The application of reed bed technology for treating oil production waters and the associated chemical and biological processes
Oil exploration and production in the Sultanate of Oman is associated with many
challenges, of which the disposal of 600,000 m3d -I of oil production water in
environmentally sound method is of foremost importance. This water is contaminated
with petroleum hydrocarbons, traces of phenols, emulsifiers, a wide range of metals
and has an electrical conductivity of 12 dS m-I.
This study evaluated the use of Nimr reed bed technology for treating oil production
water and the role of its associated chemical and biological processes in the
contaminant removal. The combined interactions between the substrate, macrophytes
and the inhabiting microorganisms resulted in considerable reductions in the inorganic
and organic contaminants simultaneously. Metals in the effluents were reduced by
78% for (AI, Ba, Cr, Cu, Zn & Li), up to 40 for Fe, Li, Mn, Pb and appreciable
reductions of As, Cd, Co, Mo, Ni, Se, TI and V. A much better and consistent
reductions were achieved total hydrocarbons averaging 96% for the three years of
operation. The contaminants were virtually eliminated within the primary reed bed by
aerobic and to a lesser extent by anaerobic processes.
Metals were adsorbed by clays, chemisorbed by oxides. precipitated as metalcarbonates
and sulphates, organically complexed. precipitated as metal sulphides and
absorbed into primary and secondary minerals. After the first year, reeds became
mature and started taking up and accumulating significant quantities of metals, which
virtually eliminated any further accumulation in the substrate.
Hydrocarbons were predominantly attenuated by the developed sediment layer and
creeping on reeds accommodating as much as 36±9 and 43±13% of their weight oil,
respectively. The dissipation of hydrocarbons was shown to being rapid and faster for
the lower molecular weight compounds than the larger ones, through volatilisation,
photooxidation, aerobic and to less extent anaerobic biodegradation. The adapted and
acclimated indigenous microbes tolerate high salinities; biodegraded hydrocarbon
loads up to 9% and tolerates the diverse range of metals at different concentrations.
The clogging problem in Nimr reduced the treatment capacity from 1500 to 400 m3d-1
however. this drawback was successfully surmounted in pot experiments using a
sandy loam instead of Nimr loamy soil, and surface instead of subsurface flow
regime. It was concluded that the technology is viable for this application and
recommendations for future work were accordingly suggested.