Water management conserves resources and cuts cost
"Off-the-shelf" industrial water management does not exist. Tailored strategies are needed for the specific industry, application and site. Water recycling based on recirculation of process water is normally only a viable option if contamination levels are low and water treatment is relatively inexpensive. Experts say that water recycling is less efficient for waste streams that are highly contaminated and/or contain substances that have a very diverse range of chemical and physical properties. The basic prerequisite for water recycling is the establishment of an efficient water management system to separate water that readily lends itself to recycling from water that is less suitable. Most of these internal recycling processes are located at or near the source where the complexity of the constituents is limited and additive techniques can be deployed with minimum effort and expense.
Zero liquid discharge - the model for the future?
Instead of purifying water to the extent possible prior to discharge, would it make more sense to eliminate water discharge altogether? Elimination of effluent from production (zero liquid discharge) is currently the subject of a highly controversial debate. 400 plants are already operating around the world. The motives can be very different, for example elimination of dependency on the local water supply particularly in regions where water is scarce, stringent environmental regulation of salt concentrations in effluent, recovery of re-usable substances or image enhancement. Experience shows that the approval process for zero liquid discharge plants is often simpler and faster, which is another interesting aspect. However treatment of the residual concentrates is problematic. Choosing a site with an abundant supply of water and implementation of an industrial water management program are generally preferable to the burdens associated with zero liquid discharge production which is very energy intensive. As a result, experts are pinning their hopes on tighter integration of water and energy management.
Recovery of energy and re-usable materials
When there is direct contact, it is impossible to prevent production materials from contaminating the process water. As a result, the process water contains varying concentrations of contaminants (ranging from a few ppb to several %). If a substance can be re-used, recovery can make economic sense in addition to helping protect the environment.
The French startup Magpie Polymers has developed a highly efficient filtration method for capturing re-usable substances even if they are only present in minute amounts. Various filters made of polymer beads are installed, and the metals form selective bonds with the beads. The technique is already being deployed at several European companies to filter out minute amounts of precious metals.
The chemical group Lanxess also provides techn ology for recovering re-usable materials. Ion exchangers function as selective adsorbers for fine purification of wastewater flows and process electrolytes. Heavy metals and other substances such as boric acid, chromate, arsenate, fluoride and ammonia in salt solutions can be selectively captured.
Little use has been made so far of wastewater as a heat source. In the past, utilization of this energy was seldom possible, one of the constraining factors being the 65°C flow temperature limit for heat pumps. Ochsner now markets high-temperature heat pumps with flow temperatures up to 100°C, opening the door to totally new industrial and commercial heat pump applications.
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