Efficient adsorption of tetracycline in aquatic system by thermally-treated sediment

Reclamation of co-pyrolyzed dredging sediment as soil cadmium and arsenic immobilization material: Immobilization efficiency, application safety, and underlying mechanisms

The safe management of toxic metal-polluted dredging sediment (DS) is imperative owing to its potential secondary hazards. Herein, the co-pyrolysis product (DS@BC) of polluted DS was creatively applied to immobilize soil Cd and As to achieve DS resource utilization, and the efficiency, safety, and mechanism were investigated. The results revealed that the DS@BC was more effective at reducing soil Cd bioavailability than the DS was (58.9-73.2% vs. 21.8-27.4%), except for the dilution effect, whereas the opposite phenomenon occurred for soil As (25.5-35.7% vs. 35.7-42.8%). The DS@BC immobilization efficiency was dose-dependent for both Cd and As. Soil labile Cd and As were transformed to more stable fractions after DS@BC immobilization. DS@BC immobilization inhibited the transfer of soil Cd and As to Brassica chinensis L. and did not cause excessive accumulation of other toxic metals in the plants. The appropriate addition of the DS@BC (8%) sufficiently alleviated the oxidative stress response of the plants and enhanced their growth. These findings indicate that the DS@BC was safe and effective for soil Cd and As immobilization. DS@BC immobilization decreased the diversity and richness of the rhizosphere soil bacterial community because of the dilution effect. The DS@BC immobilized soil Cd and As via direct adsorption, and indirect increasing soil pH, and regulating the abundance of specific beneficial bacteria (e.g., Bacillus). Therefore, the use of co-pyrolyzed DS as a soil Cd and As immobilization material is a promising resource utilization method for DS. Notably, to verify the long-term effects and safety of DS@BC immobilization, field trials should be conducted to explore the effectiveness and risk of harmful metal release from DS@BC immobilization under real-world conditions.

Enhanced aerobic granular sludge by thermally-treated dredged sediment in wastewater treatment under low superficial gas velocity

The positive contributions of carriers to aerobic granulation have been wildly appreciated. In this study, as a way resource utilization, the dredged sediment was thermally-treated to prepared as carriers to promote aerobic granular sludge (AGS) formation and stability. The system was started under low superficial gas velocity (SGV, 0.6 cm/s)for a lower energy consumption. Two sequencing batch reactors (SBR) labeled R1 (no added carriers) and R2 (carriers added), were used in the experiment. R2 had excellent performance of granulation time (shortened nearly 43%). The maximum mean particle size at the maturity stage of AGS in R2 (0.545 mm) was larger compared to R1 (0.296 mm). The sludge settling performance in R2 was better. The reactors exhibited high chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal rates. The total phosphorus (TP) removal rate in R2 was higher than R1 (almost 15% higher) on stage II (93-175d). R2 had a higher microbial abundance and dominant bacteria content. The relative abundance of dominant species was mainly affected by the carrier. However, the enrichment of dominant microorganisms and the evolution of subdominant species were more influenced by the increase of SGV. The results indicated that the addition of carriers induced the secretion of extracellular polymeric substances (EPS) by microorganisms and accelerated the rapid formation of initial microbial aggregates. This work provided a low-cost method and condition to enhance aerobic granulation, which may be helpful in optimizing wastewater treatment processes.

Is it possible for fulvic acid modified dredged sediment biochar to adsorb tetracycline and result in a novel method of resource utilization?

In this study, dredged sediment from Baiyang Lake was used as raw material to prepare DSB at a pyrolysis temperature of 600 °C and in an anoxic pyrolysis atmosphere. The adsorption and removal performance of tetracycline in water of DSB were investigated using fulvic acid (FA) as the activator. The biochar materials were first characterized (SEM, BET, XRD, FTIR, and XPS), and the elemental composition and surface functional groups of F-DSB were investigated. The maximum adsorption capacity of F-DSB, according to the Langmuir model, was 72.3 mg/g. Results demonstrated that F-DSB exhibited good adsorption performance. In conclusion, FA is a potential green modifier that can be used to improve the adsorption properties of DSB. This research will be useful in improving our understanding of the possible adsorption mechanism and process optimization of modified DSB. This work offers a novel approach to the resource utilization of dredged sediment.

Removal of tetracycline in aqueous solution by iron-loaded biochar derived from polymeric ferric sulfate and bagasse

In this study, the tetracycline (TC) removal performance of iron-loaded biochar (BPFSB) derived from sugarcane bagasse and polymerized iron sulfate was investigated, and the mechanism of TC removal was also explored by study of isotherms, kinetics and thermodynamics and characterization of fresh and used BPFSB (XRD, FTIR, SEM and XPS). The results showed that under optimized conditions (initial pH 2; BPFSB dosage 0.8 g·L-1; TC initial concentration 100 mg·L-1; Contact time 24 h; temperature 298 K), the removal efficiency of TC was as high as 99.03%. The isothermal removal of TC followed well the Langmuir, Freundlich, and Temkin models, indicating that multilayer surface chemisorption dominated the TC removal. The maximum removal capacity of TC by BPFSB at different temperatures was 185.5 mg·g-1 (298 K), 192.7 mg·g-1 (308 K), and 230.9 mg·g-1 (318 K), respectively. The pseudo-second-kinetic model described the TC removal better, while its rate-controlling step was a combination of liquid film diffusion, intraparticle diffusion, and chemical reaction. Meanwhile, TC removal was also a spontaneous and endothermic process, during which the randomness and disorder between the solid-liquid interface was increased. According to the characterization of BPFSBs before and after TC removal, H-bonding and complexation were the major interactions for TC surface adsorption. Furthermore, BPFSB was efficiently regenerated by NaOH. In summary, BPFSB had the potential for practical application in TC removal.

Co-pyrolysis with pine sawdust reduces the environmental risks of copper and zinc in dredged sediment and improves its adsorption capacity for cadmium

Proper treatment of heavy metal-contaminated dredged sediment (DS) is crucial to avoid secondary pollution. Effective and sustainable technologies are desired for the treatment of Zn- and Cu-contaminated DS. Due to the advantages of low energy consumption and time saving, co-pyrolysis technology was innovatively applied to treat Cu- and Zn-polluted DS in this study, and the effects of the co-pyrolysis conditions on Cu and Zn stabilization efficiencies, potential stabilization mechanisms, and the possibility for resource utilization of co-pyrolysis product were also investigated. The results showed that pine sawdust is an appropriate co-pyrolysis biomass for the stabilization of Cu and Zn based on the leaching toxicity analysis. The ecological risks of Cu and Zn in DS were reduced after co-pyrolysis treatment. The total concentrations of Zn and Cu in co-pyrolysis products were decreased by 5.87%-53.45% and 8.61%-57.45% of that in DS before co-pyrolysis. However, the total concentrations of Zn and Cu in DS remained basically unchanged after co-pyrolysis, which indicating the decreases in total concentrations of Zn and Cu in co-pyrolysis products were mainly related to dilution effect. Fraction analysis indicated that co-pyrolysis treatment contributed to transforming weakly bound Cu and Zn into stable fractions. The co-pyrolysis temperature and mass ratio of pine sawdust/DS had a greater influence than co-pyrolysis time on the fraction transformation of Cu and Zn. The leaching toxicity of Zn and Cu from the co-pyrolysis products was eliminated when the co-pyrolysis temperature reached 600 and 800 °C, respectively. Analysis of the X-ray photoelectron spectroscopy and X-ray diffraction results demonstrated that co-pyrolysis treatment could transform mobile Cu and Zn in DS into metal oxides, metal sulfides, phosphate compounds, etc. Batch adsorption procedures suggested that the co-pyrolysis product possessed a high adsorption capacity for Cd (95.70 mg/g at 318 K). The formation of CdCO₃ precipitates and the complexation effects of oxygen-containing functional groups were the principal adsorption mechanisms of the co-pyrolysis product. Overall, this study provides new insights into sustainable disposal and resource utilization for heavy metal-contaminated DS.

Positive feedback on dewaterability of waste-activated sludge by the conditioning process of Fe(II) catalyzing urea hydrogen peroxide

The treatment and disposal of sludge is a complex environmental problem because of the high moisture content. Herein, We reported the process of Fe(II) activating Urea hydrogen peroxide (UHP) to improve waste activated sludge (WAS) dewaterability for the first time. Fe(II)/UHP was proven to significantly improve WAS dewaterability. Specifically, under the optimal conditions with 60/35-Fe(II)/UHP mg/g TSS, the CST, SRF, and WC_SC of WAS reduced from 215.3 ± 7.5s, 9.2 ± 0.32 (× 10¹² m/kg), and 92.2 ± 0.7% (control) to 62.3 ± 4.3s, 2.8 ± 0.09 (× 10¹²m/kg), and 70.4 ± 0.4%, respectively. Further analysis revealed that •OH was generated in the Fe(II)/UHP system and played the dominant role in enhancing WAS dewaterability. •OH was found to attack extracellular polymeric substances (EPSs) and cells, causing EPSs fragmentation and decomposition part of EPSs into micro-molecule organics or even inorganics, and leading to cell destruction, thus liberating the EPSs-bound and cells-bound water. •OH also degraded the protein in centrifugal liquor (CL) into micro-molecule organics such as amino acids, which could reduce the viscosity and electronegativity of CL. The above facts ultimately reduced solid-liquid interface interaction but increased hydrophobicity, flocculation, and flowability of WAS. Meanwhile, the broken WAS flocs were then re-flocculated via adsorption bridging and charge neutralization induced by Fe(II) and Fe(III). Moreover, Fe(II)/UHP treatment achieved the reduction and stabilization of heavy metals of dewatered sludge, which further enabled its land application. Finally, the Fe(II)/UHP process was found to be more attractive than the Fe(II)/persulfate, classical Fenton processes, and cPAM in terms of cost savings and practical implementation.