Greenhouse gas emissions from integrated solid waste management: a new mathematical model

Municipal solid waste management significantly contributes to the emission in the atmosphere of greenhouse gases (e.g. CO2, CH4, N2O) and therefore the management process from collection to treatment and disposal has to be optimized in order to reduce these emissions. Many literature models developed for the evaluation of greenhouses gases emissions from the waste management system are based on the analysis of the life cycle. These models are not optimized for evaluation of emissions. The aim of this study is to overcome these limitations by proposing a mathematical model to estimate greenhouse gas emissions resulting from the integrated waste management. The model is aimed to be a verification tool for assessing the optimum system management in terms of greenhouse gas emissions. The model quantify the emissions associated with: heat treatment, landfill disposal, anaerobic digestion plants, recycling, composting. Different combinations of collection scenarios and disposal options have been considered in the Municipal Solid Waste management of the Province of Palermo. The obtained results applying the model show that limits to solid waste management must be clearly defined. In fact changing the limits, the emissions vary. The lower emissions are due to the use of different energy sources

Sensitivity and uncertainty analysis of an integrated membrane bioreactor model

Sensitivity and uncertainty analysis, although can be of primarily importance in mathematical modelling approaches, are scarcely applied in the field of membrane bioreactor (MBR). An integrated mathematical model for MBR is applied with the final aim to pin down sources of uncertainty in MBR modelling. The uncertainty analysis has been performed combining global sensitivity analysis (GSA) with the generalized likelihood uncertainty estimation (GLUE). The model and methodology were applied to a University Cape Town pilot plant. Results show that the complexity of the modelled processes and the propagation effect from the influent to the effluent increase the uncertainty of the model prediction. It was found that the uncertainty of nitrogen and phosphorus model outputs increases from the first reactor-section plant to the last. Results show also that the GSA-GLUE methodology is a valid tool for uncertainty assessment for MBR modelling. Furthermore, the GSA-GLUE allows to identify the most critical processes/plant sections and the key sources of uncertainty where attention should be paid in view of model predictions improvement

A mathematical model for a sequential batch membrane bioreactor pilot plant

A mathematical model to quantify the nitrogen removal for a membrane bioreactor (MBR) has been presented in this study. The model has been applied to a pilot plant having a pre-denitrification MBR scheme. The pilot plant was cyclically filled with real saline wastewater according to the fill-draw-batch operation. The model was calibrated by adopting a specific protocol based on extensive field dataset. The Standardized Regression Coefficient (SRC) method was adopted to select the most influential model factors to be calibrated. Results related to the SRC method have shown that model factors of the efficiency of backwashing and the biological factors affecting the soluble microbial products (utilization-associated products) (namely, fUAP and KH,UAP) strongly affects the membrane resistance. In terms of model calibration excellent results in terms of model efficiency were found for the total membrane resistance model output (efficiency equal to 0.79). Regarding the biological model outputs acceptable were found in the case an high number of measured data was available. In terms of uncertainty, it was found that for the great part of the analyzed model outputs the measured data lay inside the uncertainty bands

Global sensitivity analysis for micropollutant modeling by means of an urban integrated approach

The paper presents the sensitivity analysis of an integrated urban water quality system by means of the global sensitivity analysis (GSA). Specifically, an home-made integrated model developed in previous studies has been modified in order to include the micropollutant assessment (namely, sulfamethoxazole - SMX). The model is able to estimate also the interactions between the three components of the system: sewer system (SS), wastewater treatment plant (WWTP) and the receiving water body (RWB). The analysis has been applied to an experimental catchment nearby Palermo (Italy): the Nocella catchment. Five scenarios each characterized by different combinations of sub-systems (i.e., SS, WWTP and RWB) have been considered applying the Extended-FAST method. Results demonstrated that GSA is a powerful tool for increasing operator confidence in the modelling results; the approach can be used for blocking some non-identifiable parameters thus wisely modifying the structure of the model and reducing the related uncertainty. The model factors related to the SS have been found to be the most relevant factors affecting the SMX modeling

Urban Storm-Water Quality Management: Centralized versus Source Control

The continuous growth of urban areas and the increasing public awareness of the environmental impacts of storm water have raised interest on the quality of the receiving water bodies. In the past two decades, many efforts have been directed at improving urban drainage systems by introducing mitigation measures to limit the negative environmental impacts of storm water. These mitigation measures are generally called best management practices (BMPs), sustainable urban drainage systems, or low impact developments, and they include practices such as infiltration and storage tanks that reduce the peak flow and retain some of the polluting materials. Choosing the best mitigation measure is still a controversial topic. To gain insight on the best technique, this study compares different distributed and centralized urban storm-water management techniques, including infiltration and storage facilities. The main objective of this study is to use modeling to assess the effects of the different urban drainage techniques. To this end, a homemade model that was developed in previous studies is applied. This model enables us to simulate both combined sewer systems and ancillary structures such as storm tanks or infiltration trenches to determine water quantity and quality characteristics. A long-term simulation is employed to account for the effects of sediments in BMPs, which generally reduce the hydraulic capacity. The results allow us to draw some conclusions on the peculiarities of BMP techniques, on the possibility of integrating different techniques for improving efficiency, and on BMP maintenance planning

Assessment of landfill leachate biodegradability and treatability by means of allochthonous and autochthonous biomasses

The biodegradability and treatability of a young (3 years old) municipal landfill leachate was evaluated by means of chemical oxygen demand (COD) fractionation tests, based on respirometric techniques. The tests were performed using two different biomasses: one cultivated from the raw leachate (autochthonous biomass) and the other collected from a conventional municipal wastewater treatment plant after its acclimation to leachate (allochthonous biomass). The long term performances of the two biomasses were also studied. The results demonstrated that the amount of biodegradable COD in the leachate was strictly dependent on the biomass that was used to perform the fractionation tests. Using the autochthonous biomass, the amount of biodegradable organic substrate resulted in approximately 75% of the total COD, whereas it was close to 40% in the case of the allochthonous biomass, indicating the capacity of the autochthonous biomass to degrade a higher amount of organic compounds present in the leachate. The autochthonous biomass was characterized by higher biological activity and heterotrophic active fraction (14% vs 7%), whereas the activity of the allochthonous biomass was significantly affected by inhibitory compounds in the leachate, resulting in a lower respiration rate (SOUR = 13 mg O2 gVSS-1 h-1 vs 37 mg O2 gVSS-1 h-1). The long-term performance of the autochthonous and allochthonous biomasses indicated that the former was more suitable for the treatment of raw landfill leachate, ensuring higher removal performance towards the organic pollutants

Mathematical modelling of biogas from municipal solid waste landfil

Sanitary landfills for municipal solid wastes can be considered as large biological reactors where the organic fraction of municipal solid waste undergoes anaerobic digestion producing gas and liquid emissions. Leachate production from municipal sanitary landfills is currently recognized as a major environmental burden associated with municipal solid waste management and it may be responsible for local pollution of groundwater and soil. Moreover, the fate of the organic compounds within the landfill body is of primary importance since it directly influences the production of landfill gas. The aim of the paper is to propose an integrated mathematical model able to simulate, on one hand, the vertical leachate fluxes throughout a municipal solid waste landfill (considering the fate of both inorganic and organic contaminants within the landfill leachate pathway), while, on the other hand, the production of landfill gas by means of two different approaches. In detail, the mathematical model was based on mass balance equations and was composed by two sub-models: one for the simulation of moisture distribution, whilst the other one for the simulation of the organic/inorganic contaminant concentrations. The simulation of landfill gas production was based on two different approaches. The integrated model has been applied to a real landfill considered as a case study, the landfill of Pescantina (Italy), with the landfill body divided into N horizontal layers. The results confirmed that the proposed integrated model can be a useful tool for the landfill operator in order to analyze the physical, chemical and biological phenomena occurring within the landfill body

Physical dispersion and disappearance of bacteria in the Golfo di Palermo: the results of two surveys.

This paper reports on some results of two surveys at sea carried out in the surroundings of a urban wastewater discharge on the coast of the Golfo di Palermo, western Sicily (Italy). At the time of the surveys (year 2005) the stretch of water lying before the central part of the capital town received the untreated wastewater originating from about 200 000 inhabitants, which was discharged on-shore without any prior treatment by the free-surface outfall of “Porta Felice main sewer”. This outfall has crucial importance in the water quality; indeed, the Municipality is steadily implementing a plan featuring an intercepting main sewer along the coast and some pumping stations to connect all the main sewers to the main wastewater treatment plant, located in the SE boundary area of the town. At the moment of the surveys, however, no mitigation measure had been applied yet and the quality of the Gulf was still largely affected by it. Part of the Sanitation Plan was the characterization of the seawater; to this aim, in August and November, 2005, the Università degli Studi di Palermo - on behalf of the Municipality’s Ufficio del Centro Storico - carried out two survey cruises in which the most important seawater quality features were investigated. What will be reported on herein is the part dealing with microbiological indicators, taking the salinity field as background

Destino dei radionuclidi negli impianti di depurazione delle acque reflue urbane

Lo studio presentato in questo lavoro ha avuto come obiettivo il monitoraggio e l’analisi del destino dei radionuclidi negli impianti di depurazione ed è stato condotto in collaborazione tra l’Università di Palermo e ARPA Sicilia. Esso ha previsto lo svolgimento di due fasi sperimentali. Nel corso della prima sono stati monitorati gli impianti di depurazione a servizio dei Comuni di Palermo (in località Acqua dei Corsari e Fondo Verde), Bagheria e Cefalù; nella seconda fase l’indagine è stata limitata al solo impianto di Acqua dei Corsari, nel quale si erano riscontrati in precedenza i maggiori spunti di interesse. In entrambe le fasi sono stati prelevati campioni istantanei in diverse sezioni degli impianti oggetto del monitoraggio: influente, vasca a fanghi attivi, ricircolo di fango, effluente del sedimentatore secondario e fango disidratato. I campioni sono stati analizzati con l’obiettivo di determinare l’attività dei principali radioisotopi di origine antropica, per via del loro uso medicale, o presenti nell’ambiente. L’identificazione e la quantificazione dell’attività dei radioisotopi nei campioni prelevati sono state condotte mediante tecniche di spettrometria gamma, utilizzando le strumentazioni disponibili presso l’Università di Palermo e il Laboratorio di radioattività della Struttura Territoriale di Palermo di ARPA Sicilia. Le attività dei radionuclidi rilevate nei vari punti di campionamento sono state utilizzate per la valutazione del rischio radiologico dei lavoratori e verificare il rispetto dei limiti di esposizione. I risultati ottenuti hanno generalmente evidenziato che il radiosotopo maggiormente presente nei campioni analizzati è risultato lo 131I, verosimilmente a causa del suo elevato tempo di dimezzamento. Inoltre è stata riscontrata una maggiore affinità dei radionuclidi nei confronti della componente solida presente nelle acque reflue, circostanza questa che comporta il loro progressivo trasferimento nei fanghi di depurazione, con particolare riferimento, per lo 131I alla frazione organica in essi presente. Tuttavia le attività di 131I rilevate nei fanghi depurazione sono risultate inferiori ai valori limite imposti dalla normativa vigente (D.Lgs. 230/95, D.Lgs. 241/00), per il loro smaltimento