Reactions of chlorine and chlorine dioxide with resorcinol in aqueous solution and adsorbed on granular activated carbon

Resorcinol reacted with chlorine and chlorine dioxide at pH 7 in dilute aqueous solution and in the presence of granular activated carbon (GAC) to produce numerous chlorinated compounds. Major products included chlororesorcinols and various chlorinated cyclopentenediones. Few reaction products were found in common to both Cl₂ and ClO₂ when reacted with resorcinol in the absence of GAC. However, both oxidants produced the same major recoverable chlorinated product, a dichlorocyclopentenedione, when reacted with resorcinol preadsorbed on GAC columns. No products were found when aqueous resorcinol was applied to GAC columns following contact of the carbon with Cl₂ or ClO₂ solutions.     

Iron amendment and Fenton oxidation of MTBE-spent granular activated carbon

Fenton-driven regeneration of methyl tert-butyl ether (MTBE)-spent granular activated carbon (GAC) involves an Fe amendment step to increase the Fe content and to enhance the extent of MTBE oxidation and GAC regeneration. Four forms of iron (ferric sulfate, ferric chloride, ferric nitrate, ferrous sulfate) were amended separately to GAC. Following Fe amendment, MTBE was adsorbed to the GAC followed by multiple applications of H₂O₂. Fe retention in GAC was high (83.8-99.9%) and decreased in the following order, FeSO₄·7H₂O > Fe₂(SO₄)₃·9H₂O > Fe(NO₃)₃·9H₂O > FeCl₃. A correlation was established between the post-sorption aqueous MTBE concentrations and Fe on the GAC for all forms of Fe investigated indicating that Fe amendment interfered with MTBE adsorption. However, the mass of MTBE adsorbed to the GAC was minimally affected by Fe loading. Relative to ferric iron amendments to GAC, ferrous iron amendment resulted in lower residual iron in solution, greater Fe immobilization in the GAC, and less interference with MTBE adsorption. MTBE oxidation was Fe limited and no clear trend was established between the counter-ion (SO₄²⁻, Cl⁻, NO₃⁻) of the ferric Fe amended to GAC and H₂O₂ reaction, MTBE adsorption, or MTBE oxidation, suggesting these processes are anion independent.     

Ozonation of water containing chlorine or chloramines. Reaction products and kinetics

Ozone reacts with free aqueous chlorine when present as hypochlorite ion (OCl⁻) with a second order rate constant of 120 ± 15 M⁻¹ s⁻¹ at 20°C. About 77% of the chlorine reacts to produce Cl⁻ and 23% is oxidized to ClO⁻₃. No ClO⁻₄ is formed. Conversion of chlorine to monochloramine reduces the ozone reaction rate to 26 ± 4 M⁻¹ s⁻¹, independent of pH, NH₂Cl is transformed quantitatively to NO⁻₃ and Cl⁻ by O₃. Rate data for other chloramines are also presented. The direct reaction of ozone with chlorine accounts for a significant amount of the chlorine and ozone demand found when the two oxidants are used in combination under water works conditions.     

Nitrification kinetics in activated sludge at various temperatures and dissolved oxygen concentrations

Activated sludge from a domestic sewage works was enriched with nitrifying bacteria by running a laboratory fermenter on ammonia-supplemented sewage. This enriched culture was used to determine respirometrically the kinetics of microbial nitrification. It was demonstrated that the reaction fits the Michaelis-Menten model for temperatures from 10 to 35°C, having a temperature optimum at 15°C (K₃ 0.72 mg 1⁻¹ NH₃). Nitrification is unaffected by high dissolved oxygen concentration 38 mg 1⁻¹ O₂ at 30°C) after acclimatisation. Nitrite concentrations > 20 mg 1⁻¹ are inhibitory to the reaction.     

Reaction of ozone with Trans-trans muconic acid in aqueous solution

The ozonation of trans-trans muconic acid in aqueous solution (pH 3) leads to the formation of fumaric acid aldehyde, glyoxal, glyoxylic acid and formic acid which are oxidized into stable end products of oxalic acid, mesoxalic acid and CO₂ as the reaction goes on. Besides unstable organic peroxides H₂O₂ is observed. However, at pH 7 and pH 8 organic peroxides are not detected. Only smaller amounts of H₂O₂ than at pH 3 are formed.The specific ozone consumption was 3.2 mmol of O₃ mmol⁻¹ of acid until complete elimination of muconic acid. The reaction mechanism is discussed on the basis of quantitative tracking of the oxidation products.The reaction rates of muconic acid and of the oxidation products with ozone are compared with those of substituted aromatics.     

Rate constants of reactions of ozone with organic and inorganic compounds in water—III. Inorganic compounds and radicals

Second-order rate constants for reactions of ozone with 40 inorganic aqueous solutes are reported. Included are compounds of sulfur (e.g. H₂S, H₂SO₃, HOCH₂SO₃H), chlorine (e.g. Cl⁻, HOCl, NH₂Cl, HClO₂, ClO₂), bromine (e.g. Br⁻, HOBr), nitrogen (e.g. NH₃, NH₂OH, N₂O, HNO₂) and oxygen (e.g. H₂O₂), as well as free radicals (e.g. O₂⁻, OH^•). Most of these compounds exhibit an increase in rate constant with increasing pH corresponding to their degree of dissociation. Rate constants are based on ozone consumption rates measured by conventional batch-type or continuous-flow methods (10⁻³-10⁺⁶ M⁻¹ s⁻¹ range) and determinations of stoichiometric factors. Also listed are data determined by pulse-irradiation techniques using kinetic spectroscopy (10¹⁰ M⁻¹ s⁻¹ range). Additional literature data are reviewed for completeness. Results are discussed with respect to water treatment and environmental processes.     

The removal of chromium(VI) from dilute aqueous solution by activated carbon

The removal of chromium(VI) by activated carbon, filtrasorb 400, is brought by two major interfacial reactions: adsorption and reduction. Chemical factors such as pH and total Cr(VI) that affect the magnitude of Cr(VI) adsorption were investigated. The adsorption of Cr(VI) exhibits a peak value at pH 5–6. The particle size of carbon and the presence of cyanide species do not change the magnitude of chromium removal. The reduced Cr(VI), e.g. Cr(III) is less adsorbable than Cr(VI).The free energy of specific chemical interaction, ΔG^chem was computed by the Gouy-Chapman-Stern-Grahame model. The average values of ΔG^chem are −5.57 RT and −5.81RT, respectively, for Cr(VI) and CN. These values are significant enough to influence the overall magnitude of Cr(VI) and CN adsorption. Results also indicate that HCrO⁻₄ and Cr₂O²⁻₇ are the major Cr(VI) species involved in surface association.     

The Fe3O4-formation by the ‘Ferrite Process’: Oxidation of the reactive Fe(OH)2 suspension induced by sucrose

A mechanism of the formation of small particles of iron oxide in the wastewater treatment system ‘Ferrite Process’ is described. Small particles consisting of the Fe₃O₄−γ-Fe₂O₃ solid solution having slightly higher content of γ-Fe₂O₃ were obtained by the aerial oxidation of Fe(OH)₂ suspension in the presence of a weak dispersing reagent, sucrose, at pH 9.0. The increase of γ-Fe₂O₃ content is caused by a further oxidation of the Fe₃O₄ particles in the course of the reaction. The further oxidation was accelerated below 1000 Å of the particle size. When SO²⁻₄ ion coexisted with sucrose in the reaction medium, the further oxidation was reduced and the treatment of the wastewater was improved. At a temperature interval of 40°–65°C, the formation of α-FeOOH was completely inhibited by a small amount of sucrose and only Fe₃O₄ was obtained.     

A quantitative investigation of the reaction of ozone with p-toluenesulfonic acid in aqueous solution as a model compound for anionic detergents

The reaction of ozone with p-toluenesulfonic acid (PTA) at initial pH 3 and 12 in aqueous solutions (25°C) has been studied at initial concentration 1 mmol l⁻¹ and ozone dose is 24 mg min⁻¹ 1. and 11 mg min⁻¹ 1. respectively. The substrate elimination follow a zero order rate law. A 98% p-toluenesulfonic acid reduction requires at least 7 mol O₃ per mol PTA, however to remove 100% PTA the consumption of ozone increases to 16 mmol O₃ per mmol PTA. At this point a 28% reduction of DOC and a 74% COD reduction was achieved.The PTA decomposition is quicker at higher ozone flow rate, but the specific ozone consumption increases also. As oxidation products the following compounds were identified and their quantitative variations as function of ozonation time were measured: methylglyoxal, acetic acid, formic acid, pyruvic acid, oxalic acid, H₂SO₄ and H₂O₂. As byproduct mesoxalic acid was identified. At pH 12 lactic acid as a further oxidation product was observed.Balances of carbon, sulfur and methyl as well of the acid equivalents indicate one or more intermediates with a sulfonic acid group. These intermediates with a proportion of about 20% disappear after 100% PTA elimination. On account of these results a reaction mechanism is discussed.     

A mercury-free accelerated method for determining the chemical oxygen demand of large numbers of water samples by autoclaving them under pressure with acid-dichromate

In order to fulfill the objective of a water control program based on frequent sampling in several wastewater treatment plants, rivers and lakes a simplified method for measuring COD was developed. The procedure, in this article called the RR-method, includes: small sample and reagent volume; rapid addition of a mixture of all reagents to the sample; exclusion of mercury; autoclaving at 120°C for 1 h in flasks with fitted glass stoppers. To avoid dilution before analysis the method has been adapted for wastewater (I: 10–300 mg O₂ l⁻¹) and fresh water (II: 10–100 mg O₂ l⁻¹).Parallel analyses on different types of water samples according to Standard Methods showed that the yield by the RR-method was about 10% lower (Table 2). With water from the wastewater treatment plant at Uppsala (COD around 20 mg O₂ l⁻¹), the two methods gave an identical result. The somewhat lower yield was mostly due to decreased dichromate concentration and oxidation temperature. The lower oxidation potential made correction for chloride interference unnecessary below 1 g Cl⁻ l⁻¹ (Table 1).The RR-method also showed a good correlation to the values for KMnO₄-consumption. Parallel analyses of 318 samples from 14 wastewater receiving lakes gave the correlation coefficient r = +0.90 (Fig. 1).     

Improved ammonia oxidation by ozone in the presence of bromide ion during water treatment

Ammonia oxidation by ozone proceeds more rapidly in the presence of bromide ion than in its absence. Unlike the direct ozonation of ammonia, the bromide-catalyzed process is little affected by changes in pH. A reaction scheme is proposed in which bromide is oxidized to HOBr, which then brominates ammonia to produce NH₂Br. NH₂Br in turn reacts with O₃ to form NO₃⁻ and also to generate Br⁻, which thus acts as a catalyst. In accordance with the reaction model, zero-order kinetics for ammonia consumption are observed. This work points out once again the importance of Br⁻ as a water quality parameter due to its role as a catalyst in both ozonation and chlorination processes in general.     

Effects of activated carbon on the reactions of combined chlorine with phenols

In the presence of ammonia, prechlorination in drinking water treatment results in contact of combined chlorine (monochloramine) with activated carbon, which is used to remove organic compounds from water. Monochloramine reacts very slowly with phenolic compounds in aqueous solution, giving low yields of chlorinated phenols. When monochloramine reacts with phenols adsorbed on granular activated carbon (GAC), however, several oxidized products, principally hydroxylated biphenyls, are formed. Some of the hydroxylated biphenyls are chlorinated (hydroxylated PCBs). Their formation is particularly important because of their potential toxicity. Such compounds are major reaction products from chlorophenol, but they are also formed in small amounts from nonchlorinated phenols. Most of the monochloramine-GAC-phenolic compound reaction products are also produced in similar reactions with free chlorine, indicating that similar reaction mechanisms (free radical mechanisms) take place on carbon's surface. No organic compounds are produced from the reaction of monochloramine with GAC alone.     

Denitrification with a bacterial disc unit

An enclosed rotating disc unit was operated anaerobically as a denitrifying system, with methanol as the hydrogen donor. As the bacterial population became established, denitrification rate increased by 1·5 mg NO₃⁻—N reduced m⁻² h⁻², to a maximum rate of 260 mg NO₃⁻—N reduced m⁻²h⁻¹. The C:N ratio necessary for complete denitrification was found to be 2·6:1. Optimum pH for denitrification lay in the range between pH 7·0 and 8·5. Q₁₀ values were 1·38 between 10 and 30°C, −2·66 above 30°C and 13·06 below 10°C.     

Comparative effectiveness of antifouling treatment regimes using chlorine or a slow-releasing bromine biocide

Five chlorine (Cl₂) and three slow-releasing bromine biocide [1-bromo-3-chloro-5,5-dimethylhydantoin (BCDMH)] treatment regimes were compared under laboratory conditions to determine their effectiveness in controlling the fouling of 304L stainless steel heat exchanger tubing. The most effective Cl₂ treatments were low level (0.1 ppm or less) continuous applications. Three intermittent Cl₂ treatments (1 h day⁻¹ at 1.0 ppm, 1 h day⁻¹ at 0.5 ppm, and 3 × 20 min day⁻¹ at 0.5 ppm) were about equally effective. However, all three intermittent regimes were significantly less effective than the low level continuous treatments. The effectiveness of BCDMH treatment was similar to Cl₂ when used intermittently at similar residual concentrations as Cl₂ for 1 h day⁻¹ and continuously at low levels. These experiments indicated that low level continuous treatment was more effective than intermittent treatment for controlling biofouling.     

Iron and manganese oxides in Finnish ground water treatment plants

Large amounts of ochreous precipitates are formed on aeration of Fe containing Finnish ground waters during purification for drinking purposes. Sixty-four precipitates were characterized chemically and mineralogically. X-ray diffraction (XRD) indicated that the Fe-rich precipitates consist mainly of a poorly ordered ferrihydrite (5 Fe₂O₃ · 9 H₂O) which only has 2–3 of the 6 XRD lines characteristic of better ordered ferrihydrite. The surface area ranges between 325 and 433 m² g⁻¹ corresponding to a particle size of 5 nm. The ferrihydrites contain 3–7% Si strongly associated with the ferrihydrite as indicated by an i.r. absorption band at 960–975 cm⁻¹ which is associated to Fe-O-Si bonds. Si-containing ferrihydrite typically forms by rapid oxidation of ground waters with 1–23 mg 1⁻¹ Fe and 7–12 mg 1⁻¹ Si at pH 6–7. Very similar products formed in a simulation experiment in which artificial ground water with 20 mg 1⁻¹ Fe was oxidized in the presence of 12 mg 1⁻¹ Si. A1 < 4 mg 1⁻¹ Si lepidocrocite (γ-FeOOH) was formed showing that Si in the system prevents the formation of the more stable and better crystallized FeOOH forms. A transformation of 2-line ferrihydrite to better ordered ferrihydrite or goethite with time is indicated. The Mn-oxide birnessite was identified in black precipitates formed in one plant.     

Exchange of oxygen and carbon dioxide across the water surface during algal blooms in a pond

Exchange of O₂ and CO₂ across the water surface during algal blooms was studied in an experimental pond from measurements of O₂ and TCO₂, pH and chlorophyll-a. Production and consumption rates of O₂ due to biological activity were also measured using light and dark bottles.Algal blooms occurred twice during the experimental period of 22 days. The trajectory on the phase plane showing the time changes in concentration of O₂ and TCO₂ made a clockwise, converging loop. A new concept and quantity called total oxygen (TO₂), which is the sum of the concentrations of O₂ and TCO₂, is proposed in order to distinguish the role of gas exchange from that of deposits. From the analysis of the trajectory, the total amount of TO₂ was found to decrease during the production period, and increase during the decomposition period. This was due to the difference between O₂ and TCO₂. The mass transfer coefficient of O₂ was found to be (3.6 ± 1.9) × 10⁻⁴, and that of TCO₂ (1.0 ± 0.5) × 10⁻⁴ cm s⁻¹.During the production period, 60% of produced O₂ was lost to the atmosphere, and 20% of consumed TCO₂ was supplied from the atmosphere. During the decomposition period, 80% of consumed O₂ was supplied, and 35% of produced TCO₂ was lost.     

An improved hydrazine reduction method for the automated determination of low nitrate levels in freshwater

An automated nitrate determination is described in which nitrate is reduced to nitrite with hydrazine sulphate under alkaline conditions in the presence of Cu²⁺ and Zn²⁺. Interferances encountered in natural water samples were eliminated by the addition of Zn²⁺ to the Cu²⁺ catalyst solution.The method is suitable for the determination of low NO₃−N concentrations and compares favourably with the manual copperised cadmium technique for freshwater samples containing 10–800 mg m⁻³ NO₃−N. The method is also linear at nitrate concentrations below 10 mg N m⁻³. The standard deviations (S.D.) of blanks and of samples containing 2 mg NO₃−N m⁻³ were 0.013 and 0.06 mg N m⁻³ respectively at an analysis rate of 30 samples h⁻¹.     

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.     

The effect of polysaccharidic gums on activated carbon treatment of textile wastewater

The activated carbon treatment of wastewater originating from the Celanese Canada Ltd., Carpet plant at Sorel, Quebec, was tested in this study. Typical plant effluent was characterized and prepared. Soluble organics in the synthetic effluent varied between 75–185 mg TOC 1⁻¹, consisting of dyes (10%) process chemicals (75%) and the soluble guar gum (15%) used as a viscosity adjusting additive in the newly installed continuous dyeing process.The activated carbon adsorption of the guar gum from its pure solution was examined in laboratory tests. Improved adsorption was observed at low pH values and at elevated adsorption temperatures. Lignite-based carbon out-performed bituminous coal-based carbon. At 30 mg TOC 1⁻¹ of soluble guar gum, low carbon loading in the range of 3–8 mg TOC g^–1 was recorded for various types of carbon at 20°C and neutral pH.Activated carbon adsorption of the typical conventional prepared dyehouse wastewater resulted in non-adsorbable residues in the range of 9–18 mg TOC 1⁻¹. Presence of 50–100 mg of polysaccharidic guar gum per liter of conventional wastewater mixture had a pronounced positive effect on the adsorption process. This is reflected in an increase in both the carbon loading at initial concentration and the adsorption isotherm slope.     

Automated chemical analysis for measuring microgram levels of organic carbon in potable waters

An automated method for the direct determination of microgram levels of organic carbon in potable waters is described. The technique is that of continuous flow analysis and utilizes an automatic sampler, a multiple channel proportioning pump, and an appropriate analytical system (manifold). Samples are acidified, oxygen segmented and passed through a heated inorganic carbon stripper. The stripped liquid is resampled, mixed with silver peroxydisulphate solution and digested at 70°C. The liberated CO₂ is measured by means of infrared photometry. Complete inorganic carbon removal was not possible. From a 30 mg dm⁻³ inorganic carbon solution 0.1% residual remained after stripping. Using a sample volume of 6.3 cm³ min⁻¹, full-scale recorder deflection could be obtained for a 1 mg dm⁻³ organic carbon standard solution with a relative standard deviation of 0.9%. The lower detection limit of practical significance is 50 μg dm⁻³ organic carbon. The analysis rate is 20 samples per hour. Certain synthetic organic materials resisted complete oxidation and included the amino acids glycine, 1-alanine, leucine, iso-leucine and valine.