Volume 10 [2008]

To achieve recycling of waste gypsum boards (CaSO4), production of calcium sulfide by
reductive decomposition of CaSO4 was investigated and the decomposition product of CaS
was used as a sulfuration agent in the treatment of nickel-containing simulated wastewater. At
the end of the experiment, residual nickel concentration and filtration characteristics of the
slurry formed by adding CaS to the nickel-containing wastewater were investigated.
Regarding the reductive decomposition of CaSO4, it was found that CaS could be effectively
generated by CaSO4 reductive decomposition with graphite and the CaS content in the final
product was greater than 80% when the reductive decomposition was carried out for one hour
at a temperature of 1273 K, under N2 atmosphere.
Then, in the sulfuration treatment of nickel-containing wastewater with CaS, the applicability of
CaS as a sulfuration agent was confirmed and the nickel concentration in the simulated
wastewater was reduced from 100 mg-Ni l-1 to a value below 1.0 mg l-1, when the CaS was
added to the simulated wastewater at CaS to Ni molar ratio of 1.3. Moreover, sulfide slurry
obtained by adding CaS was characterized by lower average specific filtration resistance and
compressibility coefficient, compared to hydroxide slurry formed by the conventional
precipitation treatment.

Disposing of plastic wastes to landfill is becoming undesirable due to legislation pressures,
rising costs and the poor biodegradability of commonly used polymers. In addition,
incineration meets with strong societal opposition. Therefore, recycling either mechanical or
chemical, seems to be the only route of plastic wastes management towards sustainability.
Polyolefins, mainly polyethylene (LDPE or HDPE) and polypropylene (PP) are a major type of
thermoplastic used throughout the world in a wide variety of applications. In Western Europe
alone approximately 22 million tones of these polymers are consumed each year,
representing an amount of 56% of the total thermoplastics.
In the present investigation the recycling of LDPE, HDPE and PP was examined using two
different methods: the dissolution/reprecipitation and pyrolysis. The first belongs to the
mechanical recycling techniques while the second to the chemical/feedstock recycling. During
the first technique the polymer can be separated and recycled using a solvent/non-solvent
system. For this purpose different solvents/non-solvents were examined at different weight
percent amounts and temperatures using either model polymers as raw material or
commercial waste products (packaging film, bags, pipes and food retail products). At all
different experimental conditions and for all samples examined the polymer recovery was
always greater than 90%. The quality of the recycled polymer was examined using FTIR and
DSC. Furthermore, pyrolysis of LDPE, HDPE and PP was investigated with or without the use
of an acid FCC catalyst. Experiments were carried out in a laboratory fixed bed reactor. The
gaseous product was analyzed using GC, while the liquid with GC-MS. A small gaseous and
a large liquid fraction were obtained from all polymers. Analysis of the derived gases and oils
showed that pyrolysis products were hydrocarbons consisting of a series of alkanes and
alkenes, with a great potential to be recycled back into the petrochemical industry as a
feedstock for the production of new plastics or refined fuels.

This study reports particulate matter levels of various size fractions (PM10, PM2.5, and PM1)
and identify their controlling factors, in various locations over Greece. It combines long-term
data sets involving particle concentrations as measured in the island of Crete in the Eastern
Mediterranean and the Greater Area of Athens. Measurements were carried out in various
sites at urban (Central Athens and Heraklion, Crete), suburban (Lykovrissi, Athens) and
natural background (Finokalia, Crete) locations, for a time period extending from 2004 to
2006.
Size-segregated mass measurements of 3 sizes (PM10, PM2.5 and PM1) are reported. The EU
annual limit value of 40 μg m-3 for PM10 was exceeded on a yearly basis at both of
measurement sites in Athens, while frequent exceedances of the 24-h limit value of 50 μg m-3
were recorded. Concentration levels of PM2.5 and PM1 were also found elevated, when
regarded in perspective to either existing limit values (for PM2.5) or levels reported for other
large metropolitan areas (for PM1).
In addition even at the background station of Finokalia in Crete, average PM10 concentrations
exceeded 30 μg m-3. Moreover, at the same station, average concentrations of PM2.5, notably
exceed 15 μg m-3 (a characteristic value, relative to the USEPA PM2.5 air quality standard). At
all sites coarse particles have been found to comprise a noteworthy portion of total PM10
particles (with PM2.5/PM10 ratios ranging between 45-60%), while fine particle mass
concentrations heavily relied on those of particles in the submicron range (PM1/PM2.5 ratios
spanning between 55-75%).
The short and long-term temporal variability of each fraction were examined and spatial
associations were statistically analyzed, in an attempt to identify possible affinities in particle
level profiles, effective over a larger regional scale. It has been observed that at several
instances, severe particle episodes recorded in the region of Crete have largely affected the
Greek mainland and have triggered a response to the monitoring network in Athens. Special
focus has been given to events of dust transport from N. Africa, which is found to be more
frequent during spring and fall, and during which the PM10 limit value of 50 μg m-3 is violated
and concentrations of even finer particle fractions are affected. Air mass back trajectories
were studied, for episode days during dust transport events.
Data of particle chemical composition were utilized, contributing to an initial identification and
characterization of major natural and anthropogenic source types, which determine particle
concentrations.

Two three dimensional Eulerian air quality models, PMCAMx and UAM-AERO are used to
predict the concentrations of various pollutants in the Greater Athens Area (GAA) during the
episode of June 22-26, 2003. The predicted levels of gases and aerosol pollutants are
compared with measured concentrations from monitoring stations, in order to evaluate the
performance of the models. Comparison of the results reveals that PMCAMx simulated the
ozone diurnal pattern better than UAM-AERO, as the predicted by UAM-AERO maximum
daytime concentrations were much higher than those of PMCAMx and way above the
measured ones. PMCAMx also shows signs of superiority in terms of its ability to predict the
NO2 and NO concentrations. Two sets of simulations, one with both anthropogenic and
biogenic emissions and one without biogenic emissions were performed. Comparison of the
two simulations reveals the important role that biogenic emissions play in the formation of O3,
NOx and secondary aerosols. Additional simulations with PMCAMx show that the
concentrations of all the pollutants depict a highly non-linear behaviour, when anthropogenic
VOC emissions are reduced in the GAA.