Heavy Metals pH-Mediated Microbial-Remediation in Septic Tank Effluents

This paper studied the role of pH in the microbial remediation of heavy metals in septic tank effluents from three sample locations in the south-south region of Nigeria. The region is famous for agriculture, industrial and auto-mechanic activities leading to the uptake and bioaccumulation of heavy metal contaminants through the food chain. Heavy metals concentrations, pH, and microbial analysis in effluent samples, were determined using standard methods. The material balance approach (see Supplementary Information) was adopted to account for analytes remediation and speciation in the system according to the Law of Conservation of Mass (Matter). The pH of the study area ranged from 6.5 to 7.7. The pH conditions in location A was alkaline, while locations B and C were slightly acidic. Iron was the most abundant metal with a concentration range of 0.01 to 0 9.41 mg/L. The order of magnitude of heavy metals in the septic tanks in the study area is Fe > Pb > Cr > Zn > Cd > Mn > Cu > Ni > V. Metal removal mechanism followed the metal-microbes adsorption and precipitation processes dictated by the in situ pH of the system. Total heterotrophic bacteria were the most dominant in the septic tanks. A removal coefficient of ≤ 0.33 (i.e, 0 < x ≤ 0.33 (where x ≠ 0)) was considered optimum. The percentage metal ion removal was inversely proportional to the removal coefficient and vice versa. Acidic conditions favoured the sequestration of more heavy metals from the effluent and the attainment of the 67.0 % and 0.33 removal efficiency thresholds. Finally, the heavy metals concentrations were indicative of bioaccumulation. Secondly, the pH conditions are not ideal enough to cause the efficient remediation of heavy metals from effluents. Further treatment of the sludge component before disposal is seriously advocated.