Summary
Engineered wetlands are a promising technology for treatment of oilfield and
gasfield produced water. The engineering optimization of natural treatment
processes, adapted from chemical engineering reactor design principles, shows
that engineered wetlands are a viable alternative to mechanical produced water
treatment systems.
Engineered wetlands incorporate a subsurface flow gravel bed reactor, lined
with an impermeable liner and equipped with an aeration system to enhance
oxygen delivery. Design parameters include biodegradation rate coefficients for
biochemical oxygen demand (BOD) and individual organic compounds, produced
water flowrate, temperature, and influent and required effluent
concentrations.
An oil and gas company in the Caspian region is seeking to use engineered
wetlands for treatment of oilfield and gasfield produced water. The oilfield
produced water concentrations are high in total dissolved solids (TDS: 43048
mg/L), BOD (14693 mg/L), and oil and grease (1213 mg/L) and moderately high in
total benzene, toluene, ethylbenzene, and xylenes (BTEX; 3.067 mg/L). The
gasfield produced water concentrations are moderately high in TDS (16110 mg/L),
BOD (9910 mg/L), and oil and grease (557 mg/L) and high in total BTEX (12.393
mg/L). Pilot-scale engineered wetland treatment systems have been designed on a
flowrate basis of 100 m3/d using the first-order kinetic mass reaction model
recently published by Kadlec and Wallace (2009). This model uses a modified
tanks-in-series number that accounts for both hydraulic effects and weathering
effects in the biodegradation rate. Hydraulic effects are caused by dispersion
in the saturated gravel bed. Variation in the biodegradation rate is because of
rapid biodegradation at the upgradient portion of the engineered wetland, in
which short chain/low molecular weight organics are oxidized at rapid rates,
and slower biodegradation at the downgradient portion of the engineered
wetland, in which long chain/higher molecular weight organics are oxidized at
lower rates. This advanced design process, combined with BOD surface area
loading criteria, enables the optimization of engineered wetland design for
produced water treatment.
© 2009. Society of Petroleum Engineers
View full textPDF
(
325 KB
)
History
- Original manuscript received:
12 January 2009
- Meeting paper published:
23 March 2009
- Revised manuscript received:
7 May 2009
- Manuscript approved:
8 May 2009
- Published online:
21 September 2009
- Version of record:
21 September 2009
View Cart
