Desert sand stabilization using biopolymers: review

Wind-driven sand erosion is the leading primary reason of earth deterioration in dry lands and a major global issue. Desert dust emissions and topsoil degradation caused by wind pose a global danger to the ecosystem, economy, and individual health. The aim of the current study is to critically analyze the different types of biopolymers and their interaction mechanism with sands for desert sand stabilization. Extensive experimental data with different percentages of biopolymers has been presented on various wind erosion studies using wind tunnel testing and their control rate on desert sand stabilization. Also, studies related to evaluating the engineering properties of sand using biopolymers were analyzed. Other biological approaches, namely Microbial-induced calcite precipitation (MICP) and Enzyme-induced carbonate precipitation (EICP), have been discussed to regulate wind-driven sand erosion in terms of percentage calcite formation at different compositions of urea and calcium chloride. Comparative analysis of MICP and EICP with biopolymer treatment and their limitations have been discussed. Biopolymers are not only demonstrated adeptness in engineering applications but are also helpful for environment safety. Biopolymers are suggested to be novel and nature-friendly soil-strengthening material. This review focuses on the fundamental mechanisms of biopolymer treatment to reduce wind-driven sand loss and its future scope as a binder for sand stabilization. The mechanism of soil-biopolymer interaction under various soil conditions (water content, density, and grain size distribution) and climatic circumstances (drying-wetting cycles) needs to be explored. Furthermore, before applying on a large scale, one should evaluate sand-biopolymer interaction in terms of durability and viability.


Introduction
Sandstorms are a major worldwide environment disaster, because they harm ecosystems, ruins the land, and hinder steady economic growth in arid and semi-arid areas.As a result, fugitive dust and loose sand particles erode.Deserts occupy over 41% of Earth's land area.Around 38% of the global population gets distressed due to this catastrophe [1][2][3].Sand is naturally transported and deposited by the wind through a process called wind-driven erosion.It is a usual incidence, that typically affects, loose and arid soils with fine grains, as well as sandy soils.Due to the removal of soil from one location and its subsequent deposit in another, wind-driven erosion damages the soil and native flora.Sand is eroded mostly by wind, which also has other effects.
Three types of wind erosion are saltation, surface creep, and suspension.Trolling across the surface of big particles ranging in diameter from 0.05 cm to 0.2 cm is known as a surface creep in a wind erosion event.They collide with other particles as a result and are thrown around.These big particles only move a few meters as a result of wind erosion and surface creep.Saltation occurs in soil particles of a size between 0.005 cm and 0.05 cm.Despite being too massive to become balanced, these particles are too weightless to be lifted off the surface.In a series of low bounces, these particles move above the soil's surface and cause attrition, or the disintegration of bigger particles into smaller ones.Small particles with a diameter of less than 0.01 cm are dispersed into the atmosphere by saltation, where they are carried up into the atmosphere by impetuousness to generate dust storms.Fine dust keeps floating around in the air till it is isolated by rain.Soil moisture content and wind speed are two elements that affect wind erosion.The water molecules join together and form the bond, that holds the soil together strongly.If soil moisture is at a good percentage, cohesion will be seen in terms of the binding of particles.If soil moisture levels start to drop, there will be less water in the soil, making it dried and more susceptible to wind erosion.Calculating wind speed in terms of its ability to cause wind erosion is never easy.A specific minimum velocity is required to shuffle soil particles for diverse soil kinds and surface conditions, which is termed its threshold velocity.Once the velocity is attained, the extent of soil stimulation gets reliant upon the particles size, soil particles adhesion, and wind velocity [4].
Sand particles must be strengthened to prevent movement due to wind flow.Different techniques (grouting, consolidation, compaction, vibration, mud, lime, bitumen, cement, mechanical, and chemical stabilization) to bind sand particles have been developed, but most of them may incur the high cost or not environment friendly.Compared to these ground improvement techniques, Microbial-induced calcite precipitation (MICP) and Enzyme-induced carbonate precipitation (EICP) have become relatively more popular for sand stabilization [5][6][7].In addition, MICP have been also utilized to improve strength of clay [8].To create calcium carbonate minerals, the MICP method fundamentally forced metallic ions to interact with acidic radical ions [7,[9][10][11][12][13][14].One of the most customary ways to cause carbonate precipitation is by hydrolyses of urea through addition of highly active urease producing microbes, namely Sporosarcina pasteurii [15].It has been extensively researched that calcium carbonate precipitation has tremendous capacity as an efficient technique for bio mineralization, because the production of a calcium carbonate crust in the MICP technique reinforces the sand particles and shields it from wind effect.
Moreover, the same metabolic processes utilized in MICP, can be applied with enzymes to produce calcite, which is acknowledged as enzyme driven calcium carbonate precipitation (EICP).In EICP, instead of using bacteria to produce urease enzymes, direct urease enzymes have been used from agricultural sources.
It should be noted that techniques such as MICP and EICP can incur significant expenditure for application in large scale.Further, there might be an issue on quality control during application in field (large scale) owing to random formation of calcite precipitation.Further, bacterial solutions utilized in MICP can also releases by-products in the character of ammonium chloride [8,16].
This study critically reviews different approaches of surface strength improvement against wind induced sand erosion.Emphasis has been placed on binding sand particles using different types of biopolymers and wind tunnel testing results to control wind driven sand erosion, limitations of existing studies along with future scope is highlighted.

Effects due to wind-induced sand erosion
One of the main factors contributing to desertification, or the degradation of dryland ecosystems, is wind-driven soil erosion.Which reduces plant and soil productivity, and agricultural output, and causes environmental damage.In addition, air dust has been connected to a number of respiratory illnesses, increase road fatalities, and decreases visibility.Environmental practices and individual activities that intensify wind induced erosion and dust emanations have a major impact on global drylands and their inhabitants.One of the major natural disasters that affects 1/3 of the world's territory is wind-induced sand erosion.Due to the presence of hazardous chemicals, germs, and pollens, the wind-swept and barred soil grains in the atmosphere, may result in health risks, such as allergic reaction and breathing illness.

Conventional methods and limitations
Demarcation of soil storms and restricting land deprivation are global constraints [2].The conventional practices like sand barriers, barricades, vegetation, chemical stabilization, and engineering tactics expended for wind attrition restrain to preclude desertification are probable to be futile eventually [17].There are functioning and appliance restrictions connected by every traditional procedure.Although vegetation helps to maintain sand grains undamaged through reinforcing and sand matric ability.The main problems with vegetation are the lack of an appropriate soil temperature and nutrient conditions [18].Sand barriers and barricades are immobile and cannot be reorganized as per the situation of soil accumulation and the layer created in the domain [2].The use of chemical stabilizing agents for ground improvement is not well promoted because they cause environmental problems, especially groundwater contamination, due to the release of harmful and synthetic compounds [19].Engineering techniques is not likely to be reasonable as it involves enormous workforce and matter resources [20].Bio-stabilization techniques have emerged as alternatives to mechanical and chemical stabilization of soil.

Biological approach
In recent decades, research on wind erosion has moved from focusing on its direct consequences (damage to agricultural land) to focusing on its indirect consequences (adverse impacts on the entire environment and human wellbeing).Because wind erosion poses a hazard to human health as an indirect result of climate change, discussions regarding how it has affected social patterns in general and agriculture in particular have widened our understanding of the issue.
Although there are a number of ground improvement techniques, namely using cementation, ashes, fibers, agricultural residue, and industrial waste [13,21], they still have a number of restrictions in terms of their durability, practicality, environmentally friendliness, and cost.As a result, there is a critical need for sustainable, renewable materials that can build soil.Recent trends have seen an increase in the usage of environment friendly and sustainable materials for soil recovery processes that lessen their adverse impacts on people and the atmosphere.On the basis of microbial activities and biomaterials used, bio based soil property recovery techniques can be divided into different categories.These microbial processes include the production of biofilms, bio mineralization, biopolymers, and bio-gas, among others [16].
MICP and EICP practices have been expended for lessening wind induced sand erosion.These methods have an advantage over other conventional methods due to their potential to boost sand grains [7,22,23].The MICP and EICP process hinge on the calcite content formation.The binding of sand particles is enhanced due to formation of calcite, which in turn resist wind induced erosion.Dagliya et al. [6] observed a reduction in wind driven sand erosion by 99.7%.Other researchers [24][25][26] have also used MICP process and found satisfactory results in controlling soil erosion.Almajed et al. [27] and Miao et al. [3] performed studies using EICP and found a reduction in sand erosion by almost 99.5%.Table 1 summarizes the few recent studies related to the mitigation of wind induced sand erosion using MICP and EICP.It shows percentage formation of calcite content for diverse composition of calcium chloride and urea, and its wind erosion control rate.
Despite the trailblazer, MICP has a number of restrictions, including transportation, cultivation, the ability of bacteria to fix substances, and the by-product ammonium chloride [32].In view of limitation in terms of time and cost for MICP and EICP, the use of biopolymers is a more sustainable solution [6].

Biopolymers: as soil stabilization
Polynucleotides, polypeptides, and polysaccharides are the three main groups of biopolymers, which are organic polymers made by living organisms.The most prevalent biopolymer employed in a variety of fields, including civil and construction engineering is polysaccharides [33].Since biopolymer is made from always available crops, it is a substance that is renewable, carbon-neutral, maintainable, green, and environmental friendly [34].Biopolymers come in many forms, are available from animals, plants, and microorganisms and can be generated in the lab.Biopolymers combine elements like sugar, amino acids, and oil that have distinct capabilities.Many types of biopolymers are used in a variety of industries due to their trussing properties, including oil extraction, textile manufacturing, construction businesses, cosmetics, food preservation, and pharmaceuticals.
Largely, biopolymers of polysaccharide-type are watersoluble owing to their ample external hydroxyl units, that primarily create sticky hydrogels on combination with water [35].Biopolymer to the water ratio and the existence of counter ions determines viscidness of the biopolymer hydrogels.Kirchmajer et al. [36], where both variables are directly proportional to the thickness rates of biopolymer hydrogels.Table 2 summarizes different types of biopolymers and their structures.It also presents applications of biopolymers including geotechnical engineering tests [16,37].It also mentioned various experimental studies, which have been performed with soil by various researchers to evaluate the behavior of sand biopolymer interaction.The reinforcement process of biopolymers is controlled mainly by the rheology of their hydrogels and also the chemical interaction that occurs between the biopolymers and sand particles [33].This interaction is highly depending on soil type [38].For dried biopolymer treated granular soil, desiccated biopolymer hydrogels develop an overlay all around electrically unbiased silica-centered grain crust [39].According to research, in inundated situations, biopolymer hydrogels in pore spaces enhance the superficial consistency intercept as the ratio of biopolymer to water rises, whereas the friction angle stays the same [38].Thus, it gives the impression that the ratio of biopolymers to water and the resulting hydrogel viscosity appear to be the primary reinforcing components for coarse soils.
The amalgamation of biopolymers with the sand elements, block vacuums, ensuing in elements trussing.The biopolymers may be sourced to augment potency, [46], and confirm erosion of sand [27,41,64,65].Addition of biopolymers is also found to reduce the hydraulic conductivity [39], and the compressibility of sandy soil [66].Many experiments have been executed using sodium alginate (SA) and a variety of gums like, xanthan, gellan, and guar gum to enhance the geotechnical properties of sand [16].Moreover, the findings from literature [41,43,49,67] have indicated that biopolymers have been used to suppress the wind induced sand erosion.
It was examined that biopolymer enhanced the strength of sandy soil, but at the same time apprehension is there, that it is water sensitive i.e. strength can be reduced when it comes in contact with water [68].It was noted that durability is one of the major weaknesses of biopolymer material.Limited knowledge of available laboratory experiment data on the wetting drying cycles and lack of field scale analysis makes biopolymer behaviour unpredictable in terms of durability.The performance of  biopolymers with water is one of the key concerns, which needs to be explored [6,41].Investigation of new experimental methods to examine, assess and control the durability and biodegradability of biopolymers is required [69].Among the budding bio-based sand improvement methods, biopolymers are at the frontage of field-scale treatments and have undergone extensive research to determine how much they can affect various engineering features.Due to the diverse physical properties of the host soils and the various testing environments, suitable measurements has yet to be assembled and compared, which has troubled further development in the development of unique yet useful soil improvement methodologies.As a result, this study examines the basic workings and prospective uses of biopolymers in soil enhancement.

Biopolymers mechanism and application to control wind driven sand erosion
For building materials like concrete mix, boring fluids, and cementitious fills, biopolymers have been used as plasticizers.An attempt is made to utilize biopolymers as novel ingredients for soil remediation and ground improvement in geotechnical engineering applications.
The wetting process starts on the surface because of its hydrophilic properties, which are caused by silica, silicate, and the water solubility of biopolymers.During treatment, the solution starts penetrating through pores in sand particles.Sand Biopolymer interaction starts through coating of sand particles and formation of a strong layer.During the drying process, the biopolymer matrix is dehydrated, which reduces the pore size and makes particles more intact.Figure 1 shows the spraying and mixing method of biopolymer with sand.Shorter connecting chains make them more resistant to outside stresses, enhancing their geotechnical performance.
Natural sand is more vulnerable to erosion because of the absence of intermolecular bonding and wind resistance.Lift force (F L ) as well as drag force (F D ) are the aerodynamic forces that play a significant role in winddriven sand erosion.The resistive forces are the cohesive force (Fi) and the gravity force of the sand acting downwards (F g ).In sandy soils, the cohesion between sand grains is usually negligible, while the value of F g (single grain weight) is also much lower.To avoid erosion of the sand particles, biopolymer sand interaction plays an important role by developing inter-molecular cohesion between the soil grains and enhancing particle weight.Figure 2 shows the sand biopolymer interaction mechanism.Figure 2a shows untreated sand, which explains the flow of air among the sand The forces acting, in this case, are usually very strong lift and drag and tend to move the particle.To overcome this problem, the soil is treated with a solution of biopolymers to form the hydrogel.Through coating the soil particles and creating a strong link, this hydrogel interacts directly with the soil.In this case, the weight and cohesion amongst the particle increase which minimizes drag and lift force and help to control wind-driven sand erosion.The mechanism of sand treated with biopolymers is shown in Fig. 2b.
Sand erosion control rate analyses have been achieved with Xanthan gum, Gaur gum, Beta Glucan, Chitosan and Starch [73,77,78].In these studies, a reduction of nearly 100% in erosion rate was found.Dagliya et al. [6] and Lemboye et al. [43] conducted studies using different biopolymers, namely Pectin, Acacia Gum and Sodium alginate to treat desert sand using spray and compact method.Their method also shows nearly 100% reduction in sand erosion.Table 3 includes details of various research which have been completed using common type of biopolymers utilized in geotechnical engineering.It mainly includes biopolymer percentage, types of biopolymers used, treatment details and wind tunnel studies result to control wind driven sand erosion.

Microscopic characterization
It was observed from a micro-scale analyses [46,53,81] that soil mixing with biopolymers forms a bond and improves the mechanical characteristic of dune sand.Chang et al. [32,82] has performed the study utilizing Xanthan gum on the sand and performed microanalysis through SEM images (Fig. 3a) and observed that biopolymer enlarges the effective surface of sand particles through the coating and also improves interlinking.Fatehi et al. [41] and Dagliya et al. [22,83] have performed micro-analysis through SEM images for natural sand and biopolymer-treated sand.It was observed that natural sand has more pore spaces with no bonding between particles.However, after addition of biopolymer, pore spaces have been decreased and the contact area has been enlarged due to coating (Fig. 3b).

Conclusion and future scope
The study analyses the studies, that are related to the use of different types of biopolymers for restricting wind driven sand erosion.Limitations and future scope related to these studies is also presented.Wind driven sand erosion preceded many issues on critical fronts like health, economy, environment, etc.The majority of commonly used traditional techniques have a number  Beta-glucan (0.5%), Xanthan gum (0.5%) 30 cm × 50 cm x 5 cm tray Water erosion test [70] Xanthan gum (XG 0.6%, 1%, and 1.6%) Gaur gum (GG 0.6%, 1%, and 1.6%)  of shortcomings, many of them are either economically or environmentally unviable.Consequently, surface strength enhancement has been intensively studied and developed over centuries.However, due to growing concern of climate change, there is also an enhanced focus on developing ecological methods for ground improvement.It has become essential to identify sustainable solutions for resolving wind-driven sand erosion because of an increase in habitat, which has led to a high demand for land.The class of materials known as biopolymers has also been suggested as a substitute option for reducing wind-driven sand erosion.The inter-particle cohesion is improved using biopolymer, which also offers excellent surface erosion resilience.Additionally, biopolymers are eco-friendly since, in contrast to conventional soil binders, they mostly consist of microbial hydrocarbons with minimal carbon footprints.Biopolymers are anticipated to emerge as a brand-new, green material for geotechnical and civil engineering.A recent assessment shows that using biopolymers to stabilize the planet is feasible and has great potential.Although biopolymers exhibit greater advantages, still further study is needed to bridge the gap between laboratory research and field application.
Biopolymers are water susceptible in nature and biodegradation still poses challenge for their treatment on a huge scale.Although biopolymers are inoffensive and richly available in nature, but very costly because of their food grade production excellence.For geotechnical field applications, high grade is not essential and hence the cost can be optimized with mass production and average grade quality.In addition to paving the way for a bright green future, more research into overcoming these constraints might also provide low-carbon, sustainable ground renovation options.
In conclusion, this study demonstrated that biopolymer is practicable in soil stabilization processes but still needs substantial improvement.Biopolymer has a wide range of potential uses.However, the behavior of biopolymers may be affected by the presence of water and subsequently, the strength may be reduced, which may be a key limitation of biopolymers.Also, problems such as high costs, uneven precipitation, lack of understanding of biogeochemical interactions and influence of factors (temperature, pH and curing period) that affect the process, durability aspect (wetting and drying cycle analysis) and large-scale uses have not been fully investigated.Also, criteria such as the category and quantity of biopolymers to be used for a given soil type needs to be addressed.Finally, the treatment effectiveness is likely to vary depending on the type of soil, soil compaction conditions and also biopolymer type.Therefore, a systematic set of studies are required to quantify treatment effectiveness of biopolymers in soils under different testing conditions.
Field studies need to be performed, using biopolymers to evaluate long term erosion aspects including social and economic impacts.Fundamental understanding of soil-water-biopolymer-atmospheric interaction is important to understand the bonding of sand with different biopolymers before transferring this knowledge to commercial-scale production.

Fig. 1
Fig. 1 Synopsis of sample preparation expending biopolymer solution [6].Copyright 2022 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences

Fig. 3
Fig.3SEM images of a Xanthan gum biopolymer-treated sand[82] and b untreated sand and sodium alginate biopolymer-treated sand[41] (Copyright 2019 American Society of Civil Engineers)

Table 1
MICP and EICP studies used to mitigate wind driven sand erosion

Table 2
Application of biopolymers used in soil stabilization and test performed

Table 3
studies related wind driven sand erosion control through biopolymers