complexes in fresh water.     

Influence de la duree d'exposition sur la bioaccumulation par voie directe de deux derives du mercure par Salmo gairdneri (alevins) et relation “poids des organismes-concentration en mercure”

In the context of ecotoxicological research on the contamination of continental aquatic systems by mercury compounds, the analysis of bioaccumulation at different consumer levels (especially fish) shows that the weight of the organism affects the concentration factors measured. However, after a bibliographic synthesis it is not possible to define precisely what this effect might be, since published results show either an absence of any relationship, or a positive or negative correlation, depending on the authors and on the conditions of intoxication.Our research is based on the direct contamination of newly hatched rainbow trout (weight when time factor = zero : 0.20 g); concentration of mercury in the water was 1 μg l⁻¹ (1 ± 0.1 ppb for the duration of the experiment). Two compounds were studied : HgCl₂ and CH₃HgCl. By using automated contamination modules we were able to maintain constant biotic conditions (number of fish per tank) and abiotic conditions (temperature: 15 ± 0.5°C; photoperiod; 16h/8h; concentration of Hg in the water) for the two contaminants.An analysis of the mercury bioaccumulated was carried out after 15, 30, 60 and 83 days of exposure. For each experimental condition—e.g. HgCl₂, 15 days—25 fish were kept at time factor zero. The mercury concentration was determined by flameless atomic absorption spectrophotometry (VARIAN AA 475). A polynomial regression method, with or without transgeneration of the dependent variable, was used in order to demonstrate a possible relationship between the “weight of organism” and “concentration of mercury” parameters.A comparison of the development in weight of the organisms in all the different populations contaminated by HgCl₂ and CH₃HgCl (Fig. 1) shows that this is identical up to 30 days. Between 30 and 83 days it may be seen that methylmercury has a very strong influence on this parameter which is coupled with a reduction in food intake and a considerable increase in mortality.The dynamics of the average mercury content—μg per organism—and the corresponding concentrations (μg g⁻¹ fresh weight) over the 83 days exposure period (Fig. 2) show that the mercury content and concentration in the fish are much higher for methylmercury than for mercuric chloride and this does not depend on the length of exposure period, e.g. at 60 days the ratio between CH₃HgCl and HgCl₂ concentrations is about 7.Although the concentration of the two contaminants in the environment was kept constant (1 ppb), the curves representing mercury accumulation—expressed as a concentration—are not linear and show a fairly pronounced plateau.The relationship between “organism weight” and “concentration of mercury” was studied for both two mercury compounds during each experimental exposure period (Figs 3 and 4).The noticeable grouping of points corresponding to each population studied indicates a relationship between the weight and concentration parameters; in both contaminants the concentration factor develops in relation with the exposure period. Although it is rather simple and approximate, the linear model displays quite satisfactorily the phenomenon we are studying and its development (Table 1). However a logarithmic relationship gives a better adjustment of the results.Analysis of the results shows:A negative correlation between the weight of the organisms and their mercury concentration for both compounds. This correlation decreased as the exposure period increased. In the case of HgCl₂, after 83 days exposure, the weight no longer seemed to have an influence on the amounts of metal bioaccumulated by the fish.A difference between the adjusted straight lines for HgCl₂ and CH₃HgCl, the organism weight has a greater influence on concentration in the case of contamination by the organic compound.Observations conducted in a natural environment usually show a positive relationship between concentration and the weight of the organisms. When compared with these, our experimental results cannot be said to be contradictory since they deal with different biotic conditions: contamination methods, growth rate and age of individuals.An assessment of the level of contamination in aquatic ecosystems is usually based on an estimation of concentration levels found in the organisms, and, especially for fish, in the skeletal muscles. Our results however, show the necessity of taking organism weight into consideration; the influence of this parameter on the processes of bioaccumulation is particularly important in the case of mercury contamination in the newly hatched stage, and probably in other species with a rapid growth rate. In the case of experimental research into these processes influence of organism weight is considerable and therefore necessitates its examination especially when the object of the study is the development of a standardised toxicological test.     

Observations of the preferential loss of major ions from melting snow and laboratory ice

Two types of laboratory experiments were undertaken to understand changes in the ionic composition of solutions from melting snows: (1) a set of field-laboratory experiments which involved partially melting recently collected snows and (2) experiments on the controlled melting of artificial ices of known composition. Sulphate and nitrate ions are preferentially lost with respect to chloride during the melting process so apparent elution sequence may be written SO₄²⁻ > NO₃⁻ > Cl⁻. Of the cations, sodium appears to be removed least readily giving an elution sequence Mg²⁺ = K⁺ > Na⁺. In the laboratory the differences in the efficiency of removal of ions from ice are small in the first stages of melting, but pronounced by the end of the melt. Sodium and chloride are expected to be proportionally enriched in residual leached snow packs. This is generally born out by field observations. The preferential loss of some ions is more evident in aged laboratory ice than in the freshly made ice. The changes in the ice and meltwater composition throughout the process of melting may be understood to arise from the mixing of two types of solutions: (i) an intergranular surficial brine with high solute concentration that occupies the ice grain boundaries and (ii) the meltwater from the ice grains.     

A simple method for the rapid determination of iron in natural waters

A simple and versatile method is described for the rapid determination of iron in natural waters using the chromogen Ferrozine. The method is capable of analysing samples with concentrations from less than 5 mg m⁻³ to 3 g m⁻³ routinely, with high precision. While the method was intended for the determination of total soluble iron, the distinction between ferrous and ferric iron is also possible.