SPECIATION OF COPPER, LEAD, MANGANESE AND ZINC AND CHARACTERISATION OF SEWAGE SLUDGE FROM WUPA TREATMENT PLANT, ABUJA, NIGERIA

Abstract

Speciation of Copper, Lead, Manganese and Zinc ions in three sewage sludge samples (fresh, digested and dry) from Wupa sewage treatment plant, Abuja were investigated using sequential extraction methods. Flame atomic absorption spectrophotometer was used for instrumental analysis. The sludge physicochemical parameters, total metal concentration using aqua regia digestion, speciation of metals under study, using single extraction with EDTA and sequential extraction analytical methods were determined. Analysis of variance (ANOVA) on data obtained from the work was also carried out. Study on physicochemical parameters showed that; Samples had mean pH values of 8.48±0.13.8.50 ±0.02 and 8.37±0.17 for fresh,treated and dry sludge respectively. Samples had electrical conductivities of 520.00±0.01, 340.00±0.01 and 320.00±0.00 µScm-1 for fresh,treated and dry sludge respectively. Samples had nitrate contents of; 5.20±0.0, 4.80±0.01 and 2.50±0.01 gkg-1 for fresh, treated and dry sludge respectively. Aqua regia digestion for total metal concentration results showed values of;1418.13, 237.50, 4510.00 and 8289.60 mgkg-1 for Cu, Pb, Mn an d Zn respectively. Single extraction with EDTA results showed; 66.89, 6.90, 298.46 and 8.10 mgkg-1 for Cu, Pb, Mn and Zn respectively. Results for extraction of ions in five operational phases in sequential extraction showed; 202.15, 66.91, 385.59 and 418.79 mgkg-1 for Cu, Pb, Mn and Zn respectively. The metals; (Cu, Pb, Mn and Zn) were bound in five operational phases; (exchangeable, acid extractable, reducible, oxidizable and residual) in the sequential extraction method. Pb, Mn and Zn speciated more in the acid extractable, and reducible phases which were the carbonate and Mn/Fe oxide/hydroxide bound respectively. Cu speciated prominently in acid extractable and residual phases which were carbonate bound and occluded in organic matter respectively. The Solubility of all the metals (Cu, Pb, Mn and Zn) ranked highest in the acid extractable phase. Mn and Zn ranked lowest in the residual phase while Cu and Pb ranked lowest in the exchangeable and oxidizable phases respectively. Speciated ions in the exchangeable and acid extractable phases as soluble metal acetates and chlorides respectively are bioavailable to plants and vegetables for uptake. From the results of Cu, Pb, Mn and Zn ions obtained in the three extractions carried out it can be deduced that both ion concentrations are within the limits of regulatory agencies. However, a new method of speciation in handling trace metal pollutants will assist Wupa Treatment Plant in treating sewage sludge better. This will also boost agriculture and human health in the Federal Capital Territory in particular and in Nigeria in general which falls in line with the current Federal Government policies on food security and environmental sanitation.