Water and Effluent Treatment Magazine
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wwtonline.co.uk | JANUARY 2019 WET NEWS 11 fruit processed globally and contains up to 80 per cent water. It is a potential source of many useful products including die- tary fibre, antioxidants, food colorants and flavours, and con- tains a wide variety of com- pounds including cellulose, pectin, sugars, hemicelluloses, flavonoids and essential oils such as D-limonene. Moving towards zero liquid discharge Zero liquid discharge (ZLD) is a technique by which liquid waste streams are eliminated. Instead of being discharged at the end of the treatment cycle, any wastewater is purified and recy- cled, while other residues, which o en include the type of valuable by-products mentioned above, are extracted. Various processes are employed in ZLD, including membrane bioreaction, reverse osmosis, electrolysis, filtration and more. However, evapora- tion is also a key process, both in order to concentrate residues sufficiently to allow their eco- nomic extraction or physical removal, and as part of the water purification process. However, solid-liquid mix- tures are complex and it is important that the first stage of any potential project includes a research study to evaluate the nature of the waste stream/s and the saturation levels required. In laboratory experi- ments, HRS evaluates the maxi- mum concentrations that can be reached for different tempera- ture regimes. This then deter- mines the type of equipment we design. For example, at high temperatures more salts may be dissolved, compared to low temperatures. The importance of evaporation HRS Heat Exchangers has been involved in ZLD projects in Europe using evaporation sys- tems, including the recovery of potassium and sodium sul- phates from organic brine waste streams. A typical HRS process might consist of three steps as follows: 1. Evaporation/concentration (using one or more evapora- tors depending on the materi- als involved and the level of concentration required) to lev- els above the saturation point at high temperature 2. Cooling down of the product to provoke the formation of salt crystals 3. Further crystallisation in spe- cially designed tanks and sep- aration of the crystals that are formed to allow them to be processed for use. In the third step, a supernatant layer of concentrated solution remains a er separation of the crystals. This solution is returned to the second evapo- rator for concentrating again to above its saturation point Correct heat exchanger choice for product recovery Both the evaporation and cool- ing steps result in a high degree of material fouling on the inside of the equipment, so HRS Uni- cus Series scraped-surface heat exchangers are used to main- tain thermal efficiency and remove fouling as it occurs. Coupled with HRS R Series cool- ers and custom-designed crys- tallisation tanks, the result is an efficient process that can work continuously without requiring scheduled downtime. In the example above, two evaporators are used to concen- trate and remove pure water from the solution, which can be used elsewhere. The coolers and crystallisers produce solid crystals, and the remaining solution returns to the evapora- tion process. No liquid waste remains a er the process, so that as well as recovering valua- ble salts, waste management costs are also reduced. BOOK NOW: wwt.events/futureretail @Water_Retail #FutureRetail2 FUTURE RETAIL #2 CONFERENCE 13 March 2019 | 99 City Road Conference Centre, London The only event dedicated to promoting customer awareness and success in the open water market Emma Kelso Senior director of customers and casework Ofwat Samir Rahim CIO MOSL Andy Hughes CEO Water Plus John Reynolds CEO Castle Water Paul Stelfox Head of wholesale market services United Utilities Simon Bennett Head of wholesale services Bristol Water Pritesh Patel Commercial director First Business EXPERT SPEAKERS INCLUDE DRIVING SUCCESS IN THE OPEN WATER MARKET LEARN how to engage the 90% of customers still not bought into the open market FIND OUT what MOSL is doing to help resolve the bilaterals issue EXPLORE practical strategies to improve the wholesaler- retailer relationship Supported by SE C U R E T H E E A R L Y B O O K I N G RAT E SAVE £100 FutureRetail#2-2019-A4ad.indd 1 12/12/2018 10:05 Modular, multi- parameter water quality monitors for networks t. 0800 8046 062 www.atiuk.com