Remediation of Cd-, Pb-, Cu-, and Zn-contaminated soil using cow bone meal and oyster shell meal

Biogenic calcium improved Cd2+ and Pb2+ immobilization in soil using the ureolytic bacteria Bacillus pasteurii

Bioremediation based on microbial-induced carbonate precipitation (MICP) was conducted in cadmium and lead contaminated soil to investigate the effects of MICP on Cd and Pb in soil. In this study, soil indigenous nitrogen was shown to induce MICP to stabilize heavy metals without inputting exogenous urea. The results showed that applying Bacillus pasteurii coupled with CaCl2 reduced Cd and Pb bioavailability, which could be clarified through the proportion of exchangeable Cd and Pb in soil decreasing by 23.65 % and 12.76 %, respectively. Moreover, B. pasteurii was combined separately with hydroxyapatite (HAP), eggshells (ES), and oyster shells (OS) to investigate their effects on soil heavy metals' chemical fractions, toxicity characteristic leaching procedure (TCLP)-extractable Cd and Pb as well as enzymatic activity. Results showed that applying B. pasteurii in soil significantly decreased the heavy metals in the exchangeable fraction and increased them in the carbonate phase fraction. When B. pasteurii was combined with ES and OS, the content of carbonate-bound Cd increased by 114.72 % and 118.81 %, respectively, significantly higher than when B. pasteurii was combined with HAP, wherein the fraction of carbonate-bound Cd increased by 86 %. The combination of B. pasteurii and biogenic calcium effectively reduced the leached contents of Cd and Pb in soil, and the TCLP-extractable Cd and Pb fractions decreased by 43.88 % and 30.66 %, respectively, in the BP + ES group and by 52.60 % and 41.77 %, respectively, in the BP + OS group. This proved that MICP reduced heavy metal bioavailability in the soil. Meanwhile, applying B. pasteurii and calcium materials significantly increased the soil urease enzyme activity. The microstructure and chemical composition of the soil samples were studied, and the results from scanning electron microscope, Fourier transform infra-red spectroscopy, and X-ray diffraction demonstrated the MICP process and identified the formation of CaCO3, Ca0.67Cd0.33CO3, and PbCO3 in heavy metal-contaminated soil.

Immobilization mechanisms of heavy metals by utilizing natural cow bone waste for municipal solid waste incineration fly ash treatment

Municipal solid waste incinerator (MSWI) fly ash poses intricate compositional challenges and potential environmental hazards. Effective management of such hazardous waste is imperative to mitigate the release of toxic compounds into the environment. Solidification/stabilization (S/S) processes have emerged as a viable strategy to transform MSWI fly ash from incineration waste into a safer and more environmentally benign material. This study aims to comprehensively investigate the potential of utilizing cow bone waste to stabilize heavy metals, focusing on Pb, within municipal solid waste incineration fly ash. Experimental investigations encompassed cow bone-to-fly ash weight ratios ranging from 0.0 (control group) to 7:3, a settling time of 2 h, and a liquid-to-solid (L/S) ratio of 1.0 mL/g. Cow bone waste exhibited pronounced efficacy, particularly within the short settling time, yielding a remarkable Pb removal efficiency of up to 99% at a cow bone waste dose of merely 2% and an L/S ratio of 1.0 mL/g. Concurrently, other heavy metals such as Cd, Cu, and Zn were effectively stabilized with a cow bone waste dose of 1.5% during the same 2-h settling period. The results underscore the pivotal roles of ash/bone ratio and settling time in augmenting Pb stabilization in MSWI fly ash. The application of cow bone waste is anticipated to offer a cost-effective and environmentally sound approach, aligning with sustainable waste management principles.

Biometric and gonadosomatic indices and chemical constituents of edible tissues and exoskeletons of Callinectes amnicola and their potential for reuse in the circular economy paradigm

The study investigates some biological indices and chemical compositions of Callinectes amnicola and their potential for reuse in the context of the circular economy paradigm. The total of 322 mixed-sex C. amnicola collected over a period of six months was examined. The morphometric and meristic characteristics were estimated for biometric assessment. The gonads were obtained from the female crabs for gonadosomatic indices. The shell was obtained using the hand removal technique by detaching it from the crab body. The edible and shell portions were processed separately and subjected to chemical analysis. Our findings showed that females had the highest sex ratio across the six months. The slope values (b) for both sexes exhibited negative allometric growth across all months since the slope values obtained were less than 3 (b < 3). The values obtained for Fulton's condition factor (K) of crabs in all examined months were greater than 1. The edible portion had the highest moisture level at 62.57 ± 2.16% and varied significantly (P < 0.05). The high amount of total ash obtained in the shell sample showed that ash is the main mineral present in crab shells and showed a significant difference (P < 0.05). The shell sample had the highest concentrations of Na and CaCO₃. Based on the findings of this study, it was observed that the shell waste contains some essential and transitional minerals (Ca, CaCO₃, Na, and Mg) and can be utilized as catalysts in several local and industrial applications, such as pigments, adsorbents, therapeutics, livestock feeds, biomedical industries, liming, fertilization, and so on. Proper valorization of this shell waste should be encouraged rather than discarding it.

Remediation of Cu, Cr(VI) and Pb polluted soil with industrial/agricultural by-products in seasonally frozen areas

Soils contaminated with potentially toxic elements (PTEs) may face serious environmental problems and pose health risks. In this study, the potential feasibility of industrial and agricultural by-products as low-cost green stabilization materials for copper (Cu), chromium (Cr(VI)) and lead (Pb) polluted soil was investigated. The new green compound material SS ∼ BM ∼ PRP was prepared by ball milling with steel slag (SS), bone meal (BM), and phosphate rock powder (PRP) which had an excellent stabilization effect on contaminated soil. Under 20% SS ∼ BM ∼ PRP addition into the soil, the toxicity characteristic leaching concentrations of Cu, Cr(VI) and Pb were reduced by 87.5%, 80.9% and 99.8%, respectively, and the phytoavailability and bioaccessibility of PTEs were reduced by more than 55% and 23%. The freezing-thawing cycle significantly increased the activity of heavy metals, and the particle size became smaller due to the fragmentation of the soil aggregates while SS ∼ BM ∼ PRP could form calcium silicate hydrate by hydrolysis to cement the soil particles, which inhibited the release of PTEs. Different characterizations indicated that the stabilization mechanisms mainly involved ion exchange, precipitation, adsorption and redox reaction. Overall, the results obtained suggest that the SS ∼ BM ∼ PRP is a green, efficient and durable material for remediation of various heavy metal polluted soils in cold regions and a potential method for co-processing and reusing industrial and agricultural wastes.

Immobilization of Cd in the soil of mining areas by FeMn oxidizing bacteria

Microorganisms are widely used in large-scale pollution remediation due to their rapid reproduction and low cost. In this study, bioremediation batch experiments and characterization methods were adopted to investigate the mechanism of FeMn oxidizing bacteria on the immobilization of Cd in mining soil. The results showed that the FeMn oxidizing bacteria successfully reduced 36.84 % of the extractable Cd in the soil. The exchangeable forms, carbonate-bound forms, and organic-bound forms of Cd in the soil decreased by 11.4 %, 8 %, and 7.4 %, respectively, due to the addition of FeMn oxidizing bacteria, while FeMn oxides-bound and residual forms of Cd increased by 19.3 % and 7.5 %, as compared to the control treatments. The bacteria promotes the formation of amorphous FeMn precipitates such as lepidocrocite and goethite, which have high adsorption capacity on soil Cd. The oxidation rates of Fe and Mn in the soil treated with the oxidizing bacteria reached 70.32 % and 63.15 %, respectively. Meanwhile, the FeMn oxidizing bacteria increased soil pH and decreased soil organic matter content, further decreasing the extractable Cd in the soil. The FeMn oxidizing bacteria have the potential to be used in large mining areas to assist in the immobilization of heavy metals.

Preparation of a novel hydrogel of sodium alginate using rural waste bone meal for efficient adsorption of heavy metals cadmium ion

Adsorption has been an important method for removing heavy metals from industrial wastewater. However, there has been a lack of an environmentally friendly, low-cost, biodegradable and easily recyclable material. China produces bones are not fully utilized leads to a waste of resources Therefore, efficient application of bone meal (BM) for remediation of contaminants in water would provide a promising alternative for resource utilization of bones. In this paper, we use a combination of BM and sodium alginate (SA) to prepare a novel BM/SA/calcium ion (BM/SA/Ca²⁺) double cross-linked composite hydrogel (BMSAH). Enhance the mechanical structure of SA while making the BM easy to recycle and reuse. The morphology and structure of the BMSAH were characterized using FT-IR spectroscopy and SEM-EDS. suggesting that the BMSAH can provide a larger specific surface area and high number of adsorption sites. The effects of the solution pH, ionic strength and contact time on the adsorption capacity of the BMSAH were investigated in depth, Under different conditions, BMSAH has a strong adsorption capacity of >90 %. XPS and FT-IR analysis showed that Cd²⁺ was adsorbed mainly via coordination interactions and hydrogen bonds with the carboxyl groups and nitrogen atoms in the BMSAH. A pseudo-second-order kinetic model, particle diffusion model and Isothermal adsorption lines indicate that the surface of the BMSAH is non-uniform suggesting that the adsorption of heavy metal ions by the BMSAH involves a combination of surface adsorption and intraparticle diffusion mechanisms, which is an overall chemical-physical adsorption process. In addition, the adsorption capacity of BMSAH remained above 90 % after three desorption cycles. Our work provides a new method for the preparation of a low-cost, high mechanical performance, biodegradable and easily recyclable physical hydrogels used for the removal of heavy metal ions.

High performance self-assembled nano-chlorapatite in the presence of lactonic sophorolipid for the immobilization of cadmium in polluted sediment

A novel lactonic sophorolipid (LS) self-assembled nano-chlorapatite (LS-nClAP) was prepared for the immobilization of severe cadmium (Cd) in sediment. The experimental results indicated that the introduction of LS not only improved the dispersed performance of chlorapatite, but also brought massive hydroxyl and carboxyl groups, which significantly improved the immobilization efficiency of Cd and reduced its eco-toxicity in sediment. LS can significantly increase the effective utilization rate of phosphorus in chlorapatite, and reduce the content of available phosphorus (AP) by half after remediation compared with ClAP. Additionally, the participation of LS possessed a significant impact on the enzyme activities in the sediment, especially for urease, which was closely related to the effective stability of Cd and the introduction of LS. All experimental results of this study provided new insights into the possible effects of Cd immobilization by chlorapatite in contaminated sediments, demonstrating great application potential for sediment remediation in the future.

Study on antibacterial properties of heated oyster shell particle against Bacillus subtilis spores in rainwater by response surface methodology based on central composite design

Taiwan's oyster industry produces shell waste in abundant quantities every year. This study explored the feasibility of applying this resource as a simple and low-cost disinfectant to improve the microbial quality of harvested rainwater. Critical parameters affecting the disinfection efficacy of calcined oyster shell particles, i.e., heating temperature and duration, dosage, and contact time of the calcined shell material against Bacillus subtilis endospores in rainwater, were investigated. A central composite design of response surface methodology was employed to study the relative effects. As estimated from R² coefficients, a quadratic model was identified to predict the response variable satisfactorily. Results indicated that the heating temperature, dosage, and contact time of the calcined material in the rainwater significantly influenced (p < 0.05) the sporicidal effect, consistent with the prior literature on calcined shells of similar nature. However, heating time had a relatively low influence on the sporicidal impact, suggesting that the rate of shell activation, i.e., conversion of the carbonate compound in the shell material to oxide, occurs rapidly at high calcination temperatures. In addition, the sterilization kinetics for heated oyster shell particles in aqueous media under stagnant storage conditions were investigated and found to be in good agreement with Hom's model.

Application of bovine bone meal and oyster shell meal to heavy metals polluted soil: Vegetable safety and bacterial community

The development of efficient, environmentally friendly soil amendments is necessary in order to minimize the risk of metal contaminants (Cd, Pb, Cu, and Zn) to the soil ecosystem. As soil amendments, bovine bone meal (BM) and oyster shell meal (OS) reduced the mobility and bioavailability of metals primarily by increasing soil pH. Soil geochemical properties (pH, EC, CEC, Ca, P, and K) after amendment supplementation were more likely to affect metal migration than enzyme activity. Furthermore, BM and OS were found to suppress the Cd and Pb uptake by water spinach, keeping them below international standards for safe utilization. The protein and sugar content and peroxidase (POD) activity showed a significant negative correlation with the amount of metal in water spinach, whereas superoxide dismutase (SOD), ascorbate peroxidase (APX) activities and malondialdehyde (MDA) content exhibited a positive correlation with metal content in water spinach. We also found that BM and OS had less perturbation to phylum-level and genus-level bacterial composition during the remediation of heavy metals contaminated soil. Based on the above, we assume that BM and OS are eco-friendly soil amendments, which could improve soil nutrients contents, stabilize heavy metals and regulate bacterial community structure. Our research contributes to resource utilization of waste and holds promise for widespread application in current agricultural systems.

Effects of composite environmental materials on the passivation and biochemical effectiveness of Pb and Cd in soil: Analyses at the ex-planta of the Pak-choi root and leave

Passivation of soil heavy metals using environmental materials is an important method or important in situ remediation measure. There are more studies on inorganic environmental materials for heavy metal passivation, but not enough studies on organic and their composite environmental materials with inorganic ones. In order to reveal the passivation effect of coal-based ammoniated humic acid (CAHA), biochemical humic acid (BHA), biochar (BC) and other organic types and inorganic environmental materials such as zeolites (ZL) on soil heavy metals and their biological effectiveness. The microstructures of these materials were analyzed by Scanning electron microscope (SEM). The main components of the environmental materials were analyzed by Energy dispersive spectrometer (EDS), Fourier transforms infrared spectroscopy (FT-IR) and X-ray diffraction spectrum (XRD) to elucidate the mechanism of passivation of heavy metals in soil by these environmental materials. The study was conducted to investigate the effects of different types of environmental materials and their combinations on the passivation effect and biological effectiveness of Pb and Cd complex contamination in soil by means of soil incubation and pot experiments using single-factor and multifactor multilevel orthogonal experimental designs. Soil incubation experiments proved that the effective state of soil Pb and Cd in T₇ was reduced by 13.40% and 11.07%, respectively. The extreme difference analysis determined the optimized formulation of soil lead and cadmium passivation as BHA: CAHA: BC: ZL = 3.5:5:20:10. The pot experiment proved that the application of composite environmental materials led to the reduction of lead and cadmium content and increase of biomass of Pak-choi, and the optimal dosage of optimized composite environmental materials was 23.1 g/kg.

Effects of Tetracycline and Copper on Water Spinach Growth and Soil Bacterial Community

The effects of tetracycline (TC) and copper (Cu) on the growth of water spinach and the bacterial community structure in soil were examined in this study. The results revealed that a single Cu treatment decreased water spinach development more severely than TC, and that the toxic effects of TC and Cu on water spinach were synergistic at low doses and antagonistic at high concentrations. The single Cu treatment had the largest influence on the activities of three antioxidant enzymes (Superoxide Dismutase (SOD), Peroxidase (POD), Catalase (CAT)) and the content of Malondialdehyde (MDA) in water spinach leaves, followed by the TC and Cu composed treatment, with the single TC treatment having the least effect. The results of 16Sr RNA sequence analysis showed that the richness and diversity of soil bacterial communities were reduced by either a single TC or Cu treatment. Cu had a greater effect on the composition of the microbial community at genus level than TC. In conclusion, Cu had a greater influence on the growth of water spinach and soil microbial community composition than TC. TC and Cu exhibited synergistic effects at low concentrations and antagonistic effects at high concentrations on relevant indicators when Cu concentration was fixed.