Flow Equalization
Many municipalities are facing the challenge of having to equalize large volumes of storm water sometimes mixed with raw sewage in order to continuously meet their permit limitations. The equalized flow is stored during a storm event and then slowly diverted to the treatment facility when influent flows return to normal levels. In the past few years the need for influent storage has been driven by both the increased popularity of the MBR process and the build-out of new storm water treatment facilities. In the case of the MBR plants the need to equalize flow is directly related to maintaining a flux rate that the membranes can accommodate, ensuring the plant does not get bottle-necked. With storm water treatment facilities the need is based on making sure the solids removal processes are operating at design flow rates and are not hydraulically overloaded, which negatively impacts performance. The equalization basins for these facilities are often large tanks with diameters ranging from 140 to 200 ft. and with liquid depths ranging from 20-ft. to 50-ft. KLa jet aerators and jet mixers are the technology of choice in these applications based on the following facts: their flexibility of operation and configuration in large diameter tanks, the highly corrosion and abrasion resistant in-basin components, the use of simple external pumping systems, and a +20 year design life.
The choice of using a jet aerator or jet mixer is typically made by the consulting engineer after carefully analyzing the source of the water to be equalized. If the equalization tank will have significant amounts of sewage mixed in with the storm water, the decision will be to go with a jet aeration system as the oxygen transfer component from the addition of air ensures that there will be no odors emanating from the facility.
If it is only storm water, then in some cases the decision will be to go with hydraulic mixing with no air addition making blending and off-bottom TSS suspension the main design parameters. These tanks are typically covered for odor abatement.
KLa Technology and Experience
The jet aerator/mixer systems are available in a variety of materials of construction. Typically the piping and jets are fabricated of high grade vinylester resin FRP with a stainless steel support system. KLa jet nozzles are offered in the following materials; all FRP with proprietary abrasion liners, a combination of FRP with polypropylene, Kynar PVDF, or an all polypropylene jet is also available.
CFD Computational Domain fig. 1
Over the past 13 years KLa Systems has successfully completed more than 45 projects for jet aerating and mixing equalization tanks with 11 of those projects being for municipal customers. In all of our installations, the municipality has been able to successfully mix and equalize large volumes of storm water/sewage, maintain aerobic conditions when warranted, as well as accomplish off bottom suspension of TSS. The KLa Systems jet mixer systems designs have been confirmed by computational fluid dynamics (CFD) modeling on four different occasions.
CFD Computational Domain fig. 2
