Wastewater treatment plants provide two final products, purified water and waste in the forms of liquid and solid phases. Municipal biomass from wastewater treatment plants represents a rising ...problem since its disposal is prohibited by a European environmental directive. Currently the more popular are municipal biomass combustion and co-combustion in power plants or waste incineration plants, because the dry municipal biomass has similar calorific value as brown coal. An addition of up to 5% of municipal biomass to the system for electricity production from fossil fuels is allowed according to the European Directives and Slovenian legislation. Following these criteria the addition of around 1730 kg/h of municipal biomass with 60% of moisture is allowed in accordance with the reference thermal power plant operational data. This paper presents analyses regarding the usages of different amounts of municipal biomass in the reference thermal power plant for which process simulation is done using the Aspen Plus programme package. Furthermore, the analysis of hazardous metals such as Pb, Hg and Cd concentrations in flue gases are determined and the economic evaluation of municipal biomass exploitation within the thermal power plant is also presented.
•The 5% addition of municipal biomass (MB) to coal is allowed in thermal power plants.•The process simulation of the reference thermal power plant is done using Aspen Plus.•The influence of MB addition on electricity production is evaluated.•The economic evaluation of MB exploitation is presented.•At current conditions, the investment in such technology is acceptable.
Summary
Municipal residual waste (RW) produced in the Venice area undergoes mechanical‐biological treatment (MBT) in the Fusina plant to produce refuse‐derived fuel (RDF) that is then co‐combusted in ...a nearby coal‐fired power station. Being the first significant project for RDF co‐firing in power plants in Italy, a number of different testing phases were performed starting in 2003, aimed at evaluating differences between so‐called blank operation (i.e., with only coal feeding) and RDF co‐firing at different feeding rates.
The analysis of data gathered during the industrial experimentation shows a savings of 0.7 tonnes (t) of coal per each tonne of co‐fired RDF; stack concentrations of some pollutants (hydrochloric acid HCl, ammonia NH3, carbon monoxide CO, chromium Cr, and lead Pb) appear slightly higher during co‐combustion compared with blank operation, whereas concentrations of dust, sulfur oxides (SOx), and some metals (manganese Mn, nickel Ni, vanadium V) are lower.
To assess the overall environmental performance of this practice, a life cycle assessment (LCA) study was then performed, where different strategies of energy recovery from RW were compared: production of RDF and its co‐combustion in the Fusina power plant, RW combustion without any pretreatment in a mass‐burn waste‐to‐energy (WTE) plant, and production of RDF and its combustion in a dedicated WTE plant.
The LCA results show that co‐combustion of RDF performs better than the other strategies for all impact categories evaluated. The only exception is when the WTE plant operates in combined heat and power mode, with very high overall conversion efficiencies.
Incineration is one of the most widely used treatments in the field of sewage sludge disposal. However, the choice of sewage sludge incineration process is still controversial. In this study, the ...comparative life cycle assessment of sewage sludge incineration processes, including the mono-incineration, co-incineration in coal-fired power plants and co-incineration in municipal solid waste (MSW) incineration plants, was carried out from the perspective of environment, carbon footprint and economy. The environmental assessment results show that terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity, human carcinogenic toxicity and human non-carcinogenic toxicity are the most significant environmental impacts. And the environmental performance of co-incineration in coal-fired power plants is the best. Moreover, the environmental impact is most sensitive to the dehydrant, electricity and fly ash chelating agent. Co-incineration in MSW incineration plants has the lowest carbon emissions, with only 70.50% and 82% of the carbon emissions from mono-incineration and co-incineration in coal-fired power plants, respectively. Furthermore, sewage sludge mono-incineration has the highest disposal costs because of the higher depreciation and solid waste disposal costs. The comprehensive evaluation results reveal that the optimization should focus on the selection of dehydrant and fly ash chelating agent, as well as the improvement of the equipment efficiency.
•GHG emission is not significantly reduced when waste is co-incinerated.•The industry performance data shows a non-negligible loss of energy efficiency.•Uncertainty biases the assessment of waste ...co-incineration.•Transfer coefficients in LCA are not suitable for heavy metals flows modelling.
Life cycle assessment, LCA, has become a key methodology to evaluate the environmental performance of products, services and processes and it is considered a powerful tool for decision makers. Waste treatment options are frequently evaluated using LCA methodologies in order to determine the option with the lowest environmental impact. Due to the approximate nature of LCA, where results are highly influenced by the assumptions made in the definition of the system, this methodology has certain non-negligible limitations. Because of that, the use of LCA to assess waste co-incineration in cement kilns is reviewed in this paper, with a special attention to those key inventory results highly dependent on the initial assumptions made. Therefore, the main focus of this paper is the life cycle inventory, LCI, of carbon emissions, primary energy and air emissions. When the focus is made on cement production, a tonne of cement is usually the functional unit. In this case, waste co-incineration has a non-significant role on CO2 emissions from the cement kiln and an important energy efficiency loss can be deduced from the industry performance data, which is rarely taken into account by LCA practitioners. If cement kilns are considered as another waste treatment option, the functional unit is usually 1t of waste to be treated. In this case, it has been observed that contradictory results may arise depending on the initial assumptions, generating high uncertainty in the results. Air emissions, as heavy metals, are quite relevant when assessing waste co-incineration, as the amount of pollutants in the input are increased. Constant transfer factors are mainly used for heavy metals, but it may not be the correct approach for mercury emissions.
Agricultural activities produce an estimated amount of 32.7 MToe/year of residues in EU countries. They are mostly disposed in landfills, incinerated without any control, or abandoned in fields, ...causing severe impacts on human health and environment. Rice is one of the most consumed crops worldwide with an annual production of 782 million tons according to the Food and Agriculture Organization of the United Nations database. In this context, the EU-funded project LIFE LIBERNITRATE promotes the use of renewable residual sources (i.e., rice straw) to obtain new materials with an added value. The methodology is based on the incineration of rice straw in an own-designed and constructed valorization system. Rice straw/wood pellets are burned in optimized conditions to produce a maximized quantity of ashes with high silica content. These materials will be then used to treat water polluted with nitrates, representing an optimal example of circular economy strategy. In this work, the own-designed valorization unit is described, with special focus on its main constituting elements. The theoretical study of the co-incineration of rice straw and wood pellets identified the optimised combustion conditions. Experimental tests using the theoretical inputs confirmed the most adequate operational conditions (10 g rice straw pellets/min + 10 g wood pellets/min, 6–7 Nm3/h of air, T = 500 °C) and helped in the definition of improvements on the experimental plant.
Life cycle assessment (LCA) study was carried out with Gemis software. The aim was to evaluate the effect of future environmental law on phosphorus discharges on the sustainability of one wastewater ...treatment plants (WWTP) in Algeria. The wastewater treatment generated 6.04 kg CO2eq/cap y. It consumed 95.9 MJ/cap y of cumulative abiotic energy (CECab) and 3.84 kg/cap y of cumulative abiotic mineral (CMab), allocated respectively to energy and chloride ferric production. For extended system boundaries, two sludge recovery strategies were assessed in comparison to the current law: co- incineration and agricultural spreading. The improvement of phosphorus removal to 80% by chemical precipitation increased the global warming potential of these scenarios respectively, of 0.26 and 0.38 kg of CO2eq per g of removed phosphorus. These strategies improved the WWTP sustainability, but the new regulation reduced their substitution effect. The co-incineration with cogeneration was the best on the basis of CECab while spreading was the best one in terms of CMab, acidification, and photochemical oxidation impacts. The choice between these two strategies depends also on the (eco) toxicity impacts and the national economic context. Improving the sustainability of urban wastewater systems should take into account the decrease sludge volume and their nutrient content as well as possible updates of current and future regulations.
Important greenhouse gas (GHG) emissions related to waste incineration and co-combustion of waste were identified and considered relative to critical aspects such as: the contents of biogenic and ...fossil carbon, N2O emissions, fuel and material consumptions at the plants, energy recovery, and solid residues generated. GHG contributions were categorized with respect to direct emissions from the combustion plant as well as indirect upstream contributions (e.g. provision of fuels and materials) and indirect downstream contributions (e.g. substitution of electricity and heat produced elsewhere). GHG accounting was done per tonne of waste received at the plant. The content of fossil carbon in the input waste, for example as plastic, was found to be critical for the overall level of the GHG emissions, but also the energy conversion efficiencies were essential. The emission factors for electricity provision (also substituted electricity) affected the indirect downstream emissions with a factor of 3—9 depending on the type of electricity generation assumed. Provision of auxiliary fuels, materials and resources corresponded to up to 40% of the direct emission from the plants (which were 347—371 kg CO2-eq. tonne —1 of waste for incineration and 735—803 kg CO2-eq. tonne—1 of waste for co-combustion). Indirect downstream savings were within the range of —480 to —1373 kg CO2eq. tonne—1 of waste for incineration and within —181 to —2607 kg CO2-eq. tonne— 1 of waste for co-combustion. N2O emissions and residue management did not appear to play significant roles.
Persistent organic pollutant inhibition in the combustion process of polyvinyl chloride (PVC) by prior addition of an inhibitor is currently being studied, reducing the emission of pollutants, and ...thus reducing the large amount of waste PVC destined for landfill. In this work, the use of sewage sludge (SS) as an alternative to chemical inhibitors to improve the quality emissions of the incineration of polyvinyl chloride waste (PVC e-waste) was studied and optimized. Different combustion runs were carried out at 850 °C in a laboratory tubular reactor, varying both the molar ratio R
(0.25, 0.50, 0.75) between inhibitors (N + S) and chlorine (Cl) and the oxygen ratio λ (0.15, 0.50) between actual oxygen and stoichiometric oxygen. The emissions of several semivolatile compounds families such as polycyclic aromatic hydrocarbons (PAHs), polychlorobenzenes (ClBzs), and polychlorophenols (ClPhs), with special interest in the emissions of the most toxic compounds, i.e., polychlorinated dibenzo-
-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs), were analyzed. A notable decrease in PCDD/F and dl-PCB formation was achieved in most of the experiments, especially for those runs performed under an oxygen-rich atmosphere (λ = 0.50), where the addition of sludge was beneficial with inhibition ratios Ri ≥ 0.25. An inhibition ratio of 0.75 showed the best results with almost a 100% reduction in PCDD/F formation and a 95% reduction in dl-PCB formation.
•Performances of an innovative energy recovery pathway from the residual waste are described.•Peculiar of the analysed system is the disposal of MBT residues in a bioreactor landfill.•An LCA of the ...system is presented based on one year operational data.
The paper describes the performances of the energy recovery pathway from the residual waste based on the production of a Solid Recovered Fuel (SRF) to be exploited via co-combustion in a cement kiln. The SRF is produced in a single stream Mechanical–Biological Treatment plant, where bio-drying of the waste is followed by mechanical refining in order to fulfil the quality requirements by the cement kilns. Peculiar of this MBT is the fact that sorting residues are disposed in a nearby landfill, managed according to a bioreactor approach, where landfill gas is collected for electric energy recovery. A detailed mass and energy balance of the system is presented based on one year operational data, followed by its Life Cycle Assessment. Results show that the system is energetically and environmentally effective, with most of the impacts being more than compensated by the savings of materials and energy. Major role in determining such outcome is the displacement of petcoke in the cement kiln, both in terms of its fossil CO2 emissions and of its life cycle impacts, including the trans-oceanic transport. To check the robustness of the results, two sensitivity analyses are performed on the landfill gas collection efficiency and on the avoided electric energy mix.
In the past, due to improper sludge treatment technology and the absence of treatment standards, some municipal sludge was simply dewatered and then sent to landfills, occupying a significant amount ...of land and posing a serious threat of secondary pollution. To free up land in the landfill area for the expansion of a large-scale wastewater treatment plant (WWTP) in Shanghai, in this study, we conducted comprehensive pilot research on the entire chain of landfill sludge reprocessing and resource utilization. Both the combination of polyferric silicate sulfate (PFSS) and polyetheramine (PEA) and the combination of polyaluminum silicate (PAS) and polyetheramine (PEA) were used for sludge conditioning before dewatering, resulting in dewatered sludge with approximately 60% moisture content. The combined process involved coagulation and sedimentation, flocculation, and oxidation to treat the leachate generated during dewatering. The treatment process successfully met the specified water pollutant discharge concentration limits for the leachate, with the concentration of ammonia nitrogen in the effluent as low as 15.6 mg/L. Co-incineration in a power plant and modification were applied to stabilize and harmlessly dispose of the dewatered sludge. The coal-generating system ran stably, and no obvious problems were observed in the blending process. In the modification experiment, adding 5% to 7% of the solidifying agent increased the sludge bearing ratio by 53% and 57%, respectively. This process effectively reduced levels of fecal coliforms and heavy metals in the sludge but had a less noticeable effect on organic matter content. The modified sludge proved suitable for use as backfill material in construction areas without requirements for organic matter. The results of this study provide valuable insights for a completed full-scale landfill sludge reclamation and land resource release project.
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