Nanoflotation: Low Energy Low Cost Water Treatment
Selected by the Chinese Ministry of Environment as the one of the top environmental technologies in the world
David Bromley Engineering Ltd. has developed a unique technology called Nanoflotation. Nanoflotation uses concentrated ionically charged nano environments to cause repulsion of colloidal solids followed by attachment of solids. The repulsion and attachment processes result in a rapid, low energy method to separate colloidal solids from fluids:
Nanoflotation Overview (Patent Protected)
Description of the technology
The DBE Nanoflotation technology is an innovative approach to managing the nano-environment around colloidal solids. Most colloidal solids will not readily separate from water because of the electric double layer (EDL) around colloids. The EDL causes the colloids to remain in suspension, repelling each other. DBE’s Nanoflotation technology changes the environment around a colloidal solid for a very short time period causing the EDL to collapse. Solids for this moment in time separate from the fluid medium and attach to other solids or mediums because of van der Waal forces which overcome the diminished repulsive forces of the EDL. This concept has been attempted in the past by changing the quality of the water in which the solids are exposed. A typical method to cause the EDL to collapse is to add NaCl to water. The problem, of course, with this approach is that water quality becomes an issue that needs to be managed. The DBE Nanoflotation technology does not change the quality of the water to separate the solids. This technology greatly improves treatment of a wide variation of suspended solids, colloidal solids and nano particle concentrations. In addition it provides good reductions in scaling parameters like silica, barium, calcium, magnesium and manganese, as well as organic reduction in wastewater sourced from industrial or municipal applications. At the present time the technology has been applied to two very common methods of water treatment; flotation treatment and low pressure membrane treatment.
For flotation treatment systems, the application of the Nanoflotation technology is through the use of a surfactant and a “patent pending” high intensity mixing system. The high intensity mixing is caused by the froth generated from the use of the surfactant. The fluid containing the solids passes through a high intensity mixing zone which is also an ionically charged concentrated zone due to the surfactant that has attached to the air bubbles in the froth. This ionically charged environment causes the collapse of the EDL and the solids attach to the bubble in the froth where they float to the surface of a flotation chamber. Both the froth mixing technology and the use of the high ionically charged environment have been piloted and demonstrated with exceptional success on very difficult waters such as oil sands tailing pond waters, cooling water, landfill leachate, and refinery oily process waters.
For low pressure membrane systems such as ultrafiltration(UF), the patented membrane powder skin layer technology eliminates the problem of membrane fouling and instead encourages membrane fouling on a replaceable membrane skin layer (RSL) that is formed using a highly charged powder. The layers RSL powder media provides two environments: firstly, there is repulsion of the colloidal solids from the surface of the RSL. The EDL on the powder media at the surface of the replaceable skin layer (RSL) cause an EDL repulsion of the colloidal solids approaching the skin layer. This repulsion stops a layering or caking of the solids on the surface of the powder skin layer. In typical membrane systems a cross flow is used to stop the caking or layering of solids on the membrane skin layer. Cross flows are very energy intensive. However the reverse situation occurs once the solids enter the RSL media and move past the surface of the skin layer. The colloids eventually penetrate the RSL layer because of the pressure differential (TMP) across the RSL At this point the second environment becomes dominant. The concentrated ionically charged environment from the powder media of the RSL collapses the EDL and van der Waal forces become dominant. The colloids in the water attach to the RSL powder media or other solids due to van der Waal forces. The colloid solids are trapped within the skin layer powder layer. In the Nanoflotation Technology, the membrane skin layer is replaced in situ during a standard backwash cycle which lasts less than two minutes. A new powder media is added after backwash to create a new RSL.
The technology provides an effluent similar to other ultrafiltration membrane technologies but requires significantly less energy and capital costs. In addition, the use of the RSL increases flux rates on the membrane significantly (10 to 15 times when it was compared against a ceramic membrane competitor).
Not only is the efficiency 10 times greater, the design allows for the use of heat and corrosive resistant membrane substrates such as stainless steel. With the significantly improved flux rates, the cost of using temperature resistant material results in an overall cost similar to or less than the typically low cost polymeric membranes that are limited to a temperature of 40o C. The ability to treat at very high temperatures or in corrosive environments removes the need for energy intensive steps in the treatment process such as cooling or neutralization. For a facility that is dependent on steam generation, the Nanoflotation technology provides significant energy savings and correspondingly excellent CO2 reductions. An example of a sector that will benefit significantly from this technology is the Steam Assisted Gravity Drainage (SAGD) operations in the oil sands extraction sector.
The economic value of the technology is in its ability to treat water to ultrafiltration standards (e.g. 0.01 micron filtration) at lower capital and operating costs while improving reliability and ease of use.
- The advances in mixing allows for rapid separation of solids reducing the retention time in, and therefore size of the froth flotation component.
- The high flux rate on the membranes reduces overall tankage and membrane costs by 35% or more.
- The high flux rate and an operating pressure of less than 1 bar, reduces energy consumption by 90% or more over conventional membrane technology. In addition the pilot plant testing has shown the ability to restore 100% flux rates after backwash. This capability provides a further improvement in energy consumption compared to conventional low pressure membrane technology.
- High temperature applications eliminate the need to cool water before membrane treatment with conventional polymeric UF and RO membranes. The significant reduction in membrane area requirements, as a result of the high flux rates, allows for the use of temperature resistant materials such as stainless steel and ceramics without an increase in costs.
- The flexibility of the membrane technology allows the powder skin layer membrane to compete against the conventional multimedia filter or disposable bag and cartridge filters. The Nanoflotation membrane technology relies on the skin layer powder on the membrane substrate to remove colloidal solids and not the membrane itself. For ultrafiltration treatment, the Nanoflotation membrane uses a 1.0 micron pore size opening versus the conventional 0.01 micron pore size opening for ultrafiltration membranes. For a multimedia filter comparison or disposable bag filter, it is expected that a larger pore size on the Nanoflotation membrane substrate (e.g. 10 microns) can be used. This larger pore size will result in higher flux rates matching the flow-through capacity and water quality of multimedia filters and disposable cartridges/bag filters.
Costs of Technology and Economics
A comparison of the vendor selling price of a conventional polymeric UF membrane versus the Nanoflotation technology for a 500 m3/hr treatment plant as well as the comparable operating costs are provided in Figure 3