Enhanced remediation of an oily sludge with saline water

Abstract

This study investigates the potentials of saline (that is, brackish) water to enhance the remediation of an oily sludge, which was part of the waste stream from the improvement project of the Tank Farm at the Bonny Island in the Niger Delta region of Nigeria. Twice weekly, five separate laboratory-scale reactors (labeled A, B, C, D and O), each containing 2.0 × 10^-2 m³ of the diluted sludge samples, received 170 g of liquid 20:10:10-NPK-fertilizer (corresponding to an application rate of approximately 4.3 kg-Nm^-3, 2.1 kg-P-m^-3 and 2.1 kg-K-m^-3 of diluted sludge). On a weekly basis, control reactors A and B received 5.0 × 10-4 and 1.5 × 10^-3 m³ of fresh water respectively while ‘treatment’ reactors C and D received 5.0 × 10^-4 and 1.5 × 10^-3 m³ of saline water (containing 4.54 g/L of NaCl) respectively. Reactor O, which served as a counterfactual, was only rain-fed. Equal oxygen exposure levels, through regularly scheduled tilling, was maintained in all five reactors. After 12 weeks of treatment (that is, from May to August, 2007), sludge physicochemical characteristics showed distinct variations. The saline water treated-reactor D, had a 7-fold increment in bacterial population while the fresh water treated-reactor B, had an approximately 3-fold increment in bacterial population. The drop in the hydrocarbon content of the saline water-treated reactors ranged from 41.7 to 55.9% whereas in the fresh water-treated reactors, the hydrocarbon losses ranged from 17.3 to 25.0%. These results showed the possibility of enhanced biodegradation of oily sludge by hydrocarbon utilizing bacteria (Bacillus subtilis) at salinity (NaCl concentration) of 4.54 g/L.

Key words: Bioremediation, biostimulation, oily sludge, saline water, Bacillus subtilis.