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Creating a Sustainable Water Source with Wastewater Reuse
An expanding population and growing industry requirements, together with global climate changes, are placing greater pressure on natural water sources. There is simply not enough rainfall, rivers and other natural water sources to meet current and future demand, particularly in arid and semi-arid regions. Therefore, alternative sources and ways to augment currently available sources must be found. Wastewater reuse is one of these alternatives. Today, wastewater can be treated to a quality equal to – or better than – natural freshwater and is suitable for direct or indirect potable use.
Statistics show the growing interest and potential in this field, and published investment in planned reuse projects totals more than $18.6 billion in the United States. As the technology gains enough experience and trust, it also gains additional support from the public and decision makers.
Today, the technology is evolving in many directions such as increased recovery, removal of Contaminants of Emerging Concern (CECs), monitoring water quality, and energy savings.
The most widely accepted technology currently in use is Fully Advanced Treatment (FAT), a process that includes Ultrafiltration/Membrane Filtration (UF/MF), Reverse Osmosis (RO), and Ultraviolet/Advanced Oxidation Processes (UV/AOP) in three process units. This process meets the requirements of Title 22 (California's regulations regarding water reuse) for log removal of pathogens, as well as the requirement for three independent treatment units.
Increased recovery – The current trend is to increase the system recovery (the fraction of the produced water from the feed water) to above 80-85 percent and in cases where brine discharge is strictly regulated, to even 95 percent and higher. It is possible to reach 85 percent recovery by adding a third RO stage, whereas more sophisticated means are required to prevent membrane scaling and fouling for higher recoveries. This could include removal of specific scale-forming minerals from the water or IDE's Pulse-flow RO technology, which operates in RO pulses that are shorter than the crystals induction time, therefore crystals do not have the time to form on the membrane.
Removal of Contaminants of (Emerging) Concern (CECs) – CECs are organic contaminants from various sources, including human consumption of pharmaceuticals and personal care products (PPCPs), and residual concentrations of organic contaminants from industrial sources and organic contaminants that might be formed during the FAT reuse process, such as N-Nitrosodimethylamine (NDMA). NDMA is a suspected human carcinogen formed as a byproduct of chloramine dosing to the feed water to control biofouling. NDMA formation can be avoided by using mechanisms other than chloramine dosing to the RO. IDE already applies other mechanisms to control biofouling, such as frequent Direct (forward) Osmotic High Salinity (DOHS) treatment, which keeps the membrane constantly clean.
Water quality monitoring – Monitoring is a key facet in water reuse facilities, and very sophisticated systems are used to track the water quality in every part of the process. The purpose of this close monitoring is to locate problems, and solve these quickly. Quality tracking systems are evolving and now provide operators with a broad and accessible view of the current status, as well as previous performance of the plant.
Energy savings – Equipment manufacturers are constantly striving for equipment that is more efficient. This is especially true in water desalination and reuse facilities where membrane manufacturers are investing in the development of better membrane surface chemistry that will reduce membrane fouling and hydrophobicity and increase membrane permeability. Manufacturers of energy recovery devices are also trying to design more efficient and reliable equipment.
The water cycle is a closed cycle with a simple balance – if the water demand is higher than the water sources can refill, there is a deficit. This can be seen in basically every part of the world that faces drying climate conditions and increased demand. Municipal and industrial clients in the modern world reject a situation in which there is no immediately available water, thus there is over-pumping.
As with any other product or resource, there is a supply and demand curve. To maintain a sustainable water balance, it is equally important to reduce the demand and increase the supply. Reducing the demand is far cheaper and more cost effective than investing in the development of new water resources and can be achieved by educating for water saving and implementing a graded water tariff for consumers. For example, allowing every household to purchase sufficient water for normal human consumption at the lowest tariff, while the demand is higher (e.g. for irrigation of garden), every gallon above the quoted lowest tariff costs more. Another aspect is the water management system, which should be centrally managed to allow the relevant authority to see the overall picture and can foresee the future supply, demand, and design accordingly. Increasing the supply, though more costly, can be achieved by building seawater desalination (where applicable) and water reuse facilities to take advantage of the wastewater effluent to augment natural water bodies (or even use directly to the system in certain places).
New technologies are being developed to make the desalination and reuse treatment processes as green as possible, which is environmentally responsible and more cost effective. There are several ways to design a more energy-efficient treatment plant, for example using the largest high-pressure pumps possible, which are more efficient; implementing energy recovery devices; splitting permeate to front and rear; etc. A biologically active pretreatment process can eliminate the need for coagulant dosage.
As the water scarcity rises and affects natural water sources, there is higher demand for safer, more ecologically-friendly processes. IDE has some unique technologies and ideas that hopefully will advance the field further in all parts of the process – both in seawater desalination and water reuse facilities. These innovations include innovative intake solutions, pretreatment, RO design and post treatment. One such process is the IDE Eco-Reuse process, which eliminate the use of chloramine.
Lior Eshed, process engineer, is the water reuse product manager at IDE Technologies.