KLa Systems Jet Mixers for Anaerobic Treatment Process Case Study

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Courtesy of KLa Systems, Inc.

The Challenge
Many food processing industry wastewaters contain high concentrations of readily degradable organic material and over the past twenty years the implementation of anaerobic treatment processes has gained popularity as the preferred first stage biological process. Anaerobic processes have many advantages over aerobic processes and the two key ones are very low production of surplus biomass, and the production of methane which can be recovered as an energy source. There are a number of proprietary anaerobic processes available in the market today but the use of conventional low and medium anaerobic contact processes has gained popularity. The contact processes are often carried out in large, slope walled basins (i.e. anaerobic lagoons) or circular tanks generally ranging from 50-150-ft. in diameter.

In all cases the basins are covered in order to maintain optimum liquid temperatures and capture/recover methane. As with any process the optimization of mixing the basin contents can improve the process performance markedly. KLa jet mixers are the technology of choice in these applications due to their flexibility of configuration in any basin geometry, highly corrosion resistant in-basin components, use of simple, external pumping systems, and a +20 year design life.

Jet Mixers
Jet mixers are two-phase devices which contain an inner propulsion jet and an outer mixing jet. The key to the performance of the jet mixing system is the re-circulation of the basin contents through the jet manifold piping system which contains a number of jet nozzles. When the liquid exits the inner propulsion jet nozzle at velocities ranging from 30-50 ft./s, the high velocity stream creates a negative pressure in the outer mixing chamber. This vacuum induces additional liquid flow through the suction inlets located circumferentially around the outer mixing jet. As the liquid exits the outer jet nozzle the transfer of momentum from the high velocity plume entrains the surrounding liquid, creating a small head gain which produces a horizontal velocity. This is a key feature and allows for setting up a variety of flow patterns in any basin geometry to enhance the mixing process. Mixing intensity (power/unit volume), basin turnover time, and the even distribution of mixing energy are the other key design considerations.

The jet mixing systems are available in a variety of CIMG1131materials of construction. Typically the piping and jets are fabricated of high grade vinylester resin FRP with a stainless steel support system. The jet nozzles can be fabricated of all FRP with proprietary abrasion liners, or a combination of FRP with polypropylene, or PVDF. An all polypropylene jet is also available. The entire jet mixing system (piping, jets, and supports) is also available in Type 304L or 316L stainless steel.

KLa Experience
In all of our installations, the customer has been able to successfully reduce the wastewater organic content and recover the methane gas all while reaping the cost savings of very low biomass production. Over the past 10 years KLa Systems has successfully completed over a dozen projects for jet mixing anaerobic contact processes. The industries include snack food processing, dairy (cheese and milk production), landfill leachate, and potato processing. Four of these projects have been in large, sloped wall lagoons where the goal is to provide gentle mixing of these low rate processes where TSS concentrations are in the range of 0.50%. We have also successfully completed projects for medium and higher rate contact processes where circular tanks or rectangular basins are utilized. These processes are noted for having TSS concentrations in the 2.0-5.0% range and designed for mixing intensities that are significantly higher than in the lagoons. In keeping pace with the latest analytical software the KLa jet mixing system designs have been confirmed by computational fluid dynamics (CFD) modeling.

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