Nelson Environmental - Lagoon Aeration - Nitrification - Wastewater Treatment - Canada - United States

Raw Water Reservoir Aeration

The Problem

Nelson Environmental - Canada - United States

Raw Water Reservoirs (RWR) store water prior to passing it through a potable water treatment plant. In many cases, water quality in the raw water reservoirs is poor since surface runoff with high levels of dissolved organics, iron, and manganese, is the typical water source. These contaminants cause a brownish water color (staining) and contribute to undesirable taste and odor. Anaerobic decomposition of settled organic material generates Hydrogen Sulfide (H2S), creating a "rotten egg" taste and odor in raw water sources while increasing treatment plant chemical usage demand.

Natural atmospheric aeration in a reservoir only provides oxygenated conditions to a depth of 2 to 3 m during ice free conditions. In areas where ponds freeze over, there is no opportunity for surface re-aeration during cold periods. Typically, water intakes are located close to the bottom of the reservoir, where dense, poor water quality resides due to thermal stratification. The lack of dissolved oxygen also causes the release of phosphorus from anoxic sediments, encouraging algae growth and causing oxygen depletion during biodegradation. This further contributes to poor taste and odor.

The LINEAR Solution from Nelson Environmental

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Fine Bubble Aeration: The LINEAR fine bubble aeration diffusion tubing is laid on the bottom of the raw water reservoir to induce complete circulation and introduce oxygen at the sludge water interface. Systems are designed to turn over the water in the reservoirs multiple times per day to disrupt the formation of thermoclines and anaerobic zones. The overall aeration intensity is low so that it does not roil up the sludge and subsequently increase suspended solids.

Dissolved Oxygen: Dissolved oxygen reacts with the soluble iron and manganese in the water column creating a precipitate that settles to the bottom of the reservoir. Increased oxygen levels prevent bottom waters from becoming anoxic thus reducing the release of iron, manganese, and phosphorous from accumulated sediments back into the water column.

Oxidation eliminates undesirable tastes and odors that emanate from anaerobically decaying organic matter. It also provides useful food to support a mix of organisms that compete with undesirables, such as algae, for available nutrients.

Destratification: Destratification results when "good" and "bad" water layers are eliminated, converting the entire body of water to fully oxygenated conditions. Bottom intakes are no longer a problem as water quality is uniform throughout the pond and reservoir temperatures are equalized through destratification. Cooler water is mixed to the surface resulting in reduced algae growth and evaporation.

Aeration and mixing to destratify a reservoir will maintain dissolved oxygen levels above the 5 mg/L required to effectively reduce TOC levels and the formation potential of THMs. Conditions stressful to algae (high-light intensity and high-dissolved oxygen) can force algae into a photorespiratory state, thereby reducing THM formation potential.

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LINEAR diffuser tubing is composed of a virgin low density polyethylene (LDPE) containing >2% Carbon Black for UV resistance. An encapsulated ballast keel is located at the bottom of the tubing eliminating the need for concrete or steel weights.

Surgically produced die-cuts (air releases) in the tubing require 14 kPa (2 psi) more than hydrostatic pressure to allow air to pass through. The die-cuts act as valves throughout the life of the system, ensuring that:

  • The diffusers emit a uniform air pattern even if the pond bottom is not perfectly level. Bottom elevation variations of up to 0.5m (1.5 ft) will not compromise the bubble pattern.
  • If airflow is interrupted, the die-cuts act as one-way valves allowing water but little or no solids to enter the diffusers.

Performance

Treating water biologically by aerating a raw water reservoir is good environmental stewardship; as treatment plant chemical usage is significantly reduced from levels normally required to treat the water. Much of the organic, iron, and manganese removal occurs in the reservoir itself prior to reaching the water treatment plant.

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