Valorization of Water Hyacinth Biomass: Comprehensive Characterization and Production and Application of Activated Carbons

doi:10.21203/rs.3.rs-6098941/v1

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Valorization of Water Hyacinth Biomass: Comprehensive Characterization and Production and Application of Activated Carbons

https://doi.org/10.21203/rs.3.rs-6098941/v1

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This study explored a potential route for valorizing the entire biomass from water hyacinth. Initially, the biomass underwent complete characterization, revealing high contents of ash (35%), extractives (25%), and monosaccharides (41%), with glucose being predominant (21%). Lignin content was low (19%), with a monomeric composition rich in G- and H-units (3.6% and 3.4%, respectively). The biomass exhibited a low calorific value (11 MJ/kg) and high oxygen content (62%), contrasted with low carbon values (31%) and high H/C (14.9) and O/C (1.9) ratios. Subsequently, biochar production was conducted at two temperatures (500 and 800°C), where a high yield was obtained at 500°C (44%). Three types of activated carbon were produced using different activation processes: physical activation with CO₂ and chemical activation with K₂CO₃ and H₃PO₄. CO₂ activation yielded 34% but made almost no carbon or porosity (ABET = 9.4 m²/g). K₂CO₃ activation produced carbons with a low yield (21%) but a very high surface area (862 m²/g), featuring micropores and mesopores. In contrast, H₃PO₄ activation yielded 74%, resulting in primarily mesoporous material with minimal microporosity. The activated carbon produced with K₂CO₃ demonstrated high removal efficiency for all the tested pharmaceutical compounds.

Eichhornia crassipes characterization

HHV

Analytical pyrolysis

Carbon materials

Biowastes valorization

The present study examined the conversion of water hyacinth biomass into biochar and activated carbons to explore potential transformations into high-value products that could offset the significant costs associated with water hyacinth management. Various activation conditions were utilized to assess their impact on the properties of the carbon. As a proof of concept, the derived carbon materials were tested for their effectiveness in removing pharmaceutical compounds from water across different therapeutic categories, specifically antibiotics (tetracycline), analgesics (paracetamol), and antidepressants (fluoxetine). These emerging micropollutants pose a concern for living organisms, including humans, necessitating the development of effective mitigation strategies. To the authors’ knowledge, water hyacinth-derived carbons have not yet been studied to remove these pharmaceutical compounds. This will allow insights into their uptake capacity for these emerging organic water pollutants.

Eichhornia crassipes (Mart.) Solms, known as water hyacinth or water-lily, is a free-floating monocotyledon from the Pontederiaceae family. Originally from Brazil (Amazonia) and other Central American countries, it thrives in lakes, slowly moving rivers and swamps[1, 2]. Water hyacinth is very important in most tropical or sub-tropical places due to its biomass productivity and ability to remove pollutants from water[3]. It has been widely cultivated as an ornamental water plant due to its striking flowers. However, it spreads rapidly in suitable environmental conditions, forming extensive monotypic stands in lakes, rivers, and rice paddies. Therefore, its biomass production can reach 17.5 t/(ha.d) (wet basis) in domestic sewage lagoons during the summer months; for instance, in Madrid, a reported value of 39.58 t/(ha.d) of dry-weight biomass was observed for the period from 1984 to 1987[4]. Then, it adversely affects human activities such as fishing or water distribution for agricultural activities. Its presence promotes eutrophication that can lead to conditions for mosquito reproduction, causing diseases and harming biodiversity. Plant decomposition also reduces water quality, compromising the quantity of freshwater available[2]. Recent studies on water hyacinth invasions have shown that the species significantly reduces oxygen and nitrogen levels in the water, lowers pH, and increases the macroinvertebrate's affluence[4]. Because of all these impacts, the US Fish and Wildlife Service has considered the water hyacinth one of the 100 most invasive species in the world[1]. In Portugal, it is listed as invasive in the Decree-Law nbr. 92/2019 is on the European Union's list of exotic invaders (EU Regulation nbr. 1143/2014). Since it is an invasive species, different methods have been used to eradicate it. Still, it is a difficult task, so the main option has been to control its proliferation to reduce and minimize its economic and ecological impacts. Also, each case of invasion by this species is unique and requires specific solutions, so selecting a control method must consider several factors, such as the climatic conditions and the area to be controlled[2]. The species control can be made by: i) mechanical equipment (cutting and mechanical removal of plants from water), ii) chemical methods by using herbicides (which may affect the water and terrestrial ecosystems), or iii) biological methods (employing insects, bacteria, or fungi that attack the plant and afterward must be removed by mechanical procedures). Overall, these approaches involve high costs that are difficult for authorities or landowners to support. For example, the cost to clean one hectare of water hyacinth may vary between 3465 to 4950 USD[1]. Considering all these constraints, many researchers have studied this species and tried to valorize it. According to the Web of Science, as of February 2025, 4,060 publications mentioning "water hyacinth," with review papers accounting for 4.6% (185 papers). By February 2025, 24 papers had already been published, compared to 274 in 2024, 310 in 2023, and 295 in 2022, indicating a relatively consistent annual publication rate on this species. Research on water hyacinth spans diverse fields, including Environmental Sciences (1,155 papers), Energy & Fuels (456), Biotechnology & Applied Microbiology (396), and Environmental Engineering (419), among others (Fig. 1).

Figure 1.

Water hyacinth has a diverse array of applications as documented in the literature, including i) wastewater treatment (e.g., heavy metal decontamination[5]; or industrial dye/pigment removal[6, 7] and phytoremediation[8, 9]; ii) bioenergy (e.g., biogas[10]; biohydrogen[11, 12]; briquette[13, 14]; biochar[15][16] and its use in agroecosystems[17], or for the production of activated carbon applied in the adsorption of metals[18], micropollutants like pharmaceutical compounds[18, 19], pesticides[21], or dyes [22]. Other applications were also reported: iii) sustainable source of cellulose[23] and derived products (e.g., nanocellulose and nanocrystals[24]; fiber source for composite reinforcement[25]; and iv) animal and fish feed[9]. Critical reviews and studies have further explored its potential: i) as biofertilizers and biofuels: Ezzariai et al. [26] critically reviewed the challenges of scaling up these applications; ii) integrated valorization: Bajpai and Nemade[27] examined water hyacinth's role in a circular economy; iii) progress in biomass utilization: Nandiyanto et al. [28] reviewed recent advancements in using water hyacinth effectively. These studies highlight the versatility and potential of water hyacinths in contributing to sustainable practices and resource management.

Despite the extensive research, significant potential remains for valorizing this specific type of biomass. Therefore, this study aimed to perform a comprehensive chemical characterization of water hyacinth from a lagoon in the Aveiro District (Portugal), where its rapid spread has posed serious problems for both communities and the environment. Authors propose that the entire biomass of water hyacinth (roots, stems, and leaves) can be effectively valorized by producing activated carbons to remove emerging pollutants from liquid solutions, potentially offsetting the high costs associated with its control. It has already widely demonstrated the high efficiency of biomass-derived activated carbons for removing several micropollutants[29–31]. Therefore, by controlling water hyacinth, this work will contribute to managing the biomass of an invasive species by producing added-value products, such as biochar and activated carbons. Authors believe this strategy could be implemented in countries facing the same problem.

2.1. Raw material collection

The biomass of Eichhornia crassipes (water hyacinth) was collected in Pateira de Fermentelos (40° 34′ 48" N, 8° 31′ 12" W), a major natural lagoon on the Iberian Peninsula located in the Aveiro District of Portugal. The whole plants (roots, stems, and leaves, Figure S1.a) were air-dried, manually fractionated into small pieces, and milled in a Retsch mill (SM 2000), initially passing through sieves of 10 mm and then 2 mm. Granulometric fractionation occurred using a Retsch vibratory sieving apparatus (AS 200 basic) consisting of US standard wire sieves with mesh numbers 18, 20, 40, 60, and 80. This procedure lasted 10 minutes and involved shaking time, which was repeated five times. The mass of water hyacinth biomass retained in each sieve was collected, oven-dried at 100°C overnight, and weighed.

2.2. Chemical composition

2.2.1. Summative chemical characterization

The chemical characterization was made in the 40–60 mesh fraction (Figure S.1.b). It included the determination of the (i) ashes content by incineration at 550°C overnight (TAPPI T15 os-58), (ii) total extractives by solvent extraction with dichloromethane, ethanol, and water for 16 h each in a Soxhlet apparatus (TAPPI T204 cm-07), (iii) total lignin as the sum of Klason (TAPPI T222 om-11) and soluble lignin measuring the absorbance of the hydrolysate in a spectrophotometer at 205 nm (TAPPI UM 205 om-93). The lignin content was corrected to extractives and ashes content. The composition of the monosaccharides, uronic, and acetic acids was determined in the hydrolysate attained from lignin analysis by High-Pressure Ion-Exchange Chromatography with a pulsed amperometric detector (HPIC-PAD) and a High-Pressure Ion-exclusion Chromatography with a UV/Visible detector (HIPCE-UV). The neutral monosaccharides and uronic acids were determined by separation in a Dionex ICS-3000 HPIC-PAD system using an Aminotrap plus Carbopac PA10 column (250 mm x 4 mm); using a gradient of NaOH + CH₃COONa as eluent (1 mL/min flow) at 25°C. The acetic acid was determined in a Waters 600 HIPCE-UV system with a Biorad Aminex 87H column (300 x 7.8 mm) at 210 nm. The values attained were corrected to the content of extractives.

2.2.2. Composition of the lipophilic extracts

The dichloromethane (DCM) extracts were dried under nitrogen and in a vacuum oven. An amount of 1 mg was derivatized with 120 µl of pyridine, trimethylsilylated with 80 µl of bis(trimethylsilyl)trifluoroacetamide (BSTFA), and heated in the oven at 60°C for 30 minutes. The derivatized DCM extracts were automatically injected into an Agilent gas chromatograph (model 7890A) and a mass detector (Agilent 5975C). The volatiles produced were separated in a Zebron 5HT Inferno column (30 m x 0.25 mm i.d. x 0.25 µm film thickness). The oven was programmed to start at 100°C (held for 1 minute), increase to 150°C at a rate of 10°C/min, then reach 200°C at 5°C/min, followed by 300°C at 4°C/min, and finally increase to 380°C at 10°C/min (held for 5 minutes). The injector temperature was maintained at 280°C, and helium carrier gas (flow rate of 1 mL/min) was used. The MS source was kept at 220°C, and the electron ionization energy was set to 70 eV. The identification of the compounds (as TMS derivatives) was based on comparisons with authentic standards, literature mass spectra, Wiley 6, NIST libraries data, and the interpretation of mass spectrometric fragmentation patterns. Quantification was determined by the relative abundance of each peak area related to the total area of the total ion current chromatogram (TIC), with their relative proportions expressed as a percentage of the total area.

2.2.3. Analytical pyrolysis

The extracted samples of water hyacinth and its corresponding Klason lignin were also analyzed using analytical pyrolysis connected to a chromatographer (Agilent 7890B) and a mass detector (Agilent 5977B). First, the samples were milled in a Retsch MM20 mixer ball mill for 10 minutes. Then, approximately 0.10 mg of the sample was weighed and pyrolyzed at 550°C for 1 minute in a platinum coil Pyroprobe linked to a CDS 5150 valved interface connected to the GC-MS, which had a fused-silica capillary column (ZB-1701: 60 m x 0.25 mm i.d. x 0.25 µm film thickness) installed. The chromatographic conditions were set to 40°C, held for 4 minutes, then increased at a rate of 20°C/min to 100°C, followed by an increase of 6°C/min to 270°C, held for 5 minutes. The injector temperature was set at 270°C, and the MS interface temperature was set at 280°C. The electron ionization energy was maintained at 70 eV. Helium was the carrier gas with a 1 mL/min flow rate. The compounds were identified by comparing their mass spectra with the Wiley, NIST2014 database and literature[31]. The total area of the chromatogram was automatically obtained, and the percentage area of each identified compound was calculated.

2.2.4. Proximate analysis, elemental analysis, and thermal properties

The following parameters characterized water hyacinth biomass: (i) Proximate analysis was determined using the ASTM E870-82 method. Approximately 2 g of each sample was weighted in ceramic crucibles. Total volatile content was determined gravimetrically after incineration at 950°C for 7 min and without oxygen by covering the crucibles with a ceramic lid. After determining the ashes content, the samples were incinerated at 550°C overnight without the ceramic lid, and fixed carbon was calculated to subtract total volatiles and ashes to 100%; (ii) Moisture content was determined gravimetrically after constant weight in an oven at 105°C, overnight; (iii) The elemental analysis was conducted using the ASTM standard method D5373-08 on an Elemental Analyzer Thermo Finnigan-CE Instruments Flash EA 1112 CHNS series. The percentage of oxygen was determined by subtracting the combined content of carbon, hydrogen, nitrogen, sulfur, and ashes from 100%; (iv) The mineral content of the ash and the nitrogen content was determined following method CEN, 2001a. This highly effective method detects ammonium-N, nitrate-N, nitrite-N, and organic-N content. Aqua regia was used to extract the other major mineral elements (P, S, K, Ca, Mg, and S) and minor elements (Fe, Cu, Zn, Mn, B, Cr, Pb, Ba, and Li), which were then quantified using inductively coupled plasma optical emission spectrometry following CEN, 2001b standard; (v) The higher heating value (HHV) was determined on an adiabatic bomb calorimeter following the ABNT NBR 8663 standard; (vi) Thermogravimetric analysis (TGA) was conducted between 30–800°C, by using a heating rate of 5°C/min, under a continuous flow of argon (Setaram Lab-sys EVO).

2.3. Water hyacinth carbon materials

2.3.1. Biochar production

The dried biomass of water hyacinth (granulometric fraction 20–40 mesh) was subjected to pyrolysis/carbonization at temperatures of 500°C and 800°C in a quartz reactor set within a custom-made electric vertical tube furnace. A heating rate of 5°C/min was maintained for 1 hour under a nitrogen (N₂) flow of 150 mL/min and then cooled to room temperature consistently under an N₂ atmosphere. The biochars produced at 500°C and 800°C were designated BC-500 and BC-800, respectively.

2.3.2. Activated carbon production

Three types of activated carbons were produced from physical and chemical activations by using the same pyrolysis/carbonization installation and the same granulometric fraction of biomass described in the previous section:

a) Physical activation with CO₂ - was performed in a two-step process. Firstly, the biomass was heated to 800°C (heating rate of 5°C/min) under an N₂ flow of 150 ml/min (carbonization step). When the target temperature of 800°C was reached, the gas was changed to CO₂ with a 100 ml/min flow for 1h (activation step). Afterward, the gas was changed again to N₂ for the cooling step. The obtained carbon was designated as AC-CO₂.

b) Chemical activation with K₂CO₃ - the biomass was mixed with K₂CO₃ (dry impregnation) with a mass ratio of 1:1. The mixture was then heated at 800°C for 1 h, under an N₂ flow of 150 ml/min and a heating rate of 5°C/min, and then cooled to room temperature. The obtained sample was then washed with deionized water until it had a stable pH and dried overnight. The obtained carbon was coded as AC-K₂CO₃.

c) Chemical activation with H₃PO₄ - The biomass was impregnated with H₃PO₄ (wet impregnation) under a mass ratio of 1:1 for 5 h, at 50°C and subsequently dried at 150°C. This mixture was then activated at 500°C for 1 h under an N₂ flow (150 ml/min and heating rate of 5°C/min). The obtained carbon was washed and dried as described above, and the resulting sample was coded as AC-H₃PO₄.

2.3.3. Characterizations of carbon materials

The produced carbon materials underwent elemental and thermogravimetric analyses. The textural properties were obtained from N₂ adsorption-desorption isotherms at 77 K (Micromeritics ASAP2010). The samples were outgassed overnight at 120°C under vacuum pressure. The surface area was determined using the Brunauer–Emmett–Teller (BET) equation with a range of relative pressures (p/p0) established by the Rouquerol method[32]. The micropore volume was assessed using the t-plot method. The total pore volume was obtained from the amount of N2 adsorbed at p/p0 = 0.95. The mesopore volume was calculated by subtracting the micropore volume from the total pore volume.

2.3.4. Liquid-phase adsorption assays for the removal of pharmaceutical compounds

The developed carbon materials were applied as adsorbents to remove tetracycline hydrochloride, paracetamol, and fluoxetine from the liquid phase. Tetracycline hydrochloride (Figure S2.a) is an oral antibiotic from the group of tetracyclines with the chemical formula C₂₂H₂₄N₂O₈ClH and a molecular weight of 480.9 g/mol.

Paracetamol (Figure S2.b) is an analgesic and antipyretic compound with the chemical formula C₈H₉NO₂ and a molecular weight of 151.15 g/mol. Fluoxetine hydrochloride (Figure S2.c) is an antidepressant belonging to the selective serotonin reuptake inhibitor class, with the chemical formula C₁₇H₁₈F₃NO and a molecular weight of 345.8 g/mol.

Synthetic solutions of the pharmaceutical compounds were prepared as follows: (i) Dissolution of tetracycline hydrochloride powder (Fischer Scientific, purity ≥ 95%) in acetic acid/sodium acetate buffer solution (initial pH of the solution = 4.0); (ii) Dissolution of paracetamol powder (Sigma-Aldrich, ≥ 99%) in deionized water (initial pH of the solution = 7.6); (iii) Dissolution of fluoxetine hydrochloride (Sigma-Aldrich, ≥ 98%) in deionized water (initial pH of the solution = 6.5). Triplicate batch adsorption experiments were performed at room temperature, under constant agitation, for 24 h, in a multi-point stirrer. An adsorbent mass of 10 mg and 50 mL of solution with an initial concentration of 50 mg/L for each pharmaceutical compound was used. A contact time of 24 h was applied because preliminary assays indicated that this time was enough to reach equilibrium. After the adsorption assay, the samples were filtered. The concentrations of the compounds in the filtrates were determined by UV-Vis (GBC UV/VIS, model 916) at wavelengths of 243 nm for paracetamol, 225 nm for fluoxetine, and 275 nm for tetracycline. A blank test without adsorbents was performed to test the compounds’ retention in the vessels where the adsorption assays were performed and in the filters used.

The removal efficiency (%) was calculated using Eq. 1:

\(\:\%\:Removal=\frac{({C}_{0}-{C}_{f})}{{C}_{0}}\times\:100\)

(Eq. 1)

where \(\:{C}_{0}\:\)is the initial concentration of the compound (mg/L) and \(\:{C}_{f}\) is the final concentration (mg/L). The control tests indicated that the percentage of removal of the pharmaceutical compounds was lower than 1%.

3.1. Water hyacinth characterization

3.1.1. Chemical composition

Table 1 presents the summative chemical composition of the water hyacinth Eichhornia crassipes. Its chemical composition revealed an impressive amount of non-structural components: The ash content reaches 34.9% of oven-dry weight (odw), followed by extractives at 25.0% (odw), with ethanolic extractives predominating, representing 59% (odw) of the total extractives. The structural components of the cell walls attained values of 19.6% (odw) for total lignin and 41.4% (odw) of monosaccharides (mainly constituted by glucose with 21.4% (odw)). These values align with those of other studies on water hyacinth biomass. For example, Carlini et al. [32] in the whole plant attained 18.0% in cellulose, 28.2% in hemicelluloses, and 7.0% in lignin; Gebrehiwot et al. [33] studying different fractions of water hyacinth biomass achieved in the stems 26.8% of ashes, 58.0% of total extractives, 8.4% of cellulose, and 11.4% of holocellulose. However, as Tovar-Jiménez et al. [34] mentioned, the edapho-climatic conditions and the stage of the plant's development influence its chemical composition. For this, it is essential to consider the plants' maturation stage and geographical conditions when this biomass is used as feedstock for biobased products, as some variability can be observed.

Table 1

Summative chemical characterization of the *Eichhornia crassipes* (as % oven-dry weight, odw; Mean ± STDEV values; n = 3).
	Water hyacinth
Ashes	34.9 ± 1.9
Total extractives	25.0 ± 0.7
Dichloromethane	2.0
Ethanol	14.9
Water	8.1
Total lignin	19.6 ± 0.2
Klason lignin	17.3
Soluble lignin	2.3
Monosaccharides	41.4 ± 1.2
Rhamnose	0.3
Arabinose	5.8
Galactose	2.3
Glucose	21.4
Xylose	6.8
Galacturonic acid	3.9
Acetic acid	1.1

Table 1.

3.1.2. GC–MS characterization of lipophilic extracts

The list of the lipophilic compounds identified by GC-MS in dichloromethane extracts is presented in Supplementary information (Table S1), and the correspondent chromatogram is shown in Fig. 2. Forty-nine different types of compounds were identified. The fatty acids (FA) are the family of compounds with the major expression (47.5% of the total chromatogram area) where it is possible to find a homolog series of these compounds ranging from C4:0 to C28:0. The hexadecanoic acid (C16:0, peak 22) with 20.6%, octadecanoic acid (C18:0, peak 30) with 5.7%, 11-Octadecenoic acid (C18:1, peak 28) with 6.8% and hexanoic acid (C6:0, peak 9) with 5.3% are the most expressive compounds of FA. The phytosterols (PHS) compounds are the second group (8.5% of the total), where β-stigmasterol (3.9%, peak 45), stigmasterol-5-ene (2.1%, peak 46), and cholest-4-en-3-ol (1.3%, peak 42) were found. Also, it must be noted the presence of appreciable amounts of erythritol (11.9%, peak 11), glycerol (11.3%, peak 4), 1,2,3- butanetriol (1.3%, peak 5), and compounds with nitrogen such as urea (4.1%, peak 3) and uracil (1.2%, peak 7).

The chemical composition varies according to the extraction systems, solvent, and plant fractions. For example, Silva et al. [35], studying different morphological parts (roots, stalks, leaves, and flowers), identified 29 compounds where the most representatives were glycerol, hexadecanoic acid, linoleic acid, linolenic acid, cholesterol, methylcholesterol, stigmasterol, and β-sitosterol. Martins et al. [36], using supercritical fluid extraction (SEF), update the extraction of stigmasterol, cholesterol, methylcholesterol, and β-sitosterol from the whole plant. Fileto-Pérez et al. [37], by using Soxhlet extraction with different apolar solvents (methanol, hexane, acetone) in root, stem, and leaf fractions of the plant, identified twenty organic acids and three steroids (spirostane, cholestane, and β-stigmasterol) and one terpenoid (squalene). Other authors found phenolic compounds (resorcinol, catechol, vanillic acid, gallic acid), flavonoids (apigenin, gossypetin, kaempferol, quercetin), terpenoids (β-carotene, phytol, cholestane, β-stigmasterol), and carboxylic acids (oxalic acid, linolenic acid, palmitic acid, oleic acid, pentadecanoic acid)[33, 38].

Figure 2.

3.1.3. Py-GC/MS characterization biomass

According to the Py-GC/MS analysis (Table S2, Fig. 3), the volatile compounds obtained are similar to those of other biomasses. Their distribution in the pyrogram (Fig. 3) revealed a major relative content of compounds derived from carbohydrates and less amount of lignin (53.4 vs. 7.1%), which agrees with the summative chemical analysis mentioned before.

It was interesting to verify the presence of proteins (peak 21 (3-ethyl-1-pyrroline), peak 50 (indole), and peak 52 (5-methyl-indole)), even in small amounts (1.5% of total area, Fig. 3 and Table S2). The lignin polymer presented a monomeric composition mainly of G- (3.6%), H- (3.4%), and with the residual percentage of S-units (0.1%). However, other compounds that could not be assigned to the typical monomers and where assigned as “other lignin derivatives”, such as peaks 9 (toluene), 15 (styrene), or 39 (p-xylenol), were also identified, summing 4.6% of the total chromatographic area (Table S2). The main carbohydrate derivates were levoglucosan (peak 54), with 9.0% derived from cellulose[39], followed by low molecular compounds such as acetone (peak 1), 2-oxo-propanal (peak 2) and acetic acid (peak 7) each with 3.6%, that derived from either cellulose and hemicelluloses, while other compounds such as 1,4-anhydroarabinofuranose (peak 45, 2.1%) derived from arabinose and 1,4-anhydroxylofuranose (peak 51, 1.1%) from xylose[40]. The pyrolysis of Klason lignin (Table S2, Fig. 3) showed the residual amount of carbohydrates (1.1%), and the lignin contained more G- and H-units than the starting material. Compounds such as 4-methylphenol (peak 37) highly increased (1.6 vs. 7.4%), o-cresol (peak 36) increased from 0.4 to 1.0%, phenol (peak 33) increased from 1.1 to 5.8%, which suggest the occurrence of demethoxylation reactions by the acid attack of the starting material during Klason determination.

Figure 3.

3.1.4. Physical and thermal characterization

Water hyacinth was also characterized regarding its proximate analysis, ultimate analysis, and mineral composition (Table 2). The material presented a moisture of 10.5% wet basis (wb). The ashes content was lower than the amount attained by summative analysis (24.2 vs. 34.9%). The volatile matter represented 55.2% wb and fixed carbon 20.5% wb. HHV was 11.4 MJ/kg, a low value compared to wood biomass, ranging from 15.0 to 20.5 MJ/kg[41]. Huang et al. [42] reported HHV values of 15.71 and 14.90 MJ/kg for water hyacinth roots and leaves, respectively. Regarding the mineral composition, water hyacinth presented a predominance of potassium (42.3 g/kg), calcium (14.5 g/kg), iron (7.5 g/kg), magnesium (5.3 g/kg), sulfur (4.3 g/kg), and sodium (3.5 g/kg). According to the literature, for hardwoods like A. melanoxylon, juvenile wood prevailed K (4.7 g/kg), N_mineral (2.0 g/kg), and Ca (1.2 g/kg). In contrast, for mature wood, just K and N_mineral were predominant (2.6 and 1.3 g/kg)[43].

Thermogravimetric analysis of water hyacinth biomass showed a major weight loss between 230–340°C corresponding mainly to the decomposition of hemicellulose and between 340–450°C associated with cellulose degradation (Fig. 4.a). Above 450°C, it starts mostly the lignin decomposition and the stage of char formation[44, 45], remaining around 47% of char at 800°C.

Table 2

Proximate analysis, ultimate analysis (as % of starting wet basis, wb, biomass), and mineral ash composition (g/kg) present in *Eichhornia crassipes* biomass (Mean values ± STDEV; n = 3).
Proximate analysis (%)		Ultimate analysis		Mineral ash composition (g/kg)
Moisture	10.5 ± 0.08	C (%)	31.1	K	42.3 ± 3.3	P	3.2 ± 0.1
Ash	24.2 ± 0.54	H (%)	4.7	Ca	14.5 ± 0.4	Mn	1.3 ± 0.1
Total Volatiles	55.2 ± 1.2	N (%)	2.0	Fe	7.5 ± 1.0	Zn	0.08 ± 0.01
Fixed carbon	20.5 ± 1.6	S (%)	0.2	Mg	5.3 ± 0.3	B	0.02 ± 0.03
HHV (MJ/kg)	11.4 ± 0.7	O (%)	61.9	S	4.3 ± 0.2	Cu	0.013 ± 0.001
		H/C ratio	14.9	Na	3.5 ± 0.1
		O/C ratio	1.9

Table 2.

3.2. Carbon materials from water hyacinth

3.2.1. Physico-chemical properties

Figure 4.

Table 3 presents each carbon's yield, elemental analysis, and textural parameters of the obtained materials. The yields of biochar obtained at 500 and 800°C (BC-500 and BC-800, respectively) are pretty similar to the ones obtained by other authors at the same temperatures[46]; as expected, the yield is lower for higher carbonization temperatures due to higher devolatilization. Subsequently, BC-800 presented a slightly higher surface area (36.6 m²/g) than BC-500 (23.7 m²/g). Nevertheless, both biochars presented low surface areas, typical for biomass-derived carbon materials not subjected to an activation process.

Submitting the biomass to a physical activation process with CO₂ resulted in a material with almost no carbon and no porosity (A_BET = 9.4 m²/g). This result might be related to the high potassium content of the biomass (42.3 g/kg, Table 4), which is known to catalyze the gasification reactions that occur during CO₂ activation[42, 47]. Lower activation times or even lower temperatures are suggested for future works in which CO₂ activation will be performed. Chemical activation allowed the obtaining of activated carbons with a higher porosity, particularly the process employing K₂CO₃. The AC-H₃PO₄ carbon obtained was a mesoporous material with almost no microporosity, although it presented a high production yield (74.5% wt.). These results indicate that the activation conditions with H₃PO₄ still need to be optimized to obtain a more developed microporosity. On the contrary, the AC-K₂CO₃ sample presented a very high surface area (862 m²/g) with both micropores and mesopores. The low yield of this carbon (21.3% wt.) is balanced with the well-developed porosity, particularly in the micropore range (Figure S3). N₂ adsorption-desorption isotherms of the carbon samples are presented in the supplementary material (Figure S4).

Table 3.

Table 3

Production yield and textural parameters of biochars and activated carbons obtained from water hyacinth biomass.
	Biochars		Activated carbons
	BC-500	BC-800	AC-CO₂	AC-K₂CO₃	AC-H₃PO₄
Yield (% wt.)	44.4	40.5	33.5	21.3	74.5
Elemental analysis
C (% wt.)	26.7	27.8	1.2	26.8	31.5
H (% wt.)	0.94	0.59	0.19	2.0	2.3
N (% wt.)	1.4	1.1	0.13	0.16	1.1
S (% wt.)	0.40	0.44	0.14	0.00	0.00
Textural parameters
A_BET (m²/g)	23.7	36.6	9.4	862	68.4
V_total (cm³/g)	0.022	0.025	0.011	0.520	0.161
V_micro (cm³/g)	0.006	0.011	0.002	0.320	0.001
V_meso (cm³/g)	0.016	0.014	0.009	0.200	0.160
wt. – weight; A_BET – Surface area; V_total – Total pore volume; V_micro - Micropore volume; V_meso – Mesopore volume.

TGA analysis of carbon samples (Fig. 4.b) revealed that the most thermally stable sample was AC-CO₂, which is related to its low carbon content. Also, the mineral content of this sample is relatively stable up to 800°C. On the contrary, the chemically activated carbons presented a progressive mass loss with increasing temperature. AC-K₂CO₃ sample showed a mass loss of around 25% at 800°C, while AC-H₃PO₄ lost 28% of its mass. Both biochars presented thermal stability with a total mass loss of around 16%.

3.2.2. Exploratory adsorption assay: Removal of pharmaceutical compounds

Figure 5 presents the removal of pharmaceutical compounds from liquid solutions using the developed carbon adsorbents from water hyacinth biomass. It is possible to distinguish the superior performance of AC-K₂CO₃ carbon for all the tested pharmaceutical compounds with removal efficiencies between 84.9 and 100%. This result is related to the high surface area and micropore volume presented by this adsorbent, which is essential for removing these organic micropollutants[29, 48]. There is a clear relationship between the removal efficiency and the surface area of carbon materials. For instance, PAR removal was only significant for AC-K₂CO₃ carbon, while its removal was insignificant for the other carbons due to their low surface areas.

On the contrary, FLX and TTC removals were ruled by other features, such as surface chemistry. For instance, it is possible to observe a high removal of TTC (86.6%) with the AC-H₃PO₄ adsorbent. This carbon should have several oxygenated functional groups (e.g., -COOH) able to establish strong H-bonds with the functionalities present in the TTC molecule[49, 50]. FLX can also establish H-bonds between its nitrogen and oxygenated groups at the carbon materials’ surfaces. The significant removal of FLX by BC-800 carbon (56.3%) must be explained by π-π interactions typical in adsorption with aromatic compounds, particularly effective for alkaline carbons. It is known that biochars produced at high temperatures generally have an alkaline character[51].

Figure 5.

According to these results, it is possible to infer that AC-K₂CO₃ is the best adsorbent for this type of micropollutant. Nevertheless, AC-H₃PO₄ also seems to be a promising alternative for the adsorption of the antibiotic TTC. The performance of the BC-800 biochar sample for removing FLX should also be highlighted, even though this is a non-activated material, which represents an advantage from an economic point of view as no additional activation process is required.

Water hyacinth is an invasive species that has spread throughout Portugal, leading to various environmental and social issues. This study investigates a potential valorization method for the entire plant biomass, with an emphasis on producing biochar and activated carbons. The biochar was produced in high yields (40–44%), while the activated carbons displayed variable yields (21–74%), depending on the production process. These carbon materials showed promising properties for removing pharmaceutical compounds from liquid solutions, which is an area of increasing significance. Future research may involve gaining a deeper understanding of the adsorption mechanisms of these pharmaceutical compounds onto the produced carbon materials, in addition to studies on their application with real wastewater samples and regeneration studies of the adsorbents.

Declaration of competing interest

Conflict of interest: The authors declare that no competing financial interests or personal relationships could influence this work.

Funding

This work was supported by Fundação para a Ciência e a Tecnologia (Portugal) by i) the Grants UIDP/00239/2020 (DOI 10.54499/UIDB/00239/2020); LA/P/0008/2020 (DOI 10.54499/LA/P/0008/2020); UIDP/50006/2020 (DOI 10.54499/UIDP/50006/2020); IDB/50006/2020 (DOI 10.54499/UIDB/50006/2020); by the research contracts through the DL 57/2016 – Norma transitória; https://doi.org/10.54499/DL57/2016/CP1382/CT0007; CEECIND/004431/2022.

Acknowledgments

The authors acknowledge FCT (Fundação para a Ciência e Tecnologia, Portugal) by financing the: Forest Research Center (UIDP/00239/2020 and UID/00239 (10.54499/UIDB/00239/2020)) projects; FCT/MCTES (LA/P/0008/2020 (DOI 10.54499/LA/P/0008/2020), UIDP/50006/2020 (DOI 10.54499/UIDP/50006/2020) and IDB/50006/2020 (DOI 10.54499/UIDB/50006/2020)), through national funds. Ana Lourenço also thanks FCT for her research contract (https://doi.org/10.54499/DL57/2016/CP1382/CT0007); Maria Bernardo thanks FCT/MCTES for funding through program DL 57/2016 – Norma transitória; and Inês Matos thanks FCT/MCTES for her contract CEECIND/004431/2022.

Data availability

All data generated or used during this study are present in this article.

Sierra-Carmona CG, Hernández-Orduña MG, Murrieta-Galindo R (2022) Alternative uses of water hyacinth (Pontederia crassipes) from a sustainable perspective: A systematic literature Review. Sustainability 14:3931. 10.3390/su14073931
Rodríguez-Lara JW, Cervantes-Ortiz F, Arambula-Villa G et al (2021) Lirio acuático (Eichhornia crassipes): una revisión. Agron Mesoam 44201. 10.15517/am.v33i1.44201
Malik A (2007) Environmental challenge vis a vis opportunity: The case of water hyacinth. Environ Int 33:122–138. 10.1016/j.envint.2006.08.004
Jha RR, Li D (2025) Quantifying the effects of water hyacinth (Pontederia crassipes) on freshwater ecosystems: a meta-analysis. Biol Invasions 27:27. 10.1007/s10530-024-03499-9
Amalina F, Razak ASA, Krishnan S et al (2022) Water hyacinth (Eichhornia crassipes) for organic contaminants removal in water – A review. J Hazard Mater Adv 7:100092. 10.1016/j.hazadv.2022.100092
Sanmuga Priya E, Senthamil Selvan P (2017) Water hyacinth (Eichhornia crassipes) – An efficient and economic adsorbent for textile effluent treatment – A review. Arab J Chem 10:S3548–S3558. 10.1016/j.arabjc.2014.03.002
Nath A, Chakraborty S, Bhattacharjee C (2014) Bioadsorbtion of industrial dyes from aqueous solution onto water hyacinth (Eichornia crassipes): equilibrium, kinetic, and sorption mechanism study. Desalin Water Treat 52:1484–1494. 10.1080/19443994.2013.787028
Gong Y, Zhou X, Ma X, Chen J (2018) Sustainable removal of formaldehyde using controllable water hyacinth. J Clean Prod 181:1–7. 10.1016/j.jclepro.2018.01.220
Rezania S, Ponraj M, Din MFM et al (2015) The diverse applications of water hyacinth with main focus on sustainable energy and production for new era: An overview. Renew Sustain Energy Rev 41:943–954. 10.1016/j.rser.2014.09.006
Gao J, Chen L, Yan Z, Wang L (2013) Effect of ionic liquid pretreatment on the composition, structure and biogas production of water hyacinth (Eichhornia crassipes). Bioresour Technol 132:361–364. 10.1016/j.biortech.2012.10.136
Amulya K, Morris S, Lens PNL (2023) Aquatic biomass as sustainable feedstock for biorefineries. Biofuels Bioprod Biorefining 17:1012–1029. 10.1002/bbb.2471
Kumari K, Swain AA, Kumar M, Bauddh K (2021) Utilization of Eichhornia crassipes biomass for production of biochar and its feasibility in agroecosystems: a review. Environ Sustain 4:285–297. 10.1007/s42398-021-00185-7
Rezania S, Md Din MF, Kamaruddin SF et al (2016) Evaluation of water hyacinth (Eichhornia crassipes) as a potential raw material source for briquette production. Energy 111:768–773. 10.1016/j.energy.2016.06.026
Davies RM, Davies OA, Mohammed US (2013) Combustion characteristics of traditional energy sources and water hyacinth briquettes. Int J Sci Res Environ Sci 1:144–151. 10.12983/ijsres-2013-p144-151
Quintana-Najera J, Blacker AJ, Fletcher LA, Ross AB (2021) The effect of augmentation of biochar and hydrochar in anaerobic digestion of a model substrate. Bioresour Technol 321:124494. 10.1016/j.biortech.2020.124494
Kassa Y, Amare A, Nega T et al (2025) Water hyacinth conversion to biochar for soil nutrient enhancement in improving agricultural product. Sci Rep 15:1820. 10.1038/s41598-024-84729-x
Kumar V, Singh J, Nadeem M et al (2020) Experimental and kinetics studies for biogas production using water hyacinth (Eichhornia crassipes [Mart.] Solms) and sugar mill effluent. Waste Biomass Valoriz 11:109–119. 10.1007/s12649-018-0412-9
Liu R, Zhao Z, Liu D et al (2024) Removal of Pb(II), Cu(II), and Ag(I) from aqueous solutions using biochar derived by P-enriched water hyacinth. Environ Pollut Bioavailab. 10.1080/26395940.2024.2322491
Chemtai C, Ngigi AN, Kengara FO (2024) Ciprofloxacin sorption by non-activated and activated biochar derived from millet husks and water hyacinth. Sustain Chem Environ 5:100075. 10.1016/j.scenv.2024.100075
González-García P, Gamboa‐González S, Andrade Martínez I, Hernández‐Quiroz T (2020) Preparation of activated carbon from water hyacinth stems by chemical activation with K₂CO₃ and its performance as adsorbent of sodium naproxen. Environ Prog Sustain Energy. 10.1002/ep.13366
Ji X, Liu Y, Gao Z et al (2024) Efficiency and mechanism of adsorption for imidacloprid removal from water by Fe-Mg co-modified water hyacinth-based biochar: Batch adsorption, fixed-bed adsorption, and DFT calculation. Sep Purif Technol 330:125235. 10.1016/j.seppur.2023.125235
Carneiro MT, Morais AÍS, de Carvalho Melo ALF et al (2023) Biochar derived from water hyacinth biomass bhemically activated for dye removal in aqueous solution. Sustainability 15:14578. 10.3390/su151914578
Ewnetu Sahlie M, Zeleke TS, Aklog Yihun F (2022) Water Hyacinth: A sustainable cellulose source for cellulose nanofiber production and application as recycled paper reinforcement. J Polym Res 29:230. 10.1007/s10965-022-03089-0
Smriti SA, Haque ANMA, Khadem AH et al (2023) Recent developments of the nanocellulose extraction from water hyacinth: a review. Cellulose 30:8617–8641. 10.1007/s10570-023-05374-7
Sulardjaka S, Iskandar N, Nugroho S et al (2022) The characterization of unidirectional and woven water hyacinth fiber reinforced with epoxy resin composites. Heliyon 8:e10484. 10.1016/j.heliyon.2022.e10484
Ezzariai A, Hafidi M, Ben Bakrim W et al (2021) Identifying advanced biotechnologies to generate biofertilizers and biofuels from the world’s worst aquatic weed. Front Bioeng Biotechnol. 10.3389/fbioe.2021.769366
Bajpai S, Nemade PR (2023) An integrated biorefinery approach for the valorization of water hyacinth towards circular bioeconomy: a review. Environ Sci Pollut Res 30:39494–39536. 10.1007/s11356-023-25830-y
Nandiyanto ABD, Ragadhita R, Hofifah SN et al (2023) Progress in the utilization of water hyacinth as effective biomass material. Environ Dev Sustain 26:24521–24568. 10.1007/s10668-023-03655-6
Rehman A, Nazir G, Heo K et al (2024) A focused review on lignocellulosic biomass-derived porous carbons for effective pharmaceuticals removal: Current trends, challenges and future prospects. Sep Purif Technol 330:125356. 10.1016/j.seppur.2023.125356
Verma M, Singh P, Dhanorkar M (2024) Remediation of emerging pollutants using biochar derived from aquatic biomass for sustainable waste and pollution management: a review. J Chem Technol Biotechnol 99:330–342. 10.1002/jctb.7548
Ullah S, Shah SSA, Altaf M et al (2024) Activated carbon derived from biomass for wastewater treatment: Synthesis, application and future challenges. J Anal Appl Pyrol 179:106480. 10.1016/j.jaap.2024.106480
Carlini M, Castellucci S, Mennuni A (2018) Water hyacinth biomass: chemical and thermal pre-treatment for energetic utilization in anaerobic digestion process. Energy Procedia 148:431–438. 10.1016/j.egypro.2018.08.106
Gebrehiwot H, Dekebo A, Endale M (2022) Chemical composition, pharmacological activities, and biofuel production of Eichhornia crassipes (Water hyacinth): A review. J Turkish Chem Soc Sect Chem 9:849–866. 10.8596/jotcsa.1033493
Tovar-Jiménez X, Favela-Torres E, Volke-Sepúlveda TL et al (2019) Influence of the geographical area and morphological part of the water hyacinth on its chemical composition. Ing Agrícola y Biosist. 10.5154/r.inagbi.2017.10.013
Silva RP, de Melo MMRR, Silvestre AJDD, Silva CM (2015) Polar and lipophilic extracts characterization of roots, stalks, leaves and flowers of water hyacinth (Eichhornia crassipes), and insights for its future valorization. Ind Crops Prod 76:1033–1038. 10.1016/j.indcrop.2015.07.055
Martins PF, de Melo MMR, Sarmento P, Silva CM (2016) Supercritical fluid extraction of sterols from Eichhornia crassipes biomass using pure and modified carbon dioxide. Enhancement of stigmasterol yield and extract concentration. J Supercrit Fluids 107:441–449. 10.1016/j.supflu.2015.09.027
Fileto-Pérez HA, Miriam Rutiaga-Quiñones O, Sytsma MD et al (2015) GC/MS Analysis of some sxtractives from Eichhornia crassipes. BioResources 10:7353–7360
Ben Bakrim W, Ezzariai A, Karouach F et al (2022) Eichhornia crassipes (Mart.) Solms: A comprehensive review of its chemical composition, traditional use, and value-added products. Front Pharmacol. 10.3389/fphar.2022.842511
Lourenço A, Gominho J, Pereira H (2019) Chemical characterization of lignocellulosic materials by analytical pyrolysis. In: Kusch P (ed) Anal. Pyrolysis. IntechOpen, pp 39–61
Ralph J, Hatfield RD (1991) Pyrolysis-Gc-Ms characterization of forage materials. J Agric Food Chem 39:1426–1437. 10.1021/jf00008a014
Demirbaş A (1997) Calculation of higher heating values of biomass fuels. Fuel 76:431–434. 10.1016/S0016-2361(97)85520-2
Huang H, Liu J, Liu H et al (2020) Pyrolysis of water hyacinth biomass parts: Bioenergy, gas emissions, and by-products using TG-FTIR and Py-GC/MS analyses. Energy Convers Manag 207:112552. 10.1016/j.enconman.2020.112552
Chemetova C, Ribeiro H, Fabião A, Gominho J (2020) Towards sustainable valorisation of Acacia melanoxylon biomass: Characterization of mature and juvenile plant tissues. Environ Res 191:110090. 10.1016/j.envres.2020.110090
Pal DB, Tiwari AK, Srivastava N et al (2022) Biomass valorization of Eichhornia crassipes root using thermogravimetric analysis. Environ Res 214:114046. 10.1016/j.envres.2022.114046
Wauton I, William-Ebi D (2019) Characterization of water hyacinth (Eichhornia crassipes) for the production of thermochemical fuels. J Multidiscip Eng Sci Stud 5:2458–2925
Nguyen LX, Do PTM, Nguyen CH et al (2018) Properties of biochars prepared from local biomass in the Mekong Delta. Vietnam BioResources 13:7325–7344. 10.15376/biores.13.4.7325-7344
Mitsuoka K, Hayashi S, Amano H et al (2011) Gasification of woody biomass char with CO₂: The catalytic effects of K and Ca species on char gasification reactivity. Fuel Process Technol 92:26–31. 10.1016/j.fuproc.2010.08.015
Rocha LS, Pereira D, Sousa É et al (2020) Recent advances on the development and application of magnetic activated carbon and char for the removal of pharmaceutical compounds from waters: A review. Sci Total Environ 718:137272. 10.1016/j.scitotenv.2020.137272
Tahmasebpour R, Peighambardoust SJ (2024) Decontamination of tetracycline from aqueous solution using activated carbon/Fe3O4/ZIF-8 nanocomposite adsorbent. Sep Purif Technol 343:127188. 10.1016/j.seppur.2024.127188
Álvarez-Torrellas S, Rodríguez A, Ovejero G, García J (2016) Comparative adsorption performance of ibuprofen and tetracycline from aqueous solution by carbonaceous materials. Chem Eng J 283:936–947. 10.1016/j.cej.2015.08.023
Chávez-García E, González-Méndez B, Molina-Freaner F (2023) Biochar application on mine tailings from arid zones: Prospects for mine reclamation. J Arid Environ 217:105040. 10.1016/j.jaridenv.2023.105040

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Valorization of Water Hyacinth Biomass: Comprehensive Characterization and Production and Application of Activated Carbons

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Abstract

Figures

Statement of Novelty

1. Introduction

2. Material and methods

2.1. Raw material collection

2.2. Chemical composition

2.2.1. Summative chemical characterization

2.2.2. Composition of the lipophilic extracts

2.2.3. Analytical pyrolysis

2.2.4. Proximate analysis, elemental analysis, and thermal properties

2.3. Water hyacinth carbon materials

2.3.1. Biochar production

2.3.2. Activated carbon production

2.3.3. Characterizations of carbon materials

2.3.4. Liquid-phase adsorption assays for the removal of pharmaceutical compounds

3. Results and discussion

3.1. Water hyacinth characterization

3.1.1. Chemical composition

3.1.2. GC–MS characterization of lipophilic extracts

3.1.3. Py-GC/MS characterization biomass

3.1.4. Physical and thermal characterization

3.2. Carbon materials from water hyacinth

3.2.1. Physico-chemical properties

3.2.2. Exploratory adsorption assay: Removal of pharmaceutical compounds

4. Conclusions

Declarations

Declaration of competing interest

Funding

Acknowledgments

Data availability

References

Supplementary Files

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