Hargis + Associates Inc

Start-up readiness of the Apache wetland.

The Apache Wetland was constructed in 1997 pursuant to a U.S. Environmental Protection Agency order to treat nitrate-contaminated groundwater within the Apache Powder Superfund Site. To date, the treatment facility is entering its fourth growing season in an effort to accumulate sufficient carbonaceous detritus of principally decayed Typha latifolia biomass. This substrate is required to maintain hypoxic-anoxic conditions within four denitrification cells and thereby sustain denitrifying conditions within the flow-through cells. Adverse factors, such as multiple infestations of larval Simyra henrici and low antecedent organic carbon in the desert soils are believed to have delayed start-up to date.

In summer 2000, COD, DO, and nitrate-N concentrations within the denitrification cells were monitored during the experimental introduction of a molasses solution. This was intended to simulate the magnitude of carbon loading anticipated during full-scale operation and produced indications favoring start-up. During the spring-early summer timeframe of 2001, monitoring of start-up parameters will continue. Additionally, DO concentrations and submergent vegetation (Potamogeton pectinatus) density will be evaluated within the aerobic nitrification cell, which is designed to eliminate co-generated ammonia. This evaluation is expected to provide the basis for petitioning the agency for full- or limited-scale start-up of the facility. At full-scale operation, the system is designed to treat dissolved nitrate-N concentrations at up to 300 mg/l at a continuous influent rate of 250 gal/min. Residence times are believed to be on the order of seven to ten days.

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