The reduction of dioxin emissions from the processes of heat and power generation

Biochar from Co-Pyrolyzed Municipal Sewage Sludge (MSS): Part 2: Biochar Characterization and Application in the Remediation of Heavy Metal-Contaminated Soils

The disposal of municipal sewage sludge (MSS) from wastewater treatment plants poses a major environmental challenge due to the presence of inorganic and organic pollutants. Co-pyrolysis, in which MSS is thermally decomposed in combination with biomass feedstocks, has proven to be a promising method to immobilize inorganic pollutants, reduce the content of organic pollutants, reduce the toxicity of biochar and improve biochar's physical and chemical properties. This part of the review systematically examines the effects of various co-substrates on the physical and chemical properties of MSS biochar. This review also addresses the effects of the pyrolysis conditions (temperature and mixing ratio) on the content and stability of the emerging pollutants in biochar. Finally, this review summarizes the results of recent studies to provide an overview of the current status of the application of MSS biochar from pyrolysis and co-pyrolysis for the remediation of HM-contaminated soils. This includes consideration of the soil and heavy metal types, experimental conditions, and the efficiency of HM immobilization. This review provides a comprehensive analysis of the potential of MSS biochar for environmental sustainability and offers insights into future research directions for optimizing biochar applications in soil remediation.

Micropollutants in biochar produced from sewage sludge: A systematic review on the impact of pyrolysis operating conditions

Biochar obtained from sewage sludge serves as a valuable soil amendment in agriculture, enhancing soil properties by increasing the nutrient content, cation exchange capacity, water retention, and oxygen transmission. However, its utilisation is hampered by the presence of micropollutants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOCs). Previous studies indicate that the type and amount of micropollutants can be significantly adjusted by selecting the right process parameters. This literature review provides an overview of how (1) pyrolysis temperature, (2) carrier gas flow and type, (3) heating rate, and (4) residence time affect the concentration of micropollutants in biochar produced from sewage sludge. The micropollutants targeted are those listed by the European Biochar Certificate (EBC) and by the International Biochar Institution (IBI), including PAHs, PCDD/Fs, PCBs and VOCs. In addition, per- and poly-fluoroalkyl substances (PFAS) are also considered due to their presence in sewage sludge. The findings suggest that higher pyrolysis temperatures reduce micropollutant levels. Moreover, the injection of a carrier gas (N2 or CO2) during the pyrolysis and cooling processes effectively lowers PAHs and PCDD/Fs, by reducing the contact of biochar with oxygen, which is crucial in mitigating micropollutants. Nevertheless, limited available data impedes an assessment of the impact of these parameters on PFAS in biochar. In addition, further research is essential to understand the effects of carrier gas type, heating rate, and residence time in order to determine the optimal pyrolysis process parameters for generating clean biochar.

Influence of different kinds of incinerators on PCDD/Fs: a case study of emission and formation pathway

Few studies focused on the emission of polychlorinated-ρ-dibenzodioxins and dibenzofurans (PCDD/F) from different kinds of waste incinerators. This study was conducted in a full-scale MSW incineration plant to investigate the influence of different incinerator types on PCDD/F. Experimental results indicated that the 2,3,7,8-PCDD/F concentration in the inlet gas of the air pollution control system (APCS) in the studied fluidized bed was higher (2.03 ng I-TEQ/Nm³) than that of the grate (0.77 ng I-TEQ/Nm³). But gas in the outlet of APCS from both incinerators had an approximate concentration, lower than the Chinese emission limit of 0.1 ng I-TEQ/Nm³. Similar distribution patterns were observed for 2,3,7,8-PCDD/Fs, as well as 136 PCDD/F congeners. Specifically, OCDD and 1,2,3,4,6,7,8-HpCDD were major isomer constituents for 2,3,7,8-PCDD/F isomers. In terms of formation pathways, a similar formation mechanism was observed based on fingerprint characteristics of 136 PCDD/F congeners. De novo synthesis was the dominating formation pathway for both incinerators. Meanwhile, DD/DF chlorination was another contributor to PCDD/F formation, which in the fluidized bed was higher. In addition, little correlation (0.009 < R² < 0.533) between conventional pollutants (HCl, CO, PM) and PCDD/Fs was found, suggesting little high-temperature synthesis observed and verifying the dominance of de novo synthesis.

Elemental analysis of residual ash generated during plasma incineration of cellulosic, rubber and plastic waste

Management of plastic, rubber and cellulosic waste from various industries is a challenging task. An engineering scale plasma pyrolysis based incinerator has been commissioned for incineration of combustible waste, including plastic, rubber and cellulose. Operational trials of wastes with simulated composition show a weight reduction factor of more than 18 and volume reduction factor of more than 30. The volume reduction factor is tenfold higher than the compaction process currently practised for rubber and plastic wastes. Representative residual ash samples derived from these runs are subjected to their elemental analysis using EDXRF technique and results are comparable with the published literature. Relative variation of individual elements is attributed to the type of waste and feed composition. Analysis is aided with the calculation of index of geoaccumulation, enrichment factor (EF), contamination factor (CF) and pollution load index (PLI). From this study, it is evident that S, Cr, Zn, As, Se, Hg and Pb are of concern for environment in residual ash from plasma incineration of combustible waste. The efficacy of the incineration process is evaluated; C, H and O reduction achieved is more than 98% and overall enrichment ratio (ER) for the inorganic elements is more than 4.5. This study highlights the importance of elemental composition for the performance analysis of the plasma based incineration as well as hazards evaluation of constituents in residual ash for its further management.

Proximity to coal-fired power plants and neurobehavioral symptoms in children

BACKGROUND

Coal-fired power plants are a major source of air pollution that can impact children's health. Limited research has explored if proximity to coal-fired power plants contributes to children's neurobehavioral disorders.

OBJECTIVE

This community-based study collected primary data to investigate the relationships of residential proximity to power plants and neurobehavioral problems in children.

METHODS

235 participants aged 6-14 years who lived within 10 miles of two power plants were recruited. Exposure to particulate matter ≤10 μm (PM₁₀) was measured in children's homes using personal modular impactors. Neurobehavioral symptoms were assessed using the Child Behavior Checklist (CBCL). Multiple regression models were performed to test the hypothesized associations between proximity/exposure and neurobehavioral symptoms. Geospatial statistical methods were used to map the spatial patterns of exposure and neurobehavioral symptoms.

RESULTS

A small proportion of the variations of neurobehavioral problems (social problems, affective problems, and anxiety problems) were explained by the regression models in which distance to power plants, traffic proximity, and neighborhood poverty was statistically associated with the neurobehavioral health outcomes. Statistically significant hot spots of participants who had elevated levels of attention deficit hyperactivity disorder, anxiety, and social problems were observed in the vicinity of the two power plants.

SIGNIFICANCE

Results of this study suggest an adverse impact of proximity to power plants on children's neurobehavioral health. Although coal-fired power plants are being phased out in the US, health concern about exposure from coal ash storage facilities remains. Furthermore, other countries in the world are increasing coal use and generating millions of tons of pollutants and coal ash. Findings from this study can inform public health policies to reduce children's risk of neurobehavioral symptoms in relation to proximity to power plants.

Assessment of Air Pollution with Polychlorinated Dibenzodioxins (PCDDs) and Polychlorinated Dibenzofuranes (PCDFs) in Lithuania

Polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDD/F) are highly bioavailable in humans, either through direct inhalation or indirectly by trophic transfer from contaminated food or water. The main sources of pollution with PCDD/F include industrial and non-industrial combustion sources, like domestic contaminated wood burning, house fires, burning of leaves from trees, etc. When looking for alternative energy sources and reduced energy costs, solid waste incineration plants are intended to be built in the vicinity of urbanized areas, and thus, the need emerges for examination and prediction of to what extent the solid waste incineration plants might affect the surrounding ecosystem, air pollution, and human health. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) (or simply PCDD/F congeners) belong to the group of semi-volatile organic compounds with environmental stability and long-range transfer in the ambient air. Dioxin isomers are highly toxic and may have carcinogenic and mutagenic effects in humans. PCDD/F is detected in air, water, sediment, plants and animals. PCDD/F is generally distributed in the particulate phase in ambient air. For solid waste incineration plant emissions, the distribution of PCDD/F particles into particles with a diameter of <10 μm is more than 81% of the total particulate matter, and more than 54% of the PCDD/F is distributed into particles with a diameter of <2.5 μm. The aim of this study is to investigate the sources of PCDD/F, emissions and potential hazards, i.e., a toxic equivalent in Lithuania. The measurements were performed in two largest cities of Lithuania Vilnius and Kaunas, where the level of PCDD/F discovered was from 0.015 to 0.52 pg/m3 and from 0.02 to 0.05 pg/m3, respectively. The sites for the monitoring were selected based on their proximity to the locations of the planned cogeneration power plants in these cities.

Characteristics and Treatment Methods of Medical Waste Incinerator Fly Ash: A Review

Medical waste incinerator fly ash (MWIFA) is quite different from municipal solid waste incinerator fly ash (MSWIFA) due to its special characteristics of high levels of chlorines, dioxins, carbon constituents, and heavy metals, which may cause irreversible harm to environment and human beings if managed improperly. However, treatment of MWIFA has rarely been specifically mentioned. In this review, various treatment techniques for MSWIFA, and their merits, demerits, applicability, and limitations for MWIFA are reviewed. Natural properties of MWIFA including the high contents of chlorine and carbonaceous matter that might affect the treatment effects of MWIFA are also depicted. Finally, several commendatory and feasible technologies such as roasting, residual carbon melting, the mechanochemical technique, flotation, and microwave treatment are recommended after an overall consideration of the special characteristics of MWIFA, balancing environmental, technological, economical information.

Roles of intrinsic Mn3+ sites and lattice oxygen in mechanochemical debromination and mineralization of decabromodiphenyl ether with manganese dioxide

Commercial β-MnO₂ with a chemical formula of approximate Mn_0.77⁴⁺Mn_0.23³⁺O_1.88 was used for mechanochemical (MC) oxidative degradation of decabromodiphenyl ether (BDE209). The ball milling process initiated the degradation of BDE209 on β-MnO₂, yielding a nearly complete degradation and debromination of BDE209 within 2 h. The use of β-MnO₂ exhibited much higher MC debromination efficiency than that by using birnessite (δ-MnO₂, 40.2%), Bi₂O₃ (45.6%), CaO (65.3%), and persulfate (81.9%). It was demonstrated that the oxidative degradation of BDE209 was promoted by the redox half reactions of both Mn⁴⁺→ Mn³⁺ and Mn³⁺→ Mn²⁺, but naturally existed Mn³⁺ centers on the surface of β-MnO₂ functioned as dominant reactive species at the initial stage of the MC degradation (often before the degradation efficiency of BDE209 achieved 50%). Moreover, the surface lattice oxygen of MnO₂, rather than O₂, played a key role in the debromination and mineralization of BDE209. The Mn³⁺ sites on β-MnO₂ not only easily accepted the electron of BDE209, but also promoted the mobility of lattice oxygen from the bulk to the surface for mineralizing BDE209. These results firstly highlighted the importance of Mn³⁺ availability and oxygen mobility on the reactivity of manganese oxide for the MC oxidative degradation of organic pollutants.

Fuel modification based on some metals compounds and their environmental impact

The history of fuel additive use reflects the interplay between chemistry, technology and public health concerns related to environmental effects. Decisions to use specific type of chemical modification during combustion process have been made in the absence of toxicological data on health and environmental effects or exposure. The influence of these important issues has extended globally, and the effects of various compositions impact for decades after the removal of these compounds. Fuel modifications are widely used for petrol, oil and solid fuels. According to market screening and literature review, additives containing some dangerous compounds are still in used today. Pb(C2H5)4 was used for long time as fuel additive and is still used as an additive in some grades of aviation gasoline, and in some developing countries. It is obvious that additives containing copper, lead and cerium should be replaced by organic substitutes or inorganic oxidizers during combustion processes.

Application of microwave energy in the destruction of dioxins in the froth product after flotation of hospital solid waste incinerator fly ash

Most of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and powder-activated carbon (PAC) in hospital solid waste incinerator fly ash are enriched in the froths produced through flotation. Because PAC is an excellent microwave absorber, microwave treatment was performed on the froths in this study to decompose PCDD/Fs. The results showed that the destruction efficiency of PCDD/Fs increased with increasing microwave incident power and processing time, particularly for highly chlorinated PCDD/Fs. With a microwave incident power of 2100W at 7min, the total mass destruction efficiency of the PCDD/Fs in the froths reached 99.6wt.% and the total toxic equivalent (TEQ) of PCDD/F was substantially reduced from 29.0 to 0.08 ng-I-TEQ/g. PCDD/Fs in the froths were mostly decomposed and evaporated very little into exhaust gas under microwave treatment, especially at 2100W. The treated froths displayed good porous structures, enabling the potential recovery of PAC for reuse. Microwave treatment of the froths could promote the rapid decomposition of PCDD/Fs and the recovery of a typical waste resource; also it could present a viable alternative to combustion treatment for the froths.

Mechanochemical destruction of halogenated organic pollutants: A critical review

Many tons of intentionally produced obsolete halogenated persistent organic pollutants (POPs), are stored worldwide in stockpiles, often in an unsafe manner. These are a serious threat to the environment and to human health due to their ability to migrate and accumulate in the biosphere. New technologies, alternatives to combustion, are required to destroy these substances, hopefully to their complete mineralization. In the last 20 years mechanochemical destruction has shown potential to achieve pollutant degradation, both of the pure substances and in contaminated soils. This capability has been tested for many halogenated pollutants, with various reagents, and under different milling conditions. In the present paper, a review of the published work in this field is followed by a critique of the state of the art of POPs mechanochemical destruction and its applicability to full-scale halogenated waste treatment.

The role of CuCl on the mechanism of dibenzo-p-dioxin formation from poly-chlorophenol precursors: A computational study

A computational study is performed for the elucidation of the role played by CuCl in the condensation of two polychlorophenol molecules to yield PCDDs. The mechanism found consists of six sequential steps, which allow the final recuperation of the CuCl molecule, and applies for phenol molecules with an ortho chlorine. In the temperature range of 453-473 K (previously reported as adequate to diminish PCDDs formation in the post-combustion area), CuCl is able to softly retain chlorophenol molecules, mainly those less chlorinated. After a first HCl release, Cu(I) remains bonded to phenol oxygen atom, thus avoiding the formation of phenoxy radicals and the subsequent radical processes. A temperature raise up to 1200 K destabilizes the initial CuCl-chlorophenol complexes and causes that the rate limiting step change from the formation of the first oxygen bridge to HCl elimination. It has been checked that tetra and penta-chlorophenols undergo essentially the same reaction process of 2-chlorophenol. In view of our results and trying to arrive at a practical way to diminish the rate of formation of PCDDs, we propose that an extra addition of powdered CuCl to the post-combustion zone, cooled down to temperatures lower than 473 K, could act as an inhibitor in the formation of these pollutants.

Review of the current state and main sources of dioxins around the world

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are a group of dangerous compounds, emitted mostly from anthropogenic sources, that have negative effects on human health. Therefore, it is interesting to analyze the emission patterns of dioxins proceeding from different sources around the world, to observe the actual trend of the transmission of dioxins and furans into the atmosphere.For that reason, the main objective of the present document is to provide a general assessment about the dioxin problematic, analyzing the main parameters that influence the ambient concentration of dioxins worldwide, and describing the most characteristic features of the fingerprint from different sources, while making emphasis in the importance that non-industrial sources are gaining over the last years in front of the decreasing tendency of industrial sources. The description of the most important abatement technologies for dioxins is also included in this review.

IMPLICATIONS

Given the negative effects of dioxins in human health, it is important to depict and locate the main sources of these dangerous compounds. Emissions proceeding from industrial facilities have decreased over the last years; however, other zones where nonindustrial sources used to be relevant contributors do not show the same decreasing tendency because it is more difficult to control this type of emissions. For that reason, future studies should focus on measuring and regulating this highly uncontrolled source of dioxins.

Potential Occupational Exposures and Health Risks Associated with Biomass-Based Power Generation

Biomass is increasingly being used for power generation; however, assessment of potential occupational health and safety (OH&S) concerns related to usage of biomass fuels in combustion-based generation remains limited. We reviewed the available literature on known and potential OH&S issues associated with biomass-based fuel usage for electricity generation at the utility scale. We considered three potential exposure scenarios--pre-combustion exposure to material associated with the fuel, exposure to combustion products, and post-combustion exposure to ash and residues. Testing of dust, fungal and bacterial levels at two power stations was also undertaken. Results indicated that dust concentrations within biomass plants can be extremely variable, with peak levels in some areas exceeding occupational exposure limits for wood dust and general inhalable dust. Fungal spore types, identified as common environmental species, were higher than in outdoor air. Our review suggests that pre-combustion risks, including bioaerosols and biogenic organics, should be considered further. Combustion and post-combustion risks appear similar to current fossil-based combustion. In light of limited available information, additional studies at power plants utilizing a variety of technologies and biomass fuels are recommended.

Influence of a municipal waste landfill on the spatial distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs) in the natural environment

The paper presents the influence of a municipal waste landfill on the pollution of soil, plants and groundwater by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDDs/Fs). Analysis of their migration in the environment was made in relation to the direction of groundwater flow in the study area. Determination of PCDDs/Fs was performed by isotope dilution high resolution chromatography/tandem mass spectrometry (ID-HRGC/MS-MS) on a Thermo Scientific GCQ-1100/Trace2000 system equipped with an Xcalibur data acquisition and analysis software. The content in soil was in the range of 0.04-27.3pg I-TEQg(-1) of soil dry mass and decreased with depth. Similar values were obtained for plants: in Solidago virgaurea L. there were 0.13-1.9pg I-TEQg(-1) dry mass and in grass from the Family Poaceae - 0.12-3.18pg I-TEQg(-1) dry mass. The concentration in groundwater reached 1.16-6.6pg I-TEQdm(-3); the highest concentration was obtained in water samples collected from a ditch collecting leachates from the landfill. The study has shown that the analyzed object is not responsible for PCDDs/Fs emission to the environment. The increased concentration of these compounds in the topsoil may be influenced by processes linked with waste management (transportation and unloading) and other localized sources of low emission located beyond the landfill.

Adsorption of TCDD with 1-butyl-3-methylimidazolium dicyanamide ionic liquid: a combined molecular dynamics simulation and quantum chemistry study

The effective abatement of flue gas emissions, especially polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), is one of the challenging issues in the field of environmental science currently. Imidazolium-based dicyanamide ionic liquids (ILs) were proposed to have potential in controlling the emissions of PCDD/Fs. However, the relevant mechanism at the molecular level still remains unclear. To address this subject, we here present a combined molecular dynamics (MD) simulation and quantum chemical (QM) study on the adsorption of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener among PCDD/F family, by 1-butyl-3-methylimidazolium dicyanamide IL, a representative imidazolium dicyanoamide ILs, which were demonstrated to possess high capture capability for PCDD/Fs. The MD simulation results show that TCDD molecules can be effectively adsorbed on the IL surface to form a dense layer, but cannot enter the interior of the IL. The results of QM calculations show that the adsorption of TCDDs on the IL surface occurs via intra-molecular hydrogen bond interactions. The calculated interaction energy of the anion with TCDD molecule is two times more than that of the cation, implying that the IL anion dominates the interaction with TCDD molecules, while the cation plays a secondary role. Based on the calculated results, we propose that imidazolium dicyanamide IL films/membranes may be better materials than the corresponding bulk for capturing TCDD. The present theoretical results may be helpful to designing the functional ILs which effectively capture and concentrate PCDD/F compounds.