Organic Matter In Sewage Sludge Research Articles

A neglected contributor of thermal hydrolysis to sludge anaerobic digestion: Fulvic acids release and their influences

Fulvic acids (FAs) belong to inert organic matters in sewage sludge and their influences are often overlooked during convectional anaerobic digestion (AD). Currently, thermal hydrolysis (TH) has been widely applied on sludge pretreatment before AD processes, which makes FAs undergo drastic evolutions and aggressive to sludge AD. Results in the present study indicated that FAs concentration in the liquid was elevated by over incredible 150 folds during sludge TH, from 3.4 mg/L in raw sludge to 590.0 mg/L in hydrolyzed sludge at 180 °C. Moreover, during sludge TH, the chemical structures of FAs, including aromatic condensation degree, elemental composition and functional group, also underwent significant changes, which enhanced FAs electron transfer capability, reduced their biodegradability and promoted their roles on sludge AD. Furthermore, fortunately, the evolutions of FAs were favorable to sludge AD in general. Methane production could be promoted by about 20% under FAs concentration of 0.6 g/L, and the FAs extracted from hydrolyzed sludge presented higher promotion performances than that of the raw FAs, in which 180 °C FAs were particularly conspicuous. Furthermore, FAs evolutions would present differential influences on each phase of sludge AD, promotional to acidogenesis and methanogenesis but inhibitory to hydrolysis. Pearson correlation analysis indicated FAs influences on sludge AD, particularly the hydrolysis phase, were not only related to their concentration, but also chemical structure. The findings of this study demonstrated that FAs influences should not be negligible anymore during sludge AD with TH pretreatment. Meanwhile, since FAs promotion on sludge AD was closely related to their concentration and chemical structure, it would be significant to take FAs evolutions as auxiliary indexes for the regulations of sludge TH.

DES mediated synthesis of sewage sludge-derived B, N-doped carbons for electrochemical applications

In order to effectively utilize organic matter in sewage sludge (SS), a new porous carbon material was successfully prepared from SS with deep eutectic solvents (DES) (boric acid and urea), in which DES was firstly used to solvent to separate organic matter, also playing the role as a B and N donor as well as acid activator to form porous B, N-carbons. As-synthesized B, N-carbon electrode materials possessed a high specific capacitance of 251.4 F/g at a current density of 1 A/g. It retained 84.28% of the capacitance at an ultrahigh current density of 5 A/g. The energy density was 9.502 Wh/Kg at a power density of 245.4 W/kg in 6 M KOH in symmetric supercapacitor.

Optimization of supercritical carbon dioxide explosion for sewage sludge pre-treatment using response surface methodology

The present work was conducted to assess whether the implementation of Supercritical Carbon dioxide Explosion (SCE) is an efficient approach for sewage sludge pre-treatment. In this context, SCE was optimized with the aim to develop a method attempting to increase the biodegradability of sewage sludge's organic matter content, and thus, to enhance the subsequent anaerobic digestion and methane production. The statistical tool of response surface methodology was applied to evaluate the effects of the main pre-treatment parameters (i.e. temperature and time) and their interactions on methane yield, which was defined as the response. Temperature was found to be the most significant variable, having the greatest effect on methane yield. Following this, an optimum set of pre-treatment conditions corresponding to a temperature of 115 °C and time of 13 min, was determined. Under these optimum conditions, the predicted response value was 300 mL CH4/g of volatile solids. The corresponding experimental value obtained from the validation experiment fitted well with this value, clearly demonstrating the effective use of response surface methodology in optimizing SCE. Additionally, under optimum conditions, the methane yield presented a statistically significant increment of 8.7%, compared to untreated sludge. This revealed the impact of SCE as an effective and alternative way for the efficient pre-treatment of sewage sludge. Finally, thermal pre-treatment, alkaline and acidic hydrolysis were also applied to the already pre-treated sludge. It was concluded that the combined pre-treatment techniques contributed to a further increase of methane production compared to raw (untreated) substrate.

Multi-response optimization of sewage sludge-derived hydrochar production and its CO2-assisted gasification performance

The harmful effects of improper sewage sludge (SS) treatment on the environment inspire the search for more benign sludge processing techniques such as hydrothermal carbonization (HTC); the abundant organic matter in SS is used for energy recovery. Here, we aimed to optimize the HTC-based preparation of SS hydrochar and its gasification performance by using response surface methodology (RSM). Specifically, the hydrochar yield, higher heating value (HHV), and gasification activity index were selected as optimization goals, whereas carbonization temperature (160–260 °C), residence time (30–150 min), and acetic acid concentration (0–1.5 M) were selected as factors influencing the HTC process and CO2-assisted gasification performance. Carbonization temperature was the dominant parameter determining hydrochar yield, HHV, and gasification activity. The hydrochar yield (82.69%) and calorific value (7820.99 kJ kg−1) were maximized under comparatively mild conditions (160 °C, 30 min, and 0.07 M acetic acid), whereas the gasification activity index (0.288 s−1) was maximized under harsher conditions (211.34 °C, 88.16 min, and 1.58 M acetic acid). The results help to guide the HTC of SS intended for gasification, thus promoting the development of this promising waste-to-energy technology and may facilitate the design and further optimization of thermochemical SS conversion.

Sewage sludge gasification in supercritical water with fluidized bed reactor: Reaction and product characteristics

Sewage sludge supercritical water gasification in fluidized bed reactor was studied in this work. Effect of temperature on the distribution of products and gas compositions were researched. In order to improve the gasification process more effectively, the effect of temperature on reaction process development and gas products generation was also studied. A variety of analytical methods were used to study the detailed characteristics of products generated at different reaction conditions. The variation of product yield distribution and products properties showed that organic matter in sewage sludge was completely dissolved and hydrolyzed at 480 °C. Multiple reactions happened in these dissolved and hydrolyzed products and then gas products were formed when temperature increased from 480 to 540 °C further. At the same time, dehydrogenation and polymerization also took place in the solution and hydrolyzed products, and it could be explained by the Diels-Alder reaction mechanism well.

Comprehensive role of thermal combined ultrasonic pre-treatment in sewage sludge disposal

Thermal/ultrasonic pre-treatment of sludge has been proven to break the hydrolysis barriers of sewage sludge (SS) and improve the performance of anaerobic digestion (AD). In this study, the objective was to investigate whether the combination of two pre-treatment methods can achieve better results on the AD of SS. The results indicated that, compared with the control group and separate pre-treatment groups, the thermal combined ultrasonic pre-treatment presented more obvious solubilization of soluble proteins, polysaccharides, and other organic matters in SS. The combined method promoted the dissolution of protein-like substances more effectively, with biogas production increased by 19% and the volatile solid (VS) removal rate improved to above 50% compared with the control group. The capillary suction time is reduced by about 85%, which greatly improved the dewatering performance of SS. In addition, the combined method has advantages in degrading sulfonamide antibiotics, roxithromycin and tetracycline. Particularly, by analyzing the interaction between the degradation of different antibiotics and the composition of dissolved organic matters (DOMs), it was found that the composition of DOMs could affect the degradability of different antibiotics. Among them, the high content of tyrosine-like and tryptophan-like was conducive to the degradation of sulfamethoxazole, and the high content of fulvic acid-like and humic acid-like was conducive to the degradation of roxithromycin and tetracycline. This work evaluated the comprehensive effect of thermal combined ultrasonic pre-treatment on SS disposal and provided useful information for its engineering.

Pyrolysis characteristic and kinetic analysis of sewage sludge using model-free and master plots methods

The pyrolysis kinetics of two types of sewage sludge (municipal sludge and pharmaceutical sludge) were studied by thermogravimetry. The collected samples were pretreated and tested with nitrogen as carrier gas at different heating rates (10, 20, 30, and 40 °C/min) using a thermogravimetric analyzer. Model-free methods and master plots method were used to calculate the pyrolysis kinetic parameters of the samples. TG/DTG results showed that the thermal decomposition of the two types of sewage sludge may be divided into three stages (Dehydration, Decomposition, and Coking stage). The activation energies of the two kinds of sewage sludge were 366.58 KJ/mol (municipal sludge) and 268.36 KJ/mol (pharmaceutical sludge), respectively. The pyrolysis mechanism of two kinds of sewage sludge was discussed by the master plots method. The results showed that under a low conversion rate, the phase interface reaction model can better explain the pyrolysis mechanism of pharmaceutical sludge; under high conversion rate, the nucleation and growth model was more suitable. For municipal sludge, power law model was most suitable in the whole range. The pyrolysis characteristic of the samples was further studied. The results showed that the organic matter in sewage sludge can be decomposed into bio-oil and bio-gas at elevated temperatures and can be used as an attractive energy source.

Pyrolysis-GCMS as a Tool for Maturity Evaluation of Compost from Sewage Sludge and Green Waste

The objective of the study was to characterise co-composting dynamics and maturity of the end products of sewage sludge/ green waste mixtures. We analysed all initial substrates and co-composts, sampled at different composting times for studying (1) physicochemical parameters and (2) organic matter biodegradation and biotransformation using pyrolysis coupled to gas chromatography and mass spectrometry. Physicochemical analysis indicated compost maturity of the three co-composting mixtures after 200 days. Pyrolysis-GCMS showed that organic matter in sewage sludge generated a large number of different pyrolysis products, most of which had unspecific origin. The pyrolysis products of the three co-compost were classified according to their chemical composition (benzene derivatives, N-containing compounds, phenol derivatives, furan derivates) and according to their chemical structure (polyaromatics, aromatics compounds and aliphatic compounds). These compound classes evolved differently during composting. We suggest two new specific ratios of peak areas from pyrolysis products to describe the biodegradation and to evaluate the degree of maturity during co-composting sludge-green waste: (1) the ratio benzene, methyl (methylethenyl) /benzene, which decrease during composting, and (2) the ratio of Indene/2-methoxy-4 vinyl-phenol which increase during composting. The good correlation between these ratios and physico-chemical parameters confirms their usefulness to evaluate the co-compost maturity.

Application of Fenton Method for the Removal of Organic Matter in Sewage Sludge at Room Temperature

Cement is the most widely used construction material in the world. However, its manufacture is high energy consumption and high carbon emission owing to the high temperature calcination process. Geopolymer is an ideal alternative material for cement because it has a similar structure and performance to cement. In addition, it can be synthesized at room temperature and thus has the advantages of energy saving and carbon emission reduction. Sewage sludge (SS) can be used as raw material for geopolymer synthesis. However, the high organic matter content in SS lowers the mechanical strength of geopolymer. Although the organic matter in SS can be removed by incineration at high temperature, this consumes energy and emits carbon dioxide, which diminishes the advantages of geopolymer. In this study, the Fenton method was applied for the removal of organic matter in SS at room temperature. The parameters of the Fenton method, including the dosages of hydrogen peroxide (H2O2) and Fe2+ reagent (FeSO4·7H2O), reaction time, and initial pH value, were investigated. The results indicated that 83.7% of the organic matter in SS could be removed at room temperature by using 5.15 M H2O2 and 5.15 mM FeSO4·7H2O at pH 7, which suggested the possibility of sewage sludge reclamation through geopolymer synthesis as an alternative material for cement toward sustainability.

Valorization of sewage sludge through catalytic sub- and supercritical water gasification

Sub- and supercritical water gasification is applied to recover energy from sewage sludge in a batch reactor. The effects of reaction temperature and water-soluble additives as catalysts on gasification were examined. The resultant products, including syngas, hydrochar and liquid residues were characterized. The rise of temperature without the presence of catalysts increased the yield of H2 (0.06 (350 °C) to 1.91 mol/kg (450 °C) and enhanced the gasification efficiency (1.29–19.61%), and decreased total organic carbon (TOC) by 68.50% in liquid residue. The changes in product distribution and characteristics of hydrochar and liquid residue implied that the organic matters in sewage sludge were dissolved and hydrolyzed in sub- and supercritical water, resulting in the production of syngas. The catalytic effect of different catalysts in relation to the H2 gas yield was in the following order: KOH > NaOH > Na2CO3 ≈ K2CO3. In the case of catalytic supercritical water gasification at 400 °C, the highest molar fraction (37.28%) and yield of H2 (1.60 mol/kg) were obtained in the presence of KOH. Furthermore, the scanning electron microscopy (SEM) analysis indicated that a conversion and dissolution of the organic matters in sewage sludge to liquid and gas, produced a porous, fragmented structure and disintegrated surface of hydrochar.

Assessment of sewage sludge gasification in supercritical water for H2-rich syngas production

The potential of sewage sludge for hydrogen-rich syngas production from supercritical water gasification (SCWG) was evaluated through thermodynamic analysis and experimental work. The thermodynamic analysis was conducted by using Aspen Plus simulator based on Gibbs free energy minimization. The effect of temperature (380–460°C), sludge concentration (5–30wt%), and activated carbon addition (2–8wt%) on SCWG was experimentally studied. The solid and liquid residues were characterized by Fourier Transform Infrared (FTIR) spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), and Total Organic Carbon (TOC) Analyzer. The results showed that higher temperature and lower sludge concentration favored syngas production, leading to higher hydrogen yield. While pressure had no significant effect on the SCWG performance. The TOC and FTIR analyses revealed that organic matters in sewage sludge were decomposed and hydrolyzed into syngas. The addition of activated carbon increased the syngas yield and enhanced the cold gas efficiency. A syngas yield of 6.44mol/kg containing 38.43% H2 was obtained from SCWG at 400°C with the activated carbon loading of 8wt%. Moreover, the analysis of heavy metals indicated that SCWG had a positive effect on the stabilization of heavy metals and reduced the leaching toxicity of heavy metals in sewage sludge.

Characteristics and Heavy Metal Adsorption Performance of Sewage Sludge-derived Biochar from Co-pyrolysis with Transition Metals

To enhance the heavy metal cation adsorption capacity of sewage sludge-derived biochar in an aqueous medium with a high concentration of Ca2+, modified biochars were obtained from co-pyrolysis of sewage sludge and transition metal oxides (with a sewage sludge:transition metal mass ratio of 10:1), such as Fe2O3, MnO2, and ZnO. The properties of the modified biochars were characterized, and the Cd2+ adsorption effect of the modified biochars was determined as well. The H/C atom ratios of the modified biochars were all lower than 0.31, indicating that the transition metal oxides catalyzed the decomposition and volatilization of organic matter in sewage sludge. The majority of the added Fe and Mn remained in the modified biochars, and existed as a simple substance and oxide, respectively; while significant loss of Zn occurred. The pores of the modified biochars were mainly mesopores with an average pore size of approximately 3.8 nm, and the specific surface area of the modified biochars was larger than 50 m2·g-1. When the initial Cd2+ concentration was increased from 0 mg·L-1 to approximately 200 mg·L-1, the Cd2+ adsorption capacity of the Fe-modified biochar declined from 43.17 mg·g-1 to 27.88 mg·g-1, which was still higher than that of the unmodified biochar by at least 10 mg·g-1. In aqueous media with a high concentration of Ca2+, the Fe-modified biochar showed better Cd2+ adsorption performance; thus, compared to MnO2 and ZnO, Fe2O3 was the best choice to enhance the heavy metal adsorption performance of the sewage sludge-derived biochar.

Simple and efficient dual-wavelength spectroscopy for the determination of organic matter in sewage sludge from wastewater treatment.

In this study, a dual-wavelength spectroscopic method for rapid determination of organic matter in sludge was developed. The contents of the organic matter were calculated by determining the consumption of potassium dichromate (K2Cr2O7) based on the production of trivalent chromium ions (Cr3+). Cr3+ could be determined by subtracting the absorption at 800 nm (spectral interference) from the absorption at 650 nm (only contributed by Cr3+). The results showed that the relative standard deviation in the test was less than 5%. The same set of samples was used and when the content of organic matter was more than 150 g kg−1, the relative difference between the spectroscopic method and titration method was within 1%. Furthermore, the method does not require calibration based on the standard samples. In conclusion, the present method is simple, reliable, accurate and suitable for application in mass testing for sludge samples.

Enhanced hydrogen production in catalytic pyrolysis of sewage sludge by red mud: Thermogravimetric kinetic analysis and pyrolysis characteristics

The catalytic mechanism of red mud (RM) on the pyrolysis of sewage sludge was investigated. The thermogravimetric data were used to study the kinetic characteristics by using a discrete distributed activation energy model (DAEM) to clarify the effects of three main components (Fe2O3, Al2O3, SiO2) in the RM on the pyrolysis of organic matters in sewage sludge. The modeling results showed that the pyrolysis of organic matters, especially at the higher temperature stage, was promoted by Fe2O3 and Al2O3 in the RM. Adding Fe2O3 or the RM alone could reduce the mean activation energy of sewage sludge pyrolysis by 13.9 and 20.1 kJ mol−1, respectively. The modeling results were validated by pyrolysis experiments of raw sludge with different additives at 600, 700, 800, and 900 °C. The experimental results showed that the addition of Al2O3, Fe2O3 or the RM could produce more gas than the addition of SiO2, especially at high temperatures. Fe2O3 and Al2O3 acted as catalysts in the tar decomposition by in-situ catalyzing the cracking of CC and CH bonds to produce more gases. Especially, Fe2O3 and Al2O3 increased the H2 yield from sewage sludge pyrolysis at 700, 800, and 900 °C by 268.5 and 50.7%, 111.1 and 56.0%, 10.9 and 10.3%, respectively. The char obtained from pyrolysis of sewage sludge with the RM possessed magnetic property, which has various potential applications. The research indicates that the RM is an efficient catalyst in the pyrolysis of sewage sludge.

Molecular characteristics of the refractory organic matter in the anaerobic and aerobic digestates of sewage sludge.

The chemical characteristics of the refractory organic matter in anaerobic and aerobic digestates are hardly known although they are significant for further improving the degradation of organic matter during sludge digestion. Thus, in this study, various techniques are used to analyze the molecular properties of the total organic matter in raw sludge and mesophilic anaerobic and aerobic digestates (AnD and AoD, respectively). The results show that AnD has lower organic matter content, but the maturity and aromatization of its organic matter are lower than those of AoD. The FTIR and XPS spectra show that AoD has higher proportions of protein-like and aromatic groups and lower percentages of polysaccharide-like materials and ammonia nitrogen compared with AnD. The solid-phase fluorescence spectra indicate that AoD has a higher content of fluorescence organic matter, but its biodegradability and chemical accessibility are lower than those of AnD. Pyrolysis GC/MS analysis shows that the digestates are enriched with more lignin-like and aromatic groups and contain lower oxycompounds compared with raw sludge, especially AoD. These findings provide new insights into the molecular characteristics of the refractory organic matter in anaerobic and aerobic digestates and also provide a possible strategy to further enhance the degradation of organic matter in sewage sludge.

Degradation and characteristic changes of organic matter in sewage sludge using Vermi-biofilter system

Vermi-biofilter (VF) System could be an efficient sludge treatment unit in regard of rates and extents of total chemical oxygen demand (TCOD) removal, particularly the first 10 days earthworm-treated. This study characterized the organic matter in sludge before and after VF system treatment, with or without earthworm stage. The 60 days earthworm-treated VF system reached a TCOD removal of 10,450 mg/L, bulk DOC removal of 89.5 mg/L, and earthworm density increase from 32 g/L to 43 g/L in sludge EBOM in 60 days of VF system operation. The aromatic proteins, soluble microbial byproduct-like fluorescent compounds and carboxylic components, aliphatic components (C-H related), hydrocarbon and carbohydrate materials were identified to be principally increased by 10 days earthworm-treated and then degradation in the nest days under VF system.

Influence analysis of sewage sludge methane fermentation parameters on process efficiency

The efficiency dependence of sewage sludge organic matter decomposition from organization and conditions of the process is analyzed. Support of the optimal values of several parameters ensures to provide completeness of the sludge fermentation process and obtain biogas in calculated amount. Biogas utilization reduces costs for reactor heating and provides additional obtaining of other types of energy

Impact of sewage sludge application on the humus state of sod-podzolic soil of subcarpathia under energetic willow plantation

Aim. To determine the impact of energetic willow fertilization with sewage sludge (SS) and manure on the change in the humus state of sod-podzolic soil of Subcarpathia under energetic willow plantation. Methods. Soil samples were collected on the experimental fi eld of Ivano-Frankivsk College of LNAU. The humus con- tent was determined according to DSTU 4289:2004; that of its labile forms – according to DSTU 4732:2007, the content of organic matter in SS and manure – according to GOST 27980-88. Results. The application of sewage sludge for energetic willow grown in sod-podzolic soil of Subcarpathia led to the increase in the total humus content by 0.5–1.1 % compared to the control (without fertilizers). The use of SS preconditioned the change in the humus quality, including the increase in humic acids in humus by 0.05–0.07 %, which promoted the increase in the share of stable humus up to 68–70 % and the stabilization of the humus state of sod-podzolic soil. Conclusions. The application of sewage sludge impacts the change in the indices of humus quality, in particular, its group composition. The level of humic acids content in humus increases with the increase in the dose of the introduced sewage sludge and manure, based thereon. It ensures the increase in the share of stable humus in soil, which, in its turn, conditions the stabilization of humus state of sod-podzolic soil. However, this dependence weakens with depth.

The effectiveness of the incineration of sewage sludge on the evolution of physicochemical and mechanical properties of Portland cement

The influence of sewage sludge, treated at temperatures between 300 and 800°C, on cement-based materials has been studied in this paper. The clinker of CPJ45 cement was partially replaced by sewage sludge ash (SSA) admixture in mortar at various percentages. The sewage sludge ashes were characterized chemically, physically and mineralogically. In addition, the influences of SSA on mortar properties, including Blaine fineness, specific gravity, water demand, time of setting, compressive strength and degree of hydration were also investigated.Results show that calcination influences the microstructure of sewage sludge and increases its pozzolanic activity that reaches its maximum at 800°C. The presence of absorbed water and organic matter in sewage sludge calcined in temperature range 300–500°C prolongs strongly the setting time and affects negatively the compressive strength and the hydration degree of mortars. While the high amounts of P2O5 and SO3 in sewage sludge calcined in temperature range 700–800°C increase also water demand and setting time compared to the control mortar, however, the compressive strengths and the degree of hydration increase with time and become superior to the control mortar at 90days, for a replacement rate of 15%. The best mechanical results are obtained for the substitution of 5% of calcined sewage sludge at 28days.

Degradation of Organic Matter of Municipal Sewage Sludge Using Ultrasound Treatment in Shiraz Wastewater Treatment Plant

Background: Nowadays, the reduction of sludge production in the activated sludge process as well as disposal restrictions have drawn much attention. Objectives: The purpose of this study was to evaluate the feasibility of using ultrasound treatment in increasing the degradation of organic matter in sewage sludge from Shiraz Municipal Wastewater Treatment Plant and also to assess its effect on sludge dewatering. Materials and Methods: The samples were collected from the anaerobic digester of the Shiraz Wastewater Treatment Plant. The present study was conducted at the bench-scale method. The influence of different pH (3-9) and the effect of contact time (10-120 min) at the constant ultrasonic treatment (37 kHz) on degradation of organic matter were investigated. Since ultrasound is a cyclic sound pressure with a frequency greater than the upper limit of the human hearing range, this limit is approximately 20 kilohertz (20,000 hertz). In addition, the effect of ultrasonic treatment on the total solids (TS), volatile solids (VS), sludge volume index (SVI) and specific resistance to filtration (SRF) were determined. Results: The results of this study showed that the release of soluble chemical oxygen demand (SCOD) in the supernatant and SRF were in the range of 127.9-831 mg/L and 12.48-36.55 m/kg at 10 to 120 min ultrasonic contact time, respectively. In addition, TS and VS decreased from 57.98 and 56.31 to 52.69 and 49.87 mg/L, respectively. Despite the significant reduction in the solids, there was no considerable variation in SVI. Conclusions: This method can be used as a pretreatment method for the treatment of the sewage sludge. Moreover, a complementary treatment is necessary to reach the standard limit.