Blending microbes demands gentle touch

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Courtesy of Munson Machinery Company, Inc.

Environmental-restoration product manufacturer requires fast, uniform, gentle blending of powdered microbes, enzymes and nutrients

The microbial formulations that United-Tech, Inc. produces are used to break down or detoxify a broad array of complex, often-toxic organic compounds, greasy spills and other contaminants in a variety of environments, leaving behind carbon dioxide and water. The company's powdered formulations, which look and feel like flour, contain proprietary blends of microbial cultures, enzymes, various micro- and macronutrients and flow-enhancing additives.

'These products are designed to speed the bacterial degradation processes that already occur in nature, without the addition of any chemicals and with no further damage to the environment,' says Art Barnard, who founded the company in 1993.

Blending of bacteria with additives in ratios as low as one part to 40 presents unusual challenges. The bacteria will be destroyed unless handled gently and blended rapidly, yet, the distribution of bacteria throughout the batch must be 100 percent uniform. Also critical is the ability of the blender to fully discharge each batch and to sterilize quickly and thoroughly between runs of different products. After evaluating several types of blenders against these criteria, Barnard decided in favor of a rotary-style batch mixer.

Giving nature a boost
While most environments contain indigenous bacteria capable of degrading a range of organic compounds, the particular microbes at a site are often not the best suited or voluminous enough for the particular contaminant load. So-called bioaugmentation schemes aim to maximize natural bacterial degradation processes by delivering a targeted bacterial population and supplying micro and macro nutrients to sustain the bacterial population, and enzymes that act as catalysts, promoting and accelerating the bacterial degradation of complex organic compounds.

Today, United-Tech's bioaugmentation formulations are being used to treat chemical- and petroleum-laden soil and groundwater, to remove unwanted organics and reduce sludge volumes in both industrial and municipal wastewater-treatment facilities, to remove organic sludges from drain lines, grease traps and septic systems, and even to clean floors in settings such as automotive repair facilities, machine shops and restaurants that are prone to grease buildup.

In recent years, these formulations have also been adopted by operators of commercial shrimp farms and fisheries, and are being used to improve the water quality and break down organic bottom sludge in decorative ponds, swimming pools and spas.

Bacteria, enzymes require gentle blending
To give its products a long shelf life and make them easy to transport, store and apply, United-Tech produces its BZT and OBT product lines as powdered formulations that are typically mixed with water and sprayed on the contaminated media. United-Tech first cultivates the target bacterial cultures in sterile biofermentation reactors. After harvesting this biomass, the desired bacteria cells are concentrated through gentle centrifugation.

A two-step freeze-drying process then removes 95% of the moisture, creating a dry, powdered form of the bacteria that is then easily blended with other ingredients. This freeze-drying, coupled with a proprietary micro encapsulation step 'puts these rugged little guys into a state of suspended animation or dormancy,' says Barnard, and protects the bacteria from potential damage or deactivation that might otherwise occur during periods of extended storage.

For years, United-Tech had been outsourcing the blending of its raw ingredients into the finished formulations to a third-party vendor. But in 2002, to save money and streamline its manufacturing operations, the company brought its blending in-house.

United-Tech evaluated blenders according to their ability to provide:

  • Precise and consistent blends containing its target microbial load
  • Rapid mixing to maximize manufacturing throughput
  • Rapid, thorough cleaning for rapid changeovers
  • Gentle blending with minimal friction and shear to protect bacterial cells and other friable ingredients from mechanical degradation

After rejecting various types of ribbon and paddle blenders ('too much friction,' says Barnard) and V-cone blenders ('excessive cycle times'), United-Tech chose a Model MX-10-SS Mini Mixer from Munson Machinery, Inc., Utica, NY. The rotating mixing drum of the unit has a total volume of 22 cu.ft. and a blending volume of 11 cu.ft. Designed for laboratory mixing, pilot plant applications, pre-blending operations and relatively small production runs, the unit is a scaled-down version of Munson's Rotary Batch Mixer which ranges in blending capacity from 10 to 600 cu.ft.

The mixing vessel has no internal moving parts — rather, its interior is fitted with evenly spaced baffles that gently tumble, turn, cut and fold the powdered ingredients as the drum rotates. This cascading action creates a fluidized condition that ensures uniform blending, minimizes product degradation, and prevents the formation of stagnant zones.

The lifting action of the mixing flights also serves to direct the material to the discharge spout which, when open, promotes 100% evacuation of the batch. 'The mixer consistently discharges completely, leaving no residual material behind,' says Barnard. 'By comparison, ribbon blenders leave a heel of material along the bottom of the trough,' he explains.

'We manually dump raw materials into the mixer and discharge finished blends into the hopper of an enclosed screw conveyor feeding an automated line that fills packages ranging from 1-lb Mylar foil pouches to 400-pound fiber drums.

'We can blend 500 lbs. every 3 to 5 minutes with this blender, and have found it to be equally effective in blending batches that comprise only a small percentage of rated capacity,' says Barnard.

'The fact that it unloads quickly and thoroughly maximizes the number of batches we are able to blend, the only downtime being between product changeovers when we sterilize the unit using steam and a cleaning solution,' he says.

The mixer has run problem free since 2002 according to Barnard, who is ordering a number of the units for United-Tech's other facilities. 'Once we standardize all of our worldwide mixing operations on Munson's Mini Mixer, our engineers in the U.S. will be able to work closely with their colleagues overseas, to assist in training, operation and troubleshooting,' he says.

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