CASE STUDIES
The oxidation ditch at Huntsville used to have far toomuch oxygen, butmixers fromLandia have successfully addressed the problem.
Oxidation ditch mixers create energy savings in Arkansas
Addressing the fast-rising cost of energy is rightly high on today’s agenda, so when four hefty 40HP rotors serving one’s aeration plant are also sitting at the top of your maintenance budget, finding a better means of mixing certainly concentrates the mind.
In Huntsville, Arkansas, the route to achieving optimum mixing of its oxidation ditches has been a marathon, not a sprint; but this meticulously operatedwastewater treatment plant is nowreaping the rewards of significantly reduced horsepower and reduced repair costs.
Managing oxygen levels at Huntsville has been a major, fluctuating challenge, especially with thewastewater taken in from a large-scale food manufacturer, nearby.
The 160HP (total) rotors had to run 24/7 in order to sufficiently mix and add oxygen to Huntsville’sWWTP aeration basin, but when the expanding food manufacturer upgraded its own treatment plant, the problematical rotorswere creating far too much oxygen; contaminating the anaerobic and anoxic zones.
“We had to find a new, sub-surface means of mixing our oxidation ditch”, commented Bill Eoff,WastewaterManager at Huntsville.
“And aswe only have the one oxidation ditch”, he said, “this presented the extra challenge of finding mixers that could be installed without there being any interruption to our process”.
Bill and hisWater Department Director, Sean Davis, had tried pulsing the rotors on timers, and had also been having to feed in
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chemicals at additional expense to balance out the process, so that the ratio of BOD to ammonia could be harmonized, but to no avail. So, they consulted with their local equipment representative, Instrument & Supply, who have beenworking with Huntsville for over 20 years.
“We believed that by far the best solution for the plantwas to separate the aeration and mixing functions; and that included mixers made by Landia. This provided a subtle, but highly effective solution”, said Chris Enloe from Instrument & Supply.
“Wewere very confident of our recommendation; plus, the fact that no other mixer manufacturer could, orwas prepared to install their mixers without draining down the tank, whichwas not an option at Huntsville”.
‘Sledgehammer!’
At first, to some, the installation of a mixer to a full and operating ditch might sound rudimentary, especially with what includes about twenty solid blows with a sledgehammer (!), but in keeping with Landia’s long-established designs, no- nonsense simplicity often proves best. Actually, there’s real precision in ensuring that the (pre-marked) guide spike is installed plumb; approximately half an inch into the base, with the mixer on the guide pipe set at nine inches above the base of what is typically an eight- or nine-feet deep ditch. Installation takes just two to two and half hours.
Chris Enloe added:“The team at the plant had towork without the benefit of grants or loans
| June 2023 |
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that come with a new design. Everythingwas funded piece by piece on cash reserves. This made the task all the more trying; for example, keeping the rotors until such times that a second blower could be purchased, in order to meet the state’s requirement for redundancy to be in place”.
‘Big win for the City’
Sean Davis, Huntsville’s PublicWorks Director, continued:
“The rotorswere proving costly and time- consuming to maintain, especially the gearboxes, but although the changeswe needed to make to meet our treatment needs took longer thanwewould have liked, it has already resulted in a 15% reduction in our energy costs alone. This is a big win for the
Managing oxygen levels has been amajor challenge.
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