Dispersion by wind of CO2 leaking from underground storage: Comparison of analytical solution with simulation

The concentration of CO₂ in air near the ground needs to be predicted to assess environmental and health risks from leaking underground storage. There is an exact solution to the advection–diffusion equation describing trace gases carried by wind when the wind profile is modeled with a power-law dependence on height. The analytical solution is compared with a numerical simulation of the coupled air–ground system with a source of CO₂ underground at the water table. The two methods produce similar results far from the boundaries, but the boundary conditions have a strong effect; the simulation imposes boundary conditions at the edge of a finite domain while the analytic solution imposes them at infinity. The reverse seepage from air to ground is shown in the simulation to be very small, and the large difference between time scales suggests that air and ground can be modeled separately, with gas emissions from the ground model used as inputs to the air model.     

Analytical methods for waste minimisation in the convenience food industry

Waste creation in some sectors of the food industry is substantial, and while much of the used material is non-hazardous and biodegradable, it is often poorly dealt with and simply sent to landfill mixed with other types of waste. In this context, overproduction wastes were found in a number of cases to account for 20–40% of the material wastes generated by convenience food manufacturers (such as ready-meals and sandwiches), often simply just to meet the challenging demands placed on the manufacturer due to the short order reaction time provided by the supermarkets. Identifying specific classes of waste helps to minimise their creation, through consideration of what the materials constitute and why they were generated. This paper aims to provide means by which food industry wastes can be identified, and demonstrate these mechanisms through a practical example. The research reported in this paper investigated the various categories of waste and generated three analytical methods for the support of waste minimisation activities by food manufacturers. The waste classifications and analyses are intended to complement existing waste minimisation approaches and are described through consideration of a case study convenience food manufacturer that realised significant financial savings through waste measurement, analysis and reduction.     

Anaerobic biodegradation of cellulosic material: Batch experiments and modelling based on isotopic data and focusing on aceticlastic and non-aceticlastic methanogenesis

Utilizing stable carbon isotope data to account for aceticlastic and non-aceticlastic pathways of methane generation, a model was created to describe laboratory batch anaerobic decomposition of cellulosic materials (office paper and cardboard). The total organic and inorganic carbon concentrations, methane production volume, and methane and CO₂ partial pressure values were used for the model calibration and validation. According to the fluorescent in situ hybridization observations, three groups of methanogens including strictly hydrogenotrophic methanogens, strictly aceticlastic methanogens (Methanosaeta sp.) and Methanosarcina sp., consuming both acetate and H₂/H₂CO₃ as well as acetate-oxidizing syntrophs, were considered. It was shown that temporary inhibition of aceticlastic methanogens by non-ionized volatile fatty acids or acidic pH was responsible for two-step methane production from office paper at 35 °C where during the first and second steps methane was generated mostly from H₂/H₂CO₃ and acetate, respectively. Water saturated and unsaturated cases were tested. According to the model, at the intermediate moisture (150%), much lower methane production occurred because of full-time inhibition of aceticlastic methanogens. At the lowest moisture, methane production was very low because most likely hydrolysis was seriously inhibited. Simulations showed that during cardboard and office paper biodegradation at 55 °C, non-aceticlastic syntrophic oxidation by acetate-oxidizing syntrophs and hydrogenotrophic methanogens were the dominant methanogenic pathways.     

A Bayesian network analysis of workplace accidents caused by falls from a height

This article analyses, using Bayesian networks, the circumstances surrounding workplace tasks performed using auxiliary equipment (ladders, scaffolding, etc.) that may result in falls. The information source was a survey of employees working at a height. We were able to determine the usefulness of this approach – innovative in the accident research field – in identifying the causes that have the greatest bearing on accidents involving auxiliary equipment: in these cases, the adoption of incorrect postures during work and a worker’s inadequate knowledge of safety regulations. Likewise, the duration of tasks was also associated with both these variables, and therefore, with the accident rate. Bayesian networks also enable dependency relationships to be established between the different causes of accidents. This information – which is not usually furnished by conventional statistical methods applied in the field of labour risk prevention – allow a causality model to be defined for workplace accidents in a more realistic way. With this statistic tool, the expert is also provided with useful information that can be input to a management model for labour risk prevention.     

Increased bioavailability of metals in two contrasting agricultural soils treated with waste wood-derived biochar and ash

Recycled waste wood is being increasingly used for energy production; however, organic and metal contaminants in by-products produced from the combustion/pyrolysis residue may pose a significant environmental risk if they are disposed of to land. Here we conducted a study to evaluate if highly polluted biochar (from pyrolysis) and ash (from incineration) derived from Cu-based preservative-treated wood led to different metal (e.g., Cu, As, Ni, Cd, Pb, and Zn) bioavailability and accumulation in sunflower (Helianthus annuus L.). In a pot experiment, biochar at a common rate of 2 % w/w, corresponding to ～50 t ha^?1, and an equivalent pre-combustion dose of wood ash (0.2 % w/w) were added to a Eutric Cambisol (pH 6.02) and a Haplic Podzol (pH 4.95), respectively. Both amendments initially raised soil pH, although this effect was relatively short-term, with pH returning close to the unamended control within about 7 weeks. The addition of both amendments resulted in an exceedance of soil Cu statutory limit, together with a significant increase of Cu and plant nutrient (e.g., K) bioavailability. The metal-sorbing capacity of the biochar, and the temporary increase in soil pH caused by adding the ash and biochar were insufficient to offset the amount of free metal released into solution. Sunflower plants were negatively affected by the addition of metal-treated wood-derived biochar and led to elevated concentration of metals in plant tissue, and reduced above- and below-ground biomass, while sunflower did not grow at all in the Haplic Podzol. Biochar and ash derived from wood treated with Cu-based preservatives can lead to extremely high Cu concentrations in soil and negatively affect plant growth. Identifying sources of contaminated wood in waste stream feedstocks is crucial before large-scale application of biochar or wood ash to soil is considered.