Spatial analysis of heavy metals in septic tank sewage

Abstract

Heavy metals get to humans through food, water, air, and industrial activities. They arrive at septic tanks through the excretory products of man and undergo anaerobic bioremediation. Effluent and sludge sewage in both chambers of the tank contains various amounts of trace metals. The research analyses the spatial distribution of heavy metals in the effluent and sludge components of the septic tank during bioremediation. Effluent and sludge samples were randomly collected from three study locations in southern Nigeria, and composite samples were made for each of these study locations. Nine trace metals were analysed using standard methods by the American Public Health Association (APHA) for water and wastewater examination. Fe, Mn, Zn, Cu, and Cr were the most abundant. Effluent heavy metals concentrations were higher in the inlet chamber. There were strong positive correlation (r = 0.90, 0.99, and 0.99) between the effluent and sludge samples. P-values obtained from the ANOVA at a 0.05 significance level confirmed the correlation values. Multivariate charts and regression analysis gave R2-values in the range of 0.3045 – 0.3724 in the study with a mean value of 0.33. In conclusion, the effluent and sludge samples were strongly correlated and all the metal types analysed were also present in the sludge in similar proportions. The sludge contained significant levels of trace metals with dire implications for the environment.