Fine-pore diffuser retrofit at Ridgewood, New Jersey

The Ridgewood Wastewater Treatment Plant in Ridgewood, New Jersey underwent a retrofit from a coarse-bubble to fine-pore aeration system. Also, process modification from contact stabilization to tapered air occurred. This paper provides a review of the case history of plant and aeration performance of each system from 1981 through 1986. Non–steady state and off-gas oxygen transfer field testing at the plant over the 6-yr period provides the data base for the objective evaluation. An economic evaluation of retrofit impact is presented. Oxygen transfer efficiency of the fine pore system was approximately double that of the coarse bubble system. However, power costs were not reduced proportionately since a higher oxygen demand was supplied by the fine pore system to attain nitrification and meet the revised permit requirements. Severe nocardia foaming problems were encountered in the summer during the first three years of fine pore operation. These were controlled in the last two years by minimizing sludge recycle loads and preventing septic conditions in the aeration tanks.