Determination of odorous VOCs and the risk of occupational exposure to airborne compounds at the waste water treatment plants

Concentrations of non methane-VOCs and risk levels of employees' exposure to VOCs were determined at two Finnish waste water treatment plants. The concentration of hydrogen sulphide (H2S) reached the Finnish OEL (occupational exposure limit). The concentrations of styrene, 1,2-dichloroethane, and toluene were found to be elevated at plant A. 328.4 microg/m3 of styrene and 709.8 microg/m3 toluene was found in the sludge dewatering, and 955.8 microg/m3 of 1,2-dichloroethane was detected in the trash rake. TVOC concentrations varied from 149.8 microg/m3 in the Plant B sludge dewatering to 7719.0 microg/m3 in the Plant A sludge dewatering. Most of the detected TVOC concentrations were quite high in comparison to the indoor air regulations or recommendations. The most odorous compounds were determined by combined TD-GC-MS-sniffing analysis. Odour was mainly caused by sulphur-containing compounds, aldehydes, and butanoic acid, in addition to aromatic compounds such as styrene, toluene and 4-methylphenol.     

A simulation-based estimator for hidden Markov random fields

An estimator for estimating the parameters of a Markov random field X from inaccurate observations is introduced. The author considers first a Markov (Gibbs) random field X={X_i,j} on a lattice L={(i ,j): i=1,2,. . .,n; j=1,2,. . .,m}. The marginal distributions of (X_i,j, X_i+u,j+v) (u,v=-1,0,1) are first estimated from an image. Then, random fields X* are simulated with the probability of X*_i+u,j+v)=b nearly equal to the estimate of P{X_i,j=X _i+u,=b}. A simulation method similar to the Gibbs sampler is used. The parameters of the Markov random field model are estimated from the X*'s with the pseudolikelihood method     

Analysis of odour and taste problems in high-density polyethene

A review on the use of high-performance liquid chromatography coupled with electrochemical detection (HPLC-ED) for the measurement of nitrite (NO2-) and nitrate (NO3-) is presented. HPLC-ED has been used for the determination of NO2- and NO3- in food, biological and environmental samples. Analysis of the current literature indicates that the measurement of NO2- and NO3- by the HPLC-ED procedure is more sensitive, selective and faster than methods based on UV absorption, photometry, fluorometry or chemiluminescence.     

Analysis of a GC/MS thermal desorption system with simultaneous sniffing for determination of off-odor compounds and VOCs in fumes formed during extrusion coating of low-density polyethylene

A thermal desorption equipment introducing volatile organic compounds (VOCs) into the gas chromatographic/ mass spectrometric system (GC/MS) with simultaneous sniffing (SNIFF) is a suitable method for identifying the volatile organic off-odor compounds formed during the extrusion coating process of low-density polyethylene. Fumes emitted during the extrusion coating process of three different plastic materials were collected at two different temperatures (285 and 315 degrees C) from an outgoing pipe and near an extruder. The VOCs of fumes were analyzed by drawing a known volume of air through the adsorbent tube filled with a solid adsorbent (Tenax GR). The air samples were analyzed by using a special thermal desorption device and GC/MS determination. The simultaneous sniffing was carried out to detect off-odors and to assist in the identification of those compounds that contribute to tainting and smelling. The amounts of off-odor carbonyl compounds and the total content of the volatile organic compounds were determined. The most odorous compounds were identified as carboxylic acids while the majority of the volatile compounds were hydrocarbons. The detection and quantification of carboxylic acids were based on the characteristic ions of their mass spectra. The higher the extrusion temperature the more odors were detected. An important observation was that the total concentration of volatiles was dependent not only on the extrusion temperature but also on the plastic material.     

Identification of off-flavor compounds in high-density polyethylene (HDPE) with different amounts of abscents

The use of synthetic pipes for drinking water distribution has increased. High desnity polyethylene (HPDE) is preferred because of its favorable mechanical properties, ease of handling during manufacturing, and low permeability to external contaminants. Off-flavor drinking water is a problem with plastic pipes. The compounds causing off-flavors are mainly carbonyl compounds. A combined zeolite called Abscents is used to eliminate odors and to remove odor-causing compounds. In this study, four different amounts of Abscents were added to raw HDPE pellets, and the influence on the off-flavor properties were analyzed. When the maximum amount of Abscents was added, almost all the carbonyl compounds disappeared, and the intensities of odors also decreased. The use of Abscents notably increased the acceptability of HDPE pipes. The system used for analysis of volatile organic compounds was a gas chromatographic/mass spectrometric/sniffing system. Purge and trap techniques were used to introduce the volatile, off-flavor components into the gas chromatograph.