Pulsed Hydraulics Mixing for Wastewater Treatment Plants
Wastewater Treatment : Pulsed Hydraulics Aeration Mixing vs. No Mixing
A method that decouples the mixing from the aeration function at wastewater treatment plants using fine and coarse bubble diffuser technology and resulting in energy savings.
Item ID: 443
Process Loads & Appliances--Municipal Processes
The Pulsed Hydraulics aeration basin mixing technology, marketed by Pulsed Hydraulics, Inc., consists of forming a large, beachball-sized bubble at a forming plate every 20 seconds. The stainless steel plates squash the compressed air to form a wider bubble. The system requires a pulse of 45-psig compressed air for half a second to form each bubble. As the large bubbles rise, they lift total suspended solids (TSS) to the top of the tank, and then form a current that goes to the side of the tank before falling to the bottom, creating a circular motion. The downward movement keeps small aeration bubbles in the liquid longer, resulting in both better mixing and more effective oxygen transfer.
Fine and ultra-fine bubble aeration provide for good oxygen transfer but do not provide effective mixing. TSS concentrations often show a 15% to 20% variation from the top to the bottom of a basin. Nutrients are not equally distributed in the basin, indicating that the facility is not processing waste at design capacity.
Current designs using turbo blowers or rotary-positive displacement blowers with adjustable speed drives limit air flow turn-down as bubbles mix the aeration basin contents and provide oxygen transfer. The Pulsed Hydraulics technology decouples mixing functions from the fine bubble diffusers, allowing for reduced air flows that maintain dissolved oxygen levels at optimum concentrations. Tests show that the Pulsed Hydraulics system uses less than 50% of the energy required by two submersible mixers with propeller blades. When used in conjunction with a fine-bubble diffuser system, the Pulsed Hydraulics mixing system also enhances the oxygen transfer rate by 7.6%, resulting in reduced blower energy requirements.
Baseline Description: Turbo or rotary-positive displacement blowers
Baseline Energy Use: 78840 kWh per year per Aeration Basin
A Pulsed Hydraulics mixing system was tested against two Uniprop submersible two bladed propeller mixers at the Red Hook WPCP in New York. The testing examined uniform distributions of suspended solids, maintenance of low dissolved oxygen (DO) concentrations, and preventative maintenance and energy costs. The Pulsed Hydraulics unit required only 6 brake horsepower (bhp) per anoxic zone versus the 12 bhp required for the submersible mixers. Annual mixing energy savings are thus 50%. Another study found that the Pulsed Hydraulics system when operated in conjunction with a fine bubble diffuser aeration system enhanced the overall oxygen transfer effectiveness by 7.6% above the sum of the oxygen that would be transferred by each individual system (i.e. by the fine bubble diffuser and the pulsed hydraulic unit when operating alone). This increase in oxygen transfer rate means that the blower system serving the diffusers can be turned down, resulting in a substantial additional energy savings.
Manufacturer's Energy Savings Claims:
"Typical" Savings: 50%
Savings Range: From 50% to 66%
Best Estimate of Energy Savings:
"Typical" Savings: 50%
Energy Savings Reliability: 3 - Limited Assessment
The manufacturer does not make specific energy savings claims, but it seems it will be non-trivial, so we chose 10%.
Energy Use of Emerging Technology:
39,420 kWh per Aeration Basin per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Units: Aeration Basin
Currently no data available.
Installed first cost per: Aeration Basin
Emerging Technology Unit Cost (Equipment Only): $29000.00
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $0.00
The Pulsed Hydraulics mixing system can be part of a new installation or a retrofit to replaced existing mechanical mixers. Cost of a retrofit pulsed hydraulics unit installed at the Red Hook WPCP is $29,000. For a new installation, the mechanical mixers may actually have a higher capital cost. The unit installed at the Red Hook WPCP consists of 9 sets of two bubble forming plates, supplied by a 5 hp air compressor through 1-inch diameter PVC pipe. Solenoid valves controlled by a mixing system controller supplies the air that creates intermittent bubbles at each forming plate. Bubble formation occurs about 6 times per minute to optimize the mixing action and keep DO within regulated concentrations.
Simple payback, new construction (years): 8.2
Simple payback, retrofit (years): 8.2
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.