What is aeration of wastewater lagoon?
Lagoon aeration is the process by which both oxygen and mixing are used in a lagoon wastewater treatment system to create an aerobic treatment environment. After proper aeration and retention times, typically 20–40 days, aerated lagoons are capable of producing drains with concentrations below 10 mg / l BOD, TSS and in warmer climates, ammonia / nitrogen below 10 mg / l. The purpose of this article is to briefly describe and evaluate the various technologies of aeration of the lagoon in terms of aeration, installation and operation and maintenance.
According to the EPA newsletter, the goal of aeration in wastewater treatment is twofold: 1) to supply the necessary oxygen to the metabolizing microorganisms; and 2) to provide agitation so that the microorganisms come into contact with the dissolved and suspended organic matter (EPA 1999). This definition, despite the most important consideration in evaluating the technologies of aeration of the lagoons, since the effectiveness of the wastewater aeration system directly depends on its ability to aerate and mix. Without proper aeration, the aerated lagoon cannot meet its wastewater requirements — in this case, the costs of installation, operation and maintenance will become less significant for comparison.
There are two general categories that include lagoon aggression systems. One of them is surface aeration and is characterized by mechanical equipment floating on the surface of the water; the other is diffuse aeration, which releases bubbles from a point usually located at or near the bottom of the lagoon. In this article, we will consider mechanical aeration of the surface, diffused aorm, as well as an aeration diffuser, which combines both a coarse and a small bubble in a single portable device.
Surface aeration
Mechanical surface aerators are attached to the shore and are located on the surface of the water with floats. There is a mixture and aeration fluid using a propeller mounted on the engine. This propeller quickly moves the surrounding wastewater, which facilitates the introduction of ambient air. Engine sizes for surface aerators range from 2.5 to 100 horsepower.
The advantage of surface aerators is that they are portable and, therefore, easily installed by simply floating the aerator to its location. Moreover, they are relatively inexpensive in terms of initial capital expenditures. However, mechanical surface aeration, which constitutes 1.25–2.25 pounds of oxygen per hour of horsepower, is considered less energy efficient than diffuse aeration (EPA 2002). Given that aeration accounts for 60-80% of consumption at most sites, outdated and inefficient aeration systems are a major candidate for substitution (EPA 2006). Today, mechanical aerators are still used in thousands of wastewater treatment plants across the country, but they have no place for competitors, offering increased efficiency and low maintenance requirements.
In addition to the relatively low oxygen transfer efficiency of surface aerators, their location on the surface of the water has two distinctive disadvantages. First, surface aerators have a limited ability to mix below 6 ° below where they are located. The result is an accumulation of sediment at the bottom, which can, among other things, remove from the volume of the lagoon, thereby reducing retention time and bypassing the treatment process. Secondly, surface aerators are known to have high maintenance requirements due to the presence of an engine near the surface of the water. This is especially true in colder climates and is part of the reason that Illinois built surface aerators in new lagoon systems.
Coarse aeration of the bubble
Also known as large bubble diffusers, coarse bubble diffusers get their name from the type of bubble they produce. The coarse bubble diffusion systems consist of tens and hundreds of large bubble diffusers, each attached to an air line made of PVC or stainless steel attached to the bottom of the lagoon. The most common coarse bubble aerator for lagoons is the so-called static tube. When large bubbles are released at the bottom of the tube, they create an effect in which water falls from under the static tube and is pushed to the surface.
The main advantage of this technology is its durable construction and the possibility of mixing. Firstly, the circulation and turbulence created by the static tube ensure proper mixing of the entire thickness of the water, and sediment accumulation is limited. Secondly, the fact that there are no moving parts in the water and the holes, less than clogging, makes this a very reliable solution.
However, although more efficient than surface aerators, with aeration efficiency of between about 2-3 pounds of oxygen per horsepower, coarse bubble diffusers are 40–50% less efficient than their small bubble diffuser cousins. Moreover, the fixed aeration overhead grid makes them time consuming to install and makes it difficult to access maintenance if something goes wrong. Indeed, due to these factors it is quite rare to see diffusers of a coarse bubble, new or modified, which are installed today in aeration lagoons.
Fine bubble aeration
The thin bubble technology is a form of subsurface aeration that injects air into the water through very small (or small) bubbles (<2 mm). Thousands of small bubbles contribute to the transfer of oxygen to water because of their total large surface area and low buoyancy, which increases contact with air water. Typical systems of thin bubble diffusers for lagoons can be thrown from the surface and we can independently weigh and deliver air from a flexible suspended tube connected to an air side tube floating on the surface. The main advantage of the thin bubble technology is its high efficiency, providing 6-7 pounds / o2 hp. h, making it 40-60% more efficient than any other aeration solution for the lagoon. In addition, there are many fine bubble technologies specifically designed to reliably upgrade lagoon systems without dewatering or installing fixed pipelines, which makes installation relatively cost-effective.
There are two main disadvantages of thin bubble systems for lagoons. First, because small bubbles are so small, they are unable to create a significant amount of turbulence and mixing, which can lead to sediment accumulation and potential processing problems over time. Secondly, all small bubble diffusers require regular maintenance as they are prone to contamination / clogging. Contamination is the process by which bacteria accumulate and enter holes where air is scattered. Depending on the type of thin bubble diffuser used, be it a perforated tube, discs or EPDM tubes, regular cleaning is required.
Alternative aeration mars
MARS Aluminum Diffuser uses patented Double Bubble ™ technology, which combines two components that are integral to proper wastewater treatment. The first component is a thin vesicle membrane, which takes advantage of efficient oxygenation. The second component works in collaboration with a thin bubble membrane: an aerator of a static tube with a large bubble. This provides significant turbulence and mixing capabilities that help MARS process the entire column of water. Together, these components allow MARS to saturate with oxygen and efficiently process water, while effectively using energy. Triplepoint MARS also has a portable design - each MARS has its own weighted legs and is powered by air through a flexible weighted tube. Due to its flexibility in placement, MARS can be used to control virtually any cleaning medium for wastewater treatment, simply reducing it from the surface.
Maintenance is equally simple - each unit can be individually raised for a quick inspection, without dehydrating the lagoon. The system fans, the only components requiring regular maintenance, are located on land where they can be easily obtained. It also allows problem-free shore control processing. Designed without moving parts, the MARS system minimizes maintenance requirements — making it most accessible for treating the lagoon.
