1 Introduction

Jatropha curcas is a perennial shrub or tree belonging to the Euphorbiaceae family, it bears 5 to 7 alternately arranged lobed leaves per branch [1]. Jatropha curcas expressed high productivity yield which increased when wastewater irrigated. Moreover, it persists harsh growing conditions [2]. Jatropha leaves have low nutritional and chemical contents, therefore, their biochemical and physiological treatments like fertilizers, plant growth regulators, and soil characteristics have been suggested to enhance Jatropha curcas growth [3]. Currently, wastewater serves as a rich supply of micronutrients like Fe, Mn, Zn, and Cu that are sufficient for growth without the need for artificial fertilizers. Consequently, if processed and employed in the agriculture field, it will increase the majority of crop yields [4]. Furthermore, waste-water-sludge will speed up plant growth more effectively than any other commercial fertilizers in the soil [5]. Indeed, there is a decrease in the clean water supply all over the world. Irrigation water represents about 80% of the total freshwater usage [6]. Subsequently, it is crucial to find alternative water sources for irrigation. The reuse of wastewater is one of the most effective ways to face the decrease in water resources [7]. Moreover, Jatropha curcas is an inedible plant; thus, there is no need to worry about the balance between food and fuel needs. In addition, the dry and marginal soils are suited for growing Jatropha curcas. It can shed the majority of its leaves to reduce transpiration loss and is tolerant of drought [8]. Hence, Jatropha curcas is a great source of lignocellulosic waste for biofuel production. Jatropha plant especially Jatropha seedcake was reported to be used in the synthesis of bioethanol in several investigations [9, 10]. However, this study is the first to show that Jatropha leaves may be used to successfully bioethanol production. Recent research has identified Jatropha curcas as a viable plant for second-generation biofuels, due to the exceptional oil content of the seeds that may be used to make biodiesel [11]. Recently, it has also been suggested to use Jatropha curcas leaves, seed-cake, and other wastes for bioethanol production [12]. This is explained by the significant concentrations of cellulose, hemicellulose, and total soluble carbohydrates in these wastes. For bioethanol production, carbohydrates (cellulose and hemicellulose) can be used as the best source of fermentable sugars [13]. Accordingly, the first-aim of this study was directed to estimate the Jatropha curcas leaves in bioethanol production. Additionally, nowadays, elimination of pollutant such as heavy metals and dyes from contaminated industrial effluents becomes one of the most important concerns. The discharge of untreated industrial effluents into natural ecosystems stream is a big environmental problem that destroys the ecosystems [14]. Crystal violet (CV) also known as Gentian violet or Basic violet 3 is a synthetic dye that is classified under the cationic triphenyl methane dyes. This is the most common dye used in the paper and textile industry. It has been concluded that this dye can cause harmful effects on flora and fauna and had a carcinogenic effect on human health [15]. There are a lot of conventional strategies such as membrane-filtration, biological oxidation, coagulation, and adsorption used for dye-industrial effluent treatment [16]. However, these methods recorded some limitations, for example, their high-energy demand, high cost, slow dye removal process, large amount of chemical requirements, and hazardous byproducts [17]. There is a need for more environmentally acceptable and cost-effective techniques such as biosorption for dye-industrial effluent treatment [18]. Application of agriculture wastes, biomass, are considered an effective and low-cost biosorption materials for the safe disposal of dyes from contaminated wastewater [19]. However, there is a limitation to the application of agricultural wastes in the removal of dyes from the contaminated wastewater due to difficulty in the collection after treatment. Therefore, a combined strategy by incorporation of the agricultural wastes with a proper polymer is a good way to overcome the collection difficulty. Polymers are constructed from monomers that could be organic, inorganic, or organometallic. Looking for a low-cost and available commercial polymer that could be easily combined with the agriculture wastes attracted the attention of the scientists [20, 21]. Poly vinyl chloride (PVC) was selected as a good polymer for the intended application in the present work. Therefore, the second-aim of this work was directed to increase the applications and add more value to the Jatropha curcas leaves by utilization of the unhydrolyzed waste produced after bioethanol production. This application was in the removal of industrial wastewater contaminated with CV as a low-cost and green biosorption process. First of all, the Jatropha curcas leaves were collected from their trees that irrigated with diver’s water sources; sewage-water (A), sewage-water-sludge (B), and tap water (C) as a control. The aim of the present work was directed to increase the applicability of various Jatropha curcas leaves via two applications. The first application was in the manufacture of bioethanol using acid hydrolysis to produce simple fermentable sugars. These sugars were fermented at the batch flask level by two yeast strains before being upscaled to a fermenter scale (10-l bioreactor) for maximum bioethanol production. The second application was the formation of various composite sheets using unhydrolyzed materials (wastes left after bioethanol production). In order to characterize these composite sheets, FT-IR and SEM, porosity, and swelling were performed. These composite sheets were employed in the removal of CV from contaminated synthetic wastewater. The removal efficiency process was optimized using OFAT method and a full-factorial design. Afterwards, the Langmuir and Freundlich isotherms and kinetics studies were used to analyze the experimental data.

2 Materials and methods

2.1 Bioethanol production

2.1.1 Planting, collection, and preparation of Jatropha curcas leaves

Uniform mature leaves of Jatropha curcas were used as a feedstock in this work. Stem cuttings of the Jatropha curcas were sprayed with indole butyric acid and then transported to pots. After root and small leave formation, the plants were transported to a field in “the Drinking and Sewage-water Treatment Station in Al-Gabal Al-Asfar, Cairo, Egypt,” then divided into three groups. The first, the second, and the third were irrigated by sewage-water (A), sewage-water-sludge (B), and tap water only (C), respectively. The leaves from the all three groups were collected after a month from planting. The fresh leaves were used for the determination of photosynthetic pigments (chlorophyll (a), chlorophyll (b), and carotenoids) as previously reported [22]. Moreover, cellulose and hemicellulose estimation were detected at a room temperature using alkaline peroxide method [23]. The determination methods for extraction and determination of lignin were achieved as previously reported [24].

For bioethanol production from the collected Jatropha curcas leaves, the leaves were initially crushed into small pieces and dried in sunlight to achieve a constant weight. Afterwards, they were grinded and sieved to a constant size (≈ 0.8 − 1.0 mm). The dried leaves were reserved in a protected bottles for further work.

2.1.2 Hydrolysis of Jatropha leaves

100 ml of 4% H2SO4 and five grams of each Jatropha curcas leaves were combined in an Erlenmeyer flask (250 ml). To stop acid from evaporating, due to heat, the flasks were sealed with stoppers. The flasks were separated into solid and liquid components after being autoclaved at 120 °C for 20 min. After being neutralized, the filtrate (acid hydrolysate) was used for the fermentation process and the bioethanol production. While the solid part (the unhydrolyzed materials) was used as a biosorption material in the PVC composite sheets for CV removal.

The activated charcoal was added to the acid hydrolysate at a ratio of 1:20 w/v charcoal: sample. The mixture was then stirred for two days at room temperature using a magnetic stirrer. Following that, the charcoal was eliminated using filter paper No. 5 (Whatman, Germany) [25, 26]. At the end, the total reducing sugars (TRS) content in the acid hydrolysates were estimated as previously reported [27]. The change in color’s intensity was determined at wavelength of 540 nm, using a spectrophotometer (Model Jasco V- 570).

2.1.3 Fermentation at a flask level

The fermentation process for different Jatropha curcas leave’s hydrolysates were accomplished in 100 ml flasks with 50 ml of the fermentation media under oxygen-defined setting. The fermentation media consisted of different Jatropha curcas leave’s hydrolysates supplemented with 10 g/l peptone, 2 g/l KH2PO4, and 1 g/l MgSO4·7H2O at a pH value of 5.5. The flasks were sterilized at 120 °C for 20 min. Afterwards, the flasks were inoculated with 10% (v/v) yeast suspension (≈ 1 × 105 cells/ml). The two yeast isolates (Saccharomyces cerevisiae -Y39 and Candida tropicalis—Y26) were utilized for the fermentation process. These isolates were previously isolated from lignocellulosic wastes, characterized, evaluated for their capacity to ferment different kinds of sugars and their applicability in bioethanol production and selected upon their distinguishing characteristics [28]. The yeast suspension for inoculation was prepared as recorded previously [28]. After inoculation, the flasks were cultivated at 30 °C for an incubation period of 48 h. Then, the produced bioethanol was determined in each hydrolysate by gas chromatography with a flame ionization detector (6890, Agilent G1530A, USA).

2.1.4 Fermentation at a bioreactor level

The bioethanol batch fermentation of the optimum hydrolysate was performed separately in a self-sterilizer 10 l bioreactor (Biotron Liflus SL, Korian Republic) with a working capacity of 5 l of hydrolysate supplemented with 10 g/l peptone, 2 g/l KH2PO4, and 1 g/l MgSO4.7H2O. The pH was adjusted to 5.5. After the sterilization step, the hydrolysate was cooled and then inoculated with 10% (v/v) yeast suspension (≈ 105 cells/ml). The batch fermentation was conducted for 48 h, under anaerobic conditions at 30 °C and a stirring speed of 50 rpm. Then, the samples were collected every 6 h and the bioethanol concentrations were determined using GC with details previously reported [28].

2.2 Preparation of composite sheets

Polyvinyl chloride (PVC) sheets were prepared via using phase inversion technique as described previously in literature [29, 30]. Briefly; PVC polymer (1.5 g) was dissolved in (8.5 ml) DMF solvent under stirring for about 4 h. The dried and grinded wastes [unhydrolyzed wastes left after bioethanol production from the three types of Jatropha curcas leaves (A, B, and C)] (0.225 g) were added separately to the polymer solutions under vigorous stirring to obtain polymer solution containing 15% Jatropha curcas waste. The polymer-waste dispersion was casted on a glass plate using a film applicator with a thickness of 200 µm. The glass plate with the casted polymer dispersion were immersed directly in water as a coagulation medium to precipitate the polymer sheet. The precipitated sheets were separated from the glass plate and the water was changed to get rid of any traces of solvent. The prepared composite sheets were left in the pure water for 24 h then removed and dried in the air to be ready for characterization and adsorption study.

2.3 Characterization’s methods of the composite sheets

2.3.1 Swelling and porosity performance of the composite sheets

The swelling test of the PVC composite sheets was performed using a wet/dry weight method via immersion of the three samples (2 × 2 cm2) for each sheet in a pure water for 24 h. Afterwards, the wet weighted was listed after wiping the excess water using tissue paper; then, the sheets were dried at 100 °C until a constant weigh was reached [31]. The swelling was estimated as follows

$${W}_{s}= \left({W}_{wet}- {W}_{dry} / {W}_{dry}\right) \times 100$$
(1)

where Wwet and Wdry are the weight of the swelled and dried sheet samples, respectively

Moreover, the porosity examination of the composite sheets was assessed using a weight method. The wet and dry weight of the sheets were recorded as mention previously and the porosity was evaluated using the following equation:

$$\varepsilon \left(\%\right)= \left[\left({W}_{wet}- {W}_{dry}\right) / {d}_{w}Ah\right] \times 100$$
(2)

where ε is a porosity percentage of the composite sheets, dw is a water density (0.998 g/cm3), A is a surface-area of the wet state of the sheet (cm2), and h is the sheet’s thickness in its wet state (cm).

2.3.2 FT-IR spectra of the composite sheets

The functional groups of the dried composite sheets with and without the wastes were checked using ATR-FTIR spectra (Shimadzu 8400, Japan) at a range of 400 and 4000 cm1.

2.3.3 SEM of the composite sheets

The morphology of the composite sheets-surface and the cross-section was observed using a scanning electron microscopy (SEM) (QUANTA FEG 250 ESEM). Before the evaluation, the PVC composite sheets were coated using the gold vapor via S150A Sputter Coater- Edwards.

2.4 Removal process optimization

2.4.1 Effect of time intervals on the removal efficiency

Different time intervals 15, 30, 60, 120, 180, and 240 min were implemented in order to attain the optimum time intervals that achieves high CV removal efficiency. A 100 ppm of the CV concentration was applied in the media using 2.5 g/l of the composite sheet sorbent material at pH 7. Afterwards, the concentration before and after the process were measured using UV–vis spectroscopy (Cary 100, Agilent Technologies, Santa Clara, CA, USA) at 592 nm, and the results of removal efficiency (RE) were calculated using the following equation:

$$\mathrm{Removal efficiency} \left(\%\right)=\frac{{C}_{o}-{C}_{e}}{{C}_{o}}\times 100$$
(3)

where Co is the initial CV concentration and Ce is the final CV concentration.

2.4.2 Effect of crystal violet concentrations on the removal efficiency

Different CV concentrations—100, 200, 300, 400, and 500 ppm—were investigated by using 2.5 g/l of the composite sheets and at pH value of 7. The CV concentrations were explored after the selected contact time and their removal efficiency was computed.

2.4.3 Factorial design experiment

In order to identify the ideal parameters that provide high crystal violet removal effectiveness, a general full factorial design experiment was performed. The achieved data were analyzed using Minitab 18. Main. Furthermore, the main, interaction effects, the Pareto chart, and the response optimizer effects were plotted and discussed.

2.5 Isotherm studies

Langmuir and Freundlich isotherms were performed in order to demonstrate the composite sheets adsorption nature for the CV removal process. The isotherm models were displayed as previously described [32, 33].

Langmuir isotherm [32]

$$\frac{\text{Ce}}{{\text{Qe}}}\text{=}\frac{\text{Ce}}{{\text{Q}}{\text{max}}}\text{+}\frac{1}{{\text{b}} \, {\text{Q}}{\text{max}}}$$
(4)

where Qe is the amount of crystal violet that adsorbed per unit mass onto the composite sheets at equilibrium (mg/g), Qmax is maximum adsorption capacity of the composite sheets (mg/g), and b is Langmuir constant that relates to the heat of adsorption (l/mg).

Freundlich isotherm [33]

$${Log q}_{e}={Log K}_{f}+\frac{1}{n}{Log C}_{e}(2)$$
(5)

where qe is the equilibrium adsorption capacity (mg/g), \({C}_{e}\) is the equilibrium concentration of crystal violet in the solution (mg/l), and \({K}_{f}\) and n are the Freundlich constants that expressed the adsorption limit and adsorption density, respectively.

2.6 Kinetics modeling studies

The pseudo-first order (1st) and pseudo-second (2nd) order models [34, 35] were applied to evaluate the composite sheet adsorption kinetics of the CV removal from polluted synthetic wastewater.

Pseudo-first-order model [34] were evaluated using the following equation:

$$Ln \left({q}_{e}-{q}_{t}\right)=Ln {q}_{e}-{K}_{1} t$$
(6)

where \({q}_{t}\) and \({q}_{e}\) are the measure of the crystal violet adsorbed at time t and equilibrium (mol/g) respectively, k1(min−1) is the rate constant for this model.whereas the rate of pseudo-second-order model [35] was studied using the following equation:

$${~}^{t}\!\left/ \!{~}_{{q}_{t}}\right.= {~}^{t}\!\left/ \!{~}_{{q}_{e}}\right.+\frac{1}{{K}_{2}{q}_{e}^{2}}$$
(7)

where K2 is the rate constant of sorption for this model (g/mol min), and \({q}_{e}\) and \({q}_{t}\) are the quantities of adsorbed crystal violet at an equilibrium and at a time t (mol/g), respectively.

3 Results and discussions

3.1 Photosynthetic pigments content and chemical composition of Jatropha curcas leaves

The photosynthetic pigment’s content in the Jatropha curcas leaves can be employed as a major indicator of the physiological status of the plant. Chlorophyll (a) and chlorophyll (b) are essential pigments in converting the light energy to the chemical energy [36, 37]. Therefore, the chlorophyll (a &b) and carotenoid were determined in this study (Table 1). The sewage-water represents a rich source of both macro and micronutrients that are necessary for the plant growth such as N, P, K, Fe, Mn, Zn, and Cu [38, 39]. The transition metals have an essential role in various metabolic processes in plants particularly, the photosynthesis process as they act as regulator elements and cofactors of metalloproteins involved in the photosynthetic electron transport chain [40]. In this regard, many researchers reported that sewage-water stimulated photosynthesis in various crops [41]. In this context, it was observed that the content of the photosynthetic pigments (chlorophyll (a), chlorophyll (b), and carotenoids) in Jatropha curcas leaves was positively affected by irrigation with sewage-water alone (318.0, 153.3, and 73.7 µg/g) or with the addition of sludge (221.1, 135.3, and 62.78 µg/g) (Table 1). This result may be attributed to the increment of Mg+2 and Fe concentrations in the sewage-water which plays an important role in the biosynthesis of chlorophyll [42]. Irrigation with the sewage-water and/or the sewage-water-sludge remarkably elevated the rate of plant pigment’s biosynthesis and thus the photosynthetic rate. Furthermore, the application of the sewage sludge increased soil fertility by lowering pH and increasing nitrogen and phosphorus content. This may be due to an increase in the number and size of green leaves [43]. The significant promoting effects of the sewage-water on the photosynthetic pigment’s content was concomitant with the increases in the cellulose and hemicellulose content. Thus, the leaves of Jatropha curcas plants irrigated with the sewage-water or the sewage-water-sludge had higher cellulose (22.6 & 20.0%, respectively) and hemicellulose (19.5 & 18.1%, respectively) contents than the plants irrigated with the tap water (14.8 & 10.3%, respectively) (Table 2). These results were higher than the cellulose and hemicellulose content (8.96& 17.71%, respectively) of Jatropha curcas leaves previously reported [44].

Table 1 Effect of irrigation with different water sources; sewage water (A), sewage water and sludge (B), and tap water only as a control (C) on photosynthetic pigment’s contents of Jatropha curcas leaves
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Table 2 Effect of irrigation with different water sources; sewage water (A), sewage water and sludge (B), and tap water only as a control (C) on cellulose, hemicellulose, and lignin contents of Jatropha curcas leaves
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3.2 Bioethanol production from Jatropha curcas leaves

3.2.1 Jatropha leaves hydrolysis

The Jatropha leaves from various irrigation sources were hydrolyzed by 4% H2SO4 to achieve the maximum yield of TRS production. Acid hydrolysis is explored as the highest method for freeing the TRS from different lignocellulosic wastes [9, 10, 45, 46]. Results reported in Table 3 displayed that the hydrolysis of the Jatropha curcas leaves from the plant irrigated with the sewage-water only (A) or the combination of sewage-water-sludge (B) produced higher values of TRS (≈ 21 & 17 g/l, respectively) than the irrigation with tap water (C) (≈ 11 g/l). Because the total reducing sugars were produced by the hydrolysis of carbohydrate components, mostly cellulose and hemicellulose [47], this result can be attributed to the rising cellulose and hemicellulose concentration (see Table 2).

Table 3 The total reducing sugars (TRS) produced from acid hydrolysis (4% H2SO4) of Jatropha curcas leaves irrigated by different irrigation sources; sewage water (A), sewage water and sludge (B), and tap water only as a control (C)
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Moreover, the noticeable concentrations of the organic and inorganic minerals that detected in the sewage-water and sludge were to blame for this increase since they would enhance and improve the photosynthetic machinery and cause a significant increase in carbohydrate content [5]. Additionally, the low levels of lignin in Jatropha curcas leaves makes it easier for cellulose and hemicellulose to be hydrolyzed, and hence higher TRS concentration generation.

During acid hydrolysis, some monomeric sugars such as xylose and glucose were transformed into furfural and hydroxymethyl furfural. These compounds can prevent yeast from growing during the fermentation process because they are harmful to yeast. Effective methods for lowering the concentration of these fermentation inhibitors are detoxification treatments. One of the approaches that are most frequently used during the detoxification method is the activated charcoal [48]. Therefore, the acid hydrolysates were detoxified by the activated charcoal method in this study. The activated charcoal has many benefits, which include its structural porosity, immense surface area, high adsorption adequacy, well-developed microporosity, and a broad range of surface functional groups. Furthermore, the cost-effectiveness of activated charcoal and its lack of significant impact on the concentration of fermentable sugars recovered in the pretreatment hydrolysate [49].

3.2.2 Fermentation at a flask level

The TRS produced from different Jatropha leaves after H2SO4 hydrolysis were fermented for bioethanol production by C. tropicalis Y-26 in addition to S. cerevisiae Y-39 (see Fig. 1). The concentrations of the produced bioethanol from the Jatropha leaves hydrolysate fermentation by C. tropicalis were considerably related to treatment the irrigation by sewage-water (A) either alone (7.057 ml/l) or with sludge (B) (5.211 ml/l) than tap water only (C) (3.685 ml/l). Furthermore, the fermentation by S. cerevisiae confirmed that the fermentation of the hydrolysate of Jatropha curcas leaves that previously irrigated by the sewage-water (A) and the sewage-water-sludge (B) gave a significant increase in the ethanol concentration (4.718 & 3.476 ml/l) in comparison to the tap water (1.756 ml/l) (Fig. 1). This increase in the ethanol concentrations can be correlated with the increase in the TRS concentrations in these hydrolysates compared to the hydrolysate from the Jatropha curcas leaves that past irrigated by the tap water only (C) (Table 3). Finally, the fermentation of the leave’s hydrolysates of Jatropha curcas using C. tropicalis Y-26 gave a high bioethanol concentration than Saccharomyces cerevisiae Y-39. Furthermore, the hydrolysate obtained from the past irrigation with sewage-water (A) was the best source for ethanol production from Jatropha leaves.

Fig. 1
figure 1

The bioethanol concentration produced from the fermentation of different Jatropha curcas leaves hydrolysate (A: the plant previously irrigated by sewage-water, B: the plant previously irrigated by sewage-water-sludge, and C: the plant previously irrigated by tap water) by Candida tropicalis Y-26 and Saccharomyces cerevisiae Y-39 at a flask level

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3.2.3 Fermentation at a bioreactor level (scaling up)

After the fermentation of the Jatropha leaves hydrolysate at the flask level, the fermentation was scaled up at a bioreactor level. The hydrolysate with the maximum reducing sugar yield from acid hydrolysis of Jatropha leaves irrigated by sewage-water (A) was further fermented by C. tropicalis Y-26 in addition to S. cerevisiae Y-39 at the bioreactor level (see Fig. 2). During the fermentation by C. tropicalis Y-26, the concentration of bioethanol increased with the time, and the highest bioethanol concentration (10.014 ml/l) was obtained from the fermentation at a bioreactor after 36 h incubation period. In addition, during the fermentation process by using S. cerevisiae Y-39, the highest bioethanol concentration (6.912 ml/l) was achieved from fermentation at the bioreactor level after a 42 h incubation period. Different factors, such as temperature and pH, were easily controlled in the bioreactor and stayed within the optimal range throughout the entire fermentation period. Thus, the bioethanol concentration and yield (ml ethanol/g sugars) obtained from the bioreactor scale by C. tropicalis Y-26 (≈ 10 ml/l; 0.5 ml/g sugars) was increased relatively in comparison to the bioethanol concentration obtained from the fermentation at the flask level (≈ 7 ml/l; 0.3 ml/g sugars). In addition, during the fermentation process by using S. cerevisiae Y-39, the bioethanol concentration and yield obtained from the bioreactor scale (≈ 7 ml/l; 0.3 ml/g sugars) was also increased relatively than the bioethanol concentration obtained from the fermentation at the flask level (≈ 5 ml/l; 0.2 ml/g sugars). This result agreed with the results obtained by Madian et al. [46], they observed that the ethanol concentration from the fermentation of giant reed by Candida tropicalis at a bioreactor scale (25 g/L) was higher than those from the fermentation at flask level (21 g/L). Furthermore, the maximum concentration of ethanol produced in this study from Jatropha curcas leaves (10 ml/l) by Candida tropicalis was higher than those from Jatropha curcas seedcakes (5 ml/l) demonstrated by Taha et al. [9].

Fig. 2
figure 2

The bioethanol concentration produced during the fermentation of Jatropha curcas leaves hydrolysate (the Jatropha curcas plant previously irrigated by sewage-water only) by Candida tropicalis Y-26 and Saccharomyces cerevisiae Y-39 at a bioreactor level

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3.3 Characterization’s methods of the ground wastes

The unhydrolyzed wastes left after bioethanol production from the three types of Jatropha curcas leaves (A, B, and C) were ground using a ball mill to obtain very fine particle. The particles size of the wastes was measured using a dynamic light scattering (DLS) device (Nano ZS, Malvern Instruments Ltd., Malvern, UK) and results indicated that average particle size ranges were 143, 175, and 200 nm for the wastes of A, B, and C, respectively. Zeta potential of the ground wastes was also determined to evaluate the surface charges of the waste nanoparticles. The obtained zeta potential reading − 23.7, − 11.5, and − 13.8 mV for A, B, and c wastes, respectively. The negative zeta potential of the ground waste indicated the polar negatively charged function groups attributed mainly to the hydroxyl and carboxylate groups which may participate in adsorption process of the CV from waste water.

3.4 Characterization’s methods of the composite sheets

The FT-IR spectra of the PVC sheet (blank) and the PVC with the dried and ground wastes [unhydrolyzed wastes left after bioethanol production from the leaves of Jatropha curcas plant that previously irrigated by various irrigation sources and embedded in a PVC sheet; sewage-water (PVC-A), sewage-water-sludge (PVC-B), and tap water only as a control (PVC-C)] were shown in Fig. 3. The blank PVC sheet spectrum indicated that bands at 2850 and 2914 cm−1 corresponding to stretching modes of CH and CH2, respectively, the band at 1429 and 1330 cm−1 attributed C-H bending modes. The bands at 615 and 717 cm−1 related to C − Cl bond. After incorporation of the wastes left after bioethanol production, the spectra showed the new peaks at 1623 and 1720 cm−1 interrelated to C–O and C = O bonds, respectively. The peak appeared at 3360 cm−1 corresponding to O–H of polysaccharides present in cell wall of plant leaves [50].

Fig. 3
figure 3

FT-IR spectra of the PVC (blank sheet) and their composite sheets (the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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The morphology of the blank PVC and PVC composite sheets of the dried and ground wastes (PVC-A, PVC-B, and PVC-C) was observed (see Fig. 4). The surface of the PVC sheet (see Fig. 4 left) seemed smooth with the appearance of tiny pores that cover the whole surface of the sheet. The related cross-section of the sheet (Fig. 4 right) showed a macro-void structure resulting from a spontaneous de-mixing process of the solvent and the nonsolvent solutions during the sheet preparation process using the immersion precipitation technique [51]. After embedding the dried and ground unhydrolyzed wastes to the sheets, the results demonstrated more surface pore structure with a slightly rough structure. In some sheets, there is an appearance of some dried and ground waste particles of Jatropha leaves on the sheet surface that indicated the well mixing of the fine ground powder within the sheet matrix. The macro-voids of composite sheets were enlarged compared to the blank sheet.

Fig. 4
figure 4

SEM of surface (left) and cross-section (right) of the PVC (blank sheet) and their composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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The swelling characteristics of blank PVC and PVC composite sheets of the dried and ground unhydrolyzed wastes are presented in Table 4. The swelling properties were an indication of hydrophilicity of the sheets. As shown in Table 4, the swelling of the PVC sheet was largely increased from 260% for blank PVC to 544–617% by incorporation of the dried and ground unhydrolyzed wastes. The increase in the swelling percentage was resulted from the increasing the hydrophilic functional groups like hydroxyl-groups, amino-groups, carboxyl-groups, and other groups that may found in the cell wall components of the Jatropha curcas [52, 53].

Table 4 The swelling and the porosity measurements of the blank PVC and the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)
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The porosity of the composite sheets was also largely increased from 8.4% for the blank PVC to about 20% by incorporation of the three wastes Jatropha curcas leaves (see Table 4). The enhancement of the porosity may be due to the presence of hydrophilic powder in the polymer matrix which enhance and favor the formation of the macro-voids during sheet manufacturing. The results of the porosity measurement using this weight method are matched with our SEM results particularly with the cross section that indicated the enhanced macro-void formation and hence enhance the porosity results. The enhanced swelling and porosity properties for the composite sheets will result in free movement of the polluted water into the sheet’s matrix which favor large and free surface area for adsorption process.

3.5 Removal process optimization

3.5.1 Effect of time intervals on the removal efficiency

Figure 5 exhibits that the increase in the contact time leads to an increase in the removal efficiency of the composite sheets towards the crystal violet dye. By increasing the contact time, the swelling performance of the sheets increased, and hence, more polluted molecules diffuse into the bulk of these sheets resulted in an increase in the removal efficiency. The highest crystal violet removal efficiency of 89.3, 66.8, and 49.8% for the composite sheets of PVC-A, PVC-B, and PVC-C, respectively, was obtained after 240-min contact time when using 2.5 g/l of the composite sheet’s dose.

Fig. 5
figure 5

Effect of time intervals on the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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3.5.2 Effect of crystal violet concentrations on the removal efficiency

It was observed that the crystal violet removal efficiency was decreased by increasing the crystal violet concentration from 100 to 500 ppm (see Fig. 6). It is noted also that the removal efficiency of the PVC-A was higher than other sheets. This result may attribute to its higher swelling and porosity rather the others. The highest crystal violet removal efficiency of the PVC-A, PVC-B, and PVC-C was decreased from 89.3, 66.8, and 49% to 77.3, 63.6, and 48%, respectively, by increasing the concentration from 100 to 200 ppm crystal violet by using 2.5 g/l of the composite sheets, after 240-min contact time. The decrease in the removal efficiency by increasing the dye concentration may be due to the saturation of reactive functional groups responsible for adsorption with high density of the polluted molecules at high concentrations.

Fig. 6
figure 6

Effect of crystal violet concentrations on the removal process of crystal violet using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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3.5.3 Factorial design experiment

In the current study, the effect of different combined factors (time, dose, CV conc., and material type) on CV removal efficiency was studied. The low and high levels of all factors are summarized in Table 5. The experimental matrix design was reported in Table 6.

Table 5 Low and high levels of general full factorial design experiment for crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)
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Table 6 Matrix design of general full factorial design experiment for crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)
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Main effects

Main effects that have been showed in Fig. 1S and factor coefficient Table 7 demonstrated that time, dose, and conc. showed a significant effect on the removal process of the CV, while material type displayed no significant effect [54]. The increasing change in the levels of time and dose factors from low to high levels assumed the positive response of these two factors on the CV removal efficiency. Increasing in time and dose leaded to an increase in the removal efficiency. On the other hand, the decreasing in the CV concentration, shifted from low to high levels, indicated a negative response of the CV concentration on its removal efficiency, which means the removal efficiency decreased by increasing the concentration.

Table 7 Factors coefficient of general full factorial design experiment for the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)
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Interaction effects

The interaction plot is the studying the effect of the interacted time, dose, conc., and material type factors on the CV adsorption process [55] (see Fig. 2S). The P-value that is observed in Table 7 suggested that the interaction between time and conc., time and dose, conc, and dose, and dose and material type factors displayed a significant effect on the removal process of the crystal violet. Additionally, the non-parallel line that was observed in the interacted factors Fig. (2S) stated that dose and material type had a positive interacted effect on the CV removal efficiency.

Pareto chart

The Pareto chart graph (see Fig. 6S) recorded a t-value of 4.30 at 95% confidence’s intervals and sixteen’s freedom degrees where the values were expressed by a reference line on the Pareto chart [56]. The values, which exceeded the t-value line, were represented as significant values; nevertheless, values that did not exceed the line were represented as non-significant values. According to the previous assumption, it can be demonstrated that CV conc. (B), composite sheet dose (C), time (A), interacted factors time and dose (AC), dose and material, conc. and dose, and time and conc. were reported as significant values that have effects on the removal efficiency of the crystal violet. Furthermore, the results obtained from the Pareto chart confirmed the results previously achieved from the main and the interaction effects.

Response optimizer effects

The response optimizer is the plot that expects the best integrated-effects that display the highest CV removal efficiency [54]. In the current study, the effect of an integration between time, dose, CV conc., and material type was studied to obtain the highest CV removal efficiency. Results represented in Fig. (4S) proposed that the highest CV removal percent of 95.39% was achieved at 100 ppm CV concentration using 5 g/l from PVC-A composite sheet dose after 180-min contact time with 1° of desirability. The predicted result is nearly equal to the calculated one obtained in matrix design Table 7, where the CV removal efficiency of 94.7% was obtained at the same conditions.

3.6 Isotherm studies

The obtained data (see Figs. 7, 8 and Table 8) assumed that the Freundlich isotherm was more fitted to the data of the CV adsorption process by PVC-A, PVC-B, and PVC-C composite sheets than Langmuir isotherm as a result of high R2 that was noticed in the state of the Freundlich isotherm. This result suggested that the CV was adsorbed in multilayers on a heterogeneous surface [57]. Furthermore, the Qmax values of the composite sheets displayed that the PVC-C composite sheet was the most efficient composite sheet with Qmax of 119 mg/g followed by the PVC-A with Qmax of 112 mg/g, and 87 mg/g in the state of the PVC-B composite sheet.

Fig. 7
figure 7

The Langmuir isotherm of the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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Fig. 8
figure 8

The Freundlich isotherm of the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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Table 8 Isotherm parameters for the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)
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3.7 Kinetics studies

The linear plots of the pseudo-first-order (1st) and pseudo-second-order (2nd) are shown in Figs. 9, 10 and Table 9 for the CV removal using the three different composite sheets PVC-A, PVC-B, and PVC-C. It was observed that the 2nd order kinetics fits well with the results of the three composite sheets due to the high correlation coefficient of R2 values and the closer values of Qe experimental and calculated values as previously reported [58].

Fig. 9
figure 9

The pseudo 1st order kinetics of the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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Fig. 10
figure 10

The pseudo 2nd order kinetics of the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)

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Table 9 Kinetics parameters for the crystal violet removal using the PVC composite sheets (the PVC and the unhydrolyzed wastes left after bioethanol production; PVC-A, PVC-B, and PVC-C)
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4 Conclusion

Jatropha curcas leaves were successfully collected from the plants irrigated by different sources. The collected leaves from various irrigation sources were used as suitable renewable and available feedstock for bioethanol production and the removal of crystal violet from synthetic wastewater. After the acid hydrolysis of these leaves, the order of the TRS production was arranged as A > B > C (≈ 21, 18, 11 g/l, respectively). Then, the fermentation of these sugars at a flask level demonstrated that the fermentation of Jatropha curcas leaves hydrolysate (A) produced the maximum TRS than other treatments (B and C). The bioethanol concentration and yield obtained from the fermentation of this hydrolysate (A) by Candida tropicalis Y-26 at the bioreactor (10 l) scale (≈ 10 ml/l; 0.5 ml/g sugars) were higher than the bioethanol concentration and yield obtained from the flask (≈ 7 ml/ l; 0.3 ml/g sugars). The PVC sheet (blank) and the PVC with the dried and ground unhydrolyzed wastes (PVC-A, PVC-B, and PVC-C) were successfully achieved and applied in the removal of crystal violet from synthetic wastewater. According to the optimization process by full factorial design, 100 ppm crystal violet concentration, 2.5 g/l from PVC-A composite sheet, and 240-min contact time were the optimum factors that achieved the highest crystal violet removal percent (95.39%). The removal process was fitted more to the Freundlich isotherm and the pseudo-second order kinetics model. Finally, this study has successfully added two more potentials to the Jatropha curcas leaves as they were applied in bioethanol production, and their unhydrolyzed wastes were successfully applied in the removal of crystal violet from wastewater. In future studies, further optimization experiments could be performed in hydrolysis and fermentation processes to detect the optimal factors for maximal bioethanol production. Additionally, the ability of these sheets to remove other heavy metals and dyes from industrial wastewater has also been shown.