Threshold Odor Number Research Articles

Opportunistic pathogens relative to physicochemical factors in water storage tanks

Household water in Oman, as well as in other countries in the region, is stored in tanks placed on house roofs that can be subjected to physicochemical factors which can promote microbial growth, including pathogens and opportunistic pathogens which pose health risks. Water samples were collected from 30 houses in a heavily populated suburb of Muscat. The tanks used were either glass reinforced plastic (GRP), polyethylene or galvanised iron (GI). Heterotrophic bacteria, coliforms, faecal coliforms and iron sulphur bacteria varied significantly in the three tanks. Yeast and mould count showed significant variations. Isolation of Aeromonas spp., fluorogenic and pathogenic Pseudomonas, Pasteurella, Salmonella, Serratia and Tatumella, and Yersinia and Legionella in biofilms varied in the three tanks. The fungi isolates in the three tanks were Penicillium, Cladosporium and Aspergillus. Nephelometric turbidity unit, threshold odour number and free chlorine varied significantly in the three tanks. True colour unit values did not show a significant difference; however, GRP tanks had algae, autotrophic and pigmented microorganisms. In addition, GI tanks had sediments and corrosion. The results of this investigation are important to evaluate the status of the present household water tanks in countries with high annual temperatures, which may affect public health.

下水処理水を受水する河川での臭気強度およびアルデヒド類の濃度

Threshold odor number (TON) was measured for samples of effluents from wastewater treatment plants and river water receiving treated wastewater in the Tama and Nomi rivers to identify factors affecting the odor of treated wastewater in river environments. The TONs of the effluents were between 87 and 373. TON decreased with biodegradation and volatilization in a section of the Tama river, although the transfer rate of odor from water to air was much smaller than that of oxygen from air to water. The acetaldehyde concentrations of the effluents were more than the odor threshold concentration, although no clear correlation between acetaldehyde concentration and TON was obtained.

Control of MIB, Geosmin and TON by membrane systems

Control of taste and odour compounds in drinking water supplies represents a key treatment objective for many municipalities. Geosmin and 2-methylisoborneol (MIB) represent the primary compounds responsible for taste and odour present in surface waters throughout the world. This research evaluated the ability of membrane systems to control taste and odour when treating a highly organic surface water source and also when challenge tested with MIB and geosmin stock solutions. Reduction of taste and odour compounds by conventional coagulation-sedimentation-filtration treatment, microfiltration (MF), or ultrafiltration (UF) was only significant when oxidation and coagulation were employed. Solely using porous filtration in the form of MF or UF membrane systems resulted in variable removal between 5 and 40%. None of the three treatment technologies could consistently meet the USEPA threshold odour number (TON) secondary standard of 3 units. The cellulose acetate nanofilter consistently removed 35–50% of TON, MIB and geosmin; however, this would still not provide assurance of compliance with the TON standard of 3 units. A polyamide nanofilter provided over 99% removal of MIB and geosmin, representing the most capable system evaluated. Application of the homogeneous solution diffusion equation indicated that size exclusion drives removal of taste and odour compounds.

Sensory characterization of polyester-based bottle material inertness using threshold odour number determination

Refillable polyester bottles, for example polyethylene terephthalate (PET) bottles, are known to interact with chemicals. Aroma compounds from a product can be absorbed by the bottle material, remain after washing and remigrate when the bottle is reused, resulting in off-flavour of the new product. A certified reference material has recently been approved with which the chemical and sensory inertness of refillable bottle materials can be tested. In this study a sensory method aimed at characterizing the sensory inertness properties of the reference bottle material was developed. A use–reuse situation was simulated by storing bottle wall strips in a solution of four odour-active compounds (the loading phase) and, after cleaning, immersing them in water (the remigration phase). The remigration water was analysed with both a sensory method, i.e. determination of the threshold odour number, and chemically using gas chromatography–mass spectrometry (GC–MS). Additionally, another PET and a polyethylene naphthalate (PEN) bottle material were also tested. The sensory threshold determination method could differentiate between the PEN materials and the PET materials. Results from chemical analysis showed that the inertness properties of the PET materials were very similar. The PEN material exhibited significantly superior inertness properties, with only 3–24% of the aroma transfer properties of PET.

Volatile organic components migrating from plastic pipes (HDPE, PEX and PVC) into drinking water

High-density polyethylene pipes (HDPE), crossbonded polyethylene pipes (PEX) and polyvinyl chloride (PVC) pipes for drinking water were tested with respect to migration of volatile organic components (VOC) to water. The odour of water in contact with plastic pipes was assessed according to the quantitative threshold odour number (TON) concept. A major migrating component from HDPE pipes was 2,4-di-tert-butyl-phenol (2,4-DTBP) which is a known degradation product from antioxidants such as Irgafos 168®. In addition, a range of esters, aldehydes, ketones, aromatic hydrocarbons and terpenoids were identified as migration products from HDPE pipes. Water in contact with HDPE pipes was assessed with respect to TON, and values ⩾4 were determined for five out of seven brands of HDPE pipes. The total amount of VOC released to water during three successive test periods were fairly constant for the HDPE pipes. Corresponding migration tests carried out for PEX pipes showed that VOC migrated in significant amounts into the test water, and TON ⩾5 of the test water were observed in all tests. Several of the migrated VOC were not identified. Oxygenates predominated the identified VOC in the test water from PEX pipes. Migration tests of PVC pipes revealed few volatile migrants in the test samples and no significant odour of the test water.

Water monitoring system for oil contamination using polymer-coated quartz crystal microbalance chemical sensor

A water monitoring system with a new chemical sensor for oil contamination was developed. The sensor had an organic polymer film on a quartz crystal microbalance (QCM). The organic film was a hydrocarbon polymer and had high affinities for the organic compounds of petroleum products such as gasoline, kerosene, diesel oil and fuel oil. The monitoring system as composed of a sampling part, a purging part, a humidity control part and a sensor part. The oil in contaminated river water could be detected whose threshold odour number (TON) was less than three. The detecting time was less than 5 min depending on the oil kindness. This system was tested using artificially contaminated river water with the oils, to be found that the sensitivity was kept steady for longer than 6 months with 400 detections of diesel oil and heavy oil. Moreover, the oil kind could be discriminated with only one sensor device by analyzing the desorption response curves obtained by flowing a clean air on the sensor instead of the purging air.

Relationship between Threshold Odor Number and Quality of Irrigation and Drainage Water in Rural Areas

Relationship between Threshold Odor Number and Quality of Irrigation and Drainage Water in Rural Areas

POLYPROPYLENE PIPES FOR DRINKING WATER SUPPLY

Within this study, the influence of the migration of phenolic antioxidants, which are typically used for the stabilization of PP pipes, on the quality of drinking water has been tested. In particular, it had to be shown if the high requirements for materials in contact with drinking water can also be assured in the case of warm water and more alkaline or acidic drinking water. The used migration procedures are based on Austrian, German, and international standard methods for cold water at 23°C and for warm water at 60°C. In addition to the migration of phenolic substances, the content of total organic carbon (TOC) and the threshold odor (TON) and flavor number (TFN) have been determined. In general, not the high molecular antioxidants, but the low molecular degradation product 2,4-di-t-butylphenol was detectable in the aqueous extracts. In warm water extracts, the concentration of phenols, TOC, and also the influence on odor and flavor were considerably higher than in a cold one. Alkaline water extracted higher amounts of phenols, whereas acidic drinking water showed no effect. Thermal load of the material during the extruding procedure leads to a significant increase of extractable phenols, TOC, and TFN/TON.

The Odour Potential: A New Tool for Odour Management

AbstractThis paper outlines a recently developed test for assessing the level of odour associated with a liquid. Called the odour potential, the test involves measuring the threshold odour number of air blown through the liquid sample under conditions which are likely to establish equilibrium. The odour potential of liquids associated with wastewater treatment can vary from a few hundred for final effluents and fresh crude sewage, to over a million for septic sewage, and four million for some sludge liquors. Odour‐potential measurements may not be as useful as an odour map for ranking sources of odour at a sewage‐treatment plant, but they provide extra information for diagnosing the causes of odour.

Odour and flavour in waters: quantitative method for a new european standard

In the majority of the European Community, the assessment of odours and flavours in water supplies are carried out only by sensory analysis. Consequently it is essential for institutes and water companies to use the most accurate method in evaluating odour and flavour in drinking water. Until recently, most of the European countries had their own method or national Standard. Due to the requirements for odour and flavour in EC Directive 80/778 on drinking water quality, applicable throughout Europe, there was a need to standardise their method of evaluation. At the time, no ISO Standard for flavour and odour existed. Moreover, since the materials intended for contact with drinking water must not induce organoleptic problems, manufacturers of pipes, fittings and coatings are also concerned in a standardization. This paper presents the state of the art for flavour and odour evaluation in European countries and the next European Standard for these parameters. The Standard will be based on the dilution method to obtain a threshold flavour number (TFN) and a threshold odour number (TON) of a water. The principle is to compare the successive dilutions of water samples with a reference water. Several methods can be used, for example paired and triangle test, forced and unforced choice. The Standard also includes the selection, training and calibration of panellists. This Standard was elaborated within the scope of CEN/TC 230 “Water Analysis”, and was achieved through the active participation of experts from water institutes, water companies and manufacturers of materials.

The water quality implications of artificially fertilizing a large desert reservoir for fisheries enhancement

Multiple use management of aquatic systems frequently involves conflicting demands from the various user groups. A 4‐year program designed to evaluate large‐scale artificial fertilization as a potential management tool for enhancing the forage and game fish populations of Lake Mead, a large Colorado River reservoir, generated considerable attention from both on‐lake and downstream water users. An extensive water‐quality monitoring program, undertaken as part of the fertilization experiment, demonstrated that the nutrient additions did not produce significant negative impacts on Lake Mead water quality from either a public health (that is, drinking water) or environmental perspective. One set of parameters, for example, hypolimnetic oxygen depletion and the relative abundance of blue‐green algae, exhibited no consistent response to the fertilizer. A second group of parameters did respond to fertilizer addition, but changes were both moderate and relatively short‐term. Examples in this group include chlorophyll, threshold odor number, and trihalomethane formation potentials.

Odour and flavour in waters: quantitative method for a new European standard

In the majority of the European Community, the assessment of odours and flavours in water supplies are carried out only by sensory analysis. Consequently it is essential for institutes and water companies to use the most accurate method in evaluating odour and flavour in drinking water. Until recently, most of the European countries had their own method or national Standard. Due to the requirements for odour and flavour in EC Directive 80/778 on drinking water quality, applicable throughout Europe, there was a need to standardise their method of evaluation. At the time, no ISO Standard for flavour and odour existed. Moreover, since the materials intended for contact with drinking water must not induce organoleptic problems, manufacturers of pipes, fittings and coatings are also concerned in a standardization. This paper presents the state of the art for flavour and odour evaluation in European countries and the next European Standard for these parameters. The Standard will be based on the dilution method to obtain a threshold flavour number (TFN) and a threshold odour number (TON) of a water. The principle is to compare the successive dilutions of water samples with a reference water. Several methods can be used, for example paired and triangle test, forced and unforced choice. The Standard also includes the selection, training and calibration of panellists. This Standard was elaborated within the scope of CEN/TC 230 "Water Analysis", and was achieved through the active participation of experts from water institutes, water companies and manufacturers of materials.

Characterization and Identification of Odorous Compounds in Ozonated Waters

Combined chemical and sensory techniques were used to analyse off-flavours formed during ozonation of surface waters and fulvic acids (FA) dissolved in Milli-Q water. Chromatographic sniffing and gas chromatography - mass spectrometry (GC-MS) analysis of a dichloromethane extract of an ozonated surface water revealed n-heptanal, n-octanal, n-decanal, phenyl acetaldehyde, vanillin and several other unidentified, odorous compounds. Dissolving the dichloromethane extract in water did not, however, recreate the sweet and nauseous odour components of the original ozonated water. Continued experiments showed that FA can be important precursors of off-flavours in ozonated waters and that the major off-flavour compounds in such waters are less volatile than the above mentioned aldehydes. Furthermore, adsorption on DEAE-cellulose followed by desorption with sodium hydroxide was found to be an efficient method for concentrating the off-flavours of ozonated FA solutions. During repeated ozonation of FA solutions, both the threshold odour number (TON) and the concentrations of several organic acids first increased and then decreased.

Nitrogen and the Threshold Odor Number Produced by an Actinomycete Isolated from Lake Sediments

The objective of this study was to determine environmental factors which favor the production of Threshold Odor Number (TON) by an Actinomycete (Streptomyces sp.) isolated from a reservoir with frequent taste and odor problems. The isolate was cultured under varying conditions of form and concentration of nitrogen. Geosmin produced by the isolate was identified by GC-MS. The effect of form and concentration of nitrogen was measured as TON by an odor panel. ANOVA indicated that the TON and the cell biomass varied with the concentration of nitrogen but not the form of nitrogen supplied. There was a significantly greater TON with higher concentrations (75 to 600 µg N l−1) of nitrate and ammonia nitrogen but not organic nitrogen. Cell biomass increased with nitrate and organic nitrogen but not ammonia nitrogen. On the other hand, TON per unit biomass (specific TON) varied with the form of nitrogen but not the concentration. Specific TON was greater with ammonia nitrogen than with either nitrate or organic nitrogen. Although the differences in specific TON with concentration were not significant, rank correlation analysis showed that high values of specific TON were associated with higher values of nitrate and ammonia nitrogen. These laboratory data support field observations that taste and odor episodes occur in the reservoir after rainfall events that supply pulses of nitrogen to the system.

Correlation between Threshold Odor Numbers and the Concentration of Odorous Substances in Water

The aim of this study was to ascertain the actual correlation between the threshold odour number (TON) and concentration of odorous substances in water. The results showed that the relationship between the TON values and the concentration of off-flavor substances seemed to be appropriately explained by the Stevens Model. Also, the TON values varied remarkably due to water temperature and compounds in solution. The masking effects may be distinct even when adding small amounts of certain chemicals. This implies the possibility of using such chemicals to mask odor problems.

Tastes and Odors: The Flavor Profile Method

Flavor profile analyses have been used by The Metropolitan Water District of Southern California to assist in detecting, controlling, and understanding off‐flavors in drinking water. This method has proved to be better than the traditional threshold odor number determination. A flavor profile panel has been selected and trained in the method, and a library of reference materials has been developed. Applications have included assessments of: earthy flavors caused by geosmin and 2‐methylisobomeol (microbiological metabolites); differences in waters disinfected with chlorine and chloramines; and medicinal off‐flavors in finished waters.

Certification Corner

Questions in this Certification Corner concern the following subjects: standpipes; centrifugal‐type pumps; threshold odor number; water flow rate; rapid sand filters; Anabaena algae; parts per million dosage; and artesian systems.

Professor Opflow

The Threshold Odor Test section of Standard Methods, 14th edition, mentions two temperatures for the threshold odor number test, 40 degrees C and 60 degrees C, and the reader wants to know if the test can be accomplished using 50 degrees C. The answer is yes if the results are dependable, consistent and relevant.

Treatment for Hydrogen Polysulfide

Despite recent advances in water‐utility technology, operators are still receiving consumer complaints of funny‐tasting water. Presented here is a new technique to rid treated water of polysulfide taste by sulfonating and by monitoring the process with Threshold‐Odor‐Number (TON) determination.

Studies on the Removal of Actinomycete Musty Tastes and Odors in Water Supplies

The report attempts to correlate the effects of two well known oxidants with active carbon in treating a pure actinomycete musty compound (mucidone) in aqueous solutions. The effects of coagulation with alum and polynuclear electrolytes are also discussed. The results of this study demonstrate that while active carbon is successful in removing greater than 90 per cent of mucidone, other common treatment methods do not significantly lower the odor potential when using practical plant processes.