Synthesis of an easily recyclable and safe adsorbent from sludge pyrochar for ciprofloxacin adsorption.

Utilization of sludge pyrochar (SP) is the terminal step to loop the entire harmless disposal process of sewage sludge with pyrolysis. A new, easily recyclable, and safe adsorbent with well-immobilized heavy metals (HMs) was prepared from SP for ciprofloxacin (CIP) adsorption. The operational conditions for the adsorbent preparation were systematically optimized based on recycling rate and adsorption performance. Additionally, the adsorption conditions, adsorption kinetics, isotherms, and regeneration of adsorbents were further investigated in the present study. The results showed that easily recyclable and safe adsorbents were successfully prepared at 1100 °C under N2 atmospheric conditions (SPA-N-1100) with a maximum CIP adsorption capacity of 10.42 mg/g. SPA-N-1100 exhibited good CIP adsorption performance at an adsorption temperature of 45 °C and pH between 8.0 and 9.0. The adsorbents were regenerated by thermal desorption at 450 °C with a thorough decomposition of CIP. The adsorption mechanism was mainly dominated by its special porous microspheres-accumulation structure and surface species (e.g., FeP and graphite). Moreover, HMs in the adsorbents were well immobilized in SPA-N-1100 by the generation of new metal mineral phases and encapsulation of melting minerals, which had an ultralow potential for ecological risk during application.

Study of ciprofloxacin removal by biochar obtained from used tea leaves.

In this study, used tea leaves (UTLs) were pyrolyzed to obtain used tea-leaf biochar (UTC), and then the UTC was used as an adsorbent to remove ciprofloxacin (CIP) from aqueous solutions. Batch experiments were conducted to investigate the CIP adsorption performance and mechanism. The results showed that the CIP-adsorbing ability first increased and then declined as the UTC pyrolysis temperature increased. The UTC obtained at 450°C presented excellent CIP-absorbing ability at pH6 and 40°C. The maximum monolayer adsorption capacity was 238.10mg/g based on the Langmuir isotherm model. The pseudo-second-order kinetic equation agreed well with the CIP adsorption process, which was controlled by both external boundary layer diffusion and intra-particle diffusion. The characterization analysis revealed that the OH groups, CC bonds of aromatic rings, CH groups in aromatic rings and phenolic CO bonds play vital roles in the CIP adsorption process, and that the NC, NO, OCO and COH groups of UTC were consumed in large quantities. π-π interactions, hydrogen bonding and electrostatic attraction are inferred as the main adsorption mechanisms. The present work provides not only a feasible and promising approach for UTLs utilization but also a potential adsorbent material for removing high concentrations of CIP from aqueous solutions.

Biodegradation of sulfamethazine by an isolated thermophile-Geobacillus sp. S-07.

Sulfamethazine (SM2) is an antimicrobial drug that is frequently detected in manure compost, is difficult to degrade at high temperatures and is potentially threatening to the environment. In this study, a thermophilic bacterium was isolated from the activated sludge of an antibiotics pharmaceutical factory; this bacterium has the ability to degrade SM2 at 70 °C, which is higher than the traditional manure composting temperature. The strain S-07 is closely related to Geobacillus thermoleovorans based on its 16S rRNA gene sequence. The optimal conditions for the degradation of SM2 are 70 °C, pH 6.0, 50 rpm rotation speed and 50 mL of culture volume. More than 95% of the SM2 contained in media was removed via co-metabolism within 24 h, which was a much higher percentage than that of the type strain of G. thermoleovorans. The supernatant from the S-07 culture grown in SM2-containing media showed slightly attenuated antibacterial activity. In addition, strain S-07 was able to degrade other sulfonamides, including sulfadiazine, sulfamethoxazole and sulfamerazine. These results imply that strain S-07 might be a new auxiliary bacterial resource for the biodegradation of sulfonamide residue in manure composting.

Unveiling the migration of Cr and Cd to biochar from pyrolysis of manure and sludge using machine learning.

Heavy metal (HM) in biochar derived from pyrolysis of sludge or manure is the main issue for its large-scale application in soils for carbon sequestration. However, there is a paucity of efficient approaches to predict and comprehend the HM migration during pyrolysis for preparing low HM-contained biochar. Herein, the data on the feedstock information (FI), additive, total concentration of feedstock (FTC) of HM (i.e., Cr and Cd), and pyrolysis condition, were extracted from the literature, to predict total concentration (TC) and retention rate (RR) of Cr and Cd in sludge/manure biochar using machine learning for mapping their migration during pyrolysis. Two datasets for Cr and Cd were compiled with 388 and 292 data points from 48 and 37 peer-review papers. The results indicated that the TC and RR of Cr and Cd could be predicted by the Random Forest model with test R2 of 0.74-0.98. Their TC and RR in biochar were dominated by the FTC and FI, respectively; while pyrolysis temperature was the most important to Cd RR. Moreover, potassium-based inorganic additives decreased the TC and RR of Cr while increased those of Cd. The predictive models and insights provided by this work could aid the understanding of HM migration during manure and sludge pyrolysis and guide the preparation of low HM-contained biochar.

Wet wastes to bioenergy and biochar: A critical review with future perspectives.

The ever-increasing rise in the global population coupled with rapid urbanization demands considerable consumption of fossil fuel, food, and water. This in turn leads to energy depletion, greenhouse gas emissions and wet wastes generation (including food waste, animal manure, and sewage sludge). Conversion of the wet wastes to bioenergy and biochar is a promising approach to mitigate wastes, emissions and energy depletion, and simultaneously promotes sustainability and circular economy. In this study, various conversion technologies for transformation of wet wastes to bioenergy and biochar, including anaerobic digestion, gasification, incineration, hydrothermal carbonization, hydrothermal liquefaction, slow and fast pyrolysis, are comprehensively reviewed. The technological challenges impeding the widespread adoption of these wet waste conversion technologies are critically examined. Eventually, the study presents insightful recommendations for the technological advancements and wider acceptance of these processes by establishing a hierarchy of factors dictating their performance. These include: i) life-cycle assessment of these conversion technologies with the consideration of reactor design and catalyst utilization from lab to plant level; ii) process intensification by integrating one or more of the wet waste conversion technologies for improved performance and sustainability; and iii) emerging machine learning modeling is a promising strategy to aid the product characterization and optimization of system design for the specific to the bioenergy or biochar application.

Biosynthesis of polyhydroxyalkanoate from food waste oil by Pseudomonas alcaligenes with simultaneous energy recovery from fermentation wastewater.

Bioconversion of food waste oil (FWO) into biodegradable plastic is a promising method for converting waste into high-value products. In this study, a strain (Pseudomonas sp. H3) was isolated for polyhydroxyalkanoate (PHA) synthesis from FWO. After 72 h of cultivation with 20 g/L of FWO, the high cell dry weight (CDW) of 3.6 g/L, PHA yield of 2.4 g/L, and PHA content of 65 wt% were obtained under the optimal temperature (25 °C) and inoculum amount (6% (v/v)). Fed-batch fermentation was conducted in a 5 L bioreactor with a maximum CDW of 16 g/L, PHA content of 54 wt%, and PHA productivity of 0.23 g/(L·h) after 36 h. The PHA had a molecular weight of 54 782 Da and a low polydispersity index of 1.41 with glass transition, melting, and degradation temperatures of -20 °C, 34 °C, and 210 °C, respectively. To further utilize the wastewater after PHA production, anaerobic digestion was employed for CH4 production, and the CH4 yield was 284 mL/g volatile solids. Microbial community analysis showed that the abundance of acetate-oxidizing bacteria and Methanobacterium significantly increased during anaerobic digestion. This study describes a new strain for the economical synthesis of biodegradable plastics and presents a novel framework for fully utilizing FWO with the production of PHA and CH4.

Ciprofloxacin adsorption by biochar derived from co-pyrolysis of sewage sludge and bamboo waste.

Antibiotics residues in aqueous environment and sewage sludge accumulation have become serious environmental issues. The aim of this study is to investigate the potential of ciprofloxacin (CIP) removal by sludge-based biochar prepared from co-pyrolysis of sewage sludge and bamboo waste (BW). The stability and environmental risk of heavy metals (HMs) in the biochar were further investigated to evaluate potential risks for biochar utilization. Results showed that BW was an outstanding additive to prepare co-pyrolyzed biochar from sludge. A higher CIP removal rate (95%) of BW-sludge biochar (SBC) was obtained under initial CIP concentration of 10 mg/L, and its maximum adsorption capacity was 62.48 mg/g which was calculated from the Langmuir model. The pseudo-second-order and Freundlich model also well fit the CIP adsorption process, indicating a chemical and multilayer adsorption of CIP on a heterogeneous surface of biochar. Adsorption mechanism analysis indicated that the diverse functional groups and Fe species in biochar probably were the dominant factors in the adsorption of CIP. The π-π interaction, H-bond, ion exchange, and Fe-complexation might be the main interactions between the functional species and CIP molecules. Besides, HMs, especially the Cr, Cd, and As, were well immobilized in SBC compared with pure sludge biochar. This work suggested that sludge-based biochar, especially the co-pyrolyzed SBC, could be a potential adsorbent for CIP removal from aqueous solutions.

The synthesis of heterogeneous Fenton-like catalyst using sewage sludge biochar and its application for ciprofloxacin degradation.

The terminal utilization of sewage sludge biochar (SSB) is nonnegligible and significant for sewage sludge (SS) treatment by pyrolysis. In this paper, a novel low-cost recyclable sludge biochar catalyst (SBC) that can be employed as a heterogeneous Fenton-like catalyst was prepared using SSB from SS pyrolysis in a pilot-scale platform for ciprofloxacin (CIP) degradation. The fabricated SBC was analyzed to characterize its surface micrographs, pore structures, and chemical composition. The catalytic effect of SBC on CIP degradation was also explored to determine the feasibility of using SBC to remove aquatic organic contaminants, and its degradation mechanism and pathway were also discussed. SBC can effectively remove CIP by adsorption and enhance the degradation of CIP by its catalytic effect. >80% of the CIP was removed at pH 4.0, and the antimicrobial activity of the resulting products was considerably reduced. The possible degradation mechanism is associated with the synergetic effect of adsorption and oxidative degradation. Oxidizing radical was generated from H2O2 by the activation of Fe2+ and Fe3+, which released from SBC, and HO was the dominant radical in CIP degradation. Piperazine ring cleavage, pyridine cleavage and hydroxylation, F/OH substitution, and defluorination were the dominant degradation pathways. The heavy metal risk assessment showed that SBC exhibits low environmental and ecological risk. This study provides a prospective method for high-value utilization of SSB and a novel and potentially low-cost catalyst for CIP removal from aqueous environments, which is significant for the terminal disposal of SS.

Immobilization of heavy metals in ceramsite produced from sewage sludge biochar.

Ceramsite was prepared from sewage sludge biochar (SSB). The migration, speciation evolution, leaching toxicity, and potential environmental risk of heavy metals (HMs) in sludge biochar ceramsite (SBC) were investigated. The characteristics of the SBC met the requirements for Chinese lightweight aggregate standards (GB/T 1743.1-2010 and JT/T 770-2009) and the heavy metals (HMs: Cu, Zn, Cr, Pb, and Cd) were well immobilized in the SBC. The leaching percentages of the HMs in SBC were remarkably reduced, in particular after preheating at 400°C and sintering at 1100°C. The leaching percentages of Cu, Zn, Cr, Cd, and Pb decreased from (19.099, 18.009, 0.010, 3.952, and 0.379) % to (2.122, 4.102, 0.002, 1.738, and 0.323) %, respectively. The RAC values of the HMs in SBC were all lower than 1%, and the risk index (RI) suggested that the SBC had no HMs contamination and very low potential ecological risk when used in the environment. Furthermore, the HM-immobilization mechanisms were mainly related to the formation of new crystal phases (silicate and phosphate minerals) by incorporation of HMs, and to vitrification and encapsulation with low concentration of HMs on the surface. This work provides a useful method for large-scale reuse of SSB with very low leaching toxicity and low potential ecological risk of HMs.

Study of ciprofloxacin biodegradation by a Thermus sp. isolated from pharmaceutical sludge.

Ciprofloxacin (CIP) is an antibiotic drug frequently detected in manure compost and is difficult to decompose at high temperatures, resulting in a potential threat to the environment. Microbial degradation is an effective and environmentally friendly method to degrade CIP. In this study, a thermophilic bacterium that can degrade CIP was isolated from sludge sampled from an antibiotics pharmaceutical factory. This strain is closely related to Thermus thermophilus based on 16S rRNA gene sequence analysis and is designated C419. The optimal temperature and pH values for CIP degradation are 70°C and 6.5, respectively, and an appropriate sodium acetate concentration promotes CIP degradation. Seven major biodegradation metabolites were identified by an ultra-performance liquid chromatography tandem mass spectrometry analysis. In addition, strain C419 degraded other fluoroquinolones, including ofloxacin, norfloxacin and enrofloxacin. The supernatant from the C419 culture grown in fluoroquinolone-containing media showed attenuated antibacterial activity. These results indicate that strain C419 might be a new auxiliary bacterial resource for the biodegradation of fluoroquinolone residue in thermal environments.

[Preparation of Adsorption Ceramsite Derived from Sludge Biochar].

Adsorption ceramsite (SKC) was prepared with biochar (BC) derived from municipal sludge and kaolin (KL) based on the optimized processing parameters to adsorb ciprofloxacin (CIP) in aqueous solutions. The CIP adsorption mechanism of SKC was investigated by adsorption kinetics and isotherm adsorption models, combined with the analysis of microstructure, pore structure, phase composition, and zeta potential. Furthermore, the heavy metal leaching toxicity was assessed using the toxicity characteristic leaching procedure (TCLP) method. The results showed that SKC, with 60% BC and 40% KL calcining at 1,050℃ for 5 min, showed an outstanding removal efficiency of CIP (65.34%). The pseudo-second-order equation agreed with the adsorption behavior and the Freundlich model described the adsorption process well. The adsorption process was a multilayer adsorption controlled by physical and chemical reactions. The leaching concentration of heavy metals, trapped by the mineral phases in SKC was much lower than that in BC, indicating low ecotoxicological risk. SKC possessed the ability to adsorb CIP with its developed porosity and characteristic mineralogical phases, including silicon aluminum oxide and iron oxide. This work provides a low-cost recyclable sorbing material to remove high concentration CIP from wastewater and offers a new idea for the large-scale safe use of BC.