FULL-SCALE PILOT TESTING OF AN ATTACHED GROWTH, MOVING BED BIOREACTOR AS A RETROFIT OF THE RBC PROCESS

The Cape May County (New Jersey) Municipal Utilities Authority (CMCMUA) operates four wastewater treatment plants, each of which provides full secondary treatment using the rotating biological contactor (RBC) process. The Ocean City Wastewater Treatment Facility (WTF), placed into operation in 1982, was designed based on hydraulic loading rates, standard RBC design practice at the time. Subsequent research and experience indicated that the hydraulic loading rate approach typically resulted in an RBC system that did not meet expected BOD removals, and a more conservative design approach evolved based on soluble BOD loading rates. Operations experience at the Ocean City WTF was consistent with these findings and BOD removals were less than projected when the plant was designed. Maintaining acceptable first-stage soluble BOD loading rates and BOD removals at summer flows and loads requires the addition of ferric chloride and polymer to the primary clarifier influent to remove a portion of the soluble BOD before the RBCs. While this practice has been effective, performance at the Ocean City WTF is less consistent than at the CMCMUA's other plants designed according to the more conservative soluble BOD loading rate approach. Ferric chloride addition at the Ocean City WTF also results in additional treatment costs and affects the consistency of solids removed from the plant, creating additional operational requirements and costs for solids handling and disposal. The CMCMUA evaluated a number of alternatives for upgrading the secondary treatment process at the Ocean City WTF to provide a level of performance and consistency similar to that at their other treatment plants, and without the need for ferric chloride addition. A retrofit of the existing RBC process using an attached growth, moving bed bio-reactor (MBBR), which is designed for higher soluble BOD loading rates than the typical RBC, was identified as a costeffective approach for meeting that objective. The CMCMUA conducted a full-scale pilot test of the MBBR process during the summer of 2003 and determined that the MBBR retrofit would provide the desired level of process performance and consistency at significantly lower capital costs than other alternatives, and without the need for ferric chloride addition.