What are the operating factors for Aerated Lagoons?
One of the aerobic suspended growth techniques is “aerated lagoons”.
An aerated lagoon is a basin where wastewater is treated in one of two ways: flow through or solids recycling.
Instead of photosynthetic oxygen output as in an oxidation pond, oxygen is normally provided via surface aerators on floats or permanent platforms, or diffused air aeration systems. The contents of the basin are kept suspended by the action of the aerators and the rising air bubbles from the diffuser. They are built with a depth ranging from 2 to 5 meters.
An aerobic lagoon's contents are thoroughly mixed.
The effluent comprises 1/3 to 1/2 the value of the entering BOD in the form of cell tissue, depending on the detention duration. Solids must be settled out of the effluent before it can be released. There is no difference between this and modified ASP if the solids are returned to the lagoon.
The mean cell retention time should be chosen based on the assumptions that:
1) The suspended microorganisms will easily flocculate by sedimentation, and
2) That an acceptable safety factor is supplied when compared to the washout mean cell residence time.
The amount of oxygen required is determined by the activated sludge process. The quantity of oxygen required varies from 0.7 to 1.4 times the amount of BOD-5 eliminated in general.
Aerated lagoons offer benefits such as simplicity of operation and maintenance, wastewater equalization, and a high heat dissipation capacity when needed. Large area requirements, difficulties in process adjustment, high effluent suspended particles content, and sensitivity of process efficiency to variations in ambient air temperature are all downsides of aerated lagoons.
Factors to be considered
1: SOTE: It stands for Standard Oxygen Transfer Efficiency, which is the measurement of how much oxygen is transmitted by a specific aerator in clean water according to ASCE testing criteria. It's frequently used in aeration calculations to figure out how much air is needed to deliver the pounds/kilograms of oxygen required for aerated lagoon treatment.
The lower the SOTE %, the less air is required.The single most important aspect in determining SOTE is bubble size. The better the efficiency, the smaller the bubble. This is related to the surface area to volume ratio of the bubble, as well as the rate at which it rises through the water (the larger the bubble, the faster it rises).
SOTE has a role in aerated lagoon efficiency because if less air is required to produce the requisite oxygen, the blower horsepower may be reduced. As a result, energy expenses may be reduced. It's crucial to remember, though, that SOTE isn't a substitute for energy efficiency.
2: SAE (Standard Aeration Efficiency):It is a design tool that allows you to evaluate the running expenses of various aerators in an aerated lagoon application. It contains both SOTE and blower horsepower and is measured in pounds of oxygen per horsepower hour. As a consequence, it's a more comprehensive statistic that lets you evaluate the energy efficiency of different aerators side by side. While the SAE is rarely used in real aeration calculations, it is a useful statistic for evaluating the energy efficiency of various methods.
3: Rate of Flow: In an aerated lagoon, the quantity of air forced through a diffuser affects the efficiency with which it performs. When airflow per unit area is increased, for example, aeration efficiency falls because backpressure rises, it requires the blower to utilize more energy to produce the needed air. Running an aerator at the low end of the design range, on the other hand, can provide extremely efficient SOTE; however, this will almost certainly necessitate the addition of more aerators.
The cost of acquiring diffusers and additional pipe infrastructure for transporting air will rise as the number of aerators increases. Furthermore, adding more aeration equipment raises installation labour expenses as well as long-term maintenance expenditures.
4: Depth: The deeper the aerator is in a dispersed aeration system, the more effective it is. Many aerators give their SOTE as a measure of depth, even if it isn't precisely linear. A good coarse bubble diffuser, for example, may create 1% SOTE per foot of depth, whereas a good fine bubble diffuser may produce roughly 2% SOTE per foot of depth.
To sum it up!
It's critical to be aware of the potential difficulties and compromises while planning an efficient aerated lagoon. While SAE is a method of comparing the relative energy efficiencies of each aeration unit, it fails to account for the relevance of mixing. Blower horsepower and energy consumption are also affected by the interplay between depth, airflow per diffuser unit, and blower backpressure.
You will be better able to balance the deciding elements and tradeoffs involved in designing an optimal aerated lagoon if you understand the determining factors and tradeoffs involved.
If you need help designing an efficient aerated lagoon system, contact Netsol Water. We can provide you with design calculations, budgetary expenses, preliminary layouts, and a lifetime cost analysis.