Response of Nitrosomonas, Nitrobacter and Escherichia coli to drilling fluids

Abstract

Inhibition of ammonia oxidation by Nitrosomonas, nitrite oxidation by Nitrobacterand carbon IV oxide evolution by Escherichia coli were employed as indices to determine the effect of four drilling fluids (Paradril, IMC0-W, IMC0-O and Gel/KCL/polymer to these bacteria. The percentage survival (determined by aerobic spread plate count) of these bacteria when exposed to these fluids was also used as toxicity index. Ammonia oxidation (nitrite accumulation) and nitrite oxidation (consumption) were determined by coupling of diazotised sulfanilic acid with a-napthyl-ethylene diamine dihydrochloride. Carbon IV oxide evolution was monitored by passing air from inoculated lactose broth into calcium hydroxide solution and titration with sulphuric acid. Toxicity indices were determined throughout the following exposure period (0, 1, 2, 3, 4, 8, 12, 24, 36 and 48 h) in static shake flask systems. Percentage survival decreased with increasing concentration of the drilling fluids and increasing exposure period of the three bacteria especially at high concentrations (10.0, 100 and 1000 mg/l). At lower concentrations (0.01, 0.1 and 1.0 mg/l) some fluids stimulated bacterial growth. Controls revealed bacterial growth through out the exposure period. Nitrite accumulation by Nitrosomonas, nitrite consumption by Nitrobacter and carbon IV oxide evolution by E. coli decreased with increase in concentration and exposure time of the four fluids. Controls revealed an increase in these indices with increase in exposure period. Results showed that the drilling fluids inhibited the two stages of the nitrification in the nitrogen cycle and respiration (by E. coli). This may affect the agricultural productivity of ecosystems in the Niger Delta where they are employed by causing dislocations in the nitrogen cycle where nitrifying and aerobic bacteria participate. Key words: Nitrite accumulation, nitrite consumption, respiration, drilling fluids.