Treating Water in a Harsh Environment

Located on the coast of the Chukchi Sea, Barrow, Alaska is the northernmost community in the U.S. From mid-November to mid-January the sun never rises, leaving the city in total darkness. During the summer, the opposite occurs—the sun never sets. One thing that draws people to Barrow is the scenic beauty of the rolling ocean and tundra. There are roaming polar bears, caribou and walrus.

To help protect human health as well as the precious landscape and animal life, the North Slope Borough has installed Enviroquip’s membrane bioreactor (MBR) technology for its new wastewater treatment facility.

Historically, in many villages in Alaska, lagoons have been used to store and treat wastewater. Unfortunately, these lagoons remain frozen most of the year, and their storage volume and treatment effectiveness is not adequate to meet wastewater discharge standards.

The advent and implementation of membrane bioreactors for wastewater treatment has increasingly gained acceptance in the continental U.S. This technology is beneficial and well adapted for use in rural communities in harsh arctic environments.

The Process

Raw wastewater is delivered to the plant headworks, passes through a coarse screen and flows through the fine screens into the MBR process at the anoxic (AX) basin, where it is mixed with recycled activated sludge. A screw conveyor/compactor is supplied for collection of solids from the fine screens and automatically transferred to a collection bin.

In the absence of dissolved oxygen, microorganisms convert nitrate (NO3) to nitrogen gas (N2) in a process called denitrification. Meanwhile, BOD is consumed to synthesize cell mass. The denitrified wastewater then flows to the pre-aeration basins by gravity.

In the pre-aeration basins, fine-bubble aeration is used to provide oxygen for nitrification to converting ammonium to nitrate. From the basins, mixed liquor then flows by gravity to the MBRs, where biological treatment is completed, and the solids are separated from the clean water. In each MBR, integral diffusers furnish air for cleaning and mixing requirements. The added air also supplements the oxygen supplied in the pre-aeration basins for biological treatment.

Activated sludge is pumped back to the splitter box, completing an internal recycle. A suction-configured permeate collection system sends permeate to a UV disinfection system, which disinfects prior to discharge.

Enviroquip was selected as the most appropriate solution through a competitive membrane equipment selection and procurement process that considered both financial and nonfinancial criteria. The state-of-the-art facility is a great example of how a small community can tackle modern problems while continuing to protect the environment and natural resources.

Overcoming the extreme challenges and logistics associated with a remote project located above the Arctic Circle, the MBR treatment plant was commissioned in June 2008.