Rice Husk at a Glance:From Agro-Industrial to Modern Applications

Excessive waste production has led to the concept of a circular bioeconomy to deliver valuable by-products and improve environmental sustainability.The annual worldwide rice production accounts for more than 750 million tons of grain and 150 million tons of husk.Rice husk(RH)contains valuable biomaterials with extensive applications in various fields.The proportions of each component depend primarily on rice genotype,soil chemistry,and climatic conditions.RH and its derivatives,including ash,biochar,hydrochar,and activated carbon have been placed foreground of applications in agriculture and other industries.While the investigation on RH’s compositions,microstructures,and by-products has been done copiously,owing to its unique features,it is still an open-ended area with enormous scope for innovation,research,and technology.Here,we reviewed the latest applications of RH and its derivatives,including fuel and other energy resources,construction materials,pharmacy,medicine,and nanobiotechnology to keep this versatile biomaterial in the spotlight.

Performance Evaluation of Novel Eco-Materials Composed of Millet Husks, Rice Husks, and Polystyrene

Managing agricultural waste and expanded polystyrene (EPS) poses significant environmental and economic challenges. This study aims to create composites from millet husks, rice husks, and recycled EPS, using a manufacturing method that involves dissolving the polystyrene in a solvent followed by cold pressing. Various particle sizes and two binder dosages were investigated to assess their influence on the physico-mechanical properties of the composites. The mechanical properties obtained range from 2.54 to 4.47 MPa for the Modulus of Rupture (MOR) and from 686 to 1400 MPa for the Modulus of Elasticity in Bending (MOE). The results indicate that these composites have potential for applications in the construction sector, particularly for wood structures and interior decoration. Moreover, surface treatments could enhance their durability and mechanical properties. This research contributes to the valorization of agricultural and plastic waste as eco-friendly and economical construction materials.

Investigation of the Fermentation Mode of Rice Husk for the Stabilization of Earth Plaster

Despite its low resistance to humidity, adobe remains the most widely used material for housing construction, particularly in developing countries. The present study aims to assess different modes of use of fermented RH and to evaluate their influence on the behavior of raw earth for application in plaster. The influences of two types of RH are evaluated: granular rice husk (RHg) and powdered RH (RHp). The clay mainly consists of clay (40%), silt (22%), and sand (38.4%), with a small proportion of gravel (0.24%). Its liquidity limit is 40% and the plasticity index is 26.5%. The mixtures were designed using earth and each of the two rice husks at the volumetric content of 10%, 15% and 20% of the total volume mixed with water 36.5%, 38.5% and 40.3% and fermented for three weeks. Each fermented mixture was added to the soil to form the paste, and 40 × 40 × 160 mm3 test speciments were made for characterization. The results generally show an improvement in the physico-mechanical properties and water resistance of the mortars containing fermented RH, with an optimal content between 10% and 15%. The powdered RH improved the performance of the mortar better than granular RH.

Development and Characterization of Particle Boards Based on Sorghum Husk

This study tackles current environmental challenges by developing innovative and eco-friendly particle boards utilizing sorghum husk, combined with recycled expanded polystyrene (EPS). This dual eco-responsible approach valorizes sorghum husk, often deemed agricultural waste, and repurposes EPS, a plastic waste, thus contributing to CO2 emission reduction and effective waste management. The manufacturing process involves dissolving recycled polystyrene within a solvent to create a binder, which is then mixed with sorghum husk and cold-pressed into composite boards. The study explores the impact of two particle sizes (fine and coarse) and two different concentrations of the recycled EPS binder. Results demonstrate significant variations in the boards’ mechanical properties, displaying a range of Modulus of Rupture (MOR) from 0.84 MPa to 3.85 MPa, and Modulus of Elasticity (MOE) spanning from 658.13 MPa to 1313.25 MPa, influenced by the binder concentration and particle size. These characteristics suggest that the boards can be effectively used in various construction applications, including interior decoration, false ceilings, and potentially for furniture and door manufacturing when combined with appropriate coatings. This study not only exemplifies the valorization of plastic and agricultural wastes but also offers a practical, localized solution to global climate change challenges by promoting sustainable construction materials.

Study of Rice Husks and Expanded Polystyrene Composites for Construction Applications

In the current context of environmental challenges, this study focuses on developing innovative and eco-friendly composites using rice husk and recycled expanded polystyrene. This dual-responsibility approach valorizes a by-product like rice husk, often considered waste, and reuses polystyrene, a plastic waste, thereby contributing to CO2 emission reduction and effective waste management. The manufacturing process involves dissolving recycled polystyrene into a solvent to create a binder, which is then mixed with rice husk and cold-compacted into composite materials. The study examines the impact of two particle sizes (fine and coarse) and different proportions of recycled polystyrene binder. The results show significant variations in the mechanical characteristics of the composites, with Modulus of Rupture (MOR) values varying from 2.41 to 3.47 MPa, Modulus of Elasticity (MOE) ranging from 223.41 to 1497.2 MPa, and Stiffness Coefficient (K) from 5.04 to 33.96 N/mm. These characteristics demonstrate that these composites are appropriate for various construction applications, including interior decoration, panel claddings, and potentially for furniture and door manufacturing when combined with appropriate coatings. This study not only highlights the recycling of agricultural and plastic waste but also provides a localized approach to addressing global climate change challenges through the adoption of sustainable building materials.

The Influence of Rice Husk Ash on Mechanical Properties of the Mortar and Concrete: A Critical Review

Increasing the population and infrastructure in both emerging and developed countries requires a considerable amount of cement, which significantly affects the environment. The primary materials of concrete (‘cement’) production emit a large quantity of CO2 into the environment. Also, the cost of conventional building materials like cement gives motivation to find geopolymer waste materials for concrete. To reduce harmful effects on the environment and cost of traditional concrete substance, alternative waste materials like rice husk ash (RHA), ground granulated blast-furnace (GGBS), fly ash (FA), and metakaolin (MK) can be used due to their pozzolanic behavior. RHA waste material with a high silica concentration obtained from burning rice husks can possibly be used as a supplementary cementitious material (SCM) in the manufacturing of concrete, and its strong pozzolanic properties can contribute to the strength and impermeability of concrete. This review paper highlights a summary of the positive effect of using RHA as a partial substitute for cement in building construction, as well as its optimal inclusion of enhanced mechanical properties like compressive strength, flexural strength, and split tensile strength of mortar and concrete.

On the “Onion Husk” Algorithm for Approximate Solution of the Traveling Salesman Problem

The paper describes some implementation aspects of an algorithm for approximate solution of the traveling salesman problem based on the construction of convex closed contours on the initial set of points (“cities”) and their subsequent combination into a closed path (the so-called contour algorithm or “onion husk” algorithm). A number of heuristics related to the different stages of the algorithm are considered, and various variants of the algorithm based on these heuristics are analyzed. Sets of randomly generated points of different sizes (from 4 to 90 and from 500 to 10,000) were used to test the algorithms. The numerical results obtained are compared with the results of two well-known combinatorial optimization algorithms, namely the algorithm based on the branch and bound method and the simulated annealing algorithm. .

Preparation and activity research of ecological nano mineral admixture from rice husk charcoal

The rice husk ash （ RHA） and silica （ Si02） nanoparticles are prepared from rice husk charcoal （RHC） by the methods of ventilated calcining and chemical precipitation, respectively, to remove the residual carbon which is harmful to cement composites. The structures and morphologies of these products are investigated by the Fourier transform infrared spectroscopy, X-ray diffraction, scanning/ transmission electron microscopy and N2 adsorption- desorption analyzer. The results show that the as-produced RHA and Si02 nanoparticles exist in amorphous phase without residual carbon, and exhibit porous structures with specific surface areas of 170.19 and 248. 67 m2 /g , respectively. The micro particles of RHA are aggregated by numerous loosely packed Si02 gel particles with the diameter of 50 to 100 nm. The Si02 nanoparticles are well dispersed with the average size of about 30 nm. Both the RHA and Si02 nanoparticles can significantly reduce the conductivity of saturated Ca（OH）2 solution and increase the early strength of the cement composites. They also exhibit high pozzolanic activity, indicating that they can be used as ecological nano mineral admixtures.

Preparation and characteristic analysis of rice husk high boiling solvent lignin

Rice husk high boiling solvent lignin （RHL） was prepared by high boiling solvent method, and its characteristics was analyzed by using chemical composition analysis, infrared spectroscopy, and ^1H-NMR and ^13C-NMR spectroscopy. The optimum prepared condition was that the rice husk with 70%-90% aqueous solution of 1, 4-butanediol was mixed with autoclave, under a certain weight ratio of solid raw material and solvent, heated to 200-220℃ for 1.0-3.0 h, then water-insoluble RHL was separated from the liquor reaction mixture by water precipitation. Results suggested that the lower digestion temperature and concentration of 1,4-butanediol were both unfavorable for extracting lignin. Chemical weight-average molecular weight of RHL was 1939 g·mol^-1, and the residual polysaccharide content was 5.12%. The ^1H-NMR spectra of RHL showed the relative intensity ratio, aliphatic over aromatic methoxyl groups, situated at 3.5-3.8 and 3.8-4.0 ppm, respectively. The results from ^13C-NMR spectra showed that β-O-4 bond and β-5 carbon-carbon linkage were the major linkages between RHL units. The C9-formula of RHL was calculated by the experiment data.

Genetic dissection of husk number and length across multiple environments and fine-mapping of a major-effect QTL for husk number in maize(Zea mays L.)

Husk number(HN)and husk length(HL)influence the mechanical harvesting of maize grain.We investigated the genetic basis of HN and HL using a population of 204 recombinant inbred lines phenotypically evaluated in five environments.The two husk traits showed broad phenotypic variation and high heritability.Nine stable quantitative trait loci(QTL)were identified by single-environment mapping,comprising four QTL for HN and five for HL,and three QTL explained>10%of the phenotypic variation.Joint mapping revealed 22 additive QTL and 46 epistatic QTL.Both additive and epistatic(additive×additive)effects as well as a few large-effect QTL and some minor-effect QTL appeared to contribute to the genetic architecture of HN and HL.The QTL for HN located on chromosome 7,q HN7,which accounted for^20%of phenotypic variation,was detected in all five environments.q HN7 was fine-mapped to a 721.1 kb physical region based on the maize B73 Ref Gen_v3 genome assembly.Within this interval,four genes associated with plant growth and development were selected as candidate genes.The results will be useful for improvement of maize husk traits by molecular breeding and provide a basis for the cloning of q HN7.

Toxicity and Antifeedant Activity of Extracts from Walnut Green Husk against Wheat Aphid

[Objective] The research aimed to study the toxicity and antifeedant activity of walnut green husk extract on wheat aphid. [Method] Using ultrasonic extraction, 5 kinds of different polarity solvents were used to prepare the extracts from walnut green husk. The toxicity and antifeedant activity on wheat aphid were determined, [ Result ] Walnut green husk extracts in the solvent of ethanol, acetone, ethyl acetate had higher toxicity and antifeedant activity on wheat aphid. When the concentration was 100 mg/ml, after 24 h, the toxicity and antifeedant activity of three kinds extracts on wheat aphid were greater than 84.35% and 66.98%, respectively. After 48 h, the toxicity and antifeedant activity were greater than 85.91% and 79.34%, respectively. Among 5 kinds extracts,ethanol extracts had the highest toxicity and antifeedant activity on wheat aphid. After 24 h, the corrected mortality rate was 93.64% and the antifeedant rate was 83.61%. After 48 h,the corrected mortality rate was 94.95% and antifeedant rate was 92.21%. Petroleum ether extract had the smallest toxicity and antifeedant activity on wheat aphid. After 24 h,the corrected mortality rate and antifeedant rate were 19.54% and 34.65%, respectively. After 48 h,the corrected mortality rate and antifeedant rate were 20.13% and 39. 03%, respectively. [ Conclsion] The extracts from walnut green husk with larger polarity solvent had better toxicity and higher antifeedant activity on wheat aphid.

Reinforcement of Thermoplastic Starch Films with Cellulose Fibres Obtained from Rice and Coffee Husks

Cellulosic fibres from coffee(CF)and rice(RF)husks have been obtained applying chemical treatments and characterized as to their microstructure and thermal behaviour.These materials have been incorporated into glycerol plasticised thermoplastic starch(TPS)films obtained by melt blending and compression moulding at 1 wt%,5 wt%and 10 wt%.Microstructure,thermal behaviour and optical,tensile and barrier properties of the composites were analysed.Both kinds of micro-fibres improve the film stiffness while reduced the film stretchability.However,CF better maintained the film ductility at 1 and 5 wt%.A network of fine oriented fibres was observed on the surface of the films,while internal fibres exhibited a good adherence to the polymer network.The water vapour permeability of TPS films was not reduced in composites,although oxygen permeability was lowered by about 17%.Film transparency decreased by fibre addition in the UVVIS range.Thermal stability of composites was slightly higher than net TPS films.

Nano⁃Silica Production by Rice Husk Combustion in a 0.7 MW Double⁃Circulating Fluidized Bed after Acid Pretreatment

Rice husk is an organic silicon source for amorphous nano⁃silica particles.This paper reports the experimental study on the industrial production of nano⁃silica by rice husk combustion in a specially⁃designed 0.7 MW double⁃circulating fluidized bed(DCFB)based on acid pretreatment process.The physicochemical properties of RHA were characterized by various testing instruments.Results showed that acid pretreatment removed a large amount of metal impurities in the rice husk and thus inhibited the formation of crystalline silica or the agglomeration during the fluidized bed combustion process.The combustion efficiencies were as high as 99.5%.The obtained RHA comprised white fine particles and exhibited an amorphous structure,but factors such as collection point and acid type had certain influences on the quality of RHA.The highest SiO2 purity was greater than 98.6 wt.%,the lowest content of unburned carbon was 0.2 wt.%,the specific surface area reached 178 m2/g,and the pore size reached 5 nm.The circulating fluidized bed combustion of rice husk based on acid pretreatment can prepare nano⁃silica while providing heat for industrial processes,which is a highly energy⁃rich process.

Kinetics and isotherms of Neutral Red adsorption on peanut husk

Adsorption of Neutral Red (NR) onto peanut husk in aqueous solutions was investigated at 295 K. Experiments were carried out as function of pH, adsorbent dosage, contact time, and initial concentration. The equilibrium adsorption data were analyzed by Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Toth isotherm models. The results indicated that the Toth and Langmuir models provided the best correlation of the experimental data. The adsorption capacity of peanut husk for the removal of NR was deter...

Hard carbon derived from rice husk as low cost negative electrodes in Na-ion batteries

Here,we report the synthesis of hard carbon materials(RH) made from natural rice husk through a single pyrolysis process and their application as an anode in sodium-ion batteries.The studies show that the electrochemical properties of RHs are affected by the treatment temperatures,which determine the materials morphology,in particular,their degree of graphitization and extent of continuous channels(nanovoids).The latter are accessible to sodium ions and significantly contribute to charge storage capacity of the produced anodes.The RHs obtained at 1600 °C deliver the highest reversible capacity of276 mAh g^(-1) mainly due to insertion of sodium ions into the nanovoids.This work deepens the basic understanding of the influence of the carbonization temperature on the sodium storage mechanism.

Effect of grinding on chemical and physical properties of rice husk ash

The effect of grinding on the chemical and physical properties of rice husk ash was studied. Four rice husk ashes with different finenesses, i.e. coarse original rice husk ash （RHA0）, RHA1, RHA2, and RHA3 were used for the study. Ordinary Portland cement （OPC） was partially replaced with rice husk ash at 20% by weight of binder. The water to binder ratio （W/B） of the mortar was maintained at 110%±5% with flow table test. Specific gravity, fineness, chemical properties, compressive strength, and porosity test of mortars were determined. The differences in chemical composition of the rice husk ashes with different finenesses from the same batch are small. The use of RHA3 produces the mortars with good strength and low porosity. The strength of the mortar improves with partial replacement of RHA3 in comparison with normal coarse rice husk ash. The use of RHA3 results in a strong and dense mortar, which is due to the better dispersion and filling effect, as well as an increase in the pozzolanic reaction.

Pyrolysis of rice husk and sawdust for liquid fuel

The paper is focused on studying how to convert rice husk and sawdust into liquid fuel. Rice husk, sawdust and their mixture were pyrolyzed at the temperature between 420℃ and 540℃, and the main product of liquid fuel was obtained. The experimental result showed that the yield of liquid fuel heavily depended on the kind of feedstock and pyrolysis temperature. In the experiments, the maximum liquid yields for rice husk, sawdust and their mixture were 56% at 465 ℃, 61% at 490℃ and 60% at 475℃ respectively. Analysis with GC-MS and other apparatus indicated that the liquid fuel is a complicated organic compound with low caloric value and can be directly used as fuel oil without any up-grading. As a crude oil, the liquid fuel can be refined to be vehicle oil.

Preparation of fly ash and rice husk ash geopolymer

The geopolymer of fly ash （FA） and rice husk ash （RHA） was prepared. The burning temperature of rice husk, the RHA fineness and the ratio of FA to RHA were studied. The density and strength of the geopolymer mortars with RHA/FA mass ratios of 0/100, 20/80, 40/60, and 60/40 were tested. The geopolymers were activated with sodium hydroxide （NaOH）, sodium silicate, and heat. It is revealed that the optimum burning temperature of RHA for making FA-RHA geopolymer is 690oC. The as-received FA and the ground RHA with 1%-5% retained on No.325 sieve are suitable source materials for making geopolymer, and the obtained compressive strengths are between 12.5-56.0 MPa and are dependent on the ratio of FA/RHA, the RHA fineness, and the ratio of sodium silicate to NaOH. Relatively high strength FA-RHA geopolymer mortars are obtained using a sodium silicate/NaOH mass ratio of 4.0, delay time before subjecting the samples to heat for 1 h, and heat curing at 60oC for 48 h.

Optimization of Conditions for the Extraction of Melanin from Walnut Husk

[Objective] This study was conducted optimize the conditions for the ex- traction of melanin from walnut husk. [Method] Melanin was isolated from walnut husk through alkali extraction and acid precipitation, and the factors that may influ- ence the extraction efficiency： temperature, duration, NaOH concentration and solid- liquid ratio were set at different levels. [Result] The optimal conditions for the ex- traction of melanin from walhut husk were temperature of 80 ℃, extraction duration of 120 min, NaOH concentration of 70 mol/L, and solid-liquid ratio of 1：20. [Conclu- sion] The optimal conditions for the extraction of melanin from walnut husk deter- mined in the present study will provide references for the development and utiliza- tion of natural melanin.

Paddy Husk as Support for Solid State Fermentation to Produce Xylanase from Bacillus pumilus

To optimize culture conditions for xylanase production by solid state fermentation （SSF） using Bacillus pumilus, with paddy husk as support, solid medium contained 200 g of paddy husk with 800 mL of liquid fermentation medium [xylan, 20.0 g/L; peptone, 2.0 g/L; yeast extract, 2.5 g/L; K2HPO4, 2.5 g/L; KH2PO4, 1.0 g/L; NaCl, 0.1 g/L; （NH4）2SO4, 2.0 g/L, CaCl2-2H2O, 0.005 g/L; MgCl2.6H2O, 0.005 g/L; and FeCI3, 0.005 g/L] at pH 9.0 was applied. The highest xylanase activity （142.0 ±0.47 U/g DM] was obtained on the 6th day at 30℃ The optimized paddy husk to liquid fermentation medium ratio was 2：9, and the optimized culture temperature was 40℃. When commercial Birchwood xylan was replaced with different concentrations of corncob, xylanase production was maximized （224.2 U/g DM） in the medium with 150 g/L corncob. Xylanase production was increased by sucrose, fructose and arabinose, whereas reduced by glucose, galactose, lactose and amylose. When organic nitrogen sources were replaced with locally available nitrogen sources such as groundnut powder or sesame seedcake powder or coconut seedcake powder or soy meal powder, the highest xylanase production （290.7 U/g DM） was obtained in the medium with soy meal powder and 16.0 g/L of soy meal powder was the optimum （326.5±0.34 U/g DM）. Based on the optimization studies, B. pumilus produced 2.3 times higher xylanase activity. The medium cost was reduced from 2 458.3 to 178.3 SLR/kg and the total activity which could be obtained from 1 kg of the medium was increased from 48 624 to 220 253 Units.