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Designing a Anoxic DeNitrification Mixing System:
Anoxic Denitrification Mixing is an ecologically important bacterial process that converts reactive nitrogen compounds to inert nitrogen gas. The discharge of excessive amounts of the nutrient nitrogen can result in the growth of large amounts of algae and a zone of low dissolved oxygen (hypoxia), which can stress aquatic life in receiving waters such as streams, lakes, bays, estuaries, etc. The primary method of Denitrification is to introduce nitrogen-eating bacteria into the wastewater. Another method is to introduce a neutrally buoyant media to which the bacteria anchors itself while consuming the nitrogen so the effluent can be safely released back into the water shed or on to further processing. Generically, bacteria uses the organic carbon found in waste water as its energy source. Through bacterial action, faculative bacteria reduce nitrates into nitrites which then evolves into nitrogen gas which can be properly evolved into to the environment as an inert (non-reactive) gas (79% found in the environment -air). The process is generally a closed system in that the mixing system is designed to minimize oxygen absorption from the atmosphere. Top entering mixers are used to maintain the activated sludge, which encourages the right biological communities to form resulting in an anoxic condition suitable for denitrification. Rugged Specialty Mixer designs are generally used for this application which includes weed-less impeller designs. Anoxic Mix tanks generally contain a great deal of fibrous material that would tend to hang-up upon common propeller & hydrofoil impellers. As rotating equipment, it is impossible for example to prevent a diaper from wrapping around a top entering mixer shaft however there is a great deal that can be used to counteract the effects of this unscheduled debris. The first is to consider a design that will indicate, from a considerable distance, when the rotating shaft needs to be cleared of this excessive debris that could weigh in excess of 100 pounds. The next is to implement an impeller technology that incorporates features that are not influenced by typical accumulation around the impeller hub, which is expected. Also, to consider a polished swept back impeller leading edge which allows debris & fibers to pass through the flow zone without hanging-up on the impeller. Each of these features have been incorporated into our design. As an abusive mixing application, it is important to incorporate efficient "one-man" servicing in mind. There is nothing more disheartening to an plant operator than to have to schedule & wait for a work crew to service the equipment. Keep in mind that all rotating equipment incorporate wearing elements such as bearings, seals & gears. A plant technician or operator will needs to efficiently be able to remove the motor, disassemble the agitator shaft & then impeller suspending the shaft & impeller from the base plate. Without having to deal with the mixers support base in any way, the operator can then remove the gearbox for servicing. Believe me when I tell you there is nothing more gratifying to see a 135 pound (female) operator being able to lift this lightweight gearbox over her head knowing that prior designs required either work crews or heavy lifting equipment just to get started. Many facilities incorporate multiple Anoxic Mixing zones that duplicate several mixing stations where it is not uncommon to have a back-up spare gearbox assembly. The operator drops in the spare gearbox, as the design is common to every mixer in the plant, reassembles it, getting the process back at 100% in no time. The gearbox requiring service can then be shipped back to our facilities for a factory rebuild. Features include an all corrosion resistant design where the entire mixer is constructed of corrosion resistant material. Many specifications call out wash down duty motors which today are very cost efficient all stainless steel designs. The gearbox is constructed of corrosion resistant "High Strength) corrosion resistant light weight aluminum which is suitable for 95% plus of every mixing application. Every other mixer component is 316L {low carbon} stainless steel using 316SS hardware. As any chemical engineer worth his salt can tell you the number 1 driver of the world economy is corrosion ... meaning that you have a wining combination. Isn't it time we all veer ourselves away from the concepts of planned obsolescence. 06.22.20 |
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Industrial
Portable Mixers
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