Oyster Shell Powder Research Articles

Evaluation of the Antibacterial Activity of Eco-Friendly Hybrid Composites on the Base of Oyster Shell Powder Modified by Metal Ions and LLDPE

Transforming biological waste into high-value-added materials is currently attracting extensive research interest in the medical and industrial treatment fields. The design and use of new antibacterial systems are urgently needed. In this study, we used discarded oyster shell powder (OSP) to prepare calcium oxide (CaO). CaO was mixed with silver (Ag), zinc (Zn), and copper (Cu) ions as a controlled release and antibacterial system to test the antibacterial activity. The inhibition zones of various modified metals were between 22 and 29 mm for Escherichia coli (E. coli) and between 21 and 24 mm for Staphylococcus aureus (S. aureus). In addition, linear low-density polyethylene (LLDPE) combined with CaO and metal ion forms can be an excellent alternative to a hybrid composite. The strength modulus at 1% LLDPE to LLDPE/CaO Ag increased from 297 to 320 MPa. In addition, the antimicrobial activity of LLDPE/CaO/metal ions against E. coli had an antibacterial effect of about 99.9%. Therefore, this hybrid composite material has good potential as an antibacterial therapy and biomaterial suitable for many applications.

Effect of slow-released biomass alkaline amendments oyster shell on microecology in acidic heavy metal contaminated paddy soils

Soil ecosystem functions and microbial community structure were severely impaired with long-term cadmium (Cd) contamination and acidification. To investigate the effect of amendments on soil physiochemical parameters and soil micro-ecology in acidic Cd contaminated soil, this study was conducted in a pot experiment with the application of calcium amendments, oyster shell powders (OS) and limestone (LM). Each amendment applied at ratios of 1.0%, 3.0%, and 5.0% (w/w), respectively. The results showed that the application of amendments increased the soil pH by 2.10–2.88, the bioavailable Cd decreased by 12.49%–19.48%, and un-bioavailable Cd increased by 96.57%–200.7%. The OS increased the richness index (Chao and Ace increased by 13.23%–16.20% and 7.13%–47.63%), and LM increased the microbial diversity index (Shannon increased by 1.14%–8.72% and Simpson indexes decreased by 28.00%–63.61%). In LM groups, soil microbial communities were significantly altered with increasing application concentrations, the relative abundance of phylum Proteobacteria, Bacteroidota and Gemmatimonadota increased, while Firmicute, Actinobacteria, Chloroflexi decreased. In OS treatments, the soil microbial community structure was basically unchanged. The correlation analysis showed that pH, TN, TP, CEC, OM were the dominant factors affecting the microbial community. This study has shown that application of amendments could effectively reduce the Cd bioavailability in soil, but LM altered the soil microbial community structure, while OS maintained the soil microbiological structure.

Sustainable Use of Waste Oyster Shell Powders in a Ternary Supplementary Cementitious Material System for Green Concrete.

The increasing concern for decarbonization and sustainability in construction materials is calling for green binders to partially replace cement since its production is responsible for approximately 8% of global anthropogenic greenhouse gas emissions. Supplementary cementitious materials (SCMs), including fly ash, slag, silica fume, etc., can be used as a partial replacement for ordinary Portland cement (OPC) owing to reduced carbon dioxide emissions associated with OPC production. This study aims to investigate the sustainable use of waste oyster shell powder (OSP)-lithium slag (LS)-ground granulated blast furnace slag (GGBFS) ternary SCM system in green concrete. The effect of ternary SCMs to OPC ratio (0%, 10%, 20%, and 30%) on compressive strength and permeability of the green concrete were studied. The reaction products of the concrete containing OSP-LS-GGBFS SCM system were characterized by SEM and thermogravimetric analyses. The results obtained from this study revealed that the compressive strength of concrete mixed with ternary SCMs are improved compared with the reference specimens. The OSP-LS-GGBFS ternary SCMs-based mortars exhibited a lower porosity and permeability compared to the control specimens. However, when the substitution rate was 30%, the two parameters showed a decline. In addition, the samples incorporating ternary SCMs had a more refined pore structure and lower permeability than that of specimens adding OSP alone. This work expands the possibility of valorization of OSP for sustainable construction materials.

Strength enhancement of pumice-based geopolymer paste by incorporating recycled concrete and calcined oyster shell powders

In this research, the effect of recycled materials powder on the properties of pumice-based geopolymer paste was studied. Two waste materials viz., ground recycled concrete (RC) and calcined oyster shell (CS) were used to replace pumice powder (PM) at 0–50% by weight. Sodium hydroxide (NaOH) with a concentration of 10 M and sodium silicate (Na2SiO3) solutions at the ratio of 1.00 were used as alkali-activators. A liquid to binder ratio of 0.60 was used for all mixes. Compressive strength and microstructure analysis of geopolymer paste by SEM/EDS, XRD, FTIR, and MIP were tested. The results showed that the compressive strength increased with increasing RC and CS contents. Maximum 28-day compressive strengths of 27.1 and 26.6 MPa were achieved by incorporating 50%RC and 50%CS, respectively. The morphology analysis indicated that the crystalline phases of calcium silicate hydrate (C-S-H) were formed and coexisted with the geopolymer gel, which increased the density and homogeneity, and decreased the pore size of geopolymer pastes. Based on the results, it can be concluded that both RC and CS can be used to enhance the properties of pumice-based geopolymers.

Removing Malachite Green and Leucomalachite Green From Freshwater and Seawater With Four Water Treatment Agents

Malachite green (MG) residue in aquatic environments can adversely affect food chains. To solve this problem, many adsorbents have been developed to remove MG from aqueous solutions. These adsorbents exhibit benefits in different aspects such as low cost, nontoxicity, and environment friendliness. Zeolite, oyster shell powder (OSP), humic acid (HA), and Chloride dioxide (ClO2) are widely used agents for water purification, indicating their potential to remove MG from both freshwater and seawater. Liquid chromatography tandem mass spectrometry was performed as a valid analytical method for measuring MG and its metabolite leucomalachite green (LMG). The analysis examined linearity, specificity, accuracy, precision, and limit of quantification. We found that three agents—zeolite, OSP, and HA—have high affinity for MG and LMG in both freshwater and seawater because of their physicochemical properties; ClO2 exhibited even greater efficiency for MG and LMG degradation due to its oxidation capacity. The MG removal efficiency of zeolite, OSP and HA in freshwater was 100%, 87.52%, and 100%, respectively. In the MG-containing seawater, the removal efficiency of zeolite, OSP and HA was 95.24%, 6.57%, and 89.36%, respectively. The LMG removal efficiency of zeolite, OSP and HA in freshwater was 100%, 53.56%, and 100%, while in seawater, the LMG removal efficiency of zeolite, OSP and HA was 100%, 62.70%, and 84.65%, respectively. ClO2 treatments in both freshwater and seawater expressed 100% removal efficiency. The adsorption capacity of three water agents in MG-containing freshwater decreased in the order: zeolite = HA > OSP; in MG-containing seawater: zeolite > HA > OSP. Whereas the adsorption capacity of three water agents in LMG-containing freshwater decreased in the order: zeolite = HA > OSP; in LMG-containing seawater: zeolite > HA > OSP. In this study, four water treatment agents are reported to remove MG and LMG from freshwater and seawater, indicating their potential for reducing the amount of hazardous MG and LMG residue in aquatic environments.

Exploration and Comparison of the Effects of Vibration and Backwashing Methods on the Process of the Sulfur-Based Autotrophic Denitrification

Both the vibration and backwashing methods are efficient pathway to improve the denitrification ability in reactors. However, the comparison of the effects of vibration and backwashing on the sulfur-based autotrophic denitrification (SAD) reactor is still lacking. In this study, two SAD reactors were compared under various conditions, and the results showed that the use of the oyster shell powder could lower the sulfate productivity with better denitrification ability, and the denitrifiers could be more enriched due to the use of the oyster shell powder. In addition, vibration method performs better than backwashing in improving SAD denitrification ability, reasonable vibration intensity can not only help to reduce energy consumption, but also improve the ability of denitrification of the SAD reactors to a greater extent. Overall, the results of the experiments in this study are helpful for improving the ability of SAD reactors at low temperature and could provide the possibility for wider application of SAD technology.

Sulfidized Nanoscale Zerovalent Iron Supported by Oyster Powder for Efficient Removal of Cr (VI): Characterization, Performance, and Mechanisms

In this study, sulfidized nanoscale zerovalent iron (S-nZVI) supported by oyster shell (OS) powder (S-nZVI@OS) was synthesized by controlling the initial S/Fe ratios (0.1–0.5) to explore the potential synergistic effects during the adsorption and reduction of Cr (VI). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses showed that Fe (0) and FeS were well dispersed on the OS surface. Furthermore, the stability of S-nZVI@OS composite was higher than that of nZVI, which was proved by the material ageing experiment. The effects of different S/Fe molar ratios, time, temperature, the initial concentration of Cr (VI), and initial pH on the removal efficiency were also studied. The results indicated that with the increase of the S/Fe molar ratio, the removal capacity of Cr (VI) first increased rapidly and then decreased slowly. Batch experiments showed that an optimal S/Fe molar ratio of 0.2 offered a Cr (VI) removal capacity of about 164.7 mg/g at pH 3.5. The introduction of S can not only promote Cr (VI) reduction but also combine with Cr (III) by forming precipitate on S-nZVI@OS mainly as CrxFe(1−x) OOH and Cr2S3. The adsorption thermodynamics and kinetics demonstrated that the Langmuir model and pseudo-second-order kinetics model can describe the adsorption isotherms and kinetics. These results suggest that S-nZVI@OS is an effective and safe material for removing Cr (VI) from aqueous solutions.

Sustainable Utilization of Waste Oyster Shell Powders with Different Fineness Levels in a Ternary Supplementary Cementitious Material System

As cement manufacturing accounts for 8% of global CO2 emissions, there is an urgent need to tackle the environmental impacts of cement production and address the decarbonization of construction materials. Adopting supplementary cementitious materials (SCMs), including fly ash, slag, silica fume, etc., can be used as a partial replacement for ordinary Portland cement (OPC) to reduce CO2 emissions related to the OPC industry, while providing benefits for waste valorization. This study aims to explore the sustainable utilization of a waste oyster shell powder (OSP)–lithium slag (LS)–ground granulated blast furnace slag (GGBFS) ternary SCM system in green concrete. The effect of OSP fineness on compressive strength, hydration products, pore structure, and transport properties in ternary SCM-based mortars was studied using a wide array of experimental techniques, including thermogravimetric analysis (TGA), scanning electron microscopy (SEM) analysis, Mercury intrusion porosimetry (MIP), the water absorption test and the rapid chloride penetration test (RCPT). The results revealed that the concrete with the ternary SCMs showed equivalent compressive strength compared to reference specimens. The water absorption and chloride ion charge of the RCPT in the concrete containing the ternary SCMs decreased by up to 30% and 81.4%, respectively. It was observed that the specimens incorporating the OSP with a mesh size of 3000 exhibited the highest compressive strength and the most refined microstructure.

Production of biomaterials from seafood waste for application as vegetable wash disinfectant

The production of seafood waste was studied by analyzing calcium oxide from the shells of tropical oyster and chitosan from the shells of white shrimp to use as a vegetable wash disinfectant. The preparations used were: natural oyster shell powder (NOSP), calcined tropical oyster shell powder in a programmable furnace for 2 h at 700 °C (OSP700), 800 °C (OSP800) and 900 °C (OSP900) including white shrimp shell chitosan (CS). The physical properties of all biomaterials were analyzed using Thermogravimetric analysis, X–ray diffraction and Fourier–transformed infrared spectrometry. The results showed that NOSP and OSP700 were calcite calcium carbonate crystal, but OSP800 and OSP900 were transformed to calcium oxide and calcium hydroxide. The amino group found in the chitin from white shrimp shell was deacetylated to chitosan. By investigating the qualitative antibacterial activity of OSP900 and CS, the inhibition zone of OSP900 against E. coli was higher than that of CS (p < 0.05); however, the inhibition zone of CS against S. aureus was higher than that of OSP900 (p < 0.05). In addition, OSP900 had significantly higher quantitative antibacterial activity against E. coli than S. aureus. The MIC of OSP900 against E. coli and S. aureus for 15 min were 2.5 and 5 mg/mL, respectively; furthermore, the MBC of OSP900 against E. coli and S. aureus were 5 and 10 mg/mL, respectively. However, the inhibitory activity of CS against S. aureus was higher than against E. coli with MIC and MBC values of 5 and 10 mg/mL, respectively, for 15 min. When testing the biomaterials, OSP900 and CS, to inhibit the bacteria on kale and lettuce, 2.5 mg/mL of OSP900 for a vegetable–washing time of 15 min had the highest E. coli inhibition for both vegetables, while 2.5 mg/mL of CS for the same washing time had the highest S. aureus inhibition for both vegetables. Therefore, this research indicated that biomaterials prepared from tropical oyster shell and white shrimp shell wastes could be used as effective wash disinfectants to eliminate contaminated bacteria on vegetables.

Properties of water-repellent concrete mortar containing superhydrophobic oyster shell powder

Oyster shell powder (OSP) has been used as an alternative material for concrete aggregates to reduce shell waste. This study proposes a green preparation method using superhydrophobic OSP (S-OSP) to solve the drawback of high water absorption in OSP concrete. S-OSP was modified using stearic acid, and fabricated S-OSP was used to partially replace fine aggregate to obtain hydrophobic mortar (H-mortar) with a water contact angle of 95.2°. The water absorption test showed that compared with ordinary mortar, the water absorption of mortar mixed with S-OSP decreased by 29%. The effect of the addition rate of the S-OSP on corrosion resistance of the mortar was studied. The results showed that the addition of S-OSP improved the corrosion resistance of mortar. The proposed method is expected to recycle oyster shell waste and improve the corrosion resistance of mortar, which may have potential application in marine concrete structures.

Effect of waste oyster shell powder content on properties of cement-metakaolin mortar

Considering environmental protection and resources saving, it has been a common approach to apply industrial solid wastes and waste oyster shells (WOS) in cement-based materials. In this study, the percentages of lime (WOS powder) obtained from the calcination WOS to replace ordinary Portland cement (OPC) were 0%, 5%, 8% and 10%. And metakaolin was used as supplementary cementing material. The fresh property, mechanical property, durability of the mortars with different content of WOS powder were investigated. The results indicated that the slump flow decreased with the addition of WOS powder. The mechanical properties and drying shrinkage exhibited an increasing trend with the increase of WOS powder content. The porosity, water absorption coefficient, water permeability coefficient and chloride ion diffusion coefficient decreased with the increase of WOS powder content. Therefore, considering economic and environmental benefit of mortars with different of WOS powder, it is conductive to use 8% calcined WOS powder to replace cement for environmental protection, resource conservation and sustainable development.

Mechanical, Leaching, and Microstructure Properties of Mine Waste Rock Reinforced and Stabilised with Waste Oyster Shell for Road Subgrade Use.

Two waste materials, oyster shell (NCOS; non-calcined oyster shell as coarse aggregate and COSP; calcined oyster shell powder as total and partial cement replacement) are used to reinforce and stabilise poorly graded and heavy metal-contaminated mine waste rock (MWR) for pavement subgrade use. Mechanical, leaching, and microstructural tests and analysis were performed on reinforced and stabilised samples to evaluate the effectiveness of the reinforcement and stabilisation of the MWR. Experimental results revealed NCOS and COSP improved the mechanical, leaching, and microstructural properties of the stabilised composite, with a 5% cement–15% COSP–15% NCOS mix being optimal when compared to the control mixes of cement only and no- NCOS. Higher COSP contents beyond 10% reduced the heavy metal contents significantly, but with relatively lower unconfined compressive strengths. Microstructural test results revealed the formation of calcium silicate hydrate (CSH), calcium aluminium silicate hydrate (CASH), ettringite, and calcite as the stabilisation products. Heavy metal complexes in both the cement-only and cement–NCOS–COSP mixes were also found. It is concluded that NCOS reinforced and improved the grading of poorly graded MWR, and that COSP stabilised and immobilised heavy metals present in MWR, thereby improving strength and other engineering properties for subgrade use.

Effects of oyster shell powder on leaching characteristics of nutrients in low-fertility latosol in South China.

In this study, we analyzed the effect of oyster shell powder of different proportions on the nutrient leaching characteristics of latosol using an indoor soil column simulation test. Based on the optimized fertilizer application amount, we assessed five different amounts of oyster shell powder (0% (control, CK), 0.1% (T1), 0.2% (T2), 0.4% (T3), and 0.8% (T4)) and analyzed the intermittent and dynamic leaching characteristics of nutrients in the soil samples. The results indicated that the loss of nutrients in urea, superphosphate, and potassium chloride (due to leaching) increased linearly with the amount of fertilizer. By adding oyster shell powder, the leaching loss reduced by 23.90-57.25% for ammonium nitrogen, 6.31-10.07% for phosphorus, and 17.08-26.58% for potassium. However, the leaching loss for nitrate nitrogen increased by 2.5-5.8 times. In addition, the application of oyster shell powder to latosol provided acid adjustment and water retention enhancement, which increased the pH value of the soil by 3.77 (from pH 4.15 to 7.92) and reduced water loss by 2.52%. Thus, the application of oyster shell powder can reduce the acidity of the surface soil and retain water and fertilizer to a certain extent.

Ethylene vinyl acetate/low-density polyethylene/oyster shell powder composite films: Preparation, characterization, and antimicrobial properties for biomedical applications

BackgroundTo maintain the biocompatibility, the addition of natural antimicrobial compounds to the conventional polymeric materials is being heavily investigated to serve antimicrobial single use products. MethodsThis study focus on the fabrication of ethylene-vinyl acetate/low-density polyethylene/calcined oyster shell powder (OSP) composite films via blown film extrusion method and study of its physicochemical properties including antimicrobial properties for biomedical applications. To improve the miscibility, OSP dispersion, and mechanical properties of the composite films, polyethylene graft maleic anhydride (PEgMA) was further introduced as a compatibilizer. The prepared composites films were characterized by Fourier-transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR), solid-state 13C nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermal properties (TGA and DSC), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), mechanical properties, and water resistance. Moreover, antimicrobial properties were evaluated for the selected samples. Significant findingsOSP imparts the composite films with antimicrobial activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, in addition to remarkably enhancing the thermal stability of the resulting material. From the FESEM analysis, the morphologies of the composite films showed homogenous in the case of PEgMA (1 wt%) and OSP (3 wt%) composite film due to the low interfacial tension and high chemical tendencies in the composite matrix.

Influence of the usage of waste oyster shell powder on mechanical properties and durability of mortar

In order to investigate feasibility of waste oyster shell powder (WOSP) as fine aggregate to produce eco-friendly mortar, workability (slump flow and slump flow loss), mechanical properties (compressive strength and flexural strength), durability (sorptivity, volume of permeability coefficient, water permeability coefficient and chloride ion diffusion coefficient) and microstructure (pore size diffusion) were studied. The effect of replacing river sand with different WOSP proportions (0%, 10%, 20% and 30%) in flowability, strength, permeability and microstructure of mortar have been revealed. The results indicate that increasing substitution ratio of WOSP could decrease the mortar slump flow. The utilization of WOSP in mortar enhanced the compressive strength, flexural strength, resistance to water penetration and chloride diffusion. The WOSP addition exhibits a positive contribution to the pore size distribution of the mortar. Furthermore, it is founded that the utilization of WOSP as construction material is a satisfactory way to reduce waste pollution. Based on its superior mechanical property, durability, eco-efficiency and cost-efficiency in mortar, it is recommended to utilize WOSP alternative to river sand at 10–30% in construction engineering.

Calcined Oyster Shell Powder as a Natural Preservative for Maintaining Quality of White Shrimp (Litopenaeus vannamei).

Simple SummaryThe Food and Agriculture Organization of the United Nations (FAO) indicated that the average global production of oyster shell waste for the year 2019 was 3.08 million tons. Many serious problems include the emission of displeasing odors and pollution of the seaside, which are harmful to the environment. Nonetheless, a solution for this issue would be to reuse the waste and produce a product that has economic benefits and solves the environmental problems. Using calcined oyster shells as a natural preservative might solve the problem of oyster shell waste. In this study, we used calcined oyster shell powder (COSP) as a natural preservative for improving shrimp shelf-life during 12 days under refrigerated conditions. As compared with the control, COSP treatment effectively retarded pH change, reduced the formation of total volatile basic nitrogen, and inhibited bacterial growth during refrigerated storage. The development of preservatives for aquatic products is expected to delay the growth of and spoilage by microorganisms in the refrigerated state, thus providing more barrier protection for aquatic food safety.Oyster shell waste has led to many problems, including displeasing odors, pollution of the seaside, and harm to the environment. Using calcined oyster shells as a natural preservative might solve the problem of oyster shell waste. We studied the use of calcined oyster shell powder (COSP) as a natural preservative for improving shrimp shelf-life over 12 days under refrigerated conditions. As compared with the control, COSP treatment effectively retarded pH change, reduced the formation of total volatile basic nitrogen, and inhibited bacterial growth during refrigerated storage. In addition, shrimp muscle lipid oxidation measured by peroxide value (PV) and thiobarbituric acid (TBA) was decreased during storage. The quality was preserved up to 12 days with 2.0–4.0% COSP treatment as compared with only 6 days for un-treated shrimp. The development of preservatives for aquatic products is expected to delay growth of and spoilage by microorganisms in the refrigerated state, thus providing more barrier protection for aquatic food safety.

Process Technology for Development and Performance Improvement of Medical Radiation Shield Made of Eco-Friendly Oyster Shell Powder

As radiation-based techniques become increasingly important tools for medical diagnostics, medical professionals face increasing risk from the long-term effects of scattered radiation exposure. Although existing radiation-shielding products used in medicine are traditionally lead-based, recently, the development of more eco-friendly materials such as tungsten, bismuth, and barium sulfate has drawn attention. However, lead continues to be superior to the proposed alternative materials in terms of shielding efficiency and cost effectiveness. This study explores the feasibility of radiation shielding materials based on the shells of bivalve mollusks such as oysters that are discarded from aquaculture, thereby preventing them from going into landfills. In addition, a firing process for enhancing the shielding efficiency of the original material is proposed. Experiments show that shielding sheets comprising 0.3 mm thick layers of oyster shell achieve a shielding efficiency of 37.32% for the low-energy X-rays typically encountered in medical institutions. In addition, the shielding efficiency was improved by increasing the density of the powdered oyster shell via plastic working at 1200 °C. This raises the possibility of developing multi-material radiation shields and highlights a new potential avenue for recycling aquaculture waste.

Research on the Transformation of Oyster Shells into a Green, Recyclable, Low Carbon Emission Building Material

In response to climate change and sustainable environment, the "circular economy" that reduces energy development and waste reuse is an important carbon reduction strategy in addition to developing green energy. Based on the circular economy theory of local materials and local use, combines quenched blast furnace slag and geopolymer technology to convert waste oysters into building materials bricks for effective utilization. Our goal is to "recycle" oyster shell waste, "reduce" carbon emissions from the manufacturing, and achieve "recycling". Innovative high-pressure bricks that meet local building material standard. The experiment results show that: 1. The ratios of oyster shell and quenched blast furnace slag were 7:3 and 5:5 respectively, made under the pressure of 110kgf/cm². Curing 28 days later, the compressive strength was 27.5MPa and 38.4MPa, respectively. The bending strength was 3.6MPa and the abrasion test was 1.94mm. 2. Crushing the original high-pressure bricks made of oyster shells, added oyster shell powder and quenched blast furnace slag, remade them in a ratio of 7:3. Curing 7 days later, the compressive strength can reach 41.46 and 51.66MPa.3. Each high-pressure brick made of oyster shells will produce 0.206 to 0.219kg CO₂ emissions, which is 49% to 52% fewer carbon emissions than the 0.422kg CO₂ emitted by each high-pressure concrete brick. 4.The remade oyster shell high-pressure reformed bricks will produce 0.295 to 0.304kg CO₂ emissions, which is 28% to 30% lesser carbon emissions than each high-pressure concrete brick. This result can prove that the oyster shell high-pressure bricks can pass Taiwan’s CNS and Green-building materials standard, comply with the circular economy and achieve the goal of net-zero carbon emissions.

Oyster shell powder (Crassostrea gasar): evaluation of its potential as a natural and sustainable source of calcium in bread

PurposeThe study aims to analyze the composition and mineral profile of oyster shell powder (OSP) and assess its potential as a sustainable source of calcium.Design/methodology/approachA total of two batches of OSP with different particle sizes had been evaluated for centesimal and mineral composition and microbiological quality. OSP with smaller particles (0.85 mm) was used in the production of bread: standard bread (SB) (0%), fortified bread (FB1) (3%) and FB2 (4%). Centesimal and mineral composition and sensory acceptance had been performed. The internal preference map had been constructed using principal component analysis. The Just About Right data and the influence of sensory attributes on bread acceptance had been assessed by a penalty analysis test.FindingsOSP-0.85 mm had calcium content (478.47 ± 2.37 mg.g-1) lower than OSP-1.00 mm (521.15 ± 0.99 mg.g-1) due to retention of particles. In both batches, heavy metals such as chromium, nickel and copper had not detected. FB1 and FB2 had the best nutritional content compared to SB, with higher calcium content (mg.g-1) 0.69 ± 0.07; 13.76 ± 0.72 and 19.47 ± 1.99 for SB, FB1 and FB2, respectively. The internal preference map showed better acceptance of FB1 compared to FB2. The penalty test showed that this acceptance was penalized (p < 0.05) due to the sandy texture.Originality/valueThe large number of shells generated in the processing of oysters is an environmental problem and generates waste of a natural source of calcium. It has been demonstrated that oyster shell powder can be used as a natural and sustainable source of calcium in bread, requiring further studies to assess the bioavailability of calcium.

Phosphorus Co-Existing in Water: A New Mechanism to Boost Boron Removal by Calcined Oyster Shell Powder.

The removal of boron (B) from water by co-precipitation with hydroxyapatite (HAP) has been extensively studied due to its low cost, ease of use and high efficiency. However, there is no explicit mechanism to express how resolved B was trapped by HAP. Thus, in this work, the process of removing B from water was studied using a low-cost calcium (Ca) precipitation agent derived from used waste oyster shells. The results showed that the removal rate of B in the simulated wastewater by calcined oyster shell (COS) in the presence of phosphorus (P) is up to more than 90%, as opposed to virtually no removal without phosphate. For B removal, the treated water needs to be an alkaline solution with a high pH above 12, where B is removed as [CaB(OH)4]+ but is not molecular. Finally, the synergistic mechanism of co-precipitation between HAP and dissolved B, occlusion co-precipitation, was explained in detail. The proposed method discovered the relationship between Ca, P and B, and was aimed at removing B without secondary pollution through co-precipitation.