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Number of results: 24
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Abstract

The paper presents the results of preliminary studies on the properties of products made by vitrification of waste containing fly ashes from sewage sludge incineration. The performed tests of hazardous substances leached from the ashes, as well as the results of other laboratory tests confirmed the efficacy of vitrification. It has been found that the resulting products (sinters) could be used as a substitute aggregate for road foundations.
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Abstract

The purpose of the investigation was to assess the suitability of sewage sludge, brown coal and a mix of sewage sludge and brown coal to be used for fertilizing a light soil with an increased content of lead (I0 ) and slightly contaminated with cadmium (II0 ). The subject of tests were soil and plant samples taken from a pot experiment conducted during the years 2007-2009. The tests determined the effect of the type of fertilization on the pH and sorption properties of the soil, the contents of heavy metals in the soil and in the plants, and the volume of crops. The fertilization types applied had an effect of slightly increasing the soil pH. The application of sewage sludge, brown coal and the mix of sewage sludge with brown coal to the soil resulted in an improvement of the sorption properties of the soil. In the soil treated with sewage sludge and the mix of sewage sludge with brown coal, an increase in the contents of Cd, Zn and Pb was found. This increase was, however, small and did not change the degree of soil contamination with heavy metals. In the above-ground parts of plants fertilized with brown coal the concentration of heavy metals was lower than in biomass from plants cultivated on the control combination. The application of sewage sludge and the mix of sewage sludge with brown coal generally resulted also in a reduction of metal contents in the above-ground parts of the plants. This was the effect of enriching the soil with an organic substance that improves the sorption properties. From among the fertilization combinations tested, the application of either sewage sludge or the mix of sewage sludge with brown coal had the most favourable effect on the crop volume. It resulted in a twofold increase in the yield compared to the control combination.
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Abstract

The paper presents the investigations aimed at the determination of the effect of time and wavelength of ultrasound field on the value of capillary suction time (CST), sludge thickening and dry matter of the excess sludge subjected to the process of stabilization. The investigations were carried out on the excess sludge which comes from communal waste treatment plant. The sludge was exposed to ultrasound field, using ultrasound generator with power of 1500 W, frequency of 20 kHz and amplitude 39.42 μm (which corresponded to the amplitude of 100%). Sonication of the sludge was carried out for different amplitudes and sonication times. The non-conditioned sludge and the sludge initially conditioned with ultrasound field were subjected to the process of stabilization in laboratory flasks (V = 0.5 dm3) for the period of 10 days. On each day, sludge thickening and dewatering capacities were determined. The sludge subjected to the effect of ultrasound field exhibited elevated levels of CST. However, the sonication time had positive effect on the increase in the degree of thickening for each of the amplitudes studied. Also, the process of stabilization positively affected final thickening and dewatering of the sludge.
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Abstract

The induction of phytoremediation by addition of complex substrates, such as sewage sludge (e.g. from the food industry), allows for better conditions of plant growth, however, it also increases the risk of chemical compounds leaching to the soil solution. Biogenic compounds occurring in sludge such as nitrogen, organic carbon and phosphorus when migrating with soil solution down the soil profile can lead to underground water contamination. The paper assesses the effect of sewage sludge inducted phytoextraction of Zn, Cd and Pb with the use of Sinapis alba L. (White mustard), Medicago sativa L. (Alfalfa) and Trifolium resupinatum L. (Persian clover) as well as the migration of biogenic compounds (nitrogen, organic carbon and phosporus) in soil solution. Research was conducted in controlled conditions of a phytotronic chamber in which the lysimetric experiment was carried out in order to monitor the changes of total nitrogen, ammonia, phosphates, organic carbon and pH every 3 weeks during the 112 days of the entire experiment. Based on the obtained results it was found that there is no risk of underground water contamination by investigated substances present in sewage sludge, because there was no indication of increased ammonia and carbon migration to the deeper parts of the soil profile.The only exception was the migration of nitrogen compounds other than ammonia (possibly nitrates and nitrites). Due to sewage sludge application the highest concentrations of ammonium nitrogen (211 mgN-NH4 l -1), total nitrogen (299 mg N l-1) and organic carbon (200 mg TOC l-1) were noted at a layer of 30 cm (from top of the column/lysimeter) after 3 weeks of the conducted process. With time a decrease of ammonium nitrogen as well as organic carbon concentration in all columns was noted. There was no indication of phosphates in the soil solution during the entire experiment, which was due to the high cation exchange capacity of the soil matrix.
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Abstract

The article describes problems related to intensification of energy production at a sewage treatment plant. The authors analyze anaerobic co-digestion of sludge from a water treatment plant and sewage treatment plant. The authors proposed a methodology of the research and analyzed the preliminary results, which showed that co-digestion of sewage and water sludge enhanced biogas production. The authors hope that the results of the study will provide a basis for development of methodology for sludge control and disposal.
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Abstract

Heavy metal pollutants in the leachate of waste landfill are a potential threat to the environment. In this study, the feasibility of using municipal sewage sludge as barrier material for the containment of heavy metal pollutants from solid waste landfills was evaluated by compaction test and hydraulic conductivity test concerning compaction property, impermeability and heavy metal retardation. Results of the compaction test showed that the maximum dry density of 0.79 g·cm−3 was achieved at the optimum water content of about 60%. The hydraulic conductivities of compacted sewage sludge permeated with synthetic heavy metal solutions were in the range of 1.3×10−8 – 6.2×10−9 cm·s−1, less than 1.0 ×10−7cm·s−1 recommended by regulations for barrier materials. Chemical analyses on the effluent from the hydraulic conductivity tests indicated that the two target heavy metals, Zn and Cd in the permeants were all retarded by compacted sewage sludge, which might be attributed to the precipitation and adsorption of heavy metal ions. The results of this study suggest that specially prepared material from sewage sludge could be used as a barrier for waste landfills for its low permeability and strong retardation to heavy metal pollutants.
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Abstract

The influence of sewage sludge torrefaction temperature on fuel properties was investigated. Non-lignocellulosic waste thermal treatment experiment was conducted within 1 h residence time, under the following temperatures: 200, 220, 240, 260, 280 and 300°C. Sawdust was used as lignocellulosic reference material. The following parameters of biochar have been measured: moisture, higher heating value, ash content, volatile compounds and sulfur content. Sawdust biochar has been confirmed to be a good quality solid fuel. High ash and sulfur content may be an obstacle for biochar energy reuse. The best temperature profile for sawdust torrefaction and fuel production for 1 h residence time was 220°C. At this temperature the product contained 84% of initial energy while decreased the mass by 25%. The best temperature profile for sewage sludge was 240°C. The energy residue was 91% and the mass residue was 85%. Higher temperatures in both cases caused excessive mass and energy losses.
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Abstract

Ultrasonic disintegration, as a method of sludge pre-treatment (before the stabilization process), causes changes in their physicochemical characteristics. The aim of this study was to determine the influence of ultrasonic disintegration conditions (sonication) on the changes in the physicochemical characteristics of sonicated sludge, i.e. an increase in the content of organic substances in the supernatant, sludge dewaterability and flocs structure. Thickened and non-thickened excess sludge from the municipal wastewater treatment plant in Gliwice was disintegrated. The process was conducted, using a high-power disintegrator equipped with a lenticular horn. In order to determine the most favorable conditions, the sewage sludge was sonicated at a wave frequency of f=25 kHz (as a function of time), with a different samples volume (V1=0.5 and V2=1 L) and emitter position of 1 and the 2.5 cm from the bottom of the chamber in which the process was conducted. The disintegration of sewage sludge was carried out with a specific energy density (EV) in the range from 10 to 30 kWh/m3. The evaluation of the disintegration effects was based on changes in the physicochemical characteristics of the sludge and/or supernatant at the end of the process, expressed by commonly used and author’s disintegration indicators. The best results were obtained for the sludge disintegrated with a volume of V2=1 L and the emitter position of 2.5 cm from the bottom of the chamber. The study confirms that in various operating conditions of ultrasonic disintegration, there is a possibility for obtaining different effects which may influence the course of anaerobic stabilization and quality of the final products of the process.
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Abstract

The aim of the research was to assess the microbiological (number of heterotrophic bacteria, actinobacteria and moulds) and biochemical (urease and acid phosphatase activity) state of peat with the admixture of composts produced from sewage sludge. An additional aim of the research was to demonstrate the influence of those substrates on the morphological traits of scarlet sage (height, number and length of shoots, number of buds and inflorescences, greenness index (SPAD)). Composts produced from sewage sludge, wheat, maize and lupine straw were mixed with peat, where their percentage varied from 25% to 75%. The substrate which included the composts applied in the experiment had a higher number of heterotrophic bacteria and a higher acid phosphatase activity level than the control substrate (peat). The multiplication of moulds and actinobacteria was more intensive than in the peat only in the combinations with K3 (sewage sludge 50%+sawdust 20%+ lupine straw 30%) and K4 (sewage sludge 50%+sawdust 20%+fresh maize straw 30%) composts, whereas the highest urease activity level was observed in the soils produced from K1 (sewage sludge 50%+sawdust 20%+white straw 30%) compost. The most optimal development of plants was observed in the substrate with compost produced from wheat straw. Composts produced from municipal sewage sludge were found to be suitable for growing scarlet sage. However, their effect depends on the percentage of high peat in the substrate.
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Abstract

In the study the comparative analysis of test results of drainage of municipal wastewater sludge was conducted with the use of flocculant Praestol 855BS and the mixture of flocculant Praestol 855BS 50% + orange essential oil 50%, as the reagents supporting this process. It was also attempted to reduce unpleasant smells exuding from the drained sludge. The process of drainage of municipal wastewater sludge was conducted in the laboratory setting centrifuge of MPW-350 type. The variable independent parameters were centrifugation time, centrifugation speed, dosage of flocculant Praestol 855BS as well as dosage of mixture in the proportion of flocculant Praestol 855BS (50%) + orange essential oil (50%). The following parameters were subject to assessment: water content in the sludge, dry mass content in the reflux as well as time of maintenance of the oil’s smell in the sludge. The conducted tests demonstrated that the orange essential oil has an impact on drop in resultant quality parameters of the drainage process of municipal wastewater sludge. Batching of the orange essential oil has an impact on considerable reduction of odours exuding from drained wastewater sludge, and thus on improvement of work conditions connected with operation of centrifugal separators. Bearing in mind both the efficient drainage process of wastewater sludge as well as simultaneous reduction of unpleasant smells exuding from the sludge during this process it is assumed and recommended to simultaneously apply both reagents, that is flocculant Praestol 855BS (50%) and orange essential oil, also in the volume of 50%.
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Abstract

In Poland, according to the statistical data, about 40% of sewage sludges originating from wastewater treatment plants are applied in the agriculture. The mentioned way of application of sewage sludges causes the hazard of contamination of environment with carcinogenic compounds due to the presence of some organic micropollutants, such as polycyclic aromatic hydrocarbons (PAHs). The proposal of changing UE Directive obligates control of organic pollutants (PAHs and others) in sewage sludges applied in the agriculture. The aim of the investigations was to estimate the persistence of PAHs under stored conditions by determining half-life of their decomposition. Eight carcinogenic PAHs, among 16 compounds, listed by EPA were determined. In this study, the quantity changes in the concentration of PAHs in stored sewage sludges were investigated. Sewage sludges were stored under aerobic conditions for 16 weeks. At the same time the sewage sludges with sodium azide added, in order to deactivate the microorganisms (abiotic samples), were also stored. Gas chromatography-mass spectrometry was used to qualify and quantify PAHs in 2- and 4-week intervals. Sewage sludges were taken two fold from a municipal wastewater treatment plant. In practice, the sewage sludges are directed to the disposal site. The initial concentration of 16 PAHs in sewage sludge was equal to 582 μg/kg.d.m. The changes in the concentration of PAHs corresponded to exponential function. Values of correlation coefficients indicate a significant dependence of PAHs persistence and concentration on time exposition. Under experimental conditions the half-lives of individual compounds were diversed. In biotic samples half-life of hydrocarbons was in the range of 17 to 126 days. Half-life of PAHs in abiotic sewage sludges was in the range of 32 to 2048 days. The most persistent were benzo(a)pyrene and benzo(b) fluoranthene, respectively. A significant dependence of PAHs' decrease on the presence of microorganisms in sewage sludges after 10 weeks of storage was found.
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Abstract

The work presents examination results of the common determination of PAHs and PCBs in industrial sludge and supernatants. Sewage sludge was taken from the wastewater treatment plant, and supernatants were obtained by their centrifuging. The prepared samples of sewage sludge and supernatants were subjected to extraction with applying the mixture of organic solvents. Cyclohexane and dichloromethane were used for constant samples, and methanol, cyclohexane and dichloromethane - for liquid. Extracts, after separation from samples of sewage sludge and supernatants, were cleared on the silica gel in vacuum conditions and concentrated in the stream of nitrogen. In such prepared extracts there was conducted the qualitative-quantitative analysis of 16 PAHs using the GC-MS system. Next, the samples were evaporated and poured with water and methanol until the clear solution was obtained. Extracts were cleared on octadecyl C18 columns, and then concentrated in the nitrogen stream. In these extracts PCBs was also determined with the application of the gas chromatograph with mass spectrometer. The range of concentrations 16 PAHs in sewage sludge equalled 10-16 mg/kgd.w. Summary average concentration 16 PAHs in supernatants was reached 17 μg/L. Average recovery of PAHs introduced to sewage sludge in the form of reference mixture was 78% (with consideration of naphthalene). In the case of supernatants, the average value of recovery reached 60%. Average PCBs concentration in supernatants equalled 10 ng/L. For sewage sludge the sum of marked PCBs was an average 1.23 μg/kgd.w.. In the case of particular PCBs the percentage recovery of the reference mixture for supernatants was 86%, while for sewage sludge it was 55%.
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Abstract

One of the methods of sewage sludge disposal, which is based on its fertilizing properties, is its use in nature, e.g. in farming (if all the permissible standards are met). However, the sludge used for soil fertilization might also contain heavy metals, pathogenic microorganisms, thus causing contamination in soil foundation and deterioration of the conditions for development of indigenous organisms. Particular threat is posed by the existence of drug-resistant microorganisms in sewage sludge. This problem has not been researched in detail yet. The authors of the present study aimed to determine qualitative changes in drug-resistant microorganisms in sandy soil fertilized with selected sewage sludge. Sewage sludge after different types of drying process (natural and solar) was added to the degraded sandy soil. The effect of the methods of sewage sludge drying on concentration of drug-resistant microorganisms in soil fertilized with the sludge was analysed. The study demonstrated that sewage sludge dried naturally in drying beds pose threat to soil environment and, potentially, to people and animals which have contact with fertilized soils. In sandy soils fertilized with these types of sewage sludge, pathogenic forms which exhibit resistance to first-line antibiotics can be found.
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Abstract

In the paper, a numerical simulation of the co-combustion process of sewage sludge gasifi cation syngas in a hard coal-fi red boiler was done. Two different syngases (SS1 and SS2) were taken in consideration. Additional (reburning) fuel was injected into the combustion chamber, which was modeled as a plug fl ow reactor (PFR). The molar fl ow rates ratio of reburning fuel is assumed to be 5.0%, 7.5%, 10.0%, 12.5% and 15.0% of the whole exhaust. The simulations were conducted for constant pressure equal to 1atm for temperatures range from 600 to 1400 K. It was assumed that a fl ue gases which enters the reburning zone contains 300 ppm of NO and that during combustion only NO is formed without other NOx. Results show that that gas from sewage sludge gasifi cation gives reburning effi ciency of up to 90%. Calculation shows also an optimum value of temperature reburning for gas from sewage sludge gasifi cation which is equal to 1200 K. The type of the sewage sludge has no strong infl uence on the NO reduction.
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Abstract

According to data of the Central Statistical Office, the amount of sludge produced in municipal wastewater treatment plants in 2010 amounted to 526000 Mg d.m. The forecast of municipal sewage sludge amount in 2015 according to KPGO2014 will reach 642400 Mg d.m. and is expected to increase in subsequent years. Significant amounts of sludge will create problems due to its utilization. In order to solve this problem the use of thermal methods for sludge utilization is expected. According to the National Waste Management Plan nearly 30% of sewage sludge mass should be thermally utilized by 2022. The article presents the results of co-combustion of coal and municipal sewage sludge in a bubbling fluidized bed boiler made by SEFAKO and located in the Municipal Heating Company in Morag. Four tests of hard coal and sewage sludge co-combustion have been conducted. Boiler performance, emissions and ash quality were investigated.
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Abstract

The investigations were carried out in order to assess the effect of thermophilic fermentation on changes in concentration of seven congeners with codes: 28, 52, 101, 118, 138, 153 and 180 in sewage sludge. The total concentration of PCBs was the highest before the process of thermophilic fermentation. On the tenth day of the process of fermentation it was found that the total concentration of LCB doubled the previous level, whereas in higher chlorinated PCBs this value decreased twice. After the process of thermophilic digestion, all the determined congeners of PCBs were still present. However, their total concentration was reduced by 84% on the fourteenth day of the process. Low concentration of heavy metal ions in the liquid phase of sewage sludge was observed. The metal ions precipitated and remained bound throughout the stabilization process. Metal speciation analysis was performed, and revealed some changes in the chemical forms of the metals during the stabilization process of sludge. The highest increase of zinc, copper, nickel, cadmium, and chromium concentration was observed in the organic-sulfide fraction, whereas the highest increase of lead was found in the residual fraction. Thermophilic methane fermentation did not cause the accumulation of heavy metals in the mobile fractions of sludge.
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Abstract

One of the prerequisites for sustainable development is integrated waste management, including sewage sludge. Besides its good fertilization properties, sewage sludge, which is an inevitable by-product of sewage treatment, accumulates toxic chemical substances and dangerous pathogenic and toxicogenic organisms. Uncontrolled introduction of sewage sludge into soil might pose a serious threat to food chain and natural soil microflora. This in effect might disturb the ecological balance in a particular ecosystem. This study presents author’s own investigations of the sanitary conditions of sewage sludge and the conditions after the processes of aerobic and anaerobic stabilization. The investigated sewage sludge originated from a municipal wastewater treatment plant. The sewage sludge samples were transferred onto proliferation and diagnostic media. The results of the analysis obtained in this study confirmed that sewage sludge is a material which is rich in microorganisms, including pathogenic bacterial species such as: Escherichia coli and Salmonella typhimurium. Mycological tests demonstrated that sewage sludge is a material which is conducive to proliferation of yeast-like and mould-like fungi, among which both pathogenic and toxinogenic species can be present. Quantitative analysis of the investigated sewage sludge demonstrated that the processes of stabilization reduce the content of microorganisms but they do not guarantee product safety in sanitary terms. A huge variability and variety of biological composition points to the need for further research in the field of sanitary characteristics of sewage sludge and survival rate in microorganisms from different types of sewage sludge.
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Abstract

This study presents the rheological properties of sewage sludge after conditioning with the application of biomass ash. The impact of sewage sludge pre-treatment on its viscosity, flow curves and thixotropy was investigated. The increase of shear stress and the decrease of viscosity were observed with the increase of shear rate. Obtained results were compared with raw sewage sludge and the sludge after modification by means of polyelectrolyte in the dosage of 1.5 g (kg d.m.)-1. The findings proved that samples of raw and conditioned sewage sludge had thixotropic characteristics. The correlation between moisture content and capillary suction time reduction as well as selected rheological parameters were also determined. On the basis of the obtained results it was stated that the Ostwald de Vaele model best fits the experimental data.
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Abstract

Osier (salix viminalis) is a promising energy crop for the growing bioenergy purposes in Ukraine. It is unpretentious to the conditions of growth, marked with simplicity of cultivation technology, well-withdrawn for fertilization. Sewage sludge, due to its chemical composition and high content of organic matter, can be successfully used to fertilize the willow. The calculations of bioenergetic and economic efficiency showed that application of sewage sludge and compost with sawdust and straw in a ratio of 3: 1 at osier is marked with a high effect. In the studies performed in conditions of Ukraine’s Precarpathians on sod-podzolic soils we found that the highest biomass output and, therefore, gross energy per unit of area in agrocenoses of osier provided the application of fresh sewage sludge at a rate of 80 t / ha. In this option the dry biomass output made 39.4 t / ha, gross energy with the yield - 1,580 GJ / ha, the costs of energy generation - 6.2 UAH / GJ, the costs of gross output - 17.8 thousand UAH / ha, the rate of energy efficiency - 1.69. However, the highest rates of economic and bioenergetic efficiency after the fourth year of the willow vegetation we observed when the sewage sludge compost with straw of grain crops at a doze 40 and 60 t / ha was applied. In these variants the lowest cost of the biomass production was obtained (at the level 109 - 111 UAH / ton), the cost of the received energy from the biomass (5.6 - 5.7 UAH / GJ), the highest profitability value (97 - 101%) and the best performing of energy efficiency coefficient - 1.85 - 1.89.
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Abstract

The analysis of particle size in suspensions carried out with use of the laser diffraction method enables us to obtain not only information about the size of particles, but also about their properties, shape and spatial structure, determined basing on fractal dimension. The fractal dimension permits the evaluation of the interior of aggregates, at the same time showing the degree of complexity of the matter. In literature, much attention is paid to the evaluation of the fractal dimension of flocs in activated sludge, in the aspect of control of single processes, i.e. sedimentation, dehydration, coagulation or flocculation. However, results of research concerning the size of particles and the structure of suspensions existing in raw and treated sewage are still lacking. The study presents optical fractal dimensions D3 and particle size distributions measured with use of laser granulometer in raw and treated sewage and activated sludge collected from six mechanical-biological wastewater treatment plants located in the Lower Silesian region. The obtained test results demonstrate that wastewater treatment plants that use both sequencing batch reactors and continuous flow reactors are more efficient at capturing suspension particles of a size up to 30 μm and are characterized by an increased removal of particles of a size ranging from 30 μm to 550 μm to the outflow. Additionally, in the case of samples of treated sewage and activated sludge collected at the same location, at short intervals, similar particle distributions were observed. As far as the analysis of fractal dimensions is concerned, particles contained in the raw sewage suspension were characterized by the lowest values of the fractal dimension (median equals 1.89), while the highest values occurred in particles of activated sludge (median equals 2.18). This proves that the spatial structure of suspension particles contained in raw sewage was similar to a linear structure, with a large amount of open spaces, while the structure of particles contained in the activated sludge suspension was significantly more complex in the spatial aspect.
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Abstract

Along with the increase in popularity of the sewage sludge thermal treatment methods in Poland resulting from the implementation of European Union law, a management problem with ash, which is produced as a result of this process, appeared. The paper analyses the chemical composition and physical properties of fl y ash from thermal treatment of municipal sewage sludge in terms of its use in concrete technologies in relation to EN 450-1 Fly ash for concrete. Defi nition, specifi cations and conformity criteria (2012) and EN 197-1 Cement. Composition, specifi cations and conformity criteria for common cements (2011) standards. The tested material did not meet the requirements related to use of fl y ash for concrete production (chemical composition, low activity index, high water demand and fi neness), and as main and minor components for cement production. On the basis of the carried out research and analyses, it was found that the hardening slurry technology creates the greatest possibilities related to the management of fl y ash from thermal treatment of municipal sewage sludge.
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