Oxygen transfer is one of the essential elements in the biological treatment of wastewater. In order for the suspended growth process to achieve optimum results the supply of oxygen must equal the rate at which it is demanded. If there is an inadequate supply of oxygen the aerobic bacteria will die. In municipal wastewater treatment plants, the aeration process accounts for 50% to 75% of total energy costs.
In some instances, it becomes desirable to greatly reduce the aeration in swing zones or tapered aeration basins. Unfortunately, this often leads to conditions in which the reactor becomes mixing limited. By implementing a BioMix system in these zones or basins, energy efficient mixing is provided while also greatly reducing the amount of energy expended on aeration. In other instances it is possible to cycle between aeration and mixing in order to reduce energy. Using realtime process data, a BioCycle system can intelligently determine the most effective way to cycle between aeration and anoxic mixing in order to reduce energy expended on aeration, and mix efficiently during the anoxic cycles.
EnviroMix is providing mixing technology for this state of the art facility in the Chesapeake Bay region; more specifically, for the Versatile Bioreactors (VBR’s/Swing Zones) and the mixing limited zones, which are at the tail-end of four Aeration Basins. The BioMix™ system will use less than 25% of the energy that would have been required using submersible mixers. Due to the complicated geometry and the multiple zones, 24 submersible mixers would have been required, but the BioMix technology is able to mix the VBRs and the Aeration Basin mixing limited zones with one air compressor, greatly reducing maintenance as well.
In order to improve the nutrient removal process at this plant, the owner is implementing the BioMix compressed gas mixing in the last half of the aeration basins where reducing airflow through the fine bubble diffusers will result in mixing limited conditions. By de-coupling aeration from mixing the air can be turned down or even off to prevent high concentrations of dissolved oxygen disrupting subsequent Anoxic Zones. BioMix will be integrated with the existing fine bubble diffusers to provide the supplemental mixing energy to keep the solids suspended with less than 50% of the energy that would have been required with submersible mixers. Furthermore, there is no concern over motor cavitation that may result from concurrent operation of diffused aeration with traditional submersible mixers.
A growing need found in many wastewater treatment plants is the removal of nutrients, primarily phosphorous and nitrogen, due to the impact they have on receiving body water quality. Plants that are configured for Biological Nutrient Removal (BNR) typically include Anaerobic and Anoxic Zones to facilitate the environments that promote the biological removal of phosphrous and nitrogen. In these processes it is vital to provide proper mixing between recycle streams, keep the solids suspended effectively, and minimize the transfer of oxygen to the process. BioMix accomplishes all of these objectives using a fraction of the energy required of legacy submersible and platform type mechanical mixers.
Aging equipment and increased nutrient requirements, due to the Chesapeake Bay Initiative, required major improvements to the Abington WWTP. Land-locked, the facility required creative use of existing tankage to meet effluent requirements.
Six existing aeration basins were converted to three trains of four-stage MLE bio-reactors, each train containing three anoxic and one swing zone. In lieu of designing the system with twelve mechanical mixers, BioMix™ leverages one operating compressor for all anoxic and swing zones at an estimated 50% power reduction as compared to the standard mechanical mixer design. For the swing zones, the BioMix system was integrated with fine bubble aeration and will provide the flexibility to cycle back and forth between aeration and mixing in those zones or operate concurrently.
The absence of oxygen in the anaerobic digestion process enables microorganisms to break down organic materials. As a result of the physical and biological reactions that take place; volatile solids are reduced and biogas is produced. The biogas, a renewable energy resource, can be used directly as fuel in combined heat and power gas engines. In order to effectively digest solids, it is imperative to provide homogeneous mixing throughout the anaerobic digestion process. BioMix™-AD provides this mixing at a fraction of the energy required by legacy lance, submersible, bubble-gun, or jet-mix style systems, while also eliminating in-tank maintenance of the mixing system.
Following a comprehensive study to replace mixing technology within one of eight digesters at the facility, plant management chose the BioMix-AD system based on their confidence in BioMix creating more homogenized mixing and increased production of methane.
The innovative BioMix-AD solution provides mixing of a 100’-diameter primary anaerobic digester containing 2% sludge. The hundreds of high, localized energy inputs provide effective mixing at a low energy requirement. The sliding-vane compressor package provides mixing gas at 0.127 horsepower per 1000 cubic feet (HP/1000 cf), less than half of that required for the existing gas lance mixing system, and a third of the typical design requirements for pumped jet mixing. The plant has experienced a simultaneous decrease in energy use and increase in biogas production since retrofit with BioMix AD.
Interconnecting channels move process flows throughout a wastewater treatment facility. To keep the solids suspended, facilities typically rely on hydraulic flow rates, coarse/fine bubble diffusers, or pumps to avoid the accumulation of solids within these applications. Replacing pump or diffused aeration system with BioMix™ compressed gas mixing in channel applications provides significant energy cost savings that yield very quick payback periods, sometimes as short as one year! Moreover, with BioMix the negligible amount of oxygen transfer is especially beneficial for sensitive biological nutrient removal processes.
A large US-based wastewater treatment plant uses over 4500 linear feet of flocculation, mixed liquor recycle and primary effluent channels. Formerly they were using multiple 400 Hp blowers to provide air to coarse bubble diffusers to mix these channels. As part of ongoing energy initiatives, the facility focused on reducing energy usage by 4 million kilowatt-hours per year, yielding an estimated savings of over $300,000 annually.
Another unique challenge of this application was that the channels could only be removed from service for 12 hours at a time. In those 12 hours, the flow was interrupted, the channel drained and cleaned, the BioMix™ equipment installed and the channel returned to operation. A benefit of the EnviroMix system is that the in channel components can be preassembled, allowing for minimal downtime during installation.
The disinfection process is essential to destroying disease-causing organisms in a wastewater process. One of the most commonly used methods is the use of chlorine. During this tertiary process it is beneficial to have effective mixing in order have a more efficient disinfection process.
The Hopewell Regional Wastewater Treatment Facility (HRWTF) treats industrial and primary-clarified domestic wastewater, which is discharged into the James River and Chesapeake Bay. The facility was at the end of its useful life and increased flows, along with new regulations, had necessitated the HRWTF upgrade.
The project consisted of rehabilitating and converting three existing primary clarifiers to domestic wastewater, primary clarifier/chlorine contact tank combination units. The BioMix™ compressed gas mixing system is utilized to both keep solids in suspension and enhance chlorine contact performance in the new chlorine contact tank channels. Other, mechanical mixing technologies were not considered due to the required quantity of units and extensive maintenance.
Potable water storage tanks are kept mostly full in order to provide a sufficient quantity of water for peak demand, and for supply emergencies. On a daily basis, the level of water in these vessels does not fluctuate more than 5-10%; and therefore can create stagnant water, resulting in bacterial regrowth. By simply mixing a water storage tank, high quality water may be reliably provided to the end-user while also reducing the amount of residual disinfectant needed, resulting in a reduction in disinfection byproducts (DBPs).
EnviroMix provided Alligator Rural Water & Sewer with its mixing technology to be used as part of a potable water quality upgrade project in McBee, South Carolina. The project included the construction of a two million gallon ground storage tank.
The EnviroMix AquaBlend™ system provides the necessary tank mixing by firing programmed, short bursts of highly-filtered compressed air through engineered, floor-mounted nozzles. The large bubbles mix the tank, creating a distinct mixing pattern, or “tank roll.” The blending parameters of the AquaBlend controller can be varied for optimum mixing and power utilization. AquaBlend mixing provides a homogenous level of disinfectant and prevents issues created by thermal stratification resulting from stagnant tank water.
Implementing an equalization basin in a facility enables the plant to balance flows to the treatment plant despite variations in the influent flow. By providing mixing in the equalization basin, grit and solids deposition is minimized, reducing cleaning frequency while allowing organic solids to pass through to biological treatment processes. The BioMix™ system can provide this mixing efficiently while also accommodating significant variation in operating water levels and mixing effectively at water levels as low as 1 - 2' deep, far below that of legacy mechanical mixers.
The Mount Pleasant Waterworks enhanced the capacity of its Center Street Wastewater Treatment Plant and as part of this capital improvement project they elected to replace their existing air lance system in the equalization basin. The inability of the previous system to effectively mix at low water levels resulted in large amounts of solids deposits in the while also using a large amount of energy. By using a BioMix system, the utility will reduce the amount of energy used to mix the basin, and the 72 nozzles uniformly distributed across the basin floor will prevent solids being deposited on the basin floor. In addition, the BioMix system will be able to throttle air flow depending on the fluctuating water level in the basin, providing effective mixing at water levels as low as 1 – 2' - further saving energy.
Flocculation is the mixing of coagulant with water to flocculate particles out of suspension. As the solution is mixed the coagulant helps to form small floc particles. As smaller floc particles come into contact with one another and bond together, they form larger and larger flocs that eventually settle out of suspension. Gentle mixing helps the coagulant to more efficiently form floc particles. The AquaBlend-FT system provides this gentle mixing while facilitating variable mixing intensity (G Value) throughout various zones within the process without shearing the floc.
Pump stations are designed to move raw sewage between points in a collection system. A key part of the process is to maintain the suspension of solids and break up concentrations of fats, oils, and greases. A BioMix system can accomplish all of these objectives; providing mixing in difficult geometries without the need for any in-wetwell maintenance.
Sludge holding basins exist at Wastewater Treatment Plants as “wide spots in the line”, serving as buffering capacity for thickening, dewatering, and/or digestion. Mixing in sludge holding basins is necessary in order to keep the solids in suspension and to prevent the intakes to sludge pumps from clogging and to ensure that a consistent homogeneous feed of sludge is sent to dewatering equipment. A BioMix system can provide this mixing without any mechanical components in the sludge holding tanks, while also being able to vary the intensity of the mixing dependent on the concentration of sludge. In addition, BioMix can provide this mixing at a fraction of the energy required for submersible mixers, jet mixing systems or diffused aeration.
Following a highly successful pilot test for anaerobic biological treatment mixing, plant management requested the design of BioMix™ for new sludge storage tanks, required by increased facility solids loading. These tanks were created from the modification of an existing circular tank by building an interior sloped-floor tank for 3% primary sludge storage, with the outer ring holding 2% WAS.
These unique tank geometries presented challenges for technologies other than BioMix, which was readily adapted. BioMix provides efficient mixing while also maintaining anaerobic (PS)/anoxic (WAS) conditions prior to thickening, anaerobic digestion, and a future phosphorus recovery process. Further, energy consumption using BioMix is estimated at only 43% as compared to mechanical mixers through the use of just one compressor in lieu of five mechanical mixers.