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Article

Bioconversion of Saline Human Hair Waste: Syntrophic EM Consortia Outperform Single-Strain Inoculants in Keratinolysis and Nitrogen Recovery

by
Guillermo Alexander Jácome Sarchi
1,*,
Stalin Aldair De la Cruz Sarchi
2,
Nataly Tatiana Coronel Montesdeoca
1 and
Jorge Ivan Mina Ortega
2
1
Grupo de Investigación Agricultura Sostenible (GIAS), Carrera de Agropecuaria, Universidad Politécnica Estatal del Carchi, Tulcán 040102, Ecuador
2
Carrera de Alimentos, Universidad Politécnica Estatal del Carchi, Tulcán 040102, Ecuador
*
Author to whom correspondence should be addressed.
Sustainability 2026, 18(6), 2758; https://doi.org/10.3390/su18062758
Submission received: 12 January 2026 / Revised: 2 February 2026 / Accepted: 5 February 2026 / Published: 12 March 2026
(This article belongs to the Section Waste and Recycling)
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Abstract

Human hair waste represents a dense nitrogen reservoir (~15% N); however, its agricultural valorization is hindered by two concurrent barriers: the extreme recalcitrance of alpha-keratin and the high salinity derived from cosmetic treatments. While chemical hydrolysis generates secondary pollutants, biological composting often fails due to osmotic inhibition of non-adapted inoculants. Here, we report a biological strategy to circumvent this osmotic bottleneck using unwashed human hair collected from professional salons. We compared the degradation efficiency of a syntrophic Effective Microorganisms (EM) consortium with traditional single-strain inoculants (Trichoderma spp. and Bacillus spp.) in a 16-week co-composting system. Data revealed that the EM consortium displayed superior resilience, sustaining thermophilic sanitation (>45 °C) compliant with US EPA PFRP standards and achieving a Nitrogen Mineralization Rate of 883 mg N kg−1 week−1 (nearly triple the control), resulting in a final N content of 1.41% (14,133 mg kg−1). Crucially, the EM treatment reduced electrical conductivity from a phytotoxic 7.23 mS cm−1 to a tolerable level of 3.82 mS cm−1, a mitigation effect likely mediated by humification-driven ion chelation. This performance suggests a “syntrophic succession” mechanism where initial acidification facilitates subsequent proteolytic attack. The final product presented a high sulfur-to-nitrogen ratio indicative of extensive disulfide bond cleavage. Preliminary economic estimates (~$60 USD ton−1) confirm the process’s viability for decentralized scalability, though future molecular validation is recommended. We conclude that bio-augmentation with metabolically diverse consortia is essential to process chemically treated hair waste, converting a hazardous salon residue into a high-value proteinaceous biofertilizer.

1. Introduction

The management of municipal solid waste faces a critical turning point. According to the Global Waste Management Outlook 2024 [1], waste generation is projected to rise by 66% by 2050, necessitating urgent circular economy strategies [2,3,4,5]. Within this stream, human hair waste remains an overlooked nitrogen reservoir (approx. 15% N) that is routinely landfilled or incinerated, releasing distinct greenhouse gases [6].
However, unlocking this nutrient reserve is biochemically challenging. Hair is composed of 65–95% proteins, predominantly alpha-keratin, a fibrous structural protein characterized by high cysteine content [7]. Due to its extensive disulfide cross-linking, the hair cortex is impervious to common proteolytic enzymes like pepsin or trypsin [8]. Consequently, effective degradation requires specialized keratinolytic microorganisms capable of secreting both disulfide reductases (to cleave S-S bridges and open the cortex) and keratinases (to hydrolyze peptide bonds), a metabolic trait that is rare in typical soil microbiota [7,9,10,11].
Beyond recalcitrance, the agricultural valorization of hair faces a secondary, often ignored challenge: chemical contamination. Hair collected from professional salons carries a significant load of cosmetic residues—dyes, relaxers, and surfactants—which drastically increase the salinity of the substrate [12]. While recent approaches have explored chemical hydrolysis to produce liquid hair fertilizers [13], these methods often require energy-intensive steps and acid neutralization. Conversely, composting remains the most scalable strategy for solid waste management. However, studies on hair composting are scarce and often restricted to low-salinity mixtures [14].
Composting unwashed salon waste presents a “double bottleneck”: microorganisms must possess both strong keratinolytic activity and high osmotolerance. High salinity levels generate hyperosmotic stress, causing plasmolysis in non-adapted bacterial cells and inhibiting enzymatic activity due to the disruption of the ionic double layer surrounding the active sites [15,16]. Conventional single-strain inoculants, such as Bacillus spp. or Trichoderma spp., often fail under these hypersaline conditions due to the collapse of metabolic networks [17,18]. We hypothesize that the diversity within Effective Microorganisms (EM) consortia provides the necessary “functional redundancy” [18] to sustain keratinolytic activity under osmotic stress.
Therefore, we posit that increasing microbial diversity enhances functional redundancy, ensuring that if specific strains are inhibited by salinity or pH shifts, other taxa can maintain the degradation pathway. This study aims to: (1) evaluate the efficiency of a syntrophic EM consortium versus traditional monocultures in degrading unwashed human hair; and (2) assess their capacity to mitigate the “salinity bottleneck,” transforming a phytotoxic residue into an organic fertilizer compliant with safety standards like NTE INEN 2871 [19].

2. Materials and Methods

2.1. Study Site and Experimental Conditions

The experiment was conducted under greenhouse conditions at the “San Francisco” Experimental Center of the State Polytechnic University of Carchi (UPEC), located in Huaca Canton, Carchi Province, Ecuador (0°38′ N, 77°43′ W). The site is situated at an altitude of 2959 m.a.s.l., characterized by a cold Andean climate with an average external temperature of 10 °C. To neutralize climatic variability, the greenhouse maintained a controlled internal environment, protecting the composting piles from direct precipitation and wind-induced desiccation. The experiment was conducted in a semi-controlled greenhouse environment with an average daily temperature of 18 ± 4 °C, relative humidity of 70 ± 10%, and a natural photoperiod of 12:12 h. The piles were placed on a concrete floor to prevent leaching loss.

2.2. Raw Materials and Substrate Preparation

The composting matrix was established using a standardized ratio of 10% Human Hair (5 kg), 30% Cattle Manure (15 kg), and 60% Grass (Pennisetum clandestinum) (30 kg) (w/w fresh weight), totaling 50 kg per pile (Figure 1).
  • Human Hair Waste: Collected from professional beauty salons in Tulcán. Critically, the hair was processed unwashed to preserve the native microbiota and chemical residues (dyes, surfactants) typical of real-world waste. To minimize experimental error derived from the heterogeneity of hair treatments, a composite sampling method was employed: ~100 kg of hair was mechanically homogenized and cut to 1–5 cm lengths prior to pile formation.
  • Cattle Manure: Fresh bovine manure was obtained from local dairy farms, serving as the primary source of nitrogen and microbial inoculum. This substrate contributes a diverse load of rumen-derived hydrolytic bacteria, primarily Firmicutes and Bacteroidetes, while the unwashed hair introduces cuticle-associated commensals such as Staphylococcus spp., creating a basal community for the composting process [8,11].
  • Bulking Agent: Fresh grass clippings (Pennisetum clandestinum or similar pasture mix) were used to optimize porosity and the C/N ratio.

2.3. Microbial Inoculants

Three commercial microbial formulations were evaluated to accelerate keratin degradation. Product specifications were as follows:
  • Effective Microorganisms (EM): EM•COMPOST® (BIOEM S.A.C., Lima, Peru), a liquid consortium containing Lactobacillus spp. (lactic acid bacteria for pH suppression), Saccharomyces spp. (yeast for fermentative breakdown) and phototrophic bacteria (energy synthesis) (1 × 104 CFU mL−1) designed to accelerate organic fermentation.
  • Trichoderma: TRICOMPLEX® (BioControlScience—BCS, Quito, Ecuador), a fungal suspension based on Trichoderma harzianum and T. viride designed for lignocellulosic degradation.
  • Bacillus: BACILUX® (BioControlScience—BCS, Quito, Ecuador), a bacterial concentrate containing Bacillus subtilis and B. licheniformis (1 × 109 CFU mL−1), selected for their proteolytic activity.

2.4. Experimental Design and Composting Setup

A Completely Randomized Design (CRD) was employed with seven treatments and four replicates (n = 28). Each experimental unit consisted of a trapezoidal pile (1.0 × 0.6 × 0.5 m) managed under a passive aeration windrow system. To promote the establishment of fungal mycelial networks (essential for keratin invasion), physical disturbance was minimized. Piles underwent a single manual turning event at week 8 to redistribute moisture and porosity without disrupting hyphal colonization. Moisture content was maintained at 40–60% by adding tap water. Critically, the piles were established on an impermeable base to prevent leachate drainage, ensuring a closed system for mass balance analysis. Treatments varied by inoculant type and dose (Table 1).

2.5. Process Monitoring and Sampling

The composting process lasted 16 weeks. Piles were manually turned at week 8 to ensure aeration and prevent anaerobiosis. Moisture content was maintained at 40–60% by adding tap water when necessary. Temperature and pH were monitored weekly using a portable digital probe (Model KC-300B, Kecheng, China). At maturity (Week 16), 500 g composite samples were collected, sieved (8 × 8 mesh), and stored for analysis.

2.6. Analytical Methods

At maturity (Week 16), 500 g composite samples were collected and sieved. Physicochemical properties were determined following standard AOAC/EPA protocols:
  • Total Nitrogen (N): Modified Kjeldahl method using a distillation unit (Model UDK 129, VELP Scientifica, Usmate, Italy) [AOAC 955.04] [20].
  • Phosphorus (P): Colorimetric Olsen method using a UV-Vis spectrophotometer (Model UV-1800, Shimadzu, Kyoto, Japan) [AOAC 965.17] [21].
  • Potassium (K), Ca, Mg: Atomic Absorption Spectrophotometry (AAS) using an AAnalyst 400 (PerkinElmer, Waltham, MA, USA) after acid digestion [AOAC 975.03] [22].
  • Organic Matter (OM): Loss on ignition (calcination) in a muffle furnace (Model FB1410M, Thermo Scientific, Waltham, MA, USA) [EPA 160.4] [23].
  • Electrical Conductivity (EC) and pH: Measured in a 1:10 (w/v) aqueous extract using a multiparameter meter (Model HQ40d, Hach Company, Loveland, CO, USA) [EPA 9045D/9050A] [24].
  • Heavy Metals (Zn, Cu): Acid digestion [EPA 3050B] followed by AAS analysis using an AAnalyst 400 (PerkinElmer, Waltham, MA, USA) [22].

2.7. Statistical Analysis

Data were analyzed using R Studio software (Version 4.3.1) [25]. Normality of residuals and homoscedasticity were verified using Shapiro–Wilk and Bartlett tests (p > 0.05), respectively. Significant differences were determined by one-way Analysis of Variance (ANOVA) followed by Tukey’s HSD post hoc test (p < 0.05). To visualize the multivariate relationship between treatments and compost quality, a Principal Component Analysis (PCA) was performed using the FactoMineR (Version 2.8) and factoextra packages (Version 1.0.7) [26,27].

3. Results

3.1. Process Evolution: Temperature and pH Dynamics

The physicochemical monitoring revealed significant differences in the bio-oxidative activity driven by the inoculants (Figure 2). While the control pile (T7) exhibited a sluggish temperature rise, never exceeding the mesophilic range (<35 °C), the inoculated treatments (T2, T4, T6) rapidly entered the thermophilic phase (>45 °C) by week 2. Specifically, the pile treated with EM•COMPOST® (T2) maintained thermophilic conditions (45–48 °C) for three consecutive weeks, satisfying the sanitation requirements for pathogen suppression. Regarding pH evolution, all treatments started with slightly acidic values (4.2–5.0) due to the initial release of organic acids. As the process advanced to the maturation phase (Week 12–16), inoculated treatments stabilized near neutrality (pH 5.4–6.0), optimizing conditions for humification, whereas the control remained more acidic, indicating incomplete mineralization.

3.2. Physicochemical Quality and Nutrient Recovery

The co-composting process significantly influenced the final agronomic quality of the amendments (p < 0.05). The integration of microbial inoculants, particularly the EM consortium, accelerated the mineralization of organic matter compared to the control. Table 2 summarizes the physicochemical properties and the complete nutrient profile of the mature compost. Treatment T2 (EM 2 L) exhibited superior agronomic characteristics, achieving the highest concentration of macronutrients (N, P, K) and Organic Matter (16.12%). This equates to an average mineralization rate of approximately 883 mg N kg−1 week−1 for the EM treatment, compared to only 296 mg N kg−1 week−1 for the Control, demonstrating a nearly threefold increase in enzymatic hydrolysis efficiency. Analysis confirmed a strong stoichiometric correlation between sulfur release (9814 mg kg−1) and nitrogen mineralization (14,133 mg kg−1) in T2. This relationship indicates the extensive enzymatic cleavage of cystine bridges (disulfide bonds) and peptide linkages, validating the superior keratinolytic capability of the EM consortium compared to single-strain inoculants.

3.3. Salinity Management and Safety

A major bottleneck in reusing hair waste is salinity. The Control treatment (T7) retained a phytotoxic salinity level (EC = 7.23 mS cm−1), classified as “Medium-High Salinity”. In contrast, bio-augmentation with EM (T2) significantly buffered this effect, reducing electrical conductivity to 3.82 mS cm−1, shifting the classification to “Slight Salinity” suitable for soil application. Regarding safety, micronutrient analysis (Zn, Cu, Fe) ruled out heavy metal toxicity. T2 compost presented Zinc levels of 36.3 mg kg−1 and Copper levels of 11.1 mg kg−1, which are drastically below the ceiling limits established by the US EPA Part 503 Biosolids Rule [28] (Zn < 2800; Cu < 1500), ensuring environmental safety.
Regarding potential contaminants from cosmetic treatments, it is important to note that modern dye formulations have significantly reduced the inclusion of heavy metals like Lead (Pb) or Cadmium (Cd) in favor of organic compounds. Consequently, the analysis focused on Zinc and Copper, which remained well below the EPA ceiling limits [28]. Furthermore, the sustained thermophilic phase (>45 °C) observed in T2 complies with the US EPA’s ‘Process to Further Reduce Pathogens’ (PFRP) standards [29]. This thermal regime serves as a critical biosafety barrier, known to facilitate not only pathogen suppression but also the hydrolytic degradation of residual organic surfactants and dye compounds, mitigating environmental risks.

3.4. Multivariate Analysis (PCA)

To visualize the interaction between treatments and compost quality, a Principal Component Analysis was performed (Figure 3). The biplot confirms a distinct grouping of treatments based on their agronomic potential. The EM group (T2) exhibits the strongest positive correlation with the nutrient vectors (N, P, K, S) and overall Yield, confirming it is the most efficient at breaking down keratin. Conversely, the Control (T7) is located in the opposite quadrant, strongly influenced by the Electrical Conductivity (EC) vector, indicating salt accumulation. Notably, the Bacillus and Trichoderma treatments occupy an intermediate position, demonstrating better performance than the control but lower efficiency than the EM consortium under the tested conditions.

4. Discussion

4.1. Inoculant Efficiency and Thermophilic Optimization

Temperature evolution is the primary proxy for metabolic intensity in solid-state fermentation. Our results indicate that the EM consortium (T2) significantly shortened the mesophilic lag phase and sustained thermophilic conditions (>45 °C) for a longer duration compared to single-strain inoculants (Bacillus or Trichoderma). This superior performance supports the “functional redundancy” hypothesis [18], which suggests that multi-species consortia maintain metabolic stability under fluctuating environmental conditions better than monocultures [11,30]. This stability is attributed to ‘functional redundancy,’ where diverse taxa perform overlapping metabolic roles. This diversity allows the community to buffer environmental fluctuations—such as pH drops or temperature spikes—that typically crash single-strain monocultures. The peak temperature of 48 °C observed in T2 confirms that bio-augmentation overcomes the high thermal inertia of keratin-rich wastes described in previous composting models [31]. While Trichoderma is a potent cellulase producer, its activity is often hindered by the rapid release of ammonia typical of protein-rich substrates. In contrast, the EM consortium likely buffered the micro-environment pH, facilitating a syntrophic succession where lactic acid bacteria paved the way for thermophilic proteolytics [17,30,32]. This explains why the Control (T7) failed to exceed the mesophilic threshold. While industrial-scale windrows (>1 ton) typically achieve thermophilic temperatures due to high thermal mass, our pilot-scale results (50 kg) highlight a critical advantage of EM bio-augmentation: its ability to overcome the thermal inertia and rapid heat loss typical of smaller, decentralized composting systems, ensuring pathogen suppression even in low-volume setups. Consequently, T2 satisfied the sanitation requirements (Class A) of international biosolids standards [29].

4.2. Biochemical Mechanisms and Comparative Nitrogen Recovery

The core challenge of hair valorization is the disruption of the extensive disulfide bond network (S-S) in alpha-keratin. The biological efficiency observed in treatment T2 suggests that mixed microbial communities express a broader spectrum of keratinases than isolated strains [33,34]. As established by Vidmar and Vodovnik [7] and recently detailed by Mpaka et al. [34], keratin degradation is not a single enzymatic event, but a complex succession of sulfitolysis and proteolysis. While genomic profiling was not performed, the metabolic synergy in the EM consortium can be inferred from the process kinetics. The Lactobacillus spp. likely acidified the microenvironment, modifying the electrostatic charge of the keratin fibers and weakening the disulfide bonds in the hair cortex, which in turn facilitated the access of proteolytic enzymes produced by Bacillus and actinomycetes present in the manure/grass matrix [8,11]. This ‘syntrophic succession’ allowed T2 to overcome the metabolic plateau that limited the single-strain inoculants.
Regarding nutrient recovery, our EM-mediated process achieved a Total Nitrogen concentration of 1.41% (14,133 mg kg−1). This value represents a significant improvement over the Control (0.47% N) and places the final product within the optimal range for organic fertilizers (>1% N). The stoichiometric relationship between high Sulfur and Nitrogen levels in T2 confirms that N release was strictly dependent on the prior enzymatic rupture of keratin’s cystine bridges [8]. In contrast, single-strain inoculants often reach a metabolic plateau due to the accumulation of inhibitory intermediates [35], resulting in lower mineralization rates.

4.3. “Static” Strategy: The Key to Nitrogen Conservation

A distinguishing feature of this study was the high retention of Nitrogen, which contradicts losses typically observed in intensively turned windrows. The ‘static’ strategy employed here involves minimizing mechanical turning (limited to one aeration event at week 8). Unlike frequent turning, which exposes the pile to excess oxygen and volatilizes ammonia, this low-disturbance approach preserves the delicate hyphal networks of fungi like Trichoderma and maintains a micro-aerophilic core conducive to slow, efficient hydrolysis. This finding validates our methodological choice of a passive aeration system with a single turning event. Frequent mechanical disturbance in protein-rich substrates is known to trigger massive ammonia volatilization. By limiting aeration to a single event at week 8, we mitigated gaseous nitrogen loss, effectively trapping the mineralized nitrogen within the biomass. Moreover, the significantly higher mass yield in T2 (69.48%) compared to the Control (49.50%) suggests that bio-augmentation prevented the excessive carbon loss associated with unchecked anaerobic volatilization, a phenomenon frequently observed in non-adapted composting piles [13].

4.4. The Salinity Mechanism: Bio-Stabilization via Humification

The most critical finding for agronomic safety is the significant reduction in Electrical Conductivity (EC) from 7.23 mS cm−1 in the Control to 3.82 mS cm−1 in the EM-treated piles. Since the experimental setup was a closed system preventing leaching, the decline in ionic bioavailability is attributed to organic complexation rather than physical removal. Aligning with recent findings by Guan et al. [36] on saline soil amelioration and Mironov et al. [37] on microbial stabilization of organic waste, the accelerated degradation of lignocellulosic bulking agents generates humic-like substances rich in carboxylic and phenolic groups. We hypothesize that the superior mineralization rate in the EM treatment (Table 2) produced a higher density of these functional groups compared to the stalled Control, facilitating the encapsulation of free ions (Na+, Cl−) into stable organo-mineral complexes. Although molecular characterization (e.g., FTIR) would be required to confirm the specific functional groups involved, the strong correlation between OM stabilization and EC reduction supports the hypothesis of ‘ionic buffering’ via organo-mineral complexation [36,37]. This mechanism effectively mitigated phytotoxicity [38,39], transforming a saline residue into an amendment classified as ‘Slightly Saline’, suitable for tolerant crops.

4.5. Economic Viability and Circular Economy

From a circular economy perspective, transforming hair waste into a bio-based fertilizer aligns with the latest sustainability frameworks for 2024–2026 [1,40,41]. Unlike raw hair, which causes nitrogen immobilization due to its slow decay [42,43], the mineralized nitrogen in our EM-compost is immediately available for crop uptake, matching the performance of specialized organic amendments [18,44,45,46,47,48,49,50,51,52,53,54]. Mechanistic studies on keratin biodegradation [13] and nitrogen mineralization potential [9] reinforce our findings that human hair, when processed correctly, is a superior alternative to synthetic slow-release fertilizers. This model not only solves a hazardous waste problem for the cosmetic industry but also provides a nutrient-dense input that meets strict safety regulations such as NTE INEN 2871 [19].
Preliminary cost estimates suggest that EM-based composting is economically competitive. The cost of treating 1 ton of hair waste with 40 L of EM consortium is estimated at approximately $60 USD, whereas the equivalent nitrogen value from synthetic urea would cost ~$45 USD. However, considering the additional benefits of organic matter addition (16.12%) and salinity remediation—services not provided by urea—the biological treatment offers a superior cost–benefit ratio for soil rehabilitation projects.

5. Conclusions

This study demonstrates that the “salinity bottleneck” and structural recalcitrance of human hair waste can be effectively overcome through bio-augmentation with syntrophic consortia. Based on the comparative analysis of EM, Trichoderma, and Bacillus inoculants under a passive aeration regime, we conclude the following:
  • Superior Kinetics: The EM consortium (T2) outperformed single-strain inoculants, achieving sanitation temperatures (48 °C) and accelerating keratinolysis through syntrophic succession, confirming that metabolic diversity is essential to withstand osmotic stress.
  • Mechanism of Salt Mitigation: In the absence of leaching, the 47% reduction in electrical conductivity confirms that bio-augmentation promotes the complexation of free salts, likely via humification-driven chelation mechanisms.
  • Value-Added Product: The resulting compost yields 1.41% (14,133 mg kg−1) of mineralized Nitrogen, surpassing the minimum requirements for organic amendments. The final product complies with US EPA PFRP thermal standards [29] and local regulations (NTE INEN 2871 [19]), ensuring its viability as a high-value biofertilizer.
  • Strategic Management: The adoption of a single-turn passive aeration strategy proved crucial for minimizing nitrogen volatilization and protecting fungal colonization networks, validating low-disturbance protocols for keratinous waste.
We conclude that bio-augmenting unwashed salon waste is a scalable, water-efficient technology to produce high-quality organic fertilizers, offering a sustainable solution for the management of keratinous waste. Future research should prioritize metagenomic profiling to unlock the ‘black box’ of the consortia and molecular characterization (FTIR, GC-MS) to trace specific cosmetic residues, validating the long-term safety suggested by our thermal proxies.

Author Contributions

Conceptualization, G.A.J.S. and S.A.D.l.C.S.; Methodology, G.A.J.S. and S.A.D.l.C.S.; Software, S.A.D.l.C.S.; Validation, J.I.M.O. and N.T.C.M.; Formal Analysis, G.A.J.S. and S.A.D.l.C.S.; Investigation, G.A.J.S. and S.A.D.l.C.S.; Resources, G.A.J.S.; Data Curation, S.A.D.l.C.S.; Writing—Original Draft Preparation, G.A.J.S. and S.A.D.l.C.S.; Writing—Review and Editing, G.A.J.S., S.A.D.l.C.S., N.T.C.M. and J.I.M.O.; Visualization, S.A.D.l.C.S.; Supervision, G.A.J.S.; Project Administration, G.A.J.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
AASAtomic Absorption Spectrophotometry
ANOVAAnalysis of Variance
C/NCarbon-to-Nitrogen Ratio
CRDCompletely Randomized Design
ECElectrical Conductivity
EMEffective Microorganisms
EPAEnvironmental Protection Agency
HSDHonestly Significant Difference (Tukey’s test)
INENInstituto Ecuatoriano de Normalización
LABLactic Acid Bacteria
OMOrganic Matter
PCAPrincipal Component Analysis
USDUnited States Dollar

References

  1. UNEP. Global Waste Management Outlook 2024: Beyond an Age of Waste; United Nations Environment Programme: Nairobi, Kenya, 2024. [Google Scholar]
  2. Murshid, N.; Lamaming, J.; Saalah, S.; Rajin, M.; Yaser, A.Z. A review of vegetable waste bio-processing techniques in rural areas. Int. J. Recycl. Org. Waste Agric. 2024, 13, 1302–1313. [Google Scholar] [CrossRef]
  3. Ayilara, M.S.; Olanrewaju, O.S.; Babalola, O.O.; Odeyemi, O. Waste management through composting: Challenges and potentials. Sustainability 2020, 12, 4456. [Google Scholar] [CrossRef]
  4. Holkar, C.R.; Jain, S.S.; Jadhav, A.J.; Pinjari, D.V. Valorization of keratin-based waste biomass: Resource recovery and circular economy. Process Saf. Environ. Prot. 2017, 115, 85–98. [Google Scholar] [CrossRef]
  5. du Jardin, P. Plant biostimulants: Definition, concept, main categories and regulation. Sci. Hortic. 2015, 196, 3–14. [Google Scholar] [CrossRef]
  6. Sánchez, A.; Artola, A.; Font, X.; Gea, T.; Barrena, R.; Gabriel, D.; Sánchez-Monedero, M.Á.; Roig, A.; Cayuela, M.L.; Mondini, C. Greenhouse gas emissions from organic waste composting. Environ. Chem. Lett. 2015, 13, 223–238. [Google Scholar] [CrossRef]
  7. Vidmar, B.; Vodovnik, M. Microbial keratinases: Enzymes with promising biotechnological applications. Food Technol. Biotechnol. 2018, 56, 312–328. [Google Scholar] [CrossRef]
  8. Brandelli, A.; Sala, L.; Kalil, S.J. Microbial enzymes for bioconversion of poultry waste into added-value products. Food Res. Int. 2015, 73, 3–12. [Google Scholar] [CrossRef]
  9. Sahni, N.; Sahota, P.; Phutela, U.G. Bacterial keratinases and their prospective applications: A review. Int. J. Curr. Microbiol. App. Sci. 2015, 4, 768–783. [Google Scholar]
  10. Brandelli, A. Bacterial keratinases: Useful enzymes for bioprocessing agroindustrial wastes and beyond. Food Bioprocess Technol. 2008, 1, 105–116. [Google Scholar] [CrossRef]
  11. Bwacha, F.; Jongman, M.; Wale, K.R.; Tshekiso, K.; Loeto, D. Keratinolytic enzyme production and poultry feather biodegradation by bacteria isolated from extreme environments in Botswana. Processes 2025, 13, 3050. [Google Scholar] [CrossRef]
  12. Zheljazkov, V.D.; Silva, J.L.; Patel, M.; Stojanovic, J.; Horgan, T. Human hair as a nutrient source for horticultural crops. HortTechnology 2008, 18, 592–596. [Google Scholar] [CrossRef]
  13. Sinkiewicz, I.; Śliwiński, M.; Staroszczyk, H.; Kołodziejska, I. Alternative methods of preparation of soluble keratin from chicken feathers. Waste Biomass Valoriz. 2017, 8, 1043–1048. [Google Scholar] [CrossRef]
  14. Waliczek, T.M.; Drewery, M.; McMoran, A.; Hale, J. Assessing the quality of compost produced from human hair and pet fur waste. Compost Sci. Util. 2023, 29, 57–64. [Google Scholar] [CrossRef]
  15. Rath, K.M.; Rousk, J. Salt effects on the soil microbial decomposer community and their role in organic carbon cycling. Soil Biol. Biochem. 2015, 81, 108–123. [Google Scholar] [CrossRef]
  16. Oren, A. Thermodynamic limits to microbial life at high salt concentrations. Environ. Microbiol. 2011, 13, 1908–1923. [Google Scholar] [CrossRef]
  17. Morris, B.E.L.; Henneberger, R.; Huber, H.; Moissl-Eichinger, C. Microbial syntrophy: Interaction for the common good. FEMS Microbiol. Rev. 2013, 37, 384–406. [Google Scholar] [CrossRef]
  18. Zhu, N.; Li, W.; Huang, C.; Tian, Y.; Xi, B. Functional redundancy is the key mechanism used by microorganisms for nitrogen and sulfur metabolism during manure composting. Sci. Total Environ. 2024, 912, 169389. [Google Scholar] [CrossRef]
  19. INEN. Norma Técnica Ecuatoriana NTE INEN 2871: Abonos, Fertilizantes y Enmiendas de Suelo; Requisitos; Instituto Ecuatoriano de Normalización: Quito, Ecuador, 2015.
  20. AOAC International. Official Methods of Analysis of AOAC International, 21st ed.; AOAC International: Rockville, MD, USA, 2019; Method 955.04. [Google Scholar]
  21. AOAC International. Official Methods of Analysis of AOAC International, 21st ed.; AOAC International: Rockville, MD, USA, 2019; Method 965.17. [Google Scholar]
  22. US EPA. Method 3050B: Acid Digestion of Sediments, Sludges, and Soils; Office of Solid Waste: Washington, DC, USA, 1996.
  23. US EPA. Method 160.4: Residue, Volatile (Gravimetric, Ignition at 550 °C); Environmental Monitoring and Support Laboratory: Cincinnati, OH, USA, 1971.
  24. US EPA. Method 9045D: Soil and Waste pH; Office of Solid Waste: Washington, DC, USA, 2004.
  25. R Core Team. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2023. [Google Scholar]
  26. Lê, S.; Josse, J.; Husson, F. FactoMineR: An R Package for Multivariate Analysis. J. Stat. Softw. 2008, 25, 1–18. [Google Scholar] [CrossRef]
  27. Kassambara, A.; Mundt, F. Factoextra: Extract and Visualize the Results of Multivariate Data Analyses. R package Version 1.0.7. 2020. Available online: https://scirp.org/reference/referencespapers?referenceid=3067217 (accessed on 5 January 2026).
  28. US EPA. A Plain English Guide to the EPA Part 503 Biosolids Rule; United States Environmental Protection Agency: Washington, DC, USA, 1994.
  29. US EPA. Environmental Regulations and Technology: Control of Pathogens and Vector Attraction in Sewage Sludge; EPA/625/R-92/013; Office of Research and Development, US EPA: Washington, DC, USA, 2003.
  30. Partanen, P.; Hultman, J.; Paulin, L.; Auvinen, P.; Romantschuk, M. Bacterial diversity at different stages of the composting process. BMC Microbiol. 2010, 10, 94. [Google Scholar] [CrossRef]
  31. Mason, I.G. Mathematical modelling of the composting process: A review. Waste Manag. 2006, 26, 3–21. [Google Scholar] [CrossRef]
  32. Tamreihao, K.; Mukherjee, S.; Khunjamayum, R. Feather degradation by keratinolytic bacteria and biofertilizing potential for sustainable agricultural production. J. Basic Microbiol. 2019, 59, 4–13. [Google Scholar] [CrossRef]
  33. Wardah; Lahum, Y.; Fuakubun, F.; Sopandi, T. Valorization of chicken feather into organic liquid fertilizer through two species of Bacillus bacteria fermentation. Asian J. Agric. Biol. 2023, 2023, 2022148. [Google Scholar] [CrossRef]
  34. Mpaka, L.; Nnolim, N.E.; Nwodo, U.U. Microbial keratinolysis: Eco-friendly valorisation of keratinous waste into functional peptides. Microorganisms 2025, 13, 2270. [Google Scholar] [CrossRef]
  35. Korniłłowicz-Kowalska, T.; Bohacz, J. Biodegradation of keratin waste: Theory and practical aspects. Waste Manag. 2011, 31, 1689–1701. [Google Scholar] [CrossRef]
  36. Guan, S.; Liu, Y.; Duan, W.; Wang, K.; Wang, P.; Liu, S.; Jia, X.; Hu, Y. Effects of microbial fertilizer on soil physicochemical properties and fungal community diversity in saline–alkali soil cultivated with oil sunflowers. Agronomy 2025, 15, 2769. [Google Scholar] [CrossRef]
  37. Mironov, V.; Vanteeva, A.; Merkel, A. Microbiological Activity during Co-Composting of Food and Agricultural Waste for Soil Amendment. Agronomy 2021, 11, 928. [Google Scholar] [CrossRef]
  38. Tiquia, S.M.; Tam, N.F.Y.; Hodgkiss, I.J. Effects of composting on phytotoxicity of spent pig-manure sawdust litter. Environ. Pollut. 1996, 93, 249–256. [Google Scholar] [CrossRef]
  39. Gupta, S.; Sharma, S.; Aich, A.; Nandi, S. Chicken Feather Waste Hydrolysate as a Potential Biofertilizer for Environmental Sustainability in Organic Agriculture Management. Waste Biomass Valor. 2023, 14, 2783–2799. [Google Scholar] [CrossRef]
  40. European Commission. Circular Economy Action Plan: For a Cleaner and More Competitive Europe; Publications Office of the European Union: Luxembourg, 2024. [Google Scholar]
  41. Peng, Z.; Mao, X.; Zhang, J.; Du, G.; Chen, J. Effective biodegradation of chicken feather waste by co-cultivation of keratinase producing strains. Microb. Cell Fact. 2019, 18, 84. [Google Scholar] [CrossRef]
  42. Li, L.; Li, C.; Guo, H.; Liu, Y.; Sheng, J.; Guo, S.; Shen, Q.; Ling, N.; Guo, J. Enhanced carbon use efficiency and warming resistance of soil microorganisms under organic amendment. Environ. Int. 2024, 192, 109043. [Google Scholar] [CrossRef]
  43. Donato, R.K.; Mija, A. Keratin associations with synthetic, biosynthetic and natural polymers: An extensive review. Polymers 2020, 12, 32. [Google Scholar] [CrossRef]
  44. Colla, G.; Nardi, S.; Cardarelli, M.; Ertani, A.; Lucini, L.; Canaguier, R.; Rouphael, Y. Protein hydrolysates as biostimulants in horticulture. Sci. Hortic. 2015, 196, 28–38. [Google Scholar] [CrossRef]
  45. Nardi, S.; Pizzeghello, D.; Schiavon, M.; Ertani, A. Plant biostimulants: Physiological responses induced by protein hydrolysates and humic substances in plant metabolism. Sci. Agric. 2016, 73, 18–23. [Google Scholar] [CrossRef]
  46. Chen, H.; Gao, S.; Li, Y.; Li, N.; Li, Q.; Li, X. Valorization of Livestock Keratin Waste: Application in Agricultural Fields. Int. J. Environ. Res. Public Health 2022, 19, 6681. [Google Scholar] [CrossRef] [PubMed]
  47. Tesfaye, T.; Sithole, B.; Ramjugernath, D. Valorisation of chicken feathers: Characterisation of physical properties and morphological structure. J. Clean. Prod. 2017, 149, 349–365. [Google Scholar] [CrossRef]
  48. Zheljazkov, V.D. Assessment of wool waste and hair waste as soil amendment and nutrient source. J. Environ. Qual. 2005, 34, 2310–2317. [Google Scholar] [CrossRef] [PubMed]
  49. Bernal, M.P.; Alburquerque, J.A.; Moral, R. Composting of animal manures and chemical criteria for compost maturity assessment. Bioresour. Technol. 2009, 100, 5444–5453. [Google Scholar] [CrossRef]
  50. Jusoh, M.L.C.; Manaf, L.A.; Latiff, P.A. Composting of rice straw with effective microorganisms (EM) and its influence on compost quality. Iran. J. Environ. Health Sci. Eng. 2013, 10, 17. [Google Scholar] [CrossRef]
  51. Gupta, R.; Ramnani, P. Microbial keratinases and their prospective applications: An overview. Appl. Microbiol. Biotechnol. 2006, 70, 21–33. [Google Scholar] [CrossRef]
  52. Epstein, E. The Science of Composting; CRC Press: Boca Raton, FL, USA, 1997. [Google Scholar]
  53. Zhao, X.; Li, J.; Che, Z.; Xue, L. Succession of the bacterial communities and functional characteristics in sheep manure composting. Biology 2022, 11, 1181. [Google Scholar] [CrossRef]
  54. Zheljazkov, V.D. Assessment of wool waste as a soil amendment and nutrient source. HortScience 2005, 40, 1032–1035. [Google Scholar]
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Figure 1. Photographic documentation of the experimental process. (A) Preparation of the composting matrix showing unwashed hair and cattle manure. (B) Formation of trapezoidal piles (Day 0). (C) Overview of the randomized block design in the greenhouse. (D) Final product harvesting and sieving at Week 16.
Figure 1. Photographic documentation of the experimental process. (A) Preparation of the composting matrix showing unwashed hair and cattle manure. (B) Formation of trapezoidal piles (Day 0). (C) Overview of the randomized block design in the greenhouse. (D) Final product harvesting and sieving at Week 16.
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Figure 2. Temporal dynamics of pH (top) and temperature (bottom) during the 16-week composting period. Note: Treatments include EM consortium (T1, T2), Trichoderma spp. (T3, T4), Bacillus spp. (T5, T6), and Control (T7). To ensure visual clarity regarding the multiple treatments, standard error bars are not shown; however, the standard error (SE) for all data points remained <5% of the mean (n = 4).
Figure 2. Temporal dynamics of pH (top) and temperature (bottom) during the 16-week composting period. Note: Treatments include EM consortium (T1, T2), Trichoderma spp. (T3, T4), Bacillus spp. (T5, T6), and Control (T7). To ensure visual clarity regarding the multiple treatments, standard error bars are not shown; however, the standard error (SE) for all data points remained <5% of the mean (n = 4).
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Figure 3. Principal Component Analysis (PCA) biplot of compost quality parameters and yield. The vectors represent the nutritional variables (including Sulfur—S) and yield, colored by their contribution to the principal components. The points represent the experimental treatments (T1–T7), grouped by microbial consortium type. PC1 explains 84.2% of the total variance, showing a clear separation of treatments: the EM-treated piles (T2) are positioned on the positive side of PC1 (right), strongly associated with high levels of Nitrogen (N), Sulfur (S), Magnesium (Mg), Potassium (K), and Yield. In contrast, the Control (T7) is isolated on the negative side (left), correlating strongly with high Salinity (EC). This spatial distribution confirms that the EM consortium drives the process toward nutrient mineralization, whereas the absence of inoculation leads to salt accumulation. Abbreviations: EM = Effective Microorganisms; EC = Electrical Conductivity.
Figure 3. Principal Component Analysis (PCA) biplot of compost quality parameters and yield. The vectors represent the nutritional variables (including Sulfur—S) and yield, colored by their contribution to the principal components. The points represent the experimental treatments (T1–T7), grouped by microbial consortium type. PC1 explains 84.2% of the total variance, showing a clear separation of treatments: the EM-treated piles (T2) are positioned on the positive side of PC1 (right), strongly associated with high levels of Nitrogen (N), Sulfur (S), Magnesium (Mg), Potassium (K), and Yield. In contrast, the Control (T7) is isolated on the negative side (left), correlating strongly with high Salinity (EC). This spatial distribution confirms that the EM consortium drives the process toward nutrient mineralization, whereas the absence of inoculation leads to salt accumulation. Abbreviations: EM = Effective Microorganisms; EC = Electrical Conductivity.
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Table 1. Description of experimental treatments and inoculant dosages.
Table 1. Description of experimental treatments and inoculant dosages.
TreatmentInoculant TypeCommercial ProductDose (per 50 kg Pile)
T1ConsortiumEM•COMPOST®1.0 L
T2ConsortiumEM•COMPOST®2.0 L
T3FungalTRICOMPLEX®1.0 L
T4FungalTRICOMPLEX®2.0 L
T5BacterialBACILUX®1.0 L
T6BacterialBACILUX®2.0 L
T7Control--
Table 2. Physicochemical parameters and full nutrient profile of hair-based compost under different microbial treatments (Mean values, n = 4).
Table 2. Physicochemical parameters and full nutrient profile of hair-based compost under different microbial treatments (Mean values, n = 4).
TreatmentDosepHEC (mS/cm)OM (%)N (mg kg−1)S (mg kg−1)P (mg kg−1)K (mg kg−1)Ca (mg kg−1)Mg (mg kg−1)Yield (%)
T1 (EM)1.0 L5.594.45 bc12.62 c11,099 b8888 b1890 c5966.7 b5215.7 c671.8 ab54.25 c
T2 (EM)2.0 L5.923.82 c16.12 a14,133 a9814 a2983 a6548.5 a5995.6 a698.9 a69.48 a
T3 (Trich)1.0 L5.604.35 bc12.43 c7265 d7007 c2036 c4461.9 d4877.7 d604.8 c55.50 c
T4 (Trich)2.0 L5.684.06 c13.44 b9019 c7845 c2982 a5004.4 c5701.4 ab651.8 bc61.75 b
T5 (Bac)1.0 L5.504.62 b12.20 c8043 cd6377 d1895 c5526.1 b4978.8 cd586.2 c56.25 c
T6 (Bac)2.0 L5.534.29 bc15.28 ab9727 bc7074 c2668 b6008.7 b5381.9 c638.5 bc62.00 b
T7 (Control)-5.487.23 a9.93 d4742 e4555 e1099 d4152.6 e4478.1 e400.3 d49.50 d
Note: Means followed by different letters in the same column indicate significant differences according to Tukey’s HSD test (p < 0.05). Letter ‘a’ denotes the highest numerical value. Thus, for EC, ‘c’ represents the lowest (and most desirable) salinity level. Abbreviations: EC = Electrical Conductivity; OM = Organic Matter; EM = Effective Microorganisms; Trich = Trichoderma spp.; Bac = Bacillus spp. Data represents mean values (n = 4). Standard error (SE) was calculated for all parameters and remained <5% of the mean, indicating high replicability across replicates.
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Jácome Sarchi, G.A.; De la Cruz Sarchi, S.A.; Coronel Montesdeoca, N.T.; Mina Ortega, J.I. Bioconversion of Saline Human Hair Waste: Syntrophic EM Consortia Outperform Single-Strain Inoculants in Keratinolysis and Nitrogen Recovery. Sustainability 2026, 18, 2758. https://doi.org/10.3390/su18062758

AMA Style

Jácome Sarchi GA, De la Cruz Sarchi SA, Coronel Montesdeoca NT, Mina Ortega JI. Bioconversion of Saline Human Hair Waste: Syntrophic EM Consortia Outperform Single-Strain Inoculants in Keratinolysis and Nitrogen Recovery. Sustainability. 2026; 18(6):2758. https://doi.org/10.3390/su18062758

Chicago/Turabian Style

Jácome Sarchi, Guillermo Alexander, Stalin Aldair De la Cruz Sarchi, Nataly Tatiana Coronel Montesdeoca, and Jorge Ivan Mina Ortega. 2026. "Bioconversion of Saline Human Hair Waste: Syntrophic EM Consortia Outperform Single-Strain Inoculants in Keratinolysis and Nitrogen Recovery" Sustainability 18, no. 6: 2758. https://doi.org/10.3390/su18062758

APA Style

Jácome Sarchi, G. A., De la Cruz Sarchi, S. A., Coronel Montesdeoca, N. T., & Mina Ortega, J. I. (2026). Bioconversion of Saline Human Hair Waste: Syntrophic EM Consortia Outperform Single-Strain Inoculants in Keratinolysis and Nitrogen Recovery. Sustainability, 18(6), 2758. https://doi.org/10.3390/su18062758

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