Dried sludges and sludge-based chars for H2S removal at low temperature: influence of sewage sludge characteristics

Impact of temperature and residence time on sewage sludge pyrolysis for combined carbon sequestration and energy production

Environmental challenges related to sewage sludge call for urgent sustainable management of this resource. Sludge pyrolysis might be considered as a sustainable technology and is anticipated to support measures for mitigating climate change through carbon sequestration. The end products of the process have various applications, including the agricultural utilization of biochar, as well as the energy exploitation of bio-oil and syngas. In this research, sewage sludge was pyrolyzed at 500 °C, 600 °C, 750 °C, and 850 °C. At each temperature, pyrolysis was explored at 1hr, 2hrs, and 3hrs residence times. The ratio (H/Corg)at was tapped to imply organic carbon stability and carbon sequestration potential. Optimum operating conditions were achieved at 750 °C and 2hrs residence time. Produced biochar had (H/Corg)at ratio of 0.54, while nutrients' contents based on dry weight were 3.99%, 3.2%, and 0.6% for total nitrogen (TN), total phosphorus (TP), and total potassium (TK), respectively. Electrical conductivity of biochar was lesser than the feed sludge. Heavy metals in biochar aligned with the recommended values of the International Biochar Initiative. Heat content of condensable and non-condensable volatiles was sufficient to maintain the temperature of the furnace provided that PYREG process is considered. However, additional energy source is demanded for sludge drying.

Solubility and Thermodynamic Parameters of H2S/CH4 in Ionic Liquids Determined by 1H NMR

Natural gas remains an important global source of energy. Usually, sour gas from the well or refinery stream contains H2S among other contaminants that should be removed to fulfill permissible standards of use. Despite the use of different gas-liquid sour gas upgrading technologies, ionic liquids (ILs) have been recognized as promising materials to remove H2S from sour gas. However, data concerned with thermodynamic solution functions of H2S in ILs have scarcely been reported in the literature. In this work, solution 1H NMR spectroscopy was employed for quantifying H2S soluble in [BMIM][Cl] and for gaining a better understanding of the H2S-IL interaction. Experiments were carried out in a Young-Tap NMR tube containing a saturated solution of H2S/CH4/[BMIM][Cl] and recording spectra from 298 to 333 K. The thermodynamic solution functions, determined from the Van't Hoff equation, showed that solubility of the H2S in the [BMIM][Cl] is an exothermic gas-liquid physisorption process (ΔsolH° = -66.13 kJmol-1) with a negative entropy change (ΔsolS° = -168.19 JK-1 mol-1). 1H NMR spectra of the H2S/[BMIM][Cl] solution show a feature of strong solute-solvent interactions. However, solubility enthalpy is a fifth of the H-S bond energy value. Results from 1H NMR spectroscopy also agree with those from the bench dynamic experiments.

The efficiency and mechanism of humidity in alleviating CO2 inhibition on H2S adsorption to straw biochars

Adsorption tests were conducted to clarify the impact of carbon dioxide (CO₂) on hydrogen sulfide (H₂S) removal to straw biochars and the role of humidity in affecting the CO₂ impact. When straw biochars were dry, CO₂ proved significantly detrimental to their H₂S adsorption, regardless of the CO₂ contents. In contrast, when adjusting the humidity of the biochars to 20%, the presence of CO₂ promoted the conversion of H₂S into sulfites, though still inhibited the generation of elemental sulfur, through which the original negative CO₂ impact was nearly compensated. The presence of low to medium contents of CO₂ even slightly improved the adsorption capacity and extended the breakthrough time. This phenomenon was ascribed to a favorable carbon surface environment for H₂S dissociation and oxidation, created from the reactions of the major minerals (Ca and Mg) with CO₂ and water. To sum up, the CO₂ inhibition on the H₂S adsorption to biochars was ascribed to the competition of CO₂ for the active sites; however, humidity induced a series of CO₂-participated chemical reactions between H₂S and the minerals, sufficiently alleviating the CO₂ inhibition. The results also highlight the necessity to recognize the most critical biochar properties or an efficient balance of crucial biochar properties in achieving an optimal H₂S removal when CO₂ is present in the syngas.

Speciation Evolution of Phosphorus and Sulfur Derived from Sewage Sludge Biochar in Soil: Ageing Effects

Phosphorus (P) and sulfur (S) are usually involved simultaneously in the immobilization of heavy metals in sewage sludge during pyrolysis, and thus their speciation in sewage sludge-derived biochar (SSB) profoundly affects the recycling of the nutrients and the environmental risks of sewage sludge. Here, we investigated the speciation evolution of P and S in SSB induced by ageing processes in soil using X-ray absorption near edge structure spectroscopy. Results showed that Ca-bound compounds like hydroxyapatite dominated the P forms, while over 60% of S existed as reduced inorganic sulfides in the SSB. The stable Ca-associated P species in SSB tended to be transformed gradually into relatively soluble species during ageing in soil. The speciation composition of S in SSB remained almost unaffected when aged in pot soils, whereas about 33.6% of reduced sulfides were transformed into oxidized species after 1-year ageing in field soils. SSB significantly increased the proportion of sulfides and the contents of available P and S in the amended soil but showed relatively weak effects on the speciation distribution of P in the soil because of their similar compositions. These findings provide insights into biogeochemistry of nutrients and behaviors of heavy metals in SSB after its application to the soil environments.

Sewage sludge ash-derived materials for H2S removal from a landfill biogas

H₂S removal is a key step for biogas cleaning because this component can lead to premature corrosion of the equipment and its cleaning has a significant cost. The aim of the present work was to assess the use of sewage sludge derived ash (SSA)-materials for H₂S removal from a landfill biogas. SSA and mixtures made with SSA, activated carbon (AC) and sand were tested for H₂S removal. The best removal efficiency was obtained with the mixture 80%m SSA and 20%m AC, while SSA alone was not a good adsorbent under tested experimental conditions. The materials characterization helped the adsorption mechanism understanding. Indeed, results highlighted that SSA presence stabilizes the pH on a basic range, favorable for H₂S dissociation into HS^- then its chemisorption. On the other hand, with the microporosity of AC, the contact surface between H₂S and oxygen was sufficiently large for chemisorption kinetics. It also appeared that the mixture with sand and AC adorbs non selectively H₂S but also other volatile organic pollutants present in biogas. Contrariwise, with SSA/AC mixtures, H₂S seems to be selectively chemisorbed.

Capture of toxic gases in MOFs: SO2, H2S, NH3 and NO x

MOFs are promising candidates for the capture of toxic gases since their adsorption properties can be tuned as a function of the topology and chemical composition of the pores. Although the main drawback of MOFs is their vulnerability to these highly corrosive gases which can compromise their chemical stability, remarkable examples have demonstrated high chemical stability to SO2, H2S, NH3 and NO x . Understanding the role of different chemical functionalities, within the pores of MOFs, is the key for accomplishing superior captures of these toxic gases. Thus, the interactions of such functional groups (coordinatively unsaturated metal sites, μ-OH groups, defective sites and halogen groups) with these toxic molecules, not only determines the capture properties of MOFs, but also can provide a guideline for the desigh of new multi-functionalised MOF materials. Thus, this perspective aims to provide valuable information on the significant progress on this environmental-remediation field, which could inspire more investigators to provide more and novel research on such challenging task.

Effects of chemical modification on physicochemical properties and adsorption behavior of sludge-based activated carbon

This study aimed to explore the adsorption performance of sludge-based activated carbon (SBC) towards dissolved organic matters (DOMs) removal from sewage, and investigated the modification effect of different types of chemicals on the structure of synthesized SBC. Waste activated sludge (WAS) was used as a carbon source, and HCl, HNO₃, and NaOH were used as different types of chemicals to modify the SBC. With the aid of chemical activation, the modified SBC showed higher adsorption performances on DOMs removal with maximum adsorption of 29.05 mg/g and second-order constant (k) of 0.1367 (L/mol/sec) due to the surface elution of ash and minerals by chemicals. The surface elemental composition of MSBC suggested that the content of C-C and C-O functional groups on the surface of modified sludge-based activated carbon (MSBC) played an important role on the adsorption capacities of MSBC towards DOMs removal in sewage. Additionally, the residual molecular weight of DOMs in sewage was investigated using a 3-dimension fluorescence excitation-emission matrix (3D-EEM) and high-performance size exclusion chromatography (HP-SEC). Results showed that the chemical modification significantly improved the adsorption capacity of MSBC on humic acids (HA) and aromatic proteins (APN), and both of NaOH-MSBC and HCl-MSBC were effective for a wide range of different AMW DOMs removal from sewage, while the HNO₃-MSBC exhibited poorly on AMW organics of 2,617 Da and 409 Da due to the reducing content of macropore. In brief, this study provides reference values for the impact of the chemicals of the activation stage before the SBCs application.

Effect of temperature on the sulfur fate during hydrothermal carbonization of sewage sludge

To understand the effect of reaction temperature on sulfur during hydrothermal carbonization (HTC) of sewage sludge (SS), seven group of temperature (180-300 °C) were chosen to investigate the distributions and evolution of sulfur-containing compounds in hydrochar and the liquid products. Elemental analysis, X-ray photoelectron spectroscopy (XPS), and X-Ray powder diffraction (XRD) were used to characterize the distribution of sulfur in hydrochar. The concentrations of sulfate ions and sulfide were determined in the liquid sample. The experimental results showed that as the temperature increased, the O/C ratio decreased because of the improved carbonization degree of SS. After hydrothermal carbonization, 90% of the sulfur in SS remained in hydrochar. As the temperature increased, the amount of sulfur in the liquid, mainly in the form of sulfate ions, tended to decrease. However, the experimental results for the gas phase were the opposite of the liquid phase.

Relationship between the physicochemical properties of sludge-based carbons and the adsorption capacity of dissolved organic matter in advanced wastewater treatment: Effects of chemical conditioning

Pyrolysis carbonisation is a promising technology to convert organic waste into valuable carbon-based materials. However, sludge is generally highly compressible and difficult to dewater because of its high concentrations of biopolymers; the bound water of sludge is trapped in a network composed of biopolymers. Therefore, chemical conditioning is an indispensable step for improving sludge dewaterability performance. In the present work, the effects of different chemical conditioning agents (polymeric aluminium chloride (PACl), iron(III) chloride (FeCl₃), KMnO₄-Fe(II) and Fenton's reagent) on the physicochemical properties of sludge-based carbons (SBCs) were systematically studied and the SBCs were further used in advanced wastewater treatment. The adsorption mechanisms of dissolved organic matters (DOMs) by different SBCs were also investigated. The results showed that conditioning with KMnO₄-Fe(II) and Fenton's reagent improved the specific surface area of the SBCs, whereas inorganic salt flocculation conditioning reduced the porosity of the SBCs. In addition, we found that the Fenton-SBC and Mn/Fe-SBC performed better than the other investigated SBCs in the removal of organic compounds from secondary effluent and that the pseudo-second-order kinetic model could better describe the process of DOMs adsorption by all of the investigated SBCs. Moreover, three-dimensional fluorescence excitation-emission matrix spectroscopy in combination with an analysis of the physical and chemical fractionation of DOMs showed that all of the SBCs performed well in the adsorption of aromatic substances, hydrophobic acids and hydrophobic neutrals, whereas the Mn/Fe-SBC and Fenton-SBC performed better than the other SBCs in the removal of weakly hydrophobic acids.

A review on the removal of hydrogen sulfide from biogas by adsorption using sorbents derived from waste

Biogas is a vital renewable energy source that could play an effective role in fulfilling the world’s energy demand, not only in heat and power generation but also as a vehicle fuel in the future. Unfortunately, due to impurities, biogas requires a series of upgrading steps, which affects its economics and sustainability. Hydrogen sulfide (H2S) is one of the impurities that economically and environmentally hinder the biogas utilization as a source of energy. H2S removal from biogas using different technologies was extensively studied and established. One of such technology is adsorption. Adsorption by solid sorbents is considered as a suitable removal technique for toxic gases such as H2S because of its simplicity, easy handling, and environmental friendly sorbents. In this review, the utilization of waste material-based sorbent for H2S removal was appraised. Other gaseous components of biogas such as siloxanes, CO2, etc., are out of the scope of this work. The potential and effectiveness of the waste-derived sorbents, either raw waste or modified waste, were summarized in terms of its characteristics, suitability, and sustainability. The review provides an insightful analysis of different types of wastes such as sewage sludge, food waste, forestry waste, fly ash, and industrial wastes as an alternative to commercial adsorbents to adsorb H2S gas. Based on the analysis, it was concluded that if these sorbents are to be successfully commercialized, its economic analysis, regeneration conditions, and potential utilization of the spent sorbents has to be further exploited. Nevertheless, there is a great prospectus in the future for these waste materials to be utilized as sorbents for H2S removal.

Selective adsorption and bioavailability relevance of the cyclic organics in anaerobic pretreated coal pyrolysis wastewater by lignite activated coke

This study originally investigated the selective adsorption of cyclic organics in APCPW by LAC, corresponding to the change of the bioavailability. As a product from low rank coal, LAC showed more oxygen (O)-containing groups and mesoporous structure than PAC. Adsorption mechanisms were analyzed by equilibrium isotherms and kinetics models combined with physicochemical properties of adsorbent and adsorbates. The results indicated that selectivity of LAC was dominated by chemical interaction and its mesoporous, and was enhanced by hydrophobicity of adsorbates. In addition, PAC and LAC were applied for the treatment of APCPW. Compared with PAC, LAC adsorption exhibited superior removal efficiency of Tph, TOC and TN at 85.90%, 91.15% and 51.64%, respectively. Furthermore, preferential adsorption of biotoxic and bioresistant cyclic organics by LAC was further proved by GC-MS analysis, resulting in increased bioavailability of APCPW. Specifically, LAC exerted sustained detoxication capacity until 86.50% reduction of TU by D. magna evaluation, and lowered toxicity rank (TU = 4.51, classIII) to T. pyriformis than that after PAC adsorption (TU > 10, ClassIV). Meanwhile, biodegradability was also improved by 9.17% after LAC adsorption. Lastly, LAC would exhibit great economic benefits as an alternative for PAC in subsequent process after anaerobic pretreatment.

Visible Light Driven Organic Pollutants Degradation with Hydrothermally Carbonized Sewage Sludge and Oxalate Via Molecular Oxygen Activation

Converting sewage sludge into functional environmental materials has become an attractive sewage sludge disposal route. In this study, we synthesize a sewage sludge-based material via a facile one-pot hydrothermal carbonization method and construct a visible light molecular oxygen activation system with hydrothermally carbonized sewage sludge (HTC-S) and oxalate to degrade various organic pollutants. It was found that iron species of HTC-S could chelate with oxalate to generate H₂O₂ via molecular oxygen activation under visible light, and also promote the H₂O₂ decomposition to produce ^•OH for the fast organic pollutants degradation. Taking sulfadimidine as the example, the apparent degradation rate of HTC-S/oxalate system was almost 5-20 times that of iron oxides/oxalate system. This outstanding degradation performance was attributed to the presence of iron-containing clay minerals in HTC-S, as confirmed by X-ray diffraction measurements and Mössbauer spectrometry. In the oxalate solution, these iron-containing clay minerals could be excited more easily than common iron oxides under visible light, because the silicon species strongly interacted with iron species in HTC-S to form Fe-O-Si bond, which lowered the excitation energy of Fe-oxalate complex. This work provides an alternative sewage sludge conversion pathway and also sheds light on the environmental remediation applications of sewage sludge-based materials.

Three-dimensional hierarchical porous sludge-derived carbon supported on silicon carbide foams as effective and stable Fenton-like catalyst for odorous methyl mercaptan elimination

The poor reusability of catalysts and secondary pollution are critical issues for sulfur-containing volatile organic compounds (S-VOCs) removal. In this paper, a three-dimensional (3D) hierarchical porous sludge-derived carbon supported on silicon carbide foams (SiC) has been fabricated for deep decomposition of S-VOCs under ambient conditions. The sludge-derived Fenton-like catalyst has been confirmed to be hierarchical 3D porous structure based on detailed characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Nitrogen adsorption-desorption measurements and Raman spectroscopy. Significantly, the catalyst after KOH activation (SC_FeK-SiC) shows excellent catalytic decomposition of methyl mercaptan (CH₃SH) with almost complete CH₃SH oxidation into sulfate using hydrogen peroxide as an oxidant under ambient conditions. This catalyst also possesses relative low iron dissolution and excellent cycling performance. The efficient catalytic ability of SC_FeK-SiC can be attributed to SiC foam functioned as a stable 3D macroporous skeleton, in which the porous sludge-derived carbon immobilizes the active iron species and promotes the efficient capture of gaseous CH₃SH, thus facilitating the decomposition of CH₃SH by generating reactive species, specifically ·OH. The reaction mechanism was systematically investigated. Herein, the design of the porous sludge-derived carbonaceous Fenton-like catalyst paves an avenue for efficient VOCs treatment and rational sludge disposal.

Insight into the effects of biochar as adsorbent and microwave receptor from one-step microwave pyrolysis of sewage sludge

The effect of biochar, derived from one-step microwave pyrolysis of sewage sludge (OMPSS), on the removal of industrial wastewater (eosin and safranine T) was investigated in this study. Meanwhile, the multiple-reuse potential of biochar as microwave receptor to raise the pyrolysis temperature was also tested during the pyrolysis process. The results showed that OMPSS prepared adsorbents had excellent adsorption performance, achieving the highest removal efficiencies of 97.3 and 95.9% for eosin and safranine T, respectively. Further analysis indicated that this was due to its appropriate porous structure and surface chemistry characteristics, where the S_BET and pore volume of adsorbent AC-1 reached 459 m²/g and 0.23 cm³/g, respectively. The multiple reuses of biochar adsorbents after five times as microwave receptor was feasible, where the pyrolysis temperature could increase sharply from room temperature to 800 °C within 5 min. The mechanism analysis revealed that the limiting stage of adsorption was chemical sorption. This research provided an alternative way for the preparation of functional adsorbent and microwave receptor. Graphical abstract ᅟ.

Effect of potassium hydroxide activation in the desulfurization process of activated carbon prepared by sewage sludge and corn straw

Series sludge straw-based activated carbons were prepared by sewage sludge and corn straw with potassium hydroxide (KOH) activation, and the desulfurization performance of activated carbons was studied. To obtain the best desulfurization performance, the optimum ratio between the raw materials and the activator was investigated. The results showed that when the mass ratio of sewage sludge, corn straw, and KOH was 3:7:2, the activated carbon obtained the best breakthrough and saturation sulfur sorption capacities, which were 12.38 and 5.74 times, respectively, those of samples prepared by the nonactivated raw materials. The appropriate KOH could improve the microporosity and alkaline groups, meanwhile reducing the lactone groups, which were all beneficial to desulfurization performance. The chemical adsorption process of desulfurization can be simplified to four main steps, and the main desulfurization products are elemental sulfur and sulfate.

IMPLICATIONS

Sewage sludge (SS) and corn straw (CS) both have great production and wide distribution and are readily available in China. Much attention has been paid on how to deal with them effectively. Based on the environment protection idea of waste treatment with waste and resource recycling, low-cost adsorbents were prepared by these processes. The proposed method can be expanded to the municipal solid waste recycling programs and renewable energy plan. Thus, proceeding with the study of preparing activated carbon by SS and straw as a carbon-based dry desulfurization agent could obtain huge social, economic, and environmental benefits.

One-step synthesis of silicon carbide foams supported hierarchical porous sludge-derived activated carbon as efficient odor gas adsorbent

Hierarchical porous sludge-derived activated carbon coated on macroporous silicon carbide (SiC) foams substrate has been facilely fabricated via a simple one-step strategy by utilizing sludge as carbon source, and jointly using zinc chloride and hexadecanol as pore forming agents. The sludge-derived carbon has been confirmed to be hierarchical macro-meso-microporous structure based on detailed characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectra and nitrogen adsorption-desorption measurement. The adsorption tests showed that the hierarchical porous sludge-derived activated carbon fabricated by one-step pore-forming (zinc chloride and hexadecanol microemulsion mixture) possesses excellent adsorption capacity (259.9mgg^-1, breakthrough time reach 90min and saturation end-time up to 140min) of methyl mercaptan (CH₃SH). The excellent adsorption performance can be attributed to the macroporous SiC foam skeleton and the mesopores channel formed by nonionic surfactant hexadecanol micelles, as well as the micropores activated by ZnCl₂ as odor capture sites. The proposed pore-forming strategy paves an avenue for the sludge disposal and even the development of bio-derived materials.

Performance evaluation of zero-valent iron nanoparticles (NZVI) for high-concentration H2S removal from biogas at different temperatures

The removal performance of high-concentration H₂S (ca. 10 000 ppm) from simulated biogas by zero-valent iron nanoparticles (NZVI), with the majority of the particles in the size range of 60–150 nm, at different reaction temperatures (room temperature, 100 °C, 200 °C and 250 °C) were evaluated using a custom-designed quartz fixed-bed reactor. The results showed that the H₂S removal capacities of NZVI were quite limited at room temperature and 100 °C, being 12.56 and 14.77 mg H₂S gNZVI⁻¹, respectively. However, these values increased significantly to 391.02 (200 °C) and 488.95 (250 °C) mg H₂S gNZVI⁻¹. Scanning electron microscopy analysis showed that the products of the NZVI–H₂S reaction aggregated to form irregular polygonal-shaped structures. The main X-ray diffraction pattern peaks of the product matched well with troilite, and no pyrite was observed. The deconvolution of the X-ray photoelectron spectrometry peaks showed the presence of monosulphide (S²⁻) and disulphide (S₂²⁻) in the product, in which 36% of the sulphur existed as monosulphide and 64% as disulphide. It is proposed that the effective removal of hydrogen sulphide by NZVI at elevated temperatures can be attributed to the combination of nano-constituents, oxide shell and underlying Fe core to produce FeS similar to troilite and amorphous FeS₂.

Performances of zero-valent iron nanoparticles for high-concentration H₂S removal from biogas at different temperatures were evaluated.

Facile preparation of a novel catalytic particle electrode from sewage sludge and its electrocatalytic performance in three-dimensional heterogeneous electro-Fenton

A novel type of catalytic particle electrode (SAC-Fe) was developed from sewage sludge and iron sludge via a facile method. The catalytic particle electrodes (CPEs) were also supposed to be heterogeneous catalyst for electro-Fenton (EF). The CPEs were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). SAC-Fe showed superior porous structure and higher adsorption capacity and catalytic activity than Fe₃O₄ magnetic nanoparticles. Catechol and total organic carbon (TOC) removal efficiency can reach 96.7% and 88.3% after three-dimensional (3D) EF with SAC-Fe as CPEs. A possible mechanism was deduced based on adsorption tests and radicals detection. Meanwhile, the stability and reusability of the CPEs were evaluated.

Removal of Phenolic Compounds from Water Using Sewage Sludge-Based Activated Carbon Adsorption: A Review

Due to their industrial relevance, phenolic compounds (PC) are amongst the most common organic pollutants found in many industrial wastewater effluents. The potential detrimental health and environmental impacts of PC necessitate their removal from wastewater to meet regulatory discharge standards to ensure meeting sustainable development goals. In recent decades, one of the promising, cost-effective and environmentally benign techniques for removal of PC from water streams has been adsorption onto sewage sludge (SS)-based activated carbon (SBAC). This is attributed to the excellent adsorptive characteristics of SBAC and also because the approach serves as a strategy for sustainable management of huge quantities of different types of SS that are in continual production globally. This paper reviews conversion of SS into activated carbons and their utilization for the removal of PC from water streams. Wide ranges of topics which include SBAC production processes, physicochemical characteristics of SBAC, factors affecting PC adsorption onto SBAC and their uptake mechanisms as well as the regeneration potential of spent SBAC are covered. Although chemical activation techniques produce better SBAC, yet more research work is needed to harness advances in material science to improve the functional groups and textural properties of SBAC as well as the low performance of physical activation methods. Studies focusing on PC adsorptive performance on SBAC using continuous mode (that are more relevant for industrial applications) in both single and multi-pollutant aqueous systems to cover wide range of PC are needed. Also, the potentials of different techniques for regeneration of spent SBAC used for adsorption of PC need to be assessed in relation to overall economic evaluation within realm of environmental sustainability using life cycle assessment.

Role of carboxylic acid groups in the reduction of nitric oxide by carbon at low temperature, as exemplified by graphene oxide

Graphene oxide (GO) was utilized to investigate the role of carboxylic acid groups in the reduction of nitric oxide (NO) for the first time. As a result, GO with sufficient carboxylic acid groups reduced 45% of NO at 100 °C. However, GO without these oxygen-containing groups barely reduced NO (lower than 5%) under the same conditions. After reduction of NO, the carboxylic acid group content on GO decreased from 8.32 to 5.22 mmol g^-1. Simultaneously, the anhydride group content increased from 0.14 to 0.28 mmol g^-1. FTIR spectroscopy also indicated that the carboxylic acid groups transformed into anhydride and lactone groups. Moreover, both transient kinetics and TG-MS studies demonstrated that reactive intermediates formed during the reaction between NO and GO at 100 °C. Based on these results, it was proposed that the carboxylic acid groups participated in NO reduction by consumption and regeneration. This mechanism explains why carbon is usually an effective reductant and catalyst support for NO removal at low temperature.

Investigation on the removal of H2S from microwave pyrolysis of sewage sludge by an integrated two-stage system

In this study, an integrated two-stage system, including the in-situ catalytic microwave pyrolysis (ICMP) and subsequent catalytic wet oxidation (CWO) processes, was proposed to remove H₂S released from microwave-induced pyrolysis of sewage sludge. The emission profile and H₂S removal from the pyrolysis of raw sewage sludge (SS) and sewage sludge spiked with conditioner CaO (SS-CaO) were investigated. The results showed that CaO played a positive role on sulfur fixation during the pyrolysis process. It was found that SS-CaO (10 wt.%) contributed to about 35% of H₂S removal at the first stage (ICMP process). Additionally, the CWO process was demonstrated to have promising potential for posttreatment of remaining H₂S gas. At the Fe³⁺ concentration of 30 g/L, the maximum H₂S removal efficiency of 94.8% was obtained for a single Fe³⁺/Cu²⁺ solution. Finally, at the pyrolysis temperature of 800 °C, 99.7% of H₂S was eliminated by the integrated two-stage system meeting the discharge standard of China. Therefore, the integrated two-stage system of ICMP + CWO may provide a promising strategy to remove H₂S dramatically for the biomass pyrolysis industry.

Release of hydrogen sulfide during microwave pyrolysis of sewage sludge: Effect of operating parameters and mechanism

The effects of sludge characteristics, pyrolysis temperature, heating rate and catalysts on the release of H₂S and mechanism of H₂S formation during sludge pyrolysis were investigated in a microwave heating reactor (MHR). The evolution of sulfur-containing compounds in the pyrolysis chars obtained at temperature range of 400-800°C was characterized by XPS. For a given temperature, the maximum concentration of H₂S appeared at moisture content of 80%. Compared to the influence of heating rate on the H₂S yields, pyrolysis temperature and catalyst played a more significant role on the release of H₂S during microwave pyrolysis process. The H₂S concentration increased with increasing temperature from 400°C to 800°C while decreased with increasing heating rate. Both the Nickel-based catalyst and Dolomite displayed significant desulfurization effect and Ni-based catalyst exhibited the larger desulfurization capability than that of Dolomite. The organic sulfur compounds accounted for about 60% of the total sulfur in the sludge which was the main reason for the formation of H₂S. The mechanism analysis indicated that the cleavage reactions of mercaptan and aromatic-S compounds at temperatures below 600°C and the cracking reaction of sulfate above 700°C respectively were responsible for the H₂S release during sludge pyrolysis.

Sulfur Transformation during Microwave and Conventional Pyrolysis of Sewage Sludge

The sulfur distributions and evolution of sulfur-containing compounds in the char, tar and gas fractions were investigated during the microwave and conventional pyrolysis of sewage sludge. Increased accumulation of sulfur in the char and less production of H₂S were obtained from microwave pyrolysis at higher temperatures (500-800 °C). Three similar conversion pathways were identified for the formation of H₂S during microwave and conventional pyrolysis. The cracking of unstable mercaptan structure in the sludge contributed to the release of H₂S below 300 °C. The decomposition of aliphatic-S compounds in the tars led to the formation of H₂S (300-500 °C). The thermal decomposition of aromatic-S compounds in the tars generated H₂S from 500 to 800 °C. However, the secondary decomposition of thiophene-S compounds took place only in conventional pyrolysis above 700 °C. Comparing the H₂S contributions from microwave and conventional pyrolysis, the significant increase of H₂S yields in conventional pyrolysis was mainly attributed to the decomposition of aromatic-S (increasing by 10.4%) and thiophene-S compounds (11.3%). Further investigation on the inhibition mechanism of H₂S formation during microwave pyrolysis confirmed that, with the special heating characteristics and relative shorter residence time, microwave pyrolysis promoted the retention of H₂S on CaO and inhibited the secondary cracking of thiophene-S compounds at higher temperatures.

Kinetics and the mass transfer mechanism of hydrogen sulfide removal by biochar derived from rice hull

The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H2S) from gas phase. The surface area and pH of the biochar were compared. The biochar derived from rice hull was evaluated for its abilities to remove hydrogen sulfide (H2S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperature has great influence on the adsorption of H2S. At the different pyrolysis temperature, the H2S removal efficiency of rice hull-derived biochar was different. The adsorption capacities of biochar were 2.09 mg·g(-1), 2.65 mg·g(-1), 16.30 mg·g(-1), 20.80 mg·g(-1), and 382.70 mg·g(-1), which their pyrolysis temperatures were 100 °C, 200 °C, 300 °C, 400 °C and 500 °C respectively. Based on the Yoon-Nelson model, it analyzed the mass transfer mechanism of hydrogen sulfide adsorption by biochar.

IMPLICATIONS

The paper focuses on the biochar derived from rice hull-removed hydrogen sulfide (H2S) from gas phase. The surface area and pH of the biochar were compared. The different pyrolysis temperatures have great influence on the adsorption of H2S. At the different pyrolysis temperatures, the H2S removal efficiency of rice hull-derived biohar was different. The adsorption capacities of biochar were 2.09, 2.65, 16.30, 20.80, and 382.70 mg·g(-1), and their pyrolysis temperatures were 100, 200, 300, 400, and 500 °C, respectively. Based on the Yoon-Nelson model, the mass transfer mechanism of hydrogen sulfide adsorption by biochar was analyzed.

Self-heating of dried industrial tannery wastewater sludge induced by pyrophoric iron sulfides formation

Similarly to many powders of solids, dried sludge originated from tannery wastewater may result in a self-heating process, under given circumstances. In most cases, it causes a moderate heating (reaching 70-90°C), but larger, off-design residence times in the drier, in a suboxic atmosphere, extremely reactive solids can be produced. Tannery waste contains several chemicals that mostly end up in the wastewater treatment sludge. Unexpected and uncontrolled self heating could lead to a combustion and even to environmental problems. Elaborating on previous studies, with the addition of several analytical determinations, before and after the self-heating, we attempted to formulate a mechanism for the onset of heating. We demonstrated that the system Fe/S/O has been involved in the process. We proved that the formation of small quantities of pyrophoric iron sulfides is the key. They are converted to sulfated by reaction with water and oxygen with exothermic processes. The pyrite/pyrrhotite production depends on the sludge drying process. The oxidation of sulfides to oxides and sulfates through exothermic steps, reasonably catalyzed by metals in the sludge, occurs preferentially in a moist environment. The mechanism has been proved by reproducing in the laboratory prolonged heating under anoxic/suboxic atmosphere.

Adsorption of hydrogen sulfide by biochars derived from pyrolysis of different agricultural/forestry wastes

The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different biochars derived from agricultural/forestry wastes through pyrolysis at various temperatures (100 to 500 ºC) were investigated. In this study, the H₂S breakthrough capacity was measured using a laboratory-characterized using pH and Fourier transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H2S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface. Certain threshold ranges of the pyrolysis temperature (from 100 to 500 ºC) and pH of the surface are presented. It also concluded that the sorption capacity (for removing H₂S) of rice hull-derived biochar is the largest in three biochars (camphor-derived biochar, rice hull-derived biochar, and bamboo-derived biochar). These observations will be helpful in designing biochar as engineered sorbents for the removal of H₂S.

IMPLICATIONS

This paper focuses on the adsorption of hydrogen sulfide (H₂S) by biochars derived from wastes. The characteristics and mechanisms of hydrogen sulfide (H₂S) adsorption on three different boichars derived from agricultural/forestry wastes through pyrolysis at various temperatures were investigated. In this study, the H₂S breakthrough capacity was measured using laboratory characterization with pH and Fourier-transform infrared spectroscopy analysis. The results obtained demonstrate that all biochars were effective in H₂S sorption. The sorption capacity of the biochar for H₂S removal is related to the pyrolysis temperature and pH of the surface.

Typical MSW odor abatement using sludge derived carbon prepared by activation with Fenton’s reagent and NaClO

Sludge derived carbon (SBC) is a potential resource way for sewage sludge, and chemical pre-treatment is a necessary activation method for the improvement of the SBC quality.

Characterization of char from slow pyrolysis of sewage sludge

The effects of final pyrolysis temperature Tend from 300 ºC to 550 ºC, heating rates β of 2 ºC/min, 3 ºC/min and 5 ºC/min, retention time RT from 45 min to 90 min, and the moisture content MC from 0 to 70% on characteristics of the pyrolysis char from sewage sludge were investigated using a tube furnace in this study. The resulting chars were characterized by sorption of nitrogen (surface area and pore volume). Their adsorption characteristics were evaluated via iodine value and methylene blue value. Either the pore structures or adsorption characteristics depend on the pyrolysis processing and moisture content of the sludge precursors. In terms of iodine value and surface area of the char, Tend of 450 ºC, RT of 75 min and β of 3 ºC/min proved the optimum combination of pyrolysis parameters. The chars have an undeveloped mesopore and macropore structure and a developed micropore structure. The sodium phenoxide adsorption equilibrium data fit well with the Langmuir model of adsorption, suggesting monolayer coverage of sodium phenoxide molecules at the surface of the char. Its adsorption mechanism is mainly physical in nature, enhanced by chemisorption.

Sewage-sludge-derived carbonaceous materials for catalytic wet hydrogen peroxide oxidation of m-cresol in batch and continuous reactors

In this study, four sewage-sludge-derived carbonaceous materials (SWs) were evaluated for their catalytic wet hydrogen peroxide oxidation (CWPO) performance of m-cresol in batch reactor and continuous reactor, respectively. The SWs were produced by carbonization (SW); carbonization with the addition of CaO (CaO-SW); HNO3 pretreatment (HNO3-SW) and steam activation (Activated-SW). The properties of SW catalysts were assessed by thermogravimetric analysis, Brunauer-Emmett-Teller, Fourier Transform Infrared Spectroscopy, X-ray Fluorescence, Scanning electron microscopy, energy dispersive X-ray analysis and zeta potential. The results showed that SW treated by HNO3 (HNO3-SW) had a high conversion of m-cresol in batch reactor and continuous reactor, respectively. Under the conditions of batch reaction (Cm-cresol = 100 mg L(-1), CH2O2 = 15.7 mmol L(-1), initial pH=7.0, 0.5 g L(-1) catalyst, 80°C, 180 min adsorption and 210 min oxidation), the conversion of m-cresol reached 100% and total organic carbon removal was 67.1%. It had a high catalytic activity and stability on the treatment of m-cresol in CWPO for more than 1100 h. Furthermore, a possible reaction mechanism for the oxidation of m-cresol to 2-methyl-p-benzoquinone by CWPO was proposed.

Adsorption characteristics and mechanism of sewage sludge-derived adsorbent for removing sulfonated methyl phenol resin in wastewater

Sulfonated methyl phenol resin (SMP) is one of the most popular organic additives in drilling fluid.

Surface modification of sewage sludge derived carbonaceous catalyst for m-cresol catalytic wet peroxide oxidation and degradation mechanism

Organic synthesis is used to investigate the degradation of m-cresol and the intermediates are identified by in situ NMR.

Design of a sorbent to enhance reactive adsorption of hydrogen sulfide

A series of novel zinc oxide-silica composites with three-dimensionally ordered macropores (3DOM) structure were synthesized via colloidal crystal template method and used as sorbents for hydrogen sulfide (H2S) removal at room temperature for the first time. The performances of the prepared sorbents were evaluated by dynamic breakthrough testing. The materials were characterized before and after adsorption using scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was found that the composite with 3DOM structure exhibited remarkable desulfurization performance at room temperature and the enhancement of reactive adsorption of hydrogen sulfide was attributed to the unique structure features of 3DOM composites; high surface areas, nanocrystalline ZnO and the well-ordered interconnected macroporous with abundant mesopores. The introduction of silica could be conducive to support the 3DOM structure and the high dispersion of zinc oxide. Moisture in the H2S stream plays a crucial role in the removal process. The effects of Zn/Si ratio and the calcination temperature of 3DOM composites on H2S removal were studied. It demonstrated that the highest content of ZnO could reach up to 73 wt % and the optimum calcination temperature was 500 °C. The multiple adsorption/regeneration cycles showed that the 3DOM ZnO-SiO2 sorbent is stable and the sulfur capacity can still reach 67.4% of that of the fresh sorbent at the fifth cycle. These results indicate that 3DOM ZnO-SiO2 composites will be a promising sorbent for H2S removal at room temperature.

Comparison of sewage sludge- and pig manure-derived biochars for hydrogen sulfide removal

Biochars derived from pig manure and sewage sludge were evaluated for their abilities to remove hydrogen sulfide (H2S) from gas phase. The pig manure biochar had higher capacities for H2S sorption than sewage sludge biochar in both dynamic and static systems, and moisture improves H2S removal. Increasing the biochar moisture to 25 wt% and 100 wt% in the static system increased the pig manure biochar removal capacities by 15.9% and 58.9%, respectively, compared to the dry biochar (0 wt% moisture). The sewage sludge biochar similarly increased the removal by 1.04 and 3.30 times for 25 wt% and 100 wt% moisture, respectively. The catalytic conversion to elemental S(0) and SO4(2)(-) was the main route of H2S removal. The complete oxidation of H2S into SO4(2)(-) mainly occurred on the biochar surface, while H2S underwent incomplete oxidation into elemental S(0) in the biochar pores. The SO4(2)(-) was the dominant form in both biochars, especially for the pig manure biochar which contained 53.9% of the total sulfur at 100 wt% moisture. The SO4(2)(-) was mainly present as CaSO4 precipitate in the sewage sludge biochar, while SO4(2)(-) in the pig manure biochar was mostly soluble (K, Na)2SO4. The results indicated the waste biomass can be converted into value-added biochar as a sorbent for H2S, especially at high moisture that promotes complete oxidation of H2S into SO4(2)(-). Strong alkalinity and rich inorganic minerals originated in the biochar play an important role in its high H2S sorption ability and the final sulfur forms.

Adsorption of hydrogen sulphide from aqueous solutions using modified nano/micro fibrillated cellulose

In the present study, microfibrillated cellulose (MFC) was modified by aminopropyltriethoxysilane (APS), hydroxy-carbonated apatite (HAP), or epoxy in order to produce novel nanostructured adsorbents for the removal of hydrogen sulphide (H2S) from the aqueous solutions. Structural properties of the modified MFC materials were examined using a scanning electron microscope, Fourier transform infrared spectroscopy and acid/base titration. These methods were used to verify the presence of nanostructures on the adsorbents surfaces as well as functionalities suitable for H2S adsorption. Adsorption of H2S by prepared adsorbents was investigated in batch mode under different experimental conditions, i.e., varying pH and H2S concentrations. H2S uptake was found to be 103.95, 13.38 and 12.73 mg/g by APS/MFC, HAP/MFC and epoxy/MFC, respectively from 80 mg/L H2S solution. The equilibrium data were best described by the Langmuir isotherm for HAP/MFC and APS/MFC and the Sips isotherm for epoxy/MFC.

On the understanding and control of the spontaneous heating of dried tannery wastewater sludge

We studied the spontaneous heating of dried sludge produced by treating wastewater mainly originating from tanneries. Heating up to burning has been observed in the presence of air and moisture, starting at ambient temperature. To understand and prevent the process we combined chemical and morphological analyses (ESEM) with thermal activity monitoring in insulated vessels. Selective additions of chemicals, either to amplify or depress the reactivity, have been used to investigate and identify both the chemical mechanism causing the sludge self-heating, and a prevention or a mitigation strategy. FeS additions accelerate the onset of reactivity, while S sustains it over time. On the contrary, Ca(OH)2, Na2CO3, NaHCO3, FeCl2, EDTA, NaClO can limit, up to completely preventing, the exothermic activity. All the experimental evidences show that the reactions supporting the dried sludge self-heating involve the Fe/S/O system. The total suppression of the reactivity requires amounts of additives that are industrially incompatible with waste reduction and economics. The best prevention requires reduction or removal of S and Fe from the dried solid matrix.

Low-cost adsorbent prepared from sewage sludge and corn stalk for the removal of COD in leachate

Sewage sludge (SS) with corn stalk (CS) was used to prepare SS-based activated carbon (SAC) by pyrolysis with ZnCl2. The effects of mixing ratio on surface area and pore size distribution, elemental composition, surface chemistry, and morphology were investigated. The results demonstrated that the addition of CS into SS samples improved the surface area (from 92 to 902 m(2)/g) and the microporosity (from 1.2 to 4.1%) of the adsorbents and, therefore, enhancing the adsorption performance. The removal of leachate chemical oxygen demand (COD) was also determined. It was found that the COD removal rate reached 85% at pH 4 with the SAC (90 wt% CS) dosage of 2% (g/mL) and an adsorption time of 40 min. The adsorption experimental data were fitted by both Langmuir and Freundlich adsorption isotherms. Long-chain alkanes and refractory organics were found in raw leachate, but could be removed by SAC largely.

Enhanced adsorptive removal of naphthalene intermediates from aqueous solution by introducing reed straw into sewage sludge-based activated carbon

The disposal of sewage sludge (SS) and reed straw (RS) has becoming a critical issue due to their rapid production. In this study, the SS-based activated carbon (SSC) was produced by introducing the RS as a component material. Properties including BET surface area, pore volume, surface chemical groups, and morphologies were characterized. The adsorption of 1-diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) and 2-Naphthol (2-Nap), which differs in their physicochemical properties, on as-prepared carbons were investigated. The overall adsorption was found to be jointly controlled by external mass transfer and intraparticle diffusion, and the optimal pH was found to be 5 due to their electrostatic attraction. Further study revealed that the SS- and RS-based carbons (SC and RSC, respectively) exhibited different adsorption behavior toward 1,2,4-Acid and 2-Nap. The calculated adsorption capacity from Langmuir–Freundlich model of SC and RSC for the two intermediates was 141.0, 84.6 mg g(-1) and 48.2, 110.2 mg g(-1), respectively, whereas their hybrid product (SSC) showed comparable capacity for 1,2,4-Acid (117.8 mg g(-1)), as well as higher capacity for 2-Nap (157.5 mg g-1). It was found that the presence of meso- or macropores facilitates the precipitation of mineral phases of inorganic substances during carbonization, attracting the molecules with polar functional groups, while the introduction of C-rich RS to SS enhances the adsorption of hydrophobic molecules

Influence of generated intermediates' interaction on heterogeneous Fenton's degradation of an azo dye 1-diazo-2-naphthol-4-sulfonic acid by using sludge based carbon as catalyst

Sewage sludge based carbons have recently been used as novel catalyst in heterogeneous Fenton's reactions to degrade azo dye molecules. The carbons, functioning as both catalyst and adsorbent, play an important role in pollutants elimination, especially for those simultaneously generated organic intermediates. Different factors, i.e., H2O2 concentration, may influence the type and properties of those intermediates and may have great impacts on their elimination through the interactions with catalysts' surface. Thus, techniques including Temperature Programmed Desorption-Mass Spectrometer (TPD-MS), N2 adsorption isotherm and Scanning Electron Microscope (SEM) were used to probe the ways of the interaction between oxidation products and catalyst by using different initial H2O2 concentrations (10 and 20mM). The higher Chemical Oxygen Demand (COD) removal with 20mM H2O2 was found to be related not only to the higher hydroxyl radicals but also the specific interactions between the intermediates and catalyst' surface. The deep oxidation occurred in the conditions with higher oxidant amount enhances the intermediates' adsorption on catalyst, thus increasing the COD removal by large margin. Simulated adsorption experiments by using six primarily formed intermediates and three deeply mineralized products on three different catalysts also confirmed the assumption. Results suggested close relations between adsorption capacities and intermediates' properties such as polar surface area and octanol-water partition coefficient.

Preparation of sewage sludge based activated carbon by using Fenton's reagent and their use in 2-naphthol adsorption

In this study, Fenton's reagents (H2O2/Fe(2+)) are used to activate raw sewage sludge for the preparation of the sludge based activated carbon. The effect of the amount of hydrogen peroxide addition on carbon's chemical composition, texture properties, surface chemistry and morphology are investigated. Choosing an appropriate H2O2 dosage (5 v%) (equivalent to 70.7 mM/(g VS)), it is possible to obtain a comparatively highly porous materials with SBET and the total pore volume being 321 m(2)/g and 0.414 cm(3)/g, respectively. Continuously increasing the oxidant ratio resulted in a decreased SBET value. Further adsorption experiments by using 2-naphthol as model pollutant revealed that the adoption followed a pseudo-second-order kinetics better than pseudo-first-order. The calculated adsorption capacity is 111.9 mg/g on the carbon with 5% H2O2 pretreatment while this value is just 51.5mg/g on carbons without any pretreatment.

A comparative study of aerobically digested and undigested sludge in preparation of magnetic chars and their application in 1-diazo-2-naphthol-4-sulfonic acid adsorption

In this work, two types of sewage-sludges, aerobically digested and undigested sewage sludge, were used as precursors in the preparation of chars with magnetic property. The two solids were characterized to establish their textural and chemical properties. Due to different elemental composition, chars from the digested sludge were found to contain zeolite-like minerals such as NaP1 zeolite, which enables its abilities of anion exchange, while chars from undigested sewage sludge exhibited a well-degreed graphite structure. 1-Diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) was used as a model pollutant to investigate its adsorption on prepared chars. The adsorption kinetics of 1,2,4-Acid onto both chars followed pseudo-second-order kinetics. The simulated Langmuir-Freundlich model illustrated that the equilibrium adsorption amount of 1,2,4-Acid was 102.8 and 105.3mg/g, respectively, at 303 K. The adsorption amount declined on digested chars, whereas kept stable on the other in the presence of sodium chloride, suggesting the diversity in adsorption behavior.

Adsorption and Fenton-like degradation of naphthalene dye intermediate on sewage sludge derived porous carbon

A sewage sludge derived porous carbon (SC), which was prepared by physicochemical activation and carbonization (600°C), was applied for the adsorption and degradation of 1-diazo-2-naphthol-4-sulfonic acid (1,2,4-Acid) in the presence of H(2)O(2) and the performance was compared to that of pure Fe(3)O(4) magnetic nanoparticles (MNPs). The prepared SC showed mesoporous structure with magnetic property, which made it favorable for solid-liquid separation application. Further experiments revealed that SC had a higher adsorption capacity and degradation efficiency of 1,2,4-Acid than bare Fe(3)O(4). The Langmuir and Freundlich model fitted the isotherm data and illustrated that the equilibrium adsorption amount of 1,2,4-Acid onto SC (95.1 mg g(-1)) was quadruple as large as that on Fe(3)O(4) (26.4 mg g(-1)). The subsequent degradation experiments were conducted at conditions (pH 5.0 in the presence of 15 mM H(2)O(2)) with regard to 1,2,4-Acid degradation efficiency and metal ions leach. The 120 min's treatment in SC/H(2)O(2) system achieved 94% of 1,2,4-Acid (from 150 mg L(-1) after adsorption equilibrium to 9 mg L(-1)) and 48.1% TOC reduction, far higher than the efficiency of 46% and 24.3% by using Fe(3)O(4) MNPs. Further analysis evidenced the co-catalytic effect of iron, carbon, silicon and aluminum, which existed in large quantities in sludge derived SC. The carbonaceous phase along with silica contributes to an increase in the dispersion of catalytic centers and an adsorbent to concentrate organic pollutant whereas the iron oxide as well as alumina provides the catalytic centers for a Haber-Weiss initiated reactions.

Removal of antibiotics from water using sewage sludge- and waste oil sludge-derived adsorbents

Sewage sludge- and waste oil sludge-derived materials were tested as adsorbents of pharmaceuticals from diluted water solutions. Simultaneous retention of eleven antibiotics plus two anticonvulsants was examined via batch adsorption experiments. Virgin and exhausted adsorbents were examined via thermal and FTIR analyses to elucidate adsorption mechanisms. Maximum adsorption capacities for the 6 materials tested ranged from 80 to 300 mg/g, comparable to the adsorption capacities of antibiotics on various activated carbons (200-400 mg/g) reported in the literature. The performance was linked to surface reactivity, polarity and porosity. A large volume of pores similar in size to the adsorbate molecules with hydrophobic carbon-based origin of pore walls was indicated as an important factor promoting the separation process. Moreover, the polar surface of an inorganic phase in the adsorbents attracted the functional groups of target molecules. The presence of reactive alkali metals promoted reaction with acidic groups, formation of salts and their precipitation in the pore system.