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Sewage sludge drying is a pivotal step in sludge reduction, harmlessness, and resource utilization. Pulverizing sewage sludge can significantly increase the surface area of sludge particles available for contact with the air medium, consequently strengthening the convective drying process of the sludge. In this paper, the adopted deep drying system mainly combined sewage sludge pulverization and sewage sludge drying functions. Parametric studies were carried out to investigate the effects on the drying process. The moisture content of the sewage sludge decreased from 50.3% to 26.8% when the linear speed of the rotating blade tip of the pulverizing dryer and induced draft fan reached 28.3 m·s−1, 62.8 m−1, and air velocity reached 9.5 m·s−1, respectively. Furthermore, this work also preliminarily reveals the mechanism of the pulverizing dryer. The pores on the sludge particle surfaces are destroyed during the drying process. As the linear speed of the rotating blade tip in the pulverizing dryer increased, the hydrophilicity and the average particle size of the sewage sludge particles decreased, with the particle size representing the highest volume fraction being reduced by 62% in the particle size distribution. The pulverizing dryer not only breaks up the sludge to increase the surface area of the sludge in contact with the air but may also have a centrifugal effect. As the intensity of the pulverizing dryer increases, Nuclear Magnetic Resonance (NMR) measurements show a leftward shift in the peak of the weakly bound water in the sludge and a noticeable shortening of the transverse relaxation time. Overall, the results suggested that pulverizing is a suitable assistive method to improve the drying effect of the sewage sludge. [ABSTRACT FROM AUTHOR]

The microwave drying of sewage sludge is characterized by its speed and safety. A novel method for identifying free and bound water is proposed in this study. Experiments were performed to investigate the process performance and energy consumption in a microwave drying unit. The results indicate that the microwave drying process can be described in three stages, i.e., the preheating stage, constant-rate stage, and decreasing-rate stage. The preheating and constant-rate stages mainly remove free water, while the decreasing-rate stage mainly removes bound water. The Linear model effectively describes the kinetic processes in the constant-rate stage, and the modified Page I model is suitable for describing the decreasing-rate stage. The energy conversion process in microwave drying is explored, revealing that heat efficiency and energy consumption are consistent with microwave power changes. The heat efficiency in the constant-rate drying stage ranges from 60.33% to 71.01%, lower than that in the preheating stage but higher than that in the decreasing-rate stage. Energy consumption in the constant-rate stage ranges from 3.84 kJ/g to 8.20 kJ/g, significantly lower than in the other two stages. These results provide fundamental data for the industrial application of microwave drying of sludge and contribute to the advancement of microwave drying technology. [ABSTRACT FROM AUTHOR]

Due to the growing demand for energy, conventional fossil fuels are being depleted. Reducing dependence on energy sources based on fossil fuels is possible by using the energy potential of biomass. Sewage sludge deserves special attention. The increase in the amount of sewage sludge produced around the world poses a serious problem with its management. The use of sewage sludge to produce fuel with the possibility of energy recovery seems to be an excellent solution. The article presents the results of laboratory tests on the production of fuel in the form of granulates from mixed sewage sludge, rubber waste, and wood waste in the form of sawdust. Fuel mixtures were tested, and fuel parameters were determined. The calorific value of the tested fuel ranged from 13.92 MJ/kg to 22.15 MJ/kg, and the moisture content from 41.57% to 18.36%, depending on the percentage composition of the mixtures used to produce the granules. The ash content ranged from 14.82% to 17.40%. The composition of granulated fuel mixtures has been designed to avoid additional drying or pre-drying of sewage sludge. In this way, fuel was obtained without additional energy consumption associated with drying sewage sludge. Moreover, it should be stated that the share of sewage sludge in granulated fuel should not exceed 25%. Nowadays, such fuel can be an alternative to fossil fuels used in the cement or energy industry. [ABSTRACT FROM AUTHOR]

The volume of sewage sludge generated continues to increase, leading to harmful secondary pollution and highlighting the pressing need for sewage sludge reduction. Sewage sludge drying is a well-established method for treating municipal sewage sludge. This study systematically reviews the latest research on the formation and control of gaseous pollutants during sewage sludge thermal drying. First, this paper comprehensively introduces sewage sludge drying, covering its principles, heat sources, and the inevitable generation of waste gas during the drying process of sewage sludge rich in organic matter. Subsequently, it summarizes the methods for detecting sewage sludge drying exhaust gas and outlines the emission characteristics of such exhaust gas. The three main types of dry exhaust gases discussed include volatile nitrogen-containing compounds, represented by ammonia (NH3); volatile sulfur-containing compounds, represented by hydrogen sulfide (H2S); and the benzene series (BTEX). Finally, based on current technical capabilities, this paper proposes two methods for controlling pollution from sewage sludge drying exhaust gas: suppressing pollutant release during the drying process and treating exhaust gas at the end of drying. Inhibition of pollutant release during the drying process primarily involves reducing the types and quantities of pollutants released by adjusting the sewage sludge drying temperature and time, employing sewage sludge conditioning, and implementing others. Drying back-end exhaust gas treatment removes contaminants from the drying exhaust gas through processes like condensation, adsorption, absorption, biodegradation and other methods. This work offers a fresh perspective on understanding how various factors in the sewage sludge drying process influence the characteristics of dried exhaust gas emissions and the overall control of sewage sludge exhaust gas emissions. [ABSTRACT FROM AUTHOR]

Convective sewage sludge drying is often carried out in belt dryers, where the air flow is directed through the layer. In such a configuration, drying air properties, as well as the structure of the layer and its homogeneity are key factors affecting the drying process. In the present work, these factors were investigated using laboratory experiments on relatively large sludge samples with a mass of several kilograms. Drying was performed at relatively low drying air parameters (time-averaged temperatures of 65 to 80 °C and velocities of 0.44 to 0.78 m/s). The inhomogeneity of the sludge layer drying was observed by measuring the layer surface temperature with an IR camera. The reduction in layer thickness during drying was measured using an optical laser-based method. Analysis of the data included regression and fitting of the data to parametric drying curves, with the modified Nadhari drying law providing the best fit. The standard deviation of the layer surface thermograms (S) was used as a parameter that accounted for the layer homogeneity and consequently drying evenness. Higher values of S corresponded to lower drying rates and consequently longer drying times, highlighting the importance of producing layers with a homogenous structure. The measured layer thickness reduction rate indicated the overall drying intensity almost from the beginning of drying. Both the surface temperature unevenness and the layer height reduction measurement methods were demonstrated as viable approaches for real-time monitoring of the drying process with potential for application in real-scale dryers. [ABSTRACT FROM AUTHOR]

The programming language Python offers the opportunity to analyze and model the municipal sewage sludge (MSS) drying process in an illustrative chemical engineering practice. The drying process is performed on a flat plate while maintaining a uniform, parallel drying air speed. The Python program helps to analyze the digitalized weight measurements from each sample. The program enables the sorting of input data, determination of the drying critical point, and evaluation of the first and second drying periods. Moreover, the model calculates the fundamental drying parameter and forms a drying master curve to support the transfer to different drying conditions. The basic parameters calculated are mass transfer coefficient, heat transfer coefficient, and diffusion coefficient. The results are consistent with published data for those coefficients over the drying temperature range of 19.4–52.4 °C and relative humidity range of 8.2–33.6%. The findings of this study demonstrate the potential of Python as a powerful tool for analyzing experimental data and modeling chemical processes, which can lead to improved process design, optimization, and control. [ABSTRACT FROM AUTHOR]

The aim of this work is to investigate and model the sewage sludge drying kinetics in a lab‐scale drying bed by varying the sludge layer thickness during winter and summer. During each season, five experiments were carried out with increasing the sludge thickness by 0.5 cm each time. To achieve moisture content on a dry basis of 12%, the sludge drying period varied between 120 and 312 h in winter and between 72 and 168 h in summer. Thus, by increasing the sludge thickness, the drying time increased. The different curves of the moisture content evolution and the drying rates were analyzed. The drying curves show that the warm‐up phase (phase 0) and the constant rate phase (phase 1) are absent during the winter and summer seasons. Regardless of the sludge thickness, only the falling rate period was observed. In addition, the moisture content dropped quickly throughout the first 24 h because of the elimination of interstitial water. The drying characteristic curve has been represented by a 3rd degree polynomial. Mathematical equations were used to describe the experimental curves of drying kinetics. The logarithmic model was the most reliable for simulating the changes of reduced moisture content versus drying time in winter and summer. [ABSTRACT FROM AUTHOR]

Deammonification is a well-established process for sludge liquor treatment and promising for wastewaters with high nitrogen loads because of its low energy demand compared to nitrification/denitrification. Two wastewaters with high NH4-N concentrations and a rising significance in Germany—pig slurry (12 samples) and condensates from sewage sludge drying (6 samples)—were studied for their deammonification potential. Furthermore, a comprehensive quality assessment is presented. Both wastewaters show a wide range in terms of CODt, CODs, TN and NH4-N, whereby condensates show a greater variability with no direct relation to dryer type or temperature. In the slurries, CODt shows a relative standard deviation of 106% (mean 21.1 g/L) and NH4-N of 33% (mean 2.29 g/L), while in condensates it reaches 148% for CODt (mean 2.0 g/L) and 122% for NH4-N (mean 0.7 g/L). No inhibition of ammonium-oxidizing-bacteria was detected in the slurries, while two out of five condensates showed an inhibition of >40%, one of >10% and two showed no inhibition at all. Since the inhibition could be avoided by mixing, deammonification can be recommended for condensate treatment. For slurry treatment, the importance of employing some form of solid-liquid-separation as a pretreatment was noted due to the associated COD. [ABSTRACT FROM AUTHOR]

To govern the sewage sludge, which restricts the development of urbanization, the co-combustion of sewage sludge in coal-fired power plants is considered one of the most appropriate methods. Two methods, flue gas dehydration and electric heating dehydration, are used to dry sewage sludge to the target moisture content. And the economic impact of the two methods was evaluated on coal-fired power plants. The boiler efficiency and fuel consumption are obtained by the thermal balance calculation. When the anhydrous sludge ratio was 2% and the water content was 30%, the fuel consumption was 81.11 kg/s and the boiler efficiency was 91.32%. As the water content and the anhydrous sludge ratio increase, the fuel consumption gradually increases, while the boiler efficiency gradually decreases. And the net present value is used to evaluate the economic impact of the co-combustion of sewage sludge in coal-fired power plants. Among them, the maximum NPV value of the flue gas dehydration scheme with a sludge mass ratio of 3% and a moisture content of 40% reached 1163.34 million. Furthermore, the sensitive factors that affect the net present value are obtained as the anhydrous sludge ratio and government subsidies through sensitivity analysis. Combined with the combustion characteristics in the boiler, the recommended range for the moisture content of the sludge is 30%~40%, and the recommended range of anhydrous sludge ratio is 3–5%. [ABSTRACT FROM AUTHOR]

Copyright of Acta Scientiarum Naturalium Universitatis Sunyatseni / Zhongshan Daxue Xuebao is the property of Sun-Yat-Sen University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aims to assess the impact of using different fuels in Egyptian Titan Alexandria Portland Cement Company on emissions and concentrations of pollutants (Total suspended particles (TSP), nitrogen dioxide (NO2‎), and sulfur dioxide (SO2)) and their influence on ambient air quality during the period 2014–2020 using AERMOD dispersion model. The results showed that changing the fuel from natural gas in 2014 to coal mixed with alternative fuels (Tire-Derived Fuel (TDF), Dried Sewage Sludge (DSS), and Refuse Derived Fuels (RDF)) in 2015–2020 caused fluctuating variations in pollutant emissions and concentrations. The highest and lowest maximum concentrations of TSP occurred in 2017 and 2014 respectively, where the TSP is positively correlated with coal, RDF, and DSS and negatively correlated with natural gas, diesel, and TDF. Also, the lowest and highest maximum NO2 concentrations were detected in 2020 and 2016 followed by 2017 respectively, where NO2 is positively correlated with DSS and negatively correlated with TDF and varies with diesel, coal, and RDF. Moreover, the maximum concentrations of SO2 were the lowest in 2018 and highest in 2016 followed by 2017 because of its considerable positive correlation with natural gas and DSS and negative correlation with RDF, TDF, and coal. Generally, it was found that increasing the percentage of TDF and RDF with decreasing the percentage of DSS, diesel, and coal will reduce pollutant emissions and concentrations and enhance ambient air quality. [ABSTRACT FROM AUTHOR]

Technological comparison and system modelling of sewage sludge treatment are important in terms of sustainable development and climate change mitigation. Dewatering and drying are important processes for reducing volume for transportation and often a requirement for further sludge treatment. Inventory data on mass transfers and material and energy consumptions are therefore crucial in improving and understanding sludge management systems. Reviewing the scientific literature (2003–2021) revealed 55 and 21 datasets on dewatering and drying of sewage sludge, respectively. The scarcity of data did not allow for identifying detailed relationships between inputs and outputs for the technologies, but the reviewed data can serve as the first port of call when planning sludge management. The average total solid (TS) content obtained was statistically different for mechanical dewatering (MDW), deep dewatering, bio-drying (BDR) and thermal drying (TDR). Loss of volatile solids (VS) during dewatering is barely described, but a substantial VS loss was observed for TDR (8%) and BDR (27%). The use of chemical agents in MDW showed typical values of 5–15 g kg−1 TS. The use of energy is low for MDW (average of 0.12 and 0.26 kWh kg−1 TS for raw and digested sludges, respectively) but substantially higher for TDR (average of 3.8 kWh kg−1 TS). The justified inventory data for sludge dewatering and drying provide essential support to system modelling and technological comparison in future studies, but additional data from full-scale plants on energy consumption and the composition of removed water are strongly requested to improve the inventory. [ABSTRACT FROM AUTHOR]

This study aims to characterize concrete wash wastewater and examine the effectiveness of three different adsorbents in reducing its high pH. It is important to note that proper treatment is essential before discharging wastewater into water bodies to prevent any negative impact on the environment. Therefore, in this study, an adsorption scenario was conducted to obtain optimum treatment for concrete wash wastewater. The objectives of this study are as follows (1) to determine the typical characteristics of concrete wash wastewater based on the parameters outlined in the Ministry of Environment of The Republic of Indonesia (2014) and (2) to assess the performance of different adsorbents. Three wastewater samples were obtained from a ready-mix plant and then tested in the laboratory. The initial test was conducted to identify influent characteristics, and from this test, it was found that only the pH level exceeded the specified standard. Following this, the study then assessed the ability of three adsorbents to reduce the pH level in concrete wash wastewater using the batch test in Duplo. The pH level was measured at 0.25, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, and 24 hours. The three adsorbents tested were activated carbon, clay brick, and dried domestic sewage sludge. The result shows that dried domestic sewage sludge was the most effective at reducing alkaline wastewater due to its acidic pH. Therefore, it has the potential to replace other commercial adsorbents and reduce the problem of sludge disposal. Further research on this material is recommended, such as evaluating its performance in a more solid form, such as brick, and assessing its contamination potential. [ABSTRACT FROM AUTHOR]

• Drying shrinkage of alkali-activated material (AAM) is related to mesopore volume. • Na 2 SO 4 crystals act as expansive agents and aggregates reducing drying shrinkage. • Air pollution-controlled residue (20 %) applied to AAM is safe for the environment. Recycling air pollution-controlled residues (APCR) generated from sewage sludge incinerators can be used for waste management, but the leaching of potentially toxic heavy metals from APCR poses environmental and human health issues. The present paper describes a procedure using APCR to produce alkali-activated materials and thereby realize their disposal. The effect of APCR on the compressive strength and drying shrinkage of the alkali-activated slag/glass powder was investigated. The pore structure characteristics were analyzed for clarifying its relationship with drying shrinkage. The results indicated that the drying shrinkage of the alkali-activated material was related to the mesopore volume. The drying shrinkage was slightly increased after the incorporation of the 10 % APCR, which was likely attributed to the high volume of mesopores compared to the 20 % APCR that lowered the drying shrinkage and compressive strength. This decrease in drying shrinkage was due to the recrystallization of sodium sulfate in the pore solution that can act as expansive agents and aggregates. The growth stress of the crystalline sodium sulfate within the matrix can offset the tension stress caused by the water loss. In addition, leaching studies using the SW-846 Method 1311 showed that recycling APCR into the alkali-activated system did not present a toxicity leaching risk or release unacceptable concentrations of heavy metals. The incorporation of waste APCR and waste glass can make AAMs a very promising and safe environmental technology. [ABSTRACT FROM AUTHOR]

The treatment and disposal of sewage sludge is one of the most important and critical problems of wastewater treatment plants. 8.7 million tonnes of dry matter of sewage sludge were produced annually in the European Union in the year 2020. Due to the fact that sewage sludge contains a large number of substances that are not beneficial for human health, the conditions for sludge management will be significantly tightened in the EU countries. One option for sludge liquidation is the production of biofuel in a form of granules or pellets from sewage sludge enriched by waste celluloses. The achieved results show that the resulting quality of such alternative biofuel is fully comparable to conventional fossil fuels. The economic analysis is based on the simulation of cash flows associated with the implementation of the project over the lifetime and the calculation of levelised cost (LCOE). Results shows (under the current economic situation) that solar dryer technology ensures the lowest LCOE at the level of 26 EUR/GJ in fuel. If the LCOE of the alternative biofuel includes the price of the saved emission allowance and the future costs of sewage sludge disposal, the resulting price is directly competitive with lignite. The results thus clearly show that there is an ecological and economically competitive substitute for solid fossil fuels, which may be an important step for the future use of local combustion sources such as district heating plants. [ABSTRACT FROM AUTHOR]

Sewage sludge may pose a fire risk. The safe storage of biomass waste is a challenge due to self-heating processes. This study aims to assess the propensity to spontaneously combust of sewage sludge in order to determine safe storage and transport conditions. The evaluation of spontaneous ignition hazard was assessed according to EN 15188, by the determination of the self-ignition temperature. Certain parameters assumed to affect the inclination of sewage sludge to self-ignite, including the moisture content, bulk density, elemental composition, and particle size, were discussed. The results showed the risk of self-ignition during the storage and transport of sludge dust and pellets. The usage of the smallest basket volume resulted in the highest self-ignition temperatures, which were 186 °C and 160 °C for sludge pellets and dust, respectively. The comparison of the two forms of thermally dry sludge showed, that despite sludge pellets being easier to store and handle issues, the more favorable conditions for the management in terms of fire risk is sludge dust. Its temperatures for safe storage are slightly higher. The results highlighted that future research should focus on the hazards of silo fires and explosions in terms of silo fire prevention and management. [ABSTRACT FROM AUTHOR]

Copyright of Ecologia Mediterranea is the property of Ecologia Mediterranea and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the large volume of sewage generated every day, there is a high demand for its treatment. The by-product (called sludge) generated after the treatment process has caused problems in terms of its final disposal. Since the typical end off for this waste is landfills, it is mandatory reducing the landfill amount and the risk of soil contamination. The present work explored an adequate final disposal of the sludge as a sustainable alternative. For this purpose, briquettes were produced using dry sludge from the Sewage Treatment Plant of the Minas Gerais (Brazil) Sanitation Company and vegetable oil used to thicken the briquettes. These briquettes were compared to eucalyptus charcoal in terms of their calorific potential, through immediate analysis, since Brazil has a high demand for primary energy, especially in the industrial sphere. The calorific potential of charcoal reached 16.66 MJ/kg, while that of briquette reached 12.94 MJ/kg. However, briquettes had a density much higher than charcoal, so it takes a smaller volume of briquettes to achieve the same burning capacity as a large volume of charcoal. [ABSTRACT FROM AUTHOR]

Sewage sludge is an inevitable by-product of biological wastewater treatment process and contains various toxic substances such as pathogens, heavy metals and organic contaminants, which may cause serious pollution risks without appropriate disposals. Dewatering and drying technology play significant roles in minimizing sludge volume, facilitating transportation, increasing calorific value and reducing the leachate production in landfill sites. Various new technologies are emerging and existing ones are always evolving because of sharp growth of sewage sludge in the last decade. This paper presents a comprehensive review on recent advances in related to dewatering and drying of sewage sludge. The influencing factors of sludge dewatering are addressed out firstly. And then the conditioning methods to improve sludge dewatering performance are summarized and compared in terms of applicable occasions, material consumption, energy and environmental impacts etc. The dewatering technology is classified into common, deep and high-dry dewatering based on the degree of moisture content, and the drying method is divided into convective drying, conduction drying, radiation drying and other new drying. The present dewatering and drying technologies are reviewed and compared in order to provide useful guidelines for sludge disposal. The future demands and opportunities for sludge dewatering and drying are pointed out from industrial perspective. [ABSTRACT FROM AUTHOR]

To reduce the energy consumption and cost of the drying of sewage sludge (SS) and to ensure stability during combustion, the pyrolysis and co-combustion characteristics of semi-dry SS after the dehydration of flocculant and bituminous coal (BC) were studied in this work. The results show that the decrease in moisture content accelerates the release of volatile substances, and the increase in heating rate can also enhance the release of water and volatile matters. Furthermore, in the co-combustion of semi-dry SS and BC, the increase in mixing ratio (from 0% to 60%) of semi-dry SS caused the ignition and burnout temperature to decrease from 481 °C to 214 °C and from 702 °C to 627 °C, respectively. During co-combustion, the infrared spectra showed that the temperature range of 300–700 °C was the main gas precipitation area, and the main gaseous products were CO2, NOx, SO2, and volatile organic pollutants (VOCs). [ABSTRACT FROM AUTHOR]

• Effect of Ca conversion on syngas production during sludge gasification. • Investigation on quantitative analysis of syngas and chemical structure of chars. • Ca(OH) 2 addition promoted the conversion of aromatic C H into aliphatic C H. • Ca(OH) 2 promoted ring-opening and steam reforming reaction of tar. Gasification shows great potential as an alternative method for energy utilization from sewage sludge. Lime (CaO) is a cheap and commonly used dewatering conditioner for sewage sludge. The calcium hydroxide (Ca(OH) 2) generated during the drying process with lime can enhance the pH level of the sludge, thereby providing disinfection properties. This paper investigated enhancement mechanism of Ca(OH) 2 on hydrogen gas generation and the effect on gas product yield during the steam gasification process of lime-dried sludge. The experiments were conducted in an electrically heated reactor at 500–800 °C. The forms of calcium present in the gasified sludge char samples were analyzed using X-ray diffraction (XRD) analysis to investigate their transformation process. Fourier transform infrared spectroscopy (FTIR) was utilized to obtain information regarding the chemical structure in the gasified sludge char samples, with the aim of exploring the mechanism behind hydrogen production from lime-dried sludge. The results indicate that the CaO generated from Ca(OH) 2 dehydration acts both CO 2 adsorbent and catalyst during the gasification process. The addition of Ca(OH) 2 during the sewage sludge gasification process leads to a reduction in the aromatic C H content in the organic matter, while significantly increasing the content of reactive CH 3 -chains. It also promotes the ring-opening and rearrangement reactions of aromatic hydrocarbons and nitrogen-containing heterocycles and steam reforming reaction of tar. The combined effects of these factors contribute to an overall increase in hydrogen gas yield. [ABSTRACT FROM AUTHOR]

Deammonification is a well-established process for sludge liquor treatment and promising for wastewaters with high nitrogen loads because of its low energy demand compared to nitrification/denitrification. Two wastewaters with high NH4-N concentrations and a rising significance in Germany—pig slurry (12 samples) and condensates from sewage sludge drying (6 samples)—were studied for their deammonification potential. Furthermore, a comprehensive quality assessment is presented. Both wastewaters show a wide range in terms of CODt, CODs, TN and NH4-N, whereby condensates show a greater variability with no direct relation to dryer type or temperature. In the slurries, CODt shows a relative standard deviation of 106% (mean 21.1 g/L) and NH4-N of 33% (mean 2.29 g/L), while in condensates it reaches 148% for CODt (mean 2.0 g/L) and 122% for NH4-N (mean 0.7 g/L). No inhibition of ammonium-oxidizing-bacteria was detected in the slurries, while two out of five condensates showed an inhibition of >40%, one of >10% and two showed no inhibition at all. Since the inhibition could be avoided by mixing, deammonification can be recommended for condensate treatment. For slurry treatment, the importance of employing some form of solid-liquid-separation as a pretreatment was noted due to the associated COD.

This work reports the results obtained with an innovative configuration of a closed-static solar greenhouse for sludge drying. The novelty of the solar greenhouse configuration consisted in using a forced ventilation system to provide hot air for sludge drying and the utilization of solar irradiation for energy supply. Wet sewage sludge (97% humidity) was successfully dried up to a residual humidity close to 5% after 25 days during wintertime. The increase of the airflow rate supplied under the sludge bed improved the sludge drying rate. Moreover, the fraction of volatile suspended solids decreased from 70% to 41% after 13 days, indicating that air supply promoted the simultaneous stabilization of the sludge as a side-effect to the drying process. Overall, the specific energy consumption per ton of evaporated water was estimated to approximately 450 kWh/t, resulting in about 55% of energy demand lower than a conventional thermal drying system, while using only free solar energy. The achieved high weight reduction of up to 99% implies a noticeable reduction of the excess sludge handling costs, indicating that solar greenhouse drying is a highly interesting opportunity for sludge drying in medium-small sized WWTPs. [ABSTRACT FROM AUTHOR]

In order to investigate the effect of various pyrolysis temperatures and application amount on the remediation of Cd–Pb contaminated soil, dried sewage sludge was pyrolyzed at 300 °C (SSB300) and 500 °C (SSB500), and soil incubation experiments were conducted for 60 days with two biochars (SSB300 and SSB500) and three different application amounts (1%, 3%, and 5%). The chemical speciation and bioavailability of Cd and Pb in paddy soil were determined by BCR and DTPA. Results showed that sewage sludge-based biochar (SSB) slightly increased the soil pH, due to the neutral SSB. The specific surface area of SSB500 was increased by 40.06 m2/g compared to SSB300. FTIR showed a decrease in the hydroxyl vibrational peak of SSB500 compared to SSB300; in addition, the intensity of the aliphatic-CH2 peak decreased with increasing pyrolysis temperature, indicating a decrease in non-polar aliphatic functional groups on the surface of SSB. The incubation experiments showed that the addition of 5% SSB500 had the best performance for DTPA-extractable Cd (48 mg.kg−1 to 12.81 mg.kg−1) and Pb (90.23 mg.kg−1 to 15.91 mg.kg−1). And 5% SSB500 amendment more remarkably transformed Cd and Pb from the acid-soluble state to the residual state than other treatments, demonstrating that the high pyrolysis temperature and application amount had great influence for transformation of Cd and Pb. In addition, the microbial community in the soil was significantly changed by 5% SSB500 application. At the phylum level, Chloroflexi is the dominant species, due to its strong tolerance in Cd-contaminated soil. At the genus level, the relative abundance of Thiobacillus and Defluviicoccus increased, which would enhance inorganic ion transport and metabolism functions to promote passivation and stabilization of heavy metals throughout the remediation process. [ABSTRACT FROM AUTHOR]

Improving the dewatering performance of sludge is a necessary advancement for collaborative sludge disposal and energy-efficient utilization in power plants. Herein, the effects of temperature changes and the addition of drying accelerators derived from agricultural and industrial waste on the drying characteristics of sewage sludge (SS) were investigated from the perspectives of drying kinetics and micromorphology. According to the results, the drying time for sludge significantly showed a clear downward trend via medium–low temperature (160 °C) thermal drying, which subsequently reduced the energy input substantially. When the drying temperature was 160 °C, the ideal addition proportions of rice husk (RH), sludge ash (SA), and coal ash (CA) comprised 15%. The addition of SA prominently boosted the drying rate constant of the original sludge by 48%. Additionally, SEM images along with the spectral dimension obtained via fractal theory explicitly clearly demonstrated that SS + SA had more loose pore channels than other mixed samples. This provided a convenient approach to ensure the evaporation and migration of moisture and thereby shorten the drying time effectively. Consequently, the addition of sludge ash as a drying accelerator can promote the deep dewatering of sludge. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Deammonification Potential of Pig Slurries and Vapor Condensates from Sewage Sludge Drying¿Substrate Quality and Inhibition" published in the journal Bioengineering. The correction addresses two typographical errors in Table 2 of the original publication, specifically in the temperature column and the line of sample C-1. The corrected version of Table 2 is provided in the document. The authors state that these errors do not affect the scientific conclusions of the study. [Extracted from the article]

This paper presents the design, evaluation, and optimization of an electricity generation system based on the two-stage organic Rankine cycle (TS-ORC), which utilizes the waste heat of an existing fluidized bed sewage sludge incineration (FBSSI) facility. The facility incinerates an average of 300 tons per day of sewage sludge with a dry matter content of 22%. After the drying process, the sewage sludge is burned in a fluidized bed combustor, and exhaust gas at a temperature of about 850-900°C is released due to the combustion. The system provides the energy required to dry the sludge from this exhaust gas. In this study, a TS-ORC is designed to be coupled to the exhaust gas flowlines discharged to the atmosphere at two different points in the FBSSI plant. The exergy efficiency of the FBSSI facility is found to be 70.5%. Three different working fluids are selected to examine the variations of thermodynamic and thermoeconomic performance parameters of the designed TS-ORC system. The highest power generation in the TS-ORC system (183.40 kW) is achieved using R1234yf as working fluid. R1234yf is also the most expensive fluid for electricity generation among the other working fluids (10.57 $/h). The least electricity generation in the TS-ORC (142.70 kW) occurs at the thermoeconomically most affordable cost with R245fa (9.35 $/h). [ABSTRACT FROM AUTHOR]

Dried sewage sludge gasification was conducted using a two–stage gasifier composed of a fluidized bed gasifier and tar–cracking reactor to produce a gas with low levels of tar, NH 3 , and H 2 S. In this work, the influence of the type of gasifying agent and bed material and the equivalence ratio on the product gas quality were investigated. Furthermore, the possibility of gasification without a hot filter and electrostatic precipitator, which are usually applied to remove impurities generated during gasification, was examined. Finally, the efficiency of a Ni–coated distributor for tar and NH 3 removal was evaluated. Overall, steam/O 2 gasification produced H 2 –rich (38–39 vol%) gases. Further, olivine reduced the tar and NH 3 contents in the product gas obtained from steam/O 2 gasification to 138 mg/Nm3 and 236 ppmv, respectively. A gas cleaning system without a hot filter and electrostatic precipitator produced a gas with only 8 mg/Nm3 of tar. Moreover, a Ni-coated distributor was found to be very effective in reducing the NH 3 content to 60 ppmv. Dried sewage sludge gasification experiments in air were conducted four times for 4 h, producing gases with very low levels of tar (3–10 mg/Nm3) and NH 3 (60–90 ppmv). • Two-stage gasification of dried sewage sludge was successfully conduced for 4 h. • Gasification with steam/O2 produced H2-rich gases (38–39 vol%.). • Cyclones and condensers were sufficient for the production of clean gas. • Ni–coated distributor strongly reduced the NH3 content in gas (60 ppmv). • Activated carbon repeated deactivation and regeneration during gasification. [ABSTRACT FROM AUTHOR]

Back-mixing is an operation that can be used to reinforce the texture of soft and pasty sludges to improve the drying effect. In this study, three mass fractions in a back-mixing operation (40%, 60%, and 70% on a dry basis) were chosen for convective sludge drying in a fixed bed. The structural characteristics including the total exchange surface, object volume, and shrinkage of the sludge bed were measured by X-ray macrotomography during the drying process. The average drying rates are 0.076 g/s (original sludge), 0.079 g/s (40% back-mixed sludge), 0.092 g/s (60% back-mixed sludge), and 0.099 g/s (70% back-mixed sludge), respectively. For the original sludge and three back-mixed sludges used, both the object volume and total exchange surface decrease in a quasi-linear manner with decreasing water content in the sludge. The final total exchange surface increases by 97.1% for the 70% back-mixed sludge compared with that of the original sludge. After drying, the shrinkage ratio of the object volume of the original sludge is 82.1%, however it is decreased to 50.8% when the 70% back-mixed sludge is used. The average convective mass transfer coefficient increases by 60% for the 70% back-mixed sludge compared with that of the original sludge. It was assumed for belt drying that, the lengths of the belt used for the 40% back-mixed sludge, 60% back-mixed sludge, and 70% back-mixed sludge will be nearly 0.96, 0.83, and 0.77 times, respectively, as long as that used for the original sludge. [ABSTRACT FROM AUTHOR]

Present study aims to explore the effect of sintering temperature and dwelling time on the characteristics and morphological structure of lightweight aggregates made from dry sewage sludge and waste glass powder. The mixtures were sintered at temperatures from 1100 °C to 1200 °C at a heating rate of 10 °C/min with a dwelling time of 10, 20, and 30 min to produce lightweight aggregate samples. The thermophysical behavior of the mixtures and the physic-mechanical properties (including water absorption, particle density, and compressive strength) of the obtained lightweight aggregates were studied. The microstructure of the lightweight aggregates was also analyzed using X-ray micro-computed tomography. Results indicate that increasing the sintering temperature or extending the dwelling time will reduce the particle density and compressive strength of lightweight aggregates. Moreover, the sintering temperature and dwelling time show a considerably influence on the pore structure of lightweight aggregates, which is strongly related to the physical characteristics of the lightweight aggregates. The lightweight aggregates obtained at optimized sintering temperature of 1180 °C with an optimal dwelling time of 10 min show water absorption of 1.01%, particle density of 0.78 g/cm3, and compressive strength of 7.10 MPa, thereby meeting the standard requirement of GB/T 17431.2–2010. [ABSTRACT FROM AUTHOR]

The emission of odor compounds is a serious problem for the environment. The complaints from the residents of nearby houses about discomfort indicate that this is not a sufficiently resolved problem and involves the need to take appropriate action. The article discusses the ecological method of using a biofilter, which is an installation for removing the odors generated in the process of solar drying of sewage sludge in a municipal wastewater treatment plant (WWTP). This technology is used in many Polish dryers, it involves sludge drying in the summer. Direct air outlet from the solar dryer causes the emission of these compounds, which can be a serious problem, especially in high-capacity WWTPs. One of the most ecological methods, which consists of directing the exhaust air through water scrubbers to the biofilter, was used in the described object. The analyses were carried out on a real object, examining the ratio of biofilter filling under various atmospheric conditions to the reduction of odor compounds formed. This solution, according to research, is an effective solution, but in such a system (solar dryer - biofilter), it is still not very popular. [ABSTRACT FROM AUTHOR]

In this study, it is aimed to design an efficient and sustainable solar tunnel dryer to be used in drying process of sewage sludge. In the first step of this study, heat and flow structure of three tunnel dryers including rectangular tunnel (RSTD), quonset tunnel (QSTD) and quonset tunnel with fins (QSTD/F) have been numerically surveyed to determine the effective design. Based on CFD results, quonset-type tunnel designs have been fabricated, experimentally analyzed and compared with numerical findings. In this work, different from previous studies on quonset-type solar-thermal systems, top surface of quonset geometry was made from sheet metal as an absorber to enhance heat transfer area. The drying tests have been performed in different months of the year (June and January) by applying two different air velocities to evaluate the performance of tunnel dryers at various climatic conditions. Integrating fins to the quonset tunnel had considerable positive effects on both thermal and drying performances. According to the experimental findings, specific moisture extraction rate (SMER) value was attained on June and January in the range of 0.50–0.89 and 0.39–0.65 kg/kWh, respectively. The results indicated the successfulness of quonset solar tunnel dryer design in the dehumidification process of sewage sludge. [Display omitted] • Designing rectangular and quonset solar tunnel dryers for sewage sludge drying. • CFD analysis and experimental validation of designed tunnel dryers. • Sewage sludge drying tests under different seasonal climate conditions. • SMER value was found in the range of 0.39–0.89 kg/kWh. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the effect of weathered coal fly ash (CFA) as a drying adjuvant of sewage sludge (SS) to produce a soil amendment. The high amount of SS and CFA creates a complex waste management problem in many countries, requiring more research efforts. Towards a circular economy, CFA can be viewed as an anthropogenic inorganic by-product with valuable nutrients (e.g. K), which can be recovered in combination with SS (rich in organic matter, N, and P). Different temperatures (70, 85, 100, 115, and 130 °C) are tested to dry small SS cylinders, without and with 0.15 g CFA g−1 of SSwet basis (wb). By fitting appropriate models to the experimental drying curves, it is possible to observe an improvement of 1-17% in the diffusion coefficient and 7-19% in the kinetic constants, using CFA. The best drying conditions are achieved with CFA as an adjuvant at 130 °C, where the drying rate is 31.61 gH2O kg−1 SSwb min−1. Phytotoxicity and growth assays are performed to evaluate the effect of the produced materials in the soil. The product with SS and CFA shows the potential to improve soil condition due to (i) the organic matter, N, P, and K content, (ii) the lower phytotoxic effect when compared to raw SS; (iii) the soil pH correction. Thus, not only the addition of weathered CFA facilitates the drying of SS but also the final product has benefits to soil conditions. [ABSTRACT FROM AUTHOR]

The issue of sustainable management of biosolids (excess sludge) from wastewater treatment is an important issue in the entire developed world. Residual sludge disposal costs and environmental impact may be significant, and reducing such costs, as well as the energy consumption for dewatering and drying, is a key issue for safe and sustainable sludge disposal, considering the recent ban of some disposal options, such as landfilling, in many European countries. An alternative to thermal technologies is solar drying (not to be confused with bio-drying, very close to the concept of composting). Solar greenhouse drying technology is characterized by reduced land requirements compared with traditional outdoor drying beds, as well as by low-energy requirements compared with other thermal drying methods. Process operation is cost-efficient, with close to no maintenance, and observed specific evaporation rates up to threefold higher than conventional drying beds. Many applications of this technology exist in Poland, Germany and Austria: more than 10,000 t of wet sludge per year is treated in this way in Germany alone and almost as many (9000 t/year) in Poland. This paper examines current biosolids treatment technologies applicable to small wastewater treatment plants (2000–9999 population equivalents served) and opportunities for possible solids reuse in Poland in view of sustainable circular economy schemes. In particular, a purely solar-driven greenhouse facility for sewage sludge drying was investigated under different conditions (season, temperature, environmental humidity) and possible improvements for its efficiency evaluated. Sludge processed by solar drying could have different final disposal pathways, according to season, in accordance with the prescriptions of the new National Waste Management Plan of Poland. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel drying technique for slurry-liquid substances has been proposed. • Cyclone-based drying mechanism for slurry-liquid substances was explained. • Directly transforms industrial slurry and sewage into a resource-utilizable state. • Achieves drying below water's phase change temperature. • Enables rapid flash drying of high-moisture substances. Industrial slurry, municipal sewage, and other slurry-liquid sludges pose a formidable challenge for quick and comprehensive drying in a single step due to their large volume, and high water content. Conventional slurry sludge drying methods, driven by the necessity to overcome the latent heat associated with phase change, entail notable drawbacks, including high energy consumption, and suboptimal efficiency. In this study, we introduce a cyclone-based non-phase change drying process, specifically designed to achieve efficient, one-step drying of slurry-liquid sludge, all while operating at temperatures below the phase change of water. Our study focuses on the use of the industrial titanium gypsum slurry (TiGs) as the primary research subject, exploring the factors influencing the efficiency of cyclone non-phase change drying at both laboratory and pilot scales. Our results underscore the significant impact of temperature, gas velocity, and gas–solid ratio on the drying process of TiGs. Notably, in our pilot-scale experiments, employing an air volume of 1300 m3/h, a temperature of 90℃, and a gas–solid ratio of 16 m3/kg, we achieved an impressive reduction in water content in the TiGs, dropping from 72 % to 15 % in mere 30 s. Mechanistic investigations elucidated that the overall drying process includes several important processes, encompassing slurry hot air crushing, rotary granulation, and spin dewatering. Furthermore, our thermogravimetric and elemental analyses unveiled that the augmented expansion of pores facilitated low-temperature dehydration, thereby preserving the stability of the dried material's composition. Additionally, we ascertained that this technology also delivers highly effective drying for municipal wastewater. [ABSTRACT FROM AUTHOR]

Due to the stratification of sludge particles in the ultrasonic field, the acoustic interaction forces the particles to agglomerate on a plane perpendicular to the direction of ultrasonic propagation. Therefore, the thickness of sludge can significantly influence the characteristics of ultrasound-assisted hot air convective drying municipal sewage sludge. In this paper, the stratified aggregation phenomenon of sludge with different thicknesses was observed in the ultrasonic field using the experimental method. It was found that the stratification of the internal structure of sludge became more obvious with the increase of its thickness. The effects of ultrasound on the drying time and the drying rate of sludge with various thicknesses were studied. Meanwhile, the effective moisture diffusivity (Deff) was analyzed. The experimental results demonstrated that within a certain range, the larger the sludge thickness, the longer the time length of the first falling rate stage, and the promotion of the drying rate is worse. The situation is opposite at the constant rate stage. Among the sludge with the thicknesses of 5 mm, 10 mm, and 15 mm, the total drying time and energy consumption of the sludge with a thickness of 10 mm decreases the most substantially at different power ultrasound-assisted. The smaller the thickness of sludge is, the less obvious the effect of ultrasound on the effective moisture diffusivity (Deff), and vice versa. [ABSTRACT FROM AUTHOR]

The present study is aimed at assessing the effectiveness of solar drying process in terms of helminth egg reduction in sewage sludge (SS) generated from an activated sludge wastewater treatment plant (WWTP) in Marrakesh city (Morocco). It is also engaged to highlight a synergic effect of liming (1% CaO) and solar drying on helminth egg reduction. The solar drying process was conducted for 45 days, in summer under a semi-arid climate in a pilot scale polycarbonate-based tunnel (2 m3). Before undergoing solar drying process, data showed an important load of helminth eggs including Ascaris sp., Schistosoma spp., Capillaria spp., Trichuris spp., Ankylostome spp., Toxocara spp., and Taenia spp. in limed sludge (LS) and non-limed sludge (NLS) (15.2 and 17.9 eggs/g, respectively). Ascaris eggs were the most abundant (11.2 and 13.5 eggs/g in LS and NLS, respectively). By the end of the solar drying process, a considerable removal of the total helminth eggs was recorded in LS and NLS (92.8% and 91.6%, respectively). A complete removal of Schistosoma spp., Capillaria spp., Trichuris spp., Toxocara spp. and Taenia spp. was noted in LS and NLS. In the case of Ankylostome spp., data showed a total removal in LS and 81% in NLS; however, the final load is in agreement with the standards (0.4 egg/g). As for Ascaris spp., neither liming nor solar drying process allowed a complete removal (91% and 90% in NLS and LS, respectively) and the final load (1.1 egg/g) does not fulfill the WHO requirements for an agricultural use. Principal component analysis (PCA) demonstrated a negative correlation between dry matter (DM) content (hence temperature) and helminth egg concentration. No significant synergic effect of liming and solar drying process was showed by statistical analysis. This is substantiating that temperature is the key parameter involved in helminth egg removal while undergoing solar drying of SS. [ABSTRACT FROM AUTHOR]

During the processing of biomass as well as during waste water treatment, residual materials with a high water content are produced. They must therefore be dried prior to thermal utilization. Classical drying processes often use fossil raw materials to generate the necessary energy. With sour gas‐based drying based on carbon dioxide‐air mixtures, an alternative is presented that considers CO2 as a valuable raw material (second life) and uses it in the process for drying sewage sludge and fermentation residues. Especially in the drying of fermentation residues, significant differences in dry substance content (DS) were measured, which in individual cases amounted to up to 35 % DS with the same drying time. This is expressed, among other things, in a higher carbon content of 0.42 wt % (wf) in the dry material, accompanied by a heating and calorific value that is more than 1 MJ kg−1 higher. [ABSTRACT FROM AUTHOR]

• Economic analysis on sludge co-treatment in waste power plant was done. • Economy of different sludge drying methods was compared. • Flue gas drying had the highest economic benefit and lowest economic risk. • Dry sludge ratio and sludge treatment subsidy were sensitivity factors for NPV. • Dry sludge ratio was recommended to be in the range of 5–10%. Co-treatment in municipal solid waste power plant has been deemed to one of the most suitable ways to handle sewage sludge. Economy of the co-treatment process is very concerned in the waste incineration plant. Thermal calculation of sewage sludge co-combustion was done. Four common sludge drying schemes was compared: flue gas drying, steam drying, electric heating drying in the waste incineration plant and in situ electric heating drying in the sewage treatment plant. Sensitivity analysis was also performed. When the water content was 30–40% and the absolute-dry sludge ratio was 2–3%, the boiler efficiency was reduced by 0.56–1.12% compared with the case without mixing sludge, and the power generation decreased by 0.2568–0.3767 MW in steam drying scheme and by 0.0037–0.0094 MW in other schemes. Net present value (NPV) of flue gas drying was the highest among the four sludge drying schemes, which was more than 20 ¥ million, while the scheme of electric heating drying in the waste incineration plant had the lowest NPV , which can't recoup the initial investment. Sensitivity coefficient of flue gas drying was smallest among different schemes, showing that the risk of this program was the smallest. Absolute-dry sludge ratio and unit subsidy for sludge treatment were sensitive factors for NPV in flue gas scheme, which had a sensitivity coefficient of 1.123–1.171 and 1.232, respectively. Operating parameters optimization of co-combustion of sludge was done and ways to improve economic efficiency was discussed. [ABSTRACT FROM AUTHOR]

The draining solar drying is considered as an innovative solution in the field of sanitation. The objective of this work is to investigate the feasibility and model the kinetics of the sludge solar drying in a lab‐scale draining greenhouse by varying the air flow rate during winter and summer. The first experiment was conducted without ventilation. Then, a series of experiences was carried out with increasing the air flow. The drying period varied between 3 and 6 days in summer and between 9 and 14 days in winter. By increasing the air velocity, the drying time decreased. For the drying rate curves, in summer, only the falling rate period existed. However, in winter, the curves did not follow any regular shape of drying kinetics. Nine mathematical equations existing in the literature were tested to identify the thin‐layer drying kinetics of sewage sludge inside the draining greenhouse. The Midilli‐Kucuk model was the most reliable for describing the evolution of reduced moisture content versus drying time in hot and cold periods. However, for different drying conditions, the Wang and Singh model was the least suitable. The results revealed also that the effective diffusivity increased when the air flow rate and the ambient temperature increased. [ABSTRACT FROM AUTHOR]

Using plants for the remediation of soils contaminated with heavy metals is an economical, cheap, and effective strategy. The goal of this research was to study the effect of sewage sludge and drought stress on the remediation of cadmium in soil, root uptake by corn plant. This study was carried out on corn in factorial design experiment based on completely randomized design with three replications in three soil pollution levels, namely B1 (control soil), B2 (Cd with soil, 20 mg.kg-1), B3 (Cd with sewage sludge with soil treated, 20 mg.kg-1), and two different irrigation regimes, including A1 (full irrigation) and A2 (limited irrigation). The research included two irrigation treatments at two levels of irrigation: 100% of field capacity (A1) and deficit irrigation at 80% of field capacity (A2). The results showed that the soil treated with cadmium and sewage sludge decreased dry and fresh wet weight plant. Sewage sludge increased the amount of cadmium concentration in shoot almost 21% toward the soil treated with cadmium (soil without cadmium); however, it could not increase cadmium uptake due to the decrease in shoot and root dry matter. In limited irrigation, cadmium concentration in shoot and root was reduced by 46 and 16% toward control treatment, respectively. With increasing irrigation and in the soil treated with sewage sludge, the transfer factor of cadmium from root to shoot dry matter increased. The translocation factors were 0.65, 0.5, and 0.13 for sewage sludge contaminated treatments, cadmium-contaminated treatments, and control treatments, respectively. Based on the results, growing plants at an irrigation level of 100% offered nest advantages in terms of higher biomass and efficient Cd removal. [ABSTRACT FROM AUTHOR]

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• Experimental and CFD analysis of solar sewage sludge dryers. • Comparison of conventional and modified drying chambers. • Payback period was shortened as 20% with modification. • LCOH value was found between 1.7 and 2 $-ct/kWh for modified dryer. Disposal of sewage sludge is an important problem for the sustainability of cities. In recycling process of sewage sludge, a big part of energy demand is consumed in the drying process. Therefore, utilizing clean and sustainable energies in recycling process of sewage sludge can be a good solution. In this work, a drying chamber with transparent cover has been designed and analyzed in the process of drying sewage sludge experimentally and numerically. Also, a conventional drying chamber has been tested and its performance compared with modified drying chamber's performance. The main purpose of modifying the drying chamber using transparent cover is to harvest more solar energy in the system and consequently reduction in the drying time. Moreover, in the drying tests a single-pass conventional unglazed solar air collector has been combined with the drying chamber. The performance tests of drying systems have been conducted in two various flow rates including 0.010 and 0.014 kg/s. Experimental and numerical findings demonstrated that using drying chamber with transparent cover reduced the drying time significantly. The obtained average specific energy consumption and specific moisture extraction rate values are in the range of 1.77–2.86 kWh/kg and 0.77–1.34 kg/kWh, respectively. Moreover, levelized cost of heating values were found between 1.7 and 2.0 $-ct/kWh for the system which uses drying chamber with transparent cover. [ABSTRACT FROM AUTHOR]

Drying of the sewage sludge layer was investigated in a convective laboratory dryer at air temperatures of 65 °C and 80 °C and air speeds of 0.53 m/s and 0.83 m/s. The sludge layer was formed by loading cylindrical extrudates on a grate of 0.5 m × 0.5 m size. The drying air was directed through the layer, as typically encountered in industrial belt dryers. Under such setup, the sludge layer structure and porosity significantly affect the air flow conditions and thus the drying rates. Shrinkage and cracking of the material during drying caused changes in the layer's porous structure, that affected the pressure drop and the drag force due to passing of air through the layer. The decreasing of drag force over time was modeled by a simple function that showed excellent agreement to the selected measured data. The sludge layer drying kinetics was determined by fitting the measured data to the most common drying models. Two models, the modified Nadhari and the Wang Singh model, were determined as most suitable for modeling of drying curves. The total drying time per kilogram of sludge was modeled as a function of drying air temperature, drying air velocity and initial sludge dry matter content. The coefficient of determination (R2) of the model is 0.944. Total drying times between 43 minutes per kilogram and 76 minutes per kilogram of sludge were obtained for the investigated range of drying air conditions. [ABSTRACT FROM AUTHOR]

In a previous stage of the current study, a numerical model of sewage sludge drying was developed. Air stream with a given temperature and speed passes over the mud to dry the product. A heated floor is also added to the process to perform a proper drying of the product. This model is coupled to a heat pump model exchanging with the air stream by way of intermediate exchangers. The present paper aims at investigating the performance of this continuous dryer. The specific moisture extraction rate (SMER) is calculated for a given configuration with fixed air temperature, humidity and velocity as well as fixed dryer dimensions and mud thickness. Furthermore, a reversal product operation was performed to evaluate this technique. In this work, two cases are studied. The first one, with the weakest relative humidity of the drying air (11%), has given a SMER result of 1.44 kgw.(kW h)−1. The second one, with higher relative humidity (16%), has permitted to obtain a SMER indicator of 1.99 kgw.(kW h)−1. This comparison shows the importance of maintaining relatively high humidity conditions for the air stream entering the evaporator, notably due to a lower compressor work. Moreover, these results highlight the strong interest of a heat pump system coupled to a dryer, in comparison to a conventional dryer for which the SMER is equal to 1 kgw.(kW h)−1. [ABSTRACT FROM AUTHOR]

Stickiness is a phenomenon widely observed in drying practices of sewage sludge. This work is aimed at demonstrating the effects of sludge temperature (30–70 °C) and calcium oxide (CaO) on the stickiness of two municipal sewage sludges, based on a newly designed device which can conveniently and systematically determine the temperature-dependent variables of tensile stress (adhesion), shear stress (adhesion) and compression stress (cohesion), respectively. The results indicated that both sludges showed the highest stickiness in the moisture range of 0.43–1.50 kg H2O kg−1 DS (dried sludge). In sticky region, the compression stress was an order of magnitude higher than the shear stress, while the shear stress was about 1–4 times higher than the tensile stress. Furthermore, CaO addition (3 wt.%) led to the increase of the tensile stress, shear stress and compression stress, partially owing to the increased release of organic components (protein, polysaccharides (PSC) and total organic carbon (TOC)) from sludge. However, despite of the increased release of organic components, marked decrease of the above-mentioned stresses was observed when sludge temperature increased from 30 °C to 70 °C, indicating that the temperature-induced changes of sludge rigidity and liquid tension played more important roles in sludge stickiness than organics release. The results of the analysis of variance (ANOVA) indicated that the moisture content of the sewage sludge showed the most significant influence on the tensile stress, shear stress and compression stress, compared with that of the temperature and CaO. [ABSTRACT FROM AUTHOR]