memorandum
to:
/Dr. Kerri hickenbottom
from:
/Jonathan Sander
subject:
/arcata marsh trip
date:
/March 1, 2017
PURPOSE : The intention of this memorandum is to review the details of the trip made to the Arcata Marsh Wastewater Treatment Plant, in southern Arcata, from 3-5 P.M. on February 23rd, 2017. Included are the facility’s methods of operation and operable status, and plans for the future of the Marsh.
DISCUSSION: At the Marsh treatment facility, we were given a walk-through tour through all of the steps and methods by which the facility treats and discharges the sewage of Arcata into the Humboldt Bay safely and efficiently. We began the tour with a briefing on the basics of the plant, operating numbers and the criteria that the treated water must meet. The plant treats around 6 million gallons during storm season due to stormwater runoff. In the summertime, the volume of water treated is around 2.4 million gallons. The reason for this seasonal difference is a lower tendency for rain in the summer months, and also that some of the student population of Arcata leaves for vacation. Because of the AMWWP’s age, some aspects of the plant could use repair. We then explored the components of the treatment process, starting with the headworks. The headworks use Archimedes screw pumps to transport the water uphill. This step uses screens to separate grit and large solids from the water. Next, the water is transported to the primary clarifier, where sludge/TSS is settled out. From here, the sludge moves to the digester and is composted and processed for fertilizer, and the water moves to the innovative oxygenation ponds. In these oxygenation ponds, photosynthetic algae produce oxygen, which facilitates bacterial growth. The bacteria consume the leftover organic matter, BOD and TSS in the water. The biologically treated water then goes through the treatment wetlands, where large vegetation shades out and kills the algae that grew in the previous step, along with providing a physical obstacle to filter out and reduce bacteria. We discovered that the cattails and bullrush that made up the patch of vegetation has over time become suspended in the water, which doesn’t prove as efficient of a filter as being rooted into the bottom of the pond. After this step, the water goes through chlorination to kill the bacteria, a possible future modification to the treatment process is replacing the chlorination step with ultraviolet radiation. The water is then dechlorinated, and a portion is discharged into the Humboldt Bay. The other portion is diverted to the enhancement wetlands where it provides habitat for birds and recreation. At the end of the treatment process, the water is expected to have around 30 ppm BOD.
CONCLUSION: The trip to the Arcata Waste Water Treatment Plant was a very educational and enlightening experience, and provided relevant context to the material we are covering in our ENG115 class. Opportunities like this trip do well to inspire engineers to pursue projects of equal amounts of innovation and importance to society.