Water management conserves resources and cuts cost
- Efficiency: Water management is also energy management
- Technology: Effluent-free production (zero liquid discharge)
How well does industry manage water resources? The general tendency today is to take a holistic systems approach. More process water is being recirculated and industrial producers are recovering reusable substances and water treatment chemicals. Companies are also taking a new approach to effluent management. Partial flows are being diverted at an early stage, making treatment easier and less expensive. Technology is even available which can virtually eliminate effluent. Industrial water management will be one of three focal topics at ACHEMA 2015 on June 18th – 22nd in Frankfurt/M.
Plants, animals and humans depend on water for survival, but water is also an essential technical resource for industry – whether as cooling agent, transport medium, solvent or process water in a range of qualities from industrial water to softened or demineralized water to highly purified water for the pharmaceutical industry.
Industrial water consumption is not free. Inlet water normally needs to be conditioned, and treatment costs money. Circulation pumps consume energy. Post-treatment is also normally required so that the water can be re-circulated or discharged into receiving watercourses. For cost and environmental reasons, it is advantageous to reduce water movement, water heating and water contamination, and this is where industrial water management has a role to play. The goal is to supply water at a defined quality level while keeping the costs (including disposal) under control.
Technological complexity is lower in regions where there is an abundance of water compared to parts of the world where water is scarce making every drop that enters the process a precious commodity. The costs of closed-loop recirculation or even water-free production are more acceptable there than in countries like Germany. Whatever the water supply situation, production and water technology are always closely interrelated, creating the need for integrative technologies and water management systems.
Water recycling and elimination of production effluent
“Off-the-shelf” industrial water management does not exist. That is the conclusion reached in a ProcessNet position paper on the trends and outlook in industrial water technology, which was published in March 2014 (available at processnet.org). 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. The 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.
The integrated energy supplier Suncor Energy recycles more than 90% of the water contained in steam which the company uses to extract oil from oil sand. Instead of storing injection steam in underground disposal wells, recycled saline water is treated, the salts and solids are filtered out and the water is reused to produce steam again. This approach minimizes the extraction of ground water.
What Wabag is currently doing is another example. At the beginning of 2014, the company was awarded a contract to build a wastewater treatment plant at the new industrial park in the city of Al Kharj in Saudi Arabia. Effluent from various production facilities at the site will be treated to the maximum extent possible for re-use as process water. The stages in the purification process are mechanical pre-treatment, chemical precipitation, sedimentation, retention basin, biological purification, filtration, activated charcoal filters and disinfection. The plant will have a capacity of 10,000m3/d.
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.
Bayer Technology Services has developed a process for handling effluent which contains organic matter as well as inorganic salts at an Indian pharmaceutical plant. There was no existing infrastructure to use as a basis. The new stand-alone treatment process has three stages. The organic matter is removed by biological purification. The salt concentration is increased through reverse osmosis to minimize energy consumption in the subsequent evaporation stage.
Veolia Italy has developed a zero liquid discharge system for a global manufacturer of dispersions and adhesives. The system can treat 15 tonnes of wastewater a day. In the first stage, a heat pump vacuum evaporator with forced circulation pre-concentrates the rinsing water. A vacuum evaporator with heat pump and scraper system in the boiling chamber then produces a final concentrate which is mixed with fresh dispersion to obtain a constant density. The distillate is treated for use in washing, reducing the wastewater volume to zero. What used to be a waste product that was sent for disposal is now re-used in the production process.
As part of the EU E4Water Project, currently the world’s largest water management research project in the chemical industry, a number of plants in Belgium, France, Holland and Spain are working in unison to significantly reduce fresh water consumption. At Solvic NV and Dow Benelux, water flows from different plants are joined together. Treated effluent from one plant is used as feed water for another plant. The goal is to reduce fresh water consumption by up to 50%.
Read the second part of this report tomorrow: Membrane processes as plug-and-play modules, recovery of energy and materials, water and hygiene management.
ACHEMA is the world forum for chemical engineering, process engineering and biotechnology. Every three years the world’s major fair for the process industry attracts around 4,000 exhibitors from over 50 different countries to present new products, processes and services to 170,000 professionals from all over the world. The spectrum ranges from laboratory equipment, pumps and analytical devices to packaging machinery, boilers and stirrers through to safety technology, materials and software, thus covering the entire needs of the chemical, pharmaceutical and food production industries. The accompanying congress, featuring 800 scientific lectures and numerous guest and partner events, complements the wide range of themes of the exhibition. The next ACHEMA will take place from 15-19 June 2015 in Frankfurt am Main. More at http://www.achema.de