Arcata Marsh tertiary treatment: Difference between revisions

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Tertiary Treatment. This is a final treatment stage done to purify the effluent, and it is rarely done. It can be a chemical treatment, where reactants are added to the effluent in order to precipitate out certain substances, or radiation treatment.

In effect, tertiary treatment “polishes” the effluent. Tertiary-treated effluent is water clean enough to swim in, irrigate with, or discharge into lakes or streams, often exceeding standards for municipal drinking water. Wetlands are perfectly capable of providing all three stages of treatment, but most constructed wetlands in the US are specifically for tertiary treatment only.

The Arcata Marsh uses microscopic screening and biological breakdown and absorption. After the effluent has passed through the primary clarifier and through the secondary treatment Marshes, it is chlorinated on its way out to the tertiary treatment marshes, also called enhancement marshes, where wastes are further broken down, and then the water is de-chlorinated before it is released into Humboldt Bay. In this type of tertiary treatment, the effluent is treated further just as it was in the secondary treatment. There are bacteria in the water eating whatever left over waste there still is and converting it into nutrients that the plants that live on the edges of the ponds can use to grow. Some bacteria need oxygen to digest the particles that they eat and are called aerobic decomposers, while bacteria that don’t use oxygen to digest their food are called anaerobic decomposers. The aerobic decomposers live throughout most of the water in the ponds where there is plenty of oxygen dissolved in the water for them to breathe, and the anaerobic decomposers live in the water and the sediment at the bottom of the ponds where there is not as much oxygen available. The plants that live on the edges of the pond also play an important role. Their roots help filter out some of the particles from the effluent, but they also provide shelter for a variety of small water creatures to live and create a whole ecosystem. The plants also absorb the nutrients that are released into the water by all of the bacteria as they digest their food.

In April of 1975 California’s State Resources Control Board (SWRCB) incorporated the Bays and Estuaries Policy which states: “It is the policy of the State Board that the discharge of municipal waters (exclusive to cooling water discharges) to enclosed bays and estuaries…shall be phased out at the earliest practicable date. Exceptions to this provision may be granted by a Regional Board only when the Regional Board finds that the wastewater in question would consistently be treated and discharged in such a manner that it would enhance the quality of receiving waters above that which would occur in the absence of the discharge”. In short it meant that no treated wastewater can be discharged into any bay unless it could be proven that it had been treated above and beyond the quality that it would have been had it never been waste water in the first place, the treatment facility is responsible for the enhancement of the water that is to flow out into the bay.

Enhancement as defined by the SWRCB, as it applies to Humboldt Bayinterprets the enhancement provision as: 1) full secondary treatment, with disinfection and dechlorination, of sewage discharges; 2) compliance with any additional NPDES permit requirements issued to protect beneficial uses; and 3) the fuller realization of existing beneficial uses or the creation of new beneficial uses either by or in cojunctin with a wastewater treatment project..

Existing beneficial uses include: 1) scenic enjoyment 2) Fish and wildlife habitat 3) Water oriented recreation ( in or out of water) 4) commercial fishing 5) Shell fish harvesting (oysters) 6) Navigation 7) Industrial water supply 8) Educational study.