Relationships between ultraviolet absorbance and total organic carbon in two upland catchments

Regression equations relating u.v. absorbance to total organic carbon (TOC) in river water are compared for streams draining two upland catchments in north-east Scotland which have similar climate, topography and land use but contrasting acidic and basic parent materials. A comparison is also made of regression equations for individual tributaries contributing to the main streams in each catchment. Reasons for observed differences are suggested. Changes in u.v. absorbance vs TOC relationships through storm events are discussed, and the problems associated with using TOC/absorbance relationships to monitor changes in TOC with time through storms are briefly considered.     

Seasonal variations of disinfection by-product precursors profile and their removal through surface water treatment plants

A sampling program has been undertaken to investigate the variations of disinfection by-products (DBPs) formation and nature and fate of natural organic matter (NOM) through water treatment plants in Istanbul. Specific focus has been given to the effect seasonal changes on the formation of DBPs and organic precursors levels. Water samples were collected from the three reservoirs inlet and within three major water treatment plants of Istanbul, Turkey. Changes in the dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV(254)), specific ultraviolet absorbance (SUVA), trihalomethane formation potential (THMFP), and haloacetic acids formation potential (HAAFP) were measured for both the treated and raw water samples. The variations of THM and HAA concentrations within treatment processes were monitored and also successfully assessed. The reactivity of the organic matter changed throughout the year with the lowest reactivity (THMFP and HAAFP) in winter, increasing in spring and reaching a maximum in fall season. This corresponded to the water being easier to treat in fall and an increase in the proportion of hydrophobic content. Understanding the seasonal changes in organic matter character and their reactivity with treatment chemicals should lead to a better optimization of the treatment processes and a more consistent water quality.     

Ultra-violet absorption as a tracing technique for sewage dispersion and water masses in two red sea coastal lagoons in Jeddah

The u.v. absorbance is measured in water samples, collected on six successive cruises made within 1 year, from two Saudi sewage-affected fjord-like lagoons in Jeddah (Arbacen and Reayat Al-Shabab). The hydrochemical elements, salinity, phosphate and ammonia are also measured. The horizontal and vertical distribution pattern of u.v. absorbance and that for the other hydrochemical elements are found to coincide with each other to a great extent. The direction of the discharged wastewater spread at the surface can be easily identified. Three distinct water layers are observed. The surface layer is diluted by sewage effluent containing high values of u.v. absorbance, phosphate and ammonia. The intermediary layer has almost the same properties as the water outside the lagoon mouth at the same level where it is less diluted (i.e. less polluted). The third layer at the bottom (old water) where the water is dammed by the sills is more saline. It has exceptionally high values out of the four elements studied. This situation prevails almost throughout the year except during the intermittent flushing periods in winter and early spring, when the stratification is disturbed. The advantage of using u.v. absorbance measurement is that it can be read directly in the water samples without any chemical pre-treatment and so no special training is needed.     

Comparison of sample storage protocols for the determination of nutrients in natural waters

There have been several reports on storage protocols for the determination of nutrients in natural waters but each one has been limited to a particular sample matrix and they have reached different, matrix specific conclusions. The aim of this study was therefore to systematically apply the various recommended storage protocols to a range of natural water matrices. Samples from four contrasting sites in the UK, collected in late winter (February, 1999), were filtered and stored under different conditions (-80 degrees C, -20 degrees C, 4 degrees C and at 4 degrees C and -20 degrees C with 0.1% (v/v) chloroform) for up to 247 days prior to analysis. The sites were the River Frome in Dorset (a chalk stream catchment) and three sites from the Tamar Estuary (draining a non-chalk catchment) with salinities of 0.5 per thousand, 10 per thousand and 34 per thousand, Samples and controls were analysed for total oxidised nitrogen (TON) and filterable reactive phosphorus (FRP) using a segmented flow analyser with spectrophotometric detection. To investigate possible seasonal effects (particularly changes in biological and chemical matrix composition). a second sampling campaign was undertaken in early autumn (October, 1999). The results showed that the optimum storage conditions for the determination of TON and FRP were highly matrix dependent. with significant differences in FRP stability between the Frome and Tamar catchments (due to different calcium concentrations) and between samples of different salinities (due to different bacterial populations and/or dissolved organic matter). General guidelines for sample handling and storage are listed and matrix specific recommendations presented for samples rich in calcium and dissolved organic matter.     

Determination of alkyl benzenesulfonate in water by u.v. method

Alkyl benzenesulfonates in water were determined by u.v. method.Alkyl benzenesulfonates in water were extracted by 1,2-dichloroethane as methylene blue complexes, and, after being isolated from methylene blue by washing with cone. hydrochloric acid, were extracted by water from 1,2-dichloroethane solution.Alkyl benzenesulfonate solutions were measured by absorbance at 222 nm. This band is characteristic of benzene and alkyl benzenesulfonates separated from other anionic surfactants completely.     

Etude de l'oxydation de chloroethanes en milieu aqueux dilue par H2O2/u.v.Degradation of chloroethanes in dilute aqueous solution by H2O2/u.v.

The destruction of organic pollutants in water can be achieved by the combination of oxidants or of oxidants with u.v. radiation (O₃/H₂O₂;; H₂O₂/u.v.; O₃/u.v.). The efficiency of these advanced oxidation processes is accounted for by the generation of very reactive free radicals such as hydroxyl radicals. In this paper, experimental data are presented to examine the effect of physico-chemical parameters on the efficiency of the H₂O₂/u.v. process for the degradation of chloroethanes in dilute aqueous solution and to test a kinetic model for this oxidation process. The model is based on known reactions of OH radicals in water and on kinetic results obtained in a previous work for the photodecomposition of hydrogen peroxide (Nicole et al., 1990).     

Ultra-violet absorption characteristics of natural waters

Concurrent measurements of salinity and u.v. absorbance at selected wavelengths have been made on waters collected from an inshore sea area subject to the influence of a number of sources of land drainage. An inverse relationship between salinity and absorbance in the spectral region 250–350 nm was obtained. As a result of the persistence of differences in the magnitude of absorbance and variations in the relative absorbance in different spectral regions apparent in the fresh water sources, various water masses could be distinguished in the sea area.     

u.v.-DOC characterisation of pulp and paper bleach effluents

Flocculation characterisation of both sulphite and kraft bleach effluents, has been studied using Al salts.Plots of u.v. absorbance vs DOC obtained in a sequential flocculation procedure, produce a straight line and allow an accurate estimation of the non-u.v. absorbing DOC in the effluent to be made. These plots may be useful to estimate DOC loadings likely to be encountered when designing effluent treatment systems.     

Etude de l'oxydation de chloroethanes en milieu aqueux dilue par H2O2/u.v.

The destruction of organic pollutants in water can be achieved by the combination of oxidants or of oxidants with u.v. radiation (O₃/H₂O₂;; H₂O₂/u.v.; O₃/u.v.). The efficiency of these advanced oxidation processes is accounted for by the generation of very reactive free radicals such as hydroxyl radicals. In this paper, experimental data are presented to examine the effect of physico-chemical parameters on the efficiency of the H₂O₂/u.v. process for the degradation of chloroethanes in dilute aqueous solution and to test a kinetic model for this oxidation process. The model is based on known reactions of OH radicals in water and on kinetic results obtained in a previous work for the photodecomposition of hydrogen peroxide (Nicole et al., 1990).     

Water dechlorination by activated carbon, ultraviolet radiation and sodium sulphite: A comparison of treatment systems suitable for fish culture

The characteristics of water dechlorination by activated carbon filtration, u.v. irradiation and sodium sulphite injection were examined. A pilot plant water treatment system composed of sand and diatomaceous earth filtration, ozonation and activated carbon filtration was evaluated. Activated carbon did not completely eliminate chlorine under any conditions tested but the post-carbon chlorine concentrations were relatively insensitive to large variations in incoming chlorine levels and water flow rates. Carbon filtration also reduced total dissolved organic carbon concentrations by 65% and reduced various halogenated methane derivatives by 97–100%. Ultraviolet irradiation eliminated up to 99% of the total chlorine in municipal water but u.v.-dechlorination was sensitive to flow rate with a rate constant of 2.02 min⁻¹ between 10 and 27 l min⁻¹. Water temperatures ranging from 7.5 to 20.6°C did not affect the efficiency of dechlorination by activated carbon or u.v. irradiation. Sodium sulphite at a 3:1 molar ratio to chlorine completely eliminated chlorine from municipal water while a sulphite:chlorine ratio of 6:1 was required to completely dechlorinate water which had been partially dechlorinated by activated carbon. The results are discussed in relation to the design of a multi-stage system suitable for providing dilution water for aquatic toxicity studies and fish culture.     

有机质对软土流变性质影响的试验研究

采用人工土、自然土、半人工半自然土制备3组有机质含量不同的试样,测试其基本的物理力学特性。采用改进的直剪蠕变仪,用分级加载的试验方法在相同试验条件下对所制备试样的流变性质进行测试,得到各试样在各级荷载下的蠕变曲线,进而求得各试样的平均粘滞系数。对各组试样的粘滞系数进行对比分析,结果表明有机质及其含量是影响软土流变性质的重要因素之一,土体的粘滞系数随有机质含量的增加而减小,即流变变形阻力随有机质含量的增多而减小。试验结果分析认为,有机质通过吸附于土颗粒表面的结合水影响土的流变性质,其中强结合水是土体产生流变的主要因素,而弱结合水则是相对次要因素。文中的试验结果有助于进一步认清土体流变的起因,对改进和完善现有流变变形计算理论有一定指导意义。     

Characterizing algogenic organic matter (AOM) and evaluating associated NF membrane fouling

Occasional algal blooms, comprised of blue-green algae and/or green algae, cause significant challenges in drinking water treatment due to the release of algogenic organic matter (AOM) into water extracellularly and, upon cell lysis, intracellularly. AOM has been extracted from blue-green algae (cyanobacteria) by various means and analyzed by UV absorbance scanning, HPSEC-UV-fluorescence-DOC, UV absorbance ratio index (URI), FTIR, and fluorescence excitation emission matrix (EEM). AOM extracted in water as a solvent exhibited a high hydrophilic fraction (57.3%) with a low SUVA (1.0 L/m-mg). The molecular weight (MW) distribution showed a significant heterogeneity (high value of polydispersivity) and high protein content (as indicated by specific fluorescence). Significant amounts of proteinaceous components such as mycosporine-like amino acids (MAAs, UV-screening components) and phycobilins (light-harvesting pigment) were detected by UV/visible absorption. The presence of proteins was confirmed by FTIR (at 1661 and 1552 cm(-1)), EEM spectra (EX:278-282 nm and EM:304-353 nm), and high URI values (3.1-6.0). A bench-scale cross-flow unit, employing a flat-sheet membrane specimen, was used to examine nanofiltration (NF) membrane fouling and removal of natural organic matter (NOM) derived from different blends of Suwannee River humic acid (SRHA) and AOM: SRHA 10 mgC/L, AOM 3mg C/L + SRHA 7 mgC/L, AOM 7 mgC/L + SRHA 3 mgC/L, and AOM 10 mgC/L. The study focused mainly on the effects of two different sources of organic matter on NF (NF 200) membrane fouling under otherwise similar conditions. Flux decline and organic matter rejection as a function of delivered DOC (cumulative mass of feed DOC per unit area) showed significantly different results depending on the organic matter composition of samples even though the test conditions were the same (organic matter concentration, pH, temperature, inorganic salt composition and concentration, and recovery). A higher flux decline was observed with increasing proportions of AOM. Organic matter rejections also decreased with higher AOM contributions to the samples, indicating that lower molecular weight (MW) AOM components were not well rejected by the NF 200 membrane having a 360 Da MWCO. However, SRHA that exhibited a relatively high MW (1000-5000 Da range) and high SUVA (7.4 L/m-mg) was preferentially rejected through electrostatic repulsion/size exclusion by the NF 200 membrane, having a high negative charge, low MWCO, and relatively low hydrophobicity. Even though the DOC concentration of feed water is a decisive factor for membrane fouling along with membrane properties and operating conditions, the characteristics of organic matter are more influential in fouling potential. Protein-like and polysaccharide-like substances were found as major foulants by FTIR.     

Determination of cyanuric acid levels in swimming pool waters by u.v. absorbance, HPLC and melamine cyanurate precipitation

A u.v. method, recommended for use in surveys of the operation of swimming pools, depends on measuring the difference in absorbance at 225 nm between basified and acidified aliquots of sample and comparing with values obtained for standard solutions of cyanuric acid similarly treated. Also described is a High Performance Liquid Chromatography (HPLC) method which would be advantageous for large numbers of samples and for other analytical applications where cyanuric acid must be separated before quantitation by measuring the u.v. absorbance. Turbidimetric methods based on the precipitation of melamine cyanurate are less precise but still useful for pool-side monitoring of cyanuric acid levels. The performance of commercial test kits based on this principle should be checked by a controlling laboratory.     

Multiple linear regression modeling of disinfection by-products formation in Istanbul drinking water reservoirs

Oxidation of raw water with chlorine results in formation of trihalomethanes (THM) and haloacetic acids (HAA). Factors affecting their concentrations have been found to be organic matter type and concentration, pH, temperature, chlorine dose, contact time and bromide concentration, but the mechanisms of their formation are still under investigation. Within this scope, chlorination experiments have been conducted with water reservoirs from Terkos, Buyukcekmece and Omerli lakes, Istanbul, with different water quality regarding bromide concentration and organic matter content. The factors studied were pH, contact time, chlorine dose, and specific ultraviolet absorbance (SUVA). The determination of disinfection by-products (DBP) was carried out by gas chromatography techniques. Statistical analysis of the results was focused on the development of multiple regression models for predicting the concentrations of total THM and total HAA based on the use of pH, contact time, chlorine dose, and SUVA. The developed models provided satisfactory estimations of the concentrations of the DBP and the model regression coefficients of THM and HAA are 0.88 and 0.61, respectively. Further, the Durbin-Watson values confirm the reliability of the two models. The results indicate that under these experimental conditions which indicate the variations of pH, chlorine dosages, contact time, and SUVA values, the formation of THM and HAA in water can be described by the multiple linear regression technique.     

Molecular size and spectral characterization of organic matter in a meromictic lake

Gel filtration has been used to investigate the properties of natural organic matter in the aquatic environment. The organic compounds in colored lake water, fallen leaves and surface sediment extracts were separated into molecular size fractions which varied from larger than 50,000 to less than 700 when compared to dextrans. These fractions had different color and fluorescence properties. Spectral analysis (i.r., u.v., and fluorescence) provided evidence that fractions from Sephadex columns were fragments of a system of polymers with slightly different chemical characteristics. Degradation of the organic concentrates and molecular size fractions from Sephadex columns by alkline—CuO oxidation and sodium-amalgam reduction techniques permitted six “chemical subunits”, namely dibutyl phthalate, vanillin, catechol, 4-hydroxyacetophenone, 3,5-dihydroxybenzoic acid and resorcinol to be identified using thin layer chromatography and infrared spectroscopy.     

Isolation and characterization of polymeric organic materials in a polluted river water

Organic matter was isolated from water samples from a river mainly polluted by domestic sewage by using Amberlite XAD-2 resin after being acidified to pH 2. The amount of the isolated organic matter comprises about 40% of the total dissolved organic matter. Measurements of elementary composition, molecular weight distribution, u.v. and i.r. spectra and GC/MS analysis of alkaline potassium permanganate oxidation products were performed for the isolated matter. The results indicate that more than a half of the isolated organic matter have apparent molecular weights higher than 5000. The chemical oxidation of the isolated organic matter produced (a) aliphatic monocarboxylic acids (C₆---C₂₄), (b) aliphatic dicarboxylic acids (C₃-C₁₂) and (c) benzene-mono-di-, tri- and tetracarboxylic acids: the latter two groups (b and c) are most abundant. The relative amounts of those three groups seem to be explained in terms of the nature and degree of pollution.     

Removal of organics in water using hydrogen peroxide in presence of ultraviolet light

The optimum conditions for the removal of dissolved organic impurities from water using hydrogen peroxide (50%) followed by ultraviolet irradiation were investigated. The photochemically initiated hydroxyl radical (OH) oxidation reduced the total organic carbon (TOC) content of distilled water samples by about 88% and of tap water by 98%. Extraction with hexane of equal volumes of water samples before and after H₂O₂/u.v. treatment followed by gas chromatographic analysis of the concentrated extracts indicated that about 12% of the electron-capturing, residual organics remained after this treatment. These results support the conclusion drawn from total organic carbon analysis that this simple method yields water nearly free of organic impurities.     

The relationship between TOX formation and spectral changes accompanying chlorination of pre-concentrated or fractionated NOM

The change in the absorbance upon chlorination (the differential absorbance, AA) of natural organic matter (NOM) that has been concentrated, isolated, and/or fractionated from five sources was explored as a possible indicator of the formation of total organic halogen (TOX) in the samples. The results demonstrate that concentration and isolation of NOM using techniques that are currently in widespread use does not significantly alter the TOX-deltaA272 relationship that applies to the unprocessed NOM. However, when such samples are fractionated, the TOX-deltaA272 relationships for the different fractions are not identical. In particular, when the hydrophobic and hydrophilic neutral fractions of NOM are chlorinated, the amount of TOX formed per unit of A272 destroyed is significantly larger than the corresponding value for other NOM fractions. This observation might reflect the relatively high content of proteins and other amino acid structures that can be disinfection by-product precursors but that absorb little or no light at 272 nm.     

Integrated ion exchange mixed bed with reverse osmosis and nanofiltration for isolation of neutral dissolved organic matter from natural waters

The aim of this study was to isolate the neutral dissolved organic matter (NDOM) and the low molecular weight neutrals (LMWN) from natural waters. The coupling of an ion exchange mixed bed (IEXMB) with reverse osmosis (RO) and nanofiltration was the main hypothesis. IEXMB removed charged species, while the neutral molecules were isolated in the demineralised water and then concentrated by RO without any osmotic pressure or fouling limits. Neutrals isolation and unlimited concentration, gives this paper its originality. The nanofiltration (NF) step allows for the isolation of the LMWN. The studied reservoir water NDOM and LMWN represented respectively 35% of the dissolved organic matter (DOM) and 34% of the NDOM. Aromatic compounds were found in both fractions. The UV254 absorbance measured before and after the IEXMB evidenced the water quality ‘signature’. IEX has never been studied as fractionation method of DOM. This IEXMB approach is thus quite novel.     

Observations on the estimation of total organic carbon from u.v. absorbance for an unpolluted stream

The concentration of total organic carbon in unpolluted stream water may be estimated from measurement of absorbance at 250 nm. However, unless allowance is made for the change in the composition of this organic matter under diverse flow conditions, the estimation is subject to serious systematic errors, particularly at low carbon concentrations. Grouping data according to flow at time of sampling leads to a considerable improvement in the accuracy of the estimation, but requires the use of three regression equations. The resulting procedure is then, however, valid under a wide range of flow conditions.