Abstract

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Sludge contains nutrients, heavy metals, and metalloids some of which are essential macronutrients, such as N, P, K, Ca, Mn and other essential trace elements, such as Cu, Fe and Zn. This paper examines the heavy metals within the septic tank system and their eventual accumulation as components of sludge with implication for agricultural use. Sludge samples from the inlet and outlet chambers of the septic tank were randomly collected from three study locations in the south-south region of Nigeria. The composite samples were made for each of these study locations from which nine trace metals (Fe, Zn, Mn, Pb, Cu, Cr, Cd, Ni and Va) were analysed. The concentrations of the metals were determined using standard methods for water and wastewater examination. Results showed that sludge samples from the anaerobic bioreactors contained a high concentration of various trace metals. Iron had the highest mean concentration level of 556 ± 0.2 mg/kg – 3391 ± 1.13 in the raw sewage sludge sample, while vanadium was the least in abundance with mean concentrations of 0.86, 0.77, and 1.52 mg/kg in locations A, B and C respectively in the inlet chamber sludge samples. Although, sludge is variously used for agricultural purpose, there is need for treatment to reduce the concentration levels of heavy metals prior to its use as fertilizer as a matter of public health importance.

Keywords: Fertilizer, food chain, heavy metals, septic tank, sewage sludge