1,720,991 research outputs found
The role of food/microorganism ratio in denitrification reactors: How it affects the sizing and operation of the denitrification process
No full textTwo calculation models of the Specific Denitrification Rate (SDNR) are analyzed to highlight the sensitivity of this parameter to the Food:Microorganisms ratio in the denitrification reactor (F:MDEN). One of these models is empirical while the second was elaborated on a deterministic basis. Both models reveal a linear dependence of SDNR20°C on F:MDEN and in a first approximation they are comparable only in a narrow range of concentration of dissolved oxygen (DO) in denitrification, specifically DO=0.25-0.35 mg L-1 . These values frequently occur in well designed and well operated sewage treatment plants. Outside this range, the role of F:MDEN must necessarily be examined in combination with DO because of the relevant influence of the latter on the efficiency of the denitrification process
Study of the performance of disinfection with sodium hypochlorite on a full-scale sewage treatment plant
Full text linkA full-scale sewage treatment plant was investigated to assess the performance of the disinfection stage. Sodium hypochlorite was used as a disinfectant agent and the process efficiency was evaluated by E.coli removal. The research took place over a period of two years in order to evaluate the effect of retention time (t) and residual chlorine (Cr) under different seasonal conditions. The effectiveness of E.coli removal with sodium hypochlorite proved to be strictly dependent on the factor CR t (product of residual chlorine with the contact time). The regression line of the experimental points was, on the whole, well comparable with the model proposed by Collins, especially in the field of CRt lower than 30 mg L-1 min
Applicazione di un DSS a supporto della pianificazione sostenibile dei bacini idrici
No full textL’articolo illustra i risultati conseguibili con un modello dinamico multivalente di supporto alle decisioni (DSS) applicato alla redazione del piano direttorio per lo sviluppo sostenibile di un bacino idrico. Il modello, in grado di tener conto degli aspetti quantitativi e qualitativi delle acque, compreso il microhabitat fluviale, è stato calibrato sperimentalmente per un corso d’acqua brasiliano con particolari valenze socio-economiche e ambiental
Batchsize e criteri topologici: un approccio combinato per l'ottimizzazione in sicurezza
No full textLe piccole e medie imprese chimiche sono una tipologia di industria ampiamente diffusa in Italia. In particolare, esse operano i loro processi in modalità batch e semi-batch, lavorando spesso su commessa e facendo un uso massiccio di reattori multifunzione aventi un sistema di sfogo delle sovrappressioni già installato. Un approccio di tipo “batchsize” è un metodo focalizzato sulla ricerca del livello massimo di riempimento di un reattore multipurpose tale da portare ad un efflusso monofase vapore in caso si verifichi un incendio esterno (in tal modo il dispositivo installato può proteggere il reattore da eventuali sovrappressioni).
In questo lavoro, tale approccio è stato completamente rivisitato, scegliendo come peggior scenario incidentale il caso di reazione fuggitiva, ed integrato con un’opportuna procedura di ottimizzazione basata su criteri di tipo topologico.
Il nuovo approccio “batchsize” permette di calcolare un livello di riempimento del reattore molto più ragionevole per applicazioni industriali rispetto a quello previsto dal metodo classico, mentre l’approccio topologico permette di identificare il tempo di dosaggio minimo in grado di garantire sia la sicurezza dei reattori sia un’elevata produttività. I risultati teorici di questo studio sono stati convalidati sperimentalmente mediante dati ottenuti da test di calorimetria di reazione, condotti in un reattore RC1 operante in modalità isoperibolica, utilizzando come caso studio la polimerizzazione in soluzione dell’acrilato di butile.Small and medium chemical enterprises are widely diffused in Italy. Particularly, they operate batch and semi-batch processes working on job orders and making a massive use of multipurpose reactors having an Emergency Relief System (ERS) already installed. A batchsize approach is a method focused on finding the reactor fill level that can lead to a single phase vapor flow whether an external fire occurs, so that the installed ERS can protect the reactor from overpressures. In this work, such an approach has been revised, by choosing a runaway reaction as design incidental scenario, and integrated with a suitable optimization procedure based on topological criteria. The new batchsize approach allows for computing a reactor
fill level which is much more reasonable for industrial applications with respect to that one predicted by the older method, while the topological approach permits to identify the minimum dosing time capable of guaranteeing both reactor safety and high productivity. Theoretical results have been experimentally validated using data obtained by reaction calorimetry experiments, carried out in an isoperibolic RC1 equipment, implementing the relevant case study of the solution homopolymerization of butyl acrylate
Treatment of airborne BTEX by a two-stage biotrickling filter and biofilter, exploiting selected bacterial and fungal consortia
No full textThe pilot plant fed by a 600-Nm3 h-1 waste air flow rate consisted of a water scrubbing pre-treatment followed by a biotrickling filter and a biofilter, in series. The growth of selected bacterial and fungal consortia was promoted through the biotrickling filter and biofilter. Total BTEX levels were detected in a raw waste air stream at an average concentration of 39.07 mg Nm-3. The whole treatment achieved an average of 96.1 % removal efficiency. This performance led to very low average concentrations of individual BTEX in the final air effluent: 1.07 mg Nm-3 for benzene, 0.16 mg Nm-3 for toluene, 0.22 mg Nm-3 for ethylbenzene and 0.07 mg Nm-3 for xylene (mix). The performance and stability of both biotrickling filter and biofilter confirmed the effectiveness of the treatment in achieving low concentrations of individual BTEX in the final air effluent, which fully comply with the most stringent toxicological standard and threshold odor concentrations, for the protection of workers and local residents. This result was possible by the complementary and synergistic action of the bacterial and fungal consortia in degrading BTEX
Removal and survival of fecal indicators in a constructed wetland after uasb pre-treatment
Full text linkThe experimentation plant, based on a sub-surface horizontal flow phytodepuration (SSHFP) unit with a pre-treatment by an upflow anaerobic sludge blanket (UASB) reactor, proved valuable in treating the sewage of a small rural community located in north Brazil. During a six-month trial, the plant achieved an average removal efficiency of 98.2% (1.74 log removal) for fecal coliforms (FC) and 96.0% (1.40 log removal) for Enterococci (EN), as well as 95.6% for BOD5, 91.0% for COD,00 and 95.4% for suspended solids (SS). The contribution of the UASB reactor to this overall performance was very significant as, alone, it achieved a yield of 62.7% for FC and 60% for EN, in addition to 65.2% for BOD5 and 65.0% for SS. EN was chosen, in addition to FC, because of its higher specificity and strong environmental persistence, leading to an increased risk to human health. In fact, the experimental results confirmed its lower removal efficiency compared to FC. The mechanical and biological mechanisms that led to such a removal efficiency of the two fecal indicators (FIs) are outlined in the article. The same mechanisms led to a good level of equivalence between the removal efficiency of the two FIs with the removal efficiency of SS and BOD5, for both the whole plant and the UASB reactor alone. The research demonstrated the close correlation between the concentrations of EN and FC for the plant effluent. This correlation can be explained by the following mathematical expression of the regression line Log EN = 0.2571 Log FC + 3.5301, with a coefficient of determination R-2 = 0.912. This implies that the concentration of the more specific indicator EN could be calculated, with acceptable approximation, from the simple analysis of FC and vice versa. The experimental plant brought important health benefits to the local population. In particular, there were no significant odor emissions; moreover, the risk of fecal pathogenic diseases was drastically reduced; finally, there was no proliferation of insects and other disease vectors, due to the absence of stagnant or semi-stagnant water exposed to the atmosphere
Application Of A Decision Support System For The SustainablePlanning Of Rio Pojuca Basin (Bahia, Brazil) Water Resources
No full textThe paper presents the structure and the application of a Decision Support System (DSS) to Pojuca
River watershed placed in the Northeast Region of Brazil (Bahia State).
It is composed of surface-water quality models (total phosphorus, BOD, dissolved oxygen
concentration and thermo-tolerant coliform bacteria pollution). A model evaluates the riverine
microhabitat applying autochthonous fish species habitat suitability indexes (water depth, velocity,
substrate and dissolved oxygen) valuated by local ichthyologists. Surface-water quality and
microhabitat models are based on a hydrologic and hydraulic model. Models have been calibrated
and validated using discharge and water quality measurements collected during a 1.5-year period
of monitoring. Output data are available on a spreadsheet and ready to be spatially analyzed in a
GIS software.
We show how DSS can help the decision-making process to achieve the sustainable development
of the basin, considering population growth, economic activities, climate change, management of
sewage and wastewater treatment systems. The DSS is also applied to a challenging scenario: the
building of an in series reservoir for supplying the Capital (Salvador) of drinking water.
The experience has been characterized also by a large involvement of local specialists, with the
aim to emphasize the existing qualifications and to consider local culture
Application of a decision support system to the transport of hazardous materials
No full textThe transport of hazardous substances is an essential economic activity because it represents a quite relevant percentage of the total goods transportation. The risk associated to such an activity is fundamentally related to the possibility of an accident triggering that may cause negative environmental and public health consequences. A recent example is the Viareggio accident (2009), which involved the blast of tank wagons containing liquefied petroleum gas (LPG) and caused more than thirty deaths. In this paper, a modified algorithm for risk evaluation and a decision support system, called TrHaM (TRansport of HAzardous Materials), are proposed in order to both quantify the overall risk due to the transport of hazardous materials via road, railroad,
waterway and pipeline and help in planning transport activities. The algorithm evaluates and shows the risk distribution using a stand-alone GIS software, which also considers sensitive targets with high crowding (such as schools, hospitals, shopping malls, stadiums and camping areas). Moreover, it allows for finding the transport solution and its logistics which minimize risk distribution, including intermodal shipping.
TrHaM reliability has been tested onto the circulation of hazardous materials in the Varese district (Northern Italy). The area is characterized by a high level of both population and industrial density combined with heavy road traffic. TrHaM has been used with the aim of comparing the current scenario with a potential one that introduces some mitigating interventions which may reduce risk, such as a partial conversion of haulage from road to railway
Incineration of Pre-Treated Municipal Solid Waste (MSW) for Energy Co-Generation in a Non-Densely Populated Area
No full text
- …
