CHAPTER ONE INTRODUCTION

1.1 Background of the Study

Water is essential for life, health and industry, yet only a small fraction of the earth's water is fresh and available for human use. Living organisms cannot survive without it, and almost every industry depends on it. Population growth, urbanisation and industrial expansion have increased the demand for water while also reducing its quality, mainly through the discharge of untreated or poorly treated wastewater into the environment. Protecting freshwater bodies from contaminants has therefore become a major environmental challenge in many countries.

Industrial wastewater is a particular concern because it often contains toxic chemicals, including heavy metals such as lead (Pb), chromium (Cr), cadmium (Cd), copper (Cu) and zinc (Zn). Heavy metals are not biodegradable and several of them are carcinogenic, so their presence in water in improper amounts can cause serious health problems for living organisms (Qasem et al., 2021). Nigerian studies show that the problem is real. Ibrahim et al. (2024) assessed heavy metal pollution around an industrial area in Nigeria and found that the non-carcinogenic health risk values were substantially above acceptable limits, which indicates a threat to the wider population. In Abia State, Anyanwu et al. (2023) reported that iron, lead and cadmium in the Eme River exceeded their permissible limits. Industrial effluent standards in Nigeria are set and enforced by the National Environmental Standards and Regulations Enforcement Agency (NESREA), but untreated or inadequately treated discharges still reach water bodies.

A number of technologies exist for removing heavy metals from wastewater. They include adsorption-based, membrane-based, chemical, electrical and photocatalytic treatments (Qasem et al., 2021). Many of the advanced options are expensive to build and operate, which limits their use in developing countries such as Nigeria. Adsorption, in which dissolved pollutants adhere to the surface of a solid, has been reported to offer low operating cost, high removal capacity and easy implementation, and the amount adsorbed generally rises with the adsorbent's surface area, the adsorbent dose, the initial metal concentration and the contact time (Qasem et al., 2021). Activated carbon is the adsorbent most commonly used, but commercial activated carbon is costly. For this reason, researchers have turned to low-cost activated carbons made from agricultural waste.

Corncob is a promising precursor. Maize is widely grown in Nigeria and its cobs are produced in large quantities as a residue of very low economic value. Aliyu et al. (2024), working at Bayero University, Kano, prepared activated carbon from raw corncob and used it for batch adsorption of lead (II). They recorded a maximum removal of 95% at an adsorbent dose of 2.5 g/L and a contact time of 2 hours, with a highest adsorption capacity of 16.46 mg/g. The carbon had a specific surface area of 249 m²/g, the kinetics followed a pseudo-second-order model, and the Langmuir isotherm best described equilibrium adsorption. They concluded that agricultural waste such as corncob can be turned into an effective adsorbent for heavy metals.

The performance of such carbons depends on how they are prepared and on the conditions of the adsorption process, which makes systematic optimisation important. Statistical approaches have been used to optimise Pb(II) adsorption on activated carbon from corn husk, and the authors concluded that the statistical method simplified optimisation and produced an efficient adsorbent (Wasim et al., 2022). Similar statistical modelling and prediction have been applied to the removal of Pb(II) with other adsorbents (Ismail et al., 2023). Qasem et al. (2021) also note that future work should focus on eco-friendly, cost-effective and sustainable materials and methods. This study responds to these needs by optimising the preparation of corncob activated carbon (CCAC) and evaluating its performance in removing Pb²+ from synthetic wastewater in batch experiments.

1.2 Statement of the Problem

Lead is one of the most hazardous heavy metals found in industrial effluents. It is toxic to living organisms, it can be carcinogenic, and it is frequently found above permissible limits in Nigerian surface waters (Anyanwu et al., 2023; Qasem et al., 2021). Conventional treatment technologies can remove heavy metals, but they require large investment and are often unaffordable for developing countries. Activated carbon is effective for removing dissolved pollutants but commercial grades are expensive, which creates a need for cheaper locally available alternatives.

Agricultural waste offers such an alternative. Corncobs are plentiful and have little economic value, and attempts to use them as biomass fuel have not been very successful because of their low calorific value. Converting them to activated carbon would add value to this waste while supporting wastewater treatment. Corncob activated carbon has been shown to remove lead (Aliyu et al., 2024), but the quality of the carbon and its adsorption performance depend strongly on preparation and operating conditions. A systematic, statistically based study of these conditions is needed in order to identify optimal values and to produce models that predict the performance of the adsorbent. This study therefore investigates the optimal preparation of corncob activated carbon and its use for removing lead from wastewater before discharge.

1.3 Research Objectives

The main objective of this research is to optimise the preparation of activated carbon from corncob for wastewater treatment. The specific objectives are to:

1. determine the optimal operating conditions for the preparation of corncob activated carbon;
2. characterise the corncob activated carbon;
3. determine the effect of initial adsorbate concentration, solution pH and adsorbent dose on lead removal using a batch adsorption technique;
4. analyse the adsorptive capacity and equilibrium isotherms of corncob activated carbon in batch adsorption experiments; and
5. generate statistical models that fit the experimental data using a full factorial design approach.

1.4 Scope of the Study

The study covers the preparation of activated carbon from corncob, its characterisation, and its use in batch adsorption experiments for the removal of Pb²+ from synthetic wastewater. Real industrial effluent is not tested, and continuous-flow (column) operation is outside the scope of the study.

1.5 Significance of the Study

Many industries need solutions to effluent treatment that give both environmental and economic benefits. This study contributes in the following ways:

1. Low-cost treatment option. Because the activated carbon is derived from agricultural waste, it can serve as an economical and environmentally friendly alternative to commercial activated carbon, and it converts a low-value waste into a useful product.
2. Fundamental information. It provides basic information on the adsorption of lead ions from aqueous solution, including capacity and equilibrium behaviour.
3. Design guidance. The mathematical models developed can guide further experimental work, predict adsorption performance under different operating conditions, and supply information for the design of treatment systems for effluents containing heavy metals.
4. Environmental protection. Better treatment options support efforts to improve water quality and to reduce the risk that heavy metals pose to human health and aquatic life.

References

Aliyu, S. A., Salahudeen, N., & Rasheed, A. A. (2024). Adsorptive removal of lead (II) pollutants from wastewater using corncob-activated carbon. Journal of Engineering Sciences, 11(2), H1–H10. https://doi.org/10.21272/jes.2024.11(2).h1

Anyanwu, E. D., Adetunji, O. G., Etusim, P. E., & Umeham, S. N. (2023). Human health risk assessment of some heavy metals in Eme River, Umuahia, Abia State, Nigeria. Journal of Bioresource Management, 10(3).

Ibrahim, K. O., Orosun, M. M., Purchase, M. W., & Yusuf, M. A. (2024). Environmental assessment of heavy metal pollution around industrial area in southwestern Nigeria. Journal of Sustainable Natural Resources, 5(1), 40–51. https://doi.org/10.30880/jsunr.2024.05.01.005

Ismail, U. M., Onaizi, S. A., & Vohra, M. S. (2023). Aqueous Pb(II) removal using ZIF-60: Adsorption studies, response surface methodology and machine learning predictions. Nanomaterials, 13(8), 1402. https://doi.org/10.3390/nano13081402

Qasem, N. A. A., Mohammed, R. H., & Lawal, D. U. (2021). Removal of heavy metal ions from wastewater: A comprehensive and critical review. npj Clean Water, 4(1), Article 36. https://doi.org/10.1038/s41545-021-00127-0

Wasim, A. A., Khan, M. N., & Fazal-ur-rehaman, S. (2022). Statistically optimized adsorption of Pb(II) ion on corn husk activated carbon – An application of response surface method. Gazi University Journal of Science, 35(2), 421–432. https://doi.org/10.35378/gujs.796618