Sustainable Bioremediation of Soil Contaminated with Petroleum Sludge: A Case Study of Sultan Hamud. Kenya

Abstract

Petroleum sludge is a residue extracted mostly from petroleum storage. Contaminants in petroleum sludge (heavy metals and hydrocarbons) may exist in the soil for long periods and may be transmitted to plants and tissues of living organisms within the soil ecosystem through ground water or food chain. Disposal of raw petroleum sludge to the ground exposes the soil and underground water to pollution since contaminants in the sludge can leach and get to underground water. Alternatively, the contaminants can be taken up by plants growing in the contaminated soil depending on the concentration of the heavy metals in the soil. The goal of this Thesis was to investigate sustainable technology for enhancing bioremediation of soil contaminated with petroleum sludge. The research involved planting of bamboo and papyrus plants in soil polluted with petroleum sludge. The plants were managed in line with good agronomic practices as well as plant science during the entire period of the research. Parts of the plants (roots, stem and leaves) were periodically harvested and prepared for analysis for heavy metals (Lead, Copper and Chromium) by Atomic Absorption Spectrophotometry (AAS). The concentrations of the heavy metals from the analysis were compared to the initial concentration of the same metals in the polluted soil as well as in the plants that were used in the research. The polluted soil used in the study was sampled from Sultan Hamud dumping site. The soil was analyzed for presence and concentration of lead, copper and chromium. The soil had 107 mg/g of Lead, 151mg/g of Chromium and 204 mg/g of Copper. At the end of the experiment, Bamboo was able to accumulate a maximum of 0.055mg/g (54.45%) of lead, 0.093mg/g (53.45%) of copper, and 0.02mg/g (14.60%) of chromium. Papyrus on the other hand accumulated a maximum of 0.018mg/g (17.82%) of lead, 0.028mg/g (16.09%) of copper and 0.015mg/g (10.95%) of chromium. Notably leaching caused the washing away pf significant amounts of the metals. The success of this research so much depended on several variables and, more importantly, the time factor. This is because bio-accumulation and the rate at which plants accumulate heavy metals in their biomass, are directly dependent on the duration of growth period of the plants in the medium that is contaminated with heavy metals. Other variables such as soil characteristics and leaching are equally important. The growth rate of the plants is another aspect that is influenced by agronomical practices for the plants, besides the species of the plants used. The same factors, consequently affected the rate of accumulation of heavy metals from the soil by the plants. It is thus evident that in the long run, the output of the plants, particularly regarding bio-accumulation, is directly influenced by: the green house agronomic practices employed to the plant species, leaching of the heavy metals (Cu, Pb, and Cr) from the soil where the plants were grown to the pores at the bottom of the containers, plant growth rate, absorption rate and the duration of growth during research.