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.

A New Magnesium Phosphate Cement Based on Renewable Oyster Shell Powder: Flexural Properties at Different Curing Times

Magnesium phosphate cement (MPC), a new type of inorganic cementitious material, is favored in engineering and construction because of its fast setting speed and high bonding strength, but is limited in practical application due to its high production cost and excessive release of hydration heat. Relevant research has investigated the application of discarded oyster shell powder (OSP) replacing cement mortar and has reported certain improvements to its performance. Consequently, focusing on discovering more effects of OSP on MPC performance, this study, by using a typical three-point bending test, used 45 cuboid specimens to investigate the influences of OSP mass content on flexural properties of MPC at different curing times. Results illustrated that MPC flexural strength was first increased and then decreased, and 3% is the critical value for OSP mass content. Similarly, the stiffness of all specimens presented a tendency to increase first and then decrease, with a maximum value of 36.18 kN/mm appearing at 3%, i.e., the critical OSP mass content. Finally, scanning electron microscope (SEM) and X-ray diffraction (XRD) were employed to analyze the microstructure and composition of specimens, confirming that the specimens generated not only the hydration product potassium phosphate magnesium (MgKPO4·6H2O, MKP), but also another new reactant (CaHPO4·2H2O).

Effect of Biowaste on the High- and Low-Temperature Rheological Properties of Asphalt Binders

The growth of aquaculture has increased the production of oysters. However, the increased oyster shell volume has created serious environmental and recycling problems for the society. In order to study the sustainable utilization of waste oyster shells, asphalt binder of waste oyster shell powder was prepared by using modified asphalt material with waste oyster shells. The microstructure of oyster shell powder was analyzed by scanning electron microscopy experiments. The chemical composition of the asphalt binder was observed by Fourier transform infrared spectroscopy tests. The physical properties of the asphalt binder, including softness, high-temperature performance, and plastic deformation capacity, were initially evaluated through three indicators’ tests on asphalt. A preliminary performance evaluation of the asphalt binder was performed. The high-temperature stability of asphalt binders was evaluated using dynamic shear rheometry. The rutting resistance of the material was evaluated by temperature sweep tests, and the shear deformation resistance of the material was evaluated by frequency sweep tests. Multiple stress creep recovery tests determine the material’s ability to resist permanent deformation. The low-temperature rheological properties were evaluated by bending beam rheology tests. The study found that the waste oyster shell powder is a biomass with a porous irregular petal shape. No new characteristic absorption peaks are formed by mixing with asphalt. And, it can improve the viscosity, thermal stability, and temperature-sensitive properties of the material. It significantly improved the high-temperature rheological performance, rutting coefficient, and recovery elasticity of the material. However, it has little effect on low-temperature rheological performance. This study provides a solid foundation for the effective use of biowaste in engineering materials.

Oyster Shell Powder, Zeolite and Red Mud as Binders for Immobilising Toxic Metals in Fine Granular Contaminated Soils (from Industrial Zones in South Korea)

Low-cost absorbent materials have elicited the attention of researchers as binders for the stabilisation/solidification technique. As, there is a no comprehensive study, the authors of this paper investigated the performance of Oyster shell powder (OS), zeolite (Z), and red mud (RM) in stabilising heavy metals in three types of heavy metal-contaminated soils by using toxicity characteristic leaching procedure (TCLP). Samples were collected from surroundings of an abandoned metal mine site and from military service zone. Furthermore, a Pb-contaminated soil was artificially prepared to evaluate each binder (100× regulatory level for Pb). OS bound approximately 82% of Pb and 78% of Cu in real cases scenario. While Z was highly effective in stabilizing Pb in highly polluted artificial soil (>50% of Pb) at lower dosages than OS and RM, it was not effective in stabilising those metals in the soils obtained from the contaminated sites. RM did not perform consistently stabilising toxic metals in soils from contaminated sites, but it demonstrated a remarkable Pb-immobilisation under dosages over than 5% in the artificial soil. Further, authors observed that OS removal efficiency reached up to 94% after 10 days. The results suggest that OS is the best low-cost adsorbent material to stabilize soils contaminated with toxic metals considered in the study.