Marco Schiavon

Effluents from MBT plants: Plasma techniques for the treatment of VOCs

Mechanical-biological treatments (MBTs) of urban waste are growing in popularity in many European countries. Recent studies pointed out that their contribution in terms of volatile organic compounds (VOCs) and other air pollutants is not negligible. Compared to classical removal technologies, non-thermal plasmas (NTP) showed better performances and low energy consumption when applied to treat lowly concentrated streams. Therefore, to study the feasibility of the application of NTP to MBTs, a Dielectric Barrier Discharge reactor was applied to treat a mixture of air and methyl ethyl ketone (MEK), to simulate emissions from MBTs. The removal efficiency of MEK was linearly dependent upon time, power and specific input energy. Only 2-4% of MEK was converted to carbon dioxide (CO2), the remaining carbon being involved in the formation of byproducts (methyl nitrate and 2,3-butanedione, especially). For future development of pilot-scale reactors, acting on residence time, power, convective flow and catalysts will help finding a compromise between energy consumption, desired abatement and selectivity to CO2.

Air pollution control through biotrickling filters: a review considering operational aspects and expected performance

Abstract The biological removal of pollutants, especially through biotrickling filters (BTFs), has recently become attractive for the low investment and operational costs and the low secondary pollution. This paper is intended to investigate the state of the art on BTF applications. After an overview on the biodegradation process and the typical parameters involved, this paper presents the analysis of a group of 16 literature studies chosen as the references for this sector. The reference studies differ from one another by the pollutants treated (volatile organic compounds [VOC], hydrogen sulphide, nitrogen oxides and trimethylamine), the geometry and size of the BTFs, and the procedures of the tests. The reference studies are analyzed and discussed in terms of the operational conditions and the results obtained, especially with respect to the removal efficiencies (REs) and the elimination capacities (ECs) of the pollutants considered. Empty bed residence time (EBRT), pollutant loading rate, temperature, pH, oxygen availability, trickling liquid flow rate, inoculum selection and biomass control strategies revealed to be the most important operational factors influencing the removal performance of a BTF.

A proposal for a diet-based local PCDD/F deposition limit

This study proposes a method to estimate the maximal tolerable value for the atmospheric deposition of dioxins (PCDD/Fs) to soil. The case study for the application of this methodology is an Alpine valley where a steel production plant is present. In order to estimate the limit value for the PCDD/F deposition, consolidated food chain models were applied, but were adapted to be run backwards with respect to their original formulation, by starting from the diet of people living in the region and from the PCDD/F Tolerable Daily Intake value proposed by the World Health Organization. For this case study, the estimated limit value was 2.30 pg WHO-TEQ m(-2) d(-1) when only local diary products were taken into account and 1.91 pg WHO-TEQ m(-2) d(-1) when also the role of local cereals and vegetables was considered. The average PCDD/F deposition measured in the same region during a monitoring campaign was lower than the above limit values (1.40 pg WHO-TEQ m(-2) d(-1)). Indications on how to consider the contribution of meat and fish are provided too. The approach proposed in this paper represents a useful tool to assess the acceptable overall deposition for a specific region.

Assessment of the local role of a steel making plant by POPs deposition measurements.

Atmospheric depositions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs) were monitored at three sites in the vicinity of a steel making plant, located in an Italian alpine valley. A high variability in the deposition of PCDD/Fs was observed. The influence of the plant was noticeable at two of the sampling sites. However, as the congener profiles demonstrated, wood burning for domestic heating is an additional source of PCDD/Fs for the area under investigation, and this interferes with the characterization of the emissions from the steel plant. The influence of the plant, in terms of PCDD/F deposition, was not noticeable at the most distant site (2km), where an extremely high peak of PCDD/F deposition was measured during the period from 12 January-22 February 2012. The comparison between the congener distribution of PCDD/Fs observed in this sample and the fingerprints of different sources could justify the attribution of this anomalous peak to a possible episode of domestic waste combustion. In order to find a better correlation between the deposition to soil and emissions from the plant, the congener distribution of PCBs was studied. The PCB profiles observed at the three sites well reproduced the average profile found in samples of ash retained by the bag filter of the plant. Thus the monitoring of PCB deposition is an interesting starting point to calibrate dispersion models to assess the impact of steel making activities.

Comparison between conventional biofilters and biotrickling filters applied to waste bio-drying in terms of atmospheric dispersion and air quality

ABSTRACT Biofiltration has been widely applied to remove odours and volatile organic compounds (VOCs) from industrial off-gas and mechanical-biological waste treatments. However, conventional open biofilters cannot guarantee an efficient dispersion of air pollutants emitted into the atmosphere. The aim of this paper is to compare conventional open biofilters with biotrickling filters (BTFs) in terms of VOC dispersion in the atmosphere and air quality in the vicinity of a hypothetical municipal solid waste bio-drying plant. Simulations of dispersion were carried out regarding two VOCs of interest due to their impact in terms of odours and cancer risk: dimethyl disulphide and benzene, respectively. The use of BTFs, instead of conventional biofilters, led to significant improvements in the odour impact and the cancer risk: when adopting BTFs instead of an open biofilter, the area with an odour concentration > 1 OU m−3 and a cancer risk > 10−6 was reduced by 91.6% and 95.2%, respectively. When replacing the biofilter with BTFs, the annual mean concentrations of odorants and benzene decreased by more than 90% in the vicinity of the plant. These improvements are achieved above all because of the higher release height of BTFs and the higher velocity of the outgoing air flow.

Proposal for the correct management of the Life Cycle Assessment results from integrated municipal solid waste treatment

This study focuses on the application of the environmental part of the Life Cycle Assessment (LCA) approach to identify the best alternative among four solutions representing different integrated management systems for the treatment of municipal solid waste (MSW) fluxes. The comparison between the results is made in terms of the human toxicity potentials, with respect to other treatments, including mechanical-biological treatments (MBTs). However, findings from previous studies highlighted the potential risk deriving from the applications of MBTs in their conventional configurations. It may be important to consider the need for adopting additional methods, such as emission, dispersion and exposure models. These tools can improve the understanding of the potential constraints derived from the choice of an integrated solution for waste management and provide useful insights for the choice of the location of a plant, in order to protect fields, pasture and dwellings from potential contamination of soil, the food chain and air.

Characterisation of volatile organic compounds (VOCs) released by the composting of different waste matrices

The complaints arising from the problem of odorants released by composting plants may impede the construction of new composting facilities, preclude the proper activity of existing facilities or even lead to their closure, with negative implications for waste management and local economy. Improving the knowledge on VOC emissions from composting processes is of particular importance since different VOCs imply different odour impacts. To this purpose, three different organic matrices were studied in this work: dewatered sewage sludge (M1), digested organic fraction of municipal solid waste (M2) and untreated food waste (M3). The three matrices were aerobically biodegraded in a bench-scale bioreactor simulating composting conditions. A homemade device sampled the process air from each treatment at defined time intervals. The samples were analysed for VOC detection. The information on the concentrations of the detected VOCs was combined with the VOC-specific odour thresholds to estimate the relative weight of each biodegraded matrix in terms of odour impact. When the odour formation was at its maximum, the waste gas from the composting of M3 showed a total odour concentration about 60 and 15,000 times higher than those resulting from the composting of M1 and M2, respectively. Ethyl isovalerate showed the highest contribution to the total odour concentration (>99%). Terpenes (α-pinene, β-pinene, p-cymene and limonene) were abundantly present in M2 and M3, while sulphides (dimethyl sulphide and dimethyl disulphide) were the dominant components of M1.

Non-thermal Plasma as an Innovative Option for the Abatement of Volatile Organic Compounds: a Review

Volatile organic compounds (VOCs) cause global and local impacts, resulting in environmental, health, and economic adverse effects. Industrial and waste management activities are the main anthropogenic stationary sources of VOCs in the atmosphere. The traditional technologies for the treatment of VOC-contaminated air present several limitations when treating effluents with low VOC concentrations, high airflow rate, and with compounds with low solubility in water. However, a novel technology, based on non-thermal plasmas (NTPs) and catalysis, has shown promising results in air purification. In this framework, after an initial overview on NTP-catalysis principles, this review presents and discusses 20 recent papers, with a threefold purpose: evaluating the most recent applications of NTP and NTP-catalysis reactors to the treatment of air-VOC mixtures, analyzing all the parameters that may influence the abatement efficiency and the by-product formation, and providing the reader with insights into the choice of the preferable configurations to use, based on the effluent type and the destination of the treated air. As a result of this review, NTPs may represent a promising option for indoor air treatment, especially because of the lower expected byproduct formation when treating low-concentrated VOC mixtures with relatively low air flow rates. If the target is the abatement of higher VOC concentrations, the higher energy efficiency obtainable in such conditions makes NTP-catalysis a cost-effective option for industrial applications. In addition, the formation of simpler and more soluble by-products makes NTPs a suitable technology for air pretreatment upstream of water-based removal technologies, such as absorption columns and biofilters.

DOMESTIC ACTIVITIES AND PM GENERATION: A CONTRIBUTION TO THE UNDERSTANDING OF INDOOR SOURCES OF AIR POLLUTION

Few researches on domestic indoor air pollution have given quantitative information on the variation of the characteristics of the indoor source of particulate matter (PM). The purpose of this work was to investigate the emission characteristics of the common indoor particle sources. More specifically, this paper is intended to contribute to the understanding of how normal domestic activities could affect the human health. The emission sources of PM studied in this work was cooking, vacuuming, ironing and the use of deodorant spray.Cooking activities were expected to be one of the major sources of indoor particles and the features of the cookers may affect the characteristics of emissions resulting from cooking. For this reason, the results of a previous study based on the variability of the power of the cooker were reported, to study the sustainability of natural gas from the point of view of the induced indoor human exposure to PM. Measurements were performed by a GRIMM analyser, able to measure 16 granulometric classes from 0.3 to 20 µm. The study found that the activity of cooking and the use of deodorant spray are the sources that produce the higher indoor concentration levels compared with the other sources studied.

PCDD/Fs environmental impact from an anaerobic digestion treatment

The presence of mechanical-biological treatment (MBT) plants for municipal solid waste (MSW) in a territory could result in significant contamination by dioxins and furans (PCDD/Fs). This study points out the importance of carrying out a preliminary environmental impact assessment for MBT plants. A preliminary investigation was carried out with reference to the anaerobic digestion (AD) of MSW. A dispersion model was applied to an MBT plant. The AD process was analysed as a treatment of the filtrate, i.e., the putrescible fraction (undersieve), of screened residual MSW, before a post-biostabilisation (BS) step. A comparison with the BS of the oversieve alone, i.e., the coarse fraction of residual MSW, was made too. A conventional biofilter and a regenerative thermal oxidiser (RTO) were also compared to emission control solutions. Thanks to the increased dilution by the RTO, lower impacts are expected on the surroundings. In addition, coupling AD with post-BS results considerably lower PCDD/Fs emissions with respect to BS alone.