Innovative Water Management Re–Circulation and Re–Use: How Smart Water Comes to Life
Water re-circulation and re-use are two crucial aspects of ‘smart water’ – How well does the industry manage water resources? The general tendency today is to take a holistic systems approach. More process water is being re-circulated and industrial producers are recovering reusable substances and water treatment chemicals. Companies are also taking a new approach to effluent management.
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 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.
Production and Technology Closely Related for Water
Technological complexity is lower in regions where there is an abundance of water compared to other parts of the world where water is scarce, making every drop that enters the process a precious commodity.
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
According to a paper published in March 2014 by ProcessNet position on the trends and outlook in industrial water technology, ‘Off–the–shelf’ industrial water management does not exist. Tailored strategies are required for the specific industry, application and site.
Water recycling based on re-circulation 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 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 per cent 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.
Water is Especially Valued in the Desert
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, Saudi Arabia.
Effluents from various production facilities at the site will be treated to the maximum extent possible and will be reused as process water. The various stages in the purification process include mechanical pre-treatment, chemical precipitation, sedimentation, retention basin, biological purification, filtration, activated charcoal filters and disinfection. The plant will have a capacity of 10,000 m3/d.
Zero Liquid Discharge - the Model for the Future?
Instead of purifying water 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. About 400 plants are already operating around the world.
The motives can be different, for example elimination of dependency on the local water supply particularly in regions where water is scarce, stringent environmental regulations for salt concentrations in effluents, 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 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 effluents that contain organic matter as well as inorganic salts at an Indian pharmaceutical plant. The new stand-alone treatment process comprises three stages. The organic matter is removed by biological purification and the salt concentration is increased through reverse osmosis to minimize energy consumption in the subsequent evaporation stage.
Combined Technology for Zero Effluent
Similarly, Veolia Italy has developed a zero liquid discharge system for a global manufacturer of dispersions and adhesives. The system can treat 15 ton of wastewater per day. In the first stage, a heat pump vacuum evaporator with forced circulation pre-concentrates the rinsing water.
Next, a vacuum evaporator along with a heat pump and scraper system in the boiling chamber produces a final concentrate, which is mixed with fresh dispersion to obtain a constant density. The distillate is then treated and can be used for washing, thus, reducing the wastewater volume to zero. Hence, the 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 effluents from one plant is used as feed water for another plant. The goal is to reduce fresh water consumption by up to 50 per cent.
Membrane process: Learning from Mother Nature
The use of membranes in water treatment technology has been increasing for many years. Membranes run continuously and are fully automatic. Membrane materials are now cheaper and more effective. It operates at a lower pressure and hence, reduces energy consumption.
More than 2/3rd of the new desalination capacity being installed worldwide is now based on reverse osmosis. In contrast to traditional evaporation-based technologies, no heat energy is required for reverse osmosis. This reduces the cost of desalinated water.
Even in regions where energy costs are relatively low such as the Middle East, reverse osmosis is the preferred technology. Given the right plant design and the right equipment (60 per cent of the total energy consumption is used to power the pumps), nothing can match the reverse osmosis technology, reports Sulzer.
Sea Water is not the Only Option.
Desalinated ground water is another potential source, claims Germany Trade & Invest. Texas, Florida and California are leading users of this technology. Seawater desalination is becoming an increasingly significant factor, particularly in California where megaprojects are at the planning stage.
Demand for high-efficiency pumps and rugged membranes continue to increase. Financing for many projects is now provided by public-private partnerships. Executive Director, Association of State Drinking Water Administrators, Jim Taft says that mobile desalination systems have significant potential.
The Demand Increases...
Demand is likely to increase as these systems in the South could help the water industry to manage more frequent periods of drought or temporary supply shortages.
Some membrane system suppliers have now started to standardize their systems. Higher production volumes drive down the manufacturing costs for these plugand-play solutions which are used to purify service water and drinking water, and also for treatment of industrial wastewater. It takes minimal effort to connect the pre-assembled systems.
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. If a substance can be re-used, its recovery can make economic sense and also help to protect the environment.
Re–Using Valuable Substances in Waste Water
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 technology 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.
Turn Effluent into a Heat Source
Wastewater as a heat source has witnessed limited usage. 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.
Water and Hygiene Management
Cooling systems play an important role in industrial process flows. Cooling water needs to be treated to prevent deposits and corrosion, and also to maintain hygiene standards. The water in the cooling loop is permanently infested with legionella and pseudomonads, creating a health hazard for the staff working at industrial companies and also putting neighbors at risk. The hazard can be minimized by reducing aerosol release and implementing active legionella control measures.
The VDI guideline 2047-2 dated January 2014 contains a code of practice for hygienically sound operation of systems which release heat through the evaporation or spraying of water. The guideline recommends that a risk assessment be carried out for the complete system. The measures include inspection and documentation as well as identification, evaluation and minimization of risks.
Battling Biofilm Formation
Companies such as EnviroChemie and BWT offer legionella management solutions. The Cillit CEE Facility Management & Risk Analysis Package includes holistic risk analysis and verified monitoring of evaporative chilling systems. To eliminate water-related deposits and corrosion as a potential source of biofilm formation, Dipolique recommends installation of a properly designed water treatment system, use of suitable conditioning agents and management of total salt content based on data acquired with inductive conductivity probes.
Resource conservation and economic considerations make it imperative to carry out intelligent ‘use’ of industrial process water and to ‘consume’ as little as possible. Water should not be transported, heated or contaminated more than its process requirements.