Credit: Photo: HLB Otak

Warrenton's new wastewater treatment plant lets a nearby seafood-processing plant discharge into the outfall, thus enabling the plant to continue operations and maintain more than 200 local jobs
Treating The Wastewater

Warrenton's previous facultative lagoon system had two 12-acre cells in series. In this method, algae populates the top layer of the water column, using sunlight and producing oxygen. Aerobic bacteria grows in between, and anaerobic bacteria populates the bottom layer to treat the wastewater of organics and nutrients. The wastewater, moved by gravity, then heads through a chlorine contact chamber where it's disinfected with chlorine gas before beingdischarged into a constructed drainage ditch; it then flows into the Columbia River during low tides.

In the new process, the influent building receives incoming wastewater, which is screened and subsequently treated by a grit removal system before being dispersed into one of the three basins. The activated sludge technology uses microorganisms (bacteria) present in the reactors of the SBR basins. Treatment consists of filling, reacting, settling, and decanting. Nitrification and denitrification can occur with alternating aeration and mixing regimens.

Within the SBR, the blowers aerate the wastewater through a diffused aeration system, starting the bacteria's aerobic reaction. These bacteria are retained to maintain sufficient quantities. When the aeration process ceases (i.e., theblowers stop), the biomass settles and a decanter removes treated effluent from the top while the bacteria settle to the bottom. Sludge is then pumped to one of two digesters.

The decanted effluent flows to the final process and undergoes UV disinfection. This type of disinfection is user-friendly for operators and prevents the spread of waterborne diseases to downstream users, leaving the environmentfree of any residual effect that can be harmful to humans or aquatic life. Once the effluent is treated through the UV process, it is ready to be discharged through an outfall pipe to the Columbia River.

All Systems Go

The plant began operations June 2006 (though not fully operational until January 2007) and in less than a year, city manager Ed Madere received test results for the plant's first batches of effluent. Initial laboratory test samplesyielded =4 parts per million (ppm) biochemical oxygen demand test results, =2 ppm total suspended solids, =0.1 ppm nitrogen as ammonia, and =2 fecal coliform. The treated water is also cooler than the ColumbiaRiver, translating into cleaner, safer water than the river itself.

In addition, the project had less than 3% in change orders and came in on schedule and under budget on construction-management costs.

The advantages of the new wastewater treatment plant include greater flexibility, improved operational reliability, lower investment and recurrent cost, energy savings, and a smaller plant footprint. Warrenton's facility alsonow has the capability to treat 2.3 mgd with a peak instantaneous flow of 4.7 mgd, depending on how the plant is being operated.

Equally important, the new plant illustrates the balance that this coastal community has found between accommodating growth, ensuring the vitality of the environment, and promoting the viability of the local economy. These factors, combined with the site's scalability to four basins if the growth rate requires it, have positioned Warrenton to meet both today's desires and tomorrow's demands.

Forrester is a senior engineering technician at HLB Otak, Seaside, Ore.

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