The Dry Creek WWTP in Decatur, AL was experiencing relatively poor treatment and biological activity was insufficient. In 2009, Decatur Utilities retained Constantine Engineering, Inc. to evaluate the plant processes and identify short-term and long-term improvements. Constantine identified several significant design and operational deficiencies at the plant, as well as high loading for BOD, TSS, ammonia, and sulfate from industrial customers. Following the evaluation, Constantine provided Decatur Utilities with a two-phased approach for long-term performance of the plant, which included a new Industrial Pretreatment Ordinance and capital improvements at the plant.
The root of the biomass problems at the WWTP was that insufficient aeration combined with intermittent peak loads from industrial discharges as well as internal oxygen demands were starving the biomass. Available oxygen was insufficient to maintain cell growth and protect against shock loads. Based on biological modeling and performance testing at the plant, Constantine redesigned the aeration diffusers and air supply system for better and more energy-efficient operation. The improvements were completed in phases, starting with new fine-bubble diffusers followed by piping improvements, new high-efficiency turbo blowers, instrumentation, and SCADA. After implementation of the aeration improvements, Decatur Utilities easily achieved treatment goals and also reduced energy costs by as much as $300,000 per year.