PILOT-SCALE PERFORMANCE OF THE MBBR PROCESS AT THE CROW CREEK WWTP, CHEYENNE, WYOMING

The Cheyenne Board of Public Utilities (BOPU) needs to meet new ammonia limits and address the likely need for nitrogen and phosphorus removal within the next 10 to 15 years at their Crow Creek wastewater treatment plant (WWTP). Meeting the new ammonia limits and positioning for future nutrient removal presents a special challenge since the BOPU desires to minimize staffing levels at the Crow Creek WWTP. Historically, just one operator has been assigned to this facility.The Crow Creek WWTP's existing trickling filter (TF) system was determined to be not well-suited to meet effluent ammonia limits during the winter months, nor for positioning the WWTP for meeting nutrient limits in the future. Results of a process evaluation determined that the best overall approach for Crow Creek was to abandon the TFs and construct a single-pass, multi-stage moving bed biofilm reactor (MBBR) system⊗ to reduce biochemical oxygen demand (BOD), ammonia (NH4- N), and total inorganic nitrogen (TIN). Phosphorus removal will be added in the future via addition of a tertiary treatment step such as metal-salt addition followed by sand filtration.Full-scale MBBR facilities in a multi-stage configuration similar to that designed for Crow Creek WWTP have been effective in treating municipal wastewater in Europe. However both the BOPU and Black & Veatch (B&V) felt that a site-specific pilot study was warranted. Accordingly, an onsite pilot study was conducted for five months to confirm that the sizing parameters and conditions used for the initial design were sufficient to meet effluent NH4-N and TIN removal objectives. This paper presents the project background and pilot study methodology, the results and findings gleaned from the study, and the adjustments made to the final design as a result of the pilot work.