System Cuts Energy Costs, Improves Plant Performance
By installing a plantwide open control and energy management solution and a unique aeration/mixing system at its wastewater treatment plant, the city of Atwater, Calif., is achieving 30 percent energy savings over its former system and anticipates a savings increase when the system is fully optimized.
The new system has provided a noticeable reduction in secondary effluent suspended solids and enabled operations staff to reduce the mixed liquor concentration by 30 percent. Since its installation, there have been substantial improvements in the activated sludge aeration basin mixing, odor reduction, aerosol reduction, reduced energy consumption and improved dissolved oxygen control.
The system features the Biomixer, a self-contained aeration system equipped with an open automation control and energy management system from Cutler-Hammer. The Biomixer is manufactured by Biomixer Corp., Hawthorne, Ca. Since the Biomixer/Cutler-Hammer solution integrates control, energy management and a floating aeration/mixing system, Atwater can manage and monitor its energy usage as well as achieve key performance objectives.
Optimizing Performance
When the Atwater Canning Company installed its own treatment system, the citys activated sludge treatment system experienced a large reduction in organic loading. The system was engineered to handle large cannery loads and was now oversized for domestic loading. Mixing limitations in the activated sludge aeration basins led to an inefficient operation.
Optimizing Performance
To reduce operational costs, the city began investigating replacements for its floating mechanical aeration system. The city selected the computer controlled Cutler-Hammer/Biomixer solution because it provided good aeration/mixing and featured a control and energy management system.
Optimizing Performance
The new system allows the city to "minimize the use of expensive energy and maximize the use of inexpensive energy," said Monte Hamamoto, PSG Project Manager for the Atwater Wastewater Treatment Facility.
Optimizing Performance
"We knew that we used a lot of energy to operate our former surface aerator system, but we didnt know how much, where it was being used, how much was being used for each application, how to control it and how to reduce it. With the combination of Cutler-Hammer control and PowerNet energy monitoring software and the Biomixer, we can monitor and manage all of those parameters."
Optimizing Performance
Other key reasons the city of Atwater chose the Biomixer system were that it was available for a capital cost of $350,000 compared to $500,000+ for the other systems, it provided comparable dissolved oxygen production, good mixing action, enhanced operational control, a design that made maintenance items safely accessible from the surface on secured walkways and was available as a turnkey system that did not require capital improvements to the existing structures.
Integrating Two Technologies
The Biomixer equipment resembles an upside down helicopter with its rotating blades diffusing air bubbles, creates smaller bubbles by natural bubble shearing. These small bubbles provide oxygen transfer throughout the basin. The rotating diffuser blades automatically raise and lower to provide optimum aeration levels under a wide variety of conditions resulting in flexible energy consumption and improved dissolved oxygen production.
Integrating Two Technologies
The system uses an open automation network, which has the ability to communicate with the facilitywide network and machine control system.
Integrating Two Technologies
The Atwater facilitys system uses a Cuttler-Hammer SV9000 drive to control the rotation speed of the aerators diffuser blades. The drive provides the ability to vary the blade rotation speed to maintain a critical blade/liquid angle based on the thickness of the sludge. With closed PID loop control, the system gets a feedback signal from the drive indicating load and uses this information to control drive speed.
DO Control
Optimal operation of a wastewater treatment facility and efficient energy usage demands control of dissolved oxygen production. Since the load of BOD to the wastewater plant varies throughout the day, the amount of dissolved oxygen required by the system must vary accordingly. An on-board computer in each unit controls the submergence level of the rotating diffuser blades, which in turn controls the power consumption and dissolved oxygen production of the system. The deeper the blades are submerged, the more dissolved oxygen is produced. When the blades are at a shallower depth, the unit consumes less power and produces less dissolved oxygen.
DO Control
In contrast to other aeration systems, which attach the diffuser at the basin floor and vary the air flow to the diffuser, Biomixer varies the submergence level of the diffuser and maintains a constant air flow rate. Varying air flow limits the range over which the dissolved oxygen production level can be adjusted. In addition, as the dissolved oxygen production level (air flow rate) is decreased, mixing is greatly reduced. By varying the submergence rather than flow, the Biomixer has a full range of dissolved oxygen production level and does not reduce its mixing capabilities at reduced oxygen production levels.
DO Control
The retracting capability of the diffuser and the on-board computer provide real-time programmable control of the aeration and mixing process. The on-board computer is interfaced with industry standard dissolved oxygen probes and programmed by the operator to maintain a preset dissolved oxygen level. This provides precise process control for the operation and significant savings. Estimates are that 40 to 65 percent reductions in energy demand can be achieved by matching dissolved oxygen production with dissolved oxygen demand.
Energy Savings
When possible, dissolved oxygen production is minimized during periods of high energy cost and maximized during periods of low energy cost. Cutler-Hammers IQ Analyzer monitors the incoming electrical power of the wastewater treatment plant. Using information from the analyzer, the companys PowerNet software monitors current plant demand. The software is programmed with utility rates and structures the treatment process to maximize the use of inexpensive energy.
Energy Savings
This information is transmitted to NetSolver software, which makes a decision based on utility rates at a particular time, the dissolved oxygen level and the upcoming load that will impact the treatment plant. Once the decision is made, commands are sent to the aerators and equipment performance parameters are automatically adjusted to vary the depth of the diffuser blades, thus saving on-peak demand charges.
Energy Savings
This control technology also enables the unit to be programmed to greatly reduce the facilitys electrical demand charges. With the integration of the aeration system with the on-board energy management system, demand peaks can be reduced by reacting to other electrical loads in the plant using the power monitoring system.
Data Trending
The aeration/control system also has the ability to trend data. The Biomixers data logger logs dissolved oxygen concentrations and diffuser submergence levels. When the influent pumping system sent flow surges through the Atwater plant, this trending ability provided information that led to the correction of the problem, Hamamoto said.
Data Trending
The trend data showed that the diffusers were moving up and down in direct relation to the influent pumping sequences. Staff adjusted the influent flow, which resulted in steady operation.
Data Trending
"The performance of this unique solution has produced dramatic results at our facility," Hamamoto said. "Within the first few hours of installation, all of the undesirable foam was removed from the surface. Another illustration of the mixing improvement was that inorganic loading to the clarifiers increased for two weeks. That proved that the Biomixer systems mixed and removed inorganic solids that were not mixed by our previous aeration system.
Data Trending
"We also saw that the dissolved oxygen levels throughout the basins were evenly distributed. Prior to the systems installation, the dissolved oxygen levels were very different depending upon where the samples were taken. This required higher dissolved oxygen levels to be maintained, which resulted in increased energy costs. These uneven levels also caused poor settling in the clarifiers that led to poor effluent water quality."
Data Trending
With improved settling, total suspended solids in the secondary effluent were reduced, and the mixed liquor concentration was reduced by 30 percent. Both reductions improved secondary effluent quality, which improved the disinfection process thus benefited the environment, Hamamoto said.
Data Trending
"Improved dissolved oxygen control and improved mixing has enabled us to reduce the retention time of the micro-organisms in the basis. Consequently, our energy usage was reduced and our plant operations improved. Finally, basin cooling, which results in reduced biological activity, was reduced. The heat retention and temperature increase has enabled us to meet all of the effluent guidelines and reduce sludge disposal costs," he said.
