Chicken eggshell is one of the most common wastes generated from households, restaurants and other food processing outlets. Waste Chicken Eggshells (WCES) also constitutes an environmental nuisance and ends up discarded at dumping site with no consideration of further usage. The main constituent of WCES is calcium carbonate from which calcium or calcium oxide can be extracted for various applications. This current effort reviews recently published literature on the diverse applications of WCES. The considered utilization avenues include catalysts for biofuel production, construction industry, wastewater purification, industrial sector, food industry, medical, and agricultural applications. The specific areas of application apart from the transesterification reactions include cement additives and replacement in concrete, asphalt binder, adsorbent of metals and dyes, production of hydroxyapatite, food supplement and fortification, dentistry, therapeutics, bone formation, drug delivery, poultry feeds as well as organic fertilizer. For most of the identified applications, the WCES is subjected to pretreatment and other modification techniques before utilization. The conversion of WCES to valuable products is a cost-effective, safe, environmentally friendly, non-toxic and viable means of waste disposal and utilization. More investigations are needed to further explore the benefits derivable from this bioresource.
The utilization of food wastes for various applications has been recognized as one of the strategies for reducing the cost of production and the market price of some products. By definition, food wastes are any edible and allied inedible parts detached and discarded from the food value chain either at households, retail, or food service sectors. The wastes can either be processed, semi-processed, unprocessed, or raw food meant for human consumption. The edible parts of food are the parts that are meant for human consumption while the inedible parts, including bones, shells, peels, etc., are those that are discarded as wastes [
The Food and Agricultural Organization (FAO) estimated that the total edible food waste, globally, is 1.3 billion tonnes with a carbon footprint of 3.3 billion tonnes of CO2 equivalence per annum which is equivalent of about 1.4 hectares of land and 250 × 103 m3 of water annually [
The global production of chicken eggs increased from 73.9 million metric tonnes in 2016 to become 82.17 million metric tonnes in 2019 with China accounting for about 42.88% of the total egg production in 2019. China, the United States of America, India, Indonesia, and Brazil jointly produced 66.67% of the global egg production in 2019. Among African countries, Nigeria, South Africa, Morocco, Egypt, and Algeria top the egg production chart [
Characteristically, a fresh chicken egg is made up of three parts, i.e., the shell, egg white and egg yolk. Consumption of chicken eggs has continued to increase among various strata of the population due to its high protein content and many industrial applications. The risk of adults developing cardiovascular disease from the consumption of eggs is been overshadowed by the urge for essential nutrients contained in chicken eggs. Chicken eggs are rich in protein and essential amino acids needed for growth [
Typically, chicken eggshell is chemically composed of 94% calcium carbonate (CaCO3), 1% magnesium carbonate, 1% calcium phosphate with the balance made up of water and other insoluble proteins [
Earlier, Hamideh et al. [
Primarily, WCES is not produced to be used as food for human or animal consumption. As said earlier, the fact that an average chicken egg contains about 11% of the weight of WCES and is produced in large quantities makes researchers interested in how to put this important resource into use. Chicken eggshells are readily available for collection in large quantities from households, restaurants and food outlets, hatcheries, poultry farms, cake bakers, and other industries that use chicken eggs as raw materials. Calcium, the major constituent of chicken eggshells, has been found to possess abundant mechanical strength and is a major dietary requirement for adults. The presence of elements like boron, copper, iron, molybdenum, sulphur, silicon and zinc also makes chicken eggshells a potential raw material for many applications [
The need to reduce the production cost and, ultimately, the market price of biodiesel has escalated the search for cheap and readily available materials with high calcium content to serve as a replacement for commercial calcium oxide (CaO). Catalytic synthesis of biodiesel is one of the approaches to meet the ever-increasing request for biodiesel. Biodiesel, which is generated through the transesterification of feedstocks such as edible oils, waste cooking oil (WCO), waste animal fats, recovered fats, etc. in the presence of catalysts and alcohol (methanol, ethanol) is a sustainable alternative for fossil-based diesel fuel. The continuous use of fossil-based diesel fuel in compression ignition (CI) engines has caused poor engine performance, increased emission of carbon dioxide (CO2) and other poisonous gases which negatively impact human health, exacerbate global warming and accelerate environmental degradation [
CaO is among the oxides of alkaline earth metals with high basicity which is utilized as a heterogeneous catalyst for commercial biodiesel synthesis. Advantages of CaO derived from WCES as a candidate for large-scale catalytic biodiesel production include its availability, low cost, low solubility in biodiesel, high biodiesel yield, low energy consumption, strong basicity, less water needed for washing, ease of separation, high reusability and less impact of the environment [
The preparation protocol for the conversion of WCES catalysts is as shown in
Recent researches on the deployment of CaO obtained from WCES as a catalyst for large-scale biodiesel production revealed chicken eggshells as a promising biowaste with catalytic applications. To verify the effect of calcination on the performance of catalyst derived from WCES, Kamaronzaman et al. [
Catalyst derived from WCES was used in the conversion of WCO and other feedstocks into biodiesel under mild temperatures resulting in high product yield [
Feedstock | Catalyst modification | Calcination parameters | Characterization technique | Production method | Reaction conditions | BY (%) | Outcome | Ref. | |||||
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T (°C) | Time (h) | C (wt%) | M:O | R (h) | Rtp (°C) | Ssp (rpm) | |||||||
WCO | Non | Transesterification | 5 | 20:1 | 2 | 65 | - | 16 | [ |
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WCO | Calcination | 1000 | 4 | Transesterification | 5 | 20:1 | 2 | 65 | - | 32.76 | Calcination led to 100% improved product yield | [ |
|
Date seed oil | Calcination | 800–1000 | 2 | XRD, BET, TGA, and TPD-CO2 | Transesterification | 5 | 12:1 | 1.5 | 65 | na | 93.5 | Improved yield of 93.5% | [ |
Eucalyptus oil | Calcination | 900 | 4 | XRD, TGA, SEM, FTIR, BET | Transesterification | 6 | 6:1 | 2.5 | 65 | na | 95 | Calcination improved biodiesel yield | [ |
Waste chicken fat | Calcination | 1000 | 4 | SEM | Transesterification | 2 | 6:1 | 2 | 65 | 250 | 90.5 | Improved catalyst morphology led to increased product yield | [ |
WCO | Calcination | 600–1000 | 1–5 | FTIR, XRD | Transesterification | 5 | 15:1 | 6 | 65 | - | 92.81 | The highest yield achieved at optimal calcination conditions of 900°C and 3.5 |
[ |
WCO | Calcination | ns | ns | Esterification and transesterification | 1.62 | 1:1 | 2 | 65 | - | 96 | WCES produced 96% biodiesel yield | [ |
|
WCO | Calcination | 900 | 1 | SEM, BET | Esterification and transesterification | 1.5 | 12:1 | 1 | 60 | - | 96.23 | WCES produced high quality biodiesel from WCO | [ |
WCO | Calcination | 850 | 3 | SEM, XRD, FTIR | Transesterification | 1.5 | 10:1 | 0.9 | 60 | 300 | 96.07 | High quality products with ASTM standards | [ |
WCO | Calcination | 600 | 3 | SEM, XRD, FTIR | Transesterification | 3 | 12:1 | 1.5 | 65 | 400 | 93.1 | High quality and high yield with ASTM standards | [ |
Note: Waste cooking oil = WCO, Temperature = T, Catalyst = C, Methanol:Oil; M:O, Reaction time = Rt, Stirring speed = Ssp Reaction temperature = Rtp, Biodiesel yield = BY.
Apart from the use of WCES for catalytic biodiesel production, the production of bioethanol is also catalyzed by CaO extracted from WCES. Liu et al. [
Key conclusions: WCES can be converted into catalysts for biofuel production. Calcination improves the performance and catalytic activity of WCES in biodiesel synthesis. The economic and environmental benefits of utilization of WCES make it a viable alternative to commercial CaO.
Rapid population growth, rising urbanization, higher disposable income and increasing infrastructural development across nations have caused a steady rise in activities in the construction industries over the past few decades. Concrete, consisting of cement, fine or coarse aggregates and water, is the most frequently and extensively used composite material in the building and road construction industries. Cement is a binder and when used in conjunction with water, sets, hardens, adheres, and binds fine or coarse aggregates together. Global cement production has increased from 3.31 billion tons in 2010 to about 4.1 billion tonnes in 2020, with China contributing more than half to the total global cement production in 2020 (
The overdependence on natural raw materials like limestone (CaCO3), bauxite, clay, or rock for cement production has led to increased cost of production, depletion of reservoirs of these materials, and exacerbated environmental degradation. The exploitation and extraction of limestone, silica, and alumina have continued to damage the landscape, disrupt the ecosystem, pollute the air, and contaminate aquatic and terrestrial habitats [
The majority of the energy consumption and emission occurs during the production of clinker, a component of cement, and thermal breakdown of CaCO3 to CaO. It is estimated that between 50% and 60% of CO2 emission is produced during the decomposition of CaCO3 to CaO. If there is no deliberate strategy implemented to arrest the current rate of emission, the CO2 emission from the cement industry is predicted to reach 2.34 billion tonnes by 2050 [
The preparation techniques for the conversion of WCES to CaO powder involve washing and drying to remove all the dirt on the body of the shells, crushing and sieving into fine particles, and high temperature (700°C–900°C) calcination to convert the CaCO3 to CaO [
Documented research outcomes have shown that fragmentary replacement of Portland cement with calcinated WCES powder improves mechanical strength, compressive strength, flexural strength, and engenders better workability of the concrete [
Area of application | % WCES added | % CaO in WCES | Effect of addition on WCES on concrete | Ref. |
---|---|---|---|---|
Cement additive | 0%, 10%, 20%, and 30% | 50.7 | Improved mechanical strength | [ |
Cement additive | 0%, 5%, 10%, and 15% | 55.7 | Improved mechanical strength | [ |
Cement additive | ns | ns | Higher compressive strengths | [ |
Cement additive | 0%, 5%, 10%, 15%, and 20% | ns | Improved compressive strength | [ |
Cement additive | 0%, 5%, 10%, 15%, and 20% | ns | Improved compressive strength |
[ |
Partial cement replacement | 0% to 20% | ns | Improved compressive strength, |
[ |
Partial cement replacement | 10% and 20% | 52.75 | Accelerated cement hydration. | [ |
Partial cement replacement | 0%, 5%, 10%, 15%, and 20% | ns | Improved compressive strength and flexural strength | [ |
Concrete additive | 0%, 10%, 20%, 30%, and 40% | 64.83 | Improved density |
[ |
Concrete replacement | 0%, 10%, 20%, 30% and 40% | 93.7 | Improved compressive strength. The accelerated rate of carbonation | [ |
Portland cement mortar replacement | 0%, 5%, 10%, 15%, and 20% | 98.3 | Improved compression and flexural strength |
[ |
Replacement of cement in concrete | 0, 5%, 10%, 15%, 20%, and 25% | ns | Improved compressive and flexural strength of concrete | [ |
Partial replacement of asphalt | 0%, 5%, 10%, and 15% | ns | Improved consistency, |
[ |
As asphalt mixture | 0, 3, 6, 9, 12%, 15%, 20%, 25% and 100% | ns | Higher density, higher stability, lower flow, and higher tensile ratio value | [ |
As asphalt binder | 0%, 3%, 6%, 9%, and 12% | ns | Better moisture-damage and high rut resistance properties | [ |
Note: ns = not stated.
Key conclusions: WCES is a viable resource that can be utilized in the construction industry to substitute limestone in cement production. CaO powder derived from WCES is a good replacement for Portland cement. Mechanical properties, strength, durability, thermal stability and functionality of concrete could be improved with the inclusion of fine aggregates of WCES. The addition of WCES powder advances the stability, density, and durability of asphalt. The utilization of WCES in the construction industry guarantees waste minimization, reduces landfill wastes, ensures conversion of waste to useful materials, and decelerates environmental degradation.
Though approximately 70% of the Earth’s crust is covered with water, lack of access to safe water is a major environmental problem, exacerbating malnutrition, and a leading cause of cholera, diarrhea, typhoid, dysentery, and other infectious diseases. In 2017, about 1.23 million deaths were recorded as a result of unsafe water sources globally [
Various physical, chemical, and biological technologies have been deployed to decontaminate and purify wastewater but the adsorption method is more frequently applied due to its low cost, simplicity, flexibility, efficiency, and versatility in removing deadly contaminants. Available information from published literature lends credence to the utilization of activated charcoal and other biowastes to get rid of organic and inorganic pollutants from wastewater [
Daraei et al. [
WCES has also been demonstrated as an efficient and effective adsorbent for the removal of dyes from the ground and wastewaters. Wastewater from textile, food and beverages, cosmetics, pharmaceutical, etc., industries contain synthetic dyes that are difficult to remove. Water polluted with synthetic dyes is poisonous, mutagenic, carcinogenic and their ingestion can cause acute health and ecological worries [
Adsorbate | Preparation and modification technique | Outcome | Ref. |
---|---|---|---|
Chromium | Grinding and sieving | Fast and effective removal of the hazardous Cr(VI) ions from ground and wastewater | [ |
Nitrate | Grinding and sieving | Removal of 95% nitrate from groundwater | [ |
Oxalic acid | Grinding and sieving | WCES successfully absorbed oxalic acid from the wastewater | [ |
Chromium | Grinding, sieving, and calcination | Effective removal of chromium from wastewater | [ |
Lead | Grinding sieving, and carbonization | Successful remediation and removal of lead from contaminated groundwater | [ |
Lead | Grinding, sieving, and chemical | 97.07% lead was absorbed from contaminated water | [ |
Nickel | Grinding, sieving, and chemical | Adsorption efficiency of 91.5% was achieved | [ |
Copper (II) | Grinding, sieving, and calcination | More than 85% removal efficiency was recorded | [ |
Cadmium | Grinding and sieving | About 73% of the pollutants were adsorbed | [ |
Aluminum, iron (II), and zinc | Grinding and sieving | Removal efficiency of 100%, 74%, and 59% was achieved with aluminum, iron (II), and zinc | [ |
Remazol dye | Grinding and sieving | Removal efficiency of about 99% was reported | [ |
Cationic and anionic dyes | Grinding, sieving, and chemical | 92.34% of Methylene Blues and 64.34% Indigo Carmine was adsorbed | [ |
Cationic and anionic dyes | Grinding and sieving | Removal efficiency of 98% of Brilliant Green and 78% of Phenol Red was achieved | [ |
Key conclusions: WCES is a resource for water decontamination, purification, and removal of adsorbates. No significant modification is required for the application of WCES as an adsorbent. Diverse adsorbates, including heavy metals and synthetic dyes, can be effectively adsorbed from ground and wastewater using CaO extracted from WCES. WCES is a low-cost, non-toxic, readily available and environmentally friendly adsorbent for effective ground and wastewater purification.
The scarcity and high cost of raw materials have led to the use of waste materials for various industrial applications. WCES is one of the viable resources that has been used frequently as raw materials for the production of various products. Due to the high CaCO3 content of WCES, which can easily be converted to CaO, industrialists have used WCES as a substitute for the production of ceramics, biphasic bone, polyvinyl chloride (PVC), lithium-sulfur (Li-S) batteries, plastic, and coating pigments for ink-jet printing paper. The process of extracting CaCO3 from WCES includes washing the collected chicken eggshells with chlorinated water, drying and crushing clean dried shells. The crushed shells are subjected to further milling and sieving until a fine powder WCES, rich in CaCO3, is achieved [
The WCES collected from various sources are subjected to mechanical or chemical modification techniques to improve their performance for a particular application. The mechanical modification method may include cleaning, removal of the membrane, drying, pulverization, sieving to convert the WCES into a fine powder. When WCES is pulverized into fine particles, it increases the surface area of the material and enhances its catalytic properties. The thermal treatment may include high-temperature calcination or carbonization in a furnace under air or nitrogen. The WCES powder is characterized by x-ray fluorescence (XRF), x-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscope (SEM), x-ray diffraction (XRD), differential scanning calorimetry (DSC), Brunauer-Emmett-Teller (BET), inductively coupled plasma mass spectrometer (ICP-MS), etc., to ascertain the elemental composition, thermal, and spectroscopic behaviour. This is intended to validate the suitability and appropriateness of this resource for various industrial applications.
Area of industrial application | Preparation/modification technique | Characterization techniques | Outcome | Ref. |
---|---|---|---|---|
Coating pigment of metals | Mechanical | XRF, SEM, XRD, EDX | Unform coating at the desired thickness | [ |
Coating pigment for ink-jet printing paper | Mechanical and thermal | TGA, FTIR | The enhanced optical density of coated coloured paper | [ |
Manufacturing of Li-S batteries | Mechanical and thermal | XRD, SEM, TGA, BET, | Improved capability and cycling performance Li-S battery | [ |
Production of battery electrode and supercapacitor | Mechanical and thermal | XRD, SEM, TEM, BET, XPS | Effective production of battery electrode and supercapacitor | [ |
Production of UV protectant | Mechanical | FTIR, SEM | WCES contains UV-protective additives and raw materials for polystyrene and sunscreens. | [ |
Shielding material | Mechanical | Radiographic analysis | A good shielding material in diagnostic x-rays and an alternative to lead. | [ |
Production of hydroxyapatite | Mechanical and thermal | TGA, XRD, SEM | Effective production of hydroxyapatite | [ |
For example, CaCO3 extracted from WCES was demonstrated to be a suitable coating agent to prevent corrosion and protect welded carbon steel joints. Bakar et al. [
Fecheyr-Lippens et al. [
Key conclusions: WCES powder may be modified by mechanical or thermal techniques to improve its performance. Areas of application include metal and printing paper coating, production of UV protectants, Li-S batteries, battery electrodes, shielding material, hydroxyapatite, and energy storage.
Chicken eggshells are among the top natural sources of calcium that are cheap, readily available, and accessible to rural households. Calcium is the most common mineral in the human body and an important component of nutrition. At every stage of human life, calcium is needed for strong bones and teeth, contributes to blood clotting, neurotransmission, helps in regulating blood pressure and proper functioning of the muscular tissues [
Available information from previous researches put calcium content in WCES at between 35,000 mg/100 g and 40,000 mg/100 g [
The process of extracting calcium from WCES includes washing the collected WCES under running water, soaking the clean shells in warm water to remove the membrane, boiling the clean shells at 100°C for about 10 min, drying the boiled shells in a clean oven at 90°C for 10 min and grinding of the oven-dried shells using mechanical grinder. Grinding and sieving operations of the WCES powder will continue until a uniform fine particle powder is achieved. The dry WCES powder is stored in a clean airtight glass container and used for human consumption.
Many researchers have taken the advantage of the high concentration of calcium in WCES powder to fortify various food products with calcium. In separate researches, Platon et al. [
The pattern of results is not limited to bread and cakes alone. The fortification of muffins [
Food product | Degree of fortification | Effect on the product | Ref. |
---|---|---|---|
Bread | 0–2% (w/w) of ingredients | ↑ Nutritional value, shelf life, flavor, and appearance, physico-chemical properties |
[ |
Bread | 0–3% (w/w) of ingredients | ↑ Calcium content, water absorption, dough stability, acceptability. |
[ |
Bread | 2% (w/w) of ingredients | ↑ Calcium content, shelf life, nutritional properties, rheological characteristics, quality of bread | [ |
Chocolate cakes | 3–9% (w/w) of wheat flour | ↑Calcium content, bulk density, moisture content |
[ |
Muffin | 8 g/500 g and 16 g/500 g wheat flour | ↑Calcium contents, sensory characteristics, nutritional benefits, and acceptability | [ |
Yogurt | 0.1–0.5% (w/w) of ingredients | ↑Calcium content, textural properties, and sensory attributes | [ |
Soy milk jelly Candy | 0–0.8% of total ingredients | ↑Calcium content, moisture content, ash content, protein content, flavor, better taste, shelf life | [ |
Beef sausage | 0–0.6% (w/w) of ingredients | ↑ Acceptability, physical appeal, flavor, chewiness, and color | [ |
Fruit Juices | 0–2% (w/w) of ingredients | ↑ Calcium content, taste, micro and macro minerals |
[ |
Pizza and spaghetti | 500 mg Ca/person | ↑Texture and flavor. | [ |
Note: ↑= increased/improved, ↓= reduced.
Applications | Characterization | Outcome | Ref. | |
---|---|---|---|---|
Technique | Implications | |||
Dentistry | SEM, surface roughness | Surface condition | • Reduce the surface roughness of artificial teeth | [ |
Dentistry | XRF | XRF shows Ca concentration of 98% | • Remineralization of enamel carious lesions | [ |
Dentistry | SEM, TEM, FTIR, XRD | Surface geometry, particle size, shape and distribution | • Remineralization and protection of enamel lesions | [ |
Dentistry | XRD, ultimate tensile strength, impact, modulus of elasticity, elongation percentage at the break, fracture toughness, impact strength | Tensile strength, modulus of elasticity, impact strength and fracture toughness | • 64% increment in ultimate tensile strength, 13% increment in modulus elasticity |
[ |
Dentistry | SEM, flexural strength | Surface geometry, strength | • 30% flexural strength | [ |
Pharmaceutical | Dissolution studies | Degree of hydrophobicity | • Economically and environmentally effective tablet excipient. |
[ |
Pharmaceutical | Physical evaluation, |
Degree of surface modification | • WCES is a low-cost pharmaceutical excipient for the prompt and sustained release of drugs. | [ |
Drug delivery | FTIR, EDS | Surface modification | • Enhanced cell adhesion |
[ |
Therapeutics | XRD | Elemental composition | • Effective treatment of osteosarcoma |
[ |
Bone formation and regeneration | XRD, SEM, FTIR, TGA | Elemental composition particle size, thermal behaviour | • Stimulate bone formation, bone regeneration, and bone graft replacements | [ |
Bone formation and regeneration | TEM, histomorphometric analysis | Microscopic and macroscopic evaluation | • Speedy healing in surgical defects |
[ |
Application | Experimental procedure | Outcome | Ref. |
---|---|---|---|
Organic fertilizer | 0, 45, 60, 75, 90, and 105 g added to soil sample | ↑139–282% vegetative growth rate of the plant | [ |
Organic fertilizer | 0, 2, 4, 6, 8, and 10 g eggshell to soil sample | ↑Vegetative growth and yield of cowpea plants | [ |
Organic fertilizer | Soil diluted with eggshell powder | ↑Growth in sweet basil more than commercial fertilizer | [ |
Poultry feed | Eggshell added to poultry daily diet | ↑Growth rate, performance and egg quality. | [ |
Poultry feed | Eggshell added to the hens’ diets | ↑Egg production, egg quality ↑Calcium, and phosphorous in the serum |
[ |
Poultry feed | WCES powder added to the daily diets | ↑Egg production, egg weight and egg quality | [ |
Note: ↑ = increased/improved.
Key conclusions: The use of WCES powder for food production and fortification ensures waste recovery in the food sector, enhances food preservation and improves the nutritional enrichment of food with calcium. Food items fortified with calcium derived from WCES meet nutritional requirements, improved physicochemical properties, better sensory, and wider acceptability among the population. Food supplementation with calcium derived from WCES powder is a veritable and cost-effective way of achieving food security. Research gaps still exist in the deployment of chicken eggshells membrane powder for the fortification of diverse food products.
Apart from its utilization as food supplements, calcium has been extracted from WCES and used as a sustainable substitute for synthetic calcium for various dental, pharmaceutical, and other medical applications. Some of the factors advancing the medical application of WCES include its unrestricted availability, unhindered accessibility, biocompatibility, ease of application, inability to transmit disease, and ease of bone renewability [
Hydroxyapatite (Ca10(PO4)6(OH)2) is a useful inorganic biomaterial for various medical, adsorptions, and catalytic applications [
The use of hydrothermal, microwave irradiation, wet precipitation, sol-gel, solid-state reaction, mechanochemical, combustion, emulsion, pyrolysis, biomimetic, etc., and the peculiarities of each method, have been well reported in the literature [
The biomedical application of WCES was investigated by researchers when WCES powder was utilized as a low-cost abrasive material to reduce the surface roughness of artificial teeth, re-mineralize enamel surface lesion, and protect the enamel. They deployed various characterization techniques for the investigation and reported the capability and efficacy of calcium derived from WCES powder to reduce surface roughness, re-mineralize, and offer improved protective covering of the enamel, and ultimately leads to better oral health at a reduced cost [
In the pharmaceutical industry, the application of WCES powder as a cheap pharmaceutical excipient has been established [
The field of tissue engineering has benefitted from the new knowledge on the application of WCES powder to heal bone defects caused by trauma, tumor resections, and congenital disease. Li et al. [
Key conclusions: Hydroxyapatite derived from WCES powder is suitable for medical, dentistry, therapeutics, skin regeneration and repair, replacement of skin, tissue, and gums, remediation of orthopedic and dental defects as well as local drug delivery systems. Overconsumption of calcium from WCES should be avoided to guide against the over-concentration of calcium in the bloodstream. More researches are needed on the advantages of amorphous CaCO3 over the crystalline compound in bone grafting and osteogenesis.
One of the areas of applications of WCES is the agricultural sector for the production of fertilizers and poultry feeds. Eggshells collected from various sources can be converted to powder form and applied for agricultural and horticultural purposes. The processes for the preparation of WCES for use in the agricultural and horticultural sectors are similar to that of other aforementioned procedures which include washing of the collected WCES, drying and grinding into fine powder. In this case, there is no need for calcination as the CaCO3 is applied directly without decomposing it to CaO. The preference for CaCO3 derived from WCES over other natural sources of calcium is due to its purity and non-toxic nature. The application of crushed or powdered WCES contributes to plant vegetative growth and fruit yield more substantially than commercial fertilizer, in many cases. To enhance its solubility, WCES can be treated and dissolved into acetic acid to convert it into liquid as organic fertilizer. Besides, new methods for the conversion and application of CaCO3 derived from crushed WCES as organic fertilizers for various plants have been patented lately and documented in the literature [
Chicken eggshells are also a source of proteins and minerals for animals. The Association of American Feed Control Officials (AAFCO) has approved the use of calcium from chicken eggshells to be included in the animal feed so that the animals can meet their daily calcium need. The enrichment of animal feeds with calcium derived from WCES helps in bone development and enhances the egg-laying capability of fowls due to the presence of phosphorous in the eggshell [
In an experiment, Okpanachi et al. [
Key conclusions: Application of crushed WCES as organic fertilizer improves the vegetative growth and yield of plants. Crushed WCES subjected to high-temperature treatment is used in animal feeds production. WCES is a source of nutrients bone development, improved egg productivity and egg quality of egg-laying hens. The utilization of WCES in the agricultural sector will ensure improved soil fertility, better egg quality and productivity, contribute to food security and contribute to a cleaner environment.
Though WCES has many advantages and applications, certain obvious limitations are militating against its utilization. The textural properties of WCES inhibit its preparation and manipulation processes thereby limiting its applications. The high impact strength and toughness of WCES prevent sufficient development of active surface area and pores. This condition reduces the specific surface area available for catalytic activity and impedes its utilization as a catalyst. One of the ways to counter this limitation is to subject the WCES powder to a well-controlled method of synthesis to ensure optimal specific surface area with substantively developed pores. This is one of the reasons why it is important to subject WCES to various modification techniques to adjust the specific surface area, make more pores and channels available, and proper positioning of the active catalytic surfaces [
The low toxicity and substantial efficacy of Ca derived from WCES are never in doubt and have made the resource a viable ingredient for various medical and pharmaceutical applications. However, investigations are continuing on the effectiveness of calcium-containing supplements for the management of osteoporosis and bone fracture. There is a likelihood of reappearance of cardiovascular and gastrointestinal cases as well as renal calculi when calcium derived from eggshells was used [
In terms of the physical consumption of WCES, it must be stressed that swallowing large fragments of eggshells might injure the throat and oesophagus. Chicken eggshells must be pulverized into a fine powder before consumption. Also, chicken eggshells may be contaminated with bacteria like Salmonella enteritidis. To incapacitate the bacteria, eggshells must be boiled before consumption. Chicken eggshells may contain some amount of aluminum, lead, cadmium, mercury and other toxic metals. The consumption of these metals impacts human health and predispose consumers to serious health challenges. These gravely limit the utilization of WCES for food fortification and supplements. The processing of WCES to utilizable form is not totally carbon neutral. The thermal decomposition of CaCO3 to extract CaO also yield CO2 and contributes to global emission.
Going forward, significant opportunities exist for the modification and deployment of chicken eggshells for various applications. There is increased interest in the use of tools of mechanochemistry to advance the application of WCES. The broad application of ball milling in WCES for the formation of nanophase, synthesis of bioceramics and production of composite materials need to be further investigated. A recent breakthrough by Sari et al. [
The increased development of the egg industry in recent decades due to population explosion and increased nutritional awareness has also given rise to the generation of more chicken eggshells. Waste chicken eggshell is a natural resource with significant hidden and untapped potentials. Bearing in mind that WCES is one of the most generated food wastes and the 15th leading cause of environmental pollution, the utilization for myriads of applications will ensure the sustainable development of our planet. This review showcases the utilization of chicken eggshells in biodiesel synthesis, construction industry, wastewater purification, soil remediation, food supplements, and fortification, as well as therapeutics and pharmaceutical applications. The fact that a substantial number of publications on the utilization of waste chicken eggshells were published in the last few years indicates the level of interest the subject has attracted among various researchers globally.
Percentage
revolution per minute
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