Strategies for cost-optimized biocement production: a comprehensive review

Abstract

Biocement is a promising alternative to conventional cement, offering advantages in sustainability and reducing carbon footprints. However, its widespread adoption has been hindered by the relatively high production costs. This review aims to explore various strategies and advancements in biocement production that can contribute to cost reduction. Specifically, we discuss the selection of low-cost microbial growth media for microbially induced carbonate precipitation (MICP), the utilization of plant extractives as enzyme substitutes in enzyme-induced carbonate precipitation (EICP), the substitution of urea with urine as a low-cost source of nitrogen, the exploration of affordable alternatives to calcium ions, and the valorization of ammonia/ammonium byproducts, and other pathways. The adoption of these strategies could significantly enhance biocement’s scalability and sustainability, paving the way for more eco-friendly and cost-effective construction practices.

Introduction

Global population growth and urbanization have significantly increased infrastructure demands and placed a strain on natural resources and energy. Simultaneously, the construction industry has left a considerable environmental footprint on the planet (Giesekam et al. 2014; Onat and Kucukvar 2020; Xu et al. 2020; Labaran et al. 2022; Driver et al. 2022). To minimize this environmental burden, researchers have employed various strategies to develop more environmentally friendly and sustainable solutions within the realms of concrete and construction. Notably, Microbially Induced Carbonate Precipitation (MICP) and Enzyme-Induced Carbonate Precipitation (EICP) have garnered increasing attention and investigation (Portugal et al. 2020; Gebru et al. 2021; Ahenkorah et al. 2021; Jiang et al. 2023; Zhang et al. 2025), due to their potential to obviate the substantial energy consumption and greenhouse gas emissions associated with the cement production processes frequently utilized in the construction sector (Benhelal et al. 2013; Gao et al. 2015; Nie et al. 2022; Guo et al. 2024; Felipe Arbeláez Pérez et al. 2024).

These methods facilitate the adhesion of particles or filling of internal pores and fissures within materials, rendering their applicability across a spectrum of domains including liquefaction alleviation (Han et al. 2016; Xiao et al. 2018; Zamani et al. 2021), slope stabilization (He et al. 2023; Tian et al. 2022; Liu et al. 2022), coastal erosion management (Liu et al. 2021a; Wang et al. 2021; Miftah et al. 2022), biobrick manufacturing (Li et al. 2020; Liu et al. 2021b; Arab et al. 2021), structural fissure repair (Jongvivatsakul et al. 2019; Sun et al. 2021; Intarasoontron et al. 2021), heritage conservation (Jroundi et al. 2017; Mu et al. 2021; Dong and Liu 2022), dust suppression (Lo et al. 2020; Hu et al. 2023; Zhou et al. 2023), enhanced petroleum recovery (Wu et al. 2017; Phillips et al. 2018; Xia et al. 2023), heavy metal remediation (Dong et al. 2023; Xue et al. 2024a, b), carbon sequestration (Okyay and Rodrigues 2015; Okyay et al. 2016; Park and Choi 2022), and space construction (Gleaton et al. 2019; Dikshit et al. 2021, 2022). Nonetheless, the majority of current research remains confined to laboratory and small-scale applications, with large-scale implementation still posing significant limitations. Certain scholars have explored the drivers and barriers of construction, with cost being a predominant constraint in construction projects (Olawale and Sun 2010; Ahn et al. 2013; Tokbolat et al. 2020).

This comprehensive review delves into research focused on cost reduction in sustainable construction utilizing biocement, primarily dominated by urease-mediated MICP and EICP. MICP encompasses processes such as such as ureolysis, photosynthesis, ammonification, denitrification, sulfate reduction, anaerobic sulfide oxidation, and methane oxidation (Castanier et al. 1999; Lee and Park 2018; Castro-Alonso et al. 2019; Qin et al. 2020; Zuo et al. 2023). Among these pathways, urease-mediated MICP, due to its simplicity and ease of control, represents the most extensively studied and applied form of MICP (Krajewska 2018; Naveed et al. 2020; Rajasekar et al. 2021). The biogeochemical reactions involved utilize urease-producing bacteria or direct urease induction to generate calcium carbonate. Urease is employed to catalyze urea hydrolysis, yielding carbonate ions, subsequently precipitating calcium carbonate in the presence of calcium ions. The key determinant for cost control in MICP and EICP, as illustrated in Fig. 1, hinges upon the accessibility of cost-effective urease-producing bacteria or urease, affordable urea sources, and calcium ion reservoirs, as well as other pathways.

Fig. 1.

Schematic representation of the process flow for MICP/EICP in biocement production

Low-cost microbial growth media for MICP

Thus far, a multitude of microorganisms have been identified for their capability to facilitate MICP through urea degradation, with Sporosarcina pasteurii being the most frequently employed due to its often robust urease activity (Zhao et al. 2019; Lapierre et al. 2020a; Carter et al. 2023). Furthermore, as shown in Fig. 2, its pronounced negative charge and affinity for calcium ion supplementation facilitate its role as nucleation sites for the generation of calcium carbonate (Ghosh et al. 2019; Ma et al. 2020; Šovljanski et al. 2021). Regardless of the urease-producing bacteria employed, it was imperative to cultivate them under optimal growth conditions to enable the synthesis of a sufficient quantity of enzymes capable of catalyzing the biomineralization process and to provide an adequate bacterial population for mineralization nucleation sites.

Fig. 2.

The role of bacteria in MICP

To ensure bacterial growth, it is imperative to provide them with a suitable culture medium containing essential nutrients such as carbon, nitrogen, phosphorus, and other requisite minerals (Lapierre et al. 2020b). However, the use of standard culture media is uneconomical for large-scale applications (Silva et al. 2015). The selection of cost-effective culture media to supply microorganisms and facilitate a series of precipitation reactions is a critical factor in reducing the production costs of urease-producing bacteria and even biocement. Organic waste from kitchen waste, food industries, agriculture, and livestock directly discharged into the environment leads to various environmental issues, such as eutrophication of water bodies. Recycling these organic waste materials as potential nutrient sources for microbial growth can effectively reduce costs and turn waste into a valuable resource. Figure 3 presents the latest research progress on the use of these waste materials as specific components substitutes. Representative examples of such low-cost growth media, as described below, include kitchen waste, chicken manure wastewater, tofu wastewater, whey powder, lactose mother liquor, food-grade yeast medium, sugarcane molasses and vinasse, and corn steep liquor.

Fig. 3.

Schematic diagram of low-cost bacterial culture medium

As one of the constituents of urban waste, kitchen waste has garnered widespread attention due to the rapid urbanization of global populations and the development of the foodservice industry. The proper management of substantial volumes of kitchen waste remains a global challenge, as improper handling can lead to severe environmental pollution and resource wastage (Sharma et al. 2022; Meng et al. 2022; Cao et al. 2023). Kitchen waste primarily comprises starch, polysaccharides, proteins, cellulose, lipids, vitamins, and inorganic salts. It can serve as a nutritive substrate for supporting microbial growth, thus reducing the cost of microbial cultivation during its processing. The research investigated the feasibility of cultivating Sporosarcina pasteurii spores in kitchen waste and their application in controlling desert soil erosion through MICP (Meng et al. 2021a). Enzymatic hydrolysis was carried out using commercial enzymes to break down long-chain protein molecules into small peptides and free amino acids, enhancing the release and recovery of proteins in kitchen waste, which can subsequently be used for microbial production. After optimizing the conditions, the maximum biomass concentration determined by measuring the optical density at 600 nm reached 4.19, and urease activity reached 14.32 mM urea/min, both of which are comparable to the results obtained in traditional standard media. The harvested Sporosarcina pasteurii was then employed to catalyze calcium carbonate precipitation in desert soil, and their performance in controlling wind erosion was evaluated through wind tunnel experiments. Even after undergoing 12 cycles of wet-dry or freeze-thaw, microbially mediated calcium carbonate significantly reduced wind erosion losses in desert soil. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis confirmed the bridging effect of calcium carbonate crystals in the soil matrix. The findings validate the enormous potential of kitchen waste as a cost-effective alternative for bacterial cultivation and carbonate precipitation as nutrients in large-scale applications.

Moreover, the agricultural and food processing industries often generate substantial organic waste, raising concerns regarding potential environmental pollution. The efficacy of anaerobically digested chicken manure wastewater, following biogas processing, has been established as a cost-effective and nutrient-rich growth medium. Owing to its substantial nutrient content, this wastewater serves as a potent stimulant for bacterial growth. In comparison to three other standard growth media, it exhibits the highest urease activity, thereby facilitating calcium carbonate precipitation. Utilizing chicken manure wastewater as a growth medium results in a cost reduction of 88.2% per liter when compared to conventional growth media, underscoring its significant potential for widescale application in biomineralization (Yoosathaporn et al. 2016). The wastewater from tofu production, known as tofu wastewater (TW), is characterized by a high Chemical Oxygen Demand (COD) concentration exceeding 30,000 milligrams per liter, several hundred times higher than COD discharge standards. The study delves into the utilization of TW as a nutrient growth medium (Fang et al. 2019). Researchers conducted a comparative analysis of urease production and bacterial growth between TW and a standard nutrient broth. Importantly, both growth media exhibited no significant differences in bacterial growth. Furthermore, the study meticulously examined the properties of sandstone formed using TW as a growth medium, thereby confirming the feasibility of TW as a growth substrate. Cheese production facilities may discharge wastewater containing residual whey. Whey has been validated as a growth medium. Notably, research demonstrates that substituting disinfected growth medium for sterilized growth medium retains 64% of the optimal urease activity, resulting in reduced energy consumption and investment. Additionally, the utilization of brackish seawater as a solvent in the growth medium does not significantly alter the urease performance of bacteria, thereby contributing to water resource conservation and reducing the cost of the growth medium (Kahani et al. 2020). The industrial wastewater in the dairy industry, known as lactose mother liquor (LML), has also been validated as a cost-effective nutritional source for bacteria. Its efficiency was compared to two other standard growth media, yielding similar urease activity in cultured bacteria. Performance in terms of calcium carbonate precipitation and compressive strength improvement was closely aligned with standard media, signifying LML’s potential as an alternative growth medium for calcium carbonate precipitation. This offers an environmentally friendly choice for replacing expensive nutrient or yeast-based growth media and facilitates wastewater recycling (Achal et al. 2009).

There are several evident disadvantages that may hinder the use of waste materials for MICP applications, including potential instability of their composition and the challenges associated with collection or transportation. Therefore, it is essential to explore alternative nutrient sources that are stable, easily obtainable, and cost-effective. One promising approach investigated in this study is the feasibility of using an economical medium, specifically low/food-grade yeast extract. This study compared the performance of Sporosarcina pasteurii cultured in the low-cost food-grade yeast medium against eight laboratory-grade media (Omoregie et al. 2019), including nutrient broth, yeast extract, tryptic soy broth, luria broth, thioglycolate fluid medium, cooked meat medium, lactose broth, and marine broth. The results demonstrated that culturing in the low-cost medium containing 15 g/L (w/v) food-grade yeast extract at an initial pH of 8.5, supplemented with urea (4%, w/v), yielded the highest biomass concentration and urease activity. When compared to laboratory-grade media, the use of the food-grade medium significantly reduced bacterial cultivation costs by 99.80%. Following biomineralization experiments, X-ray diffraction (XRD) analysis confirmed the presence of CaCO₃, identified as polymorphs of calcite and vaterite. These findings indicate that from a cost-reduction perspective, food-grade yeast extract represents a promising candidate for bacterial cultivation in MICP applications.

Another approach is to utilize the abundant organic by-products generated from the agricultural and food processing industries. Byproducts such as sugarcane molasses and vinasse, originating from sugar and alcohol production, have been investigated as growth substrates in comparison to Tryptic Soy Broth (TSB) for the evaluation of MICP as an alternative soil conservation method to combat wind erosion. The study reveals that in arid environments, when compared to TSB treatment, sugarcane molasses and vinasse significantly enhance soil permeability and exhibit robust soil stabilization effects against wind erosion (Nikseresht et al. 2020). Furthermore, the low-cost byproduct of the food industry, corn steep liquor (CSL), derived from corn starch processing, has undergone extensive exploration and validation. Due to its content of amino acids, vitamins, minerals, and proteins, CSL has been recognized by numerous studies as an economical nutritional source for bacterial culture. Research utilizing MICP for sand consolidation has verified corn steep liquor as an economical nitrogen source in lieu of a portion of soy peptone in the growth medium. Specifically, by substituting 30 g/L of corn steep liquor for 25 g/L of soy peptone, this innovative medium exhibited a 24.21% increase in urease activity, a 52.5% reduction in nitrogen source cost, and an overall 50.5% cost reduction (Chen et al. 2022). Studies have also confirmed that the addition of CSL to the growth medium does not adversely affect the rheological properties of cement slurry. Furthermore, observations following bacterial treatment of concrete using CSL have revealed a significant enhancement in compressive strength and permeability performance, augmenting resistance to water and corrosive agents, all without compromising the alkalinity of the concrete (Joshi et al. 2018). In addition, a modeling approach incorporating artificial intelligence, involving multiple linear regression, adaptive neuro-fuzzy inference system, and genetic programming, was employed for modeling and optimization. The interaction of factors such as CSL-urea concentration and incubation time on urease production was investigated. Subsequently, the results of these models were compared to unveil their performance and determine the optimal conditions for urease production. It was established that the CSL-urea medium not only provides comparable urease efficiency to conventional yeast extract nutrient media but also presents significant economic advantages (Maleki-Kakelar et al. 2022).

Although low-cost alternative culture media offer significant advantages as potential nutrient sources for MICP applications, a range of potential challenges must be addressed in practical implementation. When scaling up the use of low-cost culture media, it is essential to ensure the stability of their nutrient composition and quality to avoid inconsistencies that could negatively impact microbial cultivation and subsequent carbonate precipitation. Particular attention must be paid to the safety and harmlessness of materials derived from animal waste. Furthermore, the collection, transportation, and potential preprocessing requirements, such as hydrolysis or filtration, could introduce additional costs that warrant careful consideration.

Plant extracts as cost-effective enzyme substitutes for low-cost EICP

MICP relies on the introduction of microorganisms and depends on their metabolic activities, often requiring on-site cultivation and growth. This process may pose numerous potential risks and necessitate additional measures, such as obtaining government approvals, securing permits, and conducting continuous microbial monitoring to ensure safety (Cui et al. 2021, 2022; Meng et al. 2021b). In contrast, the use of free urease in EICP offers significantly higher biosafety, as its activity and function naturally decline over time, degrading without causing any long-term ecological impacts. Furthermore, free urease can be applied to finer-grained soils, where bacterial growth and mobility are often constrained due to reduced pore space, thus limiting cementation. The smaller size of free urease provides a distinct advantage in penetrating narrow pore spaces compared to microorganisms (Ran and Kawasaki 2016; Almajed et al. 2018; Gao et al. 2019). Numerous studies on EICP have utilized purified urease. Commercially available purified urease represents one of the most expensive components of the overall process, making EICP potentially cost-prohibitive for large-scale applications. To address this, some researchers have explored the use of crude urease extracts as an economical enzyme source, paving the way for scalable applications. Unlike commercial purified enzymes that require stabilizers (e.g., skim milk) to protect urease (Hamdan and Kavazanjian 2016; Almajed et al. 2020; Martin et al. 2021), crude plant extracts often contain a wealth of proteins that naturally offer similar stabilization effects. However, these proteins may also provide additional nucleation sites due to their negative charges, potentially leading to premature precipitation near injection points and impairing the uniformity of cementation. To mitigate this, studies have suggested using low-dielectric-constant additives such as ethanol to strengthen electrostatic interactions within proteins, inducing their precipitation and thereby enhancing the uniformity of treated samples (Lai et al. 2023; Xu et al. 2023a; Ng and Chu 2024). The extraction of crude enzymes from plants remains a simple, scalable process, as shown in Fig. 4. For instance, tap water or artificial seawater has been used for extraction (Shu et al. 2022; Zhang et al. 2023; Cui et al. 2024), demonstrating its practicality for large-scale applications. While some studies have involved bacterial cultivation and subsequent extraction of bacterial urease (Hoang et al. 2019; He et al. 2020; Xie et al. 2023), such methods require additional processing steps and chemicals. This review focuses on plant-derived enzymes, which offer a more straightforward and cost-effective alternative.

Fig. 4.

Schematic diagram of low-cost crude enzyme extraction

Research has tested watermelon seeds, soybeans, and pumpkin seed powders, confirming the presence of urease. To compare the effects of plant-based urease on the mechanical properties of cement concrete, powdered seeds were incorporated into the concrete mix design. Compressive strength and water absorption tests were then conducted on all samples, with results compared to control samples without any seeds. The bending strength of the experimental specimens containing seeds was approximately 12% higher than that of the control specimens. Additionally, the splitting tensile strength of the experimental specimens increased by about 10% compared to the control specimens (Bhutange et al. 2021). Urease in cabbage was also explored, with crude extracts from cabbage yielding 40–60% of the theoretical precipitate without the need for purification (Baiq et al. 2021).

Jack bean extracts have also proven effective for EICP in biocementation. Comparisons between crude jack bean extracts and three commercial enzymes revealed that crude extracts and less purified commercial enzymes enhanced soil strength more effectively than highly purified urease. This effect is attributed to complementary proteins present in less purified enzyme sources. The simplicity of the extraction process from jack beans significantly lowers EICP costs, addressing barriers to practical applications in infrastructure and environmental protection (Khodadadi Tirkolaei et al. 2020).

Among plant enzyme sources, soybean-derived urease is the most widely used, offering advantages in reliability and consistency due to soybeans’ large-scale global cultivation. Studies have employed crude soybean urease to evaluate EICP’s ability to improve wind erosion resistance in desert sands, forming solid surface coatings to inhibit erosion. Optimization of key variables, such as enzyme-to-cementation ratios, cementation solution concentrations, and spraying volumes, demonstrated enhanced surface strength, calcium carbonate content, and layer thickness, with wind resistance achieved at speeds of up to 14 m/s (Xu et al. 2024).

Research on crude enzymes derived from agricultural byproducts or waste has clearly demonstrated their potential to further reduce raw material costs. For instance, soybean hulls, a low-cost agricultural by-product produced during the soybean manufacturing process, are commonly used in feed production (Ludden et al. 1995; Mueller et al. 2011; Krusinski et al. 2022). Valuable proteins, such as soybean urease, can be isolated from soybean hulls before they are processed into feed. Research on the use of soybean hull powder enzymes for the reinforcement of marine sand has explored the mechanical properties and disintegration behavior under wet-dry cycling conditions. The study examined the changes in urease activity under varying concentrations of soybean hull powder, extraction time, pH values, and extraction temperatures. Notably, in experiments where the soybean hull powder concentration was 100 g/L, the urease activity reached 4.23 IU/mL. When the concentration of soybean hull powder was below 100 g/L, urease activity increased with higher concentrations. However, when the concentration exceeded a certain threshold, urease activity declined. This reduction was attributed to the increased density and viscosity of the mixture at higher concentrations, which significantly affected the extraction efficiency of soybean hull urease (Xu et al. 2023b). Field trial results using soybean hull powder urease indicated that the number of EICP treatments had the most significant impact on the treatment effectiveness. After EICP treatment, the dynamic deformation modulus of the base layer reached as high as 50.55 MPa. Areas with better biocementation effects experienced higher ground stress, confirming that EICP treatment could enhance the foundation’s bearing capacity by reinforcing the base layer (Xu et al. 2023c). Recent studies have also investigated urease from weeds, demonstrating similar significant cost-effectiveness. The research employed a simple crude extraction technique to conduct a detailed urease screening of Australian local weeds and native plants, comparing the results with a standard crude extract from soybean. The crude extract from mature rice melon seeds (M-PMS), an Australian weed, exhibited the highest specific activity of 8997 U/mg. Compared to purified urease, M-PMS produced comparable strength and durability in treated samples (Rahman et al. 2023).

The application of crude enzyme extraction technologies in EICP showcases remarkable cost-effectiveness and engineering potential. By leveraging plant-derived urease, not only can treatment costs be reduced, but agricultural waste can also be valorized, contributing to economic and environmental sustainability.However, the large-scale utilization of this approach faces several challenges. The urease content in plant extracts can vary significantly depending on factors such as plant species, growth conditions, harvest time, and extraction methods. Therefore, ensuring consistency in urease activity across large-scale batches through standardization is crucial. Additionally, extracting urease from plants often requires specific processing steps, such as grinding and filtration, which consume resources and energy. These factors must be carefully reconsidered in terms of their overall resource and energy demands.

Substitutes for urea in biocement production

As shown in Fig. 5, urea as a critical substrate in biocementation, offers significant potential for cost reduction if low-grade alternatives can replace the analytical-grade urea typically used in laboratory experiments. Studies have explored the use of fertilizer-grade urea (FU), which contains 48.97% nitrogen, as a substitute for the expensive analytical-grade urea (SU). Comparative investigations revealed no significant differences in enzymatic activity during the development of Sporosarcina pasteurii bacteria when using either FU or SU. Consequently, FU is recommended as a cost-effective alternative to SU for biocement applications (Cuzman et al. 2015).

Fig. 5.

Schematic diagram of low-cost urea

However, whether analytical-grade or low-grade, the industrial production of urea relies heavily on the energy-intensive Haber–Bosch process, which consumes substantial fossil fuel resources and generates considerable carbon dioxide emissions (Masjedi et al. 2024; Muhyuddin et al. 2024; Wu et al. 2024). Thus, identifying affordable and sustainable urea substitutes could not only reduce the cost of biocement production but also significantly lower its carbon footprint. Current research has begun to explore alternative urea sources, including human urine, pig urine, cow urine, and fertilizer-grade urea. These substitutes have garnered increasing attention due to their wide availability, low cost, and relative sustainability. For instance, cow urine has been studied as a potential nutrient source for MICP in sandy soils. The stability of urea in both fresh and sterilized cow urine was monitored over a month to cover the typical duration of MICP interventions. The results indicated that the urea concentration and stability in both forms of cow urine were suitable for MICP applications. Furthermore, the carbonate concentration in cow urine with a pH of 9 exceeded that at pH 7, facilitating microbial adaptation and the generation of carbonate ions in solution, which in turn promoted carbonate mineral precipitation (Comadran-Casas et al. 2022). Experiments with quartz sand columns treated with Sporosarcina pasteurii and injected with pig urine and 1.1 M CaCl₂ solution at regular intervals showed reduced porosity and permeability after multiple treatments, indicating improved soil mechanical performance. XRD and SEM analyses confirmed the formation of CaCO₃, validating the feasibility of using pig urine in MICP (Chen et al. 2019).

Similarly, human urine has been investigated as a urea source for MICP processes. Pretreatment with calcium hydroxide was employed to stabilize the collected urine. The treated urine, combined with CaCl₂ and a nutrient solution, was injected into molds containing loose sand to produce biobricks with a maximum compressive strength of 2.7 MPa. However, the relatively low urea content in human urine presents challenges. For example, producing a single biobrick via MICP required approximately 31 L of human urine, with urea being the sole effective substrate for calcium carbonate production (Lambert and Randall 2019). To enhance processing efficiency and reduce treatment cycles, future research could focus on concentrating or recovering urea from urine (Maurer et al. 2006; Simha et al. 2018; Crane et al. 2023). Additionally, other components in urine, such as phosphorus, offer potential for further utilization, contributing to a more comprehensive and sustainable approach. However, its scalability in practical applications is limited by several factors. Firstly, large-scale urine collection presents significant logistical challenges in terms of transportation and storage. Secondly, the pre-treatment process of urine requires careful consideration of associated costs to ensure it meets the safety and quality standards required for its intended use. Furthermore, the application of urine may face societal acceptance issues, as the public may have psychological barriers or health concerns regarding the use of urine as a raw material.

Exploring cost-effective calcium alternatives in biocement production

As shown in Fig. 6, calcium sources are one of the core raw materials in biocement reactions, directly influencing economic viability. However, the high cost of high-purity chemical calcium sources, such as analytical-grade calcium chloride commonly used in laboratories, has limited the large-scale application of biocement in practical engineering projects.

Fig. 6.

Schematic diagram of sources that can be used as low-cost alternative calcium sources

Low-grade calcium chloride, such as de-icing salts, offers an alternative low-cost calcium source due to its widespread use and availability. Studies have explored the feasibility and effectiveness of using low-cost chemicals for in-situ slope stabilization, conducting field MICP experiments. Utilizing de-icing salt as a low-cost calcium source, along with other low-grade chemicals such as fertilizer-grade urea and brewery yeast, MICP treatment successfully formed a hardened surface layer 5–10 cm thick, achieving a surface unconfined compressive strength of up to 1.02 MPa and a calcium carbonate precipitation of 3.7%. This demonstrates the feasibility of replacing analytical-grade reagents with such alternatives. Cost analysis further revealed that substituting low-grade chemicals for conventional synthetic media reduced material costs for cementation media by approximately 97% (Gowthaman et al. 2023).

Eggshells and shellfish waste, such as oyster and clam shells, generated by the food and hospitality industries, are common kitchen waste materials primarily composed of calcium carbonate. Their resource utilization not only reduces kitchen waste but also provides a cost-effective calcium source. One study proposed using eggshells and vinegar to produce soluble calcium for soil improvement via the MICP process. The geotechnical properties of sand treated with this method were evaluated and compared to those treated with other calcium sources, such as calcium chloride, confirming the feasibility of using soluble calcium derived from eggshells for soil stabilization. The optimal ratio of eggshells to vinegar was also investigated. The treated sand achieved a calcium carbonate content of up to 7%, corresponding to a UCS of approximately 400 kPa, while its permeability decreased from an original value of 10^− 4 m/s to 10^− 6–10^− 7 m/s (Choi et al. 2016).

Industrial waste is also considered a potential calcium source for biocement production. Utilizing such waste not only reduces the cost of calcium procurement but also alleviates the pressure of accumulating solid waste. Steel slag, a byproduct of steel production, primarily consists of calcium, magnesium, and iron oxides and is often considered a waste material. Chemical analysis indicates that steel slag contains 17.49% CaO. By employing ammonium chloride or acetic acid, calcium can be extracted from steel slag, dissolving calcium carbonate and calcium oxide. Due to its stronger acidity, acetic acid extracted more calcium ions than ammonium chloride. Tests on sand columns treated with biocement using steel slag-derived calcium showed effective cementation, with dual-phase treatment producing higher UCS and calcium carbonate content and lower permeability compared to calcium chloride-treated sand. This demonstrates the feasibility of producing calcium acetate from steel slag as an alternative calcium source (Yu et al. 2023).

Further research explored the use of waste limestone powder from aggregate quarries combined with acetic acid derived from the fast pyrolysis of lignocellulosic biomass as a calcium ion source. Acetic acid, a major byproduct of fast pyrolysis, poses a disposal challenge for the lignocellulosic biofuel industry. This study utilized the acetic acid stream to dissolve calcium from limestone powder, applying the resultant calcium ions in MICP for sand cementation (Choi et al. 2017). XRD analysis confirmed the formation of calcium carbonate from these waste-derived materials. SEM images of MICP-treated sand columns revealed microstructures similar to those observed in previous studies using reagent-grade CaCl₂. The engineering properties of sand treated with the new calcium source were comparable to those treated with CaCl₂, achieving calcium carbonate contents ranging from 5.67 to 8.19% and reducing permeability from 1 × 10^− 4 m/s to 8.17–1.52 × 10^− 6 m/s.

The application of low-cost calcium sources not only significantly reduces the production cost of biocement but also demonstrates considerable potential in environmental protection, particularly in mitigating the adverse impacts of solid waste on the environment (Fouladi et al. 2023). As resources become increasingly scarce and the demand for sustainable development grows, converting such waste into valuable resources can effectively alleviate environmental pressure while facilitating circular economy practices in resource utilization. However, despite the comparable engineering performance of these alternative calcium sources to traditional high-purity calcium sources, their practical application faces several challenges that require further research and optimization. These low-cost calcium sources often possess complex compositions, potentially containing various impurities such as heavy metals or harmful substances, which may adversely affect the quality and stability of biocement. Therefore, an important research direction is to develop effective methods for the removal or control of these impurities, ensuring the safety and reliability of the final product. Additionally, the extraction and processing methods for low-cost calcium sources require further refinement. Many low-cost calcium sources involve complex recovery processes, often necessitating the use of acid treatment. Thus, improving the efficiency and economic feasibility of these extraction technologies is still critical.

Ammonia/ammonium recovery and other approaches to cost reduction in biocement production

The decomposition of urea in biocement production often leads to the generation of ammonia/ammonium, which, if not properly managed, is likely to cause environmental pollution at construction sites and result in various environmental issues, including haze pollution, nitrogen deposition, soil acidification, eutrophication, and loss of biodiversity (Zhan et al. 2021; Yu et al. 2021; Yan et al. 2022). Research has explored methods for handling the byproducts of ammonia/ammonium. Among these, zeolite adsorption to treat ammonia/ammonium (Su et al. 2022; Yuan et al. 2024; Hanisch et al. 2024), and the washing process followed by ammonium conversion into struvite presents a promising approach to reduce costs by transforming waste into a valuable fertilizer (Mohsenzadeh et al. 2022). Both the zeolite adsorbed ammonium and the synthesized struvite can be sold as fertilizers, offsetting a portion of the biocement production costs. Therefore, further studies could focus on designing construction processes that seamlessly integrate ammonium recovery with MICP reactions, allowing ammonia/ammonium byproducts to be repurposed as valuable resources. However, both methods face practical challenges. Although zeolites are highly effective in ammonium adsorption due to their ion-exchange properties, their selectivity may be affected by the presence of competing cations commonly found in wastewater. This can reduce ammonium removal efficiency, which may necessitate wastewater pretreatment to optimize performance. Additionally, the regeneration of zeolites, once saturated, often requires the use of chemical solutions, which not only increases costs but may also generate secondary waste streams that require further treatment. Struvite production also depends on additional chemicals, such as phosphorus and magnesium sources. Developing low-cost and sustainable magnesium and phosphorus sources is crucial for the large-scale implementation of this method.

Fermentation strategies can significantly enhance the efficiency of batch cultivation of urease-producing bacteria, thereby improving the economic feasibility of MICP applications (Lapierre and Huber 2024). Additionally, the choice of aggregates used in biocementation plays a crucial role in determining both the cost-effectiveness and the practical applicability of biocement (Mistri et al. 2021). Furthermore, since the availability of inexpensive feedstocks is often region-dependent, a dynamic Life Cycle Assessment(LCA)-based real-time optimization system can be developed. By combining local resources and continuously updating environmental and economic impact assessments, this system would enable dynamic optimization of resource allocation and process adjustments during construction, further lowering costs (Carlsson Reich 2005; Martinez-Sanchez et al. 2015; Buyle et al. 2019). Additionally, expanding LCA to include Life Cycle Sustainability Assessment(LCSA) could quantify the ecosystem services provided by biocement, such as carbon emissions reduction and the use of waste materials in biocement production, transforming these into economic value. This holistic approach can offer decision-making frameworks from a full-cost perspective, emphasizing the ecological contributions of the technology.

Policy innovation and cross-disciplinary collaboration can also contribute to cost reduction. For example, establishing a carbon credit system specifically for biocement technology could incentivize construction companies and technology providers based on their carbon capture achievements. Such a system could be integrated with existing international carbon markets, supporting the commercialization of biocement technology while offering additional subsidies to reduce costs. Furthermore, policies promoting collaboration between agriculture, construction, and waste management sectors can foster mutual support among industries. For instance, using waste materials in biocement production not only reduces the costs of waste disposal but also creates intersectoral synergies. Financial subsidies supporting cross-industry cooperation could further facilitate the diverse development of biocement technologies. Public outreach activities and community pilot projects could also be initiated to demonstrate how biocement technology, by recycling waste materials such as urine, can produce sustainable building materials, encouraging public participation in the promotion of low-carbon construction materials. Positive public feedback can drive policy support and create a favorable environment for scaling up the technology.

In conclusion, innovative ammonia/ammonium recovery pathways, dynamic LCA/LCSA-based optimization, policy support, and social collaboration are essential measures for the commercial adoption of biocement technology. These efforts will enable comprehensive cost optimization while enhancing the ecological and societal value of biocement, providing new momentum for sustainable construction globally.

Conclusion

This review comprehensively explores various strategies to reduce the production costs of biocement, including the selection of low-cost microbial growth media, the use of plant extracts as enzyme substitutes, the development of affordable urea and calcium ion sources, and the recovery of byproducts such as ammonia/ammonium. The findings indicate that these approaches not only significantly lower production costs but also transform waste into valuable resources, achieving both economic and environmental benefits. Furthermore, enhanced policy support, interdisciplinary collaboration, and the integration of dynamic LCA/LCSA will provide critical foundations for the commercialization of biocement technology. In conclusion, the combination of cost optimization measures and eco-sustainability strategies offers renewed momentum for the large-scale application and global promotion of biocement.

Author contributions

Z. Y.: Conceptualization, manuscript writing and reviewing, funding acquisition; K. N.: Resources; C. T.: Resources; S. K.: Resources, funding acquisition.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.