As with any process or technology, improvements have been made over the years, firms say. In Parker, Colo., southeast of Denver, the Parker Water District this summer completed the first large-scale potable-water treatment facility that uses ceramic, rather than  polymeric, membranes during the drinking-water  filtration process.

Originated in Japan, ceramic membranes have been used widely in Asia and Europe but, generally, have been considered to be too expensive in the U.S.

But for water that contains a large amount of biological contaminants, such as algae, they can become cost-effective, says Alan Pratt, principal engineer at Dewberry. Ceramic membranes are more robust and can hold up to stronger cleaning agents, so they generally have a longer life span than polymeric membranes, which can foul and need to be replaced after seven to 10 years, particularly in water that has a high percentage of organic contaminants.

"I think the ceramic membranes are more expensive up front, but they can be more cost-effective in the long run, depending on how long you think the polymeric membranes would hold up," he says. "In our case, we anticipated a fairly poor-quality raw water, and we do, in fact, have a fairly poor-quality raw water in terms of organic levels in the water."

The $50-million Reuter-Hess 10-mgd purification project, completed in July 2015, involves pumping a combination of surface water and reclaimed effluent to the Reuter-Hess Reservoir, which can store 75,000 acre-ft of water. The new purification facility removes dissolved organic compounds and other impurities through a series of coagulation, flocculation and sediment chambers, then uses ceramic membranes to remove turbidity and biological contaminants.

Brent Alspach, senior environmental engineer at Arcadis, says ceramic manufacturers have not yet established much of a market presence in the U.S. However, he notes, that could change. "There are a handful of companies that are making some inroads, and I think, over the course of time, you will see some utilities using ceramic membranes."

Across the board, firms and utilities agree that proper training for operators and vigilant monitoring are crucial to keeping the public safe and regulators happy, as well as winning the battle for public acceptance. "Not only do you need to make sure that treatment is robust enough to protect public health and meet drinking-water standards, but if there is a problem with one of the processes, what happens?" says Alspach.

Alspach adds that systems need to have sophisticated methods to monitor constantly how the treatment trains and processes are performing, so that if something malfunctions through technological or human error, parts or all of the system can be shut down and water diverted "well before anybody would possibly be drinking it."

Regulatory Framework

Another challenge to DPR or IPR adoption can be regulations that need to be rewritten or developed to enable these facilities to be built at all. In Oklahoma, for instance, Black & Veatch is helping Oklahoma City develop regulations for both processes.

Gary Hunter, senior wastewater process engineer for Black & Veatch, was appointed by the governor three years ago to work with the state's Dept. of Environmental Quality and the Oklahoma Water Research Board to develop regulations that would allow both direct and indirect potable-reuse projects to move forward.

Over the past four years, the city's primary sources of water supply—Lakes Canton and Hefner—have seen water levels drop by 20 ft. "They know that no matter what happens in the future … they are going to have to become a bit more aggressive in their ability to reuse their water," Hunter says. Black & Veatch is currently building a pilot facility that will help to inform the development of the regulations, he adds.