Direct Potable Reuse Vs Indirect Weighing The Pros And Cons

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Direct Potable Reuse Vs Indirect Weighing The Pros And Cons

Dwindling water supply is an issue in many areas of the world. Water use has been growing significantly in recent years, with water withdrawal predicted to rise by 50 percent in developing countries and 18 percent in developed countries by 2025, according to the United Nations Environment Programme

This increase in water use makes water scarcity a serious issue for many communities, especially those that frequently experience periods of drought and other environmental challenges. For those communities water reuse is sometimes the only practical solution.

“Treated wastewater is increasingly being seen as a resource rather than simply waste,” reports the EPA in their 2012 Guidelines for Water Reuse.

There are two potable water reuse options currently gaining prevalence: direct potable reuse (DPR) and indirect potable reuse (IPR).While all water is eventually reused in some sense in a conventional water treatment system, DPR and IPR both involve a proactive decision to transform treated wastewater into drinking water.

For IPR, this is done by releasing treated wastewater into groundwater or surface water sources with the intent of using it for drinking water supplies, and then reclaiming it and treating it to meet drinking water standards. For DPR, purified water, created from treated wastewater, is introduced directly into a municipal water supply system without an environmental “buffer” of any kind.

Experts are still weighing in on which, if either, is the solution to water scarcity. Water Online shares pros and cons of each.


Advantages Of DPR

Cost savings: Drinking water treatment and wastewater treatment typically occur in the same or nearby locations in DPR systems, requiring a short pumping distance for product delivery. The close proximity of both waste and drinking water treatment may present considerable cost savings for municipalities when compared to IPR methods, according to“Drinking Water Through Recycling”, a report by the Australian Academy of Technological Science and Engineering (ATSE). The study compared several hypothetical options for alternative water supplies for a coastal Australian city.

The study determined that a hypothetical DPR system would cost $616 million in total calculated indicative capital costs, compared to $1,287 million for an IPR system. Operating costs for the DPR system were estimated at $53 million per year, compared to $72 million per year for the IPR system.

Reduced carbon footprint: A smaller bottom line isn’t the only advantage to the shorter pipelines used in DRP systems. The energy required to pump water over short distances results in less greenhouse gas emissions than the amount needed to pump water over long distances, according to the ATSE study.

Water security: The short distance water has to travel in DPR systems also leaves little opportunity for outside factors to affect it. According to the EPA Guidelines for Water Reuse, DPR systems are less vulnerable to damage from earthquakes, floods, and other natural and human-made disasters. Long-distance water transmission systems, such as those used in IPR, are more vulnerable to damage, leading to additional costs and maintenance.

Disadvantages Of DPR

Additional setup: Some DPR systems may require additional water quality or process performance monitoring and/or an engineered storage buffer, according to the ATSE report. These items may increase costs and would require additional time, planning, and labor to implement. The purposes of a storage buffer include balancing variability between water production and water use, balancing water quality variability, and providing time to detect and respond to any contaminants in the water, according to the ATSE report

Safety concerns: There are only four municipal DPR projects currently operating, located in the Namibia, South Africa, and the United States (Texas and New Mexico), according to the ATSE report. Because DPR has not been widely implemented, there is a lack of consensus in the scientific community about its safety. There are concerns about the effectiveness of DPR systems to fully remove pharmaceuticals, personal care products, and endocrine distributing chemicals from the water. The ATSE also reports that there is a lack of faith in government agencies’ capacity to safely operate and monitor DPR projects.

Public perception: The “yuck factor” associated with DPR is one of the biggest reasons it has not been more widely implemented, reports the ATSE. Because much of the public is misinformed or has negative feelings regarding DPR, utilizing such systems may require municipalities to employ dedicated public relations managers. Phase 2 of the City of San Diego Water Purification Demonstration Project, which began in 2005, used nearly half of the project’s funding for education and outreach purposes — to make the public feel more comfortable with DPR.

Source: Water Online

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