Abstract
The technology consists on using microorganisms in biofilm in order to remove the toxicity of produced water, at low cost with a low footprint for offshore sites.
For a long time, the concentration of oil-in-water was the unique specification for water disposal into the sea. With a new European regulation and worldwide evolution, the environmental performance includes also the demonstration of toxicity removal close to the production site.
Worldwide, the quantity of produced water is increasing continuously year after year of production. Even if produced water reinjection is the favorite option within TOTAL, a large part of produced water is still released into the sea.
The technologies, currently implemented offshore, are not always sufficient to comply with this regulatory evolution: suspended hydrocarbons are well treated but dissolved compounds are not. Biological treatment can reduce the toxicity of wastewater as it will biodegrade organic pollution such as phenols, mono or Poly Aromatic Hydrocarbons. But the size of conventional biotreatment equipments is not compatible with the offshore constraints.
Among biotreatment systems, a technology called MBBR (Moving Bed Biofilm Reactor) which involves bacteria organized in biofilm attached to supports, demonstrated a strong robustness compared to conventional activated sludge. The size reduction of equipments induced by MBBR has never been evaluated on saline produced water.
Lab trials demonstrated the potential of biodegradation for saline water. The team wanted to reduce the size of equipments by dividing by at least 20 the residence time of the bioreactor.
Lab experiments with supported biomass demonstrated the efficiency of the system on produced water containing up to 15% of salinity. The ecotoxicity measured on sensitive species was removed and the concentration of hydrocarbons was drastically reduced (<3 mg/L).
The experimental pilot (0.5-4 m3/h) was operated for 10 months until May 2017 in South West of France on a production site. With only 30 min residence time, the toxicity was reduced by 85% where usual biotreatments require 24 hours of residence time.
The pilot is equipped with a final step including membrane filtration with reverse osmosis in order to demonstrate the feasibility of desalination for water reuse.
The technology is the first compact biological treatment. Stakes are huge. For a flowrate 20000 bpd, the investment cost for a TOTAL site offshore is today close to 40M$. This cost is estimated at 10M$, the footprint is divided by 3 and the weight reduced by 2 compared to extraction process. It is now possible to implement a biotreatment offshore.
