Pilot‐Plant Evaluation of Porous Biomass Supports

Abstract

Several porous biomass‐support systems are currently available for use in the activated‐sludge process. One of these systems, Captor, utilizes polyurethane foam pads to provide biofllm growth sites that transform an aerobic suspended‐growth reactor into a fixed‐film reactor. The pads are periodically withdrawn via a conveyor system and cleaned to remove excess biomass. A two‐year pilot‐plant evaluation of the Captor biomass‐support system was undertaken at the U.S. Environmental Protection Agency's Test and Evaluation Facility. Three reactors were operated under various loading conditions, dissolved‐oxygen (DO) levels, and pad‐cleaning frequencies in both series and parallel flow configurations. The system efficiently converted soluble biochemical oxygen demand (BOD) to new biomass, but the majority of the solids exited in the process effluent rather than via the pad cleaners. Increased pad cleaning provided only marginal improvement. Nitrification was evaluated during series operation. Pad durability was good, but overall system economics were not impressive. There was no evidence of enhanced oxygen transfer efficiencies as previously claimed.