The influence of various dosages of the hybrid coagulant was examined in order to evaluate the efficacy of hybrid coagulation in the treatment of wastewater. Several studies were conducted employing different dosages of aluminum chloride (AlCl₃) at doses of 0.5 g, 1 g, 1.5 g, 2 g, and 2.5 g in conjunction with an ideal concentration of Rosehip Seed Powder (RSP) coagulant (1 g/L) [4]. A single liter of wastewater gathered from the iron and steel sector was used to prepare these mixes. An orbital shaker was used to stir the mixes under the precise circumstances indicated in Section 2.3 to guarantee homogeneity. The goal was to determine the hybrid coagulant dosage that would produce the best removal efficiency during the treatment. As previously observed by [24], it is essential to acknowledge that the surface charge of the coagulant plays a substantial role in influencing coagulation performance, chiefly due to its mass. Therefore, a critical facet of this investigation involves the economic optimization of the coagulant dosage, the determination of the requisite mass for potential scale-up, and the subsequent design of large-scale equipment.

The research outcomes yielded intriguing insights into the influence of varying RSP/AlCl₃ dosages on the removal efficiencies of key parameters in the industrial wastewater treatment process. Most notably, it was evident that changes in RSP/AlCl₃ dosages had negligible effects on the removal efficiencies of TSS, color, and NH₃-N, as these parameters consistently maintained high removal rates, specifically 100%, 90%, and 95%, respectively, across all investigated RSP/AlCl₃ dosages. However, the influence of RSP/AlCl₃ dosages on COD removal was markedly distinct. The COD removal efficiency exhibited notable sensitivity to RSP/AlCl₃ dosage variations. At a 1.0/0.5 RSP/AlCl₃ dosage, the COD removal efficiency stood at approximately 70%. Remarkably, as the RSP/AlCl₃ dosage increased to 1.0/1.0, the COD removal efficiency significantly improved, reaching 90%. However, the subsequent escalation of AlCl₃ dosage resulted in a sharp decline in COD removal efficiency, plummeting to approximately 65%. This intriguing pattern in COD removal underscores the complex interplay between RSP and AlCl₃ dosages and their impact on treatment efficacy. The initial enhancement in COD removal with an increased RSP/AlCl₃ dosage suggests that the hybrid coagulant system effectively targeted the organic pollutants responsible for COD. Nonetheless, as AlCl₃ dosage continued to rise, it seemingly led to counter-destabilization effects, causing a reduction in COD removal efficiency. This phenomenon aligns with the findings reported by [25].

Adsorption-bridging mechanisms are the main driving force behind the coagulation process that uses the hybrid coagulant. Through charge neutralization—which successfully neutralizes the charges of suspended particles and promotes their aggregation—the Rosehip Seed Powder (RSP) component is crucial in this situation. In contrast, when aluminum chloride (AlCl₃) is added to a water sample, it causes a hydrolysis reaction that results in positively charged species that further encourage coagulation by generating flocs. This dual-action process increases the overall coagulation efficiency by fusing the hydrolytic activity of AlCl₃ with the charge-neutralizing qualities of RSP [26]. Charge neutralization, also known as electrostatic interaction, and sweep coagulation, also known as co-precipitation, are the two main mechanisms via which the coagulation process is generally considered to function. The process of charge neutralization entails balancing the electrical charges of suspended particles, which causes them to aggregate and eventually separate from the solution. On the other hand, sweep coagulation describes the action of coagulants creating precipitates that move through the water and pick up suspended particles. These mechanisms, which have a wealth of literature supporting them, are essential for improving the effectiveness of water treatment [27]. The coagulation process mediated by RSP can be elucidated through the charge neutralization mechanism, whereby the electrical charges of the coagulant and the suspended particles are balanced. Conversely, in the case of sweep coagulation, when AlCl₃ is dosed into the water sample, it undergoes a hydrolysis reaction, instigating a cascade of chemical transformations. These mechanisms collectively contribute to the coagulation process by facilitating the aggregation and subsequent removal of impurities from the water sample [28].

Examining the impact of different hybrid coagulant dosages on the elimination of COD, color, TSS, and NH₃-N from wastewater coming from the iron–steel (IS) sector was the goal of this study. These experiments were conducted at an initial pH of 8, and Figure 2 shows the visual representation of the results. With a hybrid coagulant dosage of 1:1 (g/g), the highest removal efficiency was recorded, with removal rates of 88.29% for COD, 91.85% for color, 99.00% for TSS, and 93.11% for NH₃-N. To put things in perspective, these results were contrasted with the removal efficiencies obtained via RSP alone, as shown in a prior study. This comparison demonstrates how well the hybrid coagulant performs in terms of improving the treatment efficiency for several important wastewater characteristics [12].

The findings demonstrated that utilizing the hybrid coagulant led to an enhancement in removal efficiency ranging from 2.2% to 14.2%, contingent upon the specific parameter being considered, as illustrated in Figure 3. Notably, the efficacy of color removal exhibited a substantial improvement of 8.3% when utilizing a hybrid dosage of 1:1 (g/g) compared to RSP alone. Furthermore, the effectiveness of NH₃-N removal displayed a significant increase of 14.2% with the exact hybrid dosage, underscoring the notable improvement achieved through hybrid coagulation in this context. On the other hand, when using the same 1:1 (g/g) hybrid coagulant dosage, the improvement in COD elimination was just 2.2% higher. This implies that the dosage of the hybrid coagulant affects NH₃-N pollutants more strongly than COD elimination. Notably, removal effectiveness dropped when the hybrid coagulant dosage was increased above the 1:1 (g/g) ratio. This decrease suggests that there may have been a coagulant overload throughout the treatment, which could have reduced efficacy.

In general, it is important to remember that the quantity of adsorption sites that are available for bridging colloidal particles gradually decreases as the dose of AlCl₃ increases. This decrease happens because of AlCl₃’s propensity to coat the natural coagulant’s surface and reduce the number of sites that can be used for efficient bridging. This result causes a considerable drop in total removal efficiency, as seen in Figure 2 and validated by another study [29,30].

Figure 4 provides a visual representation of the optimal dosage of the hybrid coagulant identified in our study, which was determined to be 1:1 (g/g). This ratio achieved the highest levels of efficiency in removing various contaminants from wastewater. The removal efficiencies at this optimal dosage were as follows: 94.3% for manganese (Mn), 98.5% for iron (Fe), 96.7% for zinc (Zn), 73.7% for aluminum (Al), and 99.3% for nickel (Ni). Figure 4 highlights the effectiveness of the 1:1 (g/g) coagulant dosage in addressing a range of contaminants, demonstrating that this ratio is particularly effective in optimizing the removal process. The substantial removal efficiencies achieved for each contaminant underscore the efficacy of the hybrid coagulant at this specific dosage. This study’s findings revealed an interesting trend in the context of varying RSP/AlCl₃/dosages and their influence on the removal efficiencies of specific heavy metals, including Mn, Fe, Al, Ni, and Zn. Remarkably, for manganese, iron, aluminum, and nickel, RSP/AlCl₃ dosage alterations had no discernible effects on their removal efficiencies. These removal rates remained relatively consistent across the investigated range of dosages, highlighting the robustness and reliability of the hybrid coagulation process for these elements. Conversely, the removal efficiency of zinc (Zn) exhibited sensitivity to variations in RSP/AlCl₃ dosages. Specifically, as the RSP/AlCl₃ dosage increased from 1:1 to 1:2 (g/g), the Zn removal efficiency experienced a notable decline, decreasing from an impressive 96% to a reduced but still considerable 61%. This distinct behavior observed in Zn removal emphasizes the nuanced interplay between coagulant dosages and the removal of specific heavy metals. While the hybrid coagulant system remained highly effective in removing Mn, Fe, Al, and Ni across the range of dosages, Zn removal efficiency was notably affected by higher RSP/AlCl₃ dosages. This observation provides valuable insights into the selective removal of heavy metals. It underscores the importance of optimizing dosages for each target pollutant, contributing to a more tailored and efficient industrial wastewater treatment process.

Upon comparing these findings with the removal efficiencies achieved using RSP as a standalone coagulant, as reported in [12], the data demonstrate that the application of the hybrid coagulant led to notable increases in removal efficiency, which varied from 6.1% to 10% based on the particular parameter assessed. Significant improvements were seen in the elimination of zinc (Zn), manganese (Mn), and iron (Fe) when comparing the efficacy of the ideal hybrid dosage of 1:1 (g/g) with the use of RSP alone. In particular, a rate of 94.4% was attained by an astounding 10% improvement in Mn removal efficiency. In a similar vein, the removal efficiencies of Zn and Fe also increased by around 7% to 98.49% and 96.76%, respectively. These results highlight the hybrid coagulant dosage’s significant beneficial effects on the elimination of pollutants containing Mn, Fe, and Zn. When compared to RSP alone, the hybrid coagulant’s improved removal efficiencies show how effective it is in greatly increasing the removal of these components.

The efficacy of different hybrid coagulant concentrations in the coagulation–flocculation process was comprehensively examined in this study. The concentration ratios that were looked at included intermediate values like 0.75:0.75, 1:1, 1.25:1.25, 1.5:1.5, and 1.75:1.75, and they varied from 0.5:0.5 to 2:2 (g/g). A distinct pattern became evident, indicating that removal efficiency improved in tandem with an increase in the hybrid coagulant concentration ratio. According to this study, most of the concentration ratios that were examined produced favorable outcomes, significantly improving the removal of NH₃-N, color, TSS, and COD. This suggests that using the hybrid coagulant at larger doses often produced better results when treating these pollutants. Figure 5 shows the remarkable removal efficiencies that were obtained from this investigation: 87.4% for COD, 92.4% for color, 96.8% for NH₃-N, and 99.0% for TSS at the hybrid coagulant concentration ratio of 0.75:0.75 (g/g). These outcomes unequivocally show how successful the adsorption-bridging mechanism used in the therapy procedure was. The mechanism’s successful implementation is shown by the high efficiencies obtained at this concentration ratio, highlighting its crucial role in improving the coagulation–flocculation process’s overall performance.

In particular, this study focused on the removal of manganese (Mn), iron (Fe), zinc (Zn), aluminum (Al), and nickel (Ni) at a pH of 8. It also examined the effectiveness of a hybrid coagulant that combined RSP and aluminum chloride (AlCl₃) in treating wastewater from iron and steel (IS) companies. The results, as illustrated in Figure 6, suggest that a decrease in the removal efficiency of these heavy metals was caused by an increase in the dosage of the hybrid coagulant. A dosage ratio of 2.25:0.75 (g/g) produced the best removal efficiency, which led to significant removal rates of 99.8% for Fe, 97.4% for Mn, 99.0% for Al, 87.5% for Zn, and 93.3% for Ni. Charge reversal is a phenomenon that can be brought about by using a high dosage of the hybrid RSP/AlCl₃ coagulant, as seen in Figure 6. The particles become stabilized because of this process, which lowers the effectiveness of heavy metal removal. To avoid this charge reversal and ensure efficient contamination clearance, it is imperative that the coagulant dosage be properly optimized.

The impact of pH on the coagulation process was rigorously examined by adjusting the pH levels of the wastewater across a comprehensive range spanning from pH 5 to pH 10. To preserve the original composition of the industrial wastewater sample, as indicated in Table 2, the coagulation tests were carried out at room temperature. An RSP and AlCl₃ hybrid mixture was used in the studies, with a constant coagulant dose of 0.75:0.75 (g/g). Adjustments were carefully made using a 1 N H₂SO₄/NaOH solution to provide exact pH control throughout the testing. The role of pH in the coagulation process is crucial, particularly in relation to the mechanisms of sweep-floc formation and adsorption-bridging. In this context, the polymer acts as a bridging agent, connecting the contaminants to the surface of AlCl₃. This interaction facilitates the effective precipitation of the contaminants, enhancing the overall coagulation efficiency. The pH level significantly influences these mechanisms by affecting the charge characteristics of the coagulants and contaminants, thereby impacting the efficacy of the coagulation process.

This study revealed that the coagulation process achieved its highest efficiency within a pH range of 7 to 8. Notably, at a pH of 8, the process demonstrated its peak performance, with removal efficiencies reaching 89.8% for COD, 92.9% for color, 99% for total suspended solids (TSS), and 74.3% for NH₃-N. The removal rates for COD and NH₃-N showed a consistent increase with rising pH levels, peaking at this optimal pH. However, deviations beyond this optimal pH range led to a reduction in the removal efficiencies for COD and NH₃-N. This decline is attributed to the increased adsorption capacity of particles under neutral electric charges, as particles become less effective at bridging and precipitating contaminants when pH levels slightly exceed the optimal range. This phenomenon is consistent with observations reported in previous studies, highlighting the importance of maintaining pH within the optimal range for effective coagulation [31].

Additionally, it was discovered that the cations in the wastewater played a critical role in enhancing the coagulation process. By neutralizing and stabilizing the negative charges connected to the coagulant’s functional groups, they made a substantial contribution. More interactions between the cations and the RSP particles are made possible by this neutralization, which encourages more efficient flocculation and coagulation [32]. Remarkably, it was noted that when RSP was employed as the coagulant, there was no imperative requirement for pH adjustment throughout the treatment process, as delineated in Figure 7. This finding underscores the self-sufficient pH buffering properties of RSP, rendering additional pH modification unnecessary during the treatment course.

On the other hand, it was amply shown that pH 8 was found to be the ideal pH for the coagulation process. The use of the hybrid RSP/AlCl₃ coagulant significantly increased removal efficiency at this pH level. Specifically, utilizing the RSP/AlCl₃ coagulant, the removal efficiencies at pH 8 for Fe, Mn, Al, Zn, and Ni were 92.7%, 90.6%, 95.00%, and 92.3%, respectively. These results are graphically represented in Figure 8. This achievement can be partially attributed to the organic content of RSP, which was crucial in preserving the pH stability of the industrial effluent. Because RSP can naturally buffer pH, using the RSP/AlCl₃ coagulant during the treatment process decreased the need for external pH modifications. Fundamentally, the inherent properties of RSP expedited the entire treatment procedure by aiding in the effective elimination of contaminants and maintaining the proper pH balance for coagulation.

The results in Table 3 present a comparison of the performance of RSP alone, AlCl₃ alone, and the combined RSP/AlCl₃ process. Each process was evaluated based on its efficiency in removing COD, color, TSS, NH₃-N, Mn, Fe, Zn, and Ni. The removal efficiencies of both RSP- and AlCl₃-only processes were recorded slightly lower than those of the combined RSP/AlCl₃ process, which demonstrated the highest removal efficiencies for all parameters. This improvement in the combined process suggests synergistic effects between RSP and AlCl₃, potentially due to enhanced coagulation and flocculation processes. In summary, the combined RSP/AlCl₃ process showed enhanced performance in terms of COD and color removal, as well as the removal of various parameters including TSS, NH₃-N, and metal ions, compared to the individual processes. This suggests the synergistic effects of combining RSP and AlCl₃. In summary, the combined RSP/AlCl₃ process showed enhanced performance in terms of COD and color removal, as well as the removal of various parameters including TSS, NH₃-N, and metal ions, compared to the individual processes. This suggests the synergistic effects of combining RSP and AlCl₃.