Optifloc - Variable Speed Mixers
he Optifloc mixing technology offers a simple and cost-effective approach to optimizing any sludge processing system that includes mechanical dewatering as a component. The Optifloc mixers are variable-speed mixers that generate high-energy mixing with a minimum of head-loss and are designed to avoid plugging or fouling.
Optifloc mixes polymer and sludge in a manner that provides well-conditioned flocs with better water release characteristics, resulting in:
- Reduced polymer demand
- Higher solids in the final cake
- Fewer solids in the filtrate/centrate
The Optifloc has found proven application in:
- Municipal biosludge
- Anaerobically digested
- Mixed raw
- Pulp and paper
- Belt presses
- Screw Presses
- Gravity Belt Thickeners
Not All Mixers Are Equal
The Optifloc™ mixer technology sets a benchmark for sludge dewatering performance. The high-intensity mixing, designed to almost instantaneously disperse the flocculating agent, provides operators with an additional degree of freedom to optimize plant parameters, and, together with chemical dosing strategies, greatly improves control of dewatering under variable sludge conditions.
- Minimal head losses
- Mixing intensity independent of flow rates
- Unimpeded flow even when the mixer is static
- Ongoing flushing of the seal and shaft to eliminate fouling or plugging
- Robust operation, with minimal maintenance
- A variable speed impeller that can be optimized for each polymer/sludge combination.
Optifloc™ mixers have demonstrated polymer savings of up to 40% in practice, with concurrent increases in processing capacity, and reduced disposal costs. Experience at full-scale installations has shown that reducing the polymer dosage by as little as 2kg/t can result in payback periods of 6 months or less.
Biosludge is comprised primarily of bacterial cells, which are very small particles, and drainage of water through this matrix occurs at a very slow rate. In order to improve the drainage rate, sludge is normally conditioned with metal salts and/or organic polymer electrolytes. The polymers are high molecular weight materials that consist of a long strand with multiple charged sites along the length of the molecule. The bacteria in the sludge have the opposite charge and are attracted to, and become attached to the charged sites on the polymer. The net result is that the small particles are agglomerated into larger ones and the drainage characteristics of the sludge/water matrix are much improved.
Historically, contact between the polymer and sludge generally relied on creating turbulence through some kind of restriction in the pipe, or static mixer. This resulted in a significant head loss for the system, and the effectiveness of mixing became dependent on the flow rate.
The dynamic in-line mixing pioneered by the Optifloc™ technology is dramatically more effective. The Optifloc™ mixers are variable speed mixers, which can generate high-shear mixing with a minimum head loss. The improved performance generally demonstrated by the Optifloc™ mixers is attributed to the fact that the high-energy mixing results in utilizing a higher proportion of the active sites on the polymer.
Why it Works
The key to effective deployment of the Optifloc™ mixers is recognizing that modern dewatering practices benefit from high-energy mixing. The more robust organic dewatering polymers that have evolved to withstand the forces in dewatering centrifuges lend themselves to more energetic mixing for short periods
The Optifloc™ technology is the first system designed specifically to provide a high-shear mixing zone for contacting polymer with sludge. The high-intensity mixing zone generated by the rotating impeller provides almost instant dispersion of the polymer solution within the sludge matrix. This results in a fundamentally more efficient use of the active sites on each polymer molecule, significantly reducing polymer demand while producing smaller, more compact floc. These small, well-conditioned flocs
- are more resistant to break-up by subsequent shear in the dewatering system
- have better water release characteristics than floc formed conventionally
- result in higher solids in the final cake and fewer solids in the filtrate/centrate.
Extensive testing shows that mixing energies (rpm x time) are not born equal. Short bursts of high energy outperform longer mixing times at lower energy. It should be noted, however, that there is an optimum mixing energy, beyond which damage to the polymer occurs. The impeller speed of the Optifloc™ mixers is variable and can be optimized for each individual sludge/polymer combination. The net effect of optimised mixing can be a substantial reduction in polymer requirements and improved dewatering performance.