Pharmaceutical load in sewage sludge and biochar produced by hydrothermal carbonization

Comprehensive assessment of cow manure hydrothermal treatment products for land application and energy recovery

In this study, cow manure was hydrothermally treated in a 2-litre reactor for 1 h at temperatures between 100 °C and 260 °C. Both the raw manure and the solid and liquid products of the hydrothermal treatment were characterized to understand the fate of the inorganic elements and to assess the suitability of the products for land applications and energy recovery. Satisfactory elemental balances were obtained for the organic and most inorganic elements and indicated that most inorganic elements were incorporated into the solids with lower solubility, with the exception of potassium and sodium, which were mostly solubilized in the process water; calcium and chlorine were also solubilized to a lesser extent in the process water. Elemental composition and surface functional groups showed that hydrochar produced within the hydrothermal carbonization range (180-260 °C) seemed better suited for utilization as a soil amendment than raw cow manure. The potential for energy recovery lies in the anaerobic digestion of the process water, from which higher methane yields can be obtained than from raw cow manure. Lower temperatures in hydrothermal carbonization are considered a compromise for the safe land applications of cow manure, energy recovery from the process water, and enhanced dewaterability. These findings can help to eliminate bottlenecks in the upscaling of cow manure hydrothermal treatment and promote the circular bio-economy.

Guidelines for efficient nitrogen preservation in sewage sludge-based fertilizers

This study explores sustainable methods to mitigate nitrogen (N) loss in agriculture amid rising food demands and limited arable land. It examines sewage sludge (SS) as an alternative to synthetic N fertilizers. SS is rich in nitrogen (4.21 ± 0.42 %) and phosphorus (3.60 ± 0.72 %), making it suitable for nutrient recovery and soil enhancement. Unfavorable sludge management methods result in the loss of 950,000 tons of nitrogen, meeting almost 10 % of the EU's nitrogen fertilization demand. This research evaluates SS treatment methods, including chemical conversion, thermal treatment, and biological composting, focusing on nitrogen conservation efficiency. Results show nitrogen loss during hydrolysis is minimized at pH 4 to 8 but increases significantly as ammonia (NH3) at pH 9 to 11, ranging from 4.2 % to 9 %. Neutralizing the hydrolysate is crucial; using solid KOH resulted in 13.5 % nitrogen loss, 11 times more than using slightly alkaline ash (1.22 %). Adding ash during drying reduced nitrogen emissions by 30 % compared to traditional drying at 105 °C. Improving the C/N ratio with food residues reduced nitrogen losses by 46.3 % during composting. These findings highlight the importance of pH control in chemical processes and temperature regulation in thermal treatments. Adding residues from other processes, such as biomass combustion waste, enhances SS processing conditions. Understanding nitrogen retention mechanisms is crucial for the environmental sustainability of SS usage. Efficient nitrogen retention strategies improve the fertilization value of SS and reduce its environmental footprint by lowering greenhouse gas emissions, particularly ammonia. Reducing nitrogen loss during SS treatment significantly lowers ammonia emissions, a major contributor to greenhouse gas emissions. These results help determine optimal methods for managing and processing SS to minimize emissions and increase agricultural usability.

Analysis of perfluorinated compounds in sewage sludge and hydrochar by UHPLC LTQ/Orbitrap MS and removal assessment during hydrothermal carbonization treatment

Wastewater treatment plants have been recognized as important sinks for per- and polyfluoroalkyl substances (PFAS) because of their ineffectiveness in removing them reflecting both water and sewage sludge discharge routes. Hydrothermal treatment represents an alternative technology for treating sludge to recover energy and other valuable products. In this study, 15 PFAS were determined in sludge and hydrochar substrates using sonication-solid phase extraction procedure and analyzed using LC-Orbitrap-High Resolution-MS/MS. The method was fully validated, exhibiting very good linearity, recoveries in the range of 48 to 126 %, low detection and quantification limits with expanded uncertainty and precision below 32 % and 21.9 %, respectively. The method was applied to sludge samples from the WWTP of Ioannina city (Greece), as well as to hydrothermally treated samples under various conditions. The most abundant PFAS were PFHxA (0.5-38.3 ng g-1) and PFOS (4.4-22.1 ng g-1). Finally, the hydrothermally treated sludge samples spiked with PFAS presented removal efficiencies for total PFAS of 86.9 %, 91.8 % and 95.7 % at three spiking levels namely 10, 50 and 200 ng g-1, respectively. Results indicated that PFCAs were almost completely removed, except for PFOA, while the concentrations of PFSAs increased in the produced hydrochar with the formation of several intermediates, as detected by HR-LC-MS/MS. The results of this study demonstrate the effect of hydrothermal treatment to the fate of PFAS in sewage sludge and contribute for further studies on design and scale up of hydrothermal carbonization technology as a management option for safer disposal of municipal wastewater sludge.

Treatment of aqueous phase from hydrothermal liquefaction of municipal sludge by adsorption: Comparison of biochar, hydrochar, and granular activated carbon

Hydrothermal liquefaction (HTL) is promising for treating waste with high moisture, such as municipal sludge, and producing biocrude (a petroleum-like biofuel). However, a large amount of wastewater byproduct, HTL aqueous, is generated. The presence of hazardous compounds (e.g., phenolic compounds and nitrogenous organics) makes HTL aqueous the biggest bottleneck for full-scale implementation at treatment plants. This study investigated the adsorption of various pollutants, focusing on chemical oxygen demand (COD), in HTL aqueous to granular activated carbon (GAC), biochar, and hydrochar. It assessed the effect of pH, temperature, time, and adsorbent concentration on adsorption efficiency and identified proper adsorbent and process conditions for removing most of the pollutants from HTL aqueous. GAC showed the highest adsorption capacity (184 mg/g) for COD, surpassing biochar (44 mg/g) and hydrochar (42 mg/g). The adsorption of COD to all adsorbents followed pseudo-second-order kinetic and Freundlich isotherm, suggesting that the adsorption of HTL aqueous pollutants is a heterogeneous and multilayer process, limited by chemosorption. The adsorption was endothermic, favored by elevated temperatures and neutral pH. This means adsorption is more efficient and economical for treating HTL aqueous that is a hot stream at the large-scale and it saves chemical needs. Lastly, GAC was highly efficient and selective in removing harmful pollutants, such as COD (up to 66%), total phenolic compounds (up to 94%), pyrazines (up to 99%), pyridines (up to 100%), and cyclic ketones (up to 95%) while preserving valuable volatile fatty acids (VFAs) and ammonia for subsequent recovery. Removal of potentially inhibitory compounds and preserving VFAs are crucial for carbon recovery in anaerobic biological treatment of HTL aqueous. The results suggested the necessity of optimizing adsorbent dose for maximizing removal of specific group of inhibitory compounds in full-strength HTL aqueous for enhancing downstream biological treatment. Lastly, this study established the groundwork for HTL aqueous adsorption, elucidating its effectiveness and mechanism for pollutant removal.

Hydrothermal recycling of carbon absorbents loaded with emerging wastewater contaminants

Adsorption using carbon materials is one of the most efficient techniques for removal of emerging contaminants such as pharmaceuticals from wastewater. However, high costs are a major hurdle for their large-scale application in areas currently under economic constraints. While most research focuses on decreasing the adsorbent price by increasing its capacity, treatment costs for exhausted adsorbents and their respective end-of-life scenarios are often neglected. Here, we assessed a novel technique for recycling of exhausted activated biochars based on hydrothermal treatment at temperatures of 160-320 °C. While a treatment temperature of 280 °C was sufficient to fully degrade all 10 evaluated pharmaceuticals in solution, when adsorbed on activated biochars certain compounds were shielded and could not be fully decomposed even at the highest treatment temperature tested. However, the use of engineered biochar doped with Fe-species successfully increased the treatment efficiency, resulting in full degradation of all 10 parent compounds at 320 °C. The proposed recycling technique showed a high carbon retention in biochar with only minor losses, making the treatment a viable candidate for environmentally sound recycling of biochars. Recycled biochars displayed potentially beneficial structural changes ranging from an increased mesoporosity to additional oxygen bearing functional groups, providing synergies for subsequent applications as part of a sequential biochar system.

Determination of pharmaceuticals and metabolites in sludge and hydrochar after hydrothermal carbonization using sonication-QuEChERS extraction method and UHPLC LTQ/Orbitrap MS

Pharmaceuticals (PhACs) are an important group of emerging contaminants that are released continuously in the environment from wastewater treatments plants (WWTPs). They can produce biological effects even though at very low concentrations. Conventional WWTPs are not able to remove or degrade completely emerging pollutants resulting in the presence of PhACs in sewage sludge after wastewater treatment. PhACs are found in sludge at low ppb-ppt levels, and their analysis and detection is a difficult task due to the complexity of sewage sludge matrices. Hydrothermal carbonization is currently being proposed as a suitable conversion technology for sewage sludge management to recover valuable products and to be used for soil amendment. In this work, a modified quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based methodology with a dispersive solid-phase extraction (d-SPE) clean-up followed by ultra-high-performance liquid chromatography coupled with high-resolution linear ion trap-Orbitrap mass spectrometry (UHPLC-LTQ/Orbitrap MS), operated in positive ionization mode, was adopted to investigate 33 multiclass pharmaceuticals in sewage sludge and in hydrochar produced after hydrothermal carbonization. The analytical method was first optimized studying various extraction parameters and finally validated in terms of linearity, recovery, intra and inter-day precisions, expanded uncertainty (%U)/Horrat ratio at three spiking levels, matrix-effects (ME), process efficiency (PE), and limits of detection and quantification. The developed methodology fulfilled all analytical requirements and was finally applied to sludge samples from the WWTP of Ioannina city where a group of antibiotics was detected at concentrations up to 15 ng g^-1 and psychiatric drugs such as amisulpride, clozapine, and citalopram were detected at higher concentration levels up to 205, 87.4 and 63.2 ng g^-1, respectively. The method was also applied to hydrothermally treated sludge sample under different reaction conditions. Most of the antibiotic compounds were not detected, and several psychiatric drugs such as mirtazapine, bupropion, valsartan, diazepam, and caffeine were found at concentrations below the LOQ.

Effects of ciprofloxacin, trimethoprim, and amoxicillin on microbial structure and growth as emerging pollutants reaching crop soils

The presence of emerging pollutants, and specifically antibiotics, in agricultural soils has increased notably in recent decades, causing growing concern as regards potential environmental and health issues. With this in mind, the current study focuses on evaluating the toxicity exerted by three antibiotics (amoxicillin, trimethoprim, and ciprofloxacin) on the growth of soil bacterial communities, when these pollutants are present at different doses, and considered in the short, medium, and long terms (1, 8 and 42 days of incubation). Specifically, the research was carried out in 12 agricultural soils having different physicochemical characteristics and was performed by means of the leucine (³H) incorporation method. In addition, changes in the structure of soil microbial communities at 8 and 42 days were studied in four of these soils, using the phospholipids of fatty acids method for this. The main results indicate that the most toxic antibiotic was amoxicillin, followed by trimethoprim and ciprofloxacin. The results also show that the toxicity of amoxicillin decreases with time, with values of Log IC₅₀ ranging from 0.07 ± 0.05 to 3.43 ± 0.08 for day 1, from 0.95 ± 0.07 to 3.97 ± 0.15 for day 8, and from 2.05 ± 0.03 to 3.18 ± 0.04 for day 42, during the incubation period. Regarding trimethoprim, 3 different behaviors were observed: for some soils the growth of soil bacterial communities was not affected, for a second group of soils trimethoprim toxicity showed dose-response effects that remained persistent over time, and, finally, for a third group of soils the toxicity of trimethoprim increased over time, being greater for longer incubation times (42 days). As regards ciprofloxacin, this antibiotic did not show a toxicity effect on the growth of soil bacterial communities for any of the soils or incubation times studied. Furthermore, the principal component analysis performed with the phospholipids of fatty acids results demonstrated that the microbial community structure of these agricultural soils, which persisted after 42 days of incubation, depended mainly on soil characteristics and, to a lesser extent, on the dose and type of antibiotic (amoxicillin, trimethoprim or ciprofloxacin). In addition, it was found that, in this research, the application of the three antibiotics to soils usually favored the presence of fungi and Gram-positive bacteria.

Changes and release risk of typical pharmaceuticals and personal care products in sewage sludge during hydrothermal carbonization process

Hydrochars were obtained by hydrothermal carbonization treatment of municipal sewage sludge. Effects of reaction temperature (180-300 °C) and reaction time (2-15 h) on structural characteristics of the hydrochars, and changes and release risk of typical pharmaceuticals and personal care products (PPCPs) in the hydrochars were investigated. Reaction temperature played a more important role than reaction time on hydrochar properties and decarboxylation reaction was the primary process during the converting of sludge to hydrochars. The sludge hydrochars had higher yields, carbon recovery rates, polarity and less aromaticity than biochars. Hydrothermal process reduced PPCPs' load in sludge hydrochars effectively except caffeine and acetaminophen. The hydrochars prepared at intermediate and high temperatures (240 and 300 °C) had higher caffeine concentrations than the original sludge, which can be ascribed to the transformation of N-containing precursors. The highest CaCl₂ extracted caffeine concentration occurred at intermediate temperature of 240 °C (48.1 μg/kg) due to the stronger affinity of caffeine in the high-temperature hydrochars. Caffeine was not detected in hydroxypropyl-β-cyclodextrin (HPCD) extract. Hydrochars prepared at low temperature (180 °C) had a higher acetaminophen concentration than the original sludge, which was attributed to the high thermal stability temperature of acetaminophen. Low- and intermediate-temperature hydrochars had higher CaCl₂ extracted acetaminophen concentrations. The HPCD extracted acetaminophen was low with a range of nd to 6.72 μg/kg. In conclusion, PPCPs are less likely to constitute a limiting factor on the farm application of sludge hydrochar. This study provides theoretical support for the safe application of sludge hydrochar in the farmland.

Hydrothermal carbonisation of mechanically dewatered digested sewage sludge-Energy and nutrient recovery in centralised biogas plant

This study aimed to assess the role of hydrothermal carbonisation (HTC) in digestate processing in centralised biogas plants receiving dewatered sludge from regional wastewater treatment plants and producing biomethane and fertilisers. Chemically conditioned and mechanically dewatered sludge was used as such (total solids (TS) 25%) or as diluted (15% TS) with reject water in 30 min or 120 min HTC treatments at 210 °C, 230 °C or 250 °C, and the produced slurry was filtered to produce hydrochars and filtrates. The different hydrochars contributed to 20-55% of the original mass, 72-88% of the TS, 74-87% of the energy content, 71-92% of the carbon, above 86% of phosphorous and 38-64% of the nitrogen present in the original digestates. The hydrochars' energy content (higher heating values were 11.3-12.2 MJ/kg-TS) were similar to that of the digestates, while the ash contents increased (from 43% up to 57%). HTC treatments produced filtrates in volumes of 42-76% of the dewatered digestate, having a soluble chemical oxygen demand (SCOD) of 28-44 g/L, of which volatile fatty acids (VFAs) contributed 10-34%, and methane potentials of 182-206 mL-CH₄/g-SCOD without any major indication of inhibition. All 32 pharmaceuticals detected in the digestates were below the detection limit in hydrochars and filtrates, save for ibuprofen and benzotriazole in filtrate, while heavy metals were concentrated in the hydrochars but below the national limits for fertiliser use, save for mercury. The integration of HTC to a centralised biogas plant was extrapolated to enhance the annual biogas production by 5% and ammonium recovery by 25%, and the hydrochar was estimated to produce 83 GJ upon combustion or to direct 350 t phosphorous to agriculture annually.

Hydrochar derived from municipal sludge through hydrothermal processing: A critical review on its formation, characterization, and valorization

Additional options for the sustainable treatment of municipal sludge are required due to the significant amounts of sludge, high levels of nutrients (e.g., C, N, and P), and trace constituents it contains. Hydrothermal processing of municipal sludge has recently been recognized as a promising technology to efficiently reduce waste volume, recover bioenergy, destroy organic contaminants, and eliminate pathogens. However, a considerable amount of solid residue, called hydrochar, could remain after hydrothermal treatment. This hydrochar can contain abundant amounts of energy (with a higher heating value up to 24 MJ/kg, dry basis), nutrients, and trace elements, as well as surface functional groups. The valorization of sludge-derived hydrochar can facilitate the development and application of hydrothermal technologies. This review summarizes the formation pathways from municipal sludge to hydrochar, specifically, the impact of hydrothermal conditions on reaction mechanisms and product distribution. Moreover, this study comprehensively encapsulates the described characteristics of hydrochar produced under a wide range of conditions: Yield, energy density, physicochemical properties, elemental distribution, contaminants of concern, surface functionality, and morphology. More importantly, this review compares and evaluates the current state of applications of hydrochar: Energy production, agricultural application, adsorption, heterogeneous catalysis, and nutrient recovery. Ultimately, along with the identified challenges and prospects of valorization approaches for sludge-derived hydrochar, conceptual designs of sustainable municipal sludge management are proposed.

Coupling hydrothermal carbonization and anaerobic digestion for sewage digestate management: Influence of hydrothermal treatment time on dewaterability and bio-methane production

Hydrothermal carbonization (HTC) technology is addressed in the framework of sewage digestate management. HTC converts digestate into a stabilized and sterilized solid (the hydrochar) and a liquor (HTCL) rich in organic carbon. This study aims to optimize the HTC operating parameters, namely the treatment time, in terms of hydrochar production, HTC slurry dewaterability, HTCL bio-methane yields in anaerobic digestion (AD), and process energy consumption. Digestate slurry was processed through HTC at different treatment times (0.5, 1, 2 and 3 h) at 190 °C, and the dewaterability of the treated slurries was addressed through capillary suction time and centrifuge lab-testing. In addition, biochemical methane potential (BMP) tests were conducted for HTCL under mesophilic conditions. Results show that by increasing the HTC treatment time the dewaterability was further improved, ammonium concentration in HTCL increased, and methane potential of HTCL decreased. 0.5 h HTCL had the highest bio-methane potential of 142 ± 3 mL CH₄/g COD yet the treatment time was not sufficient for improving the slurry's dewaterability. HTC treatment time of 1 h at 190 °C was identified as the optimum trade-off for improved dewaterability and utilisation of HTCL for biogas production. 1 h HTCL bio-methane potential can cover around 25% of the HTC and AD thermal and electrical energy needs without considering the eventual use of the hydrochar as a biofuel.

Conversion of sewage sludge into biochar: A potential resource in water and wastewater treatment

Production of biochar from sewage sludge (SS) is consistent with the goal of sustainable resource recovery and promotes a wastewater-based circular economy. Thermochemical conversion of SS to biochar resolves two major issues simultaneously as it minimizes the cost of disposal and acts as a resource to eliminate the toxic contaminants from water and wastewater. The reusability and ready availability of the biochar, irrespective of the season, makes it an economically viable material for wastewater treatment. In this review, explicit insights into the production, modification and usage of SS derived biochar are provided including (i) the production yield, (ii) characteristic features such as physical, chemical, electrochemical and morphological aspects, and (iii) impact on contaminant removal through adsorption, catalytic and electrochemical processes. Particular attention is given to the use of SS derived biochar as an adsorbent for contaminants present in wastewaters, the potential use of biochar as a catalyst and support material in advanced oxidation processes and the use of biochars as an electrode material. The effect of pyrolysis conditions and co-pyrolysis with other materials on biochar properties is explored and insight is provided into the toxicity of biochar components present at different process conditions.

Process Waters from Hydrothermal Carbonization of Sludge: Characteristics and Possible Valorization Pathways

Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable residues into value-added materials, such as hydrochar. HTC has been studied for decades, however, a lack of detailed information on the production and composition of the process water has been highlighted by several authors. In this paper the state of the art of the knowledge on this by-product is analyzed, with attention to HTC applied to municipal and agro-industrial anaerobic digestion digestate. The chemical and physical characteristics of the process water obtained at different HTC conditions are compared along with pH, color, organic matter, nutrients, heavy metals and toxic compounds. The possibility of recovering nutrients and other valorization pathways is analyzed and technical feasibility constraints are reported. Finally, the paper describes the main companies which are investing actively in proposing HTC technology towards improving an effective process water valorization.

Influence of water matrix and hydrochar properties on removal of organic and inorganic contaminants

The removal of contaminants from water using low-cost adsorbents has been widely studied, yet studies employing a realistic water matrix are still lacking. This study investigated the removal of organic compounds (trimethoprim, fluconazole, and perfluorooctanoic acid (PFOA)) and metals (As, Zn, and Cu) from landfill leachate. Additionally, tests in pure water, humic acid, and ion matrices were carried out to better understand how the water matrix affects adsorption. The hydrochars were produced from four feedstocks at three carbonization temperatures. The results show that the removal efficiencies for organic pollutants were low and metal removal by hydrochars was comparable with commercial activated carbon. The removal of all compounds from pure water was substantially lower. Tests with humic acid and ion-containing matrices could not fully explain the increased removal in the landfill leachate, which may be due to the combination of the water matrix and presence of soluble species from the hydrochars.

The impact of hydrothermal carbonization on the surface functionalities of wet waste materials for water treatment applications

Hydrothermal carbonization (HTC) is an energy-efficient thermochemical process for converting wet waste products into value added materials for water treatment. Understanding how HTC influences the physicochemical properties of the resultant materials is critical in optimizing the process for water treatment, where surface functionality and surface area play a major role. In this study, we have examined the HTC of four wet waste streams, sewage sludge, biosludge, fiber sludge, and horse manure at three different temperatures (180 °C, 220 °C, and 260 °C). The physicochemical properties of these materials were examined via FTIR, SEM and BET with their adsorption capacity were assessed using methylene blue. The yield of solid material after hydrothermal carbonization (hydrochar) decreased with increasing temperature for all samples, with the largest impact on horse manure and fiber sludge. These materials also lost the highest degree of oxygen, while HTC had minimal impact on biosludge and sewage sludge. The differences here were due to the varying compositions of each waste material, FTIR identified resonances related to cellulose in horse manure and fiber sludge, which were not detected in biosludge and sewage sludge. Adsorption capacities varied between 9.0 and 68 mg g^-1 with biosludge HTC at 220 °C adsorbing the highest amount. Adsorption also dropped drastically at the highest temperature (260 °C), indicating a correlation between adsorption capacity and HTC conditions. This was attributed to the loss of oxygen functional groups, which can contribute to adsorption. These results suggest that adsorption properties can be tailored both by selection of HTC temperature and feedstock.

Hydrothermal carbonization of sewage sludge: A critical analysis of process severity, hydrochar properties and environmental implications

Hydrothermal carbonization (HTC) of sewage sludge reduces the waste volume and can be source of energy and valuable products. Furthermore, HTC offers several advantages over conventional dry-thermal pre-treatments, as no prior drying is requested, and the high quality of the char produced promotes applications as energy production and storage, wastewater remediation, and soil amendment. Relationships between char yields, physicochemical properties and process parameters are here analysed, with the aim to provide insight into the choice of the process severity required to fit the desired application. Moreover, presence and fate of heavy metals and organic contaminants are discussed. The highest reaction temperature is the main parameter affecting the physicochemical characteristics of the char produced, while the heating rate governs the heat mass transfer and the rate of intermediates formation. Depolymerization of the biomass results in a reduction of the oxygen to carbon ratio and, therefore, in augmented high heating values, further increased by deposition of 5-(hydroxymethyl)furfural. Recirculation of process water may enhance dehydration reactions and the deposition of degraded polymers, increasing dewaterability and yield, but field trials are recommended to assess the feasibility of this option. An overuse of chars for energy generation purposes would be deleterious for the environmental life cycle. Further research is encouraged to assess the pollutants abatement and their degradation pathways when incorporated in the carbonaceous product, to promote the application of hydrochars as soil amendment, as well as for environmental remediation purposes.

Hydrothermal treatment for regeneration of activated carbon loaded with organic micropollutants

Hydrothermal treatment (HT) at 200 °C and 240 °C for 4 and 16 h was studied for the regeneration of granular activated carbon (AC) loaded with a range of organic micropollutants having a broad range of physico-chemical properties. Carbamazepine, diazinon, diclofenac, estrone, iohexol, metoprolol and sulfamethoxazole were fully converted. Limits were seen for the conversion of caffeine, ibuprofen and perfluorooctanesulfonate (PFOS). However, the degree of degradation was enhanced for the latter compounds in the adsorbed state as compared to experiments in aqueous solution. The methodology was tested in five loading and regeneration cycles for selected compounds with no change of the degradation potential and of the AC properties. In particular, the surface properties of the AC did not deteriorate upon HT as determined by the specific surface area (from BET isotherms), the point of zero charge, and the surface functional groups (from diffuse reflectance IR spectroscopy). As the total concentration of the loaded pollutants was minimized by HT, this method could be considered as a new low temperature regeneration technology for spent AC.

Facile one-step synthesis of functionalized biochar from sustainable prolifera-green-tide source for enhanced adsorption of copper ions

The use of biochars formed by hydrothermal carbonization for the treatment of contaminated water has been greatly limited, due to their poorly developed porosity and low content of surface functional groups. Also, the most common modification routes inevitably require post-treatment processes, which are time-consuming and energy-wasting. Hence, the objective of this research was to produce a cost-effective biochar with improved performance for the treatment of heavy metal pollution through a facile one-step hydrothermal carbonization process coupled with ammonium phosphate, thiocarbamide, ammonium chloride or urea, without any post-treatment. The effects of various operational parameters, including type of modification reagent, time and temperature of hydrothermal treatment, and ratio of modification reagent to precursor during impregnation, on the copper ion adsorption were examined. The adsorption data fit the Langmuir adsorption isotherm model quite well. The maximum adsorption capacities (mg/g) of the biochars towards copper ions followed the order of 40-8h-1.0-APBC (95.24)>140-8h-0-BC (12.52)>140-8h-1.0-TUBC (12.08)>140-8h-1.0-ACBC (7.440)>140-8h-1.0-URBC (5.277). The results indicated that biochars modified with ammonium phosphate displayed excellent adsorption performance toward copper ions, which was 7.6-fold higher than that of the pristine biochar. EDX and FT-IR analyses before and after adsorption demonstrated that the main removal mechanism involved complexation between the phosphate groups on the surface of the modified biochars and copper ions.

Using carbonized low-cost materials for removal of chemicals of environmental concern from water

Adsorption on low-cost biochars would increase the affordability and availability of water treatment in, for example, developing countries. The aim of this study was to identify the precursor materials and hydrochar surface properties that yield efficient removal of compounds of environmental concern (CEC). We determined the adsorption kinetics of a mixture containing ten CECs (octhilinone, triclosan, trimethoprim, sulfamethoxasole, ciprofloxacin, diclofenac, paracetamol, diphenhydramine, fluconazole, and bisphenol A) to hydrochars prepared from agricultural waste (including tomato- and olive-press wastes, rice husks, and horse manure). The surface characteristics of the hydrochars were evaluated via diffuse reflectance infrared spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and N2-adsorption. Kinetic adsorption tests revealed that removal efficiencies varied substantially among different materials. Similarly, surface analysis revealed differences among the studied hydrochars and the degree of changes that the materials undergo during carbonization. According to the DRIFTS data, compared with the least efficient adsorbent materials, the most efficient hydrochars underwent more substantial changes during carbonization.

Speciation evolution of zinc and copper during pyrolysis and hydrothermal carbonization treatments of sewage sludges

Thermal and hydrothermal treatments are promising techniques for sewage sludge management that can potentially facilitate safe waste disposal, energy recovery, and nutrient recovery/recycling. Content and speciation of heavy metals in the treatment products affect the potential environmental risks upon sludge disposal and/or application of the treatment products. Therefore, it is important to study the speciation transformation of heavy metals and the effects of treatment conditions. By combining synchrotron X-ray spectroscopy/microscopy analysis and sequential chemical extraction, this study systematically characterized the speciation of Zn and Cu in municipal sewage sludges and their chars derived from pyrolysis (a representative thermal treatment technique) and hydrothermal carbonization (HTC; a representative hydrothermal treatment technique). Spectroscopy analysis revealed enhanced sulfidation of Zn and Cu by anaerobic digestion and HTC treatments, as compared to desulfidation by pyrolysis. Overall, changes in the chemical speciation and matrix properties led to reduced mobility of Zn and Cu in the treatment products. These results provide insights into the reaction mechanisms during pyrolysis and HTC treatments of sludges and can help evaluate the environmental/health risks associated with the metals in the treatment products.

Transformations of Phosphorus Speciation during (Hydro)thermal Treatments of Animal Manures

Phosphorus (P) in animal manures is an important P pool for P recycling and reclamation. In recent years, thermochemical techniques have gained much interests for effective waste treatment and P recycling. This study comparatively characterized the transformation of P during two representative thermochemical treatments (pyrolysis and hydrothermal carbonization, HTC) of four animal manures (swine, chicken, beef, and dairy manures) by combining nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, and sequential extraction. For both pyrolysis and HTC treatments, degradation of organic phosphate and crystallization of Ca phosphate minerals were observed and were highly dependent on treatment temperature. Extensive crystallization of Ca phosphate minerals occurred at temperatures above 450 °C during pyrolysis, compared to the lower temperature (175 and 225 °C) requirements during HTC. As a result, P was immobilized in the hydrochars and high temperature pyrochars, and was extracted primarily by HCl. Because Ca is the dominating P-complexing cation in all four manures, all manures showed similar P speciation and transformation behaviors during the treatments. Results from this work provided deeper insights into the thermochemical processes occurred during the pyrolysis and HTC treatments of biological wastes, as well as guidance for P reclamation and recycling from these wastes.

The presence of contaminations in sewage sludge - The current situation

Sewage sludge/biosolids are by-wastes of municipal and industrial wastewater treatment. As sources of nutrients (C, N, P) they are widely used in intensive farming where large supplementation of organic matter to maintain fertility and enhance crop yields is needed. However, according to the report of European Commission published in 2010, only 39% of produced sewage sludge is recycled into agriculture in the European Union. This situation occurs mainly due to the fact, that the sewage sludge may contain a dangerous volume of different contaminants. For over decades, a great deal of attention has been focused on total concentration of few heavy metals and pathogenic bacteria Salmonella and Escherichia coli. The Sewage Sludge Directive (86/278/EEC) regulates the allowable limits of Zn, Cu, Ni, Pb, Cd, Cr and Hg and pathogens and allows for recovery of sludge on land under defined sanitary and environmentally sound conditions. In this paper, a review on quality of sewage sludge based on the publications after 2010 has been presented. Nowadays there are several papers focusing on new serious threats to human health and ecosystem occurring in sewage sludge - both chemicals (such as toxic trace elements - Se, Ag, Ti; nanoparticles; polyaromatic hydrocarbons; polychlorinated biphenyl; perfluorinated surfactants, polycyclic musks, siloxanes, pesticides, phenols, sweeteners, personal care products, pharmaceuticals, benzotriazoles) and biological traits (Legionella, Yersinia, Escherichia coli O157:H7).

Transformation of Phosphorus during (Hydro)thermal Treatments of Solid Biowastes: Reaction Mechanisms and Implications for P Reclamation and Recycling

Phosphorus (P) is an essential nutrient for all organisms, thus playing unique and critical roles at the food-energy-water nexus. Most P utilized by human activities eventually converges into various solid biowastes, such as crop biomass, animal manures, and sewage sludges. Therefore, integration of efficient P recovery practices into solid biowaste management will not only significantly reduce the dependence on limited geological P resources but also reduce P runoff and related water contamination issues associated with traditional waste management strategies. This study reviews the applications of (hydro)thermal techniques for the treatment of solid biowastes, which can greatly facilitate P recovery in addition to waste volume reduction, decontamination, and energy recovery. Research showed that P speciation (including molecular moiety, complexation state, and mineralogy) can experience significant changes during (hydro)thermal treatments, and are impacted by treatment techniques and conditions. Changes in P speciation and overall properties of the products can alter the mobility and bioavailability of P, and subsequent P reclamation and recycling efficiency of the treatment products. This review summarizes recent progresses in this direction, identifies the challenges and knowledge gaps, and provides a foundation for future research efforts targeting at sustainable management of nutrient-rich biowastes.

Hydrothermal carbonization of sewage sludge: The effect of feed-water pH on fate and risk of heavy metals in hydrochars

In this study, the effect of feed-water pH (pH=2-12) on fate and risk of heavy metals (HMs) in hydrochars (HCs) was investigated. Hydrothermal carbonization (HTC) of sewage sludge (SS) was carried out with different feed-water pH at 270°C. The research results showed that changing feed-water pH had a positive effect on accumulating Pb, Ni, Cd and Zn in HCs. Chemical forms of Cu and Cr converted from an unstable state to stable in the alkaline environment while in the acidic condition was opposite. The effect of feed-water pH on the chemical forms of HMs was variable but not significant. Risk assessments of Igeo, Er(i), RAC and RI were applied to evaluate the accumulation levels of individual metal, the potential ecological risks, the bio-availabilities and the comprehensive toxicity and sensitivity of HMs, respectively. The lowest pollution level of HMs was obtained at 270°C with pH=11.