Design of a Shallow Depth Settling Water Treatment Plant for Small Communities: Case of Ilara Mokin, Nigeria

ABSTRACT

Water, an essential resource for human health and socio-economic development, requires effective treatment to ensure safety and reliability for small communities. This study focuses on the design of a shallow depth settling water treatment plant for Ilara-Mokin, Ondo State, Nigeria. Population projections estimated growth from 45,000 in 2019 to 50,940 in 2025 and 75,690 by 2050, with corresponding water demands of 6.1 MLD and 7.57 MLD, respectively (based on 100 L/c/d plus 20% allowance). Raw water analysis from the Isokun River revealed poor quality, with pH ranging from 5.8–8.9, turbidity between 8.2–15.3 NTU, TDS of 680–920 mg/L, nitrate levels of 45–72 mg/L, lead concentrations of 0.018–0.032 mg/L, and bacterial loads of 85–200 CFU/100 mL, all exceeding WHO standards.
A treatment train consisting of intake screening, flash mixing, flocculation, shallow depth clarifiers, rapid sand filtration, and disinfection was designed to address these deficiencies. The flash mixer provided a 1-minute detention time at 254.2 m³/h with an alum dose of 25 mg/L (≈152.5 kg/day). Flocculation basins were designed for 30 minutes retention, while clarifiers with lamella tube settlers offered 72 m² effective surface area at an overflow rate of 4 m/h. Six rapid sand filters (3 × 3 m each) operating at 7 m³/m²·h were sized to ensure redundancy, and a 127 m³ baffled clearwell provided 30 minutes chlorine contact time at a dose of 0.36 mg/L (≈2.2 kg/day).
Treated water met WHO and SON standards, achieving pH of 7.0–7.5, turbidity