The PAD-K (Pre-thickened Aerobic Digestion) technology using the Kubota flat plate membranes process brings together Ovivo’s aerobic digestion and flat plate membrane experience into one integrated system. This combination provides owners with a truly revolutionary solids handling technology. The system consists of two or more aerobic digesters operating in conjunction with an anoxic basin and membrane thickener (MBT). One aerobic digester forms a recycle loop with the MBT and anoxic basin that causes digested sludge to be continuously thickened while undergoing both nitrification and denitrification.
Raw sludge containing organic material is introduced into the Anoxic basin, where it is vigorously mixed with nitrified sludge recycled from the in-loop digester. The combined sludge mixture contains the necessary substrates (carbon and energy sources) for the sludge to be denitrified by microbial action under anoxic conditions.
The driving force for the circulating flow of sludge through the in-loop basins is a simple airlift pump operating at approximately 3Q flow. Sludge is airlifted from the Anoxic basin into the MBT where it is thickened by the action of pulling water (permeate) through the membrane plates using a small centrifugal pump. Thickened sludge overflows from the MBT into the Aerobic Digester where it is aerated and nitrification occurs, but using less aeration than normally required in a digester, due to the effect of alternating anoxic/aerobic phases.
Digested sludge gravity flows from the Aerobic Digester to the Anoxic basin, where it is mixed with incoming raw sludge, completing the loop. In this manner the digested sludge is continually thickened and denitrified.
For larger facilities or those with dilute Waste Activated Sludge, Ovivo offers the Two pass PAD-K seen below in this video. The first pass is able to operate at a higher flux rate due to the relatively low concentration of solids while the second pass operates at a lower flux to prevent premature fouling of the membranes. This approach allows Ovivo to minimize the membrane area required thus lowering overall system costs.