Intermittently Decanted Extended Aeration (IDEA)

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In IDEA process a period of aeration, sedimentation and a period of discharge occur repeatedly in a reactor and the inlet flow enters the bottom of the reactor, where it is slowly dispersed.

The treated wastewater is then discharged intermittently during the discharge period.

The IDEA treatment process consists of 3 phases:

• Aeration
• Settling
• Decanting

IDEA process steps:

The first phase: aeration, involves rapid surface mixing to mix the influent with the activated sludge. The mixing action aids in dissolving oxygen into the water whilst forcing the sludge into suspension from its settled state. Alum is added to bind the phosphorous present in the sewage, allowing it to settle out. Nitrification also occurs at this stage to convert ammonia to nitrite.

The second phase: Settling occurs when the surface aerators are stopped, which allows solids to migrate to the bottom of the tank. At this stage, anoxic conditions predominate in the sludge due to the lack of molecular oxygen, which cause the bacteria in the sludge to use oxygen the bound in nitrates (NO3–) for metabolism. This results in the effusion of nitrogen as a gas.

The third phase: During decanting, a trough is skimmed across the top layer of the tank, collecting the water to be sent off for further processing in downstream processes.

4 hours operating cycle for normal operation; 3 phases per cycle controlled by an automatic timing device:
• Aeration: 2.5 h
• Settling: 1.0 h
• Effluent decanting: 0.5 h
This process is similar to SBR process, which has eliminated a number of SBR process problems. The average biological removal efficiency in terms of BOD removal and COD removal was about 95.5% and 90%, respectively, and the average total nitrogen removal efficiency was about 90%. Also, phosphorus removal is one of the benefits of this process.

Specifications of IDEA System:
• Ease of Design and Construction. The biological reactors, i.e.: Demand Aeration Tanks & Intermittent Aeration Tanks consist of either square or rectangular tanks which are easy and fast to design.
• IDEA sewage treatment plants do not require equalization tank or secondary clarifier; this apparently will save plenty of area as compared with the conventional sequencing batch reactor (SBR) or circular-tank structures. Due to the above reasons, huge amount of inventory cost can also be saved.
• IDEA system is an extended aeration process which produces sludge with retention time or sludge age more than 20 days. As such, the sludge generated is well stabilized and does not require further digestion in a sludge digester.
• Due to the relatively longer sludge age, IDEA sewage treatment plants can absorb the shock loads better than any other process.
• Sludge volume index as low as 100 ml/g is typically achieved for a well maintained and operated IDEA sewage treatment plant. Low SVI means good settling sludge; this will enable IDEA sewage treatment plant to have a higher MLSS operating level without incurring wash-over of suspended solid during decanting phase. Such a low SVI value is almost impossible in the SBR system.
• The inlet flow is continuous, while the treated effluent is discharged intermittently.
• IDEA system is a cyclic process which consists of Aerate, Settle and Decant occur in 6 to 8 times a day, this enables sewage to nitrified and denitrified in many cycles and ensure the nitrogen gas liberated into the sewage has never exceeded the nitrogen solubility limit in the sewage

Effective parameters in IDEA system design:

Advantages of the IDEA Process:

• Reduce construction costs
• No pre-treatment required
• smaller space
• High quality of effluent and low volume of sludge
• Minimizes fluctuations in wastewater quality
• removal of nitrogen and phosphorus
• Easy operation and easy maintenance
• Odorless

Disadvantages of the IDEA Process:

• High operation energy requirements
• Sludge is often difficult to settle
• Not suitable for large flows