This Idaho Wastewater Treatment plant’s two existing single-ring oxidation ditches were facing increased flows and a new tougher phosphorus limit of less than 2.3 kg (5 lb) of total phosphorus per day. In addition to a tight budget, the small amount of land available also hampered the city’s options.
The consultant’s evaluation confirmed fine-bubble aeration “would require a new blower building” and “a new concrete surface” would be required for surface aerators according to the project engineer. “Furthermore, the fine-bubble capital cost was about 50% higher, and the surface aerators were cost-prohibitive by 30%”.
The city chose to install the Tri-Oval® oxidation ditch system with the dNOx oxidation-reduction potential (ORP) control system by dTEC Systems to optimize nitrification/denitrification. Only minimal modifications were needed to convert the existing brush rotor basins to the Tri-Oval® system and the existing ditches did not even need to be drained for the installation.
The Tri-Oval® system, driven by the Aire-O2 Triton® process aerator/mixer’s ability to drive fine bubble aeration to a depth of 33 ft (10m) allowed the city a smaller footprint compared to other system options. The dual-mode aerator/mixers also allows for the creation of aerobic and anoxic zones in a single-ring oxidation ditch for cost-effective BNR operation. The onboard regenerative blower enables the Triton to aerate and mix or mix only without the need for large blowers, blower buildings or additional anoxic basins. Nitrification and denitrification are carried out in the same basin.
Energy savings were found with the ORP control system and dissolved oxygen (DO) controls. Some of the Tritons could be turned off completely during the anoxic (mixing only) cycles, with only two units needed to completely mix each basin. Variable frequency drives ere also installed on the blowers and were used to adjust them when in DO-control mode, also adding to energy savings.
The employees were also happy with Aeration Industries’ solution to their problem. The aerators don’t splash wastewater, pathogens or odors into the air so they are quieter and the lack of mist prevents bridge icing in the winter.
“Low maintenance is also a feature of the installation,” said the operator. In the past, the basins needed to be drained to remove the sludge deposit every two years, reducing plant capacity and taking several days and heavy equipment. The Tritons’ effective mixing eliminates sludge deposits, saving time and money previously spent on its removal. The Tritons require minimal maintenance due to the slow speed of the motor, few wearing parts and the proprietary-engineered water-lubricated bearing. Simple maintenance can be performed from the walkway without draining the basin or the use of cranes or valve or gear reducers.
This treatment plant has met their effluent requirements while staying in budget and the small area available for the installation. The project also allowed them to use their existing aeration basins with minimal structural modifications or construction costs.