Ovivo® G-TAD™ Process

Ovivo's patented G-TADTM (Gravity Thickened Aerobic Digestion) process provides for the integrated operation of a gravity sludge thickener with two or more aerobic digesters. By operating these units as a combined system, improved treatment and efficiency is achieved.
  • Guaranteed Class B biosolids
  • Little operator attention required
  • Proven, reliable technology

For those owners looking for a simple, reliable means of achieving Class B biosolids, look no further than the Ovivo G-TAD (Gravity Thickened Aerobic Digestion). The robust design makes use of common wall construction to create a system that requires little operator attention and minimal maintenance while producing biosolids suitable for land application.

  • Batch operation provides improved pathogen destruction
  • Automated controls minimize operational requirements

For over 20 years the Ovivo G-TAD has been providing value to owners. The unique batch operation capability of the digesters leads to a significant reduction of pathogens in the sludge helping to ensure Class B compliance. At the same time the automated airlift pumps and thickener drive design minimize the amount of time operators have to spend maintaining the equipment of the G-TAD.

The G-TAD consists of two Aerobic Digester basins operating in conjunction with a Pre-Mix basin and a Gravity Thickener. One digester forms a loop with the Gravity Thickener and Pre-Mix Basin. Raw sludge is introduced into the Pre-Mix basin, where it is vigorously mixed and aerated to raise microbial activity and dissolved oxygen concentration. The sludge overflows from the Pre-Mix to the Gravity Thickener where solids are allowed to settle to the bottom without aeration establishing an anoxic stage in the settled sludge. This causes the sludge to be denitrified by microbial action, raising and stabilizing the pH. Supernatant is removed from the top of the Gravity Thickener through an effluent weir trough and returned to the head of the plant.

Thickened sludge is airlifted from the bottom of the Gravity Thickener to the “in-loop” Digester where it is aerated and nitrification occurs, but using less aeration than normally required in a digester, due the effect of alternating anoxic/aerobic phases. Scum is collected in the gravity thickener using a scum collection system (e.g. scum beach or slotted pipe skimmer) and is also airlifted to the “in-loop” Digester. Digested sludge overflows from the Aerobic Digester to the Pre-Mix, where it is mixed with incoming raw sludge, completing the loop. In this manner the sludge is continually decanted and thickened.

There used to be something called a PAD-G is this similar?

The G-TAD and PAD-G are one in the same. We utilize the same process flows, operational strategy and equipment in the G-TAD as the PAD-G, we simply felt that Gravity Thickened Aerobic Digestion (G-TAD) was a more accurate description of the system.

What concentration can the thickener get my solids to?

The compaction of the sludge in the G-TAD is very dependent of the settling characteristics of the sludge being fed to the system. Ovivo designs the G-TAD assuming that the thickener will concentrate the solids to 1.5%.

Are G-TADs suitable for retrofits?

Due to the common wall construction of most G-TADs retrofits are not the preferred application of the technology.

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