Masters Thesis

Treatment capabilities of the enhancement wetlands at the Arcata wastewater treatment facility

The Arcata Wastewater Treatment Facility has proposed an upgrade to their system that will modify the flow regime through the treatment facility. This modification will increase the loading of Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS) to the Enhancement Wetlands (EWs), an important component of the natural treatment system. A review of historical data has shown that the spring and fall months are likely to result in concentrations of BOD and TSS above the permit limits into the EWs (Pt 002). The addition of the new Treatment Marshes (TMs) 5 and 6 have the potential to decrease the concentrations of BOD (by 5-30 mg/L) and TSS (by 5-15 mg/L) entering the EWs if these TMs operate with the same removal efficiency as the original four TMs. The EWs have historically operated over a narrow range of flow conditions. Under the new flow regime, the flow rate will be higher and significantly more variable in the wet season. The EWs have shown performance in the past that suggests they can handle increased loads and still meet permit requirements most of the time, but constantly varying conditions are expected to result in a wider variability of effluent conditions and increased treatment is recommended upstream to reduce the risk of permit violations.

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