Abstract
This experimental paper deals with the development of a hybrid biological reactor for the treatment of a synthetic oilfield produced water under an increase in total dissolved solids (TDS) concentration. To comply with strengthening regulations concerning produced water discharge and peculiar produced water compositions, a moving bed biofilm reactor (MBBR) consisting in a combination of free activated sludge and moving biofilm supports was compared to a fixed bed hybrid biological reactor (FBHBR) consisting in a combination of free activated sludge and a fixed biofilm support. After a 216 days experimental period, the MBBR and the FBHBR were efficient to treat a synthetic produced water with chemical oxygen demand (COD) removal rate above 90% under an increase in TDS concentrations from 1.5 to 20 g·L−1. Ecotoxicity measurements on freshwater and marine microorganisms revealed an absence of toxicity on treated waters. A decrease in bacterial diversity indices with respect to the inoculum was observed in both bioreactors. This suggests that the increase in TDS concentrations caused the predominance of a low number of bacterial species.
Highlights
Oil and gas activities generate a large amount of wastewater during crude oil and gas extraction
This decrease, due to the acclimation of the biomass, is the result of the toxicity of the produced water (PW) compounds which is lethal for some bacterial species composing the activated sludge that we used to seed our bioreactors at t = 0
We suggest that in this case, at a total dissolved solids (TDS) concentration of 8 g·L−1, the salt concentration may be too low to use a marine algae for toxicity assessment purposes
Summary
Oil and gas activities generate a large amount of wastewater during crude oil and gas extraction. This wastewater, called produced water (PW) is composed of formation water, initially present in the oil reservoir. Other sources of water may be added in the reservoir. The resulting outcoming water is produced water. The ageing of oil reservoirs is currently leading to an increase in PW flowrates [1]. The water to oil ratio (WOR) quantifies this increase. The WOR is around 3:1, but its value is expected to grow [2]
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