Dried Sewage Sludge Research Articles

Micronutrient and heavy metal bioaccumulation in Bermuda grass (Cynodon dactylon L. Pers) grown in calcareous soil using stabilized and dried sewage sludge

This study examines the micronutrients and heavy metal bioaccumulation in Bermuda grass (Cynodon dactylon L. Pers), grown in two different types of calcareous soil (CS) with the application of stabilized and dried sewage sludge (SS). At the end of the growth period, the Fe, Zn, Mn and Cu (micronutrients) concentrations in the substrate have increased. Furthermore, it was determined that the total Fe, Zn, Mn and Cu concentrations were higher in CS1 compared to CS2. For the heavy metals the concentrations of Ni and Cr have increased, and the concentration of total Cd has slightly but significantly decreased. The total Pb concentration was below the detection limit (DL for Pb <0.03 mg kg-1). It was determined that the total Ni, Cr and Cd concentrations were higher in CS1 than in CS2. In the aerial biomass of the Bermuda grass, the Fe and Zn concentrations have increased with increasing SS applications, whereas Mn concentrations have decreased. Ni, Cr, Cd and Pb concentrations were unaffected by SS applications for both types of CS. The bioconcentration factor (BCF) values for the shoot of the plant (BCFFe, BCFZn, BCFMn, BCFCu, BCFNi, BCFCr, BCFCd) were determined to be below the critical limit of 1. The application of sewage sludge has not resulted in bioaccumulation above critical limits in the shoot of the plant. However, considering Bermuda grass substrate, it can be suggested to add sewage sludge to the calcareous soil in amounts between 20–40 t ha-1, considering its long-term remanence.

Enhancing energy yield and reducing environmental impact through co-hydrothermal carbonization of undehydrated sewage sludge and fungus bran

This study presents a sustainable waste management method through co-hydrothermal carbonization (Co-HTC) of undehydrated sewage sludge (SS) and fungus bran (FB), effectively eliminating the need for additional water. The effects of the reaction severity factor (SF: 0.1, 0.2, and 0.3), the FB mixed ratio (FBMR: 0 %, 10 %, and 20 %), and the proportion of citric acid promoting agent (CAPA: 0 %, 10 %, and 20 %) on HTC performance were systematically investigated. The process was optimized for maximum energy yield (EY) using response surface methodology (RSM). The properties of the produced hydrochar, along with its EY and environmental impact, were thoroughly assessed. Results demonstrated that under optimal conditions (SF: 0.1, FBMR: 20 %, and CAPA: 20 %), EY increased by 45.84 % compared to hydrochar derived from dried SS. The dehydration and decarboxylation processes led to lower H/C and O/C ratios, producing hydrochar with reduced sulfur and nitrogen content, while the contents of alkali and alkaline earth metals, particularly calcium, increased. Furthermore, the optimized Co-HTC process had minimal environmental impact. In contrast to traditional HTC, which requires significant freshwater and involves high costs for SS drying, our innovative approach using undehydrated SS offers a cost-effective and environmentally friendly solution, paving the way for industrial-scale Co-HTC and sustainable waste valorization.

Experiment study on particle pulverization-assisted convective air drying of sewage sludge

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.

Steam gasification of lime dried sewage sludge: Effects of temperature and addition of lime

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 CO2 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 CH content in the organic matter, while significantly increasing the content of reactive CH3-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.

Biomass inertization to increase minimum ignition temperature

In the past years, the use of biomass has significantly increased and, therefore, so has the number of accidents related to its storage, transport, and use. To prevent these accidents, it is essential to properly know their flammability and explosion characteristics so their behaviour can be addressed as a first stop for preventing accidents. The present work studies the inertization with solid inerts of biomass layers and clouds (biomass powder suspended in air) as a possible solution to reduce their ignition tendency. To do so, two biomass samples were studied: wood pellets and dried sewage sludge; mixed with two different inert materials: recycled glass and sodium bicarbonate. In particular, the inert materials were mixed with biomass at three different concentrations (30%, 50% and 70%) and the ignition of the mixtures was studied, determining the minimum ignition temperature of layer and cloud (MITL and MITC) for each mixture, and detecting the needed concentration for avoiding the ignition. Additionally, samples were tested using TGA and DSC techniques to analyse their thermal behaviour and to determine the influence that the inert material has in the energetic power of the biofuel.Different behaviours were observed depending on the different inert materials, showing that not only the amount of inert added is important but also its physico-chemical properties. If the results for a layer and a cloud are compared, it was noticed that inertization effect differs between biomass and test. Regarding TGA and DSC results, it was concluded that smaller percentages of inert material should be considered, as they substantially modify the energetic value.

The effect of carbonization temperature on textural properties of sewage sludge-derived biochars as potential adsorbents

This article presents ways of recovering waste in the form of anaerobically digested and dried sewage sludge (average humidity approx. 6 wt%) by carbonization at various temperatures in the range of 400–900 °C. The resulting products, biochars, are investigated in terms of yield, surface properties and Raman spectra analysis. The sorption capacity of biochars differs depending on the carbonization temperature. The experimental amount of adsorbed CO2 slowly increases with the carbonization temperature from 0.212 mmol/g at 400 °C to the highest value of 0.415 mmol/g, which is achieved at 900 °C by slow carbonization at a rate of 10 °C/min. Additionally, there is a strong positive dependence of the adsorption capacity on the micropore volume. Higher carbonization temperatures support the powerful formation of micropores and improve their sorption capacity.

Evaluation of Hospital Wastewater Treatment Using Sewage Treatment Plant for Heavy Metals, Radionuclides, and Some Pharmaceuticals: A Case Study

This is the first study in Oman to evaluate the efficiency of a sewage treatment plant (STP) for hospital wastewater (HWW) treatment for heavy metals, radionuclides, and some selected pharmaceuticals. A sewage treatment plant (STP) at Sultan Qaboos University (SQU) receives HWW, from Sultan Qaboos University Hospital (SQUH), and municipal wastewater from non-medical facilities at SQU. Representative samples of HWW (before mixing with municipal wastewater at STP), STP-treated wastewater (TWW), and STP mixing sludge, were collected and analyzed. A method for analyzing pharmaceuticals including metformin, atenolol, chlorpheniramine, triprolidine, diphenhydramine, and citalopram was developed and validated using LC-MS-MS. HWW and TWW show low concentrations of heavy metals. Radionuclides found in HWW include Cs137, K40, Ra226, Th234, I131, Tl208, Zn65 Ac228, Sb125, Bi124 and Be7. Diphenhydramine (2.24 mg/L), chlorpheniramine (0.293 mg/L) and atenolol (0.0260 mg/L) were found in HWW. Heavy metals, radionuclides, and pharmaceuticals were found less in TWW than in HWW. STP sewage sludge showed higher levels of these pollutants than HWW or TWW. Concentrations of diphenhydramine, chlorpheniramine, and citalopram were 137, 0.950, and 169 mg/kg, respectively in dried sewage sludge. The study confirms the ineffectiveness of STP treatment to completely remediate HWW. HWW should be considered hazardous and requires physico-chemical treatment before mixing with municipal wastewater. Keywords: Hospital, pharmaceuticals, radionuclides, heavy metals, wastewater.

Physico-chemical characterization and possible uses of sludge processed from an urban sewage treatment plant

Nowadays, the challenge is to transform dehydrated sewage sludge resulting from wastewater treatment plants from waste into resource. Following this objective, the sludge was further dried and submitted to X-ray diffraction (XRD) and FTIR analysis. The sludge was first dried in ventilated and unventilated spaces at 50∘C and 100∘C, for 60 and 100 minutes (min) in each case. The final mass and evaporation degree of the sludge depends on the initial mass, ventilation type, drying time, and temperature. The ventilated drying space is preferred for temperature control, homogeneity, and higher evaporation degree. The influence of the drying process on the structure and behavior of the sewage sludge was emphasized through X-ray diffraction (XRD) and FTIR analysis. The XRD shows good structural properties of the sludge samples given by the reduction of the particle size through evaporation. According to FTIR, evaporation influences the depolymerization of the silicate network. The hydroxyl units and metallic ion modifiers can improve the sludge structure, but its intensity decreases through evaporation. With high content of solid substance, and good relation between the composition of the sludge and its structure and behavior, the dried sewage sludge can be used in: (i) agriculture, (ii) construction, (iii) the energy sector.

Study on influence factors and control optimizations of sewage sludge drying and incineration system for energy conservation

Study on influence factors and control optimizations of sewage sludge drying and incineration system for energy conservation

Microwave Drying of Sewage Sludge: Process Performance and Energy Consumption

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.

Energy recovery and waste valorization in a frozen food processing facility: a case study from Lazio, Italy

AbstractFood and Agriculture Organization of the United Nations (FAO) estimates that food, beverage, and tobacco sector is currently responsible for about 30% of total world energy consumption and approximately the same percentage of food is wasted during its industrial transformation. Improving the sustainability of food processing is fundamental to reduce the environmental impact of this sector as well as to lower the disposal cost of industrial waste. The objective of this work is to propose an efficient and technically feasible solution for the management and energy recovery of residual biomasses and industrial processing by-products, such as sewage sludge produced by industrial wastewater treatment. The above solution is developed for a real frozen food factory operating in Lazio region (Italy) introducing a sewage sludge dryer and a gasifier to produce syngas. The software Aspen Plus is adopted to numerically simulate the gasification process, using a literature validated model, while the dryer and the already present combined heat and power (CHP) plant are dynamically modelled in TRNSYS environment. The results demonstrate that the proposed solution is feasible and attractive from both an environmental and an economic perspective. The Simple Pay Back of the investment is less than 3 years, while the Net Present Value stands at about 2.4 M€. Furthermore, the CO2 proposed system allows to save 179 t of equivalent CO2 emissions compared to the current system.

Flash drying of slurry-liquid sewage sludge based on avoidance of latent heat of phase change: Laboratory to pilot-scale evolution

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.

Evaluation of sewage sludge effects on soil fertility and silage maize growth

Different methods are being tried all over the world for the safe disposal of sewage sludge. One of these methods is to evaluate the waste in plant production by applying it to the soil. In this study, the potential of using stabilized and dried sewage sludge in silage maize cultivation was investigated. Silage maize was grown by applying the sewage sludge to the soil at different rates [0 t ha-1 (SS0-Control), 20 t ha-1 (SS2), 40 t ha-1 (SS4), 60 t ha-1 (SS6), and 80 t ha-1 (SS8)]. Thus, the material's effects on soil fertility and plant growth were examined. According to the results, the sewage sludge enriched the soil, which contains restrictive factors in terms of fertility and on which maize growth is carried out, with humus and nutrients. However, it was observed that the material does not cause salinity problems in the soil. It was determined that sewage sludge positively affected the growth of silage maize but could not provide sufficient nutrition for the plant in terms of macronutrients. Considering the economic benefits and environmental risks, applying the sewage sludge with a maximum of 60 t ha-1 in silage maize growth is appropriate. However, it would be incredibly beneficial to support the material with chemical fertilizers to increase the silage yield and quality of the plant.

Solar drying of agrobiomass for biopellets production

This paper presents the results of the research devoted to the determination of the conditions of solar drying of agrobiomass waste in open area in Mediterranean climate in Aydin region. The testing was undertaken in the summer season.
 Drying tests were performed for two type mixtures i.e., sewage sludge and olive mill waste (OMW30) and sewage sludge and animal waste (DMC30).
 In order to determine the optimum conditions for the process and undertake an analysis of kinetic drying of sewage sludge, a set of tests were performed under variable parameters, i.e. for various thickness of the dried mixture of materials: 5, 10 and 20 cm and with the application of various mixing intensity: no mixing, and 6 times a day.
 The conducted tests let to the determination of the time interval necessary for the drying in the conditions of summer and also the parameters, which are optimal in terms of the time needed for the solar drying process in open sun drying.

Modeling of Gasification of Sewage Sludge for Phosphorus Recovery and Hydrogen Generation

AbstractDue to the amendment of sewage sludge ordinance in Germany, phosphorus must be recovered from sewage sludge in the future. Previously developed phosphorus recycling processes are not economically viable due to high material and energetic expenditures. Gasification of dried sewage sludge enables the energetic utilization of sewage sludge and provides the energy for phosphorus recovery. The present paper focuses on thermodynamic modeling of the gasification system to demonstrate the potential for holistic utilization of dried sewage sludge as phosphorus fertilizer. The results shows that an energy self‐sufficient, optimized process can be realized for recovery of phosphorus by gasification and subsequent thermo‐chemical treatment of dried sewage sludge.

A quantitative theory integrating solid surface hydrophilicity and pore structure features for non-phase-change drying of sewage sludge through gradient increase of ultrahigh filtration pressure

The sustainable application of thermal sludge drying process is limited by the high energy consumption due to the phase-change latent heat of moisture. This study proposed that the ultrahigh pressure filtration could realize the non-phase-change sludge drying. The lowest water content of 28.12 wt.% was realized by the filtration pressure of 21 MPa for the excess sludge with polyaluminium chloride as the conditioning agent. With the stepwise increase of filtration pressure employed (5-21 MPa), the diameter of solid pores was gradually narrowed to the same order of magnitude with the thickness of vicinal water film (i.e., 1-10 nm). As a result, the capillary water was transformed into the vicinal water, and the solid-water interface interaction played more crucial roles in water occurrence states. However, Hagen-Poiseuille equation was introduced to estimate the pore water outflow based on the pore wall hydrophilicity and the external filtration pressure, which implied that there can be always a sufficiently large driving force to maintain the water outflow rate no matter how the pore diameter is small and the sidewall is hydrophilic. Typically, the fitting results of excess sludge (R2=0.985, p-value<0.01) indicated that the pressure gradient of 2.11 × 109 Pa/m was required to maintain the pore water flow rate of 1.38 × 10−15 m3/s with the median pore diameter of 5.33 × 10−7 m. All these findings broke through the conventional cognition that only thermal drying process can decrease the sludge water content below 60 wt.%, and facilitated energy saving of sludge dewatering process through non-phase-change separation, i.e., ultrahigh pressure filtration.

Effects of layer inhomogeneities on the process of sewage sludge convective drying

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.

Amplifiers of environmental risk of microplastics in sewage sludge: Thermal drying treatment

Sewage sludge was already identified as an important source of microplastics (MPs) in the environment. Therefore, investigating the effects of sludge treatment processes on sludge-based MPs is essential for understanding the environmental risks and controlling their release. This study investigated the occurrence characteristics and elucidated the fragmentation mechanism of sludge-based MPs before and after the thermal drying treatment of sludge. The results showed that this treatment increased the abundance of sludge-based MPs by about 10-fold, with enhanced fragmentation and fracture parameters, and increased the abundance of <100 μm MPs to >60 %. Remarkably, both polypropylene-microplastics (PP-MPs) and polyethylene terephthalate-microplastics (PET-MPs) did not show significant chemical aging. The structural analysis showed that the molecular chain disorientation and secondary crystallization of PP-MPs and PET-MPs occurred. These transformations caused the contraction of the polymer molecular chains and the generation of micro-mechanical stresses, leading to the formation of warpage structures and stress cracking on the MPs' surface. These phenomena also contributed to the further fragmentation of the MPs and the development of finer MPs particles. The findings of the present investigations emphasize that the thermal drying of sewage sludge amplifies the environmental risk of sludge-based MPs.

Radiation processing in India: The voyage and present status

Establishment of first gamma radiation facility for sterilization of medical products under auspices of UNDP by the Department of Atomic Energy (DAE) in the year 1974 gave a big boost to radiation related applied research activities in India. Today radiation related research is not confined to DAE units but it is being carried out in many universities and other institutes of India. A very positive outcome of this has been that, many industries are adopting radiation technologies. Presently 18 electron beams and 24 gamma processing plants are commercially operating in India. Radiation applications are being explored for radiolysis based advanced oxidation processes (AOPs) for treatment of waste water and treatment of dry sewage sludge, synthesis of grafted membranes for separation and energy storage purpose, synthesis of high recovery shape memory polymers, synthesis of chemi-resistive, electromechanical and peizo-resistive sensors and other applications. The article briefly describes various activities being presently being pursued or have been completed in recent past. Efforts have been put to guesstimate the direction of the near future activities in-view of the present activities.

Deammonification Potential of Pig Slurries and Vapor Condensates from Sewage Sludge Drying-Substrate Quality and Inhibition.

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.