Conversion of phosphorus and nitrogen in lincomycin residue during microwave-assisted hydrothermal liquefaction and its application for Pb2+ removal

Hydrothermal pretreatment for enhanced thermochemical or biochemical conversion of pharmaceutical biowastes into fuels, fertilizers, and carbon materials

Pharmaceutical biowastes, rich in organic matter and high in moisture, are typical light industry byproducts with waste and renewable attributes. Thermochemical and biochemical conversion technologies transform these residues into value-added bioproducts, including biofuels, biofertilizers, and bio-carbon materials. Hydrothermal pretreatment effectively removes toxic substances and enhances feedstock for these processes. This review comprehensively examines its role in improving the formation of bioproducts from pharmaceutical biowastes, focusing on (i) upgrading and denitrogenating solid biofuels with better combustion performance; (ii) enhancing biodegradability and gaseous biofuel production via organic matter decomposition; (iii) enriching soluble carbon and nitrogen for liquid biofertilizer; (iv) eliminating antibiotic residues and reducing antibiotic resistance in solid biofertilizers; and (v) stabilizing carbon and nitrogen structures and optimizing pore characteristics for functionalized carbon materials. The review recommends a potential staged thermochemical approach to co-produce nitrogen-enriched liquid biofertilizers and porous carbon materials from pharmaceutical biowastes. Hydrothermal pretreatment emerges as a key technique for facilitating the migration and conversion of essential elements like carbon and nitrogen. This study reveals the potential of hydrothermal pretreatment to address the limitations of pharmaceutical biowastes and offers insights into their valorization.

Hydrochar as a bio-based adsorbent for heavy metals removal: A review of production processes, adsorption mechanisms, kinetic models, regeneration and reusability

The spread of heavy metals throughout the ecosystem has extremely endangered human health, animals, plants, and natural resources. Hydrochar has emerged as a promising adsorbent for removal of heavy metals from water and wastewater. Hydrochar, obtained from hydrothermal carbonization of biomass, owns unique physical and chemical properties that are highly potent in capturing heavy metals via surface complexation, electrostatic interactions, and ion exchange mechanisms. This review focuses on removing heavy metals by hydrochar adsorbents from water bodies. The article discusses factors affecting the adsorption capacity of hydrochars, such as contact time, pH, initial metal concentration, temperature, and competing ions. Literature on optimization approaches such as surface modification, composite development, and hybrid systems are reviewed to enlighten mechanisms undertaking the efficiency of hydrochars in heavy metals removal from wastewater. The review also addresses challenges such as hydrochar regeneration and reusability, alongside potential issues related to its disposal and metal leaching. Integration with current water purification methods and the significance of ongoing research and initiatives promoting hydrochar-based technologies were also outlined. The article concludes that combining hydrochar with modern technologies such as nanotechnology and advanced oxidation techniques holds promise for improving heavy metal remediation. Overall, this comprehensive analysis provides valuable insights to guide future studies and foster the development of effective, affordable, and environmentally friendly heavy metal removal technologies to ensure the attainment of safer drinking water for communities worldwide.

Recent advances in environmental and agricultural applications of hydrochars: A review

Hydrochar is a carbonaceous material that is generated through the process of hydrothermal carbonization (HTC) from biomass, which has garnered considerable attention in recent years owing to its potential applications in a diverse range of fields, such as environmental remediation and agriculture. Hydrochar is produced from a diverse range of biomass waste materials and retains exceptional properties, including high carbon content, stability, and surface area, making it an optimal candidate for various enviro-agricultural applications. Moreover, it delves into the production process of hydrochar, with explicit emphasis on the optimization of certain properties during the production of hydrochar from bio-waste. Furthermore, the potential of hydrochar as an adsorbent and catalyst support for heavy metals and dyes was extensively explored, along with a soil remediation potential that can improve the physical, chemical and biological properties of soil. This comprehensive review aims to provide a thorough overview of hydrochar with a particular focus on its production, properties, and prospective applications. The significance of hydrochar is accentuated and the growing need for alternative sources of energy and materials that are environmentally sustainable is highlighted in this paper. Besides, the consequence of hydrochar on soil properties such as water-holding capacity, nutrient retention, and total soil porosity, as well as its influence on soil chemical properties such as cation exchange capacity, electrical conductivity, and surface functionality is scrutinized.

Pyrolysis of Ca/Fe-rich antibiotic fermentation residues into biochars for efficient phosphate removal/recovery from wastewater: Turning hazardous waste to phosphorous fertilizer

Ca/Fe-rich antibiotic fermentation residues (AFRs), a type of hazardous waste, can be regarded as recyclable biomass and metal resources. However, concurrent detoxification and reutilization of biomass and metals resources from AFRs have never been reported before. In this study, Ca/Fe-rich vancomycin fermentation residues were pyrolyzed into biochar to adsorb phosphate for the first time. The residual vancomycin and antibiotic resistance genes were completely decomposed during pyrolysis. The resultant Ca/Fe-rich biochar exhibited excellent performance at adsorbing phosphate without further modifications. The process had rapid kinetics and a maximum adsorption capacity of 102 mg P/g. Ca and Fe were the active sites, whereas different mechanisms were observed under acidic and alkaline conditions. Surprisingly, HCO₃^- enhanced phosphate adsorption with an increase of adsorption capacity from 43.9 to 71.0 mg/g when HCO₃^- concentration increased from 1 to 10 mM. Furthermore, actual wastewater could be effectively treated by the biochar. The phosphate-rich spent biochar significantly promoted seed germination (germination rate: 96.7 % vs. 80.0 % in control group, p < 0.01) and seedling growth (shoot length was increased by 57.9 %, p < 0.01) due to the slow release of bioavailable phosphate, and thus could be potentially used as a phosphorous fertilizer. Consequently, the hazardous waste was turned into phosphorous fertilizer, with the additional benefits of detoxifying AFRs, reutilizing biomass and metal resources from AFRs, controlling phosphate pollution, and recovering phosphate from wastewater.

Nitrogen-doped biochar (N-doped BC) and iron/nitrogen co-doped biochar (Fe/N co-doped BC) for removal of refractory organic pollutants

The presence of refractory organic pollutants (ROPs) in the ecosystem is a serious concern because of their impact on environmental constituents as well as their known or suspected ecotoxicity and adverse health effects. According to previous studies, carbonaceous materials, such as biochar (BC), have been widely used to remove pollutants from ecosystems owing to their desirable features, such as relative stability, tunable porosity, and abundant functionalities. Nitrogen (N)-doping and iron/nitrogen (Fe/N) co-doping can tailor BC properties and provide supplementary functional groups as well as extensive active sites on the N-doped and Fe/N co-doped BC surface, which is advantageous for interaction with and removal of ROPs. This review investigates the impact of N-doped and Fe/N co-doped BC on the removal of ROPs through adsorption, activation oxidation, and catalytic reduction due to the synergistic Fe, N, and BC features that modify the physicochemical properties, surface functional groups, and persistent free radicals of BC to aid in the degradation of ROPs. Owing to the attractive properties of N-doped and Fe/N co-doped BCs for the removal of ROPs, this review focuses and evaluates previous experimental investigations on the manufacturing (including precursors and influencing parameters during manufacturing) and characterizations of N-doped and Fe/N co-doped BCs. Additionally, the effective applications and mechanisms of N-doped and Fe/N co-doped BCs in adsorption, activation oxidation, and reductive remediation of ROPs are investigated herein. Moreover, the application of N-doped and Fe/N co-doped BC for progressive environmental remediation based on their effectiveness against co-pollutants, regeneration, stability, affordability, and future research prospects are discussed.

Efficient removal of mercury and chromium from wastewater via biochar fabricated with steel slag: Performance and mechanisms

Biochar derived from biomass is regarded as a promising adsorbent for wastewater treatment, but the high cost of modification is still a challenge for its large-scale practical applications. In this study, we employed steel slag as a low-cost fabricant and synthesized hydrothermally carbonized steel slag (HCSS), as a stable environmentally functional material for heavy metal removal. Typically, positively and negatively charged heavy metal contaminants of Hg²⁺ and Cr₂O₇²⁻ were employed to testify the performance of HCSS as an adsorbent, and good capacities [(283.24 mg/g for Hg (II) and 323.16 mg/g for Cr (VI)] were found. The feasibility of HCSS on real wastewater purification was also evaluated, as the removal efficiency was 94.11% and 88.65% for Hg (II) and Cr (VI), respectively. Mechanism studies revealed that the modification of steel slag on bio-adsorbents offered copious active sites for pollutants. As expected, oxygen-containing functional groups in HCSS acted as the main contributor to adsorption capacity. Moreover, some reactive iron species (i.e., Fe²⁺) played an essential role in chemical reduction of Cr (VI). The adsorptive reactions were pH-dependent, owing to other more mechanisms, such as coprecipitation, ion-exchange, and electrostatic attraction. This promising recycling approach of biomass waste and the design of agro-industrial byproducts can be highly suggestive of the issues of resource recovery in the application of solid waste-derived environmentally functional materials for heavy metal remediation.

XPS and NMR analyze the combined forms of Pb in Cladophora rupestris subcells and its detoxification

In this study, the combined forms of Pb in Cladophora rupestris (L.) (C. rupestris) were investigated via X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR), different Pb concentrations (0, 0.5, and 5.0 mg/L), and C. rupestris subcells were explored. Results showed that combined forms of Pb mainly account for Pb-polysaccharides (Pb-OH of carbohydrates) in the cell wall, Pb-protein (Pb-N= and (C-N-)₂Pb) in the organelle, and Pb-organic acid (Pb-sulfates, (CO)₂-Pb and (COO)₂-Pb) in the soluble fraction. Pb-S-containing group (Pb-C-S) could formed in subcelluar when C. rupestris was subjected to high Pb stress. Meanwhile, Pb²⁺ could penetrate the C. rupestris cells via the formed chelate between GSH/MT and -OH functional groups. Results could help understand the role of subcellular fraction in the algae remediation and detoxification to heavy metal.

New insight into the co-adsorption of oxytetracycline and Pb(II) using magnetic metal-organic frameworks composites in aqueous environment: co-adsorption mechanisms and application potentials

The present study aimed to investigate the co-adsorption and application of water stabilized Fe₃O₄@ZIF-8 composite with magnetic cubic crystal structure. This new material was successfully prepared by facile modification strategy and rational design, which was used for simultaneous adsorption of oxytetracycline (OTC) and Pb(II) in aqueous solution. The co-adsorption behavior and mechanism of the composite for OTC and Pb(II) were systematically investigated by characterization techniques and batch experiments, and its application potential was effectively evaluated. The results showed that the synthesized Fe₃O₄@ZIF-8 composite innovatively retained the cubic crystal structure of ZIF-8 and was successfully loaded on the surface of Fe₃O₄ particles with small particle size to form a core-shell structure. The Fe₃O₄@ZIF-8 composite possessed a large specific surface area (1722 m²/g), magnetic separation performance (13.4 emu/g), and rich functional groups. The co-adsorption of OTC and Pb(II) on Fe₃O₄@ZIF-8 had fast reaction kinetics (equilibrium within 90 min) and large adsorption capacity (310.29 mg/g and 276.06 mg/g respectively). The adsorption process for both contaminants followed pseudo-second order kinetics and Langmuir isotherm models and had synergistic and competitive effects at the same time. π-π stacking and electrostatic interaction were the main mechanisms of adsorption. Fe₃O₄@ZIF-8 had good adsorption performance after cyclic adsorption for 4 times and it performed well in the treatment of real waste water. This study provided a new sight for the control of combined pollution of OTC and Pb(II) and proved Fe₃O₄@ZIF-8 composites have great application potentials for complex wastewater treatment.

Nitrogen migration in products during the microwave-assisted hydrothermal carbonization of spirulina platensis

Nitrogen has a vital influence on the properties of the microwave-assisted hydrothermal carbonization (MHTC) products of Spirulina platensis (SP). The effects of hydrothermal temperature (140-220 °C) and time (1-4 h) on the product distribution and nitrogen migration of SP in MHTC were studied. Increasing temperature led to an increase in the carbon content, and a decrease in the nitrogen content in hydrochar. Protein-N was the major nitrogen-containing species in hydrochar. The total nitrogen in liquid phase increased significantly with increasing temperature. Carbon dots were found to be one of the valuable products in the liquid phase. Higher temperatures improved the amine-N level and reduced the quaternary-N content in carbon dots. A close correspondence was found between the N-containing species and the luminescence centers of carbon dots. A possible nitrogen migration mechanism was proposed to provide guidance for the potential application of the products.

Influence of process parameters on hydrothermal modification of soybean residue: Insight into the nutrient, solid biofuel, and thermal properties of hydrochars

Soybean (SB) solid residue after oil extraction was investigated in a hydrothermal modification process to provide an eco-friendly solution to SB solid waste disposal for an actual environmental management effort. SB hydrochars (HCs) were derived either by conventional heating hydrothermal treatment (HTT) under intense conditions (200, 250, and 300 °C for 2 h) or by microwave-assisted hydrothermal treatment (MHTT) under mild conditions (160, 190, and 220 °C for 1 h). Physicochemical properties of SB HCs and the transformation of nitrogen (N) and phosphorus (P) functionalities during HTT and MHTT were characterized using several tools. Ultimate and XPS analyses elucidated N transformation, e.g., 5.51 wt % N of raw SB residue decreased to 3.48 and 3.51 wt % after HTT and MHTT, respectively. The P bioavailability of raw SB (3.46 mg/g) was improved after HTT (26.7 mg/g) and MHTT (10.9 mg/g), depicting the practical application of HCs for soil amendment. Atomic H/C and O/C ratios of SB HCs decreased as treatment temperature increased. HCs showed credible higher heating value (HHV; 22.3-25.5 MJ/kg for HTT and 20.5-22.1 MJ/kg for MHTT), higher than various low-rank coals. Besides, energy densification and fuel ratio improved in intense conditions. The thermogravimetric analysis showed HCs possessed better thermal stability. The improved performance of SB HCs indicated that HTT and MHTT provided a green environmental route of SB waste management, valorization, and utilization.

Combined forms of Pb and its detoxification and absorption in Cladophora rupestris subcells

This study aims to analyze the combined form, detoxification, and adsorption mechanism of Pb in Cladophora rupestris subcells. The chemical form analysis at different concentrations (0, 0.5, 1.0, 2.5, 5.0, 7.5, and 10 mg/L) indicated that most of the Pb (37%-76%) were integrated with oxalate and undissolved phosphate, which were important to the detoxification of C. rupestris. The characterization of Pb (0, 0.5, and 5.0 mg/L) at the subcellular was conducted via Fourier-transform infrared spectroscopy (FTIR), Three-dimensional excitation-emission matrix spectroscopy (3D-EEM), and protein secondary structure fitting. Results revealed that Pb-polysaccharides ((C₆H₅)-OO-Pb-OH, C-O-Pb, and symmetric Pb-O-Pb), Pb-functional-groups ((C₆H₅)-COO-Pb and (C₆H₅)-P = O-Pb), and Pb-protein complexes (OH-C₇H₆-CN-Pb-COOH, C₉H₁₀-NH-CN-C = O-Pb, Pb-S-C, and Pb-S) were formed. The cell wall produced transport proteins, such as metallothionein and glutathione, which bound and helped Pb²⁺ enter the cell. After entering the soluble fraction, the Pb-organic acid ((C₆H₅)-COO-Pb, (C₆H₅)-O-Pb, and (C₆H₅)-P = O-Pb) and Pb-sulfhydryl compound (Pb-S-C/Pb-S) assumed the most important role in resisting the toxicity of Pb²⁺. Pb²⁺ was absorbed in the organelle and formed (C₆H₅)-C-O-Pb and (C₆H₅)-P = O-Pb, and complexed with protein (Pb-C-N) when treated with 5.0 mg/L Pb. Results could help understand the role of subcellular fraction in the algal adaptation to stressful heavy metal conditions.

One-pot synthesis of spherical nanoscale zero-valent iron/biochar composites for efficient removal of Pb(ii)

In this study, a spherical Fe/C composite (AIBC) was successfully prepared via carbonization of Fe³⁺-crosslinked sodium alginate. The removal capacity and mechanism of AIBC were evaluated for the adsorption of Pb(ii) from aqueous solution and compared with that of commercial nanoscale zero-valent iron (nZVI). The effects of the initial concentration, pH of Pb(ii) solution, the contact time, coexisting anions, and aging under air were investigated. The results showed that the pH had a strong impact on the adsorption of Pb(ii) by AIBC. The adsorption data for AIBC followed the Langmuir model, while the maximum adsorption capacity at pH 5 was 1881.73 mg g⁻¹. The AIBC had a higher adsorption capability than nZVI, especially under the condition of relatively high Pb(ii) concentrations. The oxidation–reduction reaction between Fe and Pb(ii) was the main mechanism for the adsorption of Pb(ii) onto nZVI. AIBC converted the largest amount of Pb(ii) into PbO·XH₂O/Pb(OH)₂ mainly by generating Fe²⁺.

In this study, a spherical Fe/C composite (AIBC) was successfully prepared via carbonization of Fe³⁺-crosslinked sodium alginate.

Thermal effects

This review paper focuses on the researches published in 2019 in the field of thermal effects in wastewater and solid waste treatment. The content of this review paper includes five parts: wastewater and sludge treatment, nutrient removal and recovery, membrane technology, heavy metal removal and immobilization, and organic waste utilization. © 2020 Water Environment Federation PRACTITIONER POINTS: Thermal effect plays an important role in treatment of wastewater and sewage sludge. Recovery of nitrogen and phosphorus from wastewater and sewage sludge reduces environmental pollution and offers new products. Temperature improves removal and recovery of heavy metals and organic wastes.

Phosphorus and nitrogen transformation in antibiotic mycelial residue derived hydrochar and activated pyrolyzed samples: Effect on Pb (II) immobilization

In this study, lincomycin residue (LR, a type of antibiotic mycelial residue) derived hydrochar samples (LR-HCs) were obtained from hydrothermal carbonization (HTC), and pyrolysis applied to these LR-HCs to produce activated pyrolyzed samples (LR-APs). Transformation of phosphorus (P) and nitrogen (N) species during HTC and pyrolysis was of primary interest and characterized by several techniques. Nitrogen content of dry LR was calculated by elemental analysis, being 7.91 wt. %, decreasing to 2.51 after HTC and 1.12 wt. % after concesutive HTC and pyrolysis. FT-IR analysis provided evidence for amine groups in LR samples. XPS analysis described N species (Pyridinic-N, Amine-N, Protein-N, Pyrrolic-N, and Quaternary-N) and P species (ortho-P/pyro-P and Ar-P) in LR samples, effectively. Sequential extraction showed that the HTC and pyrolysis changed the proportion of the P species from labile (P-NaHCO₃ and P-NaOH) to stable ones (P-residue). Utilization and suitability of as-prepared LR-HCs and LR-APs for heavy metal Pb (II) immobilization show promising results. To help understand immobilization process, kinetic (pseudo-1st-order and pseudo-2nd-order) and isotherm (Freundlich) models were tested and verified. Results confirmed that P and N species were transformed during HTC and pyrolysis and that these processes lead to an advantageous effect on Pb (II) removal from solution.