Understanding Aeration Wastewater Treatment
What is Aeration Wastewater Treatment?
Aeration is an important step in the process of treating wastewater, including sewage effluent. Microorganisms in aeration wastewater treatment tanks break down organic compounds and nutrients. The removal of nutrients is critical, because wastewater that is overly rich in nutrients can cause ecosystem imbalances if released into the environment. One negative effect of nutrient enriched wastewater is the development of harmful algal blooms – or "dead zones"- in major bodies of water, such as the Gulf of Mexico. Dead zones are created when algae growth proceeds rapidly due to the abundance of nutrients, especially nitrogen and phosphorus, to feed on. When algal blooms grow out of control, they deprive other organisms of the oxygen they need to survive, and biodiversity suffers.
How is Aeration Wastewater Treatment Used?
Due to the ecological impact of nutrient enriched wastewater, governments enforce regulation to control the amount of nutrients allowed in wastewater discharge. To comply with regulations, industrial, agricultural, and other wastewater producers must carry out treatment. The most common type of wastewater treatment to remove nutrients is activated sludge treatment. This process begins with aeration wastewater treatment, where microorganisms are suspended and mixed into wastewater to promote the breakdown of nutrients.
Monitoring Dissolved Oxygen for Aeration Wastewater Treatment
Aeration wastewater treatment tanks are subject to careful monitoring to ensure that nutrient removal is achieved safely and efficiently. Dissolved oxygen is a critical parameter in the aeration process, because oxygen levels in the tank impact the health of the biomass (microorganisms) breaking down the nutrients. To maintain the proper oxygen levels for biomass productivity, wastewater treatment operators utilize aeration pumps, which add oxygen to the tanks.
Monitoring dissolved oxygen in the water ensures that the pumps are supplying enough oxygen for microorganisms to survive and carry out aeration wastewater treatment. It also helps promote efficiency: since aeration pumps are costly to operate, it is important to deliver enough oxygen but avoid oversupplying the tank and wasting resources. Dissolved oxygen sensors are used to collect data on the amount of oxygen in the tank, which indicates whether adjustments need to be made to the aeration pump system.
Monitoring pH for Aeration Wastewater Treatment
Another parameter that is monitored during wastewater aeration treatment is pH. Microbial communities involved in nutrient removal survive and thrive in certain pH ranges, usually between 6.5 and 8.5. Monitoring and adjusting pH helps maintain healthy communities of the microbes needed during wastewater treatment. Flat surface, self-cleaning pH probes are ideal for monitoring activated sludge treatment, as the flat glass resists breakage and build-up of suspended solids.
An aerated lagoon or aerated basin is a holding and/or treatment pond provided with artificial aeration to promote the biological oxidation of wastewaters. There are many other biological processes for treatment of wastewaters, for example activated sludge, trickling filters, rotating biological contactors and bio-filters. They all have in common the use of oxygen (or air) and microbial action to biotreat the pollutants in wastewaters.
Types of aerated lagoons or basins
There are many methods for aerating a lagoon or basin:
– Motor-driven floating surface aerators
– Motor-driven submerged aerators
– Motor-driven fixed-in-place surface aerators
– Injection of compressed air through submerged diffusers
Floating surface aerators
A Typical Surface-Aerated Basing (using motor-driven floating aerators)
Ponds or basins using floating surface aerators achieve 80 to 90% removal of BOD with retention times of 1 to 10 days. The ponds or basins may range in depth from 1.5 to 5.0 meters.
In a surface-aerated system, the aerators provide two functions: They transfer air into the basins required by the biological oxidation reactions, and they provide the mixing required for dispersing the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg O2/kWh
Animal waste-lagoon aeration
A large industrial dairy or feedlot operation can generate as much waste as a mid-sized city. While cities spend millions of dollars each year to process and dispose of municipal waste, feedlot owners cannot afford such expenditures. Factory farms are thus limited to disposing the manure in uncovered manure lagoons, or else spreading it on surrounding land.
The sheer magnitude of the waste often leads to its over-application onto nearby fields. The predictable result is a threat to the safety of the air as well as ground and surface water sources. The contaminants of concern are disease pathogens such as E.coli and salmonella, and a host of air pollutants such as hydrogen sulfide, ammonia, volatile organic compounds, and particulate matter. In addition there are concerns over antibiotics, metals, and toxic substances in the waste.
There are several types of aerators available to the confined-animal operator. These include bubble diffusers, venturis, paddle wheels, and self-aspirating aerators.
Self-aspirating aerators inject dissolved oxygen into the subsurface regions of the waste lagoon. They do this by creating a low-pressure zone at the end of an air tube. In the process they create a mild current that circulates the water without stirring up the odor.
Self-aspirating aerators normally contain a set of propellers that turn beneath the water surface. However, the latest self-aspirating aerator on the market, called the O2-Jeter, uses a circular turbine instead of propellers. According to our tests, the efficiency of the O2-Jeter series is one of the highest in the market today. The O2-Jeter uses a pontoon-mounted, highly efficient electric motor 2 horsepowers.
It is virtually impossible for the O2-Jeter to clog, even in an animal waste lagoon. The motor warranty is passed to the user, and all of the other parts are guaranteed for life. The O2-Jeter is ideal for any animal waste lagoon.
Stock Tanks & Pond Health
Three puzzling questions can arise in regard to these ponds:
1) Why did the fish suddenly die?
2) Why is the water pea green? And,
3) Why are there so many aquatic plants growing in the water?
All of these questions, and a host of others, point to a disruption in the ecosystem of the pond. The disruption usually can be traced to a drop in the level of dissolved oxygen.
Oxygen is an absolute key to a healthy pond. In a perfect world oxygen enters the pond at the surface of the water. Wave action at the surface and/or mild thermal currents carry the oxygen into the deeper depths of the water. Beneficial algae growth at various depths in the pond also produces dissolved oxygen during the daylight hours. Aerobic microorganisms (called aerobes) breathe this subsurface oxygen as they digest the organic nutrients in the water.
Dissolved oxygen promotes microbes that strip the ability of algae and pond scum to gain a foothold in the pond by robbing them of their nutrients. Did you know that some types of algea are harmful to humans.
If your pond is much more than six feet deep, then you can assume that the really deep layer has little or no dissolved oxygen. Such deep layers cannot benefit from the surface mixing of air and water. Plus, since sunlight usually cannot penetrate much more than six feet through the algae bloom, then there is no beneficial plant or algae growth in the the deep zone to produce oxygen. This condition can spell disaster if the water turns over.
Even fertilizers, pesticides, mown grass, or excessive amounts of fish food thrown into the pond can add to the nutrient load. To maintain a healthy pond, you need to control as many of these factors as possible. Even so, a good mechanical aerator is almost a must if you want to ensure that your pond stays healthy.