Airborne pathogens diffusion: A comparison between tracer gas and pigmented aerosols for indoor environment analysis.

The evaluation of airborne pathogens diffusion is a crucial practice in preventing airborne diseases like COVID-19, especially in indoor environments. Through this transmission route, pathogens can be carried by droplets, droplet nuclei and aerosols and be conveyed over long distances. Therefore, understanding their diffusion is vital for prevention and curbing disease transmission. There are different techniques used for this purpose, and one of the most common is the utilization of tracer gas, however, it has limitations such as the difference in size between the gas molecules and the respiratory droplets, as well as its incapability to take into account evaporation. For this reason, a new method for evaluating the diffusion of respiratory droplets has been developed. This approach involves the use of an ultrasonic emitter to release and disperse pigmented aerosols, and a colorimeter for the following quantitative evaluation. A comparison with the tracer gas technique has been carried out, showing for the pigmented aerosols methodology a response that is dependent on different relative humidity conditions, while there is no clear difference in the dispersion of tracer gas at high or low humidity.

Assessment of hemp hurd-derived biochar produced through different thermochemical processes and evaluation of its potential use as soil amendment.

Biochar is a carbon-rich and porous material that finds application in different sectors and can be extremely useful in agriculture as soil improver. This paper provides a comparison between biochars produced with different slow pyrolysis processes and biochar produced in a downdraft gasifier. A blend of residual lignocellulosic biomasses (hemp hurd and fir sawdust) was pelletized and used as starting feedstock for the tests. The biochars produced were analyzed and compared. Temperature proved to be the main driver in conditioning the chemical-physical characteristics of the biochars more than residence time or the configuration of the pyrolysis process. The higher the temperature, the higher the carbon and ash content and the biochar pH and the lower the hydrogen content and the char yield. The most noticeable differences between pyrolysis and gasification biochars were the pH and the surface area (considerably higher for gasification char) and the low content of hydrogen in the gasification biochar. Two germinability tests were carried out to assess the possible application of the various biochars as soil amendment. In the first germinability test, watercress seeds were placed in direct contact with the biochar, while in the second they were placed on a blend of soil (90%v/v) and biochar (10%v/v). The biochars with the best performance were those produced at higher temperatures using a purging gas and the gasification biochar (especially mixed with soil).

Effects of different gasification biochar grain size on greenhouse gases and ammonia emissions in municipal aerated composting processes.

This work is aimed at investigating the effects derived from the application of minimum amounts of two different sized biochars, obtained through biomass gasification, on the greenhouse gases and ammonia emissions from a co-composting process of the organic fraction of municipal solid waste. The chosen biochar-to-organic waste share is set to 3% w/w dry, and the results obtained are compared with a conventional composting process without biochar. Nine aerated static pilot-scale bins with a volume of 1.3 m3 were prototyped and run, three per thesis and three for the control. The trial lasted 63 days, following the same approach used in full-scale composting facilities. The testing period was divided into a forced aeration phase followed by a static phase. In terms of global warming potential, the use of fine biochar and coarse biochar resulted in 13 and 11 kg CO2eq ton-1 emitted respectively. These values are 36% and 45% lower than the 20 kg of CO2eq ton-1 emitted by the control theses. Specifically, the chosen minimum amounts of biochar produced a reduction of CH4 and N2O, while a significant reduction in NH3 emissions was not detected. Carbon dioxide showed a slight increase in biochar theses. This work has proven that fine and coarse gasification-derived biochars improve the bio-oxidative phenomena and reduce greenhouse gases emissions of the composters, regardless of the biochar particle size and regardless of the modest 3% w/w biochar-to-organic waste share used.

Impacts of gasification biochar and its particle size on the thermal behavior of organic waste co-composting process.

This work investigates the effects of gasification biochar on the thermal behavior of organic municipal waste composting. Two different biochar granulometries were mixed in a 3% w/w share with the organic fraction of municipal waste and tested in nine (three per thesis and three as control) reactors of 1 m3 of volume, designed to simulate full-scale aerated static piles. The temperatures of each composter were monitored for 31 days of the active composting phase and used as key parameters for air flow tuning. After the active phase was completed, the air was turned off and the temperatures were monitored for an additional 31 days during compost maturation. Results show that biochar-aided composters run 4 °C hotter and are more stable in temperature compared to the control thesis. Experimental data were used as a basis for thermal energy modeling: the addition of fine biochar to composting material increased the thermal energy production by 0.5 MJ kg-1 compared to the control thesis; coarse biochar increased the thermal energy production by 0.4 MJ kg-1. The standard composting process, without biochar, produced 2.5 MJ kg-1. Results might serve as a starting point for further considerations in terms of composting time reduction, improvement of the final product and reduction of process related issues, such as undesired anaerobic decomposition, leachate production and temperature instability.

Spent Coffee Grounds in the Production of Lightweight Clay Ceramic Aggregates in View of Urban and Agricultural Sustainable Development.

This paper presents an innovative application for spent coffee grounds (SCGs) used as filler for the formulation of lightweight clay ceramic aggregates (LWA). LWA can be used for urban and agricultural purposes as a sustainable solution. Spent coffee grounds were tested as a pore forming agent partially acting as a replacement for red clay in material formulation before firing. Substitutions of 10, 15, and 20 wt.% of red clay were tested. The properties of lightweight aggregates with 15 wt.% of SCGs were improved using a specifically tailored fertilizer glass due to its low pH and conductivity within the soil tolerance range. Packaging glassy sand, cattle-bone flour ash, and potassium carbonate were mixed and melted in order to obtain this glass, which when added to the clayey batch functionalized the aggregates by phosphorus and potassium nutrients. The results (in particular, porosity and bulk density) show that the lightweight aggregates obtained have interesting properties for possible uses both in urban (e.g., green roofs as a drainage layer) and agricultural purposes. Moreover, pH and conductivity are in line with the Italian Standard regarding soil amendment (D.lgs. 75/2010). In addition, several leaching tests were performed in a solution containing 2 vol.% citric acid (C6H8O7) to evaluate the release capacity not only of nutrients (P and K) but also to check the presence and release of heavy metals, such as lead (Pb), that may come from the glassy precursor. The results obtained showed that nutrients are efficiently released in 21 days (P = 87.73% and K = 25.74% of released percentage) and Pb release is under the standard threshold of 30 ppm.

Combined effects of LED lights and chicken manure on Neochloris oleoabundans growth.

In this study a photobioreactor prototype is presented for the culture growth of microalgae model organism Neochloris oleoabundans by using chicken manure waste as feedstock along with the optimum combination of led light wavelengths and light intensity. Particularly interesting results are observed on the strains fed by chicken manure medium under the proper combination of red and blue LED light illumination, the microalgal growth resulted comparable with the strains fed by the costly commercial microalgal growth medium (BG 11 medium). Cell concentration, optical density, growth rate, cell size, total lipid and photosynthetic pigment content have been monitored during a time-course experiment. The data suggest that there are difficulties due to white light diffusion into the dark chicken medium, which leads to a generally lower intensity scattered along all wavelengths; blue or combined red and blue lights resulted in a higher irradiation density, affecting microalgae cell growth.

Biodiesel and electrical power production through vegetable oil extraction and byproducts gasification: modeling of the system.

Aim of this work is to introduce an alternative to the standard biodiesel production chain, presenting an innovative in situ system. It is based on the chemical conversion of vegetable oil from oleaginous crops in synergy with the gasification of the protein cake disposed by the seed press. The syngas from the gasifier is here used to produce electrical power while part of it is converted into methanol. The methanol is finally used to transform the vegetable oil into biodiesel. Through a coupled use of ASPEN PLUS(TM) and MATLAB(TM) codes, a rapeseed, soy and sunflower rotation, with a duration of three year, was simulated considering 15ha of soil. This surface resulted sufficient to feed a 7kWel power plant. Simulation outputs proven the system to be self-sustainable. In addition, economical NPV of the investment is presented. Finally the environmental, economical and social advantages related to this approach are discussed.

Modeling and investigation of the channeling phenomenon in downdraft stratified gasifers.

Downdraft stratified gasifiers seem to be the reactors which are most influenced by loading conditions. Moreover, the larger the reactor is, the higher the possibility to stumble across a channeling phenomenon. This high sensitivity is due to the limited thickness and superficial placement of the flaming pyrolysis layer coupled with the necessity to keep all the zones parallel for a correct running of this kind of gasifier. This study was aimed at modeling and investigating the channeling phenomenon generated by loading condition variations on a 250-kWe nominal power gasification power plant. The experimental campaign showed great variations in most of the plant outputs. These phenomena were modeled on two modified mathematical models obtained from literature. The results of the models confirmed the capability of this approach to predict the channeling phenomena and its dependency on the loading method.