Constructed Wetlands: Water Treatment Technology at Shell

The relative comparisons of CAPEX and OPEX numbers show that constructed wetlands are cheaper to construct (upwards of 40% cheaper) and that the OPEX figures are considered significantly lower (>80%).

There is little literature information on the CAPEX and OPEX of water treatment via constructed wetlands vis-à-vis conventional (grey) infrastructure, and just one in the petrochemical wastewater treatment area.

In addition to the above, there are internal learnings from the PDO Nimr oil field produced water treatment reed-bed. Future projects and the debottlenecking of the existing onshore asset base can benefit from the deployment of this technology.

CONSTRUCTED WETLANDS: UNLOCKING WATER TREATMENT TECHNOLOGY AT SHELL

By Adrian Irimia, Georg Stockinger

Constructed Wetlands (CW) or engineered wetlands are water and wastewater treatment technologies well established in runoff control, acid mine water treatment, septage waste, sewage treatment and other applications. They can replace or augment conventional steel and concrete facilities (grey infrastructure), particularly in locations and climates where they offer clear advantages over the conventional approach.

In the Oil & Gas industry this technology has been also applied for a couple of decades in some services, depending on the type of feed water to be treated.

One example is the Petroleum Development Oman LLC, a joint venture with the Shell Petroleum Company and the Government of Oman, which owns the world’s largest commercial wetland covering more than 360 ha and treating more than 95,000 m3/day of produced water.

The plant is designed, built and operated by BAUER Nimr LLC. This plant has been in operation since 2011, consistently producing an effluent at below detectable Oil and Grease content (< 0.5 mg/l). To build upon this success and further capture business value, the Green Infrastructure Programme within Shell looked into the opportunity of introducing wetlands as a water/wastewater treatment technology at par with other treatment processes used within the company. Subsequently, an internal technical assessment and derisking process (Development Release) was completed.

Refinery/petrochemical Wastewater

There were a number of articles describing either full field facilities or studies carried out at mesocosm or pilot scale on refinery and petrochemical secondary treated wastewater. The plots below show the principal quality parameters within which the tests were successfully carried out.

Fig. 1 Operation envelope petrochemical water-1

Fig. 2 Operation envelope petrochemical water-2

It should be mentioned that in all cases the feed first undergoes pre-treatment (e.g. activated sludge) and the CW treatment delivers the final polishing before discharge.

Domestic Wastewater & Produced Water

Constructed wetlands have been used for treatment of municipal wastewater for a number of decades. Most of the wetlands used in the last decades have been for polishing municipal wastewater (tertiary treatment). Constructed wetland technology should be used in combination with other treatment technologies. USEPA does not recommend using constructed wetlands for primary treatment of raw municipal sewage, however.

Fig. 3 Operation envelope sewage

Produced Water

Fig.4 shows the minimum and maximum removal efficiencies for a number of significant contaminants.  

Hybrid: An example of a WWTP, involving a CW

Cross Business Applicability Within Shell

In general, there is a potential to remove most of the components of concern for Shell (a significant exception being salts), however the efficiency of the CWs seems to be highly variable and dependent on local conditions.

Treatment wetlands are very versatile and could be employed in a large spectrum of Shell businesses. For operating assets, constructed wetlands can bring benefits when replacement of existing water treatment facilities is needed either at the inlet or the outlet of the plant (such as for solids reduction in river water or wastewater polishing, respectively). New projects offer the best prospect for the design and installation of constructed wetlands, however.

In general, treatment wetlands can be applied as:

A means to strategically recapitalize aging water treatment infrastructure that need regular rejuvenation or replacement of equipment (i.e. brownfield applications)

In areas that are environmentally stressed and would benefit from improved land use, enhanced biodiversity, better management of water resources (brownfield and greenfield applications)

They can be adapted to the diverse assets in Shell. For example passive and low manned CWs could be employed in reclamation or decommissioning phases in downstream assets; while more engineered systems (e.g. aerated reed beds) can be applied in active locations where there are operation and maintenance resources available.

Read more: Water World