The Dry Creek WWTP was experiencing relatively poor treatment and biological activity was insufficient. In 2009, Decatur Utilities retained Ardurra (formerly Constantine Engineering) to evaluate the plant processes and identify short-term and long-term improvements. As part of the evaluation, Ardurra performed:  

• Design Data Review 
• Process Performance Review 
• BioWin Process Modeling 
• RAS/WAS Review 
• Solids Dewatering/Disposal Review 
• Nutrient Removal Review 
• Energy Consumption Review 
• Sulfate/Odor Control Long Term 
• Regulatory Compliance Long Term 
• Industrial Pre-treatment Ordinance Review 

Ardurra 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, Ardurra 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 (BioWin®) and performance testing at the plant, our team 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. 

Ardurra provided engineering design services, bidding assistance, services during construction, and resident observation services for the solids handling improvements at the Dry Creek WWTP for Decatur Utilities. The Dry Creek WWTP is a 36-mgd activated sludge plant that includes headworks screening, aerated grit removal, primary clarification, activated sludge reactors, secondary clarification, disinfection, anaerobic sludge digestion, and solids de-watering. 

The improvements in Phase 2 include: 

• Rehabilitation of the six (6) primary clarifiers 
• Rehabilitation of and improvements to four (4)anaerobic digesters  
• New methane gas recovery compressors and scrubbers 
• SCADA improvements and integration 
• Site electrical lighting improvements 
• New solids de-watering facilities using centrifuges   

The new solids de-watering facility included two (2) new Centrifuge Systems, a stainless steel chute and electric diverter gate connected between the cake discharge and screw conveyor, a new screw conveyor under the centrifuges, a liquid polymer system, two (2) new self-priming sludge pumps and the relocation of two (2) existing pumps in the de-watering pump station, four (4) new in-line grinders, a monorail, hoist, and trolley system; and all piping, valves, and miscellaneous appurtenances.