Texas Basic Waste Water Operations Ch#10 Stabilization Ponds

Ponds can provide another secondary aerobic treatment of wastewater. Natural processes occurring in pond water are used to treat the wastewater. The purpose of a wastewater pond is to treat wastewater by natural processes in a warm climate with ample sunshine and low rainfall. They provide necessary low-cost wastewater treatment for many communities. This module explains the purpose, types, and operating parameters of ponds in a wastewater treatment process.

In broad terms, ponds are classified as stabilization (oxidation ponds), facultative, or anaerobic ponds. The treatment of organic matter in a stabilization or facultative pond depends upon sunlight, algae, and bacteria.

Aerobic conditions exist throughout the >depth< of a stabilization pond.

Aerobic bacteria consume organics and produce carbon dioxide as a byproduct. In a process called photosynthesis, algae uses sunlight for energy, then consumes the carbon dioxide and produces oxygen as a waste byproduct. Aerobic bacteria use the oxygen for further stabilization. Oxygen production relies on algae growth and algae growth relies on sunlight. Stabilization ponds are only 3–5 feet deep to ensure sunlight penetrates the depth.

Anaerobic ponds can treat agricultural and industrial waste containing high BOD. Sunlight and algae are not required, and dissolved oxygen is absent. Facultative bacteria break down organics into organic acids. Anaerobic bacteria convert organic acids into methane and carbon dioxide.

Ponds should be in an accessible location, but where there is no surface water drainage into the pond. Use compactible soil and liner to prevent seepage into groundwater. In addition, there should be no large vegetation in or around the pond area.

To prevent seepage, construct ponds in compacted soil. If the soil is porous, plastic sheeting or clay is used as a seal. The pond bottom must be even because irregularities cause short-circuiting. The levees must have a top width of at least 10 feet for vehicles and mowing machines. The inside bank should slope 1 foot vertical rise to 3 feet horizontal run with 2–3 feet of freeboard above the water line. Protect the banks from erosion, but remove large vegetation within at least 20 feet from the embankment and maintain it at a mowing level. Cattails and other plants growing in the pond can cause short-circuiting. Fit ponds with inlet devices with multiple outlets to control short-circuiting. The effluent outlets must have baffles to prevent discharge of floating material. The prevailing wind should blow toward the inlet and parallel to the length of the pond.

To prevent seepage, construct ponds in compacted soil. If the soil is porous, plastic sheeting or clay is used as a seal. The pond bottom must be even because irregularities cause short-circuiting. The levees must have a top width of at least 10 feet for vehicles and mowing machines. The inside bank should slope 1 foot vertical rise to 3 feet horizontal run with 2–3 feet of freeboard above the water line. Protect the banks from erosion, but remove large vegetation within at least 20 feet from the embankment and maintain it at a mowing level. Cattails and other plants growing in the pond can cause short-circuiting. Fit ponds with inlet devices with multiple outlets to control short-circuiting. The effluent outlets must have baffles to prevent discharge of floating material. The prevailing wind should blow toward the inlet and parallel to the length of the pond.

To prevent seepage, construct ponds in compacted soil. If the soil is porous, plastic sheeting or clay is used as a seal. The pond bottom must be even because irregularities cause short-circuiting. The levees must have a top width of at least 10 feet for vehicles and mowing machines. The inside bank should slope 1 foot vertical rise to 3 feet horizontal run with 2–3 feet of freeboard above the water line. Protect the banks from erosion, but remove large vegetation within at least 20 feet from the embankment and maintain it at a mowing level. Cattails and other plants growing in the pond can cause short-circuiting. Fit ponds with inlet devices with multiple outlets to control short-circuiting. The effluent outlets must have baffles to prevent discharge of floating material. The prevailing wind should blow toward the inlet and parallel to the length of the pond. NOTE: one passage referenced multiple times in quick succession..... maybe its important info......

Since ponds are typically designed for loading of 35 pounds of BOD per acre per day, primary treatment could result in reduced surface acre requirements, as well as improved effluent quality. Organic loading of a stabilization pond is about 35 pounds of BOD per acre per day with a detention time of 30 days or more. However, a secondary pond may only require 21 days of detention time because of the reduced waste load to the pond.

Under these (ideal) conditions, BOD is reduced 85–90%.

One surface acre furnishes treatment for about 300 people. The long detention time, radiation of sunlight, and natural predators in the pond cause a reduction in pathogenic (disease-causing) bacteria. Therefore, effluent chlorination is often unnecessary.

Take test samples from the influent, the pond itself, and the effluent. For continuous flow-through systems, it is recommended that the following samples be collected daily: pH, temperature, and DO. BOD, TSS, and fecal coliform tests require costly equipment and formal training. A small operation may sample for these tests and send them to a laboratory. NOTE: the answer key had a blank option choice dont blame me......