Two laboratory tests were carried out to verify the suitability of an Italian commercial biochar as an adsorbing material. The chosen contaminant, considered dissolved in groundwater, was As. The circular economic concept demands the use of such waste material. Its use has been studied in recent years on several contaminants. The possibility of using an efficient material at low cost could help the use of low-impact technologies like permeable reactive barriers (PRBs). A numerical model was used to derive the kinetic constant for two of the most used isotherms. The results are aligned with others derived from the literature, but they also indicate that the use of a large amount of biochar does not improve the efficiency of the removal. The particular origin of the biochar, together with its grain size, causes a decrease in contact time required for the adsorption. Furthermore, it is possible that a strong local decrease in the hydraulic conductibility does not allow for a correct dispersion of the flow, thereby limiting its efficiency.

Two 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.

With more than 350 GWh per year and thousands of installations around the world, biogas is an appealing strategy in the field of energy production and industrial waste optimization. In this sense, it is of paramount importance to address the risk associated with such plants, as an increasing trend of accidents have been recorded in the last 20 years. In this work, a representative biogas production plant was considered, and a risk assessment was carried out through the combination of Recursive Operability Analysis and Failure Mode and Effects Criticality Analysis. The methodology is rigorous and allows for both the identification and the quantification of accidental scenarios due to procedural errors and equipment failures, which miss in the literature for the case of biogas. The analysis allows the automatic generation of the Fault Trees for the identified Top Events, which can be numerically solved. Results show that the most critical accidental scenario in the biogas plant here considered is the formation of an explosive air-biogas mixture, which can occur in both anaerobic digester and condensate trap. The calculated probabilities agree with the results available in literature on similar plants. Pumps and Distributed Control System were found to be the most critical components.

The 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 R2 = 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.

A 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.

The biological denitrification process is extensively discussed in scientific literature. The process requires anoxic conditions, but the influence of residual dissolved oxygen (DO) on the efficiency is not yet adequately documented. The present research aims to fill this gap by highlighting the effects of DO on the specific denitrification rate (SDNR) and consequently on the efficiency of the process. SDNR at a temperature of 20 °C (SDNR20°C) is the parameter normally used for the sizing of the denitrification reactor in biological-activated sludge processes. A sensitivity analysis of SNDR20°C to DO variations is developed. For this purpose, two of the main empirical models illustrated in the scientific literature are taken into consideration, with the addition of a deterministic third model proposed by the authors and validated by recent experimentations on several full-scale plants. In the first two models, SDNR20°C is expressed as a function of the only variable food:microrganism ratio in denitrification (F:MDEN), while in the third one, the dependence on DO is made explicit. The sensitivity analysis highlights all the significant dependence of SDNR20°C on DO characterized by a logarithmic decrease with a very pronounced gradient in correspondence with low DO concentrations. Moreover, the analysis demonstrates the relatively small influence of F:MDEN on the SDNR20°C and on the correlation between SDNR20°C and DO. The results confirm the great importance of minimizing DO and limiting, as much as possible, the transport of oxygen in the denitrification reactor through the incoming flows and mainly the mixed liquor recycle. Solutions to achieve this result in full-scale plants are reported.

This work is aimed at assessing the effects of pretreated aqueous wastes stream-fed to a biological nutrient removal (BNR)-activated sludge plant. Aqueous wastes (mainly landfill leachate and liquid residues from chemical and pharmaceutical factories) are pretreated by means of a traditional coagulation-flocculation stage and subsequently sent to the BNR stage together with municipal wastewater. Pretreated aqueous wastes contribute up to about 75% of the influent load, in terms of chemical oxygen demand (COD; average concentration 23,000 mg/L). The resilience of the system, that is, the capacity to maintain high and stable performances despite sudden perturbations of the input conditions, was evaluated by interrupting the aqueous waste dosage and then progressively restoring the initial condition. The consequent variation of the influent load and composition caused a reduction of the biomass activity, which led to a decrease of the nitrogen removal efficiency (from 89% down to 73%). More than 30 days were required for restoring typical working conditions (in terms of influent load, process performance, and biomass activity), the sludge retention time (SRT) being 23 days.

The increasingly occurrence of fires risk within public transport facilities prompted many countries to improve public vehicle security implementing specific researches.The provision of a useful reference point for the compatibility of passengers and goods rail transport, with final attention to the preservation of the environment and the human health, represent the general target of such investigations.As a result, this manuscript presents the outcomes of a full-scale experimentation of fire in a bilevel rail car for passengers' transport, useful to evaluate human exposure to toxic loads during a fire.The research consisted in the temperature measurement in various positions and its comparison with a simulation model based on the theoretical approach.Furthermore, visibility and air quality (O 2 , CO 2 , CO, TOC, particulate matter) were analyzed inside the rail car.The comparison between numerical methods and data obtained allow understanding that the numerical model is an effective simulation tool of fire dynamics, especially within the lower deck, although it underestimates the trend of air temperature in the upper deck.Overall, the fire causes a rapid and considerable reduction of oxygen, down to a minimum value of 9.6% by volume, and an increase of particulate matter concentration and total organic carbon, up to maximum values of respectively 2200 mg/Nm 3 and 800 mg/Nm 3 .Evaluations about the toxicological risk for human health and the environment are reported within the study, highlighting difficulties and threats in fire risk prediction and human exposure to toxic load as function of numerous factors, such as construction materials of railcars and passenger health state.

Dusts removal from gaseous streams is a very common operation carried out in a number of industrial plants, e.g.those ones dedicated to the manufacturing of cement and steel, in order to meet the more increasingly stringent law requirements.Therefore, in the last decades, such industries have been to face more and more often the necessity to improve their de-dusting systems inspired by the principle of the 'maximum safety technologically feasible', but also pushed by the increased penetration of environmental issues into the public opinion.Unfortunately, the budget dedicated for all these improvements is often very low because de-dusting is, in the major part of the practical cases, an operation having a low influence on production performances; therefore, it is seen more as a 'necessary cost' than a profit generator.The unavoidable consequence is that plant managers investments are dedicated to other more fruitful processes than de-dusting, addressing the low budget available for gas stream purification to the socalled revamping strategies: that is, the reuse of existing de-dusting plants, either by enhancing their efficiencies through the use of various technical tricks or by adding another pieces of equipment, rather than install new and more technologically advanced plants.This solution is considered very interesting in terms of profit since the costs for the decommissioning of the obsolete equipments does not exist (in fact the old plant remains).Obviously, all the economic benefits derived from these strategies are counterbalanced by a series of technical disadvantages.In particular, a systematic risk assessment of safety of the whole new configuration of the revamped plant is necessary.In fact, such an evaluation cannot be limited to a safe design of the new installed equipment, but it has to be extended to the already existing equipment also considering the impact that changes in process conditions (induced by the new equipment) can have on the whole plant.In this work, the relevant problem of an explosion in the de-dusting section of a cement plant, due to the establishment of an overpressure inside the apparatus, has been considered.Particularly, using fault tree analysis, it has been evaluated the changing in the overall risk (considering, for simplicity, 1 year of mission time) of explosion referring to a hybrid-like collector realized by introducing a Fabric Filter (FF) downstream with respect to an Electrostatic Precipitator (ESP).Results have shown that a chain of failures in the FF section may affect relevantly the explosion risk in the collector leading to the unavoidable need for the introduction of mitigation actions into the system.

A new deterministic model for the calculation of the specific denitrification rate (SDNR), useful for the design of pre-denitrification reactors, was tested on eight full-scale activated sludge plants. The model represents the SDNR at 20 degrees C (SDNR20 degrees C) as a function of the sludge loading in the denitrification reactor (F:M-DEN) and the residual dissolved oxygen in the denitrification reactor (DODEN). The results proved the ability of the model in calculating the SDNR20 degrees C. The model shows a lower degree of adaptability for small-sized plants. SDNR20 degrees C proved to have a strong sensitivity to DODEN, mainly in correspondence with low DO concentrations (less than 2 mg L-1). The sensitivity decreases at greater DO values, but with a progressively less marked gradient, up to becoming weak only at DO concentrations greater than 0.4-0.5 mg L-1, which are rarely found in full-scale plants. DO concentrations measured in real-scale facilities are mostly in the range 0.2-0.4 mg L-1. These concentrations cause adverse effects on the kinetics of nitrogen removal, and consequently on the denitrification performance. Thus, minimizing DO in the pre-denitrification reactor is relevant. The sensitivity of SDNR20 degrees C to F:M-DEN was less important, as it is characterized by a growing linear behaviour with a low slope.

The 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.

Low-permeability lenses represent potential sources of long-term release when filled from contaminant solute through direct contact with dissolved plumes. The redistribution of contaminant from low to high permeability aquifer zones (Back-Diffusion) was studied. Redistribution causes a long plume tail, commonly regarded as one of the main obstacles to effective groundwater remediation. Laboratory tests were performed to reproduce the redistribution process and to investigate the effect of pumping water on the remediation time of these contaminated low-permeability lenses. The test section used is representative of clay/silt lenses (k≈1∗10−10m/s/k≈1∗10−7m/s) in a sand aquifer (k≈1∗10−3m/s). Hence, an image analysis procedure was used to estimate the diffusive flux of contaminant released by these low-permeability zones. The proposed technique was validated performing a mass balance of a lens saturated by a known quantity of tracer. For each test, performed using a different groundwater velocity, the diffusive fluxes of contaminant released by lenses were compared and the remediation times of the low-permeability zones calculated. For each lens, the obtained remediation timeframes were used to define an analytical relation vs groundwater velocity and the coefficients of these relations were matched to grain size of the low-permeability lenses. Results show that an increase of the velocity field is not useful to diminish the total depletion times as the process mainly diffusive. This is significant when the remediation approach relies on pumping technology.

Polluted air streams can be purified using biological treatments such as biotrickling filtration, which is one of the most widely accepted techniques successfully tuned to treat a wide variety of exhausted gaseous streams coming from a series of industrial sectors such as food processing, flavor manufacturers, rendering, and composting. Since the degradation of a pollutant occurs at standard pressure and temperature, biotrickling filtration, whether compared with other more energy-demanding chemical-physical processes of abatement (such as scrubbing, catalytic oxidation, regenerative adsorption, incineration, advanced oxidation processes, etc.), represents a very high energy-efficient technology. Moreover, as an additional advantage, biodegradation offers the possibility of a complete mineralization of the polluting agents. In this work, biotrickling filtration has been considered in order to explore its efficiency with respect to the abatement of ammonia (which is a highly water-soluble compound). Moreover, a complete mathematical model has been developed in order to describe the dynamics of both absorption and biological activities which are the two dominant phenomena occurring into these systems. The results obtained in this work have shown that the absorption phenomenon is very important in order to define the global removal efficiency of ammonia from the gaseous stream (particularly, 44% of the ammonia is abated by water absorption). Moreover, it has been demonstrated (through the comparison between experimental results and theoretical simulations) that the action of bacteria, which enhance the rate of ammonia transfer to the liquid phase, can be modeled through a simple Michaelis-Menten relationship.

The paper summarizes the state-of-the-art of the most recent advances in biological nitrogen removal, including process design criteria and technological innovations. With reference to the Modified Ludzck Ettinger (MLE) process (pre-denitrification and nitrification in the activated sludge process), the most common nitrogen removal process used nowadays, a new design equation for the denitrification reactor based on specific denitrification rate (SDNR) has been proposed. In addition, factors influencing SDNR (DO in the anoxic reactor; hydrodynamic behavior) are analyzed, and technological solutions are proposed. Concerning technological advances, the paper presents a summary of various “deammonification” processes, better known by their patent names like ANAMMOX®, DEMON®, CANON®, ANITA® and others. These processes have already found applications in the treatment of high-strength wastewater such as digested sludge liquor and landfill leachate. Among other emerging denitrification technologies, consideration is given to the Membrane Biofilm Reactors (MBfRs) that can be operated both in oxidation and reduction mode.

Seven full-scale wastewater treatment plants were investigated to highlight the effectiveness of each treatment stage on removing Escherichia coli . The primary sedimentation achieved an average E. coli removal efficiency of 30.5% which was much lower than the suspended solids (58%), thus, revealing the absence of a linear relationship between the two parameters. Biological processes proved to be very important in the removal of E. coli through adsorption inside the sludge flocs and complex decay (mortality). In biological processes with a long retention time, such as activated sludge denitrification-nitrification, the decay was very important, whereas in the more traditional activated sludge process, without nitrification, the contribution of adsorption and mortality was quite balanced. Overall, the mechanical-biological treatment achieved a removal efficiency of 91.8–96.5% depending on the process. Additional removal can be achieved by disinfection. The effectiveness of E. coli removal with sodium hypochlorite was strictly depended on the product of residual chlorine ( C R ) with the contact time ( t ). The experimental curve fitted the Collins model well, with a standard deviation of less than 7%.

Small concentrations of dissolved oxygen (DO) in the range 0.2-0.4mgL(-1) normally are present in biological pre-denitrification reactors. This situation causes adverse effects on denitrification rate and, consequently, on the process efficiency. The results presented show the possibility to control the DO in the anoxic reactor by dosing ferrous Fe(II) ions. The experiments were carried out on both batch samples and a pilot plant and proved that oxidation of Fe(II) to Fe(III) is very efficient in the DO control. Moreover, Fe(III) reacts with phosphorus which precipitates as ferric orthophosphate. A dose of 6 mgFe(2+)L(-1) decreased the mean DO concentration from 0.45 to 0.28mgL(-1); as a consequence, the denitrification efficiency ((DEN)) increased from about 65-77%. (DEN) reached up to 89% with 9mgFe(2+)L(-1) (50% over the stoichiometric for phosphorus removal) thanks to an average DO concentration of 0.08mgO(2)L(-1) in the denitrification stage. The results also highlighted the strong influence of DO (and consequently the dosage of Fe2+) on the specific denitrification rate suggesting to maintain DO concentration in the pre-denitrification reactors lower than 0.2mgL(-1) in order to achieve high operation efficiencies.

Two scenarios in terms of odour impact assessment were studied during the phase of upgrading of an existing waste treatment plant: CALPUFF was used for the simulation of odour dispersion. Olfactometric measures, carried out over different periods and different positions in the plant, were used for model calibration. Results from simulations were reported in terms of statistics of odour concentrations and isopleths maps of the 98th percentile of the hourly peak concentrations, as requested from the European legislation and standards. The excess perception thresholds and emissions were utilized to address the plant upgrade options. The hourly evaluation of odours was performed to determine the most impacting period of the day. An inverse application of the numerical simulation starting from defining the odour threshold at the receptor was made to allow the definition of the required abatement efficiency at the odours source location. Results from the proposed approach confirmed the likelihood to adopt odour dispersion modelling, not only in the authorization phase, but also as a tool for driving technical and managing actions in plant upgrade so to reduce impacts and improve the public acceptance. The upgrade actions in order to achieve the expected efficiency are reported as well.

Groundwater pollution by municipal solid waste (MSW) landfill leachate is a global concern. Stripping towers are one of the most implemented techniques for the removal of ammonia pollution. This study presents a predictive computational model to estimate calcium carbonate precipitation in ammonia stripping towers. The model considers the Ca2+ super-saturation condition due to the water pH, temperature and salinity. The results have been validated through experimental data obtained from a plant fed with MSW landfill leachate-polluted groundwater. The plant consisted of two parallel lines composed of a coagulation-flocculation stage at high pH followed by a stripping tower. Six combinations of water pH and temperature conditions were tested. Maximum precipitation was 1,400 kgCaCO3 after a period of 120days, observed at inlet pH and temperatures of 10.5 and 38 °C The maximum removal efficiency of ammonia was reported as 91%, 87% and 80% respectively. Finally, a good relationship between the loss of efficiency in ammonia removal and the increase of precipitating CaCO3 to the tower plain area ratio, valid for all water pH and temperatures, has been found.

In this study, the long-term tailing derived from the storage process of contaminants in low-permeability zones is investigated. The release from these areas in the groundwater can be considered a long-term source that often undermines remediation efforts. An Image Analysis technique is used to analyze the process and evaluate the concentrations of a tracer at different points of the test section. Furthermore, the diffusive flux from the low-permeability lenses is determined. To validate the proposed technique, the results are compared with samples and the diffusive fluxes resulting from the low-permeability zones of the reconstructed aquifer are compared with a theoretical approach.