Anaerobic digestion and co-digestion of slaughterhouse waste (SHW): Influence of heat and pressure pre-treatment in biogas yield

Mesophilic anaerobic digestion (34 ± 1 °C) of pre-treated (for 20 min at 133 °C, >3 bar) slaughterhouse waste and its co-digestion with the organic fraction of municipal solid waste (OFMSW) have been assessed. Semi-continuously-fed digesters worked with a hydraulic retention time (HRT) of 36 d and organic loading rates (OLR) of 1.2 and 2.6 kg VS_feed/m³ d for digestion and co-digestion, respectively, with a previous acclimatization period in all cases. It was not possible to carry out an efficient treatment of hygienized waste, even less so when OFMSW was added as co-substrate. These digesters presented volatile fatty acids (VFA), long chain fatty acids (LCFA) and fats accumulation, leading to instability and inhibition of the degradation process. The aim of applying a heat and pressure pre-treatment to promote splitting of complex lipids and nitrogen-rich waste into simpler and more biodegradable constituents and to enhance biogas production was not successful. These results indicate that the temperature and the high pressure of the pre-treatment applied favoured the formation of compounds that are refractory to anaerobic digestion.The pre-treated slaughterhouse wastes and the final products of these systems were analyzed by FTIR and TGA. These tools verified the existence of complex nitrogen-containing polymers in the final effluents, confirming the formation of refractory compounds during pre-treatment.     

An interval-parameter stochastic robust optimization model for supporting municipal solid waste management under uncertainty

A stochastic robust interval linear programming model (IPRO) was developed for supporting municipal solid waste management under uncertainty. The model improves upon the existing stochastic robust optimization (SRO) and interval linear programming (ILP) methods by allowing evaluations of trade-offs among expected costs, cost variability, and risk of violating relax constraints simultaneously, as well as reflections of complex uncertainties through both interval and stochastic theories. A long-term waste management problem was used to demonstrate the applicability of IPRO model. The results indicated that IPRO normally led to interval solutions, where waste-management alternatives could be generated by adjusting the decision-variable values within their intervals. The model could also help waste managers to identify desired policies that under various environmental, economic, system-feasibility and system-reliability constraints.     

Influx,transport, and accumulation of cadmium in plant species grown at different Cd2+ activities

Abstract

Cadmium (Cd) has no known essential biological function, but it is toxic to plants, animals, and humans. A promising approach to prevent Cd from entering the food chain would be to select and/or create Cd‐accumulating plants to remediate contaminated soils or to develop Cd‐excluding plants to reduce Cd flow from soils into foods. The present study was undertaken to examine the differences in Cd influx, transport, and accumulation among five plant species in relation to plant tolerance to Cd toxicity. Ryegrass (Lolium perenne L.) had the least reduction in dry matter which may be due to its lowest Cd transport rate (TR) to shoots at all Cd levels among the plant species tested. White‐clover (Trifolium repens L.) was the most sensitive species to Cd toxicity, likely because of its highest Cd influx rate (IR) and high TR when plants were grown at low Cd²⁺ activity (≤8 μM). The high tolerance of cabbage (Brassica oleracea var. capitata L.) to moderate Cd toxicity (≤14 μM) appeared to be mainly due to the detoxification of Cd inside plant tissue since it recorded the highest TR and relatively high IR for Cd among the tested species. At Cd²⁺ activities up to 28 uM, the Cd uptake ratios of shoot/root for ryegrass were, on average, about 50‐fold and 27‐fold lower than that for cabbage and maize (Zea mays L.), respectively. These results showed that Cd could be easily transported into shoots of cabbage and maize, but was mainly confined to roots of ryegrass. We suggest that influx and transport rates, especially transport rate, could be used as plant physiological parameters for screening Cd‐excluding genotypes among monocotyledonous plants.     

The influence of dynamic chamber design and operating parameters on calculated surface-to-air mercury fluxes

Dynamic Flux Chambers (DFCs) are commonly applied for the measurement of non-point source mercury (Hg) emissions from a wide range of surfaces. A standard operating protocol and design for DFCs does not exist, and as a result there is a large diversity in methods described in the literature. Because natural and anthropogenic non-point sources are thought to contribute significantly to the atmosphere Hg pool, development of accurate fluxes during field campaigns is essential. The objective of this research was to determine how differences in chamber material, sample port placement, vertical cross sectional area/volume, and flushing flow rate influence the Hg flux from geologic materials. Hg fluxes measured with a Teflon chamber were higher than those obtained using a polycarbonate chamber, with differences related to light transmission and substrate type. Differences in sample port placement (side versus top) did not have an influence on Hg fluxes. When the same flushing flow rate was applied to two chambers of different volumes, higher fluxes were calculated for the chamber with the smaller volume. Conversely, when two chambers with different volumes were maintained at similar turnover times, the larger volume chamber yielded higher Hg fluxes. Overall, the flushing flow rate and associated chamber turnover time had the largest influence on Hg flux relative to the other parameters tested. Results from computational fluid dynamic (CFD) modeling inside a DFC confirm that the smaller diffusion resistance at higher flushing flows contributes to the higher measured flux. These results clearly illustrate that differences in chamber design and operation can significantly influence the resulting calculated Hg flux, and thus impact the comparability of results obtained using DFC designs and/or operating parameters. A protocol for determining a flushing flow rate that results in fluxes less affected by chamber operating conditions and design is proposed. Application of this protocol would provide a framework for comparison of data from different studies.     

Thermogravimetric analysis of biowastes during combustion

The combustion of sewage sludge (SS), animal manure (AM) and the organic fraction of municipal solid waste (OFMSW) was assessed and compared with that of a semianthracite coal (SC) and of a PET waste by thermogravimetric (TG) analysis. Differences were found in the TG curves obtained for the combustion of these materials accordingly to their respective proximate analysis. Non-isothermal thermogravimetric data were used to assess the kinetics of the combustion of these biowastes. The present paper reports on the application of the Vyazovkin model-free isoconversional method for the evaluation of the activation energy necessary for the combustion of these biowastes. The activation energy related to SS combustion (129.1 kJ/mol) was similar to that corresponding to AM (132.5 kJ/mol) while the OFMSW showed a higher value (159.3 kJ/mol). These values are quite higher than the one determined in the same way for the combustion of SC (49.2 kJ/mol) but lower than that for the combustion of a PET waste (165.6 kJ/mol).     

Evaluation of methodology for determining 1,2‐dibromoethane (EDB) in ambient air

Abstract

EDB (ethylene dibromide) is of regulatory interest because it has cancer inducing properties and is a causative agent of aspermia. Methodology used in determining the extent of exposure of workers to EDB in a citrus fumigation facility was evaluated. The purpose of this effort was to develop and/or evaluate the methodology. A number of solid adsorbents were evaluated for trapping EDB. Charcoal was found to be the most efficient for this application. The influence of a number of factors, e.g., humidity, biphenyl concentration and solvents, on trapping and elution efficiency was determined. The level of sensitivity attained in these studies exceeds that necessary to monitor the proposed standard of a maximum of 1 mg/m³ for a 15 min occupational exposure.     

Temporary structures as a generator of waste in covered trade fairs

Events like trade fairs are a complex service activity with a considerable economic, social and environmental impact due, among other factors, to their high level of waste generation. There are few studies of the environmental impact associated with waste generation and typology. An environmental analysis methodology has been developed to characterise the waste associated with the temporary structures used at trade fair events: stands and communal spaces.This methodology has been checked in a pilot test at 6 closed trade fairs in Barcelona, with a range of between 60 and 4400 exhibitors. The methodology developed has made possible to obtain a waste generation profile according to the size of the fair and the types of stands. The stages with the largest amount of temporary structure wastes generated are the assembly and the dismantling of the trade fair.The results indicate that the most common wastes generated are the protective plastic from carpets at the assembly stage and the carpet itself at the dismantling stage. The stand carpet is collected in bulk, while the carpet from the communal spaces is recycled. As the size of the fair increases, and with it the proportion of stands with customised design (or non-reusable stands), the quantity of wood and hazardous waste increases.