Industrial wastewater containing heavy metals poses significant environmental challenges due to its impact on

water quality parameters, particularly pH and contaminant concentration. The presence of copper ions can

increase the acidity of wastewater, affecting both treatment efficiency and environmental safety. Therefore, there

is a need for sustainable and cost-effective treatment methods that not only remove contaminants but also

stabilize pH levels. This study aims to evaluate the pH behaviour and adsorption performance of a coconut husk

adsorbent in industrial wastewater treatment. The adsorbent was prepared from coconut husk through washing,

chemical activation using sodium hydroxide (NaOH), and low-temperature carbonization. Synthetic wastewater

was formulated using kaolin and different concentrations of copper. Batch adsorption experiments were

adsorption efficiency at lower contaminant concentration. In conclusion, the coconut husk adsorbent

demonstrated promising potential as a low-cost and sustainable material for industrial wastewater treatment. Its

ability to improve both pH stability and adsorption performance highlights its applicability as an alternative to

conventional adsorbents, particularly under moderate to higher contaminant loading conditions.

Keywords: Adsorption; Chemical Activation; Coconut Husk; Wastewater

Industrial wastewater generated from petrochemical, manufacturing, and metal-processing industries contains a

wide range of pollutants, including suspended solids, organic compounds, and heavy metals such as copper. The

discharge of untreated or inadequately treated wastewater can significantly alter water quality parameters,

particularly pH, which plays a critical role in determining the chemical stability, toxicity, and overall treatability

energy-intensive processing, and disposal challenges have limited their large-scale application, particularly in

developing regions. These limitations have driven increasing interest in the development of low-cost,

sustainable, and environmentally friendly alternatives derived from natural materials (Реимбаев et al., 2025).

In recent years, agricultural waste materials have gained attention as potential adsorbents due to their abundance,

biodegradability, and rich lignocellulosic composition. Coconut husk, the outer fibrous layer of coconut, is one

such material that is widely available in tropical regions and often underutilized (de Araújo et al., 2024). It

contains cellulose, hemicellulose, and lignin, which provide functional groups such as hydroxyl and carboxyl

groups capable of interacting with pollutants through adsorption mechanisms. The conversion of coconut husk

into a value-added adsorbent not only contributes to wastewater treatment but also supports waste valorisation

and circular economy principles (Pandey et al., 2023).

Therefore, this study aims to evaluate the pH behaviour and adsorption performance of a coconut husk adsorbent

in industrial wastewater treatment. The adsorbent is prepared through a combination of physical and chemical

treatment processes, followed by application in synthetic wastewater containing varying concentrations of

copper. The study focuses on analysing pH changes before and after treatment, as well as assessing the adsorption

performance of the prepared material. The findings are expected to provide insights into the effectiveness of

coconut husk adsorbent as a low-cost and sustainable solution for industrial wastewater treatment, while

highlighting the importance of pH behaviour in adsorption-based processes.

Adsorption is widely recognized as an effective and versatile method for wastewater treatment due to its

simplicity, high removal efficiency, and ability to treat a wide range of contaminants including heavy metals,

particularly significant role as it governs both the surface properties of the adsorbent and the chemical behaviour

of pollutants in solution (Hu & Hao, 2025).

The influence of pH on adsorption behaviour is especially critical in the removal of heavy metals from

wastewater. Changes in pH affect the ionization of functional groups on the adsorbent surface, such as hydroxyl

and carboxyl groups, which are responsible for binding metal ions (Adeleke et al., 2023). At low pH levels, the

high concentration of hydrogen ions competes with metal ions for available adsorption sites, thereby reducing

adsorption efficiency. In contrast, at higher pH levels, the surface of the adsorbent becomes more negatively

charged, enhancing the electrostatic attraction between the adsorbent and positively charged metal ions such as

copper (Cu²⁺) (Molchanova et al., 2025). Additionally, pH influences the speciation and solubility of metal ions,

which may form different complexes or precipitates depending on the solution conditions. These changes not

biodegradability. These materials are rich in lignocellulosic components, which provide functional groups

capable of interacting with pollutants through mechanisms such as ion exchange, surface complexation, and

physical adsorption (Himu et al., 2024). The use of natural adsorbents not only reduces reliance on expensive

synthetic materials but also promotes waste valorization and environmental sustainability. However, the

performance of these materials often depends on their surface characteristics, which can be enhanced through

physical and chemical treatments such as grinding, thermal processing, and chemical activation (Himu et al.,

2024).

Among various agricultural wastes, coconut husk has emerged as a promising material for adsorbent

development due to its high lignocellulosic content and porous structure. Coconut husk, the outer fibrous layer

of the coconut, contains cellulose, hemicellulose, and lignin, which contribute to the presence of functional

Previous studies have demonstrated that coconut-based materials can achieve significant removal efficiencies

for contaminants such as copper, lead, and cadmium. The adsorption performance can be further improved

through chemical activation, for example using sodium hydroxide (NaOH), which increases surface area and

enhances the availability of active sites. Thermal treatment or carbonization processes also contribute to

improving porosity and structural stability, resulting in better adsorption performance (Jock et al., 2022).

Although coconut husk has shown considerable potential as a low-cost and sustainable adsorbent, existing

using coconut husk adsorbent in industrial wastewater treatment. Such an approach provides a more

comprehensive understanding of the adsorption process and supports the development of more effective and

sustainable treatment systems.

Coconut husk (the outer fibrous layer of coconut) was collected from local sources and used as the raw material

for adsorbent preparation. The collected husk was thoroughly washed with distilled water to remove adhering

dirt and impurities, followed by drying at ambient conditions for 24 hours to reduce moisture content. The dried

material was then cut into smaller pieces and ground using a mechanical grinder to obtain a uniform particle

size.

in a laboratory oven to improve structural stability and surface characteristics. The final product obtained was

cooled to room temperature and stored in an airtight container for further use. This processed material was

referred to as coconut husk adsorbent

Synthetic industrial wastewater was prepared to simulate contaminated water conditions commonly found in

industrial effluents. Tap water was used as the base solution, and kaolin was added to represent suspended solids.

Copper ions were introduced into the solution at three different concentrations to simulate heavy metal

contamination. The wastewater samples were prepared by dissolving measured quantities of copper salts into

the kaolin suspension, followed by continuous stirring to ensure homogeneity. The prepared solutions were

allowed to stabilize before use in adsorption experiments.

Batch adsorption experiments were conducted to evaluate the performance of the coconut husk adsorbent. A

fixed dosage of the adsorbent was added to a known volume of synthetic wastewater in a beaker. The mixture

was stirred at a constant speed using a magnetic stirrer to ensure uniform contact between the adsorbent and the

digital pH meter. Calibration was performed using standard buffer solutions (pH 4, 7, and 10) prior to

measurement to ensure accuracy. The pH values were recorded to evaluate the effect of adsorption on the acidity

or alkalinity of the solution.

Analysis Evaluation of Adsorption Performance

The adsorption performance of the coconut husk adsorbent was evaluated by analysing the reduction in

contaminant levels before and after treatment. Absorbance was measured and used as a relative indicator of

contaminant concentration to assess the effectiveness of the adsorption process. While this approach provides a

comparative evaluation of adsorption performance, it does not represent the exact concentration (mg/L) of

contaminants. Parameters such as turbidity and absorbance were measured using appropriate instruments. The

removal efficiency (%) was determined using the following equation (Equation 1):

Overall, the results indicate that the coconut husk adsorbent exhibits promising adsorption performance,

particularly at higher contaminant concentrations. Despite some variability at lower concentrations, the

adsorbent demonstrates its potential as a low-cost and sustainable material for industrial wastewater treatment,

especially when combined with its ability to influence pH behaviour. It should be noted that absorbance was

used as a relative indicator in this study. Future work should include calibration methods to convert absorbance

values into concentration (mg/L) for more accurate quantitative analysis and comparison with existing literature.

indicating effective removal of contaminants at moderate to higher concentrations. However, Sample 1 showed

a slight increase in absorbance after treatment, suggesting that adsorption efficiency may be limited at lower

contaminant concentrations or influenced by experimental factors such as particle release or insufficient

interaction. The results also revealed a relationship between pH behaviour and adsorption performance, where

the increase in pH after treatment created more favourable conditions for adsorption. This highlights the

importance of considering pH as a key parameter in adsorption-based wastewater treatment processes.

Overall, the coconut husk adsorbent demonstrated promising potential as a low-cost and sustainable material for

industrial wastewater treatment. Its ability to influence both pH stabilization and contaminant interaction

supports its applicability as an alternative to conventional adsorbents. Future studies are recommended to