Determination of physicochemical parameters and remediation of Pb (ii) using a composite of moringa oleifera seeds and kaolin clay in borehole water within Nakuru east sub county, kenya

Abstract

The contamination of borehole water in Nakuru East Sub County, primarily due to heavy metals and non-metals from natural origins and anthropogenic activities, poses significant health risks. Exposure to these contaminants, beyond the World Health Organization (WHO) and Kenya Bureau of Standards (KEBS) limits, can lead to various diseases and even death. Activities such as industrial processes, agriculture and waste disposal in the area contribute to the infiltration and leaching of toxic elements into borehole water. These toxic elements can enter the human body through ingestion, inhalation or dermal absorption. The Nakuru Water and Sanitation Service Company (NAWASSCO) operate 40 boreholes in the region; however, only 19 were functional during the sample collection, which took place in both dry and wet seasons. These boreholes supply water to Nakuru City and surrounding areas. This study aimed to determine the levels of physicochemical parameters and remediation of Pb (II) from these boreholes. Water samples were collected from six water fields: Kiundo (1 borehole), Kabatini (6 boreholes), Nairobi Road (6 boreholes), Baharini (4 boreholes), Madaraka (1 borehole) and Olbanita (1 borehole) during both seasons. The samples were analyzed for various parameters including Temperature, pH, Turbidity, Electrical Conductivity, Dissolved Oxygen, Fluoride, Lead (Pb), Cadmium (Cd) and Arsenic (As), with heavy metal concentrations measured using Flame Atomic Absorption Spectroscopy (FAAS). Results indicated that the temperature of the borehole water ranged from 23.8 to 26.4 ±0.2°C. Dissolved Oxygen levels were found to be below WHO acceptable limits in all samples. Turbidity levels ranged from 1.54 to 4.32 ±0.01 in the dry season and 0.36 to 9.30 ±0.02 in the wet season, with 36.8% of samples exceeding WHO limits in the dry season and all samples exceeding limits in the wet season. pH values were between 6.4 and 7.6 ±0.1 in the dry season and 7.0 to 7.7 ±0.2 in the wet season, mostly within WHO guidelines, except for a few boreholes that were slightly acidic. Electrical conductivity ranged from 392.0 to 823.1 ±0.1 mS/cm in the dry season and 186.7 to 350.6 ±0.2 mS/cm in the wet season; with all dry season samples above the WHO threshold of 400.0 mS/cm. Flouride had the same mean concentrations of 1.23mg/l for both the two seasons. Significant differences (P≤0.05) were noted between the physicochemical parameters and WHO standards. Correlations among parameters were observed, ranging from negative to positive (p < 0.001). Cd concentrations were below detection limits in all samples for both seasons, while Pb (II) levels exceeded the WHO limit of 0.01 mg/L in 31.6% of boreholes during the dry season and 42.1% in the wet season. Arsenic concentrations were above the WHO limit of 0.01 mg/L in both seasons. To address the contamination, a composite of Moringa oleifera seed powder obtained from Tharaka Nithi County and pure kaolin clay were used as an adsorbent for Pb (II). Characterization of the composite was conducted using Powder X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR). The adsorption study focused on Pb, revealing that the base-activated composite effectively adsorbed Pb at a dosage of 0.5 g. The adsorption data fit the Langmuir isotherm, Temkin, and Pseudo-Second-Order models. Thermodynamic studies yielded values of 25,340.57 J/mol for ΔH, 58.32 J/mol/K for ΔS and a decrease from 7.95 kJ/mol at 25°C to -3.71 kJ/mol at 225°C for ΔG. The adsorbate was effective at 83.77% in sample NR7.The results obtained indicated the urgent need for water treatment due to elevated levels of As (III) and Pb (II). The composite showed a positive effectiveness on the remediation of Pb (II), however further research should be carried out to investigate its effectives on other heavy metals remediation and outside the boreholes of the study area.