Promoting circular economy and sustainable construction practices : investigating the integration of waste upcycling for a greener future, with a focus on eggshell and eggshell membrane utilization

Abstract

As climate change continues to take the centre stage among issues of global discuss, carbon heavy industries including construction and agriculture continue to discover possible ways to foster the implementation of cleaner production technology as well as non-hazardous and sustainable waste disposal solutions. While previous studies have made commendable progress in proposing solutions, much more is still desired. A hybrid approach involving the principles of circular economy and material fusion by adsorption was employed on eggshells. Waste eggshells were valorised and up cycled with its major constituents finding effective use along the chain. This study examined the efficient separation of eggshells from its membrane, the recovery of valuable biochemical compounds and the optimized calcination of the bare shell to produce calcium oxide which is a viable cement replacement material. In addition, the adsorption kinetics of the shell membrane with silver nanoparticles and the effectiveness of the nanocomposite as a cytotoxic additive in cement mortar was investigated. The results demonstrated that in seventeen minutes, acetic acid efficiently weakened the bond between the shell and its semipermeable membrane while minimizing the dissolution of calcium and maximizing the leaching of valuable compounds and proteins like collagen. The calcined, leached, and separated shell produced calcium oxide of comparable quality to that derived from limestone during cement production. Further up the value chain, the separated membrane was employed as an adsorbent for silver nanoparticles and the antimicrobial property of the nanocomposite was exemplified on Pseudomonas aeruginosa and Bacillus subtilis. Pseudo-first order, Pseudo-second order, Two-phase adsorption, Crank internal mass transfer model, and Weber and Morris (W&M) kinetic models were employed to further understand the adsorption process. All the models were adequately fitted with R2 values ranging from 0.922 to 0.990 for both AgNPs and AgNO3. Both Langmuir and Freundlich Isotherm models were also fitted. The adsorption process was optimum at a pH of 6, 25 ◦C, and after 48 h of agitation. Compared to previous studies, a remarkable antimicrobial activity against Pseudomonas aeruginosa and Bacillus subtilis was exhibited resulting in 27.77% and 15.34% cell death, respectively. Analysis of variance and Tukey multiple comparison statistical tests were carried out to highlight the significance of the cell inhibition results at P<0.05 and 95% confidence level. B. subtilis exhibited significant tolerance to metabolic inhibition while P. aeruginosa was significantly inhibited. Following this impressive outcome, the cytotoxic property of the nanocomposite was tested in concrete mortar. This is to combat the ever-increasing nfrastructure budget relating to the maintenance of concrete structures damaged by microbial attacks in moist environments. Waste activated sludge obtained from a local domestic wastewater treatment plant, Pseudomonas aeruginosa, and Bacillus subtilis were studied in both aerobic and anaerobic conditions. Waste activated sludge was most susceptible to the nanocomposite with up to 50% cell death recorded for a 2% cement replacement. In contrast, Pseudomonas aeruginosa and Bacillus subtilis experienced a maximum of 9% and 5% cell death, respectively. For the same cement replacement approximately 5% reduction in compressive strength and no significant change in Tensile strength were measured. This minimal loss in compressive strength is negligible compared to be antimicrobial benefits. Furthermore, considering that about 8.7 million metric tons of eggshell was produced globally in 2021, this alternative use of the shell and its membrane is of great importance to the environment. This include reduction in needed landfill, cost saving and reduction in the generation of GHGs. This study presents a multifaceted approach to the valorisation of waste eggshells, demonstrating their potential as a valuable resource in addressing environmental and industrial challenges. This research underscores the importance of exploring innovative solutions that not only reduce waste but also contribute to the development of cleaner and more sustainable practices in various industries. As we continue to grapple with the pressing issues of climate change and resource conservation, such initiatives pave the way for a more environmentally responsible and economically viable future. This specific upcycling of eggshell and its membrane is of particular economic importance. To start with, the cost associated with managing over 8 million tons of eggshell waste could be invested in more profiting ventures. Through the valorisation process, the shell membrane and other biochemical compounds recovered are valuable sources of income due to the high demand of some of these substances, e.g., collagen. Also, against the backdrop of escalating infrastructure budgets worldwide, employing eggshell membrane as an antimicrobial additive in concrete could result in up to 40% savings in maintenance cost. To achieve these benefits however, it is paramount for the construction and waste industry to start looking into the possible challenges. These include collection, logistics, large scale implementation and more. Likewise, new policies surrounding waste disposal and reusage need to be implemented. Finally, new standards and safety regulations need to be developed while critically exploring and understanding the limitations of waste composites in concrete. In conclusion, this research demonstrates novelty by proposing an optimised eggshell calcination process by ensuring the recovery of the shell membrane and valuable biochemical compounds such as collagen prior to calcination. This will not only ensure the production of high-grade calcium oxide but will also in turn upcycle the net worth of eggshells. Secondly, the study proposes a novel ESM/Nanosilver antimicrobial composite through adsorption. This research also aims to enhance the adsorption efficiency of chemically produced AgNPs and AgNO3 by utilizing the eggshell membrane optimally separated from the shells. Thirdly, this research incorporated the antimicrobial ESM/Ag nanocomposite into cement mortar with the aim of producing an antimicrobial mortar. Lastly, this study demonstrated innovative contribution to academia through 5 publications and 6 conference presentations.