Suspension Fertilizers Based on Waste Organic Matter from Peanut Oil Extraction By-Products

Abstract

The use of chemical fertilizers has significantly increased crop yields but has also led to soil problems such as nutrient imbalance and salinization. In response, organic fertilizers have emerged as a crucial component for sustainable agricultural development. This study was designed to develop an easily applicable organic suspension fertilizer using peanut bran, the primary by-product of peanut oil extraction, as the main raw material. Fourier-transform infrared (FTIR) analysis revealed that 80 °C is the optimal heating temperature for forming a stable peanut-bran suspension. A comprehensive experimental investigation was conducted to evaluate the effects of different peanut bran addition levels, stabilizers, emulsifiers, and suspending agents on the stability of suspension fertilizers. The results identified the optimal suspension fertilizer formulation as comprising 20% peanut bran, 0.5% sodium bentonite, 0.1% monoglyceride, 0.2% sucrose ester, 0.02% carrageenan, and 0.3% xanthan gum. This formulation ensures good stability and fluidity of the suspension fertilizer while maintaining a low cost of 0.134 USD·kg⁻¹. The findings provide a scalable technological framework for valorizing agro-industrial waste into high-performance organic fertilizers.

1. Introduction

The use of chemical fertilizers has significantly improved crop yields in China. However, excessive and unreasonable use of chemical fertilizers has led to soil problems such as nutrient imbalance, continuous cropping obstacles, salinization, and consolidation [1]. Achieving green development while ensuring food security is of great significance. Numerous studies have shown that the application of organic fertilizers is an important way to achieve green development [2].

In China, solid organic fertilizers are mainly made from livestock manure, straw, and other organic waste materials, which are fermented and composted to meet national organic fertilizer product quality standards [3]. These fertilizers are inexpensive but they cannot be applied via drip or sprinkler irrigation. In consecutive planting orchards, such as banana and pitaya orchards in China, manual application is mainly relied upon, leading to uneven application and limited soil improvement (Figure 1 and Figure 2). With the shortage of human resources, the application method is also facing challenges [4].

Compared with solid fertilizers, liquid suspension organic fertilizers are easier to apply. Suspended fertilizers can be divided into two types: fully water-soluble and partially water-soluble. The fully water-soluble type is mostly produced with fully water-soluble large amounts of nutrients and small molecules of amino acids, humic acid, etc., as the main raw materials. The main characteristic of fully water-soluble suspended fertilizers is that they can provide high concentrations of nutrients similar to those of solid fertilizers, while remaining flowable for easy application. It is also a mainstream product in China’s suspended fertilizer market [5]. However, the problem that these products have too high production and use costs limits their popularization and large-scale application. Partially water-soluble type, on the other hand, can be selected from industrial waste processed and used, but also can be used in the production of organic waste with high water content but containing valuable fertilizer components, significantly reducing the cost of production. For example, waste sludge from phosphoric acid extraction [6], and recover protein and water from tuna defrosting wastewater [7], and waste sodium-potassium phosphate from the production of polyols [8] can be converted into suspended fertilizers using suspension aids like clay minerals. To address this limitation, the present study explored the use of organic wastes to manufacture partially water-soluble suspended fertilizers

Despite the advantages of suspension fertilizers, related research and products are rarely reported, mainly due to the high difficulty in their production process [9]. In China, there are fewer than 100 suspension fertilizer invention patents, with less than 10 using low-cost partially water-soluble raw materials (

Table 1. Patent applications and ranking of suspension fertilizer in China. (As of June 2023).

Order	Patentee/Applicant	City	Country	Applications
1	Guangzhou Yixiang Agricultural Technology Co., Ltd.	Guangzhou	China	9
2	South China Agriculture University	Guangzhou	China	6
3	Shenzhen Batian Ecotypic Engineering Co., Ltd.	Shenzhen	China	4
4	Dongguan Desheng Fertilizer Technology Co., Ltd.	Dongguan	China	3
5	Guangdong Fengkang Biotechnology Co., Ltd.	Guangzhou	China	3
6	Kingenta Ecological Engineering Group Co., Ltd.	Linyi	China	2
7	Woda Agricultural Technology Co., Ltd.	Beijing	China	2
8	South Subtropical Crops Research Institute CATAS	Zhanjiang	China	2
9	Environment and Soil Fertilizer Research Institute FJAAS	Fuzhou	China	2

).

Suspension fertilizer production mainly consists of three parts: grinding of raw materials, manufacturing of the suspension system, and mixing and dispersing.

(1)

Grinding of Raw Materials

The initial stage in suspension fertilizer production is the grinding of raw materials. This process aims to reduce particle size, addressing issues such as sedimentation and stratification caused by oversized or uneven fertilizer particles. The particle size in different suspension fertilizers is typically tailored to processing costs and application conditions [9].

(2)

Manufacturing of Suspension System

Maintaining the viscosity within the range of 30 to 100 cSt is crucial, as it effectively prevents crystal growth and solid precipitation. Excessively high viscosity can complicate filling and measuring processes, impacting usability [9]. In this stage, inorganic suspension fertilizers often mix thickeners and dispersants with water to form premixed suspension, while organic and organic-inorganic composite fertilizers can be directly converted into suspensions using organic raw materials like plant protein. Plant proteins have hydrophilic structures. When fully hydrated with water, they form gels through heating and cooling [10]. The protein gel, a balance between molecular attraction and repulsion, creates a highly ordered three-dimensional network structure or matrix that retains water. This gel is an intermediate phase between solid and liquid, maintaining fluidity with suitable auxiliaries [11].

(3)

Mixing and Dispersing

In the final stage, the ground fertilizer raw materials are added to the premixed suspension in a reactor and subjected to shear stirring. This ensures even dispersion of the fertilizer within the suspension system.

Suspension fertilizers are multi-component, inhomogeneous coarse dispersion systems. In a steady state, insoluble or slightly soluble solid particles are uniformly dispersed in water, forming a solid–liquid dispersion system with fine particles, high suspension, and flowability [12]. However, the stable state of the suspension system is easily disrupted (Figure 3). Products struggle to maintain uniform fluidity over extended periods and are prone to issues such as delamination, caking, and sedimentation [8]. Additionally, suspension fertilizers processed from organic waste are susceptible to problems like the growth of heterotrophic fungi and decay of organic matter (Figure 3). These challenges severely limit the application and popularization of the products. Ensuring the stability of the suspension system, preventing issues like delamination, precipitation, and deterioration, and maintaining product quality during storage and market circulation are the main challenges in suspension liquid fertilizer production and application.

Peanut bran, the press-cake remaining after peanut-oil extraction, was chosen as the principal feedstock for manufacturing suspension fertilizers that contain a high proportion of water-insoluble solids. China generates more than four million tonnes of this residue annually. The material contains > 50% plant protein, a key precursor for thermo-induced gel networks. Relative to lignocellulosic wastes such as maize straw, peanut bran decomposes rapidly, releases nutrients more synchronously with crop demand, and has repeatedly improved the sensory and nutritional quality of fruits and vegetables; consequently, it has been widely adopted in orchards and flue-cured tobacco systems [13].

In Chinese banana plantations, peanut bran has long been revered as a “quality enhancer.” Before fertigation became common, growers traditionally placed small quantities of bran at the pseudostem base during critical phenological stages. With the advent of drip irrigation, on-farm practices shifted to anaerobic soaking pits; the supernatant is filtered and fertigated. This approach, however, generates malodours, attracts dipteran pests, and produces highly variable agronomic responses, fuelling demand for a stable, pumpable peanut-bran suspension tailored to fertigation.

Crude protein dictates both the functionality and the physical stability of peanut bran. Among upgrading options—enzymatic hydrolysis [14] chemical modification [15], ultrasonication [16] and high-pressure processing [17]—hydrothermal treatment is the most cost-effective, intrinsically safe and readily scalable route for small- to medium-scale fertilizer plants, because it drives controlled protein gelation [18].

The secondary structure of plant proteins (α-helix, β-sheet, random coil, β-turn) directly governs their macroscopic rheology [19]. Partial unfolding of α-helix into random coils and β-turns converts a rigid gel into a shear-reversible weak gel, decreasing viscosity and enhancing thixotropy [20]. Heating temperature and protein concentration are the dominant variables [11], yet protein reconfiguration alone cannot ensure long-term colloidal stability. Targeted adjuvants are therefore essential: bentonite-type gelling agents suppress water syneresis [21]; polysaccharides reinforce the network via hydrogen bonding, van der Waals and hydrophobic interactions [22]; emulsifiers homogenize residual lipids and prevent flotation [23].

Guided by these insights, the overall goal of this study was to convert peanut-oil extraction residues into a shelf-stable, pumpable organic suspension fertilizer suitable for fertigation. Specific objectives were (i) to quantify the effect of heating temperature (30–100 °C) on peanut-bran protein secondary structure using FTIR, (ii) to identify the optimal bran solids concentration that balances nutrient density and flowability, (iii) to benchmark four clay stabilizers and optimize their dose, and (iv) to determine the best combination of emulsifiers and suspending agents via an orthogonal design.

2. Materials and Methods

2.1. Fertilizer Raw Materials

Peanut bran was supplied by Guangxi Jinsui Ecological Technology Co., Ltd., located in Nanning city, China. Its composition and nutrient contents are listed in

Table 2. Basic composition and nutrient contents of peanut bran.

Parameter	Content (%)	Fertilizing Ingredients	Value (%)
Protein	51.40	N	6.45
Oil	0.40	P2O5	1.17
Ash	5.61	K2O	1.42
Starch	17.30	Ca	0.84
Soluble Saccharide	10.87	Mg	0.19

, and the material was ground to pass a 120-mesh (≤0.125 mm) (Figure 4).

2.2. Auxiliary Agent

Peanut bran contains protein, oil, starch, and other components prone to surface oil floating and stratified condensation during production and storage, necessitating the addition of different auxiliaries for improvement.

2.2.1. Stabilizing Agent

Small molecule non-emulsifying colloidal particles like fumed silica and bentonite provide a physical barrier to retard or prevent agglomeration. These agents give the liquid non-Newtonian characteristics, inhibiting settling [24]. Four clay minerals (Yi Xin Chemical Products Business Department, Nanchang, China) were tested: bentonites, including fumed silica, Ca-bentonite, kaolinite and Na-bentonite.

2.2.2. Emulsifier and Suspending Agent

Monoglyceride and sucrose ester are commonly used emulsifying stabilizers. Sucrose is an ideal emulsifier for solving oil floating issues but is often used with other emulsifiers. Monoglyceride, when combined with emulsifiers, forms a spiral complex with amylose molecules, reducing excessive viscosity from starch gelatinization [25]. Polysaccharides as fillers can effectively improve the protein gel network structure by forming multiple protein network structures through hydrogen bonding, van der Waals forces and hydrophobic interactions. Xanthan gum is the most commonly used polysaccharide suspension aid. In aqueous solution, xanthan’s stiff double-helix chains are electrostatically repelled and bridged by hydrogen bonding and intermolecular forces, forming an entangled 3-D network whose steric and secondary interactions impede the migration, aggregation and sedimentation of dispersed phases, thereby providing simultaneous thickening and colloidal stabilization [26]. However, xanthan gum needs to be compounded with other polysaccharides to form a gel, and carrageenan has good synergistic properties with xanthan gum [27,28]. (All emulsifiers and suspending agents are purchased from Zhengzhou Cangyu Chemical Products Co., Ltd., Zhengzhou, China).

2.3. Research Methodology

2.3.1. Sample Preparation

(1)

Temperature treatments:

Peanut-bran powder was pre-dispersed in water to a solid content of 20% (w/w) and heated in a water bath at 30 °C, 60 °C, 80 °C or 100 °C for 30 min. After slow cooling to room temperature, each suspension was snap-frozen in liquid nitrogen, freeze-dried, and ground; the resulting powders were coded C (30), C (60), C (80) and C (100). In parallel, a basal fertilizer liquor containing the same solids plus selected stabilizers was prepared and subjected to the same thermal protocol; these samples were designated X (30), X (60), X (80) and X (100) to probe the thermal response of the composite system.

(2)

Formulation trials:

①

Single-factor screening: bran 16–30% (w/w); clay minerals 0–1%.

②

Orthogonal optimization: L₁₆(4⁴) matrix examining four levels each of monoglyceride, sucrose ester, κ-carrageenan and xanthan gum, using 7-day sedimentation ratio as the response.

Production protocol: A high-shear mixer with heating and homogenizing functions (AGR-HSM, AGR High-Shear Mixer) was used (Figure 5). Bran powder, additives and water were blended at 80–90 °C for 30–90 min, cooled to 40–50 °C, homogenized and canned. Each batch was 10 kg, with three replicates. The AGR-HSM was manufactured by Shengda Machinery Co., Ltd., Shijiazhuang, Hebei, China.

2.3.2. FT-IR Analysis and Spectrum Processing

Samples were pressed into thin sheets and scanned by Fourier-transform infrared spectrometer (4000–400 cm⁻¹ range, 4 cm⁻¹ resolution, 32 scans per sample, 3 replicates). Spectra were collected and analyzed using Omnic 9.1 software. Peakfit Version 4.2 software was used for baseline correction, smoothing, deconvolution, and Gaussian curve fitting in the amide I (1700–1600 cm⁻¹) and amide III (1330–1220 cm⁻¹) bands. Origin 2022 software estimated sub-peak numbers and positions, adjusting heights and half-widths for minimal residuals and complete resolution of overlapping bands. Secondary structure relative percentages were calculated based on peak areas [14].

2.3.3. Stability Tests

The basic study determining the durability of the prepared suspensions involves a sedimentation test conducted for 48 h to observe all phenomena occurring in the suspension from production to application or complete degradation. During this period, suspension fertilizers in a physically unstable state will separate a transparent liquid layer on the surface or in the middle of the suspension, referred to as supernatant. 48 h is considered the minimum time to maintain the suspension in a stable form, allowing for transportation and application.

For samples remaining unstratified within 48 h, to further evaluate their stability under long-term storage conditions, the following method was used: Weigh the non-precipitated sample in a 50 mL graduated centrifuge tube and record the total sample mass (M). After centrifuging the sample at 3000 r/min for 10 min, discard the upper solution, accurately weigh the mass of the precipitate (m), and calculate the emulsion stability using the differential equation [29].

Stability (%) = (M − m)/M × 100.

(1)

2.3.4. Castability Test

The viscosity of the suspension influences its stability and pourability. As the viscosity of the dispersion medium increases, the settling rate decreases, leading to a more stable suspension. However, excessive viscosity can cause dosing problems and consume excessive energy during manufacturing. The pourability test was conducted at 20 °C using a 100 mL Ford cup with a 4 mm diameter discharge nozzle. After filling the cup with the tested suspension, the time for all the liquid to flow freely through the nozzle at the bottom of the container was measured [9].

2.4. Statistical Analysis

The preparation and testing of all samples were conducted from June to September 2024. Each experiment was performed in triplicate (n = 3), ensuring robustness and reliability of the data. Consequently, the mean values depicted in the figures and tables represent the average of three biological replicates. These replicates were subjected to one-way ANOVA followed by Tukey’s HSD post hoc test to assess statistical significance. Data processing and visualization were carried out using Microsoft Excel 2020, while statistical analyses were performed using SPSS 20.0. Differences were deemed significant at p < 0.05. All results are presented as means.

3. Results and Discussion

3.1. Heating Temperature for Stable Suspension

(1)

Effect of Different Temperatures on Pure Peanut Bran Dispersions

FTIR spectra of pure peanut bran dispersions at different temperatures revealed varying transmittance, indicating different absorption levels, with changes concentrated in the amide I, II, and III bands. Analysis showed that the α-helix content first increased and then decreased, peaking at 45.85% at 80 °C. The β-sheet content was lowest at 18.76% at 80 °C, similar at 60 °C and 100 °C (36.25% and 36.75%). Random coil content remained between 18 and 24%, while β-turn was highest at 30 °C (21.44%), decreasing then increasing with temperature, reaching a minimum of 3.57% at 60 °C (Figure 6).

(2)

Effect of Different Temperatures on Suspension Fertilizers

All samples exhibited similar absorption peaks in the 500–4000 cm⁻¹ range, with increased intensity at 3400 cm⁻¹ (O-H stretch) and 2950 cm⁻¹ (C-H stretch) with temperature, indicating improved hydration. In amide I, II, and III bands, α-helix content was relatively low and decreased with temperature. β-sheet was the dominant structure in most samples, peaking at 53.18% at 60 °C. Random coil content first increased then decreased, peaking at 46.16% at 80 °C. β-turn content was low (2–8%) (Figure 7).

The stability of suspension liquid fertilizers is crucial in their production and application, and changes in the secondary structure of proteins significantly affect the texture and water-holding capacity of the gel, thereby influencing the stability of the suspension system. Heating is a common method to produce vegetable protein gels [30]. The effect of heating temperature on protein gels is based on the different degrees of protein denaturation at various temperatures [31]. Different heating temperatures dynamically regulate the secondary structure of peanut proteins by altering the hydrogen bonding network, hydrophobic interactions, and disulfide bond cross-linking. The low-temperature stage (65 °C and below) is dominated by reversible perturbations, where the hydrogen-bonding network starts to loosen, and the proportion of free water increases, without significant disruption of the secondary structure. The medium temperature (65–95 °C) rang triggers aggregation and structural reorganization, intensifying the disruption of the hydrogen-bonding network, leading to a decrease in α-helices and an increase in the proportion of irregularly coiled structure, which enhances emulsion stability. High temperatures (95 °C and above) cause irreversible depolymerization, where peanut globulin molecules unfold, exposing internal sulfhydryl groups and promoting disulfide-bonded cross-linking, resulting in the formation of reversible or irreversible aggregates. At this point β-folding may transiently increase due to intermolecular interactions [21,32,33,34]. In this study, FTIR spectroscopic analysis revealed that varying temperature treatments significantly affected the secondary structure of proteins in peanut bran dispersions and suspension fertilizers. Specifically, the α-helix content in pure peanut bran dispersion reached its highest at 80 °C, favoring the formation of a more stable gel network structure. In the suspension fertilizer, the irregularly coiled structure was most prevalent at 80 °C, yielding the best emulsification stability effect. Further analysis of compositional changes in the suspension fertilizer at different temperatures indicated that warming enhanced hydration and strengthened the hydrogen bonding of polysaccharides and other components, improving system stability. However, excessively high temperature may lead to excessive protein denaturation, destroying their secondary structure and consequently affecting the stability of the suspension system. Therefore, selecting an appropriate heating temperature is crucial for preparing stable suspended organic fertilizers.

3.2. Suspension Fertilizer Formulation

(1)

Peanut Bran Usage

The essence of the gelation transition is the emergence of a three-dimensional polymer network of infinite molecular weight in the system, which leads to the generation of an infinitely long relaxation time, the viscosity of the solution becomes infinite, and equilibrium begins to occur [35]. Research has shown that when the concentration is ≥17%, composite proteins can undergo gelatinization at different ratios [36]. Consequently, peanut bran and fertilizer additives were mixed with water to create a base fertilizer solution with 16%, 18%, 20%, 22%, 24%, 26%, 28%, and 30% peanut bran content.

As depicted in Figure 8, there was no significant difference in kinematic viscosity between the 18% and 20% additive treatments, but it was significantly higher than that of the 16% additive treatment. The kinematic viscosity of the 22% and 24% additive treatments was significantly higher than that of the 20% treatment, yet the samples exhibited a gel state, which is unfavorable for the production of samples with poor fluidity. The sharp transition from a pumpable dispersion to a rigid gel between 22% and 24% peanut-bran solids mirrors classic percolation behavior in biopolymer networks [37]. The treatments with ≥26% peanut bran addition lacked flowability, so further evaluation of flowability was not conducted. The stability of the samples also increased with the addition of peanut bran, but there was no significant difference in stability between the 22% and 24% additions. In summary, the stability of the samples at 18% and 20% peanut bran spiking exceeded 50%, and the samples retained a certain degree of fluidity, making these suitable spiking levels. However, the 20% spiking level has a higher total nutrient content, which is more advantageous for reducing the cost of transporting the samples.

(2)

Stabilizing Agent Selection

To identify the most cost-effective stabilizer for a 20% peanut-bran suspension, four 0.5% (w/w) candidates—fumed silica (T1), Ca-bentonite (T2), kaolinite (T3) and Na-bentonite (T4)—were benchmarked. Rheological monitoring over 7 days (Figure 9) showed that Na-bentonite produced the sharpest initial viscosity drop (−37% at 48 h) and retained the lowest values thereafter, while also delivering superior phase stability relative to Ca-bentonite and kaolinite.

A subsequent dose–response study (0.00–1.00% Na-bentonite, Figure 10) revealed a steep early viscosity reduction that plateaued beyond 0.5%; after 168 h the viscosities and stability indices of all bentonite levels were no longer statistically separable. This trend is consistent with the hypothesis that a three-dimensional “house-of-cards” network, driven by edge–face attractions between anionic clay platelets and cationic patches on denatured peanut proteins [38], reaches a percolation threshold around 0.5%. The higher layer charge and larger surface area of Na-bentonite, relative to the other clays, may favor such a network [39]. Beyond ~0.5%, any extra clay could merely add yield stress without clear gains in shelf life.

Consequently, 0.5% Na-bentonite is the economically optimal dose: it secures the lowest viscosity during the critical 48 h post-cooling filling window, thereby minimizing production losses, while avoiding superfluous raw-material cost.

(3)

Emulsifier and Suspending Agent Selection

Orthogonal tests were employed to evaluate the effects of different ratios of monoglyceride, sucrose ester, carrageenan, and xanthan gum on sample stability after 168 h. Orthogonal analysis ranked xanthan gum > monoglyceride > sucrose ester > carrageenan (

Table 3. Orthogonal test on the effect of different ratios on the stability of the samples.

Sample	Factors				HLB	Stability (%)
	A Monoglyceride	B Sucrose Ester	C Carrageenan	D Xanthan Gum
1	0.00	0.30	0.00	0.10	13.0	37.81
2	0.00	0.10	0.06	0.20	13.0	44.44
3	0.10	0.00	0.04	0.30	3.5	59.99
4	0.30	0.10	0.04	0.00	5.9	45.91
5	0.30	0.20	0.00	0.10	7.3	43.09
6	0.10	0.30	0.00	0.20	10.6	48.37
7	0.20	0.10	0.00	0.30	6.7	59.36
8	0.30	0.30	0.06	0.30	8.3	61.50
9	0.10	0.20	0.06	0.00	9.8	50.22
10	0.20	0.00	0.06	0.10	3.5	39.25
11	0.30	0.00	0.02	0.20	3.5	48.00
12	0.00	0.20	0.02	0.30	13.0	59.95
13	0.10	0.10	0.02	0.10	8.3	44.26
14	0.20	0.30	0.02	0.00	9.2	48.15
15	0.00	0.00	0.00	0.00	-	48.72
16	0.20	0.20	0.04	0.20	8.3	49.39
K1	190.91	195.95	199.54	192.98
K2	202.83	193.96	200.36	164.41
K3	196.14	202.64	193.08	190.19
K4	198.49	195.82	195.40	240.80
R	11.92	8.68	7.27	76.39
Excellent level	A2	B3	C2	D4
Priority order	D > A > B > C

). One possible interpretation attributes xanthan’s apparent primacy to its putative role in reinforcing the protein gel network [40]; Carrageenan acts as a secondary network former: its sulfate groups cross-link, further tightening the matrix [28]. The observed 1:2 (w/w) monoglyceride: sucrose ester ratio aligns—within experimental error—with the optimum HLB (hydrophilic-lipophilic balance) window proposed for 0.4% lipid O/W emulsions [41]. Under these tentative premises, the provisional “best” formulation would be 0.1% monoglyceride, 0.2% sucrose ester, 0.02% carrageenan, and 0.3% xanthan gum, corresponding to an overall HLB ≈ 9.8.

The optimized suspension supplies 1.29% N, 0.23% P and 0.28% K in a single fertigation application. Raw-material costs are 0.134 USD·kg⁻¹, broken down as peanut press-cake (USD 0.125), sodium bentonite (USD 0.0006), monoglyceride (USD 0.0025), sucrose ester (USD 0.0056), carrageenan (USD 0.00006) and xanthan gum (USD 0.00042). With 20% total solids, the formulation is substantially cheaper than fully water-soluble amino-acid fertilizers currently marketed for banana. Manufacturing is compatible with existing liquid-fertilizer reactors, enabling rapid scale-up without additional capital investment.

4. Conclusions

This study demonstrates the technical feasibility of converting peanut-oil extraction residues into a shelf-stable organic suspension fertilizer. FTIR spectroscopy indicated that heating to 80 °C maximizes the formation of the colloidal network required for long-term stability. The optimized formulation—20% (w/w) peanut press-cake, 0.5% sodium bentonite, 0.1% monoglyceride, 0.2% sucrose ester, 0.02% carrageenan and 0.3% xanthan gum—delivers 1.29% N, 0.23% P and 0.28% K at a raw-material cost of only 0.134 USD·kg⁻¹. The process is compatible with existing liquid-fertilizer reactors, providing a scalable and economically viable route to valorise peanut bran within modern fertigation systems.

Future research will (i) develop a process model to optimize unit operations, (ii) perform a life-cycle assessment contrasting the suspension with conventional peanut-bran composting, and (iii) evaluate agronomic efficacy and economic performance against commercial standards under field conditions.