Vermicompost as a natural adsorbent: evaluation of simultaneous metals (Pb, Cd) and tetracycline adsorption by sewage sludge-derived vermicompost

Protaetia brevitarsis larvae produce frass that can be used as an additive to immobilize Cd and improve fertility in alkaline soils

Bioconversion of agricultural waste by Protaetia brevitarsis larvae (PBL) holds significant promise for producing high-quality frass organic amendments. However, the effects and mechanisms of PBL frass on Cd immobilization in an alkaline environment remain poorly understood. In this study, three types of frass, namely maize straw frass (MF), rice straw frass (RF), and sawdust frass (SF), were produced by feeding PBL. The Cd immobilization efficiencies of three frass in alkaline solutions and soils were investigated through batch sorption and incubation experiments, and spectroscopic techniques were employed to elucidate the sorption mechanisms of Cd onto different frass at the molecular level. The results showed that MF proved to be an efficient sorbent for Cd in alkaline solutions (176.67-227.27 mg g-1). X-ray absorption near-edge structure (XANES) spectroscopy indicated that Cd immobilization in frass is primarily attributed to the association with organic matter (OM-Cd, 78-90%). And MF had more oxygen-containing functional groups than the other frass. In weakly alkaline soils, MF application (0.5-1.5%) significantly decreased Cd bioavailability (5.65-18.48%) and concurrently improved soil nutrients (2.21-56.79%). Redundancy analysis (RDA) unveiled that pH, CEC, and available P were important factors controlling Cd fractions. Path analysis demonstrated that MF application affected Cd bioavailability directly and indirectly by influencing soil chemical properties and nutrients. In summary, MF, the product of PBL-mediated conversion maize straw, demonstrated promise as an effective organic amendment for Cd immobilization and fertility improvement in alkaline soils.

Effect of humic compost on the adsorption of cadmium (II) in aqueous medium

The humic compost obtained from the treatment of tobacco from smuggled cigarettes (SCT) and industrial sewage sludge (ISS) was evaluated as adsorbent for Cd (II) in aqueous solution, for possible decontamination of water resources. Optimum conditions were found at pH 5 and a 3 g/L adsorbent concentration, which presented 92% Cd (II) removal and maximum adsorption capacity of 28.546 mg/g. The pseudo-second-order kinetic model presented the best fit, pointing 120 min as the time needed to attain a steady state. FTIR and EDX results suggest the formation of coordinated Cd (II) bonds by functional groups between the compost and the solution. The results obtained in real samples showed that, even under different environmental conditions, the Cd (II) adsorption varied between 80.05 and 91.61%. The results indicated that the compost evaluated can be used for remediation of Cd (II)-contaminated water resources.

Highly efficient preferential adsorption of Pb(II) and Cd(II) from aqueous solution using sodium lignosulfonate modified illite

In this study, sodium lignosulfonate modified illite (LS-ILT), an environmentally friendly adsorbent, was prepared by hydrothermal modification. An extensive study of Pb(II) and Cd(II) adsorption behavior and the mechanisms were conducted by evaluating the effects of initial pH value, sorbents dosage, and initial concentration of Pb(II) and Cd(II). Results showed that the adsorption characteristics of Pb(II) and Cd(II) by LS-ILT were well described by quasi-second-order kinetics and the Freundlich model, and the maximum adsorption capacity of Pb(II) and Cd(II) was 42.3 mg/g and 17.0 mg/g, respectively. The optimal application conditions for adsorption equilibrium were the dosage of 4 g/L and reaction pH = 5.5-5.8. The adsorption stability of Pb(II) by LS-ILT was better than that of Cd(II), and most of the existence of coexisting cations had no obvious inhibitory effect on the removal of Pb(II) and Cd(II). Furthermore, the dynamic adsorption results showed that LS-ILT can meet the ultra-low emission standard, and the adsorption capacity could maintain over 50% after four cycles, further providing certain guiding significance for the treatment of wastewater with ultra-low concentrations of heavy metals Pb(II) and Cd(II).

Remediation of heavy metal polluted waters using activated carbon from lignocellulosic biomass: An update of recent trends

The use of a cheap and effective adsorption approach based on biomass-activated carbon (AC) to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this review provides an update of recent works utilizing biomass waste-AC to adsorb commonly-encountered adsorbates like Cr, Pb, Cu, Cd, Hg, and As. Various biomass wastes were employed in synthesizing AC via two-steps processing; oxygen-free carbonization followed by activation. In recent works related to the activation step, the microwave technique is growing in popularity compared to the more conventional physical/chemical activation method because the microwave technique can ensure a more uniform energy distribution in the solid adsorbent, resulting in enhanced surface area. Nonetheless, chemical activation is still generally preferred for its ease of operation, lower cost, and shorter preparation time. Several mechanisms related to heavy metal adsorption on biomass wastes-AC were also discussed in detail, such as (i) - physical adsorption/deposition of metals, (ii) - ion-exchange between protonated oxygen-containing functional groups (-OH, -COOH) and divalent metal cations (M²⁺), (iii) - electrostatic interaction between oppositely-charged ions, (iv) - surface complexation between functional groups (-OH, O^2-, -CO-NH-, and -COOH) and heavy metal ions/complexes, and (v) - precipitation/co-precipitation technique. Additionally, key parameters affecting the adsorption performance were scrutinized. In general, this review offers a comprehensive insight into the production of AC from lignocellulosic biomass and its application in treating heavy metals-polluted water, showing that biomass-originated AC could bring great benefits to the environment, economy, and sustainability.

Activation of biochar through exoenzymes prompted by earthworms for vermibiochar production: A viable resource recovery option for heavy metal contaminated soils and water

The industrial revolution and indiscriminate usage of a wide spectrum of agrochemicals account for the dumping of heavy metals in the environment. In-situ/ex-situ physical, chemical, and bioremediation strategies with pros and cons have been adopted for recovering metal contaminated soils and water. Therefore, there is an urgent requirement for a cost-effective and environment-friendly technique to combat metal pollution. Biochar combined with earthworms and vermifiltration is a suitable emerging technique for the remediation of metal-polluted soils and water. The chemical substances (e.g., sodium hydroxide, zinc chloride, potassium hydroxide, and phosphoric acid) have been used to activate biochar, which also faces several shortcomings. Studies reveal that extracellular enzymes have been used to activate biochar which is produced by earthworms and microbes that can alter the surface of the biochar. The present review focuses on the global scenario of metal pollution and its remediation through biochar activation using earthworms. The earthworms and biochar can produce "vermibiochar" which is capable of reducing the metal ions from contaminated water and soils. The vermifiltration can be a suitable technology for metal removal from wastewater/effluent. Thus, the biochar has a trick of producing entirely new options at a time when vermifiltration and other technologies are least expected. Further attention to the biochar-assisted vermifiltration of different sources of wastewater is required to be explored for the large-scale utilization of the process.

Insight into the co-adsorption behaviors and interface interactions mechanism of chlortetracycline and lead onto struvite loaded diatomite

Finding effective methods for simultaneous removal of antibiotics and heavy metals has attracted increasing concerns. Herein, we investigated the co-adsorption behaviors of chlortetracycline (CTC) and Pb (II) onto struvite loaded diatomite (SD) in aqueous solution, and their interface interactions mechanism was investigated using crystal and microstructure analysis combined with density functional theory (DFT) calculations. The adsorption capacity at equilibrium of CTC increased from 44.28 to 87.58 mmol/kg with the presence of Pb (II), but the adsorption capacity at equilibrium of Pb (II) decreased from 4289.70 to 3559.9 mmol/kg with the presence of CTC. Besides, the effect of environmental factors (solution pH and humic acid) was also evaluated. Microstructure analysis for recovered products demonstrated that the interface interactions brought by the surface Pb(II) of Pb₅(PO₄)₃OH and carbonyl-O of CTC could facilitate the removal of CTC but inhibit the removal of Pb(II) by suppressing the crystal growth of Pb₅(PO₄)₃OH, especially the orientation growth of (0 0 1) crystal plane. DFT calculations gave theoretical support for the interface interactions between Pb₅(PO₄)₃OH and CTC.

Optimizing the amount of pig manure in the vermicomposting of spent mushroom (Lentinula) substrate

BACKGROUND

The mushroom industry produces a large amount of spent mushroom substrate (SMS), which requires a large geographical footprint and causes pollution.

METHODS

We sought to optimize the C:N ratio of the initial feedstock used in vermicomposting of SMS by adding pig manure additions. We applied five treatments to the initial feedstock (S0, S1, S2, S3, and S4) with different C:N ratio of approximately 35, 30, 25, 20, and 15, respectively.

RESULTS

Our results showed that lignin and cellulose in SMS were degraded after 56 days vermicomposting, especially in S2 (77.05% and 45.29%, respectively) and S3 (65.05% and 48.37%, respectively) treatments. We observed the degradation of the fibrous structure in SMS using pig manure treatments after vermicomposting by microscope and scanning electron microscope. Cellulase and polyphenol oxidase (PPO) were enhanced in pig manure treatments during vermicomposting, especially in the S2 and S3 treatments. The biomass of earthworms in the S2 treatments was at its highest level among all treatments at 28 to 56 days. The high level of PPO activity in the S2 treatment may protect cellulase and earthworms against the aromatic toxicity that is a byproduct of lignin degradation, particularly at 28 to 56 days of vermicomposting. Conclusively, it indicated that the C/N ratio of 25 in the S2 treatment was the optimal for SMS vermicomposting with the addition of pig manure. Our results provide a positive application for the recycling of both SMS and pig manure.

Comparison of adsorption behavior studies of Cd2+ by vermicompost biochar and KMnO4-modified vermicompost biochar

Cd²⁺ pollution in aquatic environments can pose a serious threat to human health. Biochar can remove Cd²⁺ from aquatic environments, but the Cd²⁺adsorption capacity of conventional biochar is low, therefore, we focused on exploring the Cd²⁺ adsorption capacity of modified biochar. In this study, KMnO₄ was used to modify vermicompost biochar (VBC), and static adsorption tests for Cd²⁺ were carried out. The biochar properties and its adsorption efficiency toward Cd²⁺ before and after modification were studied by kinetics and isotherm model fitting, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Additionally, an adsorption mechanism was discussed. The results showed that the KMnO₄-modification resulted in a successful loading of the vermicompost biochar with MnO₂, which greatly improved its adsorption capacity for Cd²⁺. The adsorption of Cd²⁺ by VBC and MVBC was a spontaneous, endothermic, and monolayer chemical adsorption process. Mineral precipitation mechanism accounted for the largest proportion, and CdCO₃ was the main precipitate. After modification the proportion of surface precipitation and other mechanisms (π-electron coordination and the inner/outer sphere surface coordination) increased，while adsorption via cation exchange, oxygen-containing functional groups, physical adsorption and electrostatic attraction reduced. Hence, KMnO₄ modification has a significant effect on the Cd²⁺ adsorption behavior of vermicompost biochar.

A review on tetracycline removal from aqueous systems by advanced treatment techniques

Tetracycline occurrence and advanced treatment techniques.

Remediation effectiveness of vermicompost for a potentially toxic metal-contaminated tropical acidic soil in China

Potentially toxic metal (PTM) contamination coupled with soil acidification has posed a severe threat to agricultural sustainability of tropical region in the world. In this study, a vermicopomst (VC) produced from vermicomposting cattle manure under tropical environment was applied to remediating a tropical acidic soil in Hainan, China. The effectiveness of VC in reducing available PTMs in soils was evaluated by incubation experiments with a Cd, Cr or Ni spiked soil and a Cd contaminated field soil. The dynamic changes of soil physical, chemical and biological properties after VC amendment were determined to understand the mechanisms of PTM immobilization. The results showed that VC amendment significantly reduced 0.01M CaCl₂ extractable amounts of Cd, Ni and Cr in the spiked soils, and CaCl₂ extractable Cd was reduced by 49.3% when VC was amended to the Cd contaminated field soil. Thermodynamic studies showed that VC had a high adsorption capacity for Cd, Ni and Cr, with the maximum adsorption (obtained from the Langmuir model) of 33.45, 26.17, and 20.88 mg/g, respectively. The reduction in CaCl₂ extractable metals after VC amendment was consistent with the order of maximum adsorption of VC for Cd, Ni, and Cr. Vermicompost amendment increased soil pH by 0.7 to 1.5 units, which is positively related with VC rate, but negatively with the decrease in extractable metals. These results indicates that adsorption of metals onto VC and an increase in soil pH after VC amendment are likely responsible for the decreased availability of Cd, Ni, and Cr in the contaminated soil. In addition, the addition of stable organic substances and subsequent formation of water-stable aggregates may be also beneficial for immobilizing PTMs and improving tropical soil quality.

Potential use of composts and vermicomposts as low-cost adsorbents for dye removal: an overlooked application

The use of composts and vermicomposts as adsorbents is an important topic of study in the field of environmental remediation. These materials are rich in organic matter and have functional groups that can interact with organic and inorganic compounds. They also contain microorganisms that can promote biodegradation of organic substances. Composts that cannot be used for agronomic purposes (owing to e.g. low nutrient levels or phytotoxicity) may be valuable for soil remediation or pollutant removal. In this review, we discuss papers on this topic, with the objective of drawing attention to the potential use of composts/vermicomposts and to recommend further investigation on this subject. Few published studies have investigated the use of composts/vermicomposts to remove dyes and other coloured compounds. However, preliminary results show that these materials are potentially good adsorbents, at least comparable to other low-cost adsorbents, and that, in general, basic dyes are more efficiently removed than direct, reactive or acid dyes. The results of the works reviewed also show that dye removal takes place by adsorption mechanisms, in most studies following a Langmuir model, and that the kinetics of removal are fast and follow a pseudo-second order model. However, there remain several uncertainties regarding this application. For example, very few dyes have been studied so far, and little is known about the influence of the properties of composts/vermicomposts on the dye removal process. Moreover, the possible use of compost/vermicompost to enhance biodegradation processes has not been explored. All these questions should be addressed in future research.

Is vermicompost the possible in situ sorbent? Immobilization of Pb, Cd and Cr in sediment with sludge derived vermicompost, a column study

The goal of this study was to investigate the immobilization effect of vermicomposted sewage sludge for Pb, Cd and Cr in the sediment under simulated in situ conditions using column test. Positioning 10% dw of vermicompost at the bottom layer of the column resulted in an average decrease of Pb, Cd and Cr in the leachate of 93, 97 and 75.5%, with the accumulated adsorbed amount of 11.80, 4.81 and 5.62 mg g^-1, respectively. Fluorescence Excitation‒Emission Matrix (EEM) combined with parallel factor analysis (PARAFAC) was adopted to identify the components in DOM (dissolved organic matter) that were efficient for the immobilization of heavy metals. The 4‒component PARAFAC model established showed that DOM was dominated by a protein‒like material (component C1), and three humic‒like materials (component C2, C3 and C4). The humic substances formed the organo‒metal complexes with Pb, Cr and Cd, hence, the metal ions were sequestered by the sorbent. Also, as calculated by the bivariate coefficients, the C2/C1 ratios can be liable parameters for assessing the retaining capability of vermicompost for heavy metals. Generally, vermicompost can be used as a promising in situ sorbent for the remediation of heavy metal polluted sediments.

Pb2+ adsorption by a compost obtained from the treatment of tobacco from smuggled cigarettes and industrial sewage sludge

The adsorption of Pb2+ by a compost obtained from the treatment of tobacco from smuggled cigarettes (SCT) and industrial sewage sludge (ISS) was investigated. The Pb2+ adsorption process was evaluated as function of different concentrations of adsorbent and adsorbate, pH variations, and contact time. Fourier transformed infrared spectroscopy (FTIR) and energy dispersive X-ray spectrometry (EDX) were adopted to obtain information regarding structural changes and a better understanding of the adsorption mechanism. The adsorbent maximum adsorption capacity for Pb2+, calculated using the Sips equation, was 21.454 mg/g with 3 g/L adsorbent at pH 5. The adsorption kinetics best adjustment was obtained using the pseudo-second-order model with a time of 240 min to reach the adsorption equilibrium. FTIR and EDX results suggest that Pb2+ might have bonded to phenolic, carboxylic, hydroxyl, and amine groups; they also show formation of organometallic complexes and cationic exchange between the compost and the solution. The study confirmed that the compost evaluated can be used as a potential adsorbent in environments contaminated with Pb2+.

Synthesis of a novel magnetic nano-scale biosorbent using extracellular polymeric substances from Klebsiella sp. J1 for tetracycline adsorption

The magnetic nano-scale biosorbent (Fe₃O₄/MFX) was synthesized by the chelation and cross-linking procedure with extracellular polymeric substances (MFX) and Fe₃O₄. Fe₃O₄/MFX possessed the porous structure and numerous functional groups (i.e., amino, carboxyl, and hydroxyl), and its core region had a typical size of ∼11nm. The maximum adsorption capacity was 56.04mgg^-1 at pH 6.0, 10mgL^-1 of tetracycline, and 160mgL^-1 of Fe₃O₄/MFX. The data is properly fitted by the Langmuir, Freundlich, and pseudo-second-order kinetics models. As elucidated by the model parameters and FTIR analysis, chemical ion exchange and COOH could mainly contribute to the adsorption. Meanwhile, the desorption and regeneration experiments implied the adsorption efficiency decreased by only 3.37-8.37% after five adsorption-desorption cycles, and the detection of iron leaching by ICP-OES showed a fine stability of Fe₃O₄/MFX. Therefore, this technically facile, easily recyclable, and environmentally friendly biosorbent has potential for practical applications in antibiotic removal.