User-friendly mathematical model for the design of sulfate reducing H2/CO2 fed bioreactors

The paper presents three steady-state mathematical models for the design of H2/CO2 fed gas-lift reactors aimed at biological sulfate reduction to remove sulfate from wastewater. Models 1A and 1B are based on heterotrophic sulfate reducing bacteria (HSRB), while Model 2 is based on autotrophic sulfate reducing bacteria (ASRB) as the dominant group of sulfate reducers in the gas-lift reactor. Once the influent wastewater characteristics are known and the desired sulfate removal efficiency is fixed, all models give explicit mathematical relationships to determine the bioreactor volume and the effluent concentrations of substrates and products. The derived explicit relationships make application of the models very easy, fast and no iterative procedures are required. Model simulations show that the size of the H2/CO2 fed gas-lift reactors aimed at biological sulfate removal from wastewater highly depends on the number and type of trophic groups growing in the bioreactor. In particular, if the biological sulfate reduction is performed in a bioreactor where ASRB prevail, the required bioreactor volume is much smaller than that needed with HSRB. This is because ASRB can out-compete methanogenic archarea (MA) for H2 (assuming sulfate concentrations are not limiting), whereas HSRB do not necessarily out-compete MA due to their dependence on homoacetogenic bacteria (HB) for organic carbon. The reactor sizes to reach the same sulfate removal efficiency by HSRB and ASRB are only comparable when methanogenesis is inhibited. Moreover, model results indicate that acetate supply to the reactor influent does not affect the HSRB biomass required in the reactor, but favours the dominance of MA on HB as a consequence of a lower HB requirement for acetate supply

Evaluation of biodegradation kinetic constants for aromatic compounds by means of aerobic batch experiments

Kinetics of aerobic biodegradation have been investigated for twenty aromatic species using sludges collected from the aeration basin of municipal sewage treatment plants. The reproducibility of the results is tested with respect to the sludges period of collection and the wastewater treatment plant where they are taken. The comparison of kinetic constants, estimated for the investigated chemicals, allows to evaluate the reactivity effect of single groups (i.e., -OH, -CH3, -Cl, -NO2) into the aromatic structures. The search for easy structure-reactivity relationships is also attempted by means of contributing group methods

Use of Acorn Leaves as a Natural Coagulant in a Drinking Water Treatment Plant

In this study, the use of acorn leaves as a natural coagulant to reduce raw water turbidity and globally improve drinking water quality was investigated. The raw water was collected from a drinking water treatment plant located in Mila (Algeria) with an initial turbidity of 13.0 +/- 0.1 NTU. To obtain acorn leaf powder as a coagulant, the acorn leaves were previously leaned, washed with tap water, dried, ground and then finely sieved. To improve the coagulant activity and, consequently, the turbidity removal efficiency, the fine powder was also preliminarily treated with different solvents, as follows, in order to extract the coagulant agent: (i) distilled water; (ii) solutions of NaCl (0.25; 0.5 and 1 M); (iii) solutions of NaOH (0.025; 0.05 and 0.1 M); and (iv) solutions of HCl (0.025; 0.05 and 0.1 M). Standard Jar Test assays were conducted to evaluate the performance of the coagulant in the different considered operational conditions. Results of the study indicated that at low turbidity (e.g., 13.0 +/- 0.1 NTU), the raw acorn leaf powder and those treated with distilled water (DW) were able to decrease the turbidity to 3.69 +/- 0.06 and 1.97 +/- 0.03 NTU, respectively. The use of sodium chloride solution (AC-NaCl) at 0.5 M resulted in a high turbidity removal efficiency (91.07%) compared to solutions with different concentrations (0.25 and 1 M). Concerning solutions of sodium hydroxide (AC-NaOH) and hydrogen chloride (AC-HCl), the lowest final turbidities of 1.83 +/- 0.13 and 0.92 +/- 0.02 NTU were obtained when the concentrations of the solutions were set at 0.05 and 0.1 M, respectively. Finally, in this study, other water quality parameters, such as total alkalinity hardness, pH, electrical conductivity and organic matters content, were measured to assess the coagulant performance on drinking water treatment

Enhancing Dark Fermentative Hydrogen Production from Problematic Substrates via the Co-Fermentation Strategy

The aim of the present paper is the improvement of dark fermentative hydrogen production from problematic substrates. In detail, the study is aimed at (i) investigating the inhibiting effect of two problematic biomasses (i.e., of olive mill wastewater, containing recalcitrant/toxic compounds and cheese whey, lacking pH buffering capacity) on the dark fermentation process, (ii) as well as verifying the possibility to apply a co-fermentation strategy to enhance the process. To investigate the inhibiting effect of the substrates, two experimental sets were conducted using olive mill wastewater and cheese whey alone, under different food-to-microorganism ratios (i.e., 1, 2.5, and 5). Further experiments were conducted to verify the possibility of improving hydrogen production via the co-fermentation strategy. Such experiments included two tests conducted using different volumetric percentages of olive mill wastewater and cheese whey (90% olive mill wastewater + 10% cheese whey and 80% olive mill wastewater + 20% cheese whey). Results show that using olive mill wastewater alone, the inhibiting effect increased at a higher food-to-microorganism ratio. Moreover, because of the occurrence of a metabolic shift, hydrogen was not produced using 100% cheese whey. Interestingly, compared to the 100% olive mill wastewater condition, the use of 20% cheese whey allowed to double the hydrogen yield, reaching the high cumulative hydrogen production of 2.08 LL−1. Obtained results confirm that the two investigated substrates exert inhibiting effects on microorganisms. Nevertheless, co-fermentation is an effective strategy to improve the dark fermentation process of problematic biomass. © 2022 by the authors

Structuring Vegetable Oils Through the Formation of Capillary Suspensions: Comparison of Wheat Middlings and Pure Cellulose Processed by High-pressure Homogenization

Reducing the intake of harmful trans-fats and saturated fats in the diet, by replacing detrimental fats with healthier oils, without affecting the organoleptic properties of the food product, represent a formidable challenge for the scientific community. In this scenario, this work explores a possible strategy for structuring sunflower oil by investigating the formation of capillary suspensions using wheat middlings (WM) and pure cellulose (CL) as a structuring solid fraction. High-pressure homogenization (HPH), a purely mechanical cell disruption technology, was directly applied to oil suspensions of WM or CL. Subsequently, the addition under high-shear mixing (HSM) of different amounts of an immiscible secondary fluid, water, to the oil suspensions, led to WM and CL particles bridging and network formation, through the development of attractive capillary forces among the particles. The effect of water and particles characteristics on the rheological behavior of the oil suspensions was investigated. The presence of water caused initially an increase in viscosity and then a decrease, as water concentration exceeded a critical value, with an inversion from a continuous oil phase to a continuous aqueous phase. Moreover, the oxidative stability of the capillary suspensions was evaluated, during accelerated aging. The proposed approach not only does not suffer the presence of water, but significantly improves the oxidation stability with respect to the pu

Preliminary Study on Runway Pavement Friction Decay Using Data Mining

AbstractSurfaces of airport pavements are subject to the friction decay phenomenon. A recurrent problem for the runways is represented by the deposits of vulcanized rubber of aircraft tires. This happens mainly in the touch-down areas during landing operations, and the loss of grip compromises the safety of both take-off and landing operations. This study moves from the International Civil Aviation Organization and the Italian Civil Aviation Authority provisions concerning runway friction measurement and reporting to a better way to analyze friction data. Being data mining the computational process of discovering patterns in a large data sets, data mining techniques are very helpful to reach this target. Unsupervised and supervised classification methods to analyze friction data detected by Grip Tester Trailer were employed. First, K-means and Subtractive Clustering were applied to divide data into a certain number of clusters representing the different areas of consumption. In a second time two different Classification and Regression Trees models, CART and GCHAID, were employed to split the data points of the runway into nodes. At the end of the process scatterplots were built and better visualized through non-linear regressions. The decay curves obtained were of service to compare the results achieved using data mining techniques versus the International Civil Aviation Organization and the Italian Civil Aviation Authority provisions in order to find out the best way to analyze friction data. The final goals are to assure an optimum scheduling of the Airport Pavement Management System, as well as users safety

Preliminary activity on the pyrolysis of a plastic based solid recovered fuel

Plastic is a versatile, lightweight, resistant, and inexpensive material, and an increase of its global demand has been observed in the last years (from 299 milion tonnes in 2013 to 348 in 2017) [1], with the dominant role played by the packaging sector, which absorbs almost 40% of the overall production. Management of post–consumer plastic packaging waste poses a serious environmental problem, and a number of strategies have been devised to reuse/recover these materials, mainly with the aim of recovering useful materials and avoiding landfilling. Among these strategies, pyrolysis can play a significant role for recovering useful products and energy from the post–selection mixed packaging waste, that is not amenable to other uses [1]. A large amount of studies has been developed to assess the possibility to convert waste plastic to oil by pyrolysis processes [1] either catalytic or non catalytic. Nevertheless, only a limited numbers of papers refer to the use of real plastic waste rather than simulated mixtures [2] even if the performances obtained are strongly influenced by the feedstock characteristics. Please click Additional Files below to see the full abstract

Recovery of Nanocellulose from Agri-food Residues Through Chemical and Physical Processes

This work proposes a biorefinery approach for the exploitation of agri-food by-products, such as tomato pomace (TP), through the combination of mild chemical hydrolysis and high-pressure homogenization (HPH) in water not only to promote the recovery of cellulose but also its defibrillation to obtain nanocellulose. In particular, the cellulose pulp was isolated from TP using different combinations of chemical and physical processes, by applying HPH treatment (i) directly on the raw material, (ii) after the acid hydrolysis, and (iii) after alkaline hydrolysis. Moreover, the isolated cellulose was deconstructed to obtain cellulose nanoparticles, also through the application of the HPH treatment, enhancing the polymer properties. The structural and physical features of cellulose nanoparticles from TP were analyzed through Fourier-transform infrared spectroscopy (FT-IR) analysis, ?-potential measurement, and morphological analysis with SEM. The results clearly showed that the HPH treatment (80 MPa, 20 passes) at different stages of the process caused only a slight increase in the yield of cellulose recovery, but significantly contributed to obtaining defibrillated cellulose particles, characterized by smaller irregular domains containing elongated needle-like fibers

Microaerobic Digestion of Low-Biodegradable Sewage Sludge: Effect of Air Dosing in Batch Reactors

The adoption of prolonged solid retention times during the biological treatment of urban wastewaters is a well-known strategy to reduce sewage sludge production. However, it also results in the production of a biological sludge with low percentages of biodegradable organic matter, also characterized by high humification degrees, which may hamper the anaerobic digestion treatment aimed at sludge stabilization. To accelerate the hydrolytic stage, the application of microaerobic conditions during the anaerobic digestion of low-biodegradable sewage sludge was investigated in this study. In particular, six bio-methanation tests of a real sewage sludge were carried out, introducing air in the bioreactors with doses ranging between 0 and 16.83 L air/kg VSin d, in order to evaluate the air dosage that optimizes the biomethane production and organic matter degradation. Notably, the lower air loading rates investigated in this study, such as 0.68 and 1.37 L air/kg VSin d, led to an increase in methane production of up to 19%, due to a higher degradation of total lipids and proteins. In addition, these microaerobic conditions also resulted in a decrease in the sludge humification degree and in lower volatile fatty acid accumulation