Atmospheric aerosols have been implicated in human health effects, visibility reduction in urban and regional
areas, acidic deposition, and altering the earth’s radiation balance. A major goal of scientific research
for the last fifteen years has been the development of the necessary models, using first principles,
that can be used in order to predict the size and composition of atmospheric particulate matter. A number
of such models assume that atmospheric aerosols are at thermodynamic equilibrium with the corresponding
gases, and they predict the chemical composition of atmospheric aerosols, using thermodynamic arguments.
The current state of the art of thermodynamic equilibrium models is reviewed in this paper, and the theory used is presented.
The present work investigates the hydrotreating process of a diesel in order to achieve lower sulphur and
aromatics content. The entire work was performed in a Hydrodesulphurization (HDS) pilot plant unit
located in Chemical Process Engineering Research Institute (CPERI). For the tests, a commercial HDS
catalyst (CoMo) was used while the feed was provided by the deep desulphurization unit of a Greek
refinery (Motor-Oil refinery). For the determination of diesel aromatics, a method based on the ASTM D-
2549-85 was applied. The objective of the work was to investigate the ability of a typical HDS catalyst for
aromatics saturation. The effect of the main hydrotreating operating parameters (T, P, WHSV, H2/Oil
ratio) on sulphur and aromatics removal was also investigated. In general, the data showed that the product
density and the aromatic and sulphur content of diesel decreased as the temperature or pressure increased
or space velocity decreased. It was concluded that with the present catalyst an aromatics saturation
degree of up to 40% could be achieved, giving a diesel product with aromatics content of about 20-25%
wt. However, high temperatures (>370°C) were required in order to achieve 500 ppmw sulphur in this
The soil adsorption behaviour of atrazine and its photodegradation intermediate 4,6-diamino-2-chloro-1,3,5-
s-triazine (I), was evaluated by measuring partition coefficients on five representative European topsoils using
classical batch experiments. From this study, (I) appears to be less immobilised than atrazine itself, especially
for typical agricultural soils. Consequently, (I) has a higher tendency to reach the saturated zones, and
hence, the groundwater. In order to remove atrazine and its degradation products from groundwater prior
to making it drinkable, photocatalytic degradation onto membranes immobilizing 30±3 wt.% TiO2 has been
investigated as a possible technology to mineralize these waters satisfactorily. For this purpose, experiments
have been carried out using a pilot-plant facility, with 0.02 - 0.10 mmol L-1 solutions of atrazine, as well as
of compound (I) and of 2,4,6-trihydroxy-1,3,5-s-triazine (II). When employing an excess of hydrogen peroxide
as the oxidizing agent, the monitoring of chemical oxygen demand (COD), as well as control by HPLC,
showed that (II) was a photostable degradation product, owing to its resistance to attack by hydroxyl radicals.
On the other hand, when kinetic runs were carried out onto membranes in the presence of dissolved
oxygen only or of sub-stoichiometric quantities of H2O2, (II) could be quantitatively mineralized. A mechanism
has been proposed, based on the possible direct involvement of holes in the irradiated semiconductor
surface, together with superoxide anions, these latter being produced by the reaction of conduction band
electrons with dissolved oxygen. This mechanism, which is inhibited by an excess of hydrogen peroxide,
owing to its reaction yielding hydroxyl radicals by any route, is also substantiated by previous experiments,
carried out in the presence of ozone, with and without photocatalytic promoters.
Estimates of the amount of secondary organic aerosol formed in the atmosphere from the degradation of
traffic C6-C12 hydrocarbon emissions in the city of Athens are presented. Around 1.26 tn of organic aerosol
is estimated to be produced during a six hours air pollution episode from the aromatic hydrocarbons,
the other NMHC groups contributing an additional 0.2 tn. The main contributor to the SOA production is
m-xylene. It accounts, together with toluene, for around 50% of the produced organic aerosol. The main
aerosol products that are expected to form from the Athens NMHC traffic mixture are nitrophenols. Due
to predominant wind flow to the S-SE direction in the area, a portion of these aerosols is likely to contribute
to the SOA burden of the marine atmosphere over SE Mediterranean. These results are also relevant to
ozone abatement strategies involving species-specific NMHC reductions and affecting fine particulate
composition and concentrations.
The toxic effects of the herbicide Atrazine, its degradation products deethyl-atrazine and deisopropylatrazine,
and the herbicide metolachlor were examined in unialgal cultures of Chlorella fusca var-fusca.
The toxicity of a mixture of atrazine and metolachlor was also evaluated using the same bioassay system.
Cell numbers were determined daily and growth rates were calculated for a period of 4 days. The order of
toxicity of chemicals was atrazine>metolachlor>deethyl-atrazine>deisopropyl-atrazine. The presence of a
mixture of atrazine and metolachlor in toxic concentrations lower than the EC50 resulted in reduced toxicity
(antagonism) in comparison with the toxicity caused by the sum of toxic actions of the same levels of
concentration from single chemicals.
Samples were taken from Metamorphosis/Attica combined treatment plant for municipal wastewater and
septage, which treats about 12000 m3 d-1 of municipal wastewater and 8000 m3 d-1 of septage, and analyzed
for solids, COD, ammonia, nitrate, orthophosphate, polyphosphate and total phosphorus. Ammonia is
almost completely eliminated within the plant. Orthophosphates show a removal of about 28%, while total
phosphorus is removed by about 15%. The mean value of the ratio (phosphorus eliminated)/(COD eliminated)
in mg g-1 is 8. Assuming suspended-growth nitrification and denitrification kinetics as proposed in
literature, the percentage of nitrifiers in the activated sludge population is estimated at 1.1%. Assuming
that phosphorus removal in the aeration tank is proportional to cell formation, which in turn is proportional
to substrate elimination, the phosphorus content of the activated sludge is estimated at 0.031 gP (gVSS)-1.
The photocatalytic degradation of protocatechuic acid, a biorecalcitrant polyphenolic compound typically
found in olive processing and wine distillery waste waters, has been investigated in aqueous heterogeneous
solutions containing semiconductor powders (TiO2, ZnO) as photocatalysts, both in the presence of
artificial and natural illumination. The disappearance of the organic molecule follows, approximately a
pseudo-first kinetic order according to the Langmuir-Hinshelwood model. Various commercial
photocatalysts have been compared with respect to their overall efficiency as well as the production of
CO2. Among them, ZnO shows the highest photocatalytic activity. The effect of H2O2 on the reaction rate
has been ascertained.
Anaerobic digesters often exhibit significant stability problems, that may be avoided only through appropriate
control strategies. Such strategies require, in general, the development of appropriate mathematical
models, which adequately portray the key processes that take place. This paper reviews the current
state of the art in anaerobic digestion modelling, and identifies the key areas that require further research
An attempt is made for a first general study of the relation between high/very high concentrations of
nitrogen dioxide and ozone with the discomfort index (DI) values. The nitrogen dioxide data of
«Patision» station and ozone data of «Liosia» and «Marousi» station have been analysed. The relation
between air pollution episodes and the corresponding values of DI during the period 1993-1995 have
been examined for the Greater Athens Area (GAA). For the warm period of the year, the frequency of
the DI values for different levels of air pollution in the GAA is also examined.
The greater area comprising the Attica peninsula and the Saronic Gulf is greatly influenced by various
local circulation types. During winter months, moderately high air pollutants concentrations are
observed when the prevailing condition is either stagnant or a weak southern flow. The case studied in
this paper regards an episode that occurred in mid-December. This episode is characterized by very
weak pressure gradient over Greece, and very little change in wind speed and direction with height,
without the precedence of exceptionally strong warm advection in the lower troposphere during the
days before the episode. This episode was not characterized by very high air pollution values, a rather
common feature during December, that even though it presents one of the highest episode frequencies,
the observed values are not high enough to require the enforcement of restrictive measures.