Giuseppe Genon

Perspectives and limits for cement kilns as a destination for RDF

RDF, the high calorific value fraction of MSW obtained by conventional separation systems, can be employed in technological plants (mainly cement kilns) in order to obtain a useful energy recovery. It is interesting and important to evaluate this possibility within the general framework of waste-to-energy solutions. The solution must be assessed on the basis of different aspects, namely: technological features and clinker characteristics; local atmospheric pollution; the effects of RDF used in cement kilns on the generation of greenhouse gases; the economics of conventional solid fuels substitution and planning perspectives, from the point of view of the destination of RDF and optimal cement kiln policy. The different experiences of this issue throughout Europe are reviewed, and some applications within Italy are also been considered. The main findings of the study are that the use of RDF in cement kilns instead of coal or coke offers environmental benefits in terms of greenhouse gases, while the formation of conventional gaseous pollutants is not a critical aspect. Indeed, the generation of nitrogen oxides can probably be lower because of lower flame temperatures or lower air excess. The presence of chlorinated micro-pollutants is not influenced by the presence of RDF in fuel, whereas depending on the quality of the RDF, some problems could arise compared to the substituted fuel as far as heavy metals are concerned, chiefly the more volatile ones.

Participatory approach, acceptability and transparency of waste management LCAs: Case studies of Torino and Cuneo

The paper summarises the main results obtained from two extensive applications of Life Cycle Assessment (LCA) to the integrated municipal solid waste management systems of Torino and Cuneo Districts in northern Italy. Scenarios with substantial differences in terms of amount of waste, percentage of separate collection and options for the disposal of residual waste are used to discuss the credibility and acceptability of the LCA results, which are adversely affected by the large influence of methodological assumptions and the local socio-economic constraints. The use of site-specific data on full scale waste treatment facilities and the adoption of a participatory approach for the definition of the most sensible LCA assumptions are used to assist local public administrators and stakeholders showing them that LCA can be operational to waste management at local scale.

Improvement of anaerobic digestion of sewage sludge in a wastewater treatment plant by means of mechanical and thermal pre-treatments: Performance, energy and economical assessment

Performances of mechanical and low-temperature (<100°C) thermal pre-treatments were investigated to improve the present efficiency of anaerobic digestion (AD) carried out on waste activated sludge (WAS) in the largest Italian wastewater treatment plant (2,300,000p.e.). Thermal pre-treatments returned disintegration rates of one order of magnitude higher than mechanical ones (about 25% vs. 1.5%). The methane specific production increased by 21% and 31%, with respect to untreated samples, for treatment conditions of respectively 70 and 90°C, 3h. Thermal pre-treatments also decreased WAS viscosity. Preliminary energy and economic assessments demonstrated that a WAS final total solid content of 5% was enough to avoid the employment of auxiliary methane for the pre-treatment at 90°C and the subsequent AD process, provided that all the heat generated was transferred to WAS through heat exchangers. Moreover, the total revenues from sale of the electricity produced from biogas increased by 10% with respect to the present scenario.

Modeling biogas production at landfill site

Abstract Biogas production is characteristic of municipal solid waste landfills. A knowledge of the trend of this production allows an exploitation of this energy source. The here presented model is more accurate than those that already exist as it takes the temperature variation in time and depth and the landfill settlement into account. The obtained model fits experimental data well.

Atmospheric pollutants and air quality effects: limitation costs and environmental advantages (a cost–benefit approach)

In order to improve the air quality in some very critical areas in Europe, it is required to limit the contaminant flux coming from different sources (thermal and industrial plants, transport systems, cars, and other technological apparatus). This limitation in many cases corresponds to important investment costs, and normally to a substantial increase in the operative costs; but, from the other side, by the intervention on the emitted pollutant loads it can be obtained a condition of better air quality, with consequent lower externality costs, chiefly with reference to the exposed population. By comparing the two aspects of increasing costs, and in particular the slope of the increasing trend, and from the other side the improvement in air quality, it is possible to identify as a compromise a convenient definition of the optimal intervention that must be realized, and it is possible to establish the performances that must be obtained, by arriving to an acceptable air quality with a sustainable cost. This strategy of identification of the optimal point between these two opposite trends has been illustrated in the present work, and some practical examples of implementation of different limitation strategies and consequent environmental results are presented; these results concern different scale solutions, and different geographic situations.

Activated carbon by pyrolysis of organic sludges

Abstract A study of the feasibility of subjecting organic substances in waste waters to pyrolysis prior to their employment in purification of the water itself is reported. Refinery wastes and those from a biochemical industry were examined. In the case of the refinery wastes, oil filtered on sand granules was carbonized in various gas atmospheres for various periods. The quality of the carbon obtained was determined with reference to its oil-carbon transformation yield, adsorption capacity, and residual hydrocarbon content, comparison being made with a commercial active carbon. Carbon from biochemical wastes was obtained by pyrolysis of the mycelium after fermentation and filtration. This process is promising in that an improvement in the system used for the sludges disposal is required to obtain the active carbon required for the treatment of wastes.

Solid waste and biomass gasification: fundamental processes and numerical simulation

With the aim to study the fundamental processes of MSW (Municipal Solid Waste) gasification scheme and to obtain a comparison with existing thermal utilization schemes, an useful model was realized by using the tools of energy and mass balances, and of chemical homogeneous gas equilibrium (as concerns the residual solid, it was assumed that it is constituted only of inert material). By using this model, with numerical simulation we evaluated the influence of air volume on the most important operating parameters: temperature, flue gases volume, gas heating value, gasification yield (η). On the basis of existing data and the obtained results about syngas flow rate and composition we performed a comparison between gasification and direct combustion (considered environmental performances and energetic production aspects)

Environmental evaluation of the electric and cogenerative configurations for the energy recovery of the Turin municipal solid waste incineration plant

Given the desirability of reducing fossil fuel consumption, together with the increasing production of combustible solid wastes, there is clearly a need for waste treatment systems that achieve both volume reduction and energy recovery. Direct incineration method is one such system. The aim of this work was to analyze the municipal solid waste incineration plant currently under construction in the province of Turin (Piedmont, North Italy), especially the potential for energy recovery, and the consequent environmental effects. We analyzed two kinds of energy recovery: electric energy (electrical configuration) only, and both electric and thermal energy (cogenerative configuration), in this case with a different connection hypothesis to the district heating network. After we had evaluated the potential of the incinerator and considered local demographic, energy and urban planning effects, we assumed different possible connections to the district heating network. We computed the local and global environmental balances based on the characteristics of the flue gas emitted from the stack, taking into consideration the emissions avoided by the substituted sources. The global-scale results provided relevant information on the carbon dioxide emissions parameter. The results on the local scale were used as reference values for the implementation of a Gaussian model (Aermod) that allows evaluation of the actual concentration of the pollutants released into the atmosphere. The main results obtained highlight the high energy efficiency of the combined production of heat and electricity, and the opportunity to minimize the environmental impact by including cogeneration in a district heating scheme.

The influence of different mixing heights on the ECOSENSE model results at a local scale

Abstract The ECOSENSE software has been created and applied as part of the European long term project called ExternE, a research program devoted to the assessment of external costs due to electricity production. The ECOSENSE model starts from the emission rates of a facility, calculates the yearly mean concentrations of the pollutants at the ground level on the basis of atmospheric dispersion models and characterises the subjects exposed to the pollutants in the considered area. After this, proper epidemiological exposure-response and toxicological dose-response functions are applied to determine the impact on the receptors. Finally, the methodology can monetise the calculated physical impact on the basis of selected economic evaluations. The aim of this study is to apply the software to real cases at a local scale and to compare the results based on different mixing height inputs, since the determination of this meteorological parameter is quite complex. Such a study is useful to have an idea of the sensitivity of the ECOSENSE model and make it a user-friendly instrument for administrations; this can help to create a harmonic approach to the problem of atmospheric pollution and impact evaluation. For specified facilities and meteorological conditions and, in particular, for a 100,000 t/y MSW incinerator, the mixing height can be approximated by a constant value of 1000 m throughout the year and the final results will have deviations that are lower than 10%.

PAC ACTIVITY VS BY-PRODUCT PRECURSORS IN WATER DISINFECTION

Disinfection by-products (DBP) are among the most significant negative side effects of drinking water treatments. Chlorinated disinfectants and organic precursors found in source waters are involved in their formation. Purpose of this study is to investigate the applicability of powdered activation carbon (PAC) to the adsorptive removal of precursors. Three different PACs provided by manufacturers have been applied to water samples collected from the Po River (Turin, Italy) and a specific analytical approach based on precursors concentration and DBP formation potential was used for comparison and definition of selectivity. The influence of some operating variables on PAC efficiency has been evaluated for only one of the PACs previously examined: PAC dosage and contact time, ozonation, chlorine dioxide addition, sedimentation. From the results obtained it is possible to suggest the most convenient PAC application scheme.