Preparation of an activated adsorbent from water treatment plant sludge for phosphate removal from wastewater: optimization, characterization, isotherm, and kinetics studies

Water consumption is rapidly increasing globally, as has been observed in the past two centuries. However, water quality deterioration continues to increase. Water resources are getting increasingly polluted due to anthropogenic and natural reasons (Lu et al. 2015). Phosphorus is a major source of water contamination. Eutrophication is also caused by the excessive release of phosphorus into water and results in water quality degradation. Wastewater runoff containing excess phosphorus species is a major environmental issue worldwide, as the nutrient leads surface water bodies to eutrophication. Various human activities, such as mining and industrial and agricultural use, release phosphorus into the aquatic system (Ali et al. 2019).

The increase of phosphate in water bodies promotes the growth of algae, which results in eutrophication and eventually consumes dissolved oxygen thereby adversely affecting the water quality (Xu et al. 2016; Berkessa et al. 2019). Municipal and industrial wastewaters are the main point sources for phosphate while runoff from agriculture is the dominant non-point source. Studies indicate that municipal wastewater may contain 4–15 mg/L phosphate, whereas effluent from chemical industries such as detergent manufacturing and metal coating processes may contain 14–25 mg/L phosphate (Afzaal et al. 2022; Kiprono et al. 2023). According to Kang & Cao (2014), the tolerable phosphate level in water should not exceed 0.05 mg/L to maintain an ecologically sustainable status. In such a case, lowering the phosphate loading in wastewater and runoff especially if local circumstances do not allow for advanced techniques such as membrane filtration became a challenge to local scientists and engineers (Rehman et al. 2018). The most widespread wastewater treatment technology for phosphate removal is based on precipitation processes, in which massive amounts of chemicals such as iron and aluminum salts are utilized (Adhikari et al. 2016). However, many techniques are suffering from either large amounts of sludge for disposal or high operational and maintenance costs with recurring expenses, which are not suitable for many developing countries such as Ethiopia. Therefore, searching for cost-effective and environmentally sound phosphate removal alternatives for low-income countries is essential.

A variety of physical, chemical, and biological methods have been developed in recent years for the phosphate removal from wastewater (Yan et al. 2014; Acelas et al. 2015; Mor et al. 2016; Usman et al. 2022). Advanced biological methods can remove up to 97% of phosphate and generate low amounts of sludge, but the method has limited applicability (Nobaharan et al. 2021). Similarly, physical processing (sedimentation, membrane filtration, etc.) techniques are too expensive, are accompanied by a high sludge production, and are often inefficient in the phosphate removal from wastewater effluent (Al Tahmazi 2017; Banks et al. 2020).

Adsorption emerges as a robust process that could solve the aforementioned problems and render the treatment system more economically viable, especially if low-cost adsorbents are involved (Renu et al. 2017; Nadew et al. 2023). Water treatment processes produce millions of tons of solid waste annually worldwide, and the amount of sludge produced rises in tandem with rising water consumption. With an estimated 10,000 tons of dry water treatment residual produced daily worldwide, managing water treatment plant sludge (WTPS) continues to be a difficult environmental and financial issue for all water authorities (Nguyen et al. 2022). Landfills, once the default dumping ground for water treatment sludge, are filling up and revealing their environmental downsides. The cost of this disposal method is skyrocketing, prompting a shift toward circular economy solutions. Recovering, reusing, and recycling sludge are no longer fringe ideas but essential steps for water utilities seeking sustainable resource management. Circular economy eliminates waste, not by burying it but by finding new life for materials – a paradigm shift offering a welcome escape from the linear pitfalls of the past (Jung et al. 2016).

The effectiveness of water treatment sludge as a coagulant and an adsorbent of pollutants in water treatment has been demonstrated by many studies (Drechsel et al. 2015; Ooi et al. 2018; Bensitel et al. 2023; Kumari et al. 2023). However, the use of activated water treatment sludge for water purification or removal of impurities from wastewater is not yet more common and not pronounced. Therefore, this study aimed to synthesize activated adsorbent material from WTPS for the phosphate removal impurities in water. The study mainly focused on the investigation of phosphate removal efficiency from synthetic and wastewater treatment effluents by the adsorption process.

The WTPS was collected from the Legedadi water treatment plant in Addis Ababa, Ethiopia. The treatment plant is situated at a height of 2,450 m above sea level and in the geographic coordinates of 38° 60′ to 39° 07′ E longitude and 9° 01′ to 9° 13′ N latitude. The plant is 5,324 m² in surface area, with a maximum water depth of 30m and a mean depth of 4 m. The sample was taken from the four discharging points of the treatment plant and mixed well to get a representative sample. Since the quantity and quality of the sludge vary depending on the seasons, samples were collected in the summer and winter seasons. All the reagents and chemicals used for the current investigation were analytical grades used without further purification.

The sludge samples collected from four disposal points in the two seasons were mixed to attain representative samples for further analyses, and all the samples were stored at a low temperature (4 °C). The collected samples were decanted to eliminate the liquid part and retain the sludge. Some unnecessary materials available in the sludge were removed manually, and the remaining sludge was dried in an oven at 105 °C for 24 h. The sample was cooled off to room temperature in a desiccator and then ground using a disk miller to a size of below 130 μm. The prepared sample was stored in a plastic bag to prevent any contamination (Nguyen et al. 2023).

To synthesize an activated adsorbent, the WTPS was subjected to thermal and acid activation processes in a row. The thermal activation processes were performed by putting 30 g of sample into a furnace and thermally treated with 300 °C temperature at a rate of 15 °C/min for 4 h under a continuous supply of nitrogen gas. The nitrogen environment prevents the sample from burning and allows only volatile components to escape (Volperts et al. 2021). When the volatile components are left off at elevated temperatures, it is assumed that a void volume would be created, which promotes considerable surface area of the sample. The sample was then allowed to cool to room temperature and ground to a size of below 100 μm using a hammer miller.

On top of that, the thermally semi-activated sludge was further activated chemically using phosphoric acid to enhance its surface area and porosity and modify its affinity to attract adsorbate yet the more. To that end, three parameters, namely acid concentration, activation time, and activation temperature were used to activate the intermediate adsorbent. To examine the effect that these parameters have on the activation process of WTPS, the level of each parameter was set to a wide range considering that the variables have substantial influence on the adsorbing capacity of adsorbate (Table 1) (Zakaria et al. 2021). Hence, 30 g of partially activated sludge was subjected to different acid concentrations of 1, 2, 3, 4, and 5sM heated at a constant temperature of 75 °C for 4 h to scrutinize the effect of acid concentration variations. The activation process was allowed to take place in a 1 L cylindrical beaker, and the solution was agitated at 300 rpm using a mechanical stirrer to keep uniform temperature distribution and to get a gentle acid–sludge contact. Similarly, the sample activation time was varied from 2, 3, 4, 5, and 6 h while the acid concentration and activation temperature were fixed at 3 M and 75 °C, respectively. Moreover, the range of activation temperature was from 55, 65, 75, 85, and 95 °C to observe its effect on the surface of the adsorbent at a fixed acid concentration of 3 M and activation time of 4 h. In this fashion, 15 samples were activated, settled, neutralized with distilled water, and filtered to retain the solid part. The solid part was then dried at 105 °C for 24 h to remove residual water molecules within.

Proximate determination: The proximate values such as moisture contents, volatile matters, fixed carbons, and ash contents of the raw sludge and prepared activated sludge adsorbent were studied using standard procedures of the American Society for Testing and Materials (ASTM) (Kassahun et al. 2022).

Elemental analysis: The implications of a possible application in the adsorption of phosphate impurities, as well as the suitability and impact on the environment, depend heavily on the elemental analysis. Using CHNS/O analyzers (EMA 502, VELP, China), the elemental analysis of raw and activated WTPS was examined. The elemental composition of raw and activated WTPS (C, H, N, and S) was determined using an ASTM-D5373 method. Five-milligram samples of completely dried WTPS (moisture content < 1%) were weighed into clean tin cups and analyzed using an elemental analyzer calibrated at 1,060 °C combustion furnace temperature. The EMA SoftTM software automatically calculates elemental weight percentages from real-time atomic ratios for each element. To determine the percentage of oxygen (O), the total of C, H, N, and S was deducted from 100% (Rai et al. 2016).

Point zero charge determination: The surface charge of the adsorbent depends on the pH of the solution and, furthermore, depends on its pH of point zero charges, pH_pzc, at which the net charge on the adsorbent surface is zero (Puri & Kumar 2019). The adsorbent surface is negatively charged when pH > pH_pzc and positively charged if pH < pH_pzc (Belachew & Hinsene 2020). To determine the point zero charge of the samples, 3 g of sample was mixed with 50 mL of 0.1 N KNO₃ solution of pH ranging from 2 to 14 at intervals of 2 units. The pH of the solution was made using NaOH and HCl solution in a 1 L flask and gently shaken for 48 h at ambient conditions. The pH of each solution was measured and the net charge (ΔpH) was calculated from the initial and final pH values. The pH values are plotted along the x-axis and ΔpH along the y-axis; the data obtained from the experiment are plotted, and the intersection point is taken as a reference for determining the pH_PZC.

BET surface area study: The surface areas of both raw and activated samples were determined using the surface area analyzer (Horiba 96000 series). The surface area was determined as 0.6 g of samples were weighed and put into the sample preparation unit of the analyzer. The moisture of the samples was removed (degassed) for 1 h at 150 °C temperature, and thereafter the samples were cooled off and weighed. The total surface area of activated WTPS was determined based on the surface area of a single nitrogen molecule, following the procedure used by Nadew et al. (2023).

Scanning electron microscopy (SEM) analysis: SEM was used to analyze the surface morphology and shape of the raw WTPS and activated WTPS adsorbent. The samples were dried in an oven to remove the moisture content to improve the quality of the images. The morphological characteristics of the samples were examined using SEM (JSM-IT 300) by following a standard procedure (Nohl et al. 2022).

Fourier transform infrared (FTIR) spectra analysis: The FTIR analysis was used to obtain qualitative data and complementary evidence for the functional group of the sample. FTIR spectra of both raw and activated sludge samples were performed in the region of 400–4,000 cm⁻¹ and at 32 resolutions and 16 scans (Turki et al. 2018). FTIR spectra were obtained using Spectrum (Thermo Scientific IS50 ABX, Germany) with samples prepared by the attenuated total reflection (ATR) disc method. All the spectra were recorded and processed using IR solution software.

Thermal properties: The thermal properties of raw and activated sludge samples were analyzed using differential scanning calorimetry (DSC; SKZ, 1052B). The samples were heated at a rate of 5 °C/min in a range of temperature from 25 to 125 °C with a void pan as reference. The enthalpy (ΔH, J/g) and the onset (T_on, °C), peak (T_p, °C), and offset (T_off, °C) temperatures of the observed transitions were computed from the thermal curves using the Universal Analysis Program 2,000 (TA Instruments) (Saadatkhah et al. 2020).

To investigate the phosphate removal by activated sludge, different studies with a variety of operating conditions and parameters were carried out. These parameters are contact time, pH, adsorbent dose, and initial phosphate concentration. A preliminary study based on a one variable at a time approach was conducted to limit the range of parameter levels and examine the effect of factors on the adsorption process. Better yet, the phosphate adsorption process on the surface of activated sludge was optimized using the design expert response surface methodology–central composite design (RSM–CCD) approach after the interaction effect of these parameters was studied. The phosphate molecules and activated sludge surfaces were contacted under various circumstances and stirred at 300 rpm on a hotplate magnetic stirrer to perform these experiments.

The criteria for optimization and solving the quadratic equation were set as shown in Table 2.

Isotherm models: In the event of mass transfer within a system or from high concentration to low concentration of a given species, the equilibrium condition is an inevitable phenomenon. To relate the amount of adsorbate present on the surface of the adsorbent and the amount of adsorbate present in a solution when equilibrium is attained, different models were proposed, and the common ones are the Langmuir and Freundlich isotherm models. These models provide basic information and show the distribution of adsorbate molecules in the liquid and solid phases when the system reaches equilibrium (Elkady et al. 2011).

The regeneration and reusability of the activated sludge adsorbent were studied by allowing 3 g of the adsorbent to adsorb 30 mg/L phosphate solution at a pH of 3 for 70 min. The content was shaken at 300 rpm for 70 min to give it enough time so that the adsorbent could take the maximum adsorbate. However, the desorption process was affected by adding 500 ml of 0.1 M NaOH solution to the saturated adsorbent and shaking for 2 h. Finally, it was washed several (three) times using distilled water until the pH became neutral. The supernatant solution was analyzed and the removal capacity was determined. The adsorption–desorption process was repeated five times until the capacity of the adsorbent fell to a considerable level.

The removal efficiency of the activated sludge with respect to the activation time at constant acid concentration and activation temperature is demonstrated in Figure 1(b). The activation time varied from 2 to 6 h at 1 h intervals while the acid concentration and activation temperature were kept constant at 3 M and 75 °C, respectively. It can be seen from the figure that the removal efficiency increases at a considerable rate from 58.6 to 84.1% as the activation time is changed from 2 to 4 h. Afterward, however, the efficiency changes by a small margin and tends to be almost constant to 85.4% efficiency when the activation time approaches 6 h. As time goes by, it seems that some volatile components that assume space in the sample volume escape, and pores, as a result, might be created. It also seems that the pores formed are the reason for the removal efficiency increase in this particular instance. Moreover, it is intuitive that the removal efficiency leans toward a more or less constant value even if the activation time increases yet more.

In a quite similar way, Figure 1(c) illustrates how the variation of activation temperature affects the removal efficiency of the activated WTPS in terms of phosphate molecules adsorbing. The result ascertains that the removal efficiency rapidly increases from 60 to 82.5% due to the change of activation temperature from 55 to 75 °C. Thereafter, the impact of the activation temperature on the activation process of the adsorbent and hence on the phosphate removal efficiency was less. The removal efficiency only increases from 82.5 to 84.5% despite the activation temperature increases from 75 to 95 °C. Given a 3 M acid concentration and 4 h activation temperature, it is evident that the activation temperature has a sound effect on the activation process of the sludge adsorbent. A more or less similar pattern can be seen from the results of Zakaria et al. (2021) where the authors indicated the role of activation temperature even at lower levels.

Proximate result analysis: The moisture content, volatile matter, ash, and fixed carbon content of the prepared raw and activated sludge were determined (Table 3). The physicochemical properties of the activated sludge adsorbent were enhanced following the activation process. It is evident that the activated WTPS has a high fixed carbon content, low moisture content, and low ash content. This could be because the molecules' bonds of the WTPS are broken and the carbon content rises due to the thermal and acid activation process (Kassahun et al. 2022).

Elemental Analysis: A summary of the CHNS/O analysis for the raw and activated WTPS is provided in Table 4. The raw WTPS was found to have a carbon content of 36.18%, which suggests potential uses for valuable adsorbents. The result obtained here is in the range of 25–60% carbon in the dried sludge as in the previous study by Krotz (2019). When compared to its raw WTPS, the activation of WTPS significantly increased the carbon content to 47.63% and decreased the oxygen content by 20%. This might be the result of some volatile substances being eliminated during the calcination process' chemical treatment and double-bonded carbon breakdown (Volperts et al. 2021). After the activation process, only very slight changes were seen in the other N and S.

Surface area analyses using BET: Adsorption is a surface phenomenon where adsorbate finds a way to be attached to the surfaces of the adsorbent. Surface area, therefore, is the very basic nature of the adsorption process. To determine the surface area of the raw and activated sludge, BET analyses were performed. A raw and an activated sample of 0.6 g weight was prepared at 150 °C for 1 h, and the surface area was analyzed in a helium environment and a nitrogen adsorption–desorption system. The surface areas of the raw and activated sludge were found to be 10 and 279.2 m²/g of the sample, respectively. It is evident that the activation process synthesized a relatively high surface area of adsorbent. Some authors like Ros et al. (2006) discussed that the surface area of activated sludge was found to be 200–400 m²/g of the sample when activated in different stages and using different activating agents and impregnation ratios.

Figure 7(b) depicts the removal efficiency of the adsorbent when the pH of the solution varies and contact time, adsorbent dose, and initial concentration are kept constant. It can be observed from the graph that the removal efficiency has a decreasing pattern with respect to the solution pH. From a pH of 1 to 3, it slowly decreases from 86 to 83.5% and sharply drops down to 51.8% as the pH further increases to 7. Since the surface of the adsorbent is positive at lower pH and the adsorbate has a negative nature at all times, it seems quite evident that the removal efficiency is higher at lower pH values. At relatively higher pH values, the adsorbent becomes negatively charged surfaces where both adsorbate and adsorbent assume similar charges. Vunain et al. (2021) indicated a high removal efficiency of chromium at pH in the range of 2–4 and showed a decline in efficiency at a higher pH solution.

The removal efficiency as a function adsorbent dose at constant contact time, pH, and initial concentration is demonstrated in Figure 7(c). As the adsorbent was changed from 1 to 3 g/L step by step, the removal efficiency was found to rise quickly from 60 to 83.8%. When the adsorbent was further increased to 7 g/L with an interval of 1 g/L, however, the efficacy of the activated sludge adsorbent in removing the phosphate molecules from the synthetic solution increased only by a small margin. It seems that it tends towards a constant value, in the vicinity of 85% or so. Both the rapid increment and the slow change of removal efficiency with a linear variation of adsorbent dosage are perceivable. For a given 30 mg/L initial concentration, the removal efficiency is expected to rise sharply as there is enough room for adsorption. At higher adsorbent doses, the adsorbate might be taken up or equilibrium may be attained that cause the removal performance to tend to a constant value. The result is in line with the result found by Panda et al. (2017) where the authors prepared an adsorbent by varying the contact time to 0–70 min, pH to 2–7.5, adsorbent dose to 1–10 g/L, and initial concentration to 10–50 mg/L. It was indicated that the removal efficiency increased and then approached constant values as the adsorbent dose increased (Panda et al. 2017).

At a constant contact time of 70 min, a pH of 3, and an adsorbent dose of 3 g/L, the effect of initial concentration on the performance of the activated sludge is illustrated in Figure 7(d). As with the pH, the general pattern of removal efficiency decreases as the initial concentration increases. It slowly decreases from 86 to 84% when the initial concentration increases from 10 to 30 mg/L, and thereafter it falls sharply to 50.2% as the initial concentration changes to 70 mg/L. It is apparent that the decrement in removal efficiency is with respect to the initial concentration. For a given 3 g/L, removal efficiency was expected to decrease as the initial concentration increased. Being constant implies that there is a fixed amount of surface area to adsorb phosphate molecules. When the initial concentration increases, it means that the phosphate molecules would be way more for the given adsorbent amount used. As a result, the removal efficiency declines sharply when the initial phosphate concentration upsets. Yang et al. (2022) and Chakraborty et al. (2022) showed that removal efficiency decreased when initial concentration varied in the range of 20–60 mg/L.

The response surface plot of the removal efficiency at various contact times and adsorbent dose at a given pH of 3 and initial concentration of 30 mg/L is demonstrated in Figure 9(b). A quick rise from 75 to 83.3% in removal efficiency was observed as the contact time and adsorbent dose were increased from 50 to 71 min and 2 to 3 g/L, respectively. Afterward, only a 2.5% increment was found even though both variables were allowed to increase to 90 min and 4 g/L, respectively. In line with the optics that the adsorbent dose increases the room availability for adsorbate, putting aside the mass transfer barrier it causes when piled up, the performance of the activated sludge adsorbent was boosted pretty well with the dose. It seems that both variables were highly interactive (p-value 0.0014) in the phosphate adsorption process on the activated sludge adsorbent.

Figure 9(c) illustrates the impact of contact time and initial concentration on the removal efficiency both at once while pH and adsorbent were kept at 3 and 3 mg/L in that order, respectively. As predicted by the mathematical model developed, there was a substantial change from 76.5 to 83.4% in removal efficiency when the adsorbate was allowed to contact for 22 min from 50 to 72 min with the adsorbent and as the initial concentration of the phosphate was changed between 40 and 30 mg/L. Furthermore, the removal efficiency increased to 85.6% due to the change in contact time of 90 min and when the initial concentration declined to 20 mg/L. The result suggested that higher contact time and less initial concentration are favorable for removing the adsorbate with higher efficacy.

The 3D graph of the removal efficiency of the activated sludge adsorbent, pH, and adsorbent dose is shown in Figure 9(d). The figure was plotted using the data from the mathematical model of the removal efficiency by varying the pH and adsorbent dose from 2 to 4 units and, yet, keeping the other two parameters, contact time and initial concentration, at 70 min and 30 mg/L, respectively. It can be seen from the graph that the response increases with the adsorbent dose and declines when the pH of the solution within which the adsorption was taking place increases. On the other hand, when pH declines from 4 to 2 and adsorbent increases from 2 to 4 g/L, the removal efficiency shows a general increment pattern from 76.4 to 84.4%, but at a different rate.

The interaction effect of both pH and initial concentration during phosphate molecules being adsorbed on the surface of the activated sludge adsorbent is illustrated in Figure 9(e). While studying these variables' effects using the model, contact time and adsorbent dose remain fixed at 70 min and 3 g/L, respectively. It is evident from the graph that removal efficiency increases from 78 to 85% as the pH of the solution declines from 4 to 2 and the initial concentration decreases from 40 to 20 mg/L. It is apparent that low pH and concentration of adsorbate increase the efficiency. This may be attributed to the availability of relatively enough surface in 3 g of adsorbent in a solution for the low, say 30 mg, of adsorbate in a solution. If this holds, then the results can highlight the extent to which the adsorbent capacity would be in removing phosphate molecules.

Based on the model developed from the 30 experimental data inputs, the graph of removal efficiency, adsorbent dose, and initial concentration at a given contact time and pH is shown in Figure 9(f). The graph reveals that the removal efficiency increases proportionally with the adsorbent dose and decreases with the adsorbate concentration. As can be observed from the figure, the removal efficiency increases from 76.5 to 83.8% as the adsorbent dose increases from 2 to 3.3 g/L, and the initial concentration decreases from 40 to 28 mg/L at 70 min and a pH of 3. The removal efficiency slightly increases to 85% when both parameters further change to 4 and 20 mg/L in the same order. The results unfold that the parameters are interactive in the adsorption process (with a p-value of 0.02), and both have more effect together than individually.

As is disclosed in the interaction effect of variables, the removal efficiency increases with an increment of contact time and adsorbent dose, and with pH and initial concentration, it was observed that the removal efficiency declines. The results imply that there is a trade-off between variables to get higher removal efficiency of the activated sludge adsorbent. As a consequence, a numerical optimization of the adsorption process was made that takes the positive and negative effects of all variables into consideration. The optimum operating conditions for the phosphate adsorption process by the activated sludge adsorbent are a contact time of 70 min, a pH of 3, an adsorbent dose of 3 g/L, and an initial concentration of 30 mg/L with 83% efficiency. To see if this model-predicted optimum condition is consistent with experimental data, an experiment was conducted at these values of the parameters. The experiment was done three times, and average results showed a more or less similar removal efficiency of 83.4%, with only a 1.2% deviation from the model-predicted result. The results were somehow consistent with the result found by Ahmad et al. (2022) in which case the authors got 80% removal efficiency using activated bentonite. In another scenario, however, the removal efficiency would go up to 89% as can be seen from the work of Yapo et al. (2022). Other authors such as Ahmadi & Igwegbe (2018) and Padmavathy et al. (2016) showed 40 mg/L and 2 g/L of optimum initial concentration and adsorbent dose, respectively. In that regard, the results obtained in this study are a bit different. Contact time, however, varies from 50 to 120 min as is shown in the literature (Wen et al. 2019; Elkarrach et al. 2023).

An activated sludge adsorbent was synthesized from wastewater sludge at different conditions. Thermal followed by acid activation produced a cheap and promising adsorbent. The characterization techniques used revealed that the activated sludge is a potential candidate to be used as an adsorbent for phosphate impurities in water. The efficacy of the activated sludge adsorbent was examined by allowing it to adsorb phosphate molecules. It was observed that contact time and adsorbent affected positively the phosphate adsorbing process by the activated sludge, while pH and initial concentration had a negative impact. The adsorption process was scrutinized to pinpoint the capacity of the adsorbent for wastewater treatment. To that end, the process of adsorption was optimized and 70 min contact time, pH of 3, 3 g/L adsorbent dose, and 30 mg/L initial concentration with 83% removal efficiency were obtained as optimal conditions. Adsorption kinetics and isotherm investigation show that the adsorption of phosphate on the surface of activated sludge adsorbent follows the PSO kinetics model and the Langmuir isotherm model. In addition, the reusability test revealed that the activated sludge adsorbent could be reused three times before its removal efficiency falls below 70%. Altogether, the activation and the adsorption experiments revealed that the easily available material that is being disposed of from every water treatment plant can be used for water purification purposes. It can then be concluded that WTPS can be activated and used as an effective and low-cost adsorbent for the phosphate removal at pilot or even large-scale applications with some additional scale upping experiments and modification.

The Department of Chemical and Food Engineering, Faculty of Food and Chemical Engineering, Wollo University, Kombolcha, Ethiopia, Bahir Dar University, Bahir Dar, Ethiopia, and Addis Ababa Science Technology University, Addis Ababa, Ethiopia are all acknowledged by the authors for the assistance in the research laboratory work.

ES contributed to the conceptualization, methodology, writing the draft, formal analysis, and investigation. TST contributed to the resources, data curation, software, and validation. BG contributed to reviewing and editing the writing. TTN and AGA contributed to visualization and supervision. DAM contributed to manuscript editing. After reading the final draft of the manuscript, all authors gave their approval for publication.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.