Determining effective waste human hair hydrolyzing parameters combination and its typical physicochemical characteristics in synthesizing liquid nitrogenous organic fertilizer

Abstract

Discarded Human hairs are considered as waste material in most parts of the world and its accumulation causing several environmental problems. However as a potential material resource, human hair has the advantage that it is completely biodegradable, renewable and available in every locality. Thus reutilizing human hair cut discards with a target of extracting a particular major nutrient supply, namely nitrogen, carbon, sulfur and so forth, can create a positive impact on solving soil’s infertility problems and less productivity issues of concerned agrarian communities. This study has tried to develop waste human hair based bio-fertilizer by primarily identify the better performing hydrolyzing mixture rang of formulation (H5), ratio of human hair waste mass to aqueous hydrolyzer mixture usages (1:5), favorable reacting time ( 90 min) and temperature ( 70 ^oC) values progressively. Then the physicochemical characteristics were analyzed to reveal the resulted final product’s viscosity (~ 76.0 cp.), density (~ 1.17 gm/l), pH (~ pH 9), organic nutrients availability concerning primary Macronutrients (~ 18:0.03:1 N-P-K ratio ), Secondary Macronutrients (~ 0.13:0:7 Ca-Mg-S ratio) and other trace micronutrient constituents; which are considered as requirements for the soil nutrient enrichments and plant growths.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-024-79116-5.

Introduction

Human hair is one of the highest nitrogen containing (∼16%) organic material in nature because it is predominantly made up of nitrogen-containing proteins or keratotic protein, which is 65–95% of the total mass. A great amount of waste human hair is discarded each year, which causes an environmentally difficult disposal problem. Therefore, from the view of economy and environment protection, it is quite desirable to develop effective and profitable process to use theseresources^1-17.

Conventional fertilizers are not regarded sustainable in reference to petrochemical value chain, besides the economic perspective upon conventional fertilizer shortages. Thus waste human hair discard is an optimum source for amino acids; not to mention that discarded human hair waste is considered useless and found in municipal waste and landfills. In contrast, an organic fertilizer containing amino acids derived from the discarded human hair mass increases plant growth and soil fertility in the long-term while considered sustainable regarding waste hair utilization.

Normally, plants reduce applied conventional ammonium and nitrates fertilizers into amino acids. On the other hand, applying amino acids or related derivatives directly saves energy as plants readily absorb essential nitrogen-rich content. For this reason, amino acids fertilizer is obtained by hydrolyzing waste human hair in alkaline or acidic environment in which hydrolysis is enhanced by heat treatment.

The purpose of this study was to determine the effective waste human hair mass hydrolyzing reaction parameters combinations and its typical principal physicochemical characteristics in the apparently to be synthesized bio-fertilizer products.

Materials and methods

Different methodologies for waste human hair treatments have been developed over the years predominantly focusing on the cleavage of disulfide linkages on keratin protein backbone in order to enhance its aqueous solubility. However, each of these methods have been studied in isolation and are neither fully characterized nor compared.

Here contacting of waste human hair with mixtures of alkaline aqueous solution to hydrolyze alpha-keratin followed by neutralizing with concentrated phosphoric acid were the overall applied method to produce human hair based bio-fertilizer, and a typical process flow diagram shown in Fig. 1 too. However while investigating the hydrolysis reaction, parameters including alkaline concentration, waste hair mass proportion, temperature and reaction time were considered upon mixing of the human hair waste samples in an alkaline aqueous medium.

Fig. 1.

Process flow diagram of liquid organic fertilizer production from waste human hair.

So referring the patent information KR101043568B1 for preparation of as such organic fertilizer, seven types of alkaline solution were prepared by mixing caustic soda, caustic potash and slaked lime with no more than suggested mixing ratio of (5-10):(0.5–1.5)(1): in water respectively, which is with the aim to maintain an optimum (0.3–0.9) molarity. Furthermore, likely two types of human hair waste mass proportions (1/3rd and 1/5th ), three reaction times (30’, 60’ and 90’ minutes) and three temperature ranges (50, 70 and 85 ^oC) while immersing in aqueous alkaline solution mixtures have been investigated. Lastly concentrated phosphoric acid was used to neutralize hydrolyzed amino acids to preferably pH (pH ~ 8–9), which is to make it convenient during its application to the infertile acidic soil.

On top of these, human hair discards (wastes) were collected from arbitrarily selected male beauty salons located in Hawassa city, Sidama region, Ethiopia. Then the collected waste hair samples were prepared by moving out these samples through a series of physical pretreatments like sorting, cleaning, washing, drying, and size reduction deeds. Here hot water bath, digital pH meter, kinematic viscometer, Total nitrogen meter (Kjeldahl Method), Acid Dejection and ICP OES (inductively coupled plasma atomic emission spectroscopy) are some of the used in the process of laboratory investigation time at Hawassa University and Horticoop Ethiopia analysis laboratories’.

Results and discussion

This study tries to assume hydrolysis reaction as the key process step while preparing the waste human hair mass conversion into organic fertilizer form. Hence Table 1 summarizes the process for identification of better-performing hydrolyzer mixture combinations using the amount of precipitate formed, not hydrolyzed byproduct part after the planned hydrolysis reaction completion times. So using triplicate experimental workings the obtained precipitate mass and applied initial mass of the solid human hair waste mass have been used directly to predict the conversion rate by calculating the average mass percentage yield of the hydrolysis reaction.

Table 1.

Relative values of waste human hair mass not hydrolyzed under different mass proportions and temperature use trends.

Temp. (o C)	Average mass percentage (w/w) not hydrolyzed under mass proportion usage 1:5 and 1:3
	Hydrolyzer H1	Hydrolyzer H2	Hydrolyzer H3	Hydrolyzer H4	Hydrolyzer H5	Hydrolyzer H6	Hydrolyzer H7	Mean	Stand. Dev.
50	13.78	8.89	11.67	11	8.67	12.56	13.56	11.45	2.07
70	8.56	5.22	4.22	5.56	7.67	3.67	8	6.13	1.94
85	6	14.67	6.67	6.67	6	6.33	7.33	7.67	3.12
Mean Value	9.45	9.59	7.52	7.74	7.45	7.52	9.63
Stand. Dev.	3.97	4.76	3.8	2.87	1.35	4.56	3.42
50	35.56	18.33	24.22	10.78	9.67	20.67	9.11	18.33	9.6
70	14.22	24.44	8.33	15.44	6.56	10.89	5.78	12.24	6.51
85	11.56	17.78	15.78	18.67	14.44	21.56	6.67	15.21	4.93
Mean Value	20.45	20.18	16.11	14.96	10.22	17.71	7.19	**
Stand.Dev.	13.16	3.7	7.95	3.966	3.968	5.92	1.72

So using the performed experimental study results in Table 1; Fig. 2; relatively higher rate of hydrolysis reaction conversion (low in non-hydrolyzed mass) were experienced with 70 ^oC temperature over hydrolyzer mixture H5 and H7 under the mass ratio usages of 1:5 and 1:3 respectively. Bearing this in mind, the proceeding time effect study shown in Table 2 was carried out over hydrolyzing mixture types H5 and H7 at 70 ^oC temperature values.

Fig. 2.

Comparative values of applied temperature and waste human hair mass ratio applied.

Table 2.

Effect of time on waste human hair samples hydrolysis reaction completion rate.

Hydrolysis reaction time (minutes)	Percentage Hydrolyzing with H5 and 1/5th Mass proportion (w/w)				Hydrolyzing with H7 and 1/3rd Mass proportion (Category two)
	Percentage not hydrolyzed ( precipitate )			Average mass percentage hydrolyzed (Converted)	Percentage not hydrolyzed ( precipitate )			Average mass percentage hydrolyzed (conversion)
	Range	Mean	Stand. Dev.		Range	Mean	Stand. Dev.
30	9.5 ± 1.39	0.95	0.18	89.50	23.67 ± 0.555	2.13	0.07	76.33
60	10.55 ± 0.115	0.83	0.02	89.45	13.33 ± 1.0	1.2	0.13	86.67
90	9.22 ± 0.11	1.03	0.02	91.78	12.84 ± 2.165	1.155	0.28	87.16
120	11.39 ± 1.5	1.03	0.19	88.61	12.06 ± 2.385	1.085	0.3	87.94

Thus the values from the above Table 2 shows the conversion in H5 try to show relatively faster reaction beginning with somewhat a little increasing conversion rate in the middle and decline in its later time; which is probably indicating the reversibility characteristics of the reaction. Further graphical illustration comparing these two hydrolyzing mixture solution time-wisely can be demonstrated as follow in the Fig. 3 below.

Fig. 3.

Comparative time effect values between identified hydrolyzer types and hydrolysis reaction completion rate.

Therefore based on the sequential analysis made previously; a relatively good performing hydrolyzing mixture of H5 with 1:5 waste human hair mass to hydrolyzer mass ratio combination, 90 min resident time, and 70 ^oC temperature reacting parameters have been identified.

Further this aqueous liquid sample was taken for analytical laboratory analysis in a way to reveal its principal physicochemical characteristics. Also, its pH was adjusted with a little droplet of concentrated phosphoric acid from around pH value of 13 to 9; which is with the aim of making it at somewhat convenient form (weak alkaline pH value) in its application over the concerned soil filed.

Based on the outlined results in Table 3; contacting of aqueous alkaline solution with waste human hair actually produced hydrolyzed amino acid fertilizer; which probably can be taken as of nitrogen-enriched potassium phosphate fertilizer product.

Table 3.

Physicochemical analysis result of wet-basis waste human hair based organic fertilizer.

Parameter	Representation	Resulted Value	Remark
Viscosity	v (cp.)	76.0
pH		9.0
Density	ρ( kg/l)	1.17
Color scene	Color	Black
Total Nitrogen	N (gm/ml)	45.1
Phosphorus	P (gm/ml)	0.061
Potassium	K (gm/ml)	2.446
NPK content	N-P-K (ratio)	18:0.025:1
Sulfur	S (gm/ml)	16.168
Sodium	Na (gm/ml)	11.046
Calcium	Ca (gm/ml)	0.325
Magnesium	Mg (gm/ml)	0.019
Zinc	Zn (gm/ml)	0.015
Silicon	Si (gm/ml)	0.366
Iron	Fe (gm/ml)	0.025
Other traces	Mn, B, Cu, Mo, etc.	< 0.001

Conclusion

Thus as per the study, waste human hair hydrolysis (liquefaction) using aqueous alkaline solution mixture Na: K:Ca [10:0.5:1] with one fifth of human hair waste mass fraction proportion usages applied at 70 ^oC temperature and one hour of resident time have revealed a good result. Further the analytical result showed a relatively leading mass proportion of total nitrogen availability; meaning the formed liquid product can probably be comparable to nitrogenous fertilizers, like with commercially available Urea and Ammonium sulfate inorganic fertilizers.

So organic fertilizer product developed using the waste human hair hydrolysis method can possibly be offered to prevent the environmental contamination caused by leaching of harmful chemicals resulted from use of excessive commercially fertilizers, as well as waste human hair combusting or simple surface disposal problems.

Hence this study may be used as of important inputs for such similar waste valorization as well as physicochemical studies. Also the authors suggest the further practical testing studies on plant physiology while applied as of waste human hair based bio-fertilizer practice too.

Electronic supplementary material

Below is the link to the electronic supplementary material.

Author contributions

The two authors together confirm equal responsibility for the study conception and Design, data collection, analysis and interpretation of results. Also together we organized, read and approved this final submission manuscript.

Funding

The research leading to these results received funding to conduct the study from Hawassa University under Grant Agreement with Research program director and this article’s author (No contract number). However, No funding was received to assist with the preparation and publishing of this manuscript.

Data availability

We declare that the data supporting the findings of this study are available within the paper and its Supplementary Information files. If any raw data files needed in another format; we can avail upon reasonable request.

Declarations

Competing interests

The authors declare no competing interests.