Graduation Date

Summer 2018

Document Type

Project

Program

Master of Science degree with a major in Environmental Systems, option Environmental Resources Engineering

Committee Chair Name

Dr. Eileen Cashman

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Dr. Brad Finney

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Dr. Margaret Lang

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Dr. Robert Gearheart

Fourth Committee Member Affiliation

Community Member or Outside Professional

Subject Categories

Environmental Resources Engineering

Abstract

After 33 years of operation with little maintenance, the treatment wetlands at the Arcata Wastewater Treatment Facility (AWTF) suffer from reduced treatment capacity and internal loading issues, leading to reduced performance in recent years. The next NPDES permit for the facility will regulate discharge ammonia concentrations, and internal ammonia loads, associated with accumulated solids in the system, may lead to future regulation violations.

To begin addressing this problem, the City of Arcata entered into a rental agreement with Absolute Aeration to install two Blue Frog circulators in Treatment Wetland 3 (TW3). The goal of this project was to determine if the circulators could digest settled solids in-situ, restoring the treatment capacity and reducing the internal loads of nitrogen in TW3, without causing negative impacts to downstream water quality. These questions were addressed by four periodic sludge surveys, which occurred between April 2016 and November 2017, and weekly water quality sampling. The surveys tracked volumetric changes in the settled solids layer using cut and fill analysis with ArcGIS. Survey results showed that the Blue Frog System (BFS) reduced sludge depths and restored treatment capacity in its area-of-influence, but not across the entire wetland. At the end of the project, there was a net increase in the volume of the settled solids layer of approximately 4800 ft3. The incoming volume of solids, estimated with TSS removal rates measured during the project, was approximately 6900 ft3 to 11700 ft3, meaning the estimated volumetric increase of the settled solids layer was 30% to 59% of the total volume of solids that entered the wetland. Due to the lack of a control solids survey on a wetland without the BFS in place, it is uncertain to what degree the BFS affected solids reduction compared to biochemical processes that naturally occur in wetlands. Weekly sampling of TSS, nitrogen, and BOD indicated there were no negative impacts to downstream water quality during the project. Results showed that the BFS did not reduce ammonia concentrations through TW3, seen by internal increases of ammonia over much of the project. Overall, results indicate that the BFS will not be the method to deal with the settled solids within the treatment wetlands but may be useful in restoring some capacity in open areas and potentially aid in reduction of incoming loads.

Citation Style

ASCE

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