Every Drop Counts
Zeroing In on the Water & Carbon Footprint
Drop by Drop - Recycling holds the key to sustainable use of industrial process water. Closed-loop water management reduces water consumption, provides a basis for material recycling, minimizes effluent volumes and also cuts energy consumption. Industry worldwide uses about one-fourth of the available water, in particular as a coolant, solvent and cleaning agent. Consumption varies depending on the extent of industrialization, and especially from one industry to the next. According to the German Water Association "Vereinigung Deutscher Gewässerschutz", as a rule of thumb the actual amount of water consumed to produce one dollar´s worth of goods in the U.S. is 100 l compared to 50 l in Western Europe and around 20 l in the Asian region ("water footprint" or "virtual water"). How can the water which is needed for production be used in a more sustainable manner?
21st Century Industrial Water Technology
Innovative techniques to enhance process water and effluent management are being developed to reduce the environmental impact and increase cost efficiency. These techniques can be aimed at reducing the volume of effluent released into the environment or at lowering contamination levels (e.g. residual COD (Chemical Oxygen Demand), AOX (Adsorbable Organic Halogen Compounds), trace substances and salts). Other objectives can be to extract usable substances from the effluent flow for recycling (e.g. lignin and polyphenols) or to reuse the water resources.
On the other hand, energy exploration (oil sand and shale gas) using hydrofracking is definitely not sustainable. Large volumes of water are used to bring the substances to the surface. Additives are often mixed in so that the pumps can keep the substances moving freely. Hydrofracking is common practice in the U.S. and Canada, and initial projects are now underway in Germany as well.
Apart from such "dirty technologies", industrial water technology actually is moving towards a holistic approach which includes recycling of process water and recovery of usable substances and/or chemicals used for water treatment. The approach to effluent management is also changing. Water treatment, extraction of usable substances and recycling of the treated water are easier and cheaper if the effluent flows are concentrated and unmixed.
Over and above these considerations, energy consumption and the carbon footprint throughout the equipment lifecycle are becoming an increasingly important argument in the contract award process, according to the German Engineering Federation VDMA and its Special Group Water and Wastewater Technology.
The Water Treatment Carbon Footprint
Krüger Wabag and other companies which are part of Veolia´s water management business agree with that view. As a result, they systematically assess the emissions of greenhouse gases over the entire lifecycle of the water and wastewater treatment process. Based on a positive carbon balance, the company is able to identify a range of water treatment solutions and highlight savings opportunities along with the associated costs and benefits.
On public projects in the UK for example, an assessment of the anticipated greenhouse gas emissions is now a standard part of the bid solicitation process. This is also an issue in industry as well. A number of global players including some which are involved in food production have set goals for gradually reducing their emissions, and they generate ongoing progress reports. Others are concentrating on improved energy efficiency (which is worthwhile also for monetary reasons) as well as sustainable management of natural resources. This also has a positive effect on CO2 lifecycle emissions.
When the systems are built, an emissions assessment is carried out based on a breakdown of the individual parts. The raw materials such as steel, aluminum and various types of plastic are counted up and multiplied with a CO2 emissions coefficient. The coefficients are taken from several internationally recognized databases. The major factors during ongoing operation are energy consumption, process equipment and the types of raw water used.
Integrated Water Management
A production plant that does not need to release any water is probably one of the most uncompromising examples of water conservation. The Dutch company Evides Industriewater B.V is working towards the realization of such a project in China. A demonstration effluent treatment plant to produce high-grade process water is currently under construction in the dry north of the country. The plant will be part of a process water recycling loop for the continuous recirculation of treated water. Solids left over after the highly-concentrated contaminants are put through an evaporation process will be sent away for disposal. Freshwater is scarce in the region, and there is a lack of receiving water bodies into which effluent can be released.
Water treatment for recycling is one of the technologies in which this supplier specializes. At the port of Rotterdam for example, a new approach to process design has significantly improved water quality for industrial customers. There is high demand for ultrapure demineralized water, but the salt content of ground and surface water is expected to rise. Proven process methods have been combined with new technology on this large project. Brielse Meer, a nearby lake, is the main source of water for the Demineralized Water Plant (DWP). The process design includes flotation, filtration and ion exchangers together with membranes. New membrane technology reduces the use of water purification chemicals and increases membrane life. Valves are installed on vertically mounted pressure pipes to let air in during the cleaning and reverse flush cycle. This reduces cost and also protects the environment.
Energy-efficient Sea Water Desalination
If the experts are right, water consumption worldwide will rise by 40 % over the next 15 years. Desert nations and small countries like Singapore which have few sources of freshwater are making increasing use of sea water desalination. That, however, has been very energy intensive. About 10 kWh of electricity is needed to evaporate 1 m3 of sea water. Reverse osmosis on the other hand only uses about 4 kWh for the same volume.
Siemens has reduced energy consumption for sea water desalination by more than half. A pilot plant in Singapore processes 50 m3 of water a day and uses only 1.5 kWh of electricity per m3. Demonstration plants are planned for construction in Singapore, the US and the Caribbean by mid 2012.
The new low-energy Siemens process is based on electrodialysis. The positively and negatively charged salt ions are removed from the water with the aid of an electric field. Special membranes, which only allow one type of ion to pass, form channels where saline solution or purified water collects. However, the process becomes inefficient as the salt concentration decreases, because the electrical resistance of the water increases. The final percent of salt is removed using continuous electrodeionization (CEDI). Ion exchange resin located between the membranes absorbs the ions and assures their further transport.
Electrolytic Treatment of Raw and Process Water
Electro-physical precipitation (EpF) is a process that was established at the German Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB). The water to be treated flows through a reactor in which electric current flows through sacrificial electrodes. Electrochemical reactions take place between the electrodes which dissolve, releasing their metal ions. In Advanced Oxidation Processes (AOP) reactive radicals are produced as well as metal hydroxide flocs. The metal hydroxide flocs formed through the electrolytic process are highly adsorptive and can bind to finely dispersed particles. In addition, dissolved organic and inorganic material is precipitated in the co-precipitation and occlusion precipitation reactions which also occur. The precipitated substances can then be separated out mechanically.
Oxidative and adsorptive techniques such as EpF can be combined depending on the task at hand. These techniques have the further advantage that they are suitable for stand-by operation and can be switched on and off at any time. They can easily be deployed at existing plants, and automation including autonomous operation or remote control is also not a problem. Continuous online capture of total organic carbon (TOC) data can be used to support a demand-driven, energy optimized treatment process.
Because they reduce the consumption of chemicals, electrolytic and oxidative techniques are a cost-effective and sustainable option for treatment of industrial, process and waste water which contain substances that cannot be broken down in a biological treatment process. The electricity needed to run the process can be obtained from renewable sources such as PV and wind generation.
Process water recycling in electroplating
Re-use and recycling of process water is more common in surface finishing than is generally the case in the chemical industry. The sub-process flows upon which these solutions are based offer opportunities for the deployment of membrane technology in the chemical industry as well. As a general rule however, segregation and separate treatment of sub-flows requires a new water logistics strategy at the plant, and that takes time and effort to develop. The Membrane Bio Reactor (MBR) has established a solid foothold in recent years, particularly in the pharmaceutical industry. The applications are normally end-of-the-pipe. The membrane ensures that the biological purification process is highly effective, and it acts as a barrier to solids. The very high purification performance of MBR applications is a major prerequisite for the deployment of technologies such as reverse osmosis in effective water recycling applications. The approach is already being used in the chemical and pharmaceutical industry and closely related sectors. It definitely offers an opportunity for reducing specific water consumption.
To cite one practical example, Oftech Oberflächentechnik applies coatings to automotive and electrical/electronic parts. When the company made the transition from Cr(VI) to Cr(III), it installed a mobile system containing an ion exchanger to remove contaminants from the process solutions (electrolytes) at an early stage. This resulted in a reduction in the consumption of acid pickling solution and electrolytes, and the service life of the treatment vats increased considerably.
Water Recycling in the Beverage Industry
Bottle washers use more water than any other piece of machinery at bottling plants. Bottles are rinsed with 100 to 1000 ml of cleaning solution per bottle in a multi-stage process. The rinse water is normally reused for presoak and/or in the crate washer. A considerable amount of energy is used to heat the cleaning solution.
The water recycling process philosophy at FuMA-Tech GmbH is based on the creation of a "sink" for all water contamination induced by the rinsing process. The treatment process combines ultrafiltration and reverse osmosis together with two-stage neutralization using carbonic acid. UV disinfection equipment along with automatic membrane cleaning and system disinfection on the recycling system prevent bacterial contamination even when raw water parameters are at a critical level (BOD (Biochemical Oxygen Demand), temperature). Water recycling typically reduces the consumption of fresh water by 50 % to 60 %. Most of the salt is removed from the product water, and the water meets drinking water quality standards.
Reducing Losses in the Piping Network Saves Energy
The best way to cut down on water usage is to avoid or reduce losses. Agricultural irrigation accounts for 70 % of water consumption worldwide. Efficient irrigation systems can lower evaporation losses from 50 % down to 10 %. 30 % to 50 % losses are the rule rather than the exception in drinking water supply networks. Around 900 million liters of drinking water leak out in London every day. The average rate of water loss in the developing countries is 43 %. The figure for the European water distribution networks varies between 15 % and 30 %. Germany at 8 % is at the low end of the scale. But even here, 500 million m3 of water are lost each year due to the poor state of the water pipes. 13 billion euros need to be invested to solve the problem. Reducing the losses cuts electricity consumption as well as water consumption. 90 % of the energy consumed in the municipal water system is used to convey the water.
Process analytics and process automation
There is a need for new analytical techniques to support process analytics in industrial water engineering. Data analysis and evaluation are also needed to provide a basis for generating material and process data. The goal of process automation and optimization is to maintain consistent product quality while minimizing cost and operating a safe, eco-friendly process.
Suitable techniques for making a differentiated performance assessment and carrying out quality control on water management equipment are still lacking. This applies in particular to toxic, refractory and trace substances. Putting this type of system in place requires robust methods that remain stable over a long period of time along with automated techniques that run cyclically to detect problems and trigger corrective action. To ensure that monitoring is effective, process analyzers are needed which analyze multi-component mixtures in a single operation. In addition to biological and photometric techniques, chromatographic analysis will be used more frequently in the future. This will require development of techniques for assessing the state of the analytical column and detecting degradation in the column's properties at an early stage.
ChemWater: Sustainable Industrial Water Usage
Europe will have to use its water resources more efficiently, and the chemical industry has to play a major role. It is one of the largest water consumers, and at the same time it provides key water management technologies. The goal of the EU-funded ChemWater Project is to promote synergies between European initiatives within the framework of existing technology platforms and beyond, providing a basis for evaluating new discoveries in nanotechnology, material research and process innovation. The intention is to exploit this new knowledge for the purpose of achieving sustainable industrial water management.
The essential idea behind the project is not only to look at water usage in chemical production, but also to harness the water management expertise of the chemical industry. This will reinforce the process industry's roll as a technology provider and storehouse of expertise. Taking the chemical industry as the starting point has the advantage that the new knowledge will be transferrable to many other sectors of industry.
This article is based on a trend report compiled by specialized international journalists on behalf of Dechema Gesellschaft für Chemische Technik und Biotechnologie (Society for Chemical Engineering and Biotechnology), a nonprofit scientific and technical society based in Frankfurt am Main, Germany.
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