Sludge Incineration Process Research Articles

Migration of trace elements and radioisotopes to various fractions of solid wastes generated as a result of the sewage sludge incineration process

The research was aimed at providing new knowledge in the field of chemical characteristics of solid waste generated in the process of combustion of sewage sludge in fluidized bed furnaces. The research material consisted of disposed fluidized beds (DFB), sewage sludge ash (SSA) and air pollution control residues (APC) from three Polish installations for the thermal treatment of sewage sludge. Natural radionuclides as well as anthropogenic isotope 137Cs were determined in the tested materials and the migration of a wide spectrum of trace elements to various waste fractions generated in the process of sewage sludge combustion was examined. It was observed that both radioisotopes and most of the trace elements determined accumulate in SSA and DFB, while the APC fraction contains a much smaller amount of them. The exceptions are mercury and selenium, whose volatile compounds migrate to the exhaust gas dedusting system and accumulate in the APC fraction (up to 40 mg/kg and 13 mg/kg, respectively). A potential threat from the 226Ra isotope in SSA is identified in the context of the management of this waste in the production of building materials because the typical activity of 226Ra in SSA collected from areas with very low Ra content in natural environment exceeds 1.5–6 times the activity of this isotope in conventional cement mixtures. When managing SSA and DFB, special attention should be paid to the content of metalloids such as As, B and Se, due to the high content of mobile forms of these elements in the mentioned materials.

Reduction of heavy metal emissions by adding modified attapulgite to sludge in bubbling fluidized bed incineration process

The utilization of natural mineral adsorbents to adsorb heavy metals generated from sludge incineration was currently a research hotspot. To enhance the adsorption capacity of the adsorbent, a combination of thermal activation and acid-washing modification methods was designed to modify natural attapulgite. The effects of adding the adsorbent on the distribution of heavy metals (Cr, Cu, Ni, Zn, Pb, and Cd) were tested in a laboratory-scale bubbling fluidized bed reactor. The results indicated that increasing the incineration temperature could promote the transformation of heavy metals into the stable state in the incineration ash (bottom slag and fly ash), while facilitating the volatilization and enrichment of semi-volatile heavy metals (Zn, Pb, and Cd) in the fly ash. The addition of modified attapulgite during the sludge incineration process was superior to raw attapulgite, as it enhanced the capacity of unit adsorbents to adsorb and immobilize heavy metals in flue gaseous, thus reducing the emission of heavy metals. BCR and TCLP experiments indicated that a greater proportion of heavy metals in the incineration ash were transformed into the residual fraction, thereby reducing environmental risks. Characterization revealed that the composite modification approach promoted the adsorbent to expose more active sites and increase the active amorphous components, which improved the adsorption and immobilization of heavy metals.

Bioavailability transition path of phosphorus species during the sewage sludge incineration process

Sewage sludge incineration ash (SSIA) is rich in phosphorus (P), thus being considered as a reliable source of phosphorus recovery. Different P species behaved significant bioavailability. Based on this, a comprehensive investigation into the bioavailability transition path of P species during sewage sludge (SS) incineration was conducted. P predominantly existed in the form of inorganic phosphorus (IP) in SS with a higher concentration of non-apatite inorganic phosphorus (NAIP) and less concentration of apatite inorganic phosphorus (AP). During the SS incineration process, OP existed in the flocs and cell structures of SS underwent destruction, the released P then combined with metal elements such as Ca, Mg, Fe, and Al to form AP species (Ca/Mg–P) and NAIP species (Fe/Al/Mn–P), and the NAIP decomposition to release into gas phase. This was the initial step for enhancing the bioavailability of P species. As temperature increased and the incineration process progressed, the low-temperature-resistant NAIP dissociated, and the metal-binding sites of Al, Fe and Mn in NAIP species were gradually replaced by the Ca and Mg thus forming thermal stability AP species (Ca/Mg–P, such as CaHPO4, Ca2PO4Cl, and Mg3(PO4)2 et al.). This step was crucial for the bioavailability improvement of P species during the incineration process. Therefore, the IP proportions in TP were extremely high (＞98%), and this value gradually increased as incineration temperature raised. The higher incineration temperature, the lower NAIP concentration and higher AP concentration. Besides, additives such as coal/rice husk/eggshell played a significant affect. Additives wither higher Ca content were inclined to react with P to form Ca/Mg–P (AP), while the presence of SO2 would react with Ca metals to form CaSO4 thus inhibiting the formation of AP species (such as CaHPO4 and CaPO4Cl). This results could provide theoretical support for the efficient and directional migration of P during sewage sludge incineration.

Comparative study of different sewage sludge incineration treatments based on environmental and economic life cycle assessment.

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.

Modification of Concrete Composition Doped by Sewage Sludge Fly Ash and Its Effect on Compressive Strength.

The sustainable development of construction materials is an essential aspect of current worldwide trends. Reusing post-production waste in the building industry has numerous positive effects on the environment. Since concrete is one of the materials that people manufacture and use the most, it will continue to be an integral element of the surrounding reality. In this study, the relationship between the individual components and parameters of concrete and its compressive strength properties was assessed. In the experimental works, concrete mixes with different contents of sand, gravel, Portland cement CEM II/B-S 42.5 N, water, superplasticizer, air-entraining admixture, and fly ash from the thermal conversion of municipal sewage sludge (SSFA) were designed. According to legal requirements in the European Union, SSFA waste from the sewage sludge incineration process in a fluidized bed furnace should not be stored in landfills but processed in various ways. Unfortunately, its generated amounts are too large, so new management technologies should be sought. During the experimental work, the compressive strength of concrete samples of various classes, namely, C8/10, C12/15, C16/20, C20/25, C25/30, C30/37, and C35/45, were measured. The higher-class concrete samples that were used, the greater the compressive strength obtained, ranging from 13.7 to 55.2 MPa. A correlation analysis was carried out between the mechanical strength of waste-modified concretes and the composition of concrete mixes (the amount of sand and gravel, cement, and FA), as well as the water-to-cement ratio and the sand point. No negative effect of the addition of SSFA on the strength of concrete samples was demonstrated, which translates into economic and environmental benefits.

Blockchain-like [formula omitted] analysis strategy for two distinct “White-box” modeling methodologies to simulate the incineration of oily sludge

The upstream oily sludge (UOS) incineration process conducted in a co-current flow rotary kiln was examined by TG/DTG/DSC thermal analysis and simulated by distinct “White-Box” kinetic models. Inspired by the “Blockchain” idea, novel activation energy (Eα) analysis strategy was first put forward to overcome the questions encountered in the modeling processes. Thermal analysis indicated UOS incineration was a non-isothermal process formed by three reaction stages. Full-range Eα analysis combined with core-point E analysis revealed three multi-step reactions were respectively carried out in the three stages of UOS incineration, and each multi-step reaction was dominated by a specific single-step reaction. The “White Box” kinetic models utilized to simulate the original TG data were respectively established via the Sectionalized Single-step Reaction Approach (SSRA) and the Gaussian-Distributed Activation Energy Model (G-DAEM). Data reproducibility evaluation indicated the “kinetic triplet” of the dominant single-step reaction was beneficial for the construction of SSRA models, and the “kinetic triplet matrix” of the multi-step reaction was rewarding for the establishment of G-DAEM models. Discrepancy analysis manifested the efficiency of G-DAEM models was superior to that of SSRA models because G-DAEM models are more flexible in depicting the complex UOS incineration process.

Utilization of APC residues from sewage sludge incineration process as activator of alkali-activated slag/glass powder material

In this paper, the soluble salts from the air pollution control (APC) residues of a sewage sludge incinerator and solid sodium silicate were used as a hybrid activator to prepare alkali-activated materials (AAMs) using slag and waste glass powder (GP) as the precursors. The effect of the hybrid activator on the mechanical properties and its reaction mechanism was discussed. The experimental results showed that the APC residues obviously decreased the early compressive strength of the AAMs due to its lower activity, but a steady growth of later compressive strength was achieved due to the dense microstructure. The alkali-activated slag and GP/slag suffered from severe drying shrinkage, but the drying shrinkage of the AAMs reduced by 30%–50% when the 20% APC residues were added. In addition, when the APC residues and GP was used, the insufficient aluminum and calcium contents restrained the formation of the C-(A)-S-H gels in the alkali-activated GP/slag, and the N-(C)-A-S-H gels were formed until the available Ca was exhausted. Some crystalline materials including the ettringite, hydrotalcite, albite and Friedel's salts were detected in the alkali-activated slag/GP after the incorporation of the APC residues in addition to the N–S–H gels.

Exploration of novel high-temperature heavy metals adsorbent for sludge incineration process: Experiments and theoretical calculations

Adsorption is an effective and environment-friendly method to control the pollution of volatile and semi-volatile heavy metals (HMs) produced during municipal sludge incineration. In this study, the effect of a novel high-temperature adsorbent (attapulgite) on the migration and transformation mechanisms of HMs (Cr, Cu, Zn, Ni, and Pb) was investigated and compared with the conventional adsorbent (kaolin). The results of experiments and characterization showed attapulgite possessed improved adsorption effects than kaolin due to the smaller crystal distortion and more active sites reserved at 850 ℃. Furthermore, it was found that volatile HMs (Pb, and Zn) tend to be retained in the fly ash, while low-volatile HMs were adsorbed in the bottom slag by Si-Al-based absorbents. Meanwhile, the analytical results of BCR and TCLP tests showed that the proportion of unstable fraction of HMs in the adsorption products of attapulgite was much lower than that of raw dry sludge, and exhibited better leaching stability than kaolin. Theoretical calculations revealed that the adsorption of typical heavy metal forms at high temperatures by attapulgite exhibited a tight chemical adsorption, furthermore, the heavy metal oxides were more susceptible to removal by attapulgite (1 1 0) surface than the corresponding heavy metal chlorides. This work demonstrated the effectiveness of attapulgite in controlling heavy metals in furnaces and provided a new perspective on the development of this field.

Physical, mechanical properties and durability of cement mortars containing fly ash from the sewage sludge incineration process

Pursuant to European Union regulations, waste generated during municipal sewage treatment should be managed in an environmentally friendly manner. In order to eliminate the risk to human health and to the environment, and also to minimise the volume of the resulting sludge, it is subjected to thermal treatment. The resulting ash contains heavy metals, and thus proper management is required. Since it is known that products of cement hydration reactions have a potential ability to immobilise heavy metals, a preliminary verification was conducted of the possibility of disposing of this type of waste by including it in cement composites. For this purpose, suitable tests were carried out on the mechanical properties and durability of cement binders containing ash from the incineration of sludge produced from municipal sewage (Sewage Sludge Ash – SSA). The tests were conducted for a standard mortar composition based on Portland cement CEM I and on ash obtained on a technical scale in a sewage treatment plant at a temperature of about 850 °C. This mineral addition was used to replace 10%, 20%, 30% and 40% of the cement by weight. The physical and mechanical characteristics were measured, such as compressive and flexural tensile strength after 14, 28 and 90 days of curing as well as durability characteristics such as total porosity, the ability to transport chloride ions and resistance to sulphate ions. The results obtained confirm that replacing 10% of the cement with this admixture has a beneficial effect on the mechanical and durability characteristics, but greater amounts are reflected in a clear deterioration of these characteristics.

Study and analysis of arsenic adsorption during sludge incineration

This paper studies the mechanism of arsenic adsorption by different adsorbents during sludge incineration. The mechanism of arsenic adsorption in the sludge incineration process was studied in a vertical furnace. The arsenic adsorption performance of CaCO3 and Fe2O3 at different temperatures was studied. When the temperature is 900°C, the overall adsorption performance is the best. Therefore, the arsenic adsorption performance of Al2O3, molecular sieve and its metal load at 900°C is further studied for comparison. The research results show that: the optimal adsorption temperature of CaCO3 is 900°C, the optimal adsorption temperature of Fe2O3 is 800°C, and the adsorption performance of CaCO3 is better than Fe2O3. Ca2+: Al3+=0.5 and Fe3+: Al3+=0.4 are close to the adsorption saturation state when Al2O3 adsorbs arsenic at 900°C. When the molecular sieve adsorbs arsenic at 900°C, the adsorption effect is best when the molecular sieve is 10X, Ca2+: Al3+=0.8 and Fe3+: Al3+=0.6 are close to the adsorption saturation state.

下水汚泥焼却時における溶融物生成に及ぼす下水汚泥中の無機成分の影響

下水汚泥焼却時における溶融物生成に及ぼす下水汚泥中の無機成分の影響

Towards better environmental performance of wastewater sludge treatment using endpoint approach in LCA methodology.

The aim of this study is to use the life cycle assessment method to measure the environmental performance of the sludge incineration process in a wastewater treatment plant and to propose an alternative that can reduce the environmental impact. To show the damages caused by the treatment processes, the study aimed to use an endpoint approach in evaluating impacts on human health, ecosystem quality, and resources due to the processes. A case study was taken at Bissell Point Wastewater Treatment Plant in Saint Louis, Missouri, U.S. The plant-specific data along with literature data from technical publications were used to build an inventory, and then analyzed the environmental burdens from sludge handling unit in the year 2011. The impact assessment method chosen was ReCipe 2008. The existing scenario (dewatering-multiple hearth incineration-ash to landfill) was evaluated and three alternative scenarios (fluid bed incineration and anaerobic digestion with and without land application) with energy recovery from heat or biogas were proposed and analyzed to find the one with the least environmental impact. The existing scenario shows that the most significant impacts are related to depletion in resources and damage to human health. These impacts mainly came from the operation phase (electricity and fuel consumption and emissions related to combustion). Alternatives showed better performance than the existing scenario. Using ReCipe endpoint methodology, and among the three alternatives tested, the anaerobic digestion had the best overall environmental performance. It is recommended to convert to fluid bed incineration if the concerns were more about human health or to anaerobic digestion if the concerns were more about depletion in resources. The endpoint approach may simplify the outcomes of this study as follows: if the plant is converted to fluid bed incineration, it could prevent an average of 43.2 DALYs in human life, save 0.059 species in the area from extinction, and make a 62% reduction in the plant’s current expenses needed by future generations to extract resources per year. At the same time it may prevent 36.1 DALYs in humans, save 0.157 species, and make a 101% reduction in current expenses on resources per year, if converting to anaerobic digestion.

Ammonia Emission from Sewage Sludge Incineration Process

Abstract In quantitative terms, sludge produced in the process of municipal wastewater treatment represents a small part of the total waste generated in municipal sources - its quantity represents only a few percent of the generated mass of municipal waste. However, the threats it brings, do not allow it to be neglected while designing the wastewater treatment process. At the same time, with increasing requirements regarding the quality of sewage discharged into the environment, there is an increase in the amount of sludge produced in wastewater treatment processes. In recent years, the share of thermal treatment of municipal sewage sludge has risen sharply - about 12 modern sludge incineration plants have been built and construction of new ones is considered. During more than a four-year operation of the sewage sludge incineration plant in the Combined Sewage Treatment Plant in Lodz (GOS) a large ammonia emission from the combustion process was observed. So, a decision was taken to examine this process. The paper presents results of ammonia emission from the combustion of sewage sludge from GOS as a function of temperature.

Thermodynamic Equilibrium Calculations on Cd Transformation during Sewage Sludge Incineration.

Thermodynamic equilibrium calculations were performed to reveal the distribution of cadmium during the sewage sludge incineration process. During sludge incineration in the presence of major minerals, such as SiO2, Al2O3 and CaO, the strongest effect was exerted by SiO2 on the Cd transformation compared with the effect of others. The stable solid product of CdSiO3 was formed easily with the reaction between Cd and SiO2, which can restrain the emissions of gaseous Cd pollutants. CdCl2 was formed more easily in the presence of chloride during incineration, thus, the volatilization of Cd was advanced by increasing chlorine content. At low temperatures, the volatilization of Cd was restrained due to the formation of the refractory solid metal sulfate. At high temperatures, the speciation of Cd was not affected by the presence of sulfur, but sulfur could affect the formation temperature of gaseous metals.

Full-Scale Plant Study of the Innovative Spray-Drying-Based Sludge Incineration (SDSI) Process: Behavior of Heavy Metals

Large-scale applications of sludge incineration, particularly with fluidized-bed incinerators, are extremely restricted in China at present by their high investment and operating costs. An innovative spray-drying-based sludge incineration (SDSI) process was proposed in our recent study, which has been applied in a full-scale sludge incineration plant with a capacity of 1200 tonnes/day (80% moisture). In the present research, behavior of selected heavy metals (Cu, Zn, Pb, Cd, As, Hg, Cr, and Ni) in this plant was investigated, aiming to provide further evidence about the SDSI performance. The results showed that concentrations of Cu, Zn, and Ni in the slag were higher than those in the fly ash after combustion. Nevertheless, concentrations of Pb, Cd, Hg, and As in the fly ash, particularly in the fine ash particles, were significantly higher than those in the slag. Unlike other heavy metals, the concentration of Cr in the slag was higher than that in coarse ash particles but roughly equal to that in fine a...

Effects of sulfur on lead partitioning during sludge incineration based on experiments and thermodynamic calculations

Experiments in a tubular furnace reactor and thermodynamic equilibrium calculations were conducted to investigate the impact of sulfur compounds on the migration of lead (Pb) during sludge incineration. Representative samples of typical sludge with and without the addition of sulfur compounds were combusted at 850°C, and the partitioning of Pb in the solid phase (bottom ash) and gas phase (fly ash and flue gas) was quantified. The results indicate that three types of sulfur compounds (S, Na2S and Na2SO4) added to the sludge could facilitate the volatilization of Pb in the gas phase (fly ash and flue gas) into metal sulfates displacing its sulfides and some of its oxides. The effect of promoting Pb volatilization by adding Na2SO4 and Na2S was superior to that of the addition of S. In bottom ash, different metallic sulfides were found in the forms of lead sulfide, aluminosilicate minerals, and polymetallic-sulfides, which were minimally volatilized. The chemical equilibrium calculations indicated that sulfur stabilizes Pb in the form of PbSO4(s) at low temperatures (<1000K). The equilibrium calculation prediction also suggested that SiO2, CaO, TiO2, and Al2O3 containing materials function as condensed phase solids in the temperature range of 800–1100K as sorbents to stabilize Pb. However, in the presence of sulfur or chlorine or the co-existence of sulfur and chlorine, these sorbents were inactive. The effect of sulfur on Pb partitioning in the sludge incineration process mainly depended on the gas phase reaction, the surface reaction, the volatilization of products, and the concentration of Si, Ca and Al-containing compounds in the sludge. These findings provide useful information for understanding the partitioning behavior of Pb, facilitating the development of strategies to control the volatilization of Pb during sludge incineration.

The seasonal variation of emission of greenhouse gases from a full-scale sewage treatment plant

The seasonal variety of greenhouse gas (GHGs) emissions and the main emission source in a sewage treatment plant were investigated. The emission coefficient to treated wastewater was 291gCO2m−3. The main source of GHGs was CO2 from the consumption of electricity, nitrous oxide from the sludge incineration process, and methane from the water treatment process. They accounted for 43.4%, 41.7% and 8.3% of the total amount of GHGs emissions, respectively. The amount of methane was plotted as a function of water temperature ranging between 13.3 and 27.3°C. An aeration tank was the main source of methane emission from all the units. Almost all the methane was emitted from the aeration tank, which accounted for 86.4% of the total gaseous methane emission. However, 18.4% of the methane was produced in sewage lines, 15.4% in the primary sedimentation tank, and 60.0% in the aeration tank.

The influence of thermal processing of sewage sludge on the usage properties of the formed ash

The influence of thermal processing of sewage sludge on the usage properties of the formed ash The influence of sewage sludge incineration temperature on the formed ash constitution was examined. The comparative extraction tests of two differently prepared ashes (laboratory and industrial) were carried out in order to verify if the parameters of sewage sludge incineration influence the extraction selectivity of phosphorus compounds. The laboratory ash (Alab ) were prepared from sewage sludge incinerated at 950°C on a laboratory scale while the industrial ash (Aind ) comes from thermal utilization system of the sewage sludge at the Gdynia Sewage Treatment Plant, which uses fluid-bed furnace incineration at 850 - 900°C. It was found that the temperature and the conditions of the sewage sludge incineration process have an effect on the usage properties of the formed ash. Despite the twofold lower Fe content in the industrial ash than that of the laboratory one, its content in extracts after phosphoric acid leaching is 4.7 times higher. The lower values of PO4 3- leaching degree from the industrial ash than the laboratory ash were observed, as well as a decrease of extraction productivity.

Potential method for reducing emissions of polycyclic aromatic hydrocarbons from the incineration of biological sludge for the terephthalic acid manufacturing industry.

This study illustrates a potential method for reducing PAH emissions from the incineration of biological sludge by adding a suitable and available waste as a co-fuel. The whole study was conducted on a full-scale fluidized-bed incinerator operated by a terephthalic acid (TPA) manufacturing plant for disposing of biological sludge. Two incinerating conditions were studied, one directly incinerating biological sludge (the normal incinerating condition), and the other adding the waste TPA as a co-fuel during the biological sludge incineration process (the trial incinerating condition). Both incinerating conditions used heavy oil as auxiliary fuel. Although the former had a higher heavy oil consumption rate than the latter, both had comparable combustion efficiencies. Results show that the total PAH input mass rate for the former was only 2.35 times higher than the latter, but the total PAH emission factor for the former was 6.52 times higher than the latter. Total PAH output/input mass ratios for both incinerating conditions were lower than unity, but the value for the normal incinerating condition was approximately 2.91 times higher than the trial condition. In conclusion, the use of waste TPA as a co-fuel not only saved the consumption of heavy oil but also reduced PAH emissions during the combustion process.

Research on low temperature thermo-chemical conversion to oil process for sewage sludge

The process of low temperature thermo-chemical conversion of municipal sewage sludge to oil is a new developing technology in developed countries, which is developed based on some poor fuels processing process in recent years. The process has the advantages of reasonable thermal energy recovery (the whole process is a net thermal energy exporting process), suitable cost and less secondary pollutants. This research included the reaction conditions versus the converted products distributions, the reaction conditions versus the ratio of the process thermal energy input and output, exploring of reaction mechanisms, creating of reaction kinetics models. These results contribute not only to having a clear understanding about the technological features and evaluating the prospectives of technological development, but also provide a sound basis for the technological development on a larger scale. It is concluded that: 1) the sludge treatment process is a net thermal energy producer. 2) The optimal conversion temperature is 270°C, referring to making energy recovery ratio maximum. 3) The parameters of simple conversion reaction kinetics are n=2, A=8.5 S-1 and E=37.9 KJ/mol. 4) The secondary pollutants of the process can be effectively controlled. 5) The investment intensity of the process could be similar to that of the sewage sludge incineration process, and the operational economics of the process are obviously superior to those of the sewage sludge incineration process. The research results show that the technical-economic feasibility of low temperature thermo-chemical conversion process is favorable, because the reaction conditions are more moderate and the separation process of the products is more easily realized.