Processing Magazine

Pumping advances address wastewater treatment basics

From floc formation to clump strengthening, sludge removal and disposal

December 1, 2013

By Greg Kriebel

Neptune PumpSince the beginning of recorded time, societies have found ways to properly treat and dispose of water fouled through the course of its use. Meeting these needs has made the water/wastewater-treatment industry grow to $136 billion in revenues in 2011 in the United States, with an annual growth rate between 3.0% and 4.5%.
When people hear the phrase “water treatment,” however, what comes to mind is taking water that will be used in domestic settings and removing any impurities, making it safe to drink, cook with, bathe in and wash clothes with; in other words, “municipal” water treatment. From a broader perspective, “water treatment” can have a number of completely different meanings.

In industry, for instance, water taken from a nearby river is used for boiler or cooling-tower makeups. In the oilfield, water used or produced during drilling and recovery is treated and sold to farmers for use in field-irrigation activities. In other words, there’s a whole lot of water being treated at all times, and not just so a loving parent can whip up a pitcher of lemonade for the kids.

To this point, an integrated wastewater-treatment system, with many different types of equipment working hand-in-hand — including metering and peristaltic (hose) pumps, and polymer make-down systems — can be used in a straight-line treatment process. This will deliver the most cost-effective and efficient way to treat industrial wastewater, all while making it safe for disposal or reuse in any number of additional activities.

Challenges, produced and used

Most water used or produced in industrial applications contains some level of solid particles. These particles are never consumed, of course, but particle-laden water also can’t be used, for example, in a boiler that provides steam to a turbine during power generation, lest the turbine become fouled and damaged.

Recognizing the presence of particulates in water and successfully removing them, however, are two different things. Some particles — which can be anything from bacteria and plant material to dirt or minuscule pieces of crushed stone — are so small that their response to gravity is very low. In other words, they don’t fall through water at a consistent rate because their mass is not much impacted by gravity. This means that it may take many hours, days or even weeks for the particles to settle as little as a foot. This is an unacceptable, and unpredictable, settling rate for a water or wastewater-treatment system, so the particles need some help in settling or clumping.

To speed along the settling or clumping process, the water-treatment facility introduces a coagulant or flocculant that helps the tiny particles clump together in a mass that is called a “floc,” which is easier to remove. Two of the more popular types of coagulants/flocculants that are used in water/wastewater treatment are alum and ferric chloride.

Alum is an economical way to say “hydrated potassium aluminum sulfate,” which has been used since Roman times to aid drinking and industrial-process water purification. Alum coaxes negatively charged colloidal particles to clump together so they will be able to be more easily removed from settling basins.

Ferric chloride is another name for Iron (III) chloride. It undergoes hydrolysis when dissolved in water, which gives it the ability to sufficiently form suspended solid particles into flocs.

The flocs we form

The flocs formed by alum and ferric chloride are held together rather loosely, which means that they can break apart if agitated as they settle in the clarifier or settling basin. Eliminating this break-up potential requires the introduction of a polymer solution that helps form more efficient flocs. The polymer takes the neutralized solid particle clumps and binds them together more tightly.

The clumps that settle in the basin form a material that is called “sludge.” The use of alum by itself leads to the generation of a large amount of sludge; the introduction of polymer helps further coagulate the sludge. However, the sludge requires removal and disposal. Accumulated sludge can be collected and sent to a centrifuge, or just piled up on the ground outside the water-treatment facility, allowed to dry and then removed via front-end loader and dump truck.

Removing sludge from water requires a pump that can run dry and won’t be bothered by abrasive materials. In other words, a pump that has the capability to take whatever flows into it — no matter its makeup — and deliver it out the discharge side in that same form.

Inevitable three stages

Industrial water or wastewater treatment, then, is a three-stage integrated process: initial floc formation with alum and ferric chloride, clump strengthening with polymer and removal and disposal of the sludge. Not all makers of wastewater-treatment equipment offer full lines of pumping and polymer-blending technology for water-treatment applications.

Mechanical metering pumps, such as the Neptune 7000 Series are for dosing alum and ferric chloride. Mechanically actuated pumps eliminate use of contour plates on the liquid side of the diaphragm, resulting in a simple, straight-through valve and head design that allows improved flow characteristics. These pumps handle clear liquids with viscosities ranging from water-like to 5,000 cPs, appropriate for use in industrial water and wastewater-treatment applications. Capacity is manually adjustable via micrometer dial while the pump is running. This allows the pump to produce flow rates ranging from 10 gph to 450 gph at head pressures up to 150 psi. The pump’s liquid ends are constructed of PVC, 316 stainless steel or Kynar. Washdown-duty and explosion-proof motors, as well as variable frequency drive options, are also available. The pumps are also self-priming.

Blending systems

Liquid polymer blending systems, such as Fluid Dynamics’ dynaBLEND, can have  non-mechanical mixing chambers that allow reliable delivery when activating all types of liquid polymer for use in water or wastewater treatment. The system’s injection check valve is made with easy disassembly and inspection in mind, eliminating a maintenance concern that troubles other systems. These features allow application of ultra-high mixing energy at the point of initial polymer and water contact to prevent polymer gelling and agglomeration. The prolonged turbulence created allows completion of the blending process gently and fully. Finally, after the polymer is initially activated, gentle mixing energy does not break the fragile long polymer chains formed.

Peristaltic (hose) pumps, such as the Abaque Series, ensure that “whatever goes into the pump comes out of the pump.” Applied to sludge removal, these pumps can handle solid particles up to 18 mm and soft particles as large as 31 mm. A seal-free design eliminates leaks, to handle anything from abrasive and aggressive fluids to shear-sensitive and viscous materials. Pumps can run in either forward or reverse, are self-priming, dry-running and offer suction-lift capabilities to 9 meters, as well as the ability to run dry continuously without adversely affecting the pump’s performance. Ductile-iron and steel construction lets the pump produce discharge pressures as high as 16 bar.  

Industry uses untold millions of gallons of water and produces untold millions of gallons of wastewater each and every day. Properly handling and disposal or reuse of this wastewater requires process stages that must work together seamlessly, from alum and ferric chloride introduction, to polymer injection, to sludge removal. Each stage requires different technologies, which can often have the wastewater-plant operator moving in many different directions to identify a solution. A one-stop shop for industrial wastewater treatment, with a ready supply of metering pumps, polymer make-down systems and peristaltic pumps, all of which work hand-in-hand, can be an efficient and cost-effective approach to industrial wastewater treatment. Finally, look for pre-piped and wired skid-mounted systems for installation ease.

Greg Kriebel is with Fluid Dynamics, a division of Neptune Chemical Pump Co., North Wales, Pa. Contact him at greg.kriebel@dynablend.com or 215-699-8700, ext. 3361.

Neptune is an operating company within Pump Solutions Group (PSG), Oakbrook Terrace, Ill., PSG is comprised of several leading pump companies, including Abaque®, Almatec®, Blackmer®, Ebsray, Finder, Griswold™, Maag, Mouvex®, Neptune™, Quattroflow™ and Wilden®.  Find more information on PSG at www.psgdover.com.