Evaluation of the use of Effluent Released from a Wastewater Treatment Plant in Zaria, North-West, Nigeria for Irrigation of Vegetables

The use of Water daily accounts for the generation of wastewater requiring treatment. Influent, effluent (discharge point, 400m, 500m downstream), and soil and vegetable samples from fields of effluent-irrigated tomato, lettuce, and onion were sampled. Standard methods were used to analyse physicochemical properties and coliform counts. At the effluent discharge point, values of temperature (24°C), dissolved oxygen (100 mg/L), total dissolved solids (390 mg/L), and phosphate (3.7 mg/L) comply with WHO and NESREA standards for effluent discharge. However, biochemical oxygen demand (60 mg/L), chemical oxygen demand (1200 mg/L), total suspended solids (230 mg/L), nitrate (45 mg/L), and sulphate (480 mg/L) exceeded set limits. Statistical analysis showed no significant differences (P > 0.05) in pH as well as temperature across samples. Significant differences (P ≤ 0.05) occurred in dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, turbidity, total solids, total dissolved solids, total suspended solids, conductivity, nitrate, phosphate, and sulphate. The total coliform count at the point of effluent discharge was 1.0 x106 CFU/ml, at 400 m and 500 m downstream was 5.0 x105 and 2.4x105 CFU/ml, respectively. The faecal coliform count at the point of discharge was 4.1x105 CFU/ml, and 2.8x105 and 1.5x105 CFU/ml respectively at 400 m and 500 m along the effluent flow channel. Statistical analysis indicated significant differences (P ≤ 0.05) in total and faecal coliform counts for influent and effluent samples. However, coliform counts in both soil and vegetable samples exhibited no significant variation (P > 0.05) across plots. The wastewater treatment is inadequate, as seen in the physicochemical parameters and high coliform counts. This, indicates the need for an improvement in the wastewater management.