The treatment of fully and partly weathered olive mill wastewaters by means of ozonation was investigated, with emphasis on the effect of treatment conditions (organic loading, treatment time, ozone concentration) on the extent of chemical oxygen demand (COD) and total phenol degradation, colour removal as well as ecotoxicity to the marine bacterium Vibrio fischeri. In general, ozonation was capable of substantially reducing the concentration of phenols as well as decolourising the effluent after relatively short treatment times, with the extent of phenol and colour removal exceeding 80% in most cases. The fast and selective degradation of phenols was ascribed to the direct electrophilic attack by molecular ozone (ozonolysis). Conversely, complete mineralisation proved difficult; at the conditions employed in this study, COD removal varied from as little as 10% to about 60%. Both effluents were strongly ecotoxic owing to the presence of phenols and other organics in substantial concentrations; toxicity decreased partly following considerable degradation of the organic matter.

Municipal wastewater treatment plants (WTP) emit odorous compounds that produce nuisance to the workers and nearby residents. Several chemical compounds contribute to odour problems, among them, sulphurous organic compounds, hydrogen sulphide, phenols and indoles, ammonia, volatile amines and volatile fatty acids. In the current study, hydrogen sulphide (H 2 S) concentrations were measured during the summer period of 2007 by a portable handheld device at the WTP of Chania City (Greece). Measurements were taken in several places within the facility. The highest hydrogen sulphide levels were measured close to the primary sedimentation tanks and the tanks where the recycled activated sludge is mixed, the sludge from the primary sedimentation tanks reaching 30 ppm. In conjunction with the measurements, the Gaussian dispersion model AERMOD code was modified in order to estimate the maximum odour concentration for very short time steps using peak-tomean ratios. The probability of detection of H 2 S exceeds 50% at 400 m distance from the main emission sources (time interval of 5 s) with a relative high degree of annoyance (3.2 AU) under typical summer period conditions. Furthermore, relations between odour annoyance and odour exposure concentrations have been embedded in the model, in order to express the odour impacts in terms of probability of detection and degree of annoyance of the population near the WTP of Chania.

The purpose of this paper to present a case study on how to address the odor problem from secondary sources within a municipal wastewater treatment plant (WWTP) by first identifying the locations of the problem and second by evaluating alternative treatment technologies. The WWTP of Chania is a typical 100,000 equivalent inhabitants-facility in a warm semi-arid environment which is located close to residential areas. The installation of a chemical scrubber to control major odor sources within the plant did not succeed in eliminating complaints by nearby residents, and additional measures were required. In this case study we identify all major secondary sources of odor within the plant and evaluate the effectiveness of the different technologies that were employed to address this problem (cover installation, gas and liquid phase oxidation, activated carbon/permanganate absorption, FeCl(3) addition). In particular, we found that installation of covers and reduction of turbulence at two key locations within the WWTP was the best strategy to combat unpleasant odors. Furthermore, when the central chemical scrubber was near capacity the installation of an auxiliary system of activated carbon absorption coupled to permanganate oxidation was deemed to be a safe approach. However, despite the very high removal efficiency (>99.5%) of the unit, the addition of FeCl(3) in the liquid phase was required in order to achieve complete deodorization (below the human odor threshold level).

The problem of odour nuisances in Greece was explored using: (a) field measurements of a range of malodorous compounds (hydrogen sulfide, ammonia, benzene, toluene, xylenes, formaldehyde, acetaldehyde, acetone, methyl-mercaptan and carbonyl sulfide) from selected wastewater treatment plants and composting facilities; and (b) questionnaires, completed by wastewater treatment plant operators, to investigate potential odour problems, the odour abatement technologies used, and potential interest and motives for adopting such technologies. The sparse information available in the literature is also exploited. Results indicate that on several occasions there was an odour problem, often stemming from the uncontrolled city sprawl, which results in mixed and often conflicting land uses. This is particularly true for wastewater treatment plants, which tend to be built close to built-up areas and highlights the importance of town planning as a tool to minimize odour problems. Measurement of odours and/or odour related gases is not commonly practised in Greece, while the odour abatement systems currently used are often considered inadequate by plant managers who do have an active interest in using more efficient and effective technologies. To our knowledge, this is the first systematic effort to monitor the odour nuisance in the country.

Piggeries are known for their nuisance odors, creating problems for workers and nearby residents. Chemical substances that contribute to these odors include sulfurous organic compounds, hydrogen sulfide, phenols and indoles, ammonia, volatile amines, and volatile fatty acids. In this work, daily mean concentrations of ammonia (NH3) and hydrogen sulfide (H2S) were measured by hand-held devices. Measurements were taken in several places within the facility (farrowing to finishing rooms). Hydrogen sulfide concentration was found to be 40 to 50 times higher than the human odor threshold value in the nursery and fattening room, resulting in strong nuisance odors. Ammonia concentrations ranged from 2 to 18 mL m(-3) and also contributed to the total odor nuisance. Emission data from various chambers of the pig farm were used with the dispersion model AERMOD to determine the odor nuisance caused due to the presence of H2S and NH3 to receptors at various distances from the facility. Because just a few seconds of exposure can cause an odor nuisance, a "peak-to-mean" ratio was used to predict the maximum odor concentrations. Several scenarios were examined using the modified AERMOD program, taking into account the complex terrain around the pig farm.